Which of the world’s great forests store the most carbon per hectare? The dense tropical rainforests of the Amazon, Borneo, the Congo or Papua New Guinea? The vast northern forests of Canada and Siberia, or the towering mountain ash forests of Victoria and Tasmania?
None of the above.
In fact (counting carbon stored in soils), mangrove forests store the most carbon per hectare.
Mangrove forests are amazingly tough, versatile and productive. They play a critical role in the feeding and breeding cycles of many fish and other aquatic species, and fish catches are much higher close to intact mangrove communities. They provide valuable timber and many other forest products. Recent cyclones have reminded us yet again that coastlines with intact mangroves are much more resilient.
The mangroves are disappearing
Unfortunately, the world is losing mangroves at a depressing rate, down from 19.8 million hectares in 1980 to 15 million hectares in 2005. Although rates of loss have halved from around 2% per year in the 1980s, the current rate of loss would see most of the world’s mangroves gone by the end of this century.
Achieving no net loss of mangroves worldwide would require the successful restoration of approximately 150,000 hectares per year, unless all major losses of mangroves ceased. Increasing the total area of mangroves worldwide back towards their original extent would require an even larger effort.
Indonesia has the most to lose
Indonesia is blessed with the largest area of mangrove forests in the world. Unfortunately, it also suffers from the world’s fastest rates of mangrove destruction.
Mangroves are being destroyed by conversion to agriculture, aquaculture, tourism, urban development and over-exploitation. Indonesia’s original endowment of 4.2 million hectares of mangroves has been reduced to less than 2.4 million hectares, with at least 60% of this loss due to conversion to aquaculture. More than one third of Indonesia’s mangroves were lost from 1980 to 2000, faster than the rate of loss loss of inland tropical forests and coral reefs.
The majority of mangrove forests in Indonesia have no form of national protection. Even forests with the highest degree of protection on paper, such as the Tanjung Panjang Nature Reserve in Gorontalo Province saw half of its mangrove forests converted to aquaculture between 1989 and 2010.
In 2012 a National Mangrove Strategy was developed, which mandates that mangrove management take place in coordination with stakeholder bodies within Indonesia, but the majority of these regional working groups meet only for formalities' sake.
Indonesian government records show 660,000 hectares of brackish water aquaculture ponds (called Tambak) in ex-mangrove areas, and there are conflicting accounts of strategies to expand this to up to 2.9 million hectares. These are largely shallow ponds of low productivity, managed extensively with heavy use of external inputs (pesticides, industrial feed and fertilizer) and plagued by disease and high mortality of fish.
The great tragedy is that some of the most valuable forests in the world are being converted to a relatively low value and unsustainable land use with little benefit for local communities.
The Indonesian Ministry of Fisheries wants to improve management and productivity of these ponds where possible, and to rehabilitate disused and unproductive areas to mangroves in partnership with the Ministry of Forestry and Environment, the National Mangrove Coordination Team and local stakeholders.
This Indonesian government commitment is very encouraging. We believe there is enormous scope to reverse the loss of mangrove forests in Indonesia and that this can be a great example for other developing countries.
Restoring lost mangroves is tricky, but possible
However, to date most attempts to restore mangroves in Indonesia (and elsewhere) have failed. The majority of attempts (over 90%) simply jab seedlings of one mangrove genus (Rhizophora) into inappropriate habitats - in mud flats below mean sea level - where mangroves do not grow.
Typically, attempts at mangrove restoration fail for two reasons:
- Land tenure and ownership issues make it difficult to put mangroves back where they belong.
- Poor understanding of the ecological requirements of mangroves, and the ecological and water processes that promote their establishment and early growth.
One of us (Robin Lewis) pioneered a mangrove restoration technique in Florida called Ecological Mangrove Rehabilitation (EMR). This method shows promise at even larger scales as a cost-effective method to restore or rehabilitate whole mangrove communities as resilient and productive ecosystems.
With support from the World Resource Institute and the Indonesian Ministry of Marine Affairs and Fisheries, involving researchers from Bogor, Darwin, Wageningen and Singapore, we are now assessing the potential for restoration in 8 large-scale degraded and converted mangrove forests ranging from 6,600 hectares (Tanjung Panjang, Gorontalo) to 82,500 ha (Mahakam Delta, East Kalimantan).
While we should always be wary about transplanting project ideas from one country to another, we believe there are lessons to be learned from very encouraging US examples of mangrove ecosystem repair on this scale.
Restoring mangroves works
In Florida in the 1960s, in a misguided effort at mosquito control, 16,200 hectares of saltmarshes and mangroves were impounded and flooded intentionally. This damaged fisheries, wildlife and other ecosystem services.
By 2000, over 10,000 hectares of these mosquito control impoundments had been hydrologically repaired, through strategic breaching of dike walls, culvert placement and re-grading to a natural surface elevation. This enabled mangrove communities to re-establish.
The ecological mangrove restoration method is based on relatively simple principles around restoring hydrological connectivity and allowing the natural tidal processes to assist mangrove propagules to establish and spread. But implementing these principles in practice is complicated. Densely populated and contested coastal landscapes where people are struggling to make a living and feed their families, and where land ownership and control is often far from clear cut, do not lend themselves to simple prescriptions.
In Indonesia, Blue Forests and the Mangrove Action Project have refined this method into a community-based approach. They involve local communities (including Tambak farmers) in planning, implementing and monitoring the mangrove restoration projects, parallel development of sustainable livelihoods options, and developing collaborative management of re-established mangrove ecosystems. These activities are supported and complemented by Fish Farmer Field Schools that assist tambak farmers with more sustainable options for their tambak ponds, and with mangrove restoration on disused ponds.
Jumping from small-scale to big picture
Our challenge now is to see if we can combine the social insights from our small-scale work in Indonesia with the engineering innovations from large-scale restoration practices in the US and elsewhere. This would substantially increase the speed and extent of mangrove forest rehabilitation and restoration.
Restoring mangrove forests would deliver significant benefits in reducing net greenhouse gas emissions, improving food security and livelihoods of coastal communities, increasing resilience in the face of sea level rise and extreme weather events, and improving habitat for many vulnerable species along extremely biodiverse and beautiful tropical coastlines.