Dead wood in clearcuts of semi-natural forests in Estonia: site-type variation, degradation, and the influences of tree retention and slash harvest

Semi-natural forests, which naturally regenerate after timber harvesting, provide distinct opportunities for dead wood (DW) management for biodiversity. We described DW pool and sources of its variation during the first decade after final felling in Estonia, hemiboreal Europe. Depending on forest type, the mean post-harvest volumes of above-ground DW ranged from 70 to 119 m(3) ha(-1). Final felling generally did not reduce downed coarse woody debris (CWD) because many sawn logs were left on-site, and soil scarification was rarely used. However, subsequent decay of downed CWD appears to be accelerated due to the increased ground contact of logs, so that even the relatively small inputs from live retention trees observed (5 m(3) ha(-1) per decade) can be ecologically significant. While final felling greatly reduced snag abundance, the mortality of retained live trees generally balanced their later losses. The volumes of downed fine woody debris in conventional cutover sites were roughly double that of pre-harvest forests. Slash harvest caused an approximately twofold reduction in downed DW and resulted in CWD volumes that were below mature-forest levels. The results indicate that the habitat quality of cutovers critically depends both on the retention and on the post-harvest management of biological legacies. In Estonia, the necessary improvements include more careful retention of snags in final felling, selecting larger retention trees, focusing slash harvest on the fine debris of common tree species, and providing snags of late-successional tree species.