Moss synusiae in South Estonian forests

On the Karula Upland, South Estonia, the forest moss layer was analysed using a transect of 726 contiguous 0.2×0.2 m plots. The sample plots were classified according to a multistage clustering procedure based on the sequential use of algorithms with different criteria. Several obtained clusters are rather similar in species composition, but abundance relationships among dominant species are distinctly different. For detailed analysis of mutual relations among societies a formal definition of adjacency is proposed, and two aspects of the cluster continuum — transitionality and distinctness — are estimated. It appears that almost all resulting societies are very distinct (P<0.05), but at the same time can be continual in the sense of transitionality. Spatial changes in vegetation along transects are also discontinuous. The null hypothesis assuming the independency of neighbouring sample plots type was refuted withP=0.01. The spatial extent of different synusiae is typically several times larger than it should be if there were no structure in moss vegetation.