MULTIVARIATE-ANALYSIS OF THE VEGETATION OF THE VOLCANOS TLALOC AND PELADO, MEXICO

Multivariate analysis was used to describe the composition and distrib ution of vegetation types on the slopes of the volcanoes Tlaloc and Pe lado, Mexico. These volcanoes are situated in the transitional zone be tween the Holarctic and Neotropical floristic regions, which offers a partial explanation for the relatively high alpha and beta diversities . Previous research argued that human activities, i.e. burning and raz ing, rather than abiotic factors, play a major role in determining the distribution and floristic composition of the vegetation. TWINSPAN, D etrended Correspondence Analysis and Canonical Correspondence Analysis were used to test this hypothesis. Floristic and environmental data f rom 138 releves and seven explanatory environmental variables were inc luded: elevation, soil depth, soil moisture, percentage litter cover, percentage cover of bare ground, burning and grazing were included in the analysis. Soil moisture and elevation accounted for ca. 63 % of th e residual inertia and none of the remaining explanatory variables pro ved to be correlated significantly with the first two axes. The presen t results suggest that burning and grazing operate on a finer scale. I n conclusion, soil moisture and elevation are the most relevant variab les to explain the distribution of the vegetation under study.