Distribution trends of rare vascular plant species in Estonia

On the basis of quantitative analysis of the vascular plant distribution maps for Estonia, we specified the list of rare species which occur in less than 5% of grid quadrangles, and studied the possible correlations between their rarity and habitat preference, distribution, and sensitivity to human impact. Rare species occur statistically more often among species that are at the limit of their geographical range. The proportion of rare species was significantly higher among arctomontane and disjunct circumpolar taxa. Among apophytes, there were less rare taxa than would be expected according to the common native flora, but among hemerophobes, there were significantly more rare species than would be expected. The number of rare species was in strong positive correlation with the species richness of the region. Besides the western part of Estonia, where the greatest number of rare species occur, some small areas rich in rare species also lie in East and North Estonia.