Cut stumps vs broken stumps: Does it make any difference in the maintenance of plant and lichen biodiversity in Central European mountain forests?

Excessive forest exploitation significantly contributes to land degradation and the creation of human-made deadwood. Stumps are sometimes ignored in studies on the biodiversity of coarse woody debris. We investigated whether the type of stump, i.e. broken stumps (naturally created) and cut stumps (formed during forestry operations) had an impact on the species composition and species diversity as well as due to this fact they can be characterized by plant indicators. The research covered 728 spruce stumps (287 broken and 441 cut stumps) that were inhabited by lichens, liverworts, mosses and vascular plants in mountain forest belt (Karkonosze Mts., Poland). The following types of microhabitats were included in the research: the upper surface and the lateral surface of a stump with both bark and wood. There are statistically significant compositional differences between the two types of stumps, which was demonstrated by ordination analyses and indicator species analysis. According to the generalized linear models, the probability of occurrence increases in cut stumps in case of liverworts and vascular plants and also along the decomposition stages. The generalized linear mixed-effects model showed that there was a higher species richness of liverworts, mosses and vascular plants on the cut stumps and less drier but the reverse situation was in lichens. The generalized additive models for their cover showed similar trends. Almost all of the taxonomic groups were affected by altitude both in terms of species composition and total cover on the stumps. We concluded that cut stumps are an important type of deadwood for biodiversity and provide a convenient habitat, especially for many lichens and bryophytes.