Our planet is on the precipice of a sixth mass extinction event.
But unlike the five previous mass extinctions, this one is man-made: a global biodiversity crisis in which species are disappearing three to 12 times faster than the “normal” rate of extinction.
Australia is not immune from this crisis. In fact, we are in the thick of it: approximately half of all global extinctions of mammals in the last 200 years have been in Australia – more than any other country.
The fundamental driver behind this biodiversity crisis is the unprecedented success of a single species – humans – to manipulate and alter the environment (including moving other species around) to serve its needs.
A key cause of this biodiversity crisis is agriculture. While it has enabled humans to prosper and occupy all corners of the globe, it has also been the most profound agent of ecological change in the history of life on Earth.
But, we have to eat, right?
As our global population barrels towards 9 billion, can we fulfil our moral obligation to feed and clothe humanity equitably? And can we do so while avoiding a biodiversity catastrophe?
A study published last week in the prestigious journal Science (by ecologists from the University of Cambridge) used data from India and Ghana to contrast two potential approaches to this problem:
“Land sparing” is where conservation reserves are set aside for biodiversity protection with food grown intensively on the remaining land.
“Land sharing” is where biodiversity conservation and food production happen on the same land.
The researchers found that more species of trees and birds survive under “land sparing” than “land sharing”.
These results are not surprising because (as a general principle) biodiversity and agriculture don’t mix.
Some generalist “hardy” species – such as magpies and galahs – may persist and even thrive in agricultural landscapes but most indigenous species are “losers”.
The Cambridge research suggests the best way to avoid a massive biodiversity collapse is to conserve as many species as possible in reserves. The remaining land should then be dedicated to higher-yield farming.
But the solution is not that straightforward.
Can we save all species? Should we try? How much land do we need to protect to conserve species? Where should those reserves be located in the landscape? Is a dichotomy between conservation reserves and agriculture really helpful?
Even in “frontier” landscapes where virgin habitat is being converted into farmland, decisions about how much land to spare and where to spare it are more often influenced by human needs than ecological considerations.
The Australian dimension
So how do we do things here in Australia?
Well, we have a world-class network of parks and nature reserves, with nearly 13% of our land mass in the national reserve system. These reserves are essential for protecting ecosystems and the species they support.
Yet there are thousands of species officially listed as threatened and many more in precipitous decline that have not yet made it on to threatened species lists.
Further additions to the reserve system are necessary to prevent species extinctions, with targets ranging from 15-35% of the landscape.
Thankfully, there are now many players in this field, with Indigenous Protected Areas and non-government organisations (such as Bush Heritage Australia and the Australian Wildlife Conservancy) sharing the load.
But conservation reserves alone will rarely be enough to ensure the survival of all species.
This is because, traditionally, the reserve system has been made up of “left-overs” – the least arable areas that were not suitable for farming or forestry.
The most productive ecosystems (such as riverine floodplains and flats, grasslands and lowland woodlands) are also the most depleted, least protected and most endangered.
So, if the priority in “land sparing” is on agricultural yield, and the “best” parts of the landscape are devoted to agriculture, it is likely to disadvantage a whole suite of species dependent on those depleted ecosystems.
A blurry line
The trade-off between conservation and production is rarely clear-cut.
In intensively farmed landscapes, typical of much of eastern, southern and south-western Australia, the last remaining fragments of native vegetation are often small, isolated and degraded.
These fragments may not be large enough, good enough or sufficiently connected to support viable populations of many species. We require a more sophisticated approach to managing biodiversity in these landscapes.
A landscape mosaic is one such approach.
In this approach the landscape is viewed as a mosaic containing patches of differing habitat quality.
By recognising the variability in conservation and agricultural value of different patches of the landscape, a mix of land uses can be applied across the mosaic:
patches with high conservation value can be reserved solely for biodiversity conservation;
patches with medium conservation value can provide habitat for a different suite of species while co-existing with low intensity agriculture;
patches with low conservation value can be farmed productively and intensively.
The mosaic approach emphasises connectivity through the landscape and interactions across patch boundaries.
This approach may be applied to large expanses of arid and northern Australia. These are areas which have been grazed but where native vegetation remains largely intact.
Here, we must turn our attention to managing threatening processes such as fire regimes, invasive species and grazing. While this is best achieved through conservation reserves, it is not entirely incompatible with farming.
But ultimately, the greatest threat to producing enough food for our increasing population is unlikely to come from biodiversity conservation.
Can we save nature and feed the world? We have no choice but to try.
We can begin by recognising the complexity of landscapes and the need for nature to have space to live, survive and evolve.
For another view on land sharing and land sparing, read “Food vs fauna: can we have our biodiversity and eat too?”