The effect of natural disturbances and forest structure on tree-related microhabitats and saproxylic beetles in primary mountain forests

Ing. Daniel Kozák

Doctoral thesis

Abstract:

Natural disturbances shape forest structure, dynamics, ecosystem functions and services. Disturbance legacies such as deadwood, canopy gaps and habitat trees greatly influence the amounts of suitable habitats for forest dwelling species. Understanding the importance of disturbance legacies for supporting biodiversity is crucial in understanding any biotic responses in the face of the expected future intensification of forest disturbance as a consequence of ongoing anthropogenic climate change. The main objective of this thesis is to observe how natural disturbances and current forest structure of primary mountain forests of Europe impacts forest habitats and forest dwelling species. We use tree-related microhabitats (TreMs) and saproxylic beetles as the objects of the study, since TreMs encompass a variety of habitats suitable for feeding, dwelling or shelter of forest species and saproxylic beetles because of their close relationship to deadwood substrate and forest structure conditions. Thus we first aimed to i) investigate the influence of historical disturbances and forest structure on the taxonomic, functional and phylogenetic diversity of current saproxylic beetle communities (Section 5.1), ii) characterize the TreM profile and evaluate the importance of local plot structure and spatial variability for TreM density and diversity (Section 5.2), iii) compare the TreM richness of primary and managed forests on a tree level (Section 5.3) and iv) evaluate the effect of tree age on TreM abundance and richness in primary spruce and beech-dominated forests (Section 5.4). For these aims we used a large database of permanent study plots from primary forests of Central, Eastern and Southeastern Europe and managed forests from the Black Forest region. We combined the dendroecological database from more than 350 plots with the survey of TreMs and samples of saproxylic beetles on a subset of plots. The main findings of this thesis are: i) Historical disturbances have significant effects on current beetle communities. Contrary to our expectations, different aspects of beetle communities, that is, abundance, taxonomic, phylogenetic and functional diversity, responded to different disturbance regime components. Past disturbance frequency was the most important component influencing saproxylic beetle communities and available habitats via multiple temporal and spatial pathways. The quantity of deadwood and its diameter positively influenced saproxylic beetle abundance and functional diversity, whereas phylogenetic diversity was positively influenced by canopy openness (Section 5.1). ii) TreM density and diversity were significantly positively related with tree species richness and the proportion of snags. Root mean square of the tree diameters were significantly related to alpha and gamma diversity of TreMs. Both regions reached similarly high values of total TreM densities, and total TreM densities and diversity were not significantly different between the two regions. However, we observed significant differences between the two regions in regard to the densities of two TreM groups, conks of fungi and epiphytes. The density and diversity of TreMs were very high in beech-dominated primary forests, but their occurrence and diversity were highly variable within the landscape over relatively small spatial gradients (plot and stand levels; Section 5.2) iii) We found congruent results based on the models for overall richness and the vast majority of TreM groups. Trees in primary forests hosted greater richness of all and specific types of TreMs than individuals in managed forests. The main driver of the difference was the long-term natural development with the absence of human management, followed by tree species and DBH. iv) Tree diameter and age were the most important factors significantly increasing TreM abundance and richness, whereas tree species played a lesser but significant role in overall TreM abundance and richness across the

Abstract:

primary forests. We observed the major role played by tree age in increasing the richness of specific TreM groups, such as concavities, insect galleries and exposed sapwood on studied trees. Additionally, we provide general as well as specific recommendations for conservationists and forest managers based on our results, on how to conserve and increase the habitat amount and quality of forest stands in order to host a rich array of biodiversity.

Keywords

natural disturbances, primary forest, biodiversity indicators, saproxylic beetles, tree-related microhabitats, forest structure, disturbance legacies

Language used: English

Date on which the thesis was submitted / produced: 15. 12. 2020

Thesis defence

• Supervisor: prof. Ing. Miroslav Svoboda, Ph.D.

Czech University of Life Sciences Prague

Faculty of Forestry and Wood Sciences

Doctoral programme / field:
Forestry Engineering / Forest Biology