Modelo de estados y transiciones de los ñirantales del NO de la Patagonia como herramienta para el uso silvopastoril sustentable

Abstract

We built a state and transition model (S&TM) for the ñire forest system under silvopastoral use in northwestern Patagonia, with the aim to identify management effects on the vegetation. The model can help design practices that maintain the system within ‘desired' conditions in the long term. Based on a review of published and unpublished literature, an expert workshop and consultation, and field surveys we proposed alternative states and their response to natural disturbances and current management practices. We defined seven states, 13 degradation and four restoration transitions, and the factors and levels that trigger the transitions (i.e., grazing, frewood extraction, fire and/or dispersal of invasive plants). The best-conserved forest is dominated by ñire (Nothofagus antarctica) and cane (Chusquea couleou), while the most degraded state corresponds to subshrubby steppes dominated by Acaena splendens (cadillo). The intermediate states are likely to be the most suitable for silvopastoral use (open ñire and cane forest, and ñire forest with grassland) but are highly unstable. Therefore, with the common current practices, the tree component and cane cover are lost with time. Invasion of exotic species, competition with the herbaceous vegetation, mortality of trees and cane, and soil erosion are the processes that trigger transitions. Most degradation transitions are difficult to revert because they require highcost practices and/or have a long recovery time. Building the S & TM brought together scattered information about longterm changes in the vegetation. The identification of risk phases enables early warning of degradation.