Diversity, functionality, and resilience under increasing harvesting intensities in woodlands of northern Patagonia

Abstract

Sustainable forest management relies on the understanding of biodiversity response to disturbance and the ecological resilience of the system. The dynamic equilibrium hypothesis (DEM) predicts that site productivity will modulate the effects of disturbance gradient on biodiversity. Also, considering functional diversity (eco-morfo-phisicological traits related to resource usage) is needed to understand the effect of species gains and losses on ecosystem functionality. Here we assess the response of understory plant taxonomic and functional diversity to increasing harvesting intensities (0, 30, 50 and 70% of basal area removed) at three woodland sites of contrasting biomass growth (productivity) in northern Patagonia. Also, we assessed resilience based on comparisons with undisturbed treatments four years after initial harvest. In agreement with DEM, both taxonomic and functional diversity peaked at high, medium, or low harvesting intensities in the high-, medium-, or low-productivity site, respectively. Taxonomic composition was clearly determined by site productivity (biomass growth), while no pattern emerged for functional composition. Functional traits related to light use showed different responses: specific leaf area was only affected by site productivity while leaf chlorophyll content was affected by an interaction between harvesting intensity and site productivity. Interestingly, there was no effect of harvesting intensity on the resilience of taxonomic diversity and functional composition. Only for functional diversity, harvesting intensity was as important as site productivity. In the high and intermediate productivity sites the traits that characterizes the system were more resilient and resembled the control treatment after four years of low or high (but not intermediate) harvesting intensities. Our results support the use of the DEM on forest interventions and the importance of considering both taxonomic and functional composition, as the consideration of functional traits related to resource use strategies have different implications when considering the resilience of the system.