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B1) Epiphyte & Microhabitat Diversity

Epiphyte and microhabitat diversity and function on habitat trees

Markus Hauck 1 & Stefan Kaufmann 1 (since 2019)
Albert Reif 2 (until 2019) &
Stefanie Gärtner 3 (until 2019)
Doctoral researchers: Diane Stevenson 2 (since 2016) & Dina Emrich 1(since 2019)

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

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

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 and to the impact of anthropogenic disturbance, including effects of forest management or air pollutants.

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 and edge effects. 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.

(7) Habitat trees with high lichen and bryophyte species richness differ from other trees in structural, microclimatic and chemical site conditions.

 

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, 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 %. 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. 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, B8-B9) to analyse diversity patterns across different organism groups. We are especially interesting in analyzing common and divergent patterns of lichens and bryophytes with fungi (B9) and vascular plants (B2), but also with insects (B3, B4) and vertebrates (B4, B5, B8). 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

In the first stage (PhD1; Albert Reif), 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 2 m), 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.

The second phase (PhD2; Markus Hauck & Stefan Kaufmann) focused on a systematic sampling approach to analyze diversity patterns of epiphytic lichens and bryophytes in response to tree size (large-diameter ‘habitat’ trees vs. ‘average’ trees around mean stem diameter), tree species, and forest connectivity.

Here, we showed so far that Abies alba as a habitat tree promoted lichen and bryophyte species richness compared to average trees of that species or of Fagus sylvatica and Picea abies. Furthermore, beech had a positive effect on bryophyte diversity, whereas lichen diversity was promoted by the presence of large diameter trees and increased with increased elevation

 

Future projects

Next PhD project (starting 1 July 2022).

The next PhD student to be hired now will analyze mechanisms, which cause the observed diversity patterns of lichens and bryophytes, and will search for joint diversity patterns with other groups of organisms. The key research questions include:

  • How do microclimate and chemical site conditions on the trees vary with tree species and tree size?
  • How do proximity effects of tree neighbors of the same or different tree species affect the site conditions for epiphytes?
  • How are microclimatic and chemical site factors on a tree influenced by stand size and the proximity to agricultural land?
  • Are patterns of bryophyte and lichens different from those of vascular plants, fungi and invertebrates?

The planned work will include the analyses of microclimatic, chemical, and structural traits for different tree species, of stem diameter (= tree age) sequences, and of tree clusters with differences in the species identity of the nearest tree neighbors.

Skills required for PhD3 applicants in B1:

In addition to the general requirements described in the job advertisement, applicants who wish to apply for B1 should bring lichenological and/or bryological skills including survey methodology, good knowledge of cryptogam species, and hold a driving licence. Candidates should in the best case have a profound knowledge of both lichen and bryophyte species identification, but are at least required to have proven skills in one of these groups and must be willing to learn species identification in the other group during work. Applicants should also have experiences related to the ecology or ecophysiology of lichens and/or bryophytes.

 

ConFoBi publications by B1

Kaufmann, Stefan; Funck, Sarah-Katharina; Paintner, Franziska; Asbeck, Thomas & Hauck, Markus (2021). The efficiency of retention measures in continuous-cover forestry for conserving epiphytic cryptogams: A case study on Abies alba. Forest Ecology and Management, 502, 119698. www.doi.org/10.1016/j.foreco.2021.119698.

Wirth, Volkmar; Tønsberg, Tor; Reif, Albert; Stevenson, Diane (2018): Loxospora cristinae found in Germany. Herzogia 31: 995. https://doi.org/10.13158/heia.31.2.2018.995