Effect of Combined Factors on Moth Communities in Western Hungarian Sessile Oak–Hornbeam Forests

The many publications on forests and moth communities accomplished in different sampling regions and habitat types have produced diverse results and conclusions. The multiplicity of outcomes requires regional or local investigations on forest traits and herbivores to determine optimal management methods to maintain biodiversity and ecological stability in woodlands. Our study focused on sessile oak–hornbeam forests, which are economically and ecologically significant in many European countries. Samplings were performed in 2011–2012 using portable light traps in a highly forested area in western Hungary. We used 16 variables for PCA from the sampling of vascular plants and the local forest management plan document. These newly created variables (i.e., principal components) were related (used generalized linear models) to different groups of sampled moth communities: Macrolepidoptera, Microlepidoptera, and ecological groups (according to the host vegetation layer). Based on these significant relations, thinning activity may have various effects on moth communities, through the changed light regime and microclimate conditions. Temperature growth in the gaps could lead to the increasing abundance of heat-preferred Lepidoptera species; however, the decreasing species richness of trees (as a result of thinning) is less favourable for moth assemblages. Increasing herb coverage supports moth communities in the investigated forest stands, which may also be induced by the lower canopy closure. Besides the increasing coverage in the lower vegetation layers, plant species richness is also an important element for moth communities; this was demonstrated by the negative relation between the PC4, PC6 (weighted toward coverage), and Lepidoptera groups. Our results supported the fact that a single study on forest management practice or on vegetation traits is not sufficient to indicate their exact effect on moth communities, because their influence is complex. In order to halt the loss in diversity of the examined forest type, we suggest an overall approach to define the optimal forest management practice and tree mixture rate, regarding a larger area.