Less shelter in shelterwoods: Management strategies change epiphytic microarthropod communities

Tahnee Ames, David A. Bullis and Gregory G. McGee, Environmental Biology, SUNY College of Environmental Science and Forestry, Syracuse, NY

Background/Question/Methods
Epiphytic lichens and bryophytes are often indicators of old-growth forests, and provide important ecological services such as shelter and nutrition to a host of animals. A more species-rich and abundant community of lichens and bryophytes allows for a more diverse community of associated microarthropods, consequently increasing high-level trophic diversity. The response of these epiphytic communities to disturbance and management strategies, however, is not well known. In this study, we compare forest management impacts on richness, abundance, and diversity of microarthropods, and compare the microarthropod communities between epiphytes in two contiguous northern hardwood stands in the Adirondack Mountains, NY. In July 2020, eight 25cm2 samples of four epiphytic bryophyte and three epiphytic lichen species were extracted from sugar maple (Acer saccharum) trees in both the shelterwood and in the interior of reserve strips of an adjacent stand that received a strip clear-cut which served as a proxy for a full forest. Extracted microarthropods were resolved to the family level and stored in ~90% EtOH. A Two-way ANOVA was computed to test for differences in abundance, richness and diversity between epiphytes within treatment levels. A PERMANOVA was performed to compare microarthropod communities between these factors, and an indicator analysis was computed to determine the taxa driving these community differences.
Results/Conclusions
Abundance, richness, and diversity of microarthropods associated with bryophytes are negatively affected by the decrease in canopy cover in the shelterwood, with a 54% decrease in mean richness, 45% decrease in abundance, and 24% decrease in diversity in bryophyte-associated microarthropods between the two treatments. Beta-diversity is likewise affected by these changes in abiotic condition, with healthy bryophytes hosting a wider and more highly-structured community of microarthropods compared to the desiccated bryophyte mats in the shelterwood (F1,108=5.21, p=0.001). The shelterwood logging method creates gaps in canopy cover, leading to increased light penetration compared to a fully-stocked forest. This increase in temperature and resulting loss of water content in bryophytes causes desiccation under low canopy cover in the shelterwood. Conversely, bryophytes are better buffered from harsh understory conditions within the residual patches in the strip cuts, creating optimal habitat for microinvertebrates which ultimately leads to greater complexity of community structure. This study elucidates impacts of different harvesting strategies on nuanced biodiversity patterns in often overlooked but very biodiverse microhabitats.