University of Montana researchers have examined the impact of converting natural land to cropland on global vegetation growth, as measured by satellite-derived net primary production (NPP). They found that measures of terrestrial vegetation growth actually decrease with agricultural conversion, which has important implications for terrestrial carbon storage.
The research has been reported in UM News.
Postdoctoral researcher Bill Smith and UM faculty members Steve Running and Cory Cleveland, along with a former UM postdoctoral researcher and USGS scientist Sasha Reed, used estimates of agricultural NPP and satellite-derived estimates of natural NPP to evaluate the impact of expanding agricultural land to meet needs for food and fibre.
Terrestrial NPP represents the total annual growth of vegetation on the land, which is a critical factor that helps determine how much carbon can be absorbed and stored from the atmosphere.
The research results show that agricultural conversion has reduced this productivity by about 7 per cent. A small percentage of intensively managed, irrigated or fertilised agricultural land shows an increase in productivity. But productivity is reduced in 88 per cent of agricultural lands globally.
The biggest reductions are in former tropical forests and savannas.
“Current forecasts suggest that global food demand will likely double by 2050,” Smith said.
“We hope that this research will help to identify strategies that, from a carbon balance perspective, should be avoided due to the potential for severe degradation of global vegetation growth and carbon storage.”
The research was published in Geophysical Research Letters and highlighted in the February 2014 issue of Nature Geoscience.