Investigating the biodiversity of the forest strata: The importance of vertical stratification to the activity and development of saproxylic beetles in managed temperate deciduous forests

Abstract

Saproxylic beetles represent an important part of the chain of decay processes and are of high interest for understanding the main drivers of forest community succession.The main aims of this paper were to determine (i) the differences between communities of the crown and stem strata and (ii) the effect of fine vertical stratification within the studied strata on adult saproxylic beetle activity and the success of larval development.The study was performed over three years in mature oak-dominated managed forests in Poland. The activity and development of the beetles was evaluated based on sampling from 60 traps and 60 logs, respectively.In total, 11,237 individuals representing 364 species of saproxylic beetles were trapped and 388 individuals representing 38 species were reared. Compared with most previous studies, our results indicated that the majority of dependent variables (the species richness and abundance of saproxylic beetles and their functional groups, sub-guilds, and conservation-related and functional traits) revealed a significant preference for the crown, specifically the lower part. For example, predators searched for the transition zone between the crown and stem, which has a high prey density. The preferences of guild specialists and threatened species indicated that micro-habitats (e.g., hollows or fungi) are more frequent in the crown stratum than in the stem in managed forests, and the higher biomass of saproxylic beetles likely reflects the amount of energy produced in lower parts of crowns.Compared with that observed in previous studies, the opposite pattern of preference for crowns was likely related to the higher anthropogenic pressure in managed forests, which is an important insight that can inform the future management (e.g., biocontrol by natural enemies or conservation) of these forest types.