Climate, land-use and Prosopis ferox recruitment in the Quebrada de Humahuaca, Jujuy, Argentina

Prosopis ferox grows in upper-elevation, inter-montane valleys between 2600 and 3800 m in Northwestern Argentina and Southern Bolivia. Throughout its range, P. ferox has largely been used as local fuel, building material and food for livestock. In order to evaluate the causes of the recent increase in P. ferox density and range distribution, we compare tree recruitment of P. ferox at 15 stands in the Quebrada de Humahuaca, Jujuy, Argentina, with the environmental and socioeconomic changes in the past 150-200 years. Based on tree recruitment, a general pattern of greater establishment from the mid-1970s to 1990 was identified. This regional pattern is consistent with precipitation variations during the 20th century showing abundant rainfall in the 1970s and 1980s. In addition, historical records indicate that the density of domestic grazers decreased dramatically in the second half of the 20th century. The reduction of browsing by livestock might have also favored the P. ferox recruitment over this interval. However, during the 1990s reduced establishment has occurred at a time of low stock densities suggesting significant precipitation is necessary for the expansion and establishment of these forests. Simply reducing stocking levels will not lead to the long-term recovery of these forests.