Spatial patterns and relations with site factors in a campos grassland under grazing.

Spatial distribution patterns and their relations with environmental factors at different scales were identified in ca. 100-ha grassland under cattle and sheep grazing, in Eldorado do Sul, RS, Brazil (30 degrees 05'S, 51 degrees 40'W). The field survey used 138 0.5 x 0.5 m quadrats located systematically on transects along relief gradients. The quadrats were arranged in groups of 3 contiguous quadrats, which were pooled for the analysis, thus forming 46 quadrats 1.5 x 0.5 m, in this way defining two observation scales. Vegetation description involved recording the presence and the visual estimation of cover-abundance of species in each quadrat. A total of 148 species belonging to 30 families was detected. The environmental conditions at each site were described by 30 variables related to soil chemical and physical properties, slope, exposure and relief position. Data analysis used cluster analysis, evaluation of group partition sharpness, ordination, significance of ordination axes, evaluation of environmental congruence and randomization testing. The results of the analysis with 46 quadrats supported those found with 138 quadrats. The vegetation patterns in the study area are associated to relief position and other related factors such as soil moisture. Two clearly defined grassland community types were detected, one occurring on the slopes and another on the wet lowlands.