Temporal variation of stocking rate and primary production in the face of drought and land use change

Abstract

Rangeland stocking rate is subjected to opposite forces. On the one hand, it is expected to fluctuate with interannual variations of aboveground net primary production (ANPP). On the other hand, it is expected to be stabilized by human interventions aimed at keeping a constant monetary flow. The global drought experienced during the first decade of the current century decreased ANPP in many regions. Argentinean rangelands suffered such drought amid an expansion of crop area. We assessed the relative impact of precipitation trends and human interventions on stocking rate and its components across a wide ANPP gradient in Argentina (from 1000 to 7000 kg.ha−1.year−1). We estimated ANPP through remote sensing, from 2001 to 2009, and gathered data on beef cattle stocking numbers per class and rangeland area (n = 67 political districts of Argentina) from 2002 to 2009. All the significant temporal trends of ANPP were negative (36% of the districts). Fifty-one percent of the districts showed a significant temporal trend of stocking rate. Despite the negative trend of ANPP, stocking rate increased in 76% of these districts. The decrease in the remaining 24% was less than expected from the reduction of ANPP. Positive trends of stocking rate were associated with an increase of total livestock in the same rangeland area, and negative ones with a decrease of total stocking and an increase of total rangeland area. Steers accounted for most of the stocking rate changes. As expected from this decoupling between stocking and ANPP, the interannual CV of stocking rate was about half the CV of ANPP. In the face of drought and strong land use changes, human interventions uncoupled or softened the response of stocking rate to ANPP. These responses were probably driven by economic factors and may have profound negative consequences on ecological sustainability.