Impacts of introduced large herbivores on Austrocedrus chilensis forests in northern Patagonia, Argentina

Abstract

Austrocedrus chilensis (D. Don) et Boutleje (Cupressaceae) is an endemic conifer of northern Patagonia, Argentina and south-central Chile, which has been affected by browsing by livestock and introduced deer (especially red deer). In northern Patagonia, we studied the effects of livestock and deer on the densities and heights of Austrocedrus saplings and on the structure and floristic composition of the vegetation in which this species occurs under a variety of different browsing regimes. Twenty-seven stands were sampled within the `Compact' forest type (i.e., dense and pure) of Austrocedrus in both national reserves and on unprotected properties. Principal components analysis (PCA) indicates that greater abundance of Austrocedrus saplings is associated with lower stand basal areas as expected for this relatively shade-intolerant species. Although browsing does not directly reduce the abundance of saplings, it has an important influence in terms of reducing height growth and producing deformed stems. Multiple correspondence analysis (MCA) indicates that saplings between 0.5 and 1 m in height were more frequently browsed than other height classes; saplings shorter than 0.3 m in height were not greatly influenced by browsing. Saplings of intermediate heights (0.5–1 m) were scarce at sites lacking any current browsing, but this may reflect release of saplings from earlier browsing and subsequent inhibition of continued recruitment into intermediate height classes. High browsing indexes occur beneath canopy gaps, which are also sites of higher sapling densities. In the present study, sites characterized by heavy browsing also have a high cover of spiny shrubs ( Berberis spp.) and other unpalatable woody species (e.g., Lomatia hirsuta). Where the preferred browse species, Schinus patagonicus, is abundant, Austrocedrus is less influenced by browsing. However, as browsing reduces the abundance of S. patagonicus, Austrocedrus becomes a preferred species. Austrocedrus stands that are in a phase of fine-scale gap-phase regeneration are the most susceptible to inhibition of tree regeneration by livestock and deer browsing. In such stands, long-term persistence of a forest cover requires protection from large browsing animals.