Amount and distribution of coarse woody debris in Dalby Söderskog national park

Sammanfattning: Coarse Woody Debris (CWD) is a critical structural and functional component of all forest ecosystems and comprises non-living woody biomass, standing or lying, larger than 10 cm in diameter. This study provides the first inventory of coarse woody debris in the temperate broadleaf forest of Dalby Söderskog national park in southern Sweden. Specifically, the aims were (1) to quantify the amount of standing and lying CWD, and (2) to study the diameter distribution of CWD in Dalby Söderskog. Length and diameter of coarse woody debris including dead standing trees, cut stumps, and dead downed trees and branches were registered in 50 circular 100 m2 (5.64 m radius) sample plots. According to the results, Dalby Söderskog had an average of 227 m3/ha coarse woody debris. Out of this volume, 174 m3/ha were logs, 49 m3/ha were snags, and 4 m3/ha were cut stumps. The number of snags and logs was highest in the smallest diameter class (10-19 cm) and decreased with increasing diameter. However, the overall volume increased from the dbh class 10-19 cm to a maximum at the dbh class 30-39 cm, and decreased again at larger dbh classes. The amount of CWD per hectare measured in Dalby Söderskog is roughly ten times the average amounts found in both Swedish woodland key habitats, formally protected forests, and Natura 2000 forest areas in Sweden, which all contain around 20 m3/ha. Similar volumes as in Dalby Söderskog can, however, be found in central European temperate old-growth forests. Although no attempt was made in the present study to determine CWD to tree species, comparisons with previous tree inventories suggest that the exceptional high amount of CWD in Dalby Söderskog is related to greatly increased tree mortality during the past three decades caused by Dutch elm disease and ash dieback.