Elsevier

Acta Oecologica

Volume 84, October 2017, Pages 64-71
Acta Oecologica

Spatial pattern of occurrence of epiphytic lichens on oaks in a heterogeneous landscape

https://doi.org/10.1016/j.actao.2017.09.005Get rights and content

Highlights

  • We studied lichens on large oaks selected to be uniformly distributed within a study area.

  • One landscape factor – oak density – stood out as being important, while the others four were not.

  • Despite ranging from only 3.1–4.1 m, oak circumference was consistently important.

  • Occurrence of three species as well as richness were best explained by density of oaks within 200–500 m.

Abstract

Quercus robur (oaks) provides an important substrate for many epiphytic lichens, and with increasing age the bark becomes suitable for some rare species. These species may respond to environmental and landscape factors differently, and at different spatial scales. We tested the effect of factors related to the individual tree and the surrounding landscape on the occurrence and richness patterns of lichens species. The study system consisted of 213 oaks selected in a grid system within a 400 km2 heterogeneous oak-rich area in south-eastern Sweden. Oaks had been selected to be relatively uniform in size (circumference 3.1–4.1 m), and as uniformly distributed as possible in the study area. Landscape factors were calculated for various spatial scales (circles with radius ranging from 28 to 1225 m from a studied oak). One of the landscape factors stands out as of general importance – oak density in the surrounding – while the others (amount of forest, water, houses and arable field) had no effects, or weak effects on only some species. Among the tree specific variables, circumference was consistently important (despite ranging from only 3.1–4.1 m) while inconsistent effects were seen by sun exposure of oak trunk (Chaenotheca phaeocephala, Ramalina baltica) and density of shrubs and trees near the tree (Ch. phaeocephala). The occurrence patterns of Cliostomum corrugatum, Ch. phaeocephala, R. baltica and richness (number of eleven target lichens) were best explained by the density of oaks within radii of 401, 199, 199 and 303 m, respectively. In conclusion, our study highlighted the importance of spatial scale for understanding the occurrence of epiphytic lichens and suggests spatial scales and oak densities that could be targeted for landscape and conservation planning.

Introduction

Old growth trees are of particular interest for conservation, since they are an important substrate for a number of organisms from several taxonomic groups, e.g., epiphytic lichens and bryophytes and many insects (Ek and Johannesson, 2005, Jansson et al., 2009, Lindenmayer et al., 2012). Trunks of old growth oaks (Quercus robur) host a diverse lichen flora and with increasing age the bark of oaks becomes suitable for rare and threatened species (Johansson et al., 2009, Paltto et al., 2010, Thor et al., 2010, Jönsson et al., 2011). The decline of old oaks in the landscape may be the main reason why many epiphytic lichens only seem to exist in remnant populations in patches with high density of old oaks (Johansson et al., 2009, Johansson et al., 2012, Scheidegger and Werth, 2009), and why many oak lichen species are threatened and red-listed (Paltto et al., 2010, Ranius et al., 2008). Most often a reduction of habitat involves increasing isolation of habitat patches, and that may add to the expected decline in species richness (Ranius et al., 2008, Steffan-Dewenter et al., 2002, Löbel et al., 2006).

Conservation of rare and threatened epiphytic lichens need to estimate the densities of old oaks that are needed for continued survival. It is further important to know at what spatial scales to consider such densities. Furthermore, other landscape variables – in addition to substrate availability – may affect lichen species distribution, e.g. forest openness and landscape composition (Jüriado et al., 2003, Bolliger et al., 2007). One way to approach these problems is to explore current species occupancy patterns in relation to potential substrates in small to large scales (Paltto et al., 2006, Paltto et al., 2010, Snäll et al., 2003, Holland et al., 2004, Bergman et al., 2012, Musa et al., 2013), which could add to our understanding of the dynamics of species and build better strategies for preservation (Löbel et al., 2006, Sillett et al., 2000, Lättman et al., 2009, Lättman et al., 2014).

In a recent study, Paltto et al. (2010). showed that species richness and the occurrence of three of five red-listed epiphytic lichen species on oaks were best explained by increasing density of oaks within 0.5 km in a large region (10,000 km2). However, this study tested scales in fixed steps from 0.5 km and upwards (1, 2, 3, 4 km etc.). Considering these results it would therefore be valuable to explore the spatial scales around 500 m in more detail. For conservation, it is also important to know how to manage the immediate surroundings of valuable oak trees as, for instance, sun exposure of the oak and density of surrounding shrubs and trees can affect the probability of occurrence of lichens (Johansson et al., 2009, Johansson et al., 2012, Jüriado et al., 2003, Paltto et al., 2011).

The aim of this study was to investigate the spatial distribution of eleven epiphytic lichens species preferring large and old oaks in a heterogeneous landscape, and to identify the spatial scales, in the range of 28–1225 m, at which species occurrence is best explained. Landscape variables included density of other large oaks in the surrounding of a target tree, as well as potentially important land use types (the amount of houses, and water, agricultural and forested land (Styers et al., 2010, Svoboda et al., 2010)). Furthermore, two tree-specific factors that could be affected by management (sun exposure, and density of nearby trees and shrubs) were also considered. The study was conducted in one of the few remaining landscapes in Northern Europe with a high density of old oaks: the province of Östergötland, south-eastern Sweden (Antonsson and Wadstein, 1991).

Section snippets

Study species

The eleven lichen species targeted are known to be strongly associated with large oaks, but differing in frequency and abundance (Table 1). For most of these lichens, it has been confirmed that they are very rare outside old oaks (Ranius et al., 2008). All species except Chrysothrix candelaris are listed on the Swedish Red List or used as signal species in the woodland key habitat survey in Sweden indicating forests of high conservation value (Table 1 (Gärdenfors, 2010, Johansson et al., 2010

Results

Lichen species richness varied between 0 and 7 species per tree (mean 2.14; median 2). Nine of the eleven target species were found and their occupancy varied between 99% and 0.5% (Table 1).

Discussion

There are several factors affecting the occurrence of lichens (Pinho et al., 2008), but their relative contribution have been difficult to assess. We compared the relative effect of land use (forest, arable, houses and water), tree variables (circumference, sun exposure, trees and shrubs near the oak) and oak density at different spatial scales and found that they often showed a clear peak of response between 200 and 400 m. Moreover, oak density had the largest overall effect while tree

Conclusion

The occurrence and richness of red-listed lichens on oaks was mainly affected by oak density. The second most important factor was circumference while land use was of less importance. Furthermore, this study highlighted the importance of spatial scale for understanding the occurrence of epiphytic lichens, where the species responded to landscape factors at the scale of 20–50 ha. These finding have implication for conservation efforts – management, restoration, reserve allocation – in oak

Author contributions

LMW, KOB and PM conceived the study; all authors contributed to the design; UHM collected the data; UHM and LMW analysed the data; all authors contributed to evaluation and interpretation of the results; UHM drafted the text (as part of a MSc thesis) with all authors contributing substantially to the current version.

References (48)

  • C. Scheidegger et al.

    Conservation strategies for lichens: insights from population biology

    Fungal Biol. Rev.

    (2009)
  • D.M. Styers et al.

    Developing a land-cover classification to select indicators of forest ecosystem health in a rapidly urbanizing landscape

    Landsc. Urban Plan.

    (2010)
  • D. Svoboda et al.

    Epiphytic lichen diversity in central European oak forests: assessment of the effects of natural environmental factors and human influences

    Environ. Pollut.

    (2010)
  • K. Antonsson et al.

    Eklandskapet [The Oak District]

    (1991)
  • J.J. Barkman

    Phytosociology and Ecology of Cryptogamic Epiphytes

    (1958)
  • J. Bolliger et al.

    Predicting the potential spatial distributions of epiphytic lichen species at the landscape scale

    Lichenologist

    (2007)
  • L. Dymytrova

    Epiphytic lichens and bryophytes as indicators of air pollution in Kyiv city (Ukraine)

    Folia Cryptogam. Est.

    (2009)
  • T. Ek et al.

    Multi-purpose Management of Oak Habitats. Examples of Best Practice from the County of Östergötland, Sweden

    (2005)
  • ESRI

    ArcGIS Desktop: Release 10.1

    (2011)
  • U. Gärdenfors

    Rödlistade Arter I Sverige [The 2010 Redlist of Swedish Species]

    (2010)
  • J. Holland et al.

    Determining the spatial scale of species' response to habitat

    BioScience

    (2004)
  • N. Jansson et al.

    An indicator system for identification of sites of high conservation value for saproxylic oak (Quercus spp.) beetles in southern Sweden

    J. Insect Conserv.

    (2009)
  • V. Johansson et al.

    Tree and site quality preferences of six epiphytic lichens growing on oaks in southeastern Sweden

    Ann. Bot. Fenn.

    (2009)
  • V. Johansson et al.

    Detection probability and abundance estimation of epiphytic lichens based on height-limited surveys

    J. Veg. Sci.

    (2010)
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