Effects of deer on multiple levels of biodiversity in European mixed montane forests

Medientyp: E-Book

Titel: Effects of deer on multiple levels of biodiversity in European mixed montane forests

Beteiligte: Schwegmann, Sebastian [Verfasser]; Storch, Ilse [Akademischer Betreuer]; Kjellander, Petter [Sonstige]; Scherer-Lorenzen, Michael [Sonstige]

Körperschaft: Albert-Ludwigs-Universität Freiburg, Professur für Wildtierökologie und Wildtiermanagement ; Albert-Ludwigs-Universität Freiburg, Fakultät für Umwelt und Natürliche Ressourcen

Erschienen: Freiburg: Universität, 2023

Umfang: Online-Ressource

Sprache: Englisch

DOI: 10.6094/UNIFR/237637

Identifikator:

Schlagwörter: Biodiversität ; (local)doctoralThesis

Entstehung:

Hochschulschrift: Dissertation, Universität Freiburg, 2023

Anmerkungen:

Beschreibung: Abstract: Deer are the most abundant keystone herbivores in forest ecosystems of the northern hemisphere. They affect vegetation and fauna through a range of multiple direct and indirect interactions, and thus fulfil a range of ecosystem functions (e.g., seed dispersal, carrion provisioning, selective browsing). However, high population densities of deer have often been found to be a detrimental for elements of forest ecosystems. From a forestry perspective, deer impede natural succession of young trees and may act as a biotic filter reducing the tree species richness of future forests. This is problematic in the context of making forests more resilient towards climate change induced calamities such as drought and bark-beetle outbreaks, as often those tree species that foresters wish to promote are also preferred by deer, as for example silver fit (Abies alba) In my thesis, I explore the impact of deer on forest biodiversity by assessing how deer relate to woody vegetation as well as faunistic groups in a managed production forest. My study is integrated into the Research Training Group ConFoBi (Conservation of Forest Biodiversity in Multiple-Use Landscapes of Central Europe, DFG RTG 2123), which assesses the success of promoting forest biodiversity in production forests through retaining deadwood and habitat trees, i.e., retention forestry. In this context, I used the 135 ConFoBi-research plots in the southern Black Forest, Germany, to assess the influence of deer in managed forests. In my first chapter, I assessed the effect of small-scale food abundance, large-scale forest structure and landscape matrix on roe deer (Capreolus capreolus) habitat use using detection rates of camera traps. Additionally, I investigated whether lying deadwood can physically obstruct deer movement. I found that landscape and small-scale food abundance did not affect roe deer habitat use in my system. Variables of forest structure indirectly affecting food and cover availability on the stand scale (e.g., tree species richness or vertical complexity) were the strongest drivers of roe habitat use. Higher volumes of lying deadwood reduced roe deer detection rates in autumn but not in spring. Small-scale food availability might not be a suitable scale to assess roe deer habitat use, while I assume that high hunting and recreational pressure in the study area might reduce the use of open and ecotone habitat of roe deer. Variables of forest structure that likely improved forage availability or quality (canopy cover, tree species richness) or cover (vertical complexity) made forest sites more attractive to roe deer. In my second chapter, I assessed possible associational effects of forest understory on browsing pressure of roe deer. Additionally, I assessed whether lying deadwood can shelter woody vegetation physically from browsing, and how relative roe deer abundance relates to browsing pressure. I used data from extensive browsing surveys and camera trapping from the same study sites as in Chapter 1. I found species-specific associational effects of forest understory characteristics for woody plant taxa that were of intermediate preference to deer. Woody taxa that were either always avoided or strongly preferred and thus always browsed were not affected by understory vegetation. The volumes of deadwood on my research sites did not significantly reduce browsing pressure on the woody vegetation. This may have been because deadwood volume had not yet accumulated enough to be effective. In my study area, deadwood retention has only been implemented in the last decades, and it is possible that different effects of deadwood will arise over time as more deadwood accumulates. Relative roe deer abundance was only significantly related to browsing pressure on some woody plants. These results support the notion that culling alone might sometimes not be enough to reduce browsing impact, as some taxa were not affected by the gradient of roe deer abundance on my study sites. Other aspects like overall food availability or disturbance might be stronger drivers of browsing pressure than deer abundance in some situations. In my third chapter, I systematically reviewed studies assessing the effects of native deer on abundance and species richness of faunistic communities in temperate and boreal forests of the northern hemisphere. Effects of deer varied in directionality and for most taxa there were reports of both positive and negative effects. Some groups like carabids were frequently reported to be positively affected, while other like understory birds were frequently reported to be negatively affected. Overall, it is still difficult to generalize patterns as very often only two levels of deer abundance were studied, while the effects of deer are most likely non-linear. While high deer population densities can be negative for forest faunal diversity low to intermediate populations might not be detrimental. In my fourth chapter, I experimentally assessed the use of evisceration residues from hunted roe deer by necrophagous insects. I compared insect abundances using pit-fall traps at three different treatments: sites with evisceration residues sites, sites with roe deer carcasses and controls sites. The results showed that evisceration residues are used by all necrophagous coleopteran families found at entire carcasses. Most differences in abundance were most likely due to differences in carrion biomass. While I found a lower species richness of Silphidae on residues sites, community composition and diversity between carcass and residues sites must be compared with a larger sample size. Overall, evisceration residue retention might contribute to maintaining specialized necrophagous insect communities. In my fifth chapter, I assessed how evisceration residues from hunting are used by vertebrate scavengers to infer how available evisceration residues are invertebrates if the residues are exposed to vertebrate scavenging. I found that, while most samples were used up by vertebrates some were not removed or even fed upon by vertebrates, and thus available for invertebrates. A large proportion of the occurring scavenger fauna used evisceration residues with a total of twelve wild taxa detected and ten native taxa detected feeding. Only some species removed the entire samples, of which the red fox was the most dominant. In summary, the results of my thesis suggest that deer cannot be considered generally detrimental for forest biodiversity. The relationship between deer and biodiversity depends on a range of variables, such as characteristics of the understory and preference by roe deer, while deer abundance only explains browsing intensity for some woody taxa. Furthermore, while some faunistic groups may be frequently negatively affected by deer, this is in part due to very high deer population densities which do not occur in all forests. In forests with less dense roe deer populations, roe deer may provide services such as ecosystem engineering and resource provisioning. To better understand the relationship between deer and faunistic groups, future researchers, need to consider that these relationships might often not be linear

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