Analysis of some limiting ecological factors on the example of the distribution of the genus Tilia L. cultivated in Latvia

The study was performed on the basis of an inventory of the genus Tilia in Latvia. A total of 134 dendrological objects were inventoried in order to clarify factors limiting the distribution of linden in the territory of Latvia. During the 2007-2013 inventory 47 taxa of Tilia were found. The taxa and their winter hardiness were evaluated according to the Sokolov scale. In the interpretation of the distribution of taxa 16 geographical and climatic factors were used. Spearman's rank correlation indicated a connection with 11 factors, among them distance to the sea, height above sea level, average January temperature, sum of negative temperatures, and amount of annual precipitation. The results of statistical analysis demonstrated an irregular connection between the geographical distribution of the genus Tilia and ecological factors. A negative correlation with height above sea level was observed for T. americana, T. × moltkei, and T. platyphyllos subsp. platyphyllos. Analysis of winter hardiness of trees revealed that trees get frozen in hard winters although they grow in hardiness zones that fit linden.