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B1) Epiphyte & Microhabitat Diversity

Epiphyte and microhabitat diversity and function on habitat trees

Albert Reif 1, Markus Hauck 2 (since 1.7.2019) & Stefanie Gärtner 3
Doctoral researchers: Diane Stevenson1 (since 2016) & Dina Emrich (since 2019)

University of Freiburg, Faculty of Environment & Natural Resources, Institute of Forest Sciences,
Chair of Site Classification and Vegetation Science

2 University of Freiburg, Faculty of Environment & Natural Resources, Institute of Forest Sciences,
Chair of Applied Vegetation Ecology

3 National Park Black Forest, Working Group Conservation of Processes & Development of Vegetation

Background

Epiphytic lichens and bryophytes respond more sensitively to changes in the site condition of forests than vascular plants. This applies both to natural fluctuations in site conditions in the course of forest aging and disturbance dynamics(1) and to the impact of anthropogenic disturbance, including effects of forest management or air pollutants(2, 3). A key reason for the high responsiveness of epiphytic lichen and bryophyte species richness and species composition to changes in the forest structure and in forest management is their direct dependence on trees and deadwood, whereas the forest floor vegetation is only indirectly affected via changes in microclimate and soil conditions. Epiphytic lichens and bryophytes are also heavily affected by forest fragmentation and the disruption of habitat continuity as the result of dispersal limitations(4) and edge effects(5). Old large-diameter trees and deadwood are usually particularly rich in epiphyte species because they offer special microhabitats and long habitat continuity.

 

Research questions and hypotheses

The role of habitat trees (defined as trees of an age and tree diameter that is clearly above the stand average) for conserving the total forest epiphyte diversity will be quantified by the comparative study of habitat trees and ‘average’ trees that represent the typical tree diameter and tree species of the stand. Using the complete plot design of 135 sample plots, we will address the questions how habitat trees differ in their epiphytic lichen and bryophyte diversity from the remaining forest stand in variation of (1) the species identity of the habitat tree, (2) the main tree species of the stand, (3) the diameter and microhabitat characteristics of the habitat tree, and (4) forest connectivity. We will further analyse how these factors interact with elevation, aspect, and tree species richness.

Our key hypotheses include:

(1) Habitat trees are generally richer in epiphytic lichens and bryophytes both in terms of species richness (α-diversity) and turnover (β-diversity) than the average trees of a stand.

(2) The epiphytic lichen and bryophyte species richness of habitat trees is strongly dependent on tree species identity.

(3) The tree species composition of the surrounding stand exerts a significant influence on the epiphyte diversity of the habitat tree.

(4) Broad-leaved habitat trees in conifer-dominated forest stands contribute disproportionally to the epiphyte diversity of the total stand.

(5) High forest connectivity has a beneficial influence on the epiphyte diversity of habitat trees.

(6) The increase in epiphytic lichen and bryophyte diversity with elevation is steeper in conifers than in broad-leaved trees.

 

Approach, methods and linkages

Based on the stand structural data from A2, the 5 habitat trees with the highest diameter at breast height (dbh) will be selected on every plot. These trees will be compared with 5 ‘average’ trees representing the respective plot’s most common tree species close to the mean dbh of these trees in that plot. The average trees will be selected by choosing the closest tree from each sampled habitat tree, which (1) belongs to the plot’s most common tree species and (2) has a dbh equalling the stand’s mean dbh (± 15 %). In accordance with many other studies of our group, e.g. references(1-5), all epiphytic lichens and bryophytes at a stem height of 0-2 m above the ground will be recorded and their cover will be estimated in percent classes. Limiting the vegetation survey to the lower 2 m of the trunk, which are easily accessible from the ground, is necessary to cope with the high number of sample trees. Based on our previous work in primeval Fagus sylvatica forests, we expect that this limitation will lead to an underestimation of total epiphytic bryophyte species richness on the sample plot by 10 %(6). For lichens, which are less restricted to the tree base than bryophytes due to their different ecology (i.e. the lower moisture demand of most lichen species), the underestimation will be much higher(6). Nevertheless, the plot level diversity patterns are little influenced by the restriction of vegetation sampling to the lowest 2 m of the stem. Light microscopy and thin-layer chromatography will be employed for species identification.

The results can be linked to the other biodiversity work packages (B2-B6) to analyse diversity patterns across different organism groups. We will closely cooperate with A1 and A2 to integrate their stand structural data into our analyses. Our results can furthermore be used (together with other biodiversity data) as the basis of analyses in the C and D modules, for example, by verifying stakeholder perceptions that are surveyed in C2.

 

Findings

25 beech (Fagus sylvatica) trees were inventoried on 25 plots located in the submontane zone of the Black Forest. Each beech tree was sampled for all microsites. To date, over 170 species of epiphytes were recorded: 76 bryophytes and over 100 lichens. Of these, nine red list (RL) species for Germany were recorded: Ulota coarctata (RL 2), Orthotrichum rogeri (RL 2), Orthotrichum scanicum (RL 0; still listed as “extinct”, but in fact found recently in several locations), Fuscidea cyathoides (RL 3), Parmotrema arnoldii (RL 1), Thelotrema lepadinum (RL 2), Phaeophyscia endophoenicea (V), Melanohalea exasperata (RL 2), Rinodina sophodes (RL 1). Of these, Orthotrichum scanicum and Orthotrichum rogeri are European protected species. One lichen species new to Germany was found (Loxospora cristinae). When compared to the lower tree trunk (up to 2m), the tree canopy has a greater species richness and the largest number of rare epiphyte species. No single microhabitat was considered as being of greater importance for epiphytic diversity, although microhabitats in the canopy had a greater species richness than that of the lower trunk. The maximum number of species per microhabitat is 14, the minimum is 1, and the average is 5.

 

Current doctoral researcher project: Effects of landscape-scale forest connectivity and plot-scale forest structure on epiphytic lichen and bryophyte diversity

With Dina Emrich we will be able to quantify the contribution of habitat trees to the conservation of epiphytic lichen and bryophyte species in managed temperate forests. The sampling design will allow us to answer several key questions that are highly relevant with respect to nature conservation and forest management. Using multivariate data analysis, we will determine whether habitat trees are capable of significantly increasing the epiphyte diversity of the total forest, if it matters whether the habitat tree belongs to the same tree species as the surrounding stand, if certain tree species should be selected as habitat trees with higher priority than others, and if forest connectivity exerts a significant influence on the prospects of successfully conserving epiphyte diversity by sparing habitat trees from harvesting.

 

Perspectives

After working on live habitat trees, the third doctoral researcher project in B1 will focus on the significance of standing and downed deadwood for the total species pool of lichens and bryophytes in the studied forest stands and thus in relation to forest connectivity, structural diversity as well as tree species diversity, tree species identity, and elevation. In addition to biodiversity analyses, we plan to integrate analyses of changes in nutrient availability from deadwood at different stages of decay and in the surrounding soil.