The Use of Tree-Related Microhabitats as Forest Biodiversity Indicators and to Guide Integrated Forest Management

Abstract

Purpose of the Review The concept of tree-related microhabitats (TreMs) is an approach to assess and manage multi-taxon species richness in forest ecosystems. Owing to their provision of special habitat features, TreMs are of special interest as a surrogate biodiversity indicator. In particular, in retention forestry, TreMs have gained attention over the past decade as a selection criterion for retained structural elements such as habitat trees. This review seeks to (a) address the suitability of TreMs as biodiversity indicator in the context of retention forestry, (b) summarize drivers of TreM occurrence and the status quo of the implementation of TreM-based retention concepts in forest management, and (c) discuss current and future challenges to the use of TreMs as biodiversity indicator. Recent Findings The TreM concept originated in Europe where it is now increasingly implemented. Most studies of the quantity, quality, and diversity of TreMs are focused on tree species from this region, although it is increasingly applied in other contexts. In addition to tree species, tree dimensions and live status have been identified as the main drivers of TreM occurrence. One major remaining research challenge is to verify relationships between the occurrence and abundance of forest-dwelling species from different taxonomic groups and TreMs to improve the evidence basis of this concept and thus increase its integration in forest conservation approaches. Summary TreMs are not the “silver bullet” indicator to quantify biodiversity of forest dwelling species, but they provide an important tool for forest managers to guide the selection of habitat trees for the conservation of the associated biodiversity.

Tree-Related Microhabitats Are Promising Yet Underused Tools for Biodiversity and Nature Conservation: A Systematic Review for International Perspectives

“…We thus performed a backward and forward search as a second step of our review. We identified three relevant literature reviews that specifically study TreMs (Larrieu et al, 2018b;Asbeck et al, 2021a;Kõrkjas et al, 2021a). For other landmark articles that were not reviews, we selected ten research articles presenting a detailed TreM typology [i.e., more than four different TreM forms, so more than half of the seven forms identified by Larrieu et al (2018b)] and published before Larrieu et al (2018b) homogenized typology (Winter and Möller, 2008;Michel and Winter, 2009;Michel et al, 2011;Vuidot et al, 2011;Regnery et al, 2013a;Larrieu et al, 2014aLarrieu et al, ,b, 2017Winter et al, 2015).…”

“…In contrast, dendrotelms (a cup-shaped concavity that retains water) host very few taxa; however, most of these taxa are strictly associated with this type of TreM (Dajoz, 2007), and dendrotelms are more generally an important resource for hydration and nutrition of animal species (Gossner et al, 2020;Kirsch et al, 2021). For this reason, TreMs have proven to be indicators of forest biodiversity (Paillet et al, 2018;Larrieu et al, 2019;Basile et al, 2020), although the direct links between TreMs and species occurrence at the stand scale are not always clear (Asbeck et al, 2021a). The richness and diversity of TreMs, as well as the occurrence of specific types, are also relevant indicators of naturalness or old-growthness (Winter and Möller, 2008;Michel and Winter, 2009;Vuidot et al, 2011;Paillet et al, 2017;Asbeck et al, 2021b).…”

Species co-occurrence and management intensity modulate habitat preferences of forest birds

“…TreMs are considered to be “a distinct, well delineated structure occurring on living or standing dead trees, that constitutes a particular and essential substrate or life site for species or species communities during at least a part of their life cycle to develop, feed on, using as shelter or to breed” [ 57 ] and have shown correlations to the richness and abundance of forest-dwelling vertebrates and (saproxylic) insects [ 5 , 6 , 97 ]. TreMs are usually grouped into seven forms, including cavities, tree injuries and exposed wood, crown deadwood, excrescences, fruiting bodies of saproxylic fungi and slime molds, epiphytic, epixylic and parasitic structures, and fresh exudates such as sap run and heavy resinosis [ 98 ]. The forest management intensity index (ForMI), calculated from forest variables, measured three different management aspects [ 95 ]: (a) the proportion of harvested tree volume compared to the maximum volume, (b) the proportion of tree species not belonging to the natural species composition, and (c) the ratio of artificial (showing signs of cutting) vs. natural deadwood.…”

Vertical Stratification of Insect Species Developing in Water-Filled Tree Holes

“…Tree-related microhabitats (TreM) have been shown to be crucial for promoting biodiversity in forests and have therefore become an important measure for forest conservation and management (Asbeck et al, 2021). One type of TreM that occurs throughout the vertical extent of trees is the water-filled tree hole or dendrotelma (Kitching, 2000;Larrieu et al, 2018).…”