The dying legacy of green-tree retention: Different habitat values for polypores and wood-inhabiting lichens

Abstract

The expanding practice of live-tree retention on clear-cuts represents a model case for conservation planning, because the high mortality of those trees requires balancing conflicting management goals in unpredictable conditions over long time frames. We explored the habitat provisioning function of dying retention trees for polypore and epixylic lichen assemblages. We sampled fallen trunks and snags created by known retention-tree deaths during the first post-harvest decade on 46 cut areas in Estonia, hemiboreal Europe. Those trees (particularly large fallen aspens) hosted a species-rich polypore assemblage that included several species of conservation concern. Lichen colonization of wood was slower and most species were found on pine snags. At the tree scale, the total species richness was highest on the trees that had died by trunk breakage creating both a snag and a log. To represent all species at the cutover scale, equal retention of different tree species and dead-wood types was sufficient for common species, but selective retention appeared necessary for species of conservation concern. The most frequent polypore species of conservation concern were either characteristic of specific substrates (notably aspen trunks) or early-successional stand conditions. We conclude that (i) dying retention trees are unlikely to provide dead-wood continuity at the stand scale and this function should be assessed at the landscape scale; (ii) effective habitat provisioning should include predicting and affecting the causes of tree death and linked management decisions based on the diversity, size, and longevity of the trees in specific landscape contexts.