| Fire, climate and human impact on recruitment of Prosopis caldenia in the Argentinean pampas |
| Paper ID : 1047-ADA2013 |
| Authors: |
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Stella Marys Bogino *1, Catalina Roa Jiménez2, Ana Teresa Velasco Sastre2, María Laura Cangino3, Lucía Verónica Risio Allione2 1Avenida 25 de Mayo 384 2University of Valladolid 3State University of San Luis, Argentina |
| Abstract: |
| Semiarid woodlands dominated by caldén (Prosopis caldenia Burkart) thrive at the dry edge of the Argentinean Pampas. Currently, as a result of a 0.86% per year deforestation rate, only the 18% of the original area of caldén woodlands remains. While the area of original woodlands shrinks, the relicts of adjacent grasslands, which have not been occupied by crops, experience woody encroachment by caldén. The aim of this study was to determine the factors that favoured recruitment of P. caldenia in its natural distribution area and in adjacent grasslands. Seven sampling sites were selected, three of them in the calden’s woodlands and four in the adjacent original grassland. Sampling sites were placed between 33º 26’S and 36º 39’S. Standard dendrochronological techniques were applied on dominant and codominant trees for determining the years of establishment and the data of fire events. Historical data related to woodland’s uses and cattle and sheep stock were also analysed. Results allowed us to estimate that there were two episodic and massive recruitment events in the woodland sites. The first one in the 1790’s decade, matched with the massive cattle movement made by aborigines and the establishment of their first cazicazos. The second one started in the 1920’s decade. The establishment of caldén in the grassland area also started in 1920’s. This decade was considered as the agricultural penury period since, 70% of the crops disappeared and almost 40% of cattle died, as a result of severe droughts. This period matched with the driest decade along the century in the area (mean rainfall 100 mm below the average) and with severe changes in land use due to railway establishment and changes in land occupancy. This period took place one decade after the highest rate sheep stock in the area (6.800.000 heads) which was reduced to the half during the 1920’s decade. Cattle, which are considered as a favourer of recruitment, increased a 25% during this decade. In the grassland sites, fires took place before, and two o three years after the establishment of trees but these events were not of high magnitude, affecting a few individuals. We concluded that recruitment of P. caldenia is affected by a group of factors that acting together allows the massive establishment of this species. First, a severe land use and degradation due to severe deforestation and sheep introduction, which allowed low competition between grasses and calden’s seedlings. Secondly, drought events that implied the abandon of crop areas. Third, massive cattle introduction that favour recruitment. Finally, fire events that reduce grass competition without destroying caldén trees which are well adapted to fire events. We concluded that caldén recruitment should be seen as a multi-causal process that integrates the effects of several factors mostly driven by anthropogenic changes. |
| Keywords: |
| Prosopis, encroachment, deforestation, Argentina |
| Status : Abstract Accepted |
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