The impact of natural disturbance and forest structure on the biodiversity of temperate spruce-dominated primary forests in the Western Carpathians

RNDr. Matej Ferenčík

Doctoral thesis

Abstract:

Understanding the processes shaping the species assemblages at multiple spatial and temporal scales in response to natural disturbances and their legacies is crucial for preventing ongoing worldwide biodiversity loss, and for improving forest management practices aimed at mitigating accelerating changes in environmental conditions and enhancing forest resilience. Spruce primary forests are critical habitats for a wide spectrum of forest-dwelling taxa. However, because of the higher frequency and severity of natural disturbances in the last decades, and the subsequent salvage logging, these ecosystems are incredibly rare and are disappearing rapidly. Although we have sufficient evidence for the fundamental role of structural variables for forest biodiversity, the influence of long-term natural disturbance regimes - which are the primary driver of these variables - has not been sufficiently documented. To address this knowledge gap, we sampled four taxonomic groups: birds, epiphytic and epixylic lichens, saproxylic beetles, and deadwood-inhabiting fungi at 58 locations within ten of the best-preserved spruce primary forest stands distributed across the Western Carpathians Mountains and investigated the drivers of their assemblages. Our dataset combines disturbance history variables (frequency and severity), forest structural variables (e.g. tree age, quantity and quality of deadwood, canopy openness), and biodiversity data. The four taxonomic groups were selected because of their particular sensitivity to forest management. We applied a dendroecological approach (using tree-ring data) to describe the effect of 250-years of historical natural disturbances on current species richness of deadwood-inhabiting fungi at a plot-level (local) and stand level (regional). The magnitude of inter-site differences in species assemblages for four taxonomic groups were used to quantify corresponding levels of total beta-diversity, which were then decomposed into nestedness and turnover components. We also assessed the degree of congruence among groups for beta-diversity metrics. Finally, using regression methods, we investigated relationships between habitat features and observed alpha-diversity and red-listed species incidence. The main findings of this thesis are: I) Historical disturbances shaped the contemporary local and regional species richness of deadwood-inhabiting fungi, with contrasting impacts of disturbance regime components at different spatial scales. While the local diversity of red-listed species increased due to higher disturbance frequency, the regional diversity of all species decreased due to the higher severity of historical disturbances. The deadwood volume positively influenced the species richness of deadwood-inhabiting fungi, while canopy openness had a negative impact. II) The number of species found exclusively at the respective stand and the total number of species were similar for all stands for fungi and lichens but varied more strongly for beetles and birds. Except for birds, the individual stands generally hosted less than half of the species identified in the total regional species pool. Thus, variability in species composition among stands was large relative to the number of species found exclusively at the respective stand in the beetle, fungi, and lichen groups. III) We found evidence for a congruence among taxonomic groups in terms of total beta-diversity. All groups were significantly correlated with at least one other group. The bird group was congruent with all other groups, while beetles were correlated with birds only. In contrast, we did not find evidence for a significant correspondence between groups in terms of the two components of beta-diversity, namely turnover and nestedness. The single exception was a congruence of spatial turnover between fungi and lichens. IV) For beetles and lichens, local species richness (alpha-diversity) was influenced by characteristics associated with both the l

Abstract:

iving tree canopy and the local deadwood supply. Specifically, the richness of the beetle group increased with both canopy openness (light levels) and volume of relatively intact (decay stage 1) lying deadwood. For lichens, the mean age of the five oldest trees and the volume of standing deadwood promoted local alpha-diversity. The local diversity of both lichen and fungi red-listed species was positively affected by stand conditions. Again, the mean age of the oldest trees, as well as the volume of highly decomposed lying deadwood (decay stages 4 and 5), positively influenced the number of red-listed species for these two groups. The number of rare lichens also covaried with elevation. V) Spatial turnover for all taxonomic groups was significantly higher than nestedness. Each primary forest stand had unique and unrepeatable species composition and contributed equally to the total regional species pool. Our results bring new and valuable insight into forest dynamics and biodiversity patterning at the local and regional landscape scale in montane temperate spruce-dominated primary forests in the Western Carpathians. From a landscape perspective, we can conclude that the distribution of species from the regional species pool is driven by past spatiotemporal patterns of disturbance events and by spatial turnover. Natural disturbances occurring at higher frequencies that create multiscale habitat patchiness through disturbance legacies are necessary for a wide range of biodiversity, especially for rare and endangered species. The high number of observed rare species also highlights the importance of primary forests for biodiversity conservation. Thus, both creating a network of strict forest reserves with sufficient area and landscape connectivity at the regional scale, as refuges and sources for management-sensitive forest-dwelling taxa, and forest management practices that emulate natural disturbance processes, are recommended to support habitats for biodiversity and their associated ecosystem functions.

Keywords

Natural disturbances, Old-growth forests, Forest-dwelling taxa, Beta-diversity, Forest structure, Dendrochronology, Species richness, Species turnover

Language used: English

Date on which the thesis was submitted / produced: 3. 10. 2024

Thesis defence

• Supervisor: Ing. Martin Mikoláš, Ph.D.
• Reader: Miroslav Šálek, prof. Dr. Mgr., Jan Vondrák, externi, Karol Ujházy, externi

Czech University of Life Sciences Prague

Faculty of Forestry and Wood Sciences

Doctoral programme / field:
Forestry Engineering / Forest Biology