La heterogeneidad ambiental en un matorral xerófilo

Biotic and abiotic heterogeneity in spatial and temporal scales were characterized for two areas of the xerophytic shrubland of the Pedregal de San Angel (REPSA) ecological reserve. Nine fl oristic groups were identifi ed and they showed a differential dis- tribution of the plant species that inhabit this community. Each one of the groups was named according to the key species, therefore they were considered as determinants in the communities physiognomy. Through the use of multivariate analysis (TWINSPAN and CANOCO) we observed that species composition in the groups is modifi ed in spatial and temporal scales. This study suggests that variation of some abiotic factors such as soil depth and slope infl uences differentially the systems heterogeneity. Temporal hetero- geneity was evident since there was a different fl oristic composition in this area during the dry and the rainy season.