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 browsin g pressure in Bridgesia incisifolia (Bert. ex Cambess) shrublands is elabor ated. This procedure is based on the assumption that shrubs modify paramete rs 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 classifi cation function (F) of a discriminant analysis (DA) using six indexes based on these variables was tested. The three treatments of browsing used in th e 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 wit hout exclusion periods (F = 2). All the indexes show significant difference s between treatments. The first function of DA shows a percentage of explai ned variability of 83.99%. This function permits us to quantify the grade o f browsing of B. incisifolia, the most palatable and therefore the most vul nerable of browsing shrub in the semi-arid region of Northern Chile. (C) 19 99 Academic Press.