Habitat availability is assumed to be a major driver of organismic diversity and related ecosystem processes. A Tree related Microhabitat (TreM) is a distinct, well-delineated morphological singularity occurring on living or standing dead trees. It constitutes a crucial substrate or life site for species. Communities associ-ated with TreMs are predicted to be organised in metacommunities. However, it is not well understood if small scale differences in habitat availability affect the diversity and composition of these specialised communities and related process-es in TreMs due to e.g. dispersal limitations within metacommunities. We mapped all water-filled tree holes on a 10 ha plot in the primeval beech forest of Uholka, Ukraine, and a managed beech-dominated forest nearby. We installed in each forest 27 artificial water-filled containers with 2 g dried beech leaves each on a regular grid in both forest to assess the spatial distribution of insect functional community composition as well as leaf decomposition rates in the artificial con-tainers. We did a spatial correlation analyses to test whether communities in these TreMs are affected by the spatial distribution in habitat availability and whether this translates into a change in leaf decomposition. We found substantial small-scale variability in habitat availability in the primeval as well as managed forest and this was a strong driver of the functional composition of TreM associated communities and leaf decomposition rates. This suggest that dispersal limitations might affect the colonization of habitats within metacommunities already at a very small scale and that this translates into a change in ecosystem processes.