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B5) Bats and Forest Structure

Landscape-moderated use of forest structures by bats

Veronika Braunisch 1,2 & Ilse Storch 3
Doctoral researchers: Marlotte Jonker 1,3 (since 2016) & Anna-Lena Hendel (since 2019)

1 Forest Research Institute of Baden-Württemberg (FVA), Department of Forest Conservation

2 University of Bern, Faculty of Science, Department of Biology, Institute of Ecology & Evolution,
   Division of Conservation Biology

3 University of Freiburg, Faculty of Environment & Natural Resources, Institute of Forest Sciences,
   Chair of Wildlife Ecology and Management

Background and state of research

Bats are considered to be indicators of forest structural complexity and are frequently selected as target species for conservation programs integrating key structural elements in forest management. Forest-dwelling bat species use old and dead trees as roosting sites and forest gaps and linear elements for foraging and commuting. Retention of old-growth structures may be beneficial, yet, as recent studies indicate, their use and usability by bats may strongly depend on the landscape context. Species-specific association of bat occurrence with forest structures has been shown at the plot level (1 ha), yet minimum landscape-scale requirements for abundance, distribution and connectivity of such structural elements are lacking.

 

Research questions and hypotheses

B5 will relate bat diversity, activity, and type of use to forest characteristics at the local and landscape level, expecting:

(1) Effects on species presence, activity and diversity:

  • The activity and diversity of forest-specialists will increase with the abundance of habitat trees, dead wood and associated microhabitats at the plot level.
  • The species-specific use of these structural elements at the local scale will be modulated by their abundance in the surrounding landscape.
  • The diversity of bat species and guilds will increase with structural heterogeneity at both the forest-stand and landscape scale.

(2) Effects on ecological functions:

  • Landscape permeability, especially gaps and linear structures in the forest landscape, explain local-scale variance in bat activity.
  • Food abundance and foraging activity of bats is related to local forest structure, but foraging activity will be modulated by matrix permeability and connecting structures at the landscape scale.

 

Approach, methods, and linkages

Automated acoustic recorders will be deployed to detect bat species(-groups) and to quantify their activity. Species presence, richness, diversity, and activity will then be related to forest structure and landscape conditions, assessed by remote sensing and plot-scale terrestrial mapping. LiDAR-information capturing the 3D-characteristics of sub-canopy space (A1) and forest structure mapping (A2, C1) will be used to predict bat occurrence at the stand scale. Landscape-scale variables will be derived from GIS-databases and stereo-aerial photographs which allow deriving connecting structures, such as forest edges, and gaps, as well as the area-wide distribution of standing deadwood. Assessment of food availability (collaboration with B3, B4, and B6) will allow for elucidating functional relationships. By relating bat presence and diversity to structural characteristics at multiple spatial scales, quantitative target values for integrative forest management will be derived.

 

Findings

During the first two years, bats were repeatedly recorded at all 135 ConFoBi plots and species abundance and diversity-related habitat structure were measured at plot and landscape level. The ongoing analyses show the importance of tree-related microhabitats (Basile et al., 2020) as well as of gaps and canopy openings at the plot level for bat activity. The latter structures are now further elucidated for their connecting function. In addition, in a pilot phase, light traps were employed on a subset of plots to sample moth and other nocturnal invertebrates to link food abundance to forest structures. Further data is currently being collected to link food supply with foraging activity in order to understand the indirect effects of forest structures on the habitat functionality of bats.

 

Perspectives

In addition, B5 plans to link the identified key structures for bats to forest management intensity. For this, the data sampled on the ConFoBi plots (i.e. representing different levels of retention) will be compared with data from a related project, in which similar data have been collected at the extremes of the management gradient (i.e. unmanaged forests and experimental clear-cuts). Based on these results, B5 aims to provide forest managers with quantitative target values for the abundance and configuration of stand-scale and landscape-scale structural habitat elements for bats and compare the potential of different management regimes to provide these elements.