A small-scale mixed crop-and-livestock farmer in Oyo State, Nigeria (photo credit: ILRI/Mann).

From the University of Minnesota come this news yesterday of a new scientific paper showing the environmental importance of intensifying rather than expanding tropical farmlands to feed the world’s growing human populations and to provide poor people with livelihoods.

‘According to a study published online today in the Proceedings of the National Academy of Sciences (PNAS), nature’s capacity to store carbon, the element at the heart of global climate woes, is steadily eroding as the world’s farmers expand croplands at the expense of native ecosystem such as forests.

‘The tradeoff between agricultural production and maintaining nature’s carbon reservoirs—native trees, plants and their carbon-rich detritus in the soil—is becoming more pronounced as more and more of the world’s natural ecosystems succumb to the plow. The problem, experts say, is most acute in the tropics, where expanding agriculture often comes at the expense of the tropical forests that act as massive carbon sinks because of their rich diversity and abundance of plant life.

‘“This study is important, because it asks how we make tradeoffs between producing more food and sustaining key aspects of the environment, especially our tropical forests”, says Jonathan Foley, director of the University of Minnesota’s Institute on the Environment, and a co-author on the study.

‘The seriousness of the problem is documented in the most comprehensive and fine-grained analysis of the world’s existing carbon stocks and global crop yields. The PNAS study was prepared by a team of researchers from the University of Minnesota, the University of Wisconsin-Madison, Stanford University, Arizona State University and The Nature Conservancy. The article is part of a special PNAS feature on climate mitigation and agricultural productivity in the tropics. . . .

‘In the tropics . . . it is estimated that for every ton of crop yield, carbon stocks are diminished by as much as 75 tons. Such attrition, say West and his colleagues, makes a strong case for intensifying agriculture on already-converted land instead of putting new fields into production. . . .

‘Today, about 20 percent of the land in temperate regions is in cropland. In the tropics, 11 percent of the land is farmed. However, in the tropics pressure to plant more land is growing fastest due to increasing human population, changing diets, food security concerns, and a rising demand for the raw materials of biofuels. . . .’

Read the whole news release at University of Minnesota News: Expanding croplands chipping away at world’s carbon stocks, new study says, 1 November 2010.