Human migration impact on the dynamics of the Prosopis ferox woodlands in the

MARIANO MORALES; RICARDO VILLALBA

Merida, Mexico

Conferencia; Ecology in an Era of Globalization; 2006

Ecological Society of America

The upland area of Prepuna (2100-3400m) in Jujuy, Northwestern Argentina, was demographically and economically important during colonial times. After this period, the Prepuna become marginal in comparison with adjacent, recent-expanding regions located at lower elevations. Although the increasing process of rural-to-urban migration in the last decades of the 20th century has exacerbated the Prepuna socio-economical marginality, the abandonment of agricultural and grazing lands could have reduced the human pressure on native vegetation and facilitated the recovery of the Prepuna ecosystems. Prosopis ferox woodlands form an important community in the upland area of the Argentine and Bolivian Prepuna. The leaves of P. ferox are highly palatable for goats and the wood heavily use for cooking and local constructions. Similar to most Prosopis species, P. ferox modifies microenvironmental conditions, increasing spatial heterogeneity and therefore the local biodiversity. Browsing by domestic goat and sheep represented, and in some areas remains today, the major disturbance factor in the region. The aim of this study was determine how changes in the intensity of human-related activities affect the dynamics of the Prosopis ferox woodlands and therefore landscape changes in the Prepuna. We determined dates of establishment for more than 800 trees of P. ferox from 28 plots located in four different geomorphology units across the region. Regional human demography and changes in livestock over time were examined from the Argentinean National Surveys. During the past 50 years, the rural population in the Humahuaca and Tilcara counties, Jujuy province, migrated to the main urban centers in the region, reducing 40% the total rural population. Many fields were abandoned and the browsing pressure substantially reduced. This significant reduction in the human-induced pressure on P. ferox has largely favor the establishment of new individuals during the period 1970-90. On the other hand, P. ferox expansion might have also been benefited from the documented increase in precipitation during the past decades in the region. Decrease in human-related pressure on P. ferox, add to precipitation increase, has favored the expansion of the woodlands in many areas and consequently the recovery of the local biodiversity.