FINE-SCALE SPATIAL-ORGANIZATION OF TALLGRASS PRAIRIE VEGETATION ALONGA TOPOGRAPHIC GRADIENT

Fine-scale spatial patterns of native tallgrass prairie vegetation wer e studied on Konza Prairie, Kansas, USA. Three sites, upland, slope, a nd lowland, were sampled in an ungrazed watershed. Presence of vascula r plant species was recorded in two 25.6 m long transects of contiguou s 5 x 5 cm micro-quadrats on each topographic position. Spatial patter ns of species and functional groups were analyzed by information theor y models of JUHASZ-NAGY. Within-community variability of coexistence w as expressed by the diversity and spatial dependence of local species combinations. Considerable diversity in the local coexistence of speci es was found on each site. Upland and hillside communities were richer and more diverse in species combinations than lowland. Spatial scale effected coexistence relationships. The maxima of information theory e stimates varied between 15 and 30 cm. There was no trend in the variat ion of characteristic scales along the topographical gradient Above 10 m, all sites tended to be homogeneous. The analysis of spatial associ ations revealed that variability in the local coexistence of species w as strongly constrained in all topographic positions. Overall spatial association of species was the lowest on lowland. The characteristic s cales of maximum association were between 1.2 m and 3 m at all sites. The maxima of information theory estimates for the functional group-ba sed data appeared at smaller plot sizes than for the species based ana lyses. Only weak spatial associations were detected among the function al groups indicating that individuals of functional groups coexist wel l at small scales, and form combinations close to random expectations. The length of transects did not effect the relative associations. Str ong positive correlations were found between the number of components (species or functional groups) and the maxima of information theory mo dels suggesting that richness is a good predictor of within-community coexistence relations. However, there was no relationship between rich ness and the characteristic scales of community patterns.