INFLUENCE OF DROUGHT ON TREE GROWTH IN SOME SLOVENE REGIONS

Abstract

The influence of precipitation and temperature on tree growth in submediterranean Slovenia, on gravel terraces in central Slovenia and near the upper forest boundary in the Alps was analyzed using the dendroclimatological method. Trees growing in the submediterranean climate of the coastal region most easily withstand drought, both on flysch and Karst soil. The most significant factors are aboveaverage precipitation and below-average temperatures in the vegetation period and during the preparation of trees in autumn for winter dormancy. In very dry years, when summer precipitation falls below 50% of the average rate, the annual growth increment in tree trunks may also decrease by 25 to 35%. A similar, yet slightly weaker relation between climate and tree growth is also evident in the gravel deposits of central Slovenia covered with a thin layer of soil, despite the generally more humid climate. Below-average precipitation also has a negative effect on tree growth in some mountain areas with a perhumid climate, where the generally above-average precipitation in the vegetation period impedes tree growth. In these areas rainwaters drain rapidly, since the sparse soil is unable to retain them. Such forest areas can be found in the highly karstened mountain terraces of the Julian Alps, which are generally ranked among the most watered regions in Slovenia, as well as on the steep, limy (dolomitic) slopes of the eastern Karavanke mountains, which receive less rainfall than the western Slovene Alps.