XVI International Botanical Congess

Patchiness in plant communities may result from environmental heterogeneity or from species interactions. The relative importance of abiotic vs biotic factors is of particular interest because of its implications for community structure. I investigated patchiness in an Icelandic mire where the major species, all clonal graminoids of similar growth habit (Carex rostrata, C. nigra, C. chordorrhiza and Eriophorum angustifolium), formed easily recognizable patches. Although the mire was topographically level, C. rostrata patches had lower groundwater level and shallower soil depth than other species patches. Conductivity, pH, N, K and Mg concentrations did not differ significantly among species but C. nigra had higher P than C. chordorrhiza patches. Patches of C. rostrata and C. nigra were least invaded by other species. C. rostrata was also the least invasive species.The foraging behaviour of the highly stoloniferous C. chordorrhiza was compared among species patches. It produced significantly longer stolons (with longer internodes and more numerous modules)in E. angustifolium patches than in C. rostrata or its own patches.