Dreams of using abandoned farmland to fight climate change or restore ecosystems are difficult to realise, a new study suggests.
A team led by researchers from Princeton University, US, has investigated the fate of disused agricultural land using land-cover maps based on satellite imagery dating from 1987 to 2017. The study looked at 11 sites across four continents, including locations in the US, Brazil, Bosnia and Herzegovina, China, Iraq, Kazakhstan, Belarus and Russia.
Farmland may be abandoned for several reasons, including owners moving to cities to look for better opportunities, previously cultivable land becoming unviable due to climate or environmental change, and war or conflict.
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The cessation of agricultural activity in a landscape can provide opportunities for the landscape to regenerate. Disused agricultural lands can also become carbon sinks, whether through deliberate planting of trees or the natural regeneration of vegetation.
“As people move from rural areas into cities, there is a chance for wildlife and the climate to gain ground — literally — as abandoned farms and pastures revert back to forests and grasslands,” explains study co-author David Wilcove, a professor of ecology and evolutionary biology and public affairs at the High Meadows Environmental Institute (HMEI) at Princeton.
However, the data showed that most study sites were only abandoned for a short time – a little over 14 years, on average – before eventually being recultivated. That’s not long enough to provide much opportunity for carbon sequestration or benefits to wildlife.
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“For abandoned croplands to reach levels of carbon stocks and biodiversity comparable to more intact natural ecosystems, they typically need at least 50 years of regeneration,” says lead author Christopher Crawford, currently completing a PhD under Wilcove’s supervision.
The researchers estimated that more than 50% of abandoned croplands would be returned to farming within 30 years, meaning that they can’t achieve the same carbon storage capacity as old-growth forests. Restoration of both forest and grassland ecosystems to pre-farming levels of biodiversity also generally takes multiple decades.
Areas with specific policies to promote reforestation of disused cropland, such as northern China, saw land remain uncultivated for longer periods. In that region, a government program called “Grain for Green” provided financial incentives for reforestation.
The authors point out that reforestation of abandoned farmland is often invoked in models and forecasts of reversing biodiversity loss or limiting climate change. Yet, their results suggest these goals are unlikely to be met under the status quo.
“Unless countries and policymakers develop better regulations and incentives to allow these lands to recover, this chance to restore ecosystems will not be fully realised,” says Crawford. “It will remain a missed opportunity to fight climate change and biodiversity loss.”