Spatial patterns of tree-related microhabitats: key factors and ecological significance for the conservation of the associated biodiversity

Abstract

Tree-related microhabitats (TreMs) are specific, well delineated above-ground tree morphological singularities occurring on living or standing dead trees. TreMs are key features for many taxa and contribute in the complex network of forest resources for biodiversity (1). Large and broadleaved trees bear most of the TreMs within a forest stand (2). The spatial pattern of TreMs is however not only influenced by the spatial distribution of these noteworthy trees, but also by a wide range of natural stochastic, abiotic and biotic processes as well as forestry operations (3).

A better knowledge of spatial patterns of TreMs in contrasted forest conditions would help us to promote more biodiversity-friendly forest management practices. First we explored spatial patterns of two TreM types, pivotal for saproxylic beetles, i.e. cavities and polypores, in temperate old-growth forests and compared them with patterns in stands in managed forests, analyzing a compiled European database focusing on beech and oak trees. Secondly, we analyzed the response of TreM-associated saproxylic beetle assemblages, sampled by emergence traps set up on targeted TreMs, to variations in spatial patterns of cavities and polypores. For instance, based on several case studies, we addressed the following questions: is the dissimilarity of assemblages hosted by cavities related to the between-cavity geometric distance? How is the occupancy probability of a cavity-dwelling beetle affected by the distance to the closest occupied cavity? Does an increasing sporocarp density at local scales foster the species richness of fungus-dwelling beetles at the sporocarp scale?

Finally, we discuss deemed consequences for conservation of TreM-associated taxa in managed forests.

1-Larrieu L., Paillet Y., Bütler R., Kraus D., Krumm F., Lachat T., Michel A. K., Regnery B., Vandekerkhove K., Winter S. (2018). Tree related microhabitats in temperate and Mediterranean forests of Europe: a reference list and inventory baseline for forest biodiversity research and monitoring. Ecological Indicator 84: 194-207

2-Larrieu L., Cabanettes A. (2012). Species, live status, and diameter are important tree features for diversity and abundance of tree-microhabitats in subnatural montane beech-fir forests. Canadian Journal of Forest Research 42: 1433-1445.

3-Larrieu L., Cabanettes A., Brin A., Bouget C., Deconchat M. (2014). Tree microhabitats at the stand scale in montane beech-fir forests: practical information for taxa conservation in forestry. European journal of Forest Research, 133:355-367