Climatic and anthropogenic influences on the dynamics of Prosopis ferox forests in the Quebrada de Humahuaca, Jujuy, Argentina

MARIANO MORALES; RICARDO VILLALBA

Land use change and mountain biodiversity

Taylor and Francis Group

Lugar: Florida; Año: 2006; p. 275 - 282

The recent increase of Prosopis ferox, both in density and distribution range in the Quebrada de Huamahuaca, Jujuy, Argentina, appears to be related to major changes in land-use and regional precipitation. P. ferox grows between 2400 and 3800 m elevation at the upper-elevation inter-montane valleys in northwestern Argentina and southern Bolivia. Across its range of distribution, P. ferox has been largely used as local fuel, material for constructions and food for the livestock. In order to determine the factors affecting the recent changes in population structure of P. ferox, we compared the age structure of the woodlands with human demographic and land use changes, and with regional variations in precipitation. Based on age structures from twelve stands, four periods of recruitment were identified. Reduced recruitment was recorded until 1960 followed by a gradual increase between 1960 and 1970. An abrupt increase was observed around 1974 and persisted to 1990. Finally, low recruitment was recorded during the past 10 years. These regional patterns of recruitment are consistent with the recent expansion of the woodlands. Variations of recruitments parallel regional variations in precipitation since the middle of the 20th century. On the other hand, demographic and agrarian censuses show significant changes in the relation between rural and urban populations, and a substantial reduction of livestock density between 1974 and 1988. Reduced browsing by livestock during this interval might have also favored the recruitment of P. ferox trees. Similar or lower browsing pressure during the 90s suggests a greater influence of precipitation than livestock on the reduced tree establishment during this decade.