Informations et ressources scientifiques
sur le développement des zones arides et semi-arides

Titre : La clausura como estrategia de restauración en bosques heterogéneos comunales del Chaco semiárido. Un enfoque socio-ecológico

Auteur : Miguel Cotroneo, Santiago

Université de soutenance : Universidad de Antioquia, Medellín

Grade : Doctor en Agroecologia 2018

Résumé partiel
Chaco region is the largest extension of land covered by xerophytic vegetation in South America. During the last century, grazing, logging and deforestation have transformed the natural landscape of forests and savannas into a heterogeneous matrix of shrublands and forests in different stages of degradation. The symptoms of this process include less tree cover and herbaceous, bush encroachment, more nude soil, and less water and nutrients availability in the soil, due to less litter contribution, soil compaction and exposition to high temperatures. All these changes reduce the forage production and increase its seasonality, therefore worsening the effect of a marked dry season that lasts 5-7 months over the livestock production. Closures, where grazing is excluded during the rainy season, are used in communal rangelands of Africa and South America, to defer fodder to the dry season and to restore vegetation. Nevertheless, its effectiveness could be conditioned by ecological and socio-ecological factors. The objective of this thesis was to assess the potential of closures as restoring strategy in communal heterogeneous woodlands of semi-arid Chaco region. This was done through two complementary approaches : (a) ecological and (b) socio-ecological. (a) It was assessed the effect of seasonal closures (versus open areas) in three patch types of woodland, with a progressive level of tree canopy degradation (mature forests, secondary forests and shrublands) on the vegetation of the understory and biotic and abiotic factors that determine its regenerative potential. For this purpose, a four-year experiment was done in four sites (true replicates) in different communal woodlands of Santiago del Estero Province (Argentina). The central hypothesis of the experiment was that the higher the degradation status of the woodland the lower the effectiveness of enclosures as restoring strategy because differences in the dominant woody layer would impose differential resource availability in the understory, so controlling vegetation responses to grazing rest. (b) It was developed a theoretical model about factors and processes (ecological, productive, cultural, economic and institutional) associated to degradation. In this context, the role of closures was studied through methodological and theoretical frameworks for complex systems analysis. Perceptions form producers from 10 rural communities and also from technicians (n > 50), were revealed ; decision makers who affect directly or indirectly to the system.

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