Relocating croplands could drastically reduce their environmental impact

Approximately half of the Earth’s land area has been converted for agricultural use and this has led to three of humanity’s most urgent environmental challenges. Agriculture is responsible for the majority of greenhouse gas emissions, demands around 70 percent of global freshwater use, and is the largest driver of habitat loss, which in turn threatens terrestrial biodiversity. 

A team of international scientists has now proposed that if current croplands could be relocated to more suitable and productive locations around the globe, while allowing ecosystems in the then-abandoned farming areas to regenerate, the carbon and biodiversity footprints of agricultural production would be minimized. And locating the new croplands in areas where rainfall provides all the necessary water would removing the need for systematic irrigation. 

Details of their reimagined world maps of agriculture are published today in the journal Nature Communications Earth & Environment. The experts propose large new farming areas for many major crops around the Cornbelt in the mid-western US, and south of the Sahara desert, while huge areas of current farmland in Europe and India would be allowed to revert to natural habitat.

“In many places, cropland has replaced natural habitat that contained a lot of carbon and biodiversity – and crops don’t even grow very well there. If we let these places regenerate, and moved production to better suited areas, we would see environmental benefits very quickly,” said study first author Dr. Robert Beyer, formerly a researcher in the Department of Zoology at the University of Cambridge.

The researchers used global maps of the current growing areas of 25 major crops, including wheat, barley and soybean, which together account for 77 percent of croplands worldwide. For each crop they assessed the carbon impact by comparing the carbon stocks present in the crops with the carbon that would be bound up in local natural vegetation and soil. Similarly, they estimated the difference between local biodiversity in natural vegetation and in croplands. 

The same methods enabled the researchers to predict the potential biodiversity and carbon impacts of crop production in locations that are currently not cultivated. They then developed a mathematical model to look at all possible ways to distribute this cropland across the globe, while maintaining overall production levels for each crop. They used potential yield estimates for three different farming scenarios representing the range from traditional, subsistence-based organic farming systems to advanced, fully mechanized production with high-yielding crop varieties and optimum fertilizer and pesticide application.

According to the model’s predictions, the proposed redistribution of croplands, under a high-input, mechanized farming scenario, would cut the carbon impact of crop agriculture by 71 percent, as long as the original croplands were allowed to return to their natural, forested states. This is the equivalent of capturing 20 years’ worth of the current net CO₂ emissions. Trees capture carbon as they grow, and also enable more carbon to be captured by the soil than when crops are grown in it.

In this optimized scenario, the impact of crop production on the world’s biodiversity would be reduced by 87 percent, which would drastically reduce the extinction risk for many species for which agriculture is a major threat. The researchers say that croplands would quickly revert back to their natural state, often recovering their original carbon stocks and biodiversity within a few decades.

The authors recognize that it is not currently possible to relocate croplands on a global scale to the new and more productive locations they have identified. However, their maps and models highlight places were croplands are currently very unproductive, but have potential to be hotspots for biodiversity and carbon storage.

Even considering less extreme changes and only redistributing croplands within national borders, rather than globally, would result in significant benefits: global carbon impact would be reduced by 59 percent and biodiversity impact would be 77 percent lower than at present.

A third, even more realistic option of only relocating the worst-offending 25 percent of croplands nationally would result in half of the benefits of optimally moving all croplands.

“It’s currently not realistic to implement this whole redesign. But even if we only relocated a fraction of the world’s cropland, focusing on the places that are least efficient for growing crops, the environmental benefits would be tremendous,” said Beyer.

Their study predicts that the optimal distribution of croplands will change very little until the end of the century, irrespective of the specific impacts of climate change.

“Optimal cropping locations are no moving target. Areas where environmental footprints would be low, and crop yields high, for the current climate will largely remain optimal in the future,” said study senior author Professor Andrea Manica.

While other studies have shown that moving to more plant-based diets would significantly reduce the environmental impacts of agriculture, the researchers say that, in reality, diets aren’t changing quickly. Their model assumes that diets will not change, and focuses on producing the same types of food as today but in an optimal way.

Many of the world’s croplands are located in areas where they have a huge environmental footprint, having replaced carbon-rich and biodiversity-rich ecosystems, and are a significant drain on local water resources. These locations were chosen for historical reasons, such as their proximity to human settlements, but the researchers say it is now time to grow food in a more optimal way.

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By Alison Bosman, Earth.com Staff Writer