Climate, land-use and Prosopis ferox establishment in the high-elevation deserts of subtropical South America.

MARIANO S. MORALES; RICARDO VILLALBA; JOSE A. BONINSEGNA

Mendoza, Argentina

Workshop; Fourth annual science meeting, IAI CRN 03. The assessment of past, present and future climate variability from treeline environments.; 2003

IAI, Ianigla

Prosopis ferox grows in upper-elevation, inter-montane valleys between 2400 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 fifteen 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.