Local forest continuity – important for species-rich Micarea lichen communities, but less so for decomposers

Abstract

Fragmentation has a negative effect on forest continuity, i.e. availability of a suitable habitat for the target species over a time period (1). The dependence of wood-inhabiting fungi on landscape level continuity is well acknowledged, but the role of local continuity has remained unclear. We explored the effects of local forest continuity (microhabitat and stand level) on the diversity of fungi inhabiting standing dead trunks of Scots pine (Pinus sylvestris L.). Specifically, we studied the species richness and community composition of decomposers and Micarea lichens. The study included 70 trunks in 14 forests in central Finland with varying state of continuity. We assessed the detailed history of each study trunk with dendrochronological methods to estimate microhabitat continuity. Dead wood diversity and past management intensity (number of cut stumps) were used as estimates for stand continuity. Altogether, we recorded 107 species (91 decomposers and 16 Micarea lichens) with 510 occurrences. To study the effects of environmental variables, we used generalized linear mixed models for species richness, and Bioenv-analysis and Nonmetric Multidimensional Scaling for community composition. None of the variables explained species richness of decomposers, but there was a positive correlation between Micarea species richness and the time since tree death. The results for community composition analyses were rather tentative. Nevertheless, the community composition of decomposers was best explained by dead wood diversity, and for Micarea lichens, the community composition was mostly determined by the combined effect of years from tree death, site, and dead wood diversity. Our results are in line with those of previous studies suggesting the restricted significance of local forest continuity for wood-inhabiting fungi. However, species-rich Micarea lichens communities seemed to depend on standing pines that have been available over long periods after their death. Local forest continuity might be more important for rare specialists (e.g. on veteran trees), and therefore, future research should focus on such species.

1. Nordén, B., Dahlberg, A., Brandrud, T.E., Fritz, Ö., Ejrnaes, R., Ovaskainen, O., 2014. Effects of ecological continuity on species richness and composition in forests and woodlands: a review. Ecoscience 21, 34–45. doi:10.2980/21-1-3667