Growing cities and crops means the forests fall


A new report in Nature Geoscience that studied high-resolution satellite imagery from 41 countries shows that deforestation is being driven by urban population growth and agricultural trade in the 21st century.

This may not sound like news to many, but it's one of the first times we have seen documented evidence that the emptying of rural areas is contributing to deforestation. It's previously been widely assumed that increasing urbanisation and modern ultra-efficient mass agriculture may contribute to a slowing of global deforestation rates.

Forest being burnt for agriculture

This settler in the Mau Forest, Kenya is clearing land for subsistence agriculture, which was previously thought to be one of the main factors contributing to deforestation. The new study shows that the most important causes of deforestation in the 21st century are probably an expanding urban population and global agricultural trade. © Christian Lambrechts, UNEP

This assumption came on the back of studies in the late 20th century that showed rural growth was the cause of much deforestation. As the forests were opened up by roads and other infrastructure so people could move in to previously inaccessible landscapes to practice subsistence agriculture.

But 2009 marked a remarkable turning point in the history of mankind. It was the first year on record where an equal number of the human population lived in urban and rural areas. And this swinging trend in the way we live seems to have set in as the report states "population growth rates are slowing overall, but urban growth is vastly outpacing rural growth."

The research team aimed to identify the factors most closely related to tropical forest loss, rather than predict forest loss per se. By studying 10 possible factors - four related to agricultural production, four demographic factors, and two economic factors - and correlating them it was possible to see which may prove to have the biggest impact on the humid tropic biome.

Both the research methods, linear regression and regression tree, show a positive relationship between urban growth, agricultural exports, and forest loss. The most significant factors associated with satellite-derived forest loss are urban growth rate and net agricultural trade per capita. The researchers are keen to stress this does not necessarily indicate "causality", but the "positive correlations do suggest that the traditional mode of clearing in frontier landscapes for small-scale production to support subsistence needs or local markets is no longer the dominant driver of deforestation in many places."

The challenges facing tropical forests, as more and more people try and get more and more out of them, are unrelenting. They are also now embroiled in the political climate football, REDD. The ambition of REDD is to value and maintain standing forests, but this relies on agricultural production being displaced somewhere else.

Tough questions will face the rainforest conservation community and how best to marry the opportunities of relatively small-scale community led conservation while maximising yields on already converted land to avoid more mass clearance of forest.

Full report in Nature Geoscience

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