Sustainability and food researchers Joseph Poore, Hannah Ritchie and Charles Godfray look at places where shrinking farmland has freed up land for nature – and ask how far the trend could go.

Throughout the 20th Century, humanity demanded more and more land leading to the loss of vast areas of natural forest and grassland. Today, around half the world's land is farmed, used to grow crops or graze animals.

However, according to the UN's Food and Agriculture Organization (FAO), global agricultural land use peaked in the early 2000s and has been slowly falling ever since. Around the world, farmland is being replaced by grasslands, trees and bush. Wild animals are returning to abandoned pasturelands in areas they had once dominated.

Reaching "peak agricultural land" does not mean the problem of deforestation is solved. Growing demand for products like beef, soy, cocoa and palm oil has put increasing pressure on land across South America, South East Asia and Africa. In the last decade, the world lost an area of tropical forest twice the size of Spain.

Still, acre-for-acre across the world there has been yet more farmland abandonment, driven by reforestation in Europe and North America and the abandonment of pastures in Australia and Central Asia.

There are a few different reasons for this. Firstly, farming has become more efficient. The use of improved seeds, fertilisers, pesticides and irrigation has in recent decades vastly increased how productive the land we farm is, doubling, tripling and even quadrupling yields depending on the crop and country. Since 1961, FAO data shows that productivity increases have spared 1.8 billion hectares (4.4 billion acres, or around 35 Spains) of land from being brought into cultivation.

We've also squeezed more efficiency improvements in animal agriculture through intensive farming, productive animal strains and optimised feeding regimes. As these systems intensified, lower productivity lands have been abandoned in many countries.

But it's not all about intensification. We have also replaced some land-hungry crops with near-landless alternatives: wool and cotton have been to a major extent replaced by synthetic fibres; tobacco is rapidly being replaced by synthetic nicotine; flavourings in food such as vanilla are now largely synthetic; the global caffeine (although not coffee) market is dominated by production in labs; synthetic sweeteners have replaced substantial amounts of sugar cane and sugar beet. We estimate that these synthetic substitutes have spared over 110 million hectares (two Spains) of land from farming.

One particularly striking example is the shrinkage of the global wool industry. Production has fallen by around 50% from its peak in 1990. Grazing lands in Australia, New Zealand and Argentina – countries that use to be amongst the largest wool producers – have declined by 25%. Large areas of pasture have returned to nature, some of which is actively protected and home to unique species. For example, the huge 70,000 hectare (173,000 acre) White Wells sheep farm in Australia is now the Charles Darwin Reserve, home to 700 species of plant and 230 animals. Another 70,000 hectare (173,000 acre) area in Argentina, previously the Chacabuco sheep ranch, is now a nature reserve and home to the rhea or ñandú, an uncommon bird related to ostriches and emus. There are many similar examples worldwide.

While the use of synthetic alternatives has taken pressure off land, they have come with other issues, particularly plastic pollution and an increased reliance on fossil fuels. There are solutions to these new problems however, such as landless biodegradable bio-plastics based on fungal mycelium or microbial processes, and they are beginning to scale up. Further, while agricultural land use........

© BBC