Bark stripping, the crucial factor affecting stem rot development and timber production of Norway spruce forests in Central Europe

Bark stripping damage and the resultant stem rot to Norway spruce (Picea abies [L]. Karst), one of the most important tree species, poses a serious problem for forest management in Europe. Our research objective was to determine the effect of bark stripping, the subsequent rot decay and the impact of climatic factors in young (42-49 years) spruce stands. Moreover, we compared the differences between damage caused by red deer (Cervus elaphus L.) and sika deer (Cervus nippon Temminck). In all the cases studied, game damage was lower in forest stands when caused by sika deer (SD - 77.3%) compared to red deer (RD - 88.8%); 27.8% (SD) - 32.0% (RD) of stem circumference was damaged in average. Damaged trees showed higher growth variability and were more sensitive to a lack of precipitation and droughts, while air temperature had a higher effect on the growth of healthy trees. The initial game damage was observed in the 11 (SD) - 14 (RD) year of the mean tree age. The stem volume was lower by 25% (SD) - 28% (RD) in lightly damaged trees, and 50% (SD) - 71% (RD) in heavily damaged trees compared to healthy trees. The vertical stem decay reached a maximum of up to 4.5 m (SD) - 6.0 m (RD) (mean 1.9-3.1 m) with the mean speed of vertical spreading of 5.7 cm yr(-1) (SD) - 9.6 (RD) cm yr(-1). The mean decayed wood accounted for 30% (SD) - 39% (RD) of the stem volume. The peripheral stem damage by bark stripping and the age of the first occurrence were significant factors in predicting damaged crosscut area and vertical rot spreading in the stem. During this time of climate change, the stability of damaged spruce stands has been significantly disturbed by deer game.