tag:theconversation.com,2011:/us/topics/leaves-77519/articlesLeaves – The Conversation2024-03-11T12:25:42Ztag:theconversation.com,2011:article/2229722024-03-11T12:25:42Z2024-03-11T12:25:42ZWhy do trees need sunlight? An environmental scientist explains photosynthesis<figure><img src="https://images.theconversation.com/files/578432/original/file-20240227-20-s7p24d.jpg?ixlib=rb-1.1.0&rect=0%2C0%2C2048%2C1364&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">The reason trees need sunlight is the same reason their leaves are green.</span> <span class="attribution"><a class="source" href="https://www.flickr.com/photos/scottb211/10108377914/"> Scottb211/Flickr</a>, <a class="license" href="http://creativecommons.org/licenses/by/4.0/">CC BY</a></span></figcaption></figure><figure class="align-left ">
<img alt="" src="https://images.theconversation.com/files/281719/original/file-20190628-76743-26slbc.png?ixlib=rb-1.1.0&q=45&auto=format&w=237&fit=clip" srcset="https://images.theconversation.com/files/281719/original/file-20190628-76743-26slbc.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=293&fit=crop&dpr=1 600w, https://images.theconversation.com/files/281719/original/file-20190628-76743-26slbc.png?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=293&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/281719/original/file-20190628-76743-26slbc.png?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=293&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/281719/original/file-20190628-76743-26slbc.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=368&fit=crop&dpr=1 754w, https://images.theconversation.com/files/281719/original/file-20190628-76743-26slbc.png?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=368&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/281719/original/file-20190628-76743-26slbc.png?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=368&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
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<p><em><a href="https://theconversation.com/us/topics/curious-kids-us-74795">Curious Kids</a> is a series for children of all ages. If you have a question you’d like an expert to answer, send it to <a href="mailto:curiouskidsus@theconversation.com">curiouskidsus@theconversation.com</a>.</em></p>
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<p><strong>Why do trees need sunlight? – Tillman, age 9, Asheville, North Carolina</strong></p>
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<p>Trees need sunlight for the same reason you need food. The energy from the Sun’s rays is a crucial ingredient in how plants make their own food that helps them power all their cells. Since trees don’t harvest or hunt food, they have to produce their own. The way they make their food is a unique and important chemical process called photosynthesis.</p>
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<a href="https://images.theconversation.com/files/574698/original/file-20240209-30-3fr5f.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="honey-comb pattern of rings each containing many small green spheres" src="https://images.theconversation.com/files/574698/original/file-20240209-30-3fr5f.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/574698/original/file-20240209-30-3fr5f.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=406&fit=crop&dpr=1 600w, https://images.theconversation.com/files/574698/original/file-20240209-30-3fr5f.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=406&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/574698/original/file-20240209-30-3fr5f.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=406&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/574698/original/file-20240209-30-3fr5f.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=510&fit=crop&dpr=1 754w, https://images.theconversation.com/files/574698/original/file-20240209-30-3fr5f.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=510&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/574698/original/file-20240209-30-3fr5f.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=510&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
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<span class="caption">Chlorophyll is what makes leaves green.</span>
<span class="attribution"><a class="source" href="https://commons.wikimedia.org/wiki/File:Plagiomnium_affine_laminazellen.jpeg">Kristian Peters-Fabelfroh/Wikimedia</a>, <a class="license" href="http://creativecommons.org/licenses/by-sa/4.0/">CC BY-SA</a></span>
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<h2>What is photosynthesis?</h2>
<p>The cells in plants and all other living things have microscopic components called <a href="https://www.genome.gov/genetics-glossary/Organelle">organelles</a>. One type of organelle in plant cells is the chloroplast, and it contains the <a href="https://www.kidzone.ws/science/lessons/pigments.html">pigment</a> chlorophyll, which is what makes leaves green. When chlorophyll receives sunlight, it starts the <a href="https://education.nationalgeographic.org/resource/photosynthesis">photosynthesis</a> reaction.</p>
<p>The name photosynthesis comes from the ancient Greek words “photo,” which means light, and “synthesis,” which means to make. During this food-making process, plants take carbon dioxide from the air and water from the ground, and with the energy from sunlight, make glucose. Glucose is a very simple type of sugar. Because it is a simple compound, it is simple to make.</p>
<p>Most of the time, photosynthesis occurs in leaves, and leaves take in sunlight to make food. There are some special plants, though, that actually absorb sunlight on their stems. Some of these include cactuses like the balloon-shaped <a href="https://www.gardenia.net/plant/echinocactus-grusonii-golden-barrel-cactus">golden barrel cactus</a>, the spiky <a href="https://huntington.org/educators/learning-resources/spotlight/cylindropuntia-munzii">Munz’s Cholla</a> and the paddle-shaped <a href="https://huntington.org/educators/learning-resources/spotlight/opuntia-ficus-indica">prickly pear</a>. Some plants even have roots that can photosynthesize, like the rare palm <em><a href="https://huntington.org/educators/learning-resources/spotlight/cryosophila-albida">Cryosophila albida</a></em>.</p>
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<a href="https://images.theconversation.com/files/579708/original/file-20240304-28-wxa438.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="A graphic diagram of a plant showing sun, soil, roots, leaves and a flower" src="https://images.theconversation.com/files/579708/original/file-20240304-28-wxa438.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/579708/original/file-20240304-28-wxa438.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=601&fit=crop&dpr=1 600w, https://images.theconversation.com/files/579708/original/file-20240304-28-wxa438.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=601&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/579708/original/file-20240304-28-wxa438.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=601&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/579708/original/file-20240304-28-wxa438.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=755&fit=crop&dpr=1 754w, https://images.theconversation.com/files/579708/original/file-20240304-28-wxa438.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=755&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/579708/original/file-20240304-28-wxa438.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=755&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
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<span class="caption">Sunlight gives plants the energy to turn water and carbon dioxide into carbohydrates – the food their cells need to live and grow.</span>
<span class="attribution"><a class="source" href="https://commons.wikimedia.org/wiki/File:Photosynthesis_en.svg">At09kg/Wikimedia</a>, <a class="license" href="http://creativecommons.org/licenses/by-sa/4.0/">CC BY-SA</a></span>
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<h2>Photosynthesis is billions of years old</h2>
<p>Photosynthesis evolved more than <a href="https://doi.org/10.1104%2Fpp.110.161687">3.5 billion years ago</a>. Initially, only single-celled organisms, kind of like today’s algae, could make sugar this way. Oxygen is a waste product from the photosynthesis process, and over time, these single-celled organisms released enough oxygen to change the Earth’s atmosphere. Ultimately, we and all other animals needed this to happen to be able to live and breathe. </p>
<p>Over time, aquatic plants developed, and gradually plants <a href="https://doi.org/10.1126/science.aat3642">moved to land</a> around 500 million years ago to better access their most vital resource: sunlight. Plants eventually got taller by around <a href="https://doi.org/10.1126/science.aar2986">350 million years ago</a>. This is when the first tree evolved, which grew up to 150 feet tall. These trees looked like the evergreen trees we see today – sort of like pines, firs and spruce. And about 125 million years ago, trees that looked like the maples, oaks and beech trees we see today shared the landscape when <a href="https://new.nsf.gov/news/dinosaur-age-fossils-provide-new-insights-origin">dinosaurs ruled the Earth</a>.</p>
<h2>Not just good for plants</h2>
<p>The Sun provides energy for the Earth. However, we humans are not capable of taking in the sun directly and using it to power our bodies. So how do we make use of the Sun’s energy? Plants do it for us.</p>
<p>Plants take in that energy and make food for us and other animals to eat and oxygen for us to breathe. We wouldn’t exist without plants and photosynthesis.</p>
<p>Like the ancient tiny single-celled organisms from 3.5 billion years ago, some microorganisms today use photosynthesis. Specifically, the algae that you might see living on top of lakes and the ocean do. Chlorophyll is why algae is green. </p>
<p>There are <a href="https://news.asu.edu/20191114-asu-study-shows-some-aquatic-plants-depend-landscape-photosynthesis">aquatic plants</a> that use sunlight to grow. They typically make use of less sunlight because sunlight does not travel well through water.</p>
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<a href="https://images.theconversation.com/files/578425/original/file-20240227-30-2rnnkd.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="yellowish green grass-like plants underwater" src="https://images.theconversation.com/files/578425/original/file-20240227-30-2rnnkd.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/578425/original/file-20240227-30-2rnnkd.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=400&fit=crop&dpr=1 600w, https://images.theconversation.com/files/578425/original/file-20240227-30-2rnnkd.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=400&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/578425/original/file-20240227-30-2rnnkd.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=400&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/578425/original/file-20240227-30-2rnnkd.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=503&fit=crop&dpr=1 754w, https://images.theconversation.com/files/578425/original/file-20240227-30-2rnnkd.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=503&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/578425/original/file-20240227-30-2rnnkd.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=503&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
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<span class="caption">Some plants can do photosynthesis underwater, where there is less sunlight.</span>
<span class="attribution"><a class="source" href="https://www.flickr.com/photos/chesbayprogram/32446887586/">Chesapeake Bay Program/Flickr</a>, <a class="license" href="http://creativecommons.org/licenses/by-nc/4.0/">CC BY-NC</a></span>
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<p>In addition, there are a very few animals that can photosynthesize. The <a href="https://doi.org/10.1038/nature.2012.11214">pea aphid</a> uses pigment to harvest sunlight to make energy. The <a href="https://phys.org/news/2011-01-physicists-outer-shell-hornet-harvest.html">Oriental hornet</a> uses a pigment in its exoskeleton to make energy from sunlight. The <a href="https://www.nationalgeographic.com/animals/article/solar-powered-photosynthetic-sea-slugs-in-decline-news">emerald-green sea slug</a> eats algae and then incorporates chlorophyll from the algae into its body to photosynthesize. Because of this strategy, the sea slug can go nine months without eating. </p>
<p>So the answer to this question – why do trees need sunlight – is to make their food. And thanks to trees and other plants turning sunlight into their food, most of the rest of the living things on Earth get to eat, too!</p>
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<p><em>Hello, curious kids! Do you have a question you’d like an expert to answer? Ask an adult to send your question to <a href="mailto:curiouskidsus@theconversation.com">CuriousKidsUS@theconversation.com</a>. Please tell us your name, age and the city where you live.</em></p>
<p><em>And since curiosity has no age limit – adults, let us know what you’re wondering, too. We won’t be able to answer every question, but we will do our best.</em></p><img src="https://counter.theconversation.com/content/222972/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Rebekah Stein does not work for, consult, own shares in or receive funding from any company or organization that would benefit from this article, and has disclosed no relevant affiliations beyond their academic appointment.</span></em></p>Trees – and all plants – harvest sunlight to gain the energy they need to live and grow.Rebekah Stein, Assistant Professor of Environmental Science, Quinnipiac UniversityLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/2046732024-01-29T13:35:17Z2024-01-29T13:35:17ZThat sharp, green smell of freshly cut grass? It’s a plant’s cry for help – and it may work as a less toxic pesticide for farmers<figure><img src="https://images.theconversation.com/files/570226/original/file-20240118-15-wd2xly.jpg?ixlib=rb-1.1.0&rect=0%2C0%2C4928%2C3260&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">Green leaf volatiles are a plant's rapid response to threats.</span> <span class="attribution"><a class="source" href="https://commons.wikimedia.org/wiki/File:Green_leaf_vein.jpg">Star61/Wikimedia Commons</a>, <a class="license" href="http://creativecommons.org/licenses/by-sa/4.0/">CC BY-SA</a></span></figcaption></figure><p>Have you ever wondered about that sharp, green note that hits your nose when you mow the lawn or cut flower stems? Those are <a href="https://doi.org/10.1093/pcp/pcac117">green leaf volatiles, or GLVs</a>: easily evaporated oils that plants use to communicate with other plants and defend themselves against herbivores or pathogens like bacteria or fungi.</p>
<p>Almost every green plant can quickly <a href="https://doi.org/10.1093/pcp/pcac117">synthesize and release GLVs</a> when attacked, both directly warding off attackers as well as indirectly attracting predators of herbivores like insects and priming the plant’s other defense mechanisms. Researchers know that GLVs play an important role in protecting plants, but how they work remains unclear.</p>
<p>I am a <a href="https://sc.edu/study/colleges_schools/chemistry_and_biochemistry/our_people/students_researchers_emeritus/tan-arsuwongkul_sasimonthakan.php">biochemistry researcher</a>, and through a collaboration between the <a href="https://qianwanggroup.com/">Wang Lab</a> and <a href="http://research.cas.sc.edu/stratmann/">Stratmann Lab</a> of the University of South Carolina, my colleagues and I study how plant cells deploy green leaf volatiles. In our <a href="http://doi.org/10.1111/pce.14795">recently published research</a>, we identified the potential signaling pathways GLVs use to induce defense responses in tomato cells. Our ultimate goal is to figure out ways to use GLVs to control agricultural pests for cleaner farming.</p>
<h2>Defense systems in plants</h2>
<p>Plants employ many defense systems to protect themselves. The <a href="https://doi.org/10.3389/fpls.2019.00646">first line of defense</a> involves detecting microbial invaders and the presence of damage using <a href="https://doi.org/10.1146/annurev-phyto-082718-100146">damage-associated molecular patterns, or DAMPs</a>, which are molecules released by damaged or dying cells.</p>
<p>When a cell identifies a DAMP, it triggers an immune response and promotes repair mechanisms. It also leads to <a href="https://doi.org/10.3389/fpls.2021.795353">changes in calcium ion concentration</a>, further activating immune-related genes and proteins. DAMPs also <a href="https://doi.org/10.1111/jipb.13215">turn on proteins</a> common in many stress-signaling pathways that activate other defense responses.</p>
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<figcaption><span class="caption">Plants have several means of defense.</span></figcaption>
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<p>Many studies have shown that the <a href="https://doi.org/10.3389/fpls.2014.00578">effects of</a> <a href="https://doi.org/10.1111/nph.12977">GLVs are</a> <a href="https://doi.org/10.3389/fpls.2020.583275">similar to</a> <a href="https://doi.org/10.1584/jpestics.d18-020">DAMPs</a>. Therefore, my team and I wanted to prove whether GLVs may also act as DAMPs.</p>
<p>To do this, we studied which proteins are turned on or off in tomato cells. Chemically changing the structure of a protein through a process called <a href="https://doi.org/10.1038/ncb0502-e127">phosphorylation</a> turns it on or off. Protein phosphorylation plays a central role in regulating a great number of cellular processes and involves many signal transmission pathways. <a href="https://doi.org/10.1186%2Fgb-2005-6-9-230">Studying the phosphoproteome</a>, or all the proteins that are phosphorylated in one system, of tomato cells could help us compare the signaling pathways of GLVs and DAMPs.</p>
<p>We found that many of the proteins involved in green leaf volatile signaling pathways were involved in regulating stress. These included many components of DAMP signaling pathways, supporting our hypothesis that GLVs function like DAMPs in activating defense responses.</p>
<h2>Using GLVs in agriculture</h2>
<p>Agriculture often places significant pressure on natural resources and the environment. For example, the use of conventional pesticides can lead to <a href="https://theconversation.com/farmers-and-cropdusting-pilots-on-the-great-plains-worried-about-pesticide-risks-before-silent-spring-91976">environmental degradation and pest resistance</a>. </p>
<p><a href="https://doi.org/10.3389/fsufs.2021.619058">Biopesticides</a> are rising in popularity as a less toxic alternative. These are naturally occurring organisms or compounds that suppress the growth and spread of pests. For example, <a href="https://doi.org/10.1016/j.jafr.2021.100127">volatile organic compounds</a> from plants are a type of biopesticide that have been proven to allow for reduced use of synthetic insecticides to manage pests in stored food grains.</p>
<p>Therefore, GLVs may also be effective biopesticides in farming. One study has shown that GLVs can attract a plant pest, the <em>Apion miniatum</em> beetle, <a href="https://doi.org/10.3390/app13042253">to feed on</a> an invasive and difficult to control weed, <em>Rumex confertus</em>. In addition, field studies on wild tobacco plants found that releasing GLVs can attract enemies of herbivores. The presence of these herbivore competitors can not only control insect pests but also <a href="http://dx.doi.org/10.7554/elife.00007">increase the production of infested plants</a>.</p>
<p>With further research, we believe GLVs have the potential to naturally control pests and support sustainable agriculture.</p><img src="https://counter.theconversation.com/content/204673/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Sasimonthakan Tanarsuwongkul does not work for, consult, own shares in or receive funding from any company or organization that would benefit from this article, and has disclosed no relevant affiliations beyond their academic appointment.</span></em></p>Green plants produce a specific gas when under attack to both directly ward off herbivores and pathogens and indirectly lure in herbivore predators.Sasimonthakan Tanarsuwongkul, Ph.D. Candidate in Biochemistry, University of South CarolinaLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/2025912023-06-19T12:23:19Z2023-06-19T12:23:19ZHow do spices get their flavor?<figure><img src="https://images.theconversation.com/files/525195/original/file-20230509-18-suu7hu.jpg?ixlib=rb-1.1.0&rect=0%2C7%2C5184%2C3437&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">Without spices, our meals would have less color and flavor.</span> <span class="attribution"><a class="source" href="https://www.gettyimages.com/detail/photo/spices-royalty-free-image/556881787">Helaine Weide/Moment via Getty Images</a></span></figcaption></figure><figure class="align-left ">
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<p><em><a href="https://theconversation.com/us/topics/curious-kids-us-74795">Curious Kids</a> is a series for children of all ages. If you have a question you’d like an expert to answer, send it to <a href="mailto:curiouskidsus@theconversation.com">curiouskidsus@theconversation.com</a>.</em></p>
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<p>How do spices get their flavor? – Liam, age 6, San Francisco</p>
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<p>I love savory and spicy foods. Lasagna laden with basil and oregano. Beautifully golden curries <a href="https://www.britannica.com/search?query=turmeric">infused with turmeric</a>, or rice <a href="https://www.britannica.com/search?query=saffron">flavored with saffron</a>. I can’t pass up a cinnamon-dusted snickerdoodle cookie. And some of my favorite childhood memories center on my mom’s nutmeg-infused sweet potato pie.</p>
<p>These ingredients come from many different plants and distinct plant parts, including leaves, seeds, bark and plant oils. Their flavors are created by accumulated <a href="https://lpi.oregonstate.edu/mic/dietary-factors/phytochemicals">phytochemicals</a> – substances the plants make. “Phyto” comes from the Latin word for plant.</p>
<p>Plants produce chemicals for different purposes. In my recent book, “<a href="https://www.hup.harvard.edu/catalog.php?isbn=9780674241282">Lessons from Plants</a>,” I explore how plants use some of those compounds to communicate with one another.</p>
<p>Many of the chemicals that make up spice flavors can play important roles, such as protecting the plant against pests or pathogens. Known as secondary compounds, they can also help plants adapt to changes in the world around them. And, as spices, they communicate powerfully to our taste buds. </p>
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<iframe width="440" height="260" src="https://www.youtube.com/embed/DzOcZlmeaH0?wmode=transparent&start=0" frameborder="0" allowfullscreen=""></iframe>
<figcaption><span class="caption">Harvesting Ceylon cinnamon in Sri Lanka involves a lot of handwork.</span></figcaption>
</figure>
<p>Common kitchen herbs like basil and oregano come from leafy plants. Essential aromatic oils that accumulate in the plants’ leaves produce their flavors. For basil, those oils are called <a href="https://www.sciencedirect.com/topics/agricultural-and-biological-sciences/basil">eugenol and linalool</a>; oregano gets its flavors from <a href="https://draxe.com/essential-oils/oregano-oil-benefits/#">carvacrol and thymol</a>. Oils from both of these herbs have medicinal uses against infections, pain and swelling.</p>
<p>Other common spices, such as pepper and red chili, come from the berries or fruits of plants. Black pepper is made by grinding the small berries, known as peppercorns, from the plant <em>Piper nigrum</em>. Red pepper comes from ground-up dried chiles – <a href="https://cpi.nmsu.edu/chile-info/for-kids-pages/the-story-of-chile-peppers.html">small, hot-tasting fruits</a> that grow on low bushes.</p>
<p>Turmeric spice comes from another plant part – the rhizomes, or underground stems, of the flowering plant <em>Curcuma longa</em>. Rhizomes often are confused with roots, but they are more like stems that grow sideways underground and help the plant spread. A relative of ginger, another rhizome-derived spice, turmeric is beautifully orange and is used in a range of cooking that includes my beloved curries. </p>
<p>Saffron is from the red-colored, threadlike <a href="https://en.wikipedia.org/wiki/Stigma_(botany)">stigmas</a> of the plant <em>Crocus sativus</em>. The stigma is one component of the female part of a flower. Saffron is one of the most expensive spices, because harvesting stigmas is very labor-intensive – it’s typically <a href="https://www.youtube.com/watch?v=qwJkN3EaJW0">done by hand with tweezers</a>. Saffron is high in antioxidants and has been used as a medicine, dye and perfume. </p>
<figure class="align-right zoomable">
<a href="https://images.theconversation.com/files/525972/original/file-20230512-24221-upuv0q.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="A six-petaled purple flower with bright red threads extending from its center." src="https://images.theconversation.com/files/525972/original/file-20230512-24221-upuv0q.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=237&fit=clip" srcset="https://images.theconversation.com/files/525972/original/file-20230512-24221-upuv0q.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=450&fit=crop&dpr=1 600w, https://images.theconversation.com/files/525972/original/file-20230512-24221-upuv0q.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=450&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/525972/original/file-20230512-24221-upuv0q.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=450&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/525972/original/file-20230512-24221-upuv0q.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=566&fit=crop&dpr=1 754w, https://images.theconversation.com/files/525972/original/file-20230512-24221-upuv0q.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=566&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/525972/original/file-20230512-24221-upuv0q.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=566&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">Saffron comes from the vivid red stigma of <em>Crocus sativus</em>, commonly known as the ‘saffron crocus’.</span>
<span class="attribution"><a class="source" href="https://en.wikipedia.org/wiki/Saffron#/media/File:Saffron8.jpg">Serpico/Wikipedia</a>, <a class="license" href="http://creativecommons.org/licenses/by-sa/4.0/">CC BY-SA</a></span>
</figcaption>
</figure>
<p>Cinnamon, which cooks use in all kinds of baked goods, is derived from yet another plant part: the inner bark of tree species from the genus <em>Cinnamomum</em>. The phytochemical that gives cinnamon its distinctive smell and its rich woody flavor is the aromatic compound <a href="https://en.wikipedia.org/wiki/Cinnamaldehyde">cinnamaldehyde</a>. </p>
<p>Rich in antioxidants, cinnamon may help <a href="https://www.healthline.com/nutrition/10-proven-benefits-of-cinnamon#">control blood pressure and reduce inflammation</a>. It also has natural antifungal and antimicrobial properties that may serve to protect the trees that produce it.</p>
<p>The <a href="https://www.britannica.com/topic/nutmeg">dried nutmeg</a> that my mom used in her legendary pie comes from grinding the seed of the tropical evergreen tree family <em>Myristica fragrans</em>. The same plant produces another spice, called mace, which is often used to flavor baked custards and to spice sausages or other meat. </p>
<p>Plants can teach us all kinds of meaningful lessons. One of their powerful truths is that variety is literally the spice of life. I’m thankful for their tasty chemical defenses every time I cook. </p>
<hr>
<p><em>Hello, curious kids! Do you have a question you’d like an expert to answer? Ask an adult to send your question to <a href="mailto:curiouskidsus@theconversation.com">CuriousKidsUS@theconversation.com</a>. Please tell us your name, age and the city where you live.</em></p>
<p><em>And since curiosity has no age limit – adults, let us know what you’re wondering, too. We won’t be able to answer every question, but we will do our best.</em></p><img src="https://counter.theconversation.com/content/202591/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Beronda L. Montgomery receives funding from the National Science Foundation. </span></em></p>Humans have figured out how to season their food with virtually every part of plants.Beronda L. Montgomery, Vice President of Academic Affairs and Dean of the College, Grinnell CollegeLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/2009752023-03-14T12:24:27Z2023-03-14T12:24:27ZClimate change threatens spring wildflowers by speeding up the time when trees leaf out above them<figure><img src="https://images.theconversation.com/files/514776/original/file-20230311-17-7x9lo1.jpg?ixlib=rb-1.1.0&rect=23%2C0%2C3970%2C2952&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">Native wildflowers, such as these Dutchman’s breeches (_Dicentra cucullaria_) that bloom early in spring are losing access to sunlight as trees leaf out earlier.</span> <span class="attribution"><a class="source" href="https://flic.kr/p/26pTuFq">Katja Schulz/Flickr</a>, <a class="license" href="http://creativecommons.org/licenses/by/4.0/">CC BY</a></span></figcaption></figure><p>For <a href="https://nativeplantherald.prairienursery.com/2020/04/spring-ephemerals-in-the-woodland/">short-lived spring wildflowers</a> such as <a href="https://www.wildflower.org/plants/result.php?id_plant=anqu">wood anemone (<em>Anemone quinquefolia</em>)</a> and <a href="https://www.wildflower.org/plants/result.php?id_plant=dicu">Dutchman’s breeches (<em>Dicentra cucullaria</em>)</a>, timing is everything. These fleeting plants, known as ephemerals, grow in temperate forests around the world, leafing out and flowering early in spring before the trees towering above them leaf out. Emerge too early, and it will still be winter; emerge too late, and it will be too shady under the forest canopy for essential photosynthesis to happen. </p>
<p>Over their evolutionary history, these plants have figured out the best timing for their survival. But climate change is altering spring growing conditions, and plant life is changing along with it. </p>
<p>There are many examples of plants shifting flowering time in response to warming temperatures, such as <a href="http://dx.doi.org/10.1088/1748-9326/ac6bb4">cherry blossoms opening earlier and earlier</a> each year. However, when one part of an ecosystem shifts, will all the organisms that depend on it successfully shift too? Or will they be out of luck? And what if interconnected species respond to change at different rates, leading to disruptions in long-standing ecological relationships?</p>
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<iframe width="440" height="260" src="https://www.youtube.com/embed/vg0dAcZo3Fw?wmode=transparent&start=0" frameborder="0" allowfullscreen=""></iframe>
<figcaption><span class="caption">Participants in the federally funded USA National Phenology Network collect, store and share data on the timing of life cycle events in plants and animals and how climate change is altering those cycles.</span></figcaption>
</figure>
<p>Researchers have been asking these types of questions about phenology – the timing of biological events – <a href="https://press.uchicago.edu/ucp/books/book/chicago/W/bo8829988.html">related to climate change</a> for years. But most studies have focused on plant-animal interactions, like pollinators coming out at the <a href="https://doi.org/10.1042/ETLS20190139">wrong time for flowers</a>. Far fewer have analyzed plant-plant interactions, such as spring ephemerals that need time to grow before trees leaf out above them and block the sunlight.</p>
<p><a href="https://www.rprimacklab.com/">Our research group</a> has investigated the mismatch between understory wildflowers and canopy trees around Concord, Massachusetts, using historical observations recorded by Henry David Thoreau, the author of “<a href="https://www.gutenberg.org/files/205/205-h/205-h.htm">Walden,” his classic account of life in the woods</a>. We found that trees in Concord were more sensitive to spring temperatures than wildflowers were, and that this resulted in earlier tree leaf-out that <a href="https://doi.org/10.1111/ele.13224">reduced available light in the understory</a>. </p>
<p>This finding was an important first step, but we wanted to know whether these patterns persisted in other temperate forests in North America and across the Northern Hemisphere. Our 2023 study shows that <a href="https://doi.org/10.1111/1365-2745.14021">the answer is yes</a>.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/514778/original/file-20230311-16-lzomuu.jpeg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="A plant with small purple flowers on the forest floor." src="https://images.theconversation.com/files/514778/original/file-20230311-16-lzomuu.jpeg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/514778/original/file-20230311-16-lzomuu.jpeg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=509&fit=crop&dpr=1 600w, https://images.theconversation.com/files/514778/original/file-20230311-16-lzomuu.jpeg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=509&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/514778/original/file-20230311-16-lzomuu.jpeg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=509&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/514778/original/file-20230311-16-lzomuu.jpeg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=640&fit=crop&dpr=1 754w, https://images.theconversation.com/files/514778/original/file-20230311-16-lzomuu.jpeg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=640&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/514778/original/file-20230311-16-lzomuu.jpeg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=640&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">Round-lobed hepatica (<em>Hepatica americana</em>) is an early-blooming wildflower with blue, white or pink flowers, most often found in shaded woodlands.</span>
<span class="attribution"><a class="source" href="https://plants.ces.ncsu.edu/plants/hepatica-americana/">Frtiz Flohr Reynolds/NC State Extension</a>, <a class="license" href="http://creativecommons.org/licenses/by-sa/4.0/">CC BY-SA</a></span>
</figcaption>
</figure>
<h2>North American mismatches</h2>
<p>For this research we used specimens from herbariums – collections of plants that have been pressed, dried and cataloged. The plants we examined were collected across eastern North America over the past 100 years. We evaluated over 3,000 pressed plant specimens to chart leafing-out time for trees and flowering time for spring wildflowers. </p>
<p>The vast scale of this study was made possible because herbaria have digitized millions of photographs of plant specimens and <a href="https://naturalhistory.si.edu/research/botany/news-and-highlights/digitized">made them available online</a> over the past decade. Before this resource existed, researchers had to travel to many museums scattered around the country. </p>
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<figcaption><span class="caption">The herbarium at the Royal Botanic Gardens in Kew, England, is one of the world’s largest and supports genetic research on plants from around the globe.</span></figcaption>
</figure>
<p>Historical weather records are <a href="https://prism.oregonstate.edu">also available online now</a>. This allows researchers to determine spring temperatures for the year and place where each specimen was collected.</p>
<p>Our study enabled us to confirm the results of our work in Concord. We found that as temperatures warm, deciduous trees across eastern north America are advancing their leaf-out timing faster than native wildflowers are responding.</p>
<p>For example, during cooler springs with 24-hour average March and April temperatures of 41 degrees Fahrenheit (5 degrees Celsius), trees leafed out 13 days after native wildflowers. This gave the flowers almost two weeks of full sun on the forest floor. However, during warmer springs, with average temperatures of 58 F (15 C), trees leafed out only 10 days after native wildflowers. This gave the wildflowers about 25% less full sunlight time during which to photosynthesize. </p>
<p>As spring temperatures warm even further with climate change, we expect wildflowers will have even shorter periods of full sunlight. This can mean a sizable decrease in the flowers’ energy supply and ability to survive, grow and reproduce.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/514779/original/file-20230311-3323-eiamcv.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="A pink three-lobed wildflower." src="https://images.theconversation.com/files/514779/original/file-20230311-3323-eiamcv.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/514779/original/file-20230311-3323-eiamcv.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=400&fit=crop&dpr=1 600w, https://images.theconversation.com/files/514779/original/file-20230311-3323-eiamcv.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=400&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/514779/original/file-20230311-3323-eiamcv.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=400&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/514779/original/file-20230311-3323-eiamcv.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=502&fit=crop&dpr=1 754w, https://images.theconversation.com/files/514779/original/file-20230311-3323-eiamcv.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=502&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/514779/original/file-20230311-3323-eiamcv.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=502&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">Trilliums, like this <em>Trillium grandiflorum</em>, bloom from February through June across North America depending on their location.</span>
<span class="attribution"><a class="source" href="https://en.wikipedia.org/wiki/Trillium_grandiflorum#/media/File:Trillium_grandiflorum_pink1.jpg">Eric Hill/Wikipedia</a>, <a class="license" href="http://creativecommons.org/licenses/by-sa/4.0/">CC BY-SA</a></span>
</figcaption>
</figure>
<p>We also observed that trees and wildflowers in the warmer southern part of their ranges advanced their leaf-out and flowering times faster, respectively, than those in colder northern locations. In these zones, we found greater timing differences between trees and wildflowers. This means the potential for phenological mismatch, where native wildflowers are more likely to be shaded out by trees, is greater in the southeast U.S. than in areas farther north.</p>
<h2>Parallels and differences on other continents</h2>
<p>For a 2022 study, we collaborated with colleagues from China and Germany to evaluate over 5,000 tree and wildflower specimens collected over the past 120 years. We wanted to see to whether the phenological mismatches that we documented in North America could also be found in temperate forests of <a href="https://doi.org/10.1038/s41467-022-34936-9">East Asia and central Europe</a>. </p>
<p>Our team found a common pattern across all three continents. Trees and wildflowers are active earlier now than in the past, and they are active earlier in warm years and places. </p>
<p>However, in a surprising twist, we didn’t see the North American pattern of trees being more sensitive than wildflowers on the other two continents. In Europe, wildflowers and canopy trees seemed to be shifting together over time. In Asia, the understory wildflowers were shifting more than the trees — meaning they might get more light, not less, in a warmer future.</p>
<p>The differences we found among the three regions were due primarily to variation in the sensitivities of the trees to temperature. Trees in eastern North America responded more strongly to temperature shifts, while Asian trees responded less strongly.</p>
<p><div data-react-class="Tweet" data-react-props="{"tweetId":"1633812385709408256"}"></div></p>
<p>These results suggest that eastern North American trees have become especially sensitive to temperature as a way of adapting to this region’s <a href="https://earthathome.org/hoe/ne/climate/#">highly variable climate</a>. In contrast, trees in East Asia are apparently more sensitive to other environmental cues, such as day length, when it comes to the timing of spring growth.</p>
<h2>Informing forest management</h2>
<p>Our results pose questions for further research. If spring temperatures aren’t the primary cues determining leaf-out and flowering times of trees and wildflowers in East Asia, what are those cues? How does the declining spring light window for wildflowers in eastern North America affect their energy budgets and ability to survive, grow and flower?</p>
<p>Another question is whether there are any practical management techniques, such as thinning overstory trees or removing invasive plants, that can help wildflowers deal with the ongoing challenges of climate change. Such strategies could help people appreciate and conserve the full range of plants in the forests we depend on and cherish around the world.</p><img src="https://counter.theconversation.com/content/200975/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Richard B. Primack receives funding from the National Science Foundation. </span></em></p><p class="fine-print"><em><span>Benjamin R. Lee receives funding from the National Science Foundation and Morton Arboretum</span></em></p><p class="fine-print"><em><span>Tara K. Miller received funding from the National Science Foundation. </span></em></p>Many beloved wildflowers bloom in early spring, while trees are still bare and the flowers have access to sunlight. Climate change is throwing trees and wildflowers out of sync.Richard B. Primack, Professor of Biology, Boston UniversityBenjamin R. Lee, Postdoctoral Fellow in Biology, University of PittsburghTara K. Miller, Policy Research Specialist, Repair Lab, University of VirginiaLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/1903952022-10-23T12:30:30Z2022-10-23T12:30:30ZWhy the spongy moth outbreak has vanished in Québec<figure><img src="https://images.theconversation.com/files/490979/original/file-20221020-12-78hpos.jpg?ixlib=rb-1.1.0&rect=155%2C0%2C2578%2C1660&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">While the European spongy moth outbreak reached a dramatic peak in parts of Canada last year, these caterpillars have completely vanished this year.</span> <span class="attribution"><a class="source" href="https://www.flickr.com/photos/wsdagov/37105301613/in/photolist-YwSnrx-ZvgxqN-YtqysS-ZtNokh-CrXJN5-Zvgw7A-Ytqwrh-YwSmJk-CrXJAm-ZvgvA5-YwSjCM-CrXJmy-ZvgwDC-ZtNmvq-ZtNnTW-Ytqvi5-Ytqx7q-CrXHdG-YwSnJg-YtqxkG-CrXJH5-CrXJu9-ZvgwMy-ZtNody-ZvgvMY-Ytqw9o-ZtNo9A-ZtNkwS-ZtNmp3-ZtNonS-CrXHUb-ZtNoHm-Zui2CC-ZvgwR1-YtqzbW-CrXHCE-YwSjNr-WgGfzb-Zy4Tng-Zui2Hh-Zui2B5-Zui31G-Zui35u-ZvgwA1-Ytqz4b-YwSkeB-2bhnF27-Zui2Xf-Zui2wW-YtUWTN">(Washington State Department of Agriculture/flickr)</a>, <a class="license" href="http://creativecommons.org/licenses/by-nc/4.0/">CC BY-NC</a></span></figcaption></figure><p>Last year, forests across southern Québec and Ontario and much of New England turned <a href="https://www.journaldemontreal.com/2021/06/23/en-images-les-forets-du-quebec-ravagees-par-la-chenille-spongieuse">eerily leafless</a>. The air hummed with the sound of munching mandibles and tree trunks were covered with a writhing carpet of caterpillars, while showers of caterpillar poop fell softly on the heads of unsuspecting hikers and campers. </p>
<p>The population of the European spongy moth, which had been gradually increasing since 2019, reached a dramatic peak in 2021 and completely vanished this year.</p>
<p>In 2020, the hungry caterpillar <a href="http://nfdp.ccfm.org/en/data/insects.php">damaged 583,157 hectares of forests in Ontario</a> and this number is bound to go up when the 2021 numbers are revealed. </p>
<p>Insect outbreaks are one of the most important <a href="https://www.ccfm.org/healthy-forests/natural-disturbances/">natural disturbances</a> in Canadian forests. As a biologist who has been working on plant-insect interactions for over 20 years, I see that the frequency, intensity and range of insect outbreaks keeps changing. To protect trees in our forests and cities, we need tree diversity.</p>
<h2>Insect outbreaks</h2>
<p>An insect outbreak can be frightening. In deserts around the world, <a href="https://www.youtube.com/watch?v=qNpTsn4l0S4">vast swarms of locusts</a> can blot out the sun for hours as they fly overhead. In the Rocky Mountains, hillsides are covered with dead trees, killed by the inner-bark-eating <a href="https://www.britannica.com/video/179774/mountain-pine-beetle-destruction-forests-Canadian">mountain pine beetle</a>. </p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/489742/original/file-20221014-25-6tyf4n.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="Trees with their leaves eaten" src="https://images.theconversation.com/files/489742/original/file-20221014-25-6tyf4n.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/489742/original/file-20221014-25-6tyf4n.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=396&fit=crop&dpr=1 600w, https://images.theconversation.com/files/489742/original/file-20221014-25-6tyf4n.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=396&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/489742/original/file-20221014-25-6tyf4n.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=396&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/489742/original/file-20221014-25-6tyf4n.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=497&fit=crop&dpr=1 754w, https://images.theconversation.com/files/489742/original/file-20221014-25-6tyf4n.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=497&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/489742/original/file-20221014-25-6tyf4n.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=497&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">Trees with their leaves eaten by spongy moth caterpillars seen on Montréal’s Mount Royal on July 7, 2021. Insect outbreaks stimulate nutrient cycling, accelerate forest succession and can renew forests.</span>
<span class="attribution"><span class="source">THE CANADIAN PRESS/Paul Chiasson</span></span>
</figcaption>
</figure>
<p>However, insect outbreaks are not a new phenomenon. Chinese historical records document <a href="https://doi.org/10.1073/pnas.1100189108">locust outbreaks for almost 2,000 years</a>, while paleo-ecological studies show that Québec’s boreal forests have witnessed <a href="https://doi.org/10.1139/cjfr-2017-0009">spruce budworm outbreaks for at least 8,000 years</a>. </p>
<p>Such insect outbreaks are part of how temperate and boreal forests — as well as semi-arid grasslands and deserts — function. Insect outbreaks stimulate nutrient cycling, accelerate forest succession and can <a href="https://www.nrcan.gc.ca/our-natural-resources/forests/wildland-fires-insects-disturbances/why-forests-need-fires-insects-and-diseases/13081">renew forests</a>. </p>
<figure class="align-right ">
<img alt="A moth laying eggs" src="https://images.theconversation.com/files/490978/original/file-20221020-23-f2351s.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=237&fit=clip" srcset="https://images.theconversation.com/files/490978/original/file-20221020-23-f2351s.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=845&fit=crop&dpr=1 600w, https://images.theconversation.com/files/490978/original/file-20221020-23-f2351s.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=845&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/490978/original/file-20221020-23-f2351s.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=845&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/490978/original/file-20221020-23-f2351s.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=1062&fit=crop&dpr=1 754w, https://images.theconversation.com/files/490978/original/file-20221020-23-f2351s.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=1062&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/490978/original/file-20221020-23-f2351s.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=1062&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">Female insects can produce hundreds of offspring and only two of these need to survive for a stable population.</span>
<span class="attribution"><span class="source">(AP Photo/Bob Child, File)</span></span>
</figcaption>
</figure>
<p>Female insects can produce hundreds of offspring and for the population to remain stable, only two of these need to survive. A small increase in survival, due to factors like favorable weather conditions, can lead to a population explosion and an outbreak.</p>
<p>In the case of the <a href="http://dx.doi.org/10.1641/B580607">mountain pine beetle</a> and the <a href="https://doi.org/10.1038/s41558-020-0835-8">desert locust</a>, warming temperatures, increased cyclone activity and other such effects of climate change are bringing these favorable conditions more frequently to new areas, thus dramatically increasing the extent of outbreaks. </p>
<p>However, these outbreaks always come to an end because of what ecologists call <a href="https://www.nature.com/scitable/knowledge/library/dynamics-of-predation-13229468/">lagged-density dependent population dynamics</a>. Here, density-dependent means that the insects’ mortality rate depends on the density of its population. As the population increases, mortality also increases and survival rate decreases. Meanwhile, lagged means there is a delay in this process — the insect mortality increases more slowly than population growth, causing an outbreak.</p>
<p>The outbreak crashes when the insect mortality eventually catches up with its population size. This usually happens due to a combination of factors including low food supply and increase in predators, parasitoids — insects that lay their eggs inside other insects — and diseases. </p>
<h2>Where did the spongy moth go?</h2>
<p><a href="https://www.concordia.ca/artsci/biology/faculty.html.html?fpid=emma-despland">Students in my laboratory</a> have been rearing spongy moth caterpillars for the past three years and have found that the mortality of these caterpillars gradually increased as the population grew. </p>
<p>In 2019, one student, Pamela Yataco Marquez reared over 300 caterpillars and observed an 80 per cent survival rate. However, this year, despite an extensive search, Marie-Eve Jarry, Geovana Demarchi and Victoria Yip were able to find and rear only 97 caterpillars and only six survived to adult. </p>
<figure class="align-center ">
<img alt="A freshly emerged lab-reared moth." src="https://images.theconversation.com/files/490736/original/file-20221019-13-8iisbk.JPG?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/490736/original/file-20221019-13-8iisbk.JPG?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=795&fit=crop&dpr=1 600w, https://images.theconversation.com/files/490736/original/file-20221019-13-8iisbk.JPG?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=795&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/490736/original/file-20221019-13-8iisbk.JPG?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=795&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/490736/original/file-20221019-13-8iisbk.JPG?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=999&fit=crop&dpr=1 754w, https://images.theconversation.com/files/490736/original/file-20221019-13-8iisbk.JPG?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=999&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/490736/original/file-20221019-13-8iisbk.JPG?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=999&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">This freshly emerged lab-reared female spongy moth is one of the few survivors of 2022.</span>
<span class="attribution"><span class="source">(Victoria Yip)</span>, <span class="license">Author provided</span></span>
</figcaption>
</figure>
<p>Several <a href="https://doi.org/10.2737/NRS-GTR-179">mortality agents</a> including a virus <em>Lymantria dispar multiple nucleopolyhedrovirus</em>, the fungal disease <em>Entomophaga maimaiga</em> and two tiny parasitoid wasps called <em>Cotesia melanoscela</em> and <em>Ooencyrtus kuvanae</em> finally caught up with the insect population.</p>
<p>When parasitoids eggs — laid inside either the eggs or the bodies of other insects — hatch, they devour their host from the inside and eventually emerge from the dead host, ready to start the life-cycle anew. </p>
<p>They are more like predators than parasites because they kill their host, and are efficient biocontrol agents that decrease pest insect populations. </p>
<h2>Creeping across borders</h2>
<p>While the spongy moth is native to Europe, it has been in eastern North America since the 1860s and <a href="https://www.invasivespeciescentre.ca/invasive-species/meet-the-species/invasive-insects/gypsy-moth/">is part of our fauna now</a>.</p>
<p>It has not reached the western part of the continent yet and the best way to stop this is to inspect outdoor gear for caterpillars or egg masses before travelling and <a href="http://www.invadingspecies.com/invaders/forest/spongy-moth/">not to move firewood</a>. </p>
<p>The Asian spongy moth population has not spread in North America yet, and <a href="https://www.nrcan.gc.ca/simply-science/canadian-forest-service-research-keeping-agm-invaders-out-canada/20992">entomologists are working hard to keep it out</a>.</p>
<figure class="align-center ">
<img alt="A moth caterpillar on a partially eaten leaf." src="https://images.theconversation.com/files/490738/original/file-20221019-16005-mk4ufs.jpeg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/490738/original/file-20221019-16005-mk4ufs.jpeg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=800&fit=crop&dpr=1 600w, https://images.theconversation.com/files/490738/original/file-20221019-16005-mk4ufs.jpeg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=800&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/490738/original/file-20221019-16005-mk4ufs.jpeg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=800&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/490738/original/file-20221019-16005-mk4ufs.jpeg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=1005&fit=crop&dpr=1 754w, https://images.theconversation.com/files/490738/original/file-20221019-16005-mk4ufs.jpeg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=1005&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/490738/original/file-20221019-16005-mk4ufs.jpeg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=1005&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">The current range of the spongy moth distribution in North America extends up to southern Canada.</span>
<span class="attribution"><span class="source">(Geovana Demarchi)</span>, <span class="license">Author provided</span></span>
</figcaption>
</figure>
<p>In the past 150 years, many of the European spongy moth’s natural enemies, including the fungal disease mentioned above and several parasitoids, have also been <a href="https://fyi.extension.wisc.edu/spongymothinwisconsin/biological-control/">introduced, either inadvertently or deliberately</a>. Our findings show that these natural enemies are well established in our region and have been effective in collapsing the outbreak.</p>
<p>The current range of the spongy moth distribution in North America extends up to southern Canada. Here, the <a href="https://doi.org/10.1111/jbi.13474">eggs that spend the winter on tree trunks suffer high mortality due to cold,</a> knocking down the survival rate irrespective of population size. </p>
<p>Forest managers in <a href="https://mffp.gouv.qc.ca/documents/forets/RA_2021_DPF.pdf">Québec</a> and <a href="https://www.ontario.ca/page/lymantria-dispar-dispar-ldd-moth">Ontario</a> are on the alert for increases in spongy moth outbreaks — including both more severe and longer duration outbreaks similar to those seen in the U.S. — and a possible northward shift of the distribution range. </p>
<h2>Diverse forests</h2>
<p>While a tree that is leafless in July may appear dead, many trees can survive a few years of defoliation, drawing on stored reserves to flush out new leaves. </p>
<p>The spongy moth outbreak in the Montréal area in the late 1970s slowed tree growth, but did not cause the widespread death of forest trees. However, <a href="https://academic.oup.com/forestscience/article/45/1/74/4627518">tree mortality</a> does occur further south in the U.S. and depends on the diversity of trees in the forest area. The death of tree species preferred by the caterpillar is lower in diverse forests that mix in less-vulnerable species. </p>
<p><a href="http://dx.doi.org/10.1111/conl.12829">Diverse forests</a> are more resilient under various stresses than more homogeneous ones. We need to create and preserve such diverse forests to help prepare for new types of insect outbreaks in our changing world.</p><img src="https://counter.theconversation.com/content/190395/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Emma Despland receives funding from the NSERC Alliance-Mitacs Accelerate grant.</span></em></p>Creating and preserving diverse forests can help us prepare for the next insect outbreak and protect our trees.Emma Despland, Professor, Biology Department, Concordia UniversityLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/1847302022-07-12T12:33:24Z2022-07-12T12:33:24ZLight pollution is disrupting the seasonal rhythms of plants and trees, lengthening pollen season in US cities<figure><img src="https://images.theconversation.com/files/473427/original/file-20220711-13-xmyjzd.jpg?ixlib=rb-1.1.0&rect=0%2C1772%2C3712%2C2160&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">Some cities never sleep.</span> <span class="attribution"><a class="source" href="https://www.gettyimages.com/detail/photo/light-trails-on-city-street-against-sky-at-night-royalty-free-image/1311603238">Noam Cohen/EyeEm via Getty Images</a></span></figcaption></figure><p><em>The <a href="https://theconversation.com/us/topics/research-brief-83231">Research Brief</a> is a short take about interesting academic work.</em></p>
<h2>The big idea</h2>
<p>City lights that blaze all night are profoundly disrupting urban plants’ phenology – shifting when their buds open in the spring and when their leaves change colors and drop in the fall. New research I coauthored shows how nighttime lights are <a href="https://doi.org/10.1093/pnasnexus/pgac046">lengthening the growing season in cities</a>, which can affect everything from <a href="https://doi.org/10.1001/jamanetworkopen.2020.7551">allergies</a> to local economies.</p>
<p>In our study, my colleagues and I analyzed trees and shrubs at about 3,000 sites in U.S. cities to see <a href="https://doi.org/10.1093/pnasnexus/pgac046">how they responded</a> under different lighting conditions over a five-year period. Plants use <a href="https://islandpress.org/books/ecological-consequences-artificial-night-lighting">the natural day-night cycle</a> as a signal of seasonal change along with <a href="https://doi.org/10.1073/pnas.1911117117">temperature</a>.</p>
<p>We found that artificial light alone <a href="https://doi.org/10.1093/pnasnexus/pgac046">advanced the date that leaf buds broke</a> in the spring by an average of about nine days compared to sites without nighttime lights. The timing of the fall color change in leaves was more complex, but the leaf change was still delayed on average by nearly six days across the lower 48 states. In general, we found that the more intense the light was, the greater the difference.</p>
<p><iframe id="gSKIJ" class="tc-infographic-datawrapper" src="https://datawrapper.dwcdn.net/gSKIJ/9/" height="400px" width="100%" style="border: none" frameborder="0"></iframe></p>
<p>We also projected the future influence of nighttime lights for five U.S. cities – Minneapolis, Chicago, Washington, Atlanta and Houston – based on different scenarios for future global warming and up to a 1% annual increase in nighttime light intensity. We found that increasing nighttime light would likely continue to shift the start of the season earlier, though its influence on the fall color change timing was more complex.</p>
<h2>Why it matters</h2>
<p>This kind of shift in plants’ biological clocks has important implications for the <a href="https://doi.org/10.1016/j.tourman.2018.08.021">economic</a>, <a href="https://theconversation.com/satellites-zoom-in-on-cities-hottest-neighborhoods-to-help-combat-the-urban-heat-island-effect-182925">climate</a>, <a href="https://doi.org/10.1001/jamanetworkopen.2020.7551">health</a> and <a href="https://doi.org/10.1098/rsbl.2014.0586">ecological</a> services that urban plants provide.</p>
<p>On the positive side, longer growing seasons could allow urban farms to <a href="https://doi.org/10.2134/jeq2013.01.0031">be active over longer periods of time</a>. Plants could also provide shade to cool neighborhoods earlier in spring and later in fall as global temperatures rise.</p>
<p>But changes to the growing season could also increase plants’ <a href="https://doi.org/10.1038/s41586-018-0399-1">vulnerability to spring frost damage</a>. And it can create a mismatch with the timing of other organisms, <a href="https://doi.org/10.1042/ETLS20190139">such as pollinators</a>, that some urban plants rely on.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/473542/original/file-20220712-22-1d5slr.png?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="Charts show the intensity of urban light in seven representative cities" src="https://images.theconversation.com/files/473542/original/file-20220712-22-1d5slr.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/473542/original/file-20220712-22-1d5slr.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=403&fit=crop&dpr=1 600w, https://images.theconversation.com/files/473542/original/file-20220712-22-1d5slr.png?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=403&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/473542/original/file-20220712-22-1d5slr.png?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=403&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/473542/original/file-20220712-22-1d5slr.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=506&fit=crop&dpr=1 754w, https://images.theconversation.com/files/473542/original/file-20220712-22-1d5slr.png?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=506&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/473542/original/file-20220712-22-1d5slr.png?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=506&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">Urban light intensity varies among cities, and among neighborhoods within cities.</span>
<span class="attribution"><span class="source">Yuyu Zhou</span>, <a class="license" href="http://creativecommons.org/licenses/by-nd/4.0/">CC BY-ND</a></span>
</figcaption>
</figure>
<p>A longer active season for urban plants also suggests an earlier and longer pollen season, which can exacerbate asthma and other breathing problems. A study in Maryland found a <a href="https://doi.org/10.1001/jamanetworkopen.2020.7551">17% increase</a> in hospitalizations for asthma in years when plants bloomed very early.</p>
<h2>What still isn’t known</h2>
<p>How the fall color timing will change going forward as night lighting increases and temperatures rise is less clear. Temperature and artificial light together influence the fall color in a complex way, and our projections suggested that the delay of coloring date due to climate warming might stop midcentury and possibly reverse because of artificial light. This will require more research.</p>
<p>How urban artificial light will change in the future also remains to be seen.</p>
<p>One study found that urban light at night had increased <a href="https://doi.org/10.1126/sciadv.1701528">by about 1.8% per year</a> worldwide from 2012-2016. However, many cities and states are <a href="https://www.ncsl.org/research/environment-and-natural-resources/states-shut-out-light-pollution.aspx">trying to reduce light pollution</a>, including requiring shields to control where the light goes and shifting to LED street lights, which use less energy and have <a href="https://doi.org/10.1111/1365-2664.12927">less of an effect</a> on plants than traditional streetlights with <a href="https://doi.org/10.1038/35036500">longer wavelengths</a>.</p>
<figure class="align-center ">
<img alt="Cars are parked on an old brick residential street at dusk with street lights and trees lining the sidewalks." src="https://images.theconversation.com/files/473435/original/file-20220711-14-a2ls8a.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/473435/original/file-20220711-14-a2ls8a.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=450&fit=crop&dpr=1 600w, https://images.theconversation.com/files/473435/original/file-20220711-14-a2ls8a.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=450&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/473435/original/file-20220711-14-a2ls8a.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=450&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/473435/original/file-20220711-14-a2ls8a.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=566&fit=crop&dpr=1 754w, https://images.theconversation.com/files/473435/original/file-20220711-14-a2ls8a.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=566&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/473435/original/file-20220711-14-a2ls8a.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=566&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">Baltimore has been converting its streetlights to LED to save money on energy. LEDs also have less of an impact on plants.</span>
<span class="attribution"><a class="source" href="https://www.gettyimages.com/detail/photo/cobblestone-street-and-fells-point-neighborhood-at-royalty-free-image/1179432549">Cyndi Monaghan via Getty Images</a></span>
</figcaption>
</figure>
<p>Urban plants’ phenology may also be influenced by other factors, such as carbon dioxide and soil moisture. Additionally, the faster increase of temperature at night compared to the daytime could lead to different day-night temperature patterns, which might <a href="https://doi.org/10.1016/j.agrformet.2019.107832">affect plant phenology in complex ways</a>.</p>
<p>Understanding these interactions between plants and artificial light and temperature will help scientists <a href="https://doi.org/10.1038/s41558-022-01331-7">predict changes in plant processes under a changing climate</a>. Cities are already serving as natural laboratories.</p><img src="https://counter.theconversation.com/content/184730/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Yuyu Zhou receives funding from the College of Liberal Arts and Sciences at Iowa State University. </span></em></p>Artificial light is upending trees’ ability to use the natural day-night cycle as a signal of seasonal change.Yuyu Zhou, Associate Professor of Environmental Science, Iowa State UniversityLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/1798122022-04-13T12:13:16Z2022-04-13T12:13:16ZRedwood trees have two types of leaves, scientists find – a trait that could help them survive in a changing climate<figure><img src="https://images.theconversation.com/files/457498/original/file-20220411-11-h2ic9b.jpg?ixlib=rb-1.1.0&rect=16%2C0%2C5542%2C3709&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">Coastal redwoods in Felton, California.</span> <span class="attribution"><a class="source" href="https://www.gettyimages.com/detail/news-photo/coastal-redwoods-stand-in-the-henry-cowell-redwoods-state-news-photo/915647562">Carolyn Van Houten/The Washington Post via Getty Images</a></span></figcaption></figure><p>Coast redwoods are amazing trees that scientists have studied for generations. We know they are <a href="https://doi.org/10.1038/nature02417">the tallest living trees</a> and have survived for millennia, <a href="https://academic.oup.com/jof/article-abstract/29/6/939/4719848">resisting fire</a> and <a href="https://nzjforestryscience.springeropen.com/articles/10.1186/s40490-014-0017-4">pests</a>. Because redwoods are long-lived, large and decay-resistant, the forests they dominate store <a href="https://doi.org/10.1016/j.foreco.2016.05.018">more above-ground mass, and thus presumably more carbon</a>, than any other ecosystem on Earth. </p>
<p>Nonetheless, while working on a recently published study, colleagues at the <a href="https://scholar.google.com/citations?user=qeqqJqwAAAAJ">University of California</a>, <a href="https://scholar.google.com/citations?user=S3LivCgAAAAJ&hl=es">Davis</a>, and <a href="https://scholar.google.com/citations?user=5dqacuQAAAAJ&hl=en">Cal Poly</a> <a href="https://kerhoulasforestlab.weebly.com/">Humboldt</a> and <a href="https://scholar.google.com/citations?hl=en&user=Qv4DpXAAAAAJ">I</a> learned a secret that had been sitting right under our noses. </p>
<p>Redwoods, it turns out, have two types of leaves that look different and perform very different tasks. This previously unknown feature helps the trees adapt to both wet and dry conditions – an ability that could be key to their survival in a changing climate.</p>
<figure>
<iframe width="440" height="260" src="https://www.youtube.com/embed/-swLTsWXPII?wmode=transparent&start=0" frameborder="0" allowfullscreen=""></iframe>
<figcaption><span class="caption">Redwoods can live for more than 2,000 years and grow to more than 350 feet tall.</span></figcaption>
</figure>
<h2>Just enough water</h2>
<p>Wherever trees grow, sooner or later their leaves get wet. For trees in wet environments, this can be a problem if films of water <a href="https://doi.org/10.1111/j.1365-3040.1995.tb00377.x">cover their stomata</a>. These tiny pores allow carbon dioxide to enter leaves so the tree can combine it with water to make plant tissue through <a href="https://www.usda.gov/media/blog/2015/03/17/power-one-tree-very-air-we-breathe">photosynthesis</a>. Many trees that are common to wet forests have leaves with adaptations that <a href="https://doi.org/10.1073/pnas.95.24.14256">prevent these water films from forming</a>. </p>
<p>In contrast, trees growing in dry environments take advantage of brief bouts of leaf wetness to <a href="https://doi.org/10.1111/nph.15307">take up valuable water</a> directly across the surfaces of their leaves, <a href="http://dx.doi.org/10.1111/pce.13439">through special leaf structures</a>, and even <a href="https://doi.org/10.1111/pce.14041">through their stomata</a>. But some trees, including coast redwoods, live in both wet and dry environments with intense seasonal variation. </p>
<p>For broad-leaved trees like the <a href="https://doi.org/10.1104/pp.114.242040">holm oak</a>, which grows in Mediterranean climates with dry summers and rainy winters, this seasonal wetness challenge is relatively easy to overcome. Their stomata are on the sheltered undersides of their leaves, which keeps them clear of water, while the leaves’ top surfaces absorb water. But redwoods are conifers, or cone-bearing trees, with <a href="https://ucanr.edu/sites/forestry/California_forests/http___ucanrorg_sites_forestry_California_forests_Tree_Identification_/Coast_Redwood_Sequoia_sempervirens_198/">thin, flat needlelike</a> leaves, and they need a different way to balance the competing goals of repelling and absorbing water. </p>
<figure class="align-right zoomable">
<a href="https://images.theconversation.com/files/457504/original/file-20220411-11-gw6ixl.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="Oval-shaped opening on a wavy green surface." src="https://images.theconversation.com/files/457504/original/file-20220411-11-gw6ixl.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=237&fit=clip" srcset="https://images.theconversation.com/files/457504/original/file-20220411-11-gw6ixl.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=615&fit=crop&dpr=1 600w, https://images.theconversation.com/files/457504/original/file-20220411-11-gw6ixl.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=615&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/457504/original/file-20220411-11-gw6ixl.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=615&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/457504/original/file-20220411-11-gw6ixl.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=772&fit=crop&dpr=1 754w, https://images.theconversation.com/files/457504/original/file-20220411-11-gw6ixl.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=772&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/457504/original/file-20220411-11-gw6ixl.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=772&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">A single stoma on a tomato leaf, shown via electron microscope.</span>
<span class="attribution"><a class="source" href="https://en.wikipedia.org/wiki/Stoma#/media/File:Tomato_leaf_stomate_1-color.jpg">Photohound/Wikipedia</a></span>
</figcaption>
</figure>
<p>We knew we wanted to explore how redwoods met the paradoxical challenge of leaf wetness, how much water redwoods could absorb and which leaf features caused differences in water uptake capacity. What we learned came as a total surprise.</p>
<h2>Big trees with big secrets</h2>
<p>Scientists have long known about redwoods’ <a href="https://doi.org/10.1111/j.1365-3040.2004.01207.x">ability to absorb water through their leaves</a>. But figuring out how much water redwoods can absorb this way, and how the capacity to do so might vary from one type of climate to another, is a real challenge in this species. </p>
<p>First, a big redwood has over 100 million leaves with a <a href="https://doi.org/10.1016/j.foreco.2016.05.018">massive amount of surface area</a> for water absorption. And these leaves <a href="https://doi.org/10.1016/j.foreco.2016.05.018">drastically change structure with height</a>, going from long and flat to short and awllike. So we couldn’t get this right by simply picking leaves at ground level.</p>
<p>To complicate matters further, gravity is always pushing down on the giant column of water rising upward through a redwood’s trunk. As a result, leaves at the top of the tree <a href="https://doi.org/10.1038/nature02417">always have less available water</a> than those lower down. The treetop’s inherent dryness should pull water into the leaf more quickly than into water-rich leaves at the bottom, just as a dry sponge picks up water faster than a damp one. </p>
<figure class="align-right zoomable">
<a href="https://images.theconversation.com/files/457508/original/file-20220411-26-5iu2ea.png?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="Map showing historic and current distribution of coast redwoods." src="https://images.theconversation.com/files/457508/original/file-20220411-26-5iu2ea.png?ixlib=rb-1.1.0&q=45&auto=format&w=237&fit=clip" srcset="https://images.theconversation.com/files/457508/original/file-20220411-26-5iu2ea.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=716&fit=crop&dpr=1 600w, https://images.theconversation.com/files/457508/original/file-20220411-26-5iu2ea.png?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=716&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/457508/original/file-20220411-26-5iu2ea.png?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=716&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/457508/original/file-20220411-26-5iu2ea.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=899&fit=crop&dpr=1 754w, https://images.theconversation.com/files/457508/original/file-20220411-26-5iu2ea.png?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=899&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/457508/original/file-20220411-26-5iu2ea.png?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=899&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">Coast redwoods’ range extends from southern Oregon to California’s Big Sur coast.</span>
<span class="attribution"><a class="source" href="https://www.parks.ca.gov/?page_id=24723">California Department of Parks and Recreation</a></span>
</figcaption>
</figure>
<p>For an accurate picture of how redwoods absorbed water, we needed leaves from trees in wet and dry environments, and from multiple heights on those trees. To get them to their natural gravity-based water levels for analysis, we put our leaf samples in a <a href="https://doi.org/10.1111/pce.13327">fog chamber</a> – in this case, an ice chest hooked up to a room humidifier – and measured weight gain over time to see how much water they could absorb.</p>
<h2>A trail of clues</h2>
<p>As we took apart clusters of redwood shoots to immerse them in fog, we divided each cluster into pieces. Redwood shoot clusters fan out from a woody core and are segmented into individual shoots of multiple ages, each with its own set of leaves. We separated shoots along <a href="https://doi.org/10.1093/treephys/tpu011">the woody central axis</a> from the much more common pliable shoots on the outer edges of each cluster. </p>
<p>It quickly became obvious that shoots from the center axis had leaves that could absorb water three times faster than peripheral leaves. When we looked inside the leaves with a microscope, we understood that they were two completely different types. They don’t look the same on the outside either, but this was so unexpected that we needed to see their internal structure to really convince ourselves. </p>
<p>The axial leaves were packed with water storage cells, but their phloem – tubes in the leaves that export photosynthetic sugars to the tree – appeared to be blocked and useless. If a tree has leaves, the conventional wisdom is that they are there for photosynthesis, but we wondered whether the axial leaves had a different purpose.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/457500/original/file-20220411-13-ve7ex9.jpeg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="Two types of redwood shoots" src="https://images.theconversation.com/files/457500/original/file-20220411-13-ve7ex9.jpeg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/457500/original/file-20220411-13-ve7ex9.jpeg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=450&fit=crop&dpr=1 600w, https://images.theconversation.com/files/457500/original/file-20220411-13-ve7ex9.jpeg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=450&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/457500/original/file-20220411-13-ve7ex9.jpeg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=450&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/457500/original/file-20220411-13-ve7ex9.jpeg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=566&fit=crop&dpr=1 754w, https://images.theconversation.com/files/457500/original/file-20220411-13-ve7ex9.jpeg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=566&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/457500/original/file-20220411-13-ve7ex9.jpeg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=566&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">Redwoods’ broad peripheral leaves, shown at left, make up about 95% of the trees’ leaf area and do all the photosynthesis. Their axial leaves, at right, are adept at absorbing water.</span>
<span class="attribution"><span class="source">Alana Chin</span>, <a class="license" href="http://creativecommons.org/licenses/by-nd/4.0/">CC BY-ND</a></span>
</figcaption>
</figure>
<p>With some additional measurements, we found that redwoods’ axial leaves are specialized for absorbing water. Differences between the surfaces of axial and peripheral leaves, especially their wax coverage, cause the differences in their water absorption rates.</p>
<p>Unlike the axial leaves, redwoods’ peripheral leaves have waxy surfaces with lots of stomata. This helped to explain how they <a href="https://academic.oup.com/treephys/article/30/10/1260/1658568">photosynthesize year-round</a> regardless of the long wet season in much of their current habitat.</p>
<p>Further analysis showed that the redwoods’ axial leaves account for only about 5% of the trees’ total leaf area, and barely produce enough energy through photosynthesis to maintain themselves. But they contribute up to 30% of the trees’ total water absorption capacity. Together these two types of leaves balance the dueling requirements of photosynthesis and water absorption, allowing redwoods to thrive in both wet and dry habitats. </p>
<p>[<em>More than 150,000 readers get one of The Conversation’s informative newsletters.</em> <a href="https://memberservices.theconversation.com/newsletters/?source=inline-150K">Join the list today</a>.]</p>
<p>Using large-scale <a href="https://www.youtube.com/watch?v=B4JAyIAhgIU&t=89s">tree measurements</a> and <a href="https://doi.org/10.1890/14-1016.1">equations for estimating redwood leaf area</a>, we estimated that these thirsty giants can absorb as much as 105 pounds (48 kilograms) of water in the first hour of a rainfall wetting their leaves. That’s equivalent to 101 pints of beer.</p>
<h2>The significance to redwoods</h2>
<p>Understanding what causes the variation in redwood leaves’ uptake capacity can help us gauge differences in water uptake capabilities among trees and environments, now and in the future. In my opinion, this is the most potentially useful part of our study.</p>
<p>Redwoods vary their two leaf types to suit their local climates. In wet rainforests in the northern part of their range, above Mendocino County, the trees invest in fewer of the axial leaves that are specialized for absorbing water. These leaves are concentrated in the trees’ lower crowns, leaving the photosynthetically <a href="https://doi.org/10.1093/treephys/tpp037">high-performing treetops</a> free to maximize sugar production in the bright sun. </p>
<figure class="align-right zoomable">
<a href="https://images.theconversation.com/files/457510/original/file-20220411-6515-ece0z9.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="Leaf under a microscope, covered with white dots." src="https://images.theconversation.com/files/457510/original/file-20220411-6515-ece0z9.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=237&fit=clip" srcset="https://images.theconversation.com/files/457510/original/file-20220411-6515-ece0z9.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=510&fit=crop&dpr=1 600w, https://images.theconversation.com/files/457510/original/file-20220411-6515-ece0z9.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=510&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/457510/original/file-20220411-6515-ece0z9.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=510&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/457510/original/file-20220411-6515-ece0z9.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=641&fit=crop&dpr=1 754w, https://images.theconversation.com/files/457510/original/file-20220411-6515-ece0z9.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=641&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/457510/original/file-20220411-6515-ece0z9.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=641&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">Wax on the surface of a redwood leaf. The white dots are water-resistant plugs in the stomata.</span>
<span class="attribution"><span class="source">Marty Reed</span>, <a class="license" href="http://creativecommons.org/licenses/by-nd/4.0/">CC BY-ND</a></span>
</figcaption>
</figure>
<p>In dry forests on the southern margins of redwoods’ range, trees have more axial leaves in their water-stressed tops. This allows them to take better advantage of briefer leaf-wetting events, but it means they photosynthesize less per leaf area than redwoods in wetter areas. </p>
<p>Redwoods’ ability to shift leaf types to match regional climatic differences may help them adjust to climate change in an <a href="https://theconversation.com/californias-water-supplies-are-in-trouble-as-climate-change-worsens-natural-dry-spells-especially-in-the-sierra-nevada-173142">ever-drier California</a>. That would be good news for conserving these epic trees, and it may be a promising feature to investigate as scientists try to <a href="https://onlinelibrary.wiley.com/doi/epdf/10.1111/tpj.15592">link drought tolerance traits</a> to regional differences among redwood populations.</p><img src="https://counter.theconversation.com/content/179812/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Alana Chin received funding from the NSF GRFP</span></em></p>New research shows that coast redwood trees have a surprising adaptation that helps them thrive in both wet and dry environments.Alana Chin, Postdoctoral Fellow in Plant Ecology, Swiss Federal Institute of Technology ZurichLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/1601602021-06-09T12:38:29Z2021-06-09T12:38:29ZA volcanic eruption 39 million years ago buried a forest in Peru – now the petrified trees are revealing South America’s primeval history<figure><img src="https://images.theconversation.com/files/398215/original/file-20210501-17-1d2fvcu.png?ixlib=rb-1.1.0&rect=0%2C2%2C1497%2C958&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">With the evidence uncovered by paleontologists, an artist sketched El Bosque Petrificado Piedra Chamana as it might have looked long before humans.</span> <span class="attribution"><a class="source" href="https://www.nps.gov/flfo/learn/nature/peru-eocene-forest.htm">Mariah Slovacek/NPS-GIP</a></span></figcaption></figure><p>In the hills outside the small village of <a href="https://www.nps.gov/flfo/learn/photosmultimedia/the-petrified-forest-of-sexi-peru-gallery.htm">Sexi, Peru</a>, a fossil forest holds secrets about South America’s past millions of years ago.</p>
<p>When we first visited these petrified trees more than 20 years ago, not much was known about their age or how they came to be preserved. We started by <a href="https://www.nature.com/scitable/knowledge/library/dating-rocks-and-fossils-using-geologic-methods-107924044">dating the rocks</a> and studying the volcanic processes that preserved the fossils. From there, we began to piece together the story of the forest, starting from the day 39 million years ago when a volcano erupted in northern Peru.</p>
<p>Ash rained down on the forest that day, stripping leaves from the trees. Then flows of ashy material moved through, breaking off the trees and carrying them like logs in a river to the area where they were buried and preserved. Millions of years later, after the <a href="https://pubs.geoscienceworld.org/gsa/gsabulletin/article-abstract/112/7/1091/183664/Uplift-history-of-the-Central-and-Northern-Andes-A">modern-day Andes rose</a> and carried the fossils with them, the rocks were exposed to the forces of erosion, and the fossil woods and leaves again saw the light of day.</p>
<p>This petrified forest, <a href="https://www.nps.gov/flfo/learn/nature/sexi-peru.htm">El Bosque Perificado Piedra Chamana</a>, is
the first fossil forest from the South American tropics to be studied in detail. It is helping <a href="https://scholar.google.com/citations?user=b6PMkG0AAAAJ&hl=en">paleontologists</a> <a href="https://www.researchgate.net/scientific-contributions/Herbert-W-Meyer-2110283149">like us</a> to understand the history of the megadiverse forests of the New World tropics and the past climates and environments of South America. </p>
<p>By examining thin slices of petrified wood under microscopes, we were able to map out the mix of trees that thrived here long before humans existed. </p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/403437/original/file-20210529-15-1nkuxl4.png?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="An artist's illustrations of each of the most common variety of trees found, plus cross-sections of the fossil wood as seen under a microscope" src="https://images.theconversation.com/files/403437/original/file-20210529-15-1nkuxl4.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/403437/original/file-20210529-15-1nkuxl4.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=825&fit=crop&dpr=1 600w, https://images.theconversation.com/files/403437/original/file-20210529-15-1nkuxl4.png?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=825&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/403437/original/file-20210529-15-1nkuxl4.png?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=825&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/403437/original/file-20210529-15-1nkuxl4.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=1037&fit=crop&dpr=1 754w, https://images.theconversation.com/files/403437/original/file-20210529-15-1nkuxl4.png?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=1037&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/403437/original/file-20210529-15-1nkuxl4.png?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=1037&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">The tree key from Sexi, Peru, with cross-sections of the wood.</span>
<span class="attribution"><a class="source" href="https://www.nps.gov/flfo/learn/nature/peru-eocene-forest.htm">Mariah Slovacek/National Park Service</a>, <a class="license" href="http://creativecommons.org/licenses/by-nd/4.0/">CC BY-ND</a></span>
</figcaption>
</figure>
<h2>Petrified wood under a microscope</h2>
<p>To figure out the types of trees that had been growing in the forest before the eruption, we needed thin samples of the petrified wood that could be studied under a microscope. That was not so easy because of the volume and diversity of fossil wood at the site.</p>
<p>We tried to sample the diversity of the woods by relying on features that could be observed with the naked eye or with small hand-held microscopes, things like the arrangement and width of <a href="https://www.wood-database.com/wood-articles/hardwood-anatomy/">the vessels</a> that carry water upwards within the tree or the presence of tree rings. Then we cut small blocks from the specimens, and from those we were able to prepare petrographic thin sections in three planes. Each plane gives us a different view of the tree’s anatomy. They allow us to see many detailed features relating to the vessels, the wood fibers and the living-tissue component of the wood. </p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/404127/original/file-20210602-27-19scww6.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="Three magnified cross-sections from a tree fossil" src="https://images.theconversation.com/files/404127/original/file-20210602-27-19scww6.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/404127/original/file-20210602-27-19scww6.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=254&fit=crop&dpr=1 600w, https://images.theconversation.com/files/404127/original/file-20210602-27-19scww6.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=254&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/404127/original/file-20210602-27-19scww6.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=254&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/404127/original/file-20210602-27-19scww6.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=319&fit=crop&dpr=1 754w, https://images.theconversation.com/files/404127/original/file-20210602-27-19scww6.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=319&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/404127/original/file-20210602-27-19scww6.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=319&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">Thin sections of wood identified as <em>Cynometra</em>, a tree in the legume family. The vessels in the cross section are about one-tenth of a millimeter wide. The two sections on the right show details of the wood structure at a higher magnification.</span>
<span class="attribution"><span class="source">Woodcock et al. 2017</span>, <a class="license" href="http://creativecommons.org/licenses/by-nd/4.0/">CC BY-ND</a></span>
</figcaption>
</figure>
<p>Based on these features, we were able to consult past studies and use information in <a href="https://insidewood.lib.ncsu.edu/search?1">wood databases</a> to find out what types of trees were present. </p>
<h2>Clues in the woods and leaves</h2>
<p>Many of the fossil trees have close relatives in the present-day lowland tropical forests of South America. </p>
<p>One has features typical of lianas, which are woody vines. Others appear to have been large canopy trees, including relatives of modern <em>Ceiba</em>. We also found trees that are well known in the forests of South America like <em>Hura</em>, or sandbox tree; <em>Anacardium</em>, a type of cashew tree; and <em>Ochroma</em>, or balsa. The largest specimen at the Sexi site – a fossil trunk about 2.5 feet (75 cm) in diameter – has features like those of <em>Cynometra</em>, a tree in the legume family. </p>
<p>The discovery of a mangrove, <em>Avicennia</em>, was more evidence that the forest was growing at a low elevation near the sea before the Andes rose.</p>
<p>The fossil leaves we found provided another clue to the past. All had smooth edges, rather than the toothed edges or lobes that are more common in the cooler climates of the mid- to high latitudes, indicating that the forest experienced quite warm conditions. We know the forest was growing at a time in the geologic past when the Earth <a href="https://www.pnas.org/content/115/52/13288">was much warmer</a> than today. </p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/403438/original/file-20210529-16-gv81xm.png?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="Fossilized leaves with clear detail." src="https://images.theconversation.com/files/403438/original/file-20210529-16-gv81xm.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/403438/original/file-20210529-16-gv81xm.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=410&fit=crop&dpr=1 600w, https://images.theconversation.com/files/403438/original/file-20210529-16-gv81xm.png?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=410&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/403438/original/file-20210529-16-gv81xm.png?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=410&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/403438/original/file-20210529-16-gv81xm.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=515&fit=crop&dpr=1 754w, https://images.theconversation.com/files/403438/original/file-20210529-16-gv81xm.png?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=515&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/403438/original/file-20210529-16-gv81xm.png?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=515&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">These leaf fossils belonged to a type of mangrove, indicating the forest was originally near the sea.</span>
<span class="attribution"><a class="source" href="https://www.nps.gov/flfo/learn/nature/peru-eocene-forest.htm">National Park Service</a>, <a class="license" href="http://creativecommons.org/licenses/by-nd/4.0/">CC BY-ND</a></span>
</figcaption>
</figure>
<p>Although there are many similarities between the petrified forest and present-day Amazonian forests, some of the fossil trees have anatomical features that are unusual in the South American tropics. One is a species of <em>Dipterocarpaceae</em>, a group that has <a href="https://doi.org/10.2307/2807116">only one other representative in South America</a> but that is common today in the rainforests of South Asia.</p>
<h2>An artist brings the forest to life</h2>
<p>Our concept of what this ancient forest was like expanded when we had an opportunity to collaborate with an artist at <a href="https://www.nps.gov/flfo/index.htm">Florissant Fossil Beds National Monument</a> in Colorado to reconstruct the forest and landscape. Other locations with fossil trees include Florissant, which has giant petrified redwood stumps, and <a href="https://www.nps.gov/pefo/index.htm">Petrifed Forest National Park</a> in Arizona. </p>
<p>Working with the artist, <a href="https://www.researchgate.net/scientific-contributions/Mariah-Slovacek-2135795828">Mariah Slovacek</a>, who is also a paleontologist, made us think critically about many things: What would the forest have looked like? Were the trees evergreen or deciduous? Which were tall and which shorter? What would they have looked like in flower or in fruit?</p>
<p>We knew from our investigation that many of the fossil trees were likely to have been growing in a streamside or flooded-forest location, but what about the vegetation growing back from the watercourses on higher ground? Would the hills have been forested or supported drier-adapted vegetation? Mariah researched today’s relatives of the trees we identified for clues to what they might have looked like, such as what shape and color their flowers or fruits might have been.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/403439/original/file-20210529-23-1a4za2s.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="A large petrified log on open ground with rugged hills in the background" src="https://images.theconversation.com/files/403439/original/file-20210529-23-1a4za2s.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/403439/original/file-20210529-23-1a4za2s.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=449&fit=crop&dpr=1 600w, https://images.theconversation.com/files/403439/original/file-20210529-23-1a4za2s.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=449&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/403439/original/file-20210529-23-1a4za2s.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=449&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/403439/original/file-20210529-23-1a4za2s.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=564&fit=crop&dpr=1 754w, https://images.theconversation.com/files/403439/original/file-20210529-23-1a4za2s.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=564&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/403439/original/file-20210529-23-1a4za2s.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=564&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">A large petrified log near Sexi, Peru.</span>
<span class="attribution"><a class="source" href="https://www.nps.gov/media/photo/gallery-item.htm?pg=2273150&id=F0B974CC-155D-451F-672612C41E8CE76B&gid=F0B97461-155D-451F-6713726C4134D4E9">National Park Service</a>, <a class="license" href="http://creativecommons.org/licenses/by-nd/4.0/">CC BY-ND</a></span>
</figcaption>
</figure>
<p>No fossils of mammals, birds or reptiles from the same time period have been found at the Sexi site, but the ancient forest certainly would have supported a diversity of wildlife. Birds had diversified by that time, and reptiles in the crocodile family had long swum the tropical seas.</p>
<p>Recent paleontological discoveries found that two important groups of animals – <a href="http://doi.org/10.1038/nature14120">monkeys and caviomorph rodents</a>, which include guinea pigs – had arrived on the continent at about the time the fossil forest was growing.</p>
<p>With this information, Mariah was able to populate the ancient forest. <a href="https://www.nps.gov/flfo/learn/nature/peru-eocene-forest.htm">The result</a> is a lush, waterside forest of tall flowering trees and woody vines. Birds swoop through the air and a crocodile splashes just offshore. You can almost imagine that you were there in the world of 39 million years ago.</p><img src="https://counter.theconversation.com/content/160160/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Deborah Woodcock has received funding from the American Philosophical Society, the National Science Foundation, and National Geographic. </span></em></p><p class="fine-print"><em><span>Herb Meyer has been supported in this project as an employee of the National Park Service, with additional funding provided by The Friends of the Florissant Fossil Beds, the National Science Foundation, and National Geographic.</span></em></p>Using remnants of fossilized trees, scientists and an artist figured out what the forest looked like long before humans existed.Deborah Woodcock, Research Scientist, Clark UniversityHerb Meyer, Paleontologist, National Park ServiceLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/1509512020-12-16T19:05:04Z2020-12-16T19:05:04ZHow the size and shape of dried leaves can turn small flames into colossal bushfires<figure><img src="https://images.theconversation.com/files/374743/original/file-20201214-15-1o7shbl.jpg?ixlib=rb-1.1.0&rect=14%2C22%2C4905%2C3231&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">
</span> <span class="attribution"><span class="source">Shutterstock</span></span></figcaption></figure><p>The 2020-21 fire season is well underway, and we’ve watched in horror as places like K'gari (Fraser Island) <a href="https://theconversation.com/the-kgari-fraser-island-bushfire-is-causing-catastrophic-damage-what-can-we-expect-when-its-all-over-151664">burn uncontrollably</a>, threatening people and their homes and <a href="https://theconversation.com/a-season-in-hell-bushfires-push-at-least-20-threatened-species-closer-to-extinction-129533">devastating the environment</a>. </p>
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<p>
<em>
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Read more:
<a href="https://theconversation.com/the-kgari-fraser-island-bushfire-is-causing-catastrophic-damage-what-can-we-expect-when-its-all-over-151664">The K'gari-Fraser Island bushfire is causing catastrophic damage. What can we expect when it's all over?</a>
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</p>
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<p>To lessen the impact of fires, we need to know when they are likely to burn and how intensely. Central to this is the flammability of litter beds — the layer of dead leaves, needles, twigs and bark on the forest floor. </p>
<p>Every large fire begins as a small fire, igniting and initially spreading through the litter bed, but what makes some litter beds more flammable than others? </p>
<h2>Aerated litter beds fuel bigger fires</h2>
<p>Over the past few years, fire scientists across the world have been busy tackling this burning question. In <a href="https://www.publish.csiro.au/wf/wf14182">tropical forests in the Amazon</a>, <a href="https://cdnsciencepub.com/doi/abs/10.1139/x2012-138">oak forests in North America</a> and <a href="https://onlinelibrary.wiley.com/doi/abs/10.1111/oik.03886">eucalypt woodlands in Australia</a>, they have been collecting leaf litter beds and burning them in the laboratory to understand why litter beds from some plant species burn differently to others.</p>
<p>Each of these studies focused on leaf litter beds made up of a single species, and each identified a range of drivers of flammability. These drivers relate to both the characteristics of the individual litter particle (leaf, needle or branch) and the litter bed itself. </p>
<hr>
<p>
<em>
<strong>
Read more:
<a href="https://theconversation.com/not-all-blackened-landscapes-are-bad-we-must-learn-to-love-the-right-kind-129547">Not all blackened landscapes are bad. We must learn to love the right kind</a>
</strong>
</em>
</p>
<hr>
<p>Our <a href="https://besjournals.onlinelibrary.wiley.com/doi/10.1111/1365-2745.13561">new research</a> sought to consolidate these studies to find the common drivers of flammability between different single-species litter beds from different parts of the world.</p>
<p>From our meta-analysis, we found “litter packing” and “litter bulk density” were key factors in litter bed flammability. </p>
<p>Litter packing is a measure of how many gaps are between the dried leaves, needles and branches, and is important for determining how much air is available for burning. Likewise, litter bulk density is a measure of how much litter there is, and is important for determining how quickly and how long litter burns. </p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/374733/original/file-20201214-21-qs6xyb.JPG?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="Oak tree litter bed" src="https://images.theconversation.com/files/374733/original/file-20201214-21-qs6xyb.JPG?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/374733/original/file-20201214-21-qs6xyb.JPG?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=450&fit=crop&dpr=1 600w, https://images.theconversation.com/files/374733/original/file-20201214-21-qs6xyb.JPG?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=450&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/374733/original/file-20201214-21-qs6xyb.JPG?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=450&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/374733/original/file-20201214-21-qs6xyb.JPG?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=566&fit=crop&dpr=1 754w, https://images.theconversation.com/files/374733/original/file-20201214-21-qs6xyb.JPG?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=566&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/374733/original/file-20201214-21-qs6xyb.JPG?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=566&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">The litter bed from oak trees. The curly leaves create air gaps throughout the litter bed, which lead to bigger fires.</span>
<span class="attribution"><span class="source">Jamie Burton</span>, <span class="license">Author provided</span></span>
</figcaption>
</figure>
<p>We found loosely packed litter beds spread fire faster, burned for shorter periods of time and were more consumed by the flames. Importantly, we found this was universal across different types of litter beds. </p>
<p>We also identified the characteristics of leaves, needles and branches that cause variations in litter packing and litter bulk density. </p>
<p>For example, if the litter particles are “curly” and have a high surface area to volume ratio, then they’ll form litter beds with low packing ratios which burn faster and have higher consumption. Examples include leaves from some oak (<em>Quercus</em>) species.</p>
<hr>
<p>
<em>
<strong>
Read more:
<a href="https://theconversation.com/tree-ferns-are-older-than-dinosaurs-and-thats-not-even-the-most-interesting-thing-about-them-138435">Tree ferns are older than dinosaurs. And that's not even the most interesting thing about them</a>
</strong>
</em>
</p>
<hr>
<p>At the opposite end, small and less curly leaves form densely packed litter beds which are less aerated. Examples include coast tea tree (<em>Leptospermum laevigatum</em>) and conifers with small needles such as <em>Larix</em> and <em>Picea</em>. This results in slower moving fires, which do not consume all the litter.</p>
<p>For eucalypt litter beds, things are a little more complicated. <a href="https://onlinelibrary.wiley.com/doi/abs/10.1111/oik.03886">Some species have thick and flat leaves</a> which pack densely, so fire spreads more slowly and less litter is consumed. Other species, <a href="https://www.publish.csiro.au/wf/wf07111">such as the southern blue gum</a> (<em>Eucalyptus globulus</em>), have larger leaves which tend to pack less densely, so fires burn more quickly with taller flames.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/374734/original/file-20201214-16-1lipc9e.JPG?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="Eucalyptus litter bed" src="https://images.theconversation.com/files/374734/original/file-20201214-16-1lipc9e.JPG?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/374734/original/file-20201214-16-1lipc9e.JPG?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=450&fit=crop&dpr=1 600w, https://images.theconversation.com/files/374734/original/file-20201214-16-1lipc9e.JPG?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=450&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/374734/original/file-20201214-16-1lipc9e.JPG?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=450&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/374734/original/file-20201214-16-1lipc9e.JPG?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=566&fit=crop&dpr=1 754w, https://images.theconversation.com/files/374734/original/file-20201214-16-1lipc9e.JPG?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=566&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/374734/original/file-20201214-16-1lipc9e.JPG?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=566&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">The litter bed of eucalyptus trees.</span>
<span class="attribution"><span class="source">Jamie Burton</span>, <span class="license">Author provided</span></span>
</figcaption>
</figure>
<h2>How can this information help us manage fires?</h2>
<p>Of course, under extreme fire weather conditions, any litter bed will burn. However, at the beginning of a fire or under mild conditions, differences in litter characteristics may strongly influence how that fire spreads. Research on this can be useful for many aspects of fire management and planning.</p>
<p>For example, if we know which plants produce less flammable litter, we can select them for <a href="https://www.cfa.vic.gov.au/plan-prepare/plant-selection-key">planting around houses</a>, <a href="https://cdn.cfa.vic.gov.au/documents/20143/72271/landscaping_for_bushfire.pdf/1c6084e1-159e-a820-b0b3-6dc077e661c0">landscaping in fire-prone areas</a> and also use them as <a href="https://theconversation.com/low-flammability-plants-could-help-our-homes-survive-bushfires-53870">green firebreaks</a> to reduce the risk to people and homes. If a fire was to start, it may spread less quickly and be less intense, making it easier to contain and put out.</p>
<figure class="align-right zoomable">
<a href="https://images.theconversation.com/files/374740/original/file-20201214-15-15gn931.JPG?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="_Allocasuarina_ needle litter" src="https://images.theconversation.com/files/374740/original/file-20201214-15-15gn931.JPG?ixlib=rb-1.1.0&q=45&auto=format&w=237&fit=clip" srcset="https://images.theconversation.com/files/374740/original/file-20201214-15-15gn931.JPG?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=450&fit=crop&dpr=1 600w, https://images.theconversation.com/files/374740/original/file-20201214-15-15gn931.JPG?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=450&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/374740/original/file-20201214-15-15gn931.JPG?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=450&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/374740/original/file-20201214-15-15gn931.JPG?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=566&fit=crop&dpr=1 754w, https://images.theconversation.com/files/374740/original/file-20201214-15-15gn931.JPG?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=566&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/374740/original/file-20201214-15-15gn931.JPG?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=566&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption"><em>Allocasuarina</em> species with long thin needles tend to pack loosely, leading to faster flame spread and shorter burning times.</span>
<span class="attribution"><span class="source">Jamie Burton</span>, <span class="license">Author provided</span></span>
</figcaption>
</figure>
<p>But also it may not be that straightforward. When deciding which species to plant, the flammability of living plants needs to be considered, as well. Some plants that have less flammable litter may actually be <a href="https://www.researchgate.net/publication/324985407_Does_plant_flammability_differ_between_leaf_and_litter_bed_scale_Role_of_fuel_characteristics_and_consequences_for_flammability_assessment">highly flammable as a living plant</a>. For example, although coast tea tree may form densely packed litter beds, the high oil content in the leaves makes it highly flammable as a living plant.</p>
<p>Our findings could also be used for predicting fire behaviour. For example, our results could be integrated into fire behaviour models, such as the <a href="https://theconversation.com/new-modelling-on-bushfires-shows-how-they-really-burn-through-an-area-63943">Forest Flammability Model</a>, which uses information on the composition and structure of the plant community to predict fire behaviour. </p>
<h2>Next steps</h2>
<p>Our study provides information on what leaf and litter characteristics affect flammability in litter beds composed of a single species. But in many forests, litter beds are made up of a variety of plant species, and more research is needed to understand what happens to litter packing and flammability in these multi-species litter beds. </p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/374955/original/file-20201214-13-w3gd1z.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="Sydney red gum" src="https://images.theconversation.com/files/374955/original/file-20201214-13-w3gd1z.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/374955/original/file-20201214-13-w3gd1z.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=397&fit=crop&dpr=1 600w, https://images.theconversation.com/files/374955/original/file-20201214-13-w3gd1z.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=397&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/374955/original/file-20201214-13-w3gd1z.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=397&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/374955/original/file-20201214-13-w3gd1z.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=499&fit=crop&dpr=1 754w, https://images.theconversation.com/files/374955/original/file-20201214-13-w3gd1z.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=499&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/374955/original/file-20201214-13-w3gd1z.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=499&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">The bark of the Sydney red gum tends to take longer to ignite, but burns for longer than its leaves.</span>
<span class="attribution"><span class="source">Shutterstock</span></span>
</figcaption>
</figure>
<p>Besides different species, litter beds also contain different components such as twigs and bark. For example, in a mature wet eucalypt forest, <a href="https://www.publish.csiro.au/bt/bt9750413">bark and twigs can make up to 44% of the litter bed</a>. </p>
<p>And for some eucalypt species, we already know <a href="https://www.publish.csiro.au/bt/bt16258">bark burns differently to leaves</a>. For example, the flaky bark of the Sydney red gum (<em>Angophora costata</em>) tends to take longer to ignite, but burns for a longer time compared to its leaves. </p>
<p>With fires becoming more frequent and fire seasons becoming longer, research into litter bed flammability has never been more needed.</p>
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Read more:
<a href="https://theconversation.com/i-felt-immense-grief-one-year-on-from-the-bushfires-scientists-need-mental-health-support-148251">'I felt immense grief': one year on from the bushfires, scientists need mental health support</a>
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<img src="https://counter.theconversation.com/content/150951/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Jamie Burton receives funding from Department of Environment, Land, Water and Planning.</span></em></p><p class="fine-print"><em><span>Alexander Filkov is affiliated with BNHCRC. </span></em></p><p class="fine-print"><em><span>Jane Cawson receives funding from the Victorian Department of Environment, Land, Water and Planning. </span></em></p>New research found curly leaves on the forest floor create litter beds with more air gaps. And this fuels bigger fires.Jamie Burton, PhD Candidate, The University of MelbourneAlexander Filkov, Senior research fellow, The University of MelbourneJane Cawson, Research Fellow in Bushfire Behaviour and Management, The University of MelbourneLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/1237442019-10-21T12:17:22Z2019-10-21T12:17:22ZWhy don’t evergreens change color and drop their leaves every fall?<figure><img src="https://images.theconversation.com/files/297827/original/file-20191021-56242-1wgq120.jpg?ixlib=rb-1.1.0&rect=51%2C0%2C3399%2C2291&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">What's happening with the trees that stay green?</span> <span class="attribution"><a class="source" href="https://www.shutterstock.com/image-photo/beautiful-fall-foliage-golden-yellow-aspen-1503622133?src=Hr3x35_H4DbsNorTrIHA5Q-1-7">BingHao/Shutterstock.com</a></span></figcaption></figure><p>It’s autumn in the Northern Hemisphere – otherwise known as leaf-peeping season. Now is when people head outside to soak up the annual display of orange, red and yellow foliage painted across the landscape.</p>
<p>But mixed among those bright, colorful patches are some trees that stay steadfastly green. Why do evergreen conifers sit out this blazing seasonal spectacle?</p>
<p>Like so many other challenges, the problem of winter can be solved by trees in more than one way.</p>
<p>As temperatures begin to dip, broad-leafed temperate trees – think maples and oaks – withdraw the green chlorophyll from their leaves. That’s the pigment that absorbs sunlight to power photosynthesis. Trees store the hard-won minerals, chiefly nitrogen, they’ve invested in chlorophyll in their wood for reuse in a future growing season. Yellows and oranges and reds are left fleetingly visible before the leaves drop for winter.</p>
<p>Evergreen conifers – cone-bearing trees – retain their foliage year-round and have a different strategy for withstanding winter’s stresses.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/297828/original/file-20191021-56215-2mmbil.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/297828/original/file-20191021-56215-2mmbil.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/297828/original/file-20191021-56215-2mmbil.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=400&fit=crop&dpr=1 600w, https://images.theconversation.com/files/297828/original/file-20191021-56215-2mmbil.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=400&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/297828/original/file-20191021-56215-2mmbil.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=400&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/297828/original/file-20191021-56215-2mmbil.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=503&fit=crop&dpr=1 754w, https://images.theconversation.com/files/297828/original/file-20191021-56215-2mmbil.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=503&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/297828/original/file-20191021-56215-2mmbil.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=503&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">Green starts to stand out in the fall woods.</span>
<span class="attribution"><a class="source" href="https://www.shutterstock.com/image-photo/wonderful-autumn-landscape-evergreen-pine-tree-1531872623">Michele Ursi/Shutterstock.com</a></span>
</figcaption>
</figure>
<h2>Return on investment in leaves</h2>
<p>Staying evergreen is not about continuing to conduct photosynthesis throughout the winter. Cold temperatures affect conifers’ metabolism just as they do any other organism’s. In fact, on cold wintry days, evergreen conifers <a href="https://doi.org/10.1641/0006-3568(2004)054%5B0041:PSOOE%5D2.0.CO;2">perform no more photosynthesis</a> than their leafless neighbors.</p>
<p>The best way to understand the benefit of evergreenness is by considering the construction costs of leaves. Needles are really just modified leaves, after all. How do trees balance the energy it takes to grow a leaf with the energy that leaf produces via photosynthesis? In other words, how long do the leaves take to repay their construction costs and offer the tree a return on its investment?</p>
<p>Deciduous trees must recoup their investment in their leafy canopy in only a single growing season. In contrast, evergreen conifers, by hanging onto their needles, grant those needles multiple growing seasons to contribute to their tree’s balance sheets. That’s the real benefit to staying green.</p>
<p>Evergreens’ greater leaf longevity means they can survive in environments that just don’t work for their deciduous cousins. At higher latitudes and elevations, shorter and cooler growing seasons can limit photosynthetic activity. Drought can further interfere with photosynthesis. In these harsher conditions, a year may not be long enough for a leaf to produce enough energy to pay back its growth costs to the tree.</p>
<p>This may explain why evergreen conifers dominate mountaintops and the boreal forests that stretch across high latitudes in Alaska, Canada and Northern Europe. Deciduous broad-leafed trees largely drop out of such habitats – conditions mean they can’t balance their accounts with respect to investments in leaves and leaves’ photosynthetic return in a single season.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/297829/original/file-20191021-56207-5szf6d.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/297829/original/file-20191021-56207-5szf6d.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/297829/original/file-20191021-56207-5szf6d.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=402&fit=crop&dpr=1 600w, https://images.theconversation.com/files/297829/original/file-20191021-56207-5szf6d.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=402&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/297829/original/file-20191021-56207-5szf6d.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=402&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/297829/original/file-20191021-56207-5szf6d.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=505&fit=crop&dpr=1 754w, https://images.theconversation.com/files/297829/original/file-20191021-56207-5szf6d.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=505&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/297829/original/file-20191021-56207-5szf6d.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=505&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">White pine needles need to withstand only one winter.</span>
<span class="attribution"><a class="source" href="https://www.shutterstock.com/image-photo/white-pine-branch-118531429">Candia Baxter/Shutterstock.com</a></span>
</figcaption>
</figure>
<p>Evergreen needle longevity varies widely and maps onto the degree of growing season stress. Some temperate trees common to southern New England, such as white pine, retain needles for only two growing seasons. Any individual white pine needle overwinters only once, minimally meeting the definition of evergreen.</p>
<p>Some conifers, such as larch, do not achieve even that, instead shedding their entire crown of needles each autumn in a luminously golden display that can be a highlight of the autumn foliage splendor where they are found.</p>
<p>In contrast, bristlecone pines, inhabitants of high elevations in the arid Southwest, hang onto individual needles for almost 50 years. It may take nearly that long for bristlecone pine needles to achieve a photosynthetic return on the investment in their construction, given the growing-season stresses they confront.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/297830/original/file-20191021-56220-nv8teh.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/297830/original/file-20191021-56220-nv8teh.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/297830/original/file-20191021-56220-nv8teh.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=477&fit=crop&dpr=1 600w, https://images.theconversation.com/files/297830/original/file-20191021-56220-nv8teh.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=477&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/297830/original/file-20191021-56220-nv8teh.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=477&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/297830/original/file-20191021-56220-nv8teh.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=599&fit=crop&dpr=1 754w, https://images.theconversation.com/files/297830/original/file-20191021-56220-nv8teh.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=599&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/297830/original/file-20191021-56220-nv8teh.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=599&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">Tough bristlecone pine needles last for decades in their harsh habitat.</span>
<span class="attribution"><a class="source" href="https://www.shutterstock.com/image-photo/bristlecone-pines-oldest-living-things-on-54172333">Darren J. Bradley/Shutterstock.com</a></span>
</figcaption>
</figure>
<h2>Adapting to deal with winter stresses</h2>
<p>Overwintering is profoundly stressful for trees.</p>
<p>Subzero temperatures bring the risk of cellular freezing in evergreen needles – which would be lethal. To prevent freezing, evergreen conifers accumulate high concentrations of <a href="https://doi.org/10.1242/jeb.01730">dissolved substances</a> <a href="https://www.ncbi.nlm.nih.gov/pubmed/15660165">known as cryoprotectants</a> that <a href="https://press.princeton.edu/books/paperback/9780691612638/biochemical-adaptation">lower the freezing point</a> of water in their cells and <a href="https://doi.org/10.1046/j.1365-3040.1998.00309.x">protect key cell structures</a>, while not interfering with metabolism.</p>
<p>Cold, snow and blowing ice, along with the demands of longevity, lead evergreen conifers to invest their energy in the toughness of needles. Conifer needles vary in toughness; for instance, relatively short-lived white pine needles are more delicate. The fibrous materials that make needles more durable further deepen coniferous trees’ investment, extending the period required to achieve a return on needle construction costs.</p>
<p>Heavy loads of snow can result in broken branches, a prevailing risk of evergreenness. Thin, often drooping conifer needles catch less snow than the broad leaves of deciduous trees. Indeed, when deciduous trees lose branches to snowstorms, it is generally during storms on the edges of the snow season – in autumn or spring – not midwinter storms, when the crowns are leafless. If you’ve ever wondered why deciduous trees are taking so long in spring to leaf out, missing out on some excellent growing days as a result, keep in mind that trees don’t want to risk the damage that could result from a freak spring storm.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/297831/original/file-20191021-56194-p4ls9f.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/297831/original/file-20191021-56194-p4ls9f.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/297831/original/file-20191021-56194-p4ls9f.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=400&fit=crop&dpr=1 600w, https://images.theconversation.com/files/297831/original/file-20191021-56194-p4ls9f.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=400&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/297831/original/file-20191021-56194-p4ls9f.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=400&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/297831/original/file-20191021-56194-p4ls9f.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=503&fit=crop&dpr=1 754w, https://images.theconversation.com/files/297831/original/file-20191021-56194-p4ls9f.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=503&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/297831/original/file-20191021-56194-p4ls9f.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=503&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">Evergreen branches are built to let snow slide off them so they don’t snap under the weight.</span>
<span class="attribution"><a class="source" href="https://www.shutterstock.com/image-photo/snow-covered-fir-trees-heavy-snowfall-764380549">Melinda Nagy/Shutterstock.com</a></span>
</figcaption>
</figure>
<p>Conifer branch architecture is also adapted to shedding snow. Conifer branches generally sweep outwards and downwards from the trunk: Think of a Christmas fir. Not only that, conifer branches are generally more flexible than their counterparts on deciduous trees. Collecting heavy snow weighs down conifer branches until they reach an angle where it sloughs off. </p>
<p>No matter the species, at midlatitudes, where the snow flies in winter and growing seasons are generally mild and favorable, trees need strategies to make it through. Some recreate a crown of leaves each spring. Evergreens equip their needles and branches with features necessary to survive winter and thus live to see another spring – and, for some, many springs thereafter.</p>
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<p class="fine-print"><em><span>Barry Logan does not work for, consult, own shares in or receive funding from any company or organization that would benefit from this article, and has disclosed no relevant affiliations beyond their academic appointment.</span></em></p>Many deciduous trees put on a dazzling fall foliage display. But coniferous evergreens hold on to their needles and stay green. A biologist breaks down these different survival strategies.Barry Logan, Professor of Biology, Bowdoin CollegeLicensed as Creative Commons – attribution, no derivatives.