Annual tree mortality and felling rates in the Czech Republic and Slovakia over three decades

Although tree mortality is an essential process in forests, tree death still remains one of the least understood phenomena of forest development and dynamics. Therefore, we focused on annual mortality rates together with annual felling rates in the Slovak and Czech forests. We used data from the long-term national monitoring (periods of 1988–2017 in Slovakia and 1992–2017 in the Czech Republic). More than 24.6 thousand trees were assessed together in both countries. We calculated mortality and felling rates derived from two variables: basal area and number of trees. For these purposes, we selected five tree species/genera, specifically: Norway spruce, pines, European beech, oaks and common hornbeam. We recorded large inter-annual fluctuations of mortality rates in all tree species/genera. In both countries, spruce and pines had the highest mortality rates, while beech had the lowest mortality rates. Confrontation of long-term climatic data (especially annual precipitation totals) with mortality data indicated that drought was probably the most relevant factor causing tree death. On the other hand, no significant temporal trend, either increasing or decreasing, in tree mortality was found for any tree species/genera. As for all five selected tree species/genera together, significantly higher mean annual mortality rate derived from the number of trees was found in the Czech Republic (1.09%) than in Slovakia (0.56%). This finding indicates that tree mortality is often caused by combined effects of external unfavourable factors and competition pressure in forest stands.