Analysis of a multivariate model for detecting browsing pressure by goats in the arid zone of Northern Chile. Application to Bridgesia incisifolia (Bert. ex Cambess) shrublands

A statistical methodology for the analysis of the effect of caprine browsing pressure in Bridgesia incisifolia (Bert. ex Cambess) shrublands is elaborated. This procedure is based on the assumption that shrubs modify parameters such as twig length (TL), twig weight (TW), number of leaves on the twig (NL) and leaf weight (LW) due to the stress caused by browsing. A classification function (F) of a discriminant analysis (DA) using six indexes based on these variables was tested. The three treatments of browsing used in the DA were: non-browsed areas during a period of 13 years (F=0), moderate browsing with exclusion of 4 and 5 years (F=1) and intensive browsing without exclusion periods (F=2). All the indexes show significant differences between treatments. The first function of DA shows a percentage of explained variability of 83•99%. This function permits us to quantify the grade of browsing of B. incisifolia, the most palatable and therefore the most vulnerable of browsing shrub in the semi-arid region of Northern Chile