Alvar grasslands in Estonia: variation in species composition and community structure

In order to understand the variation of Estonian calcareous thin-soil grass lands on Ordovician or Silurian lime stone (alvars), 58 stands, distributed over the whole alvar region of Estonia, were described and clustered numer ically using TABORD. Alvars are characterized by a high species richness. T hese mainly semi-natural communities have mostly developed after clear-cutt ing of forests. Grazing by domestic animals and removal of woody plants is needed for their maintenance. Primary (natural) alvar grasslands are found in a few places in coastal regions or in areas with thin-soil on monolithic bedrock. In data processing a whole stand, described by several small rele ves, was used in the classification as one description, including species f requencies as a quantitative measure. Seven clusters were separated and the ir configuration checked in a PCA-ordination. The resulting classification agreed with the previous 'rough' classification. Both geographical and ecol ogical factors were related with the clustering and the ordination. The bro ad classification units, suggested for Estonian alvar grasslands, were quit e similar to the ones described earlier for alvar vegetation on Oland, Swed en. Clusters differed in their species richness, environmental conditions a nd life-form spectra. Differences in species richness were defined by regio nal species pools. Compared to earlier surveys, only a small fraction of al vars still remains in Estonia. Active conservation, i.e. suitable manage me nt is needed to protect the still surviving valuable plant communities. The present study can provide guidelines on how to protect and manage differen t types of alvars in Estonia.