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

Abstract

Sustainable management of forest ecosystems requires the use of reliable and easy to implement biodiversity and naturalness indicators. Tree-related microhabitats (TreMs) can fulfill these roles as they harbor specialized species that directly or indirectly depend on them, and are generally more abundant and diverse in natural forests or forests unmanaged for several decades. The TreM concept is however still recent, implying the existence of many knowledge gaps that can challenge its robustness and applicability. To evaluate the current state of knowledge on TreMs, we conducted a systematic review followed by a bibliometric analysis of the literature identified. A total of 101 articles constituted the final corpus. Most of the articles (60.3%) were published in 2017 or after. TreM research presented a marked lack of geographical representativity, as the vast majority (68.3%) of the articles studied French, German or Italian forests. The main themes addressed by the literature were the value of TreMs as biodiversity indicators, the impact of forest management on TreMs and the factors at the tree- and stand-scales favoring TreMs occurrence. Old-growth and unmanaged forests played a key role as a “natural” forest reference for these previous themes, as TreMs were often much more abundant and diverse compared to managed forests. Arthropods were the main phylum studied for the theme of TreMs as biodiversity indicators. Other more diverse themes were identified, such as restoration, remote sensing, climate change and economy and there was a lack of research related to the social sciences. Overall, current research on TreMs has focused on assessing its robustness as an indicator of biodiversity and naturalness at the stand scale. The important geographical gap identified underscores the importance of expanding the use of the TreMs in other forest ecosystems of the world. The notable efforts made in recent years to standardize TreM studies are an important step in this direction. The novelty of the TreM concept can partially explain the thematic knowledge gaps. Our results nevertheless stress the high potential of TreMs for multidisciplinary research, and we discuss the benefits of expanding the use of TreMs on a larger spatial scale.

Pioneer tree species accelerate restoration of tree‐related microhabitats in 50‐year‐old reserves of Białowieża Forest, Poland

“…Large individuals of species such as Populus and Betula were associated as well with the occurrence of some TreM groups, for instance of rot-holes and epiphytes. While DBH is an important driver of TreM occurrence in most studies (Asbeck et al, 2021;Courbaud et al, 2022;Larrieu et al, 2022;Martin et al, 2022), it was not a significant predictor for concavities, exposed sapwood and exposed sap-and heartwood occurrence in this study. The two latter TreM groups were found on pioneer tree species, similar to the overall TreM abundance and richness.…”

“…In addition, such tree-and stand-level attributes of TreMs have been used as indicators of naturalness and to assess the effectiveness of retention forestry or restoration projects not only in Europe but also in North America (Asbeck et al, 2021;Larrieu et al, 2017;Martin et al, 2021Martin et al, , 2022. Many studies have shown that the main tree-level drivers of TreM abundance and richness were tree species, diameter at breast height (DBH) and status (live or dead), along with interactions of these factors (e.g., Asbeck et al, 2019;Kaufmann et al, 2018;Michel & Winter, 2009;Paillet et al, 2017;Spînu et al, 2022;Vuidot et al, 2011).…”

Old forest structural development drives complexity of nest webs in a naturally disturbed boreal mixedwood forest landscape

“…However, the conservation of old forest tracks alone is not sufficient in the context of extensive forestry presently occurring in the Canadian boreal forest. There is also a critical need to adjust forestry practices in managed forest landscapes to increase at the landscape level the amount of old forests by combining the use of longer rotations, partial harvesting under continuous forest cover (Bergeron et al, 2002;Gauthier et al, 2009) and in managed clearcut landscapes, enhanced retention through a mesofilter approach (sensu Hunter, 2005) of keystone tree species for a range of tree decay stages (structural heterogeneity generated by tree senescence) for key excavators (Martin et al, 2004;Drapeau et al, 2009b;Drever and Martin, 2010;Edworthy and Martin, 2013) and other dendromicrohabitats that are critical for biodiversity (Larrieu et al, 2018;Martin et al, 2022).…”

An adapted typology of tree-related microhabitats including tropical forests

“…In forests, examples of such indicators are stand structure, tree species composition, tree age, diameter distribution, tree regeneration, and deadwood amount and diversity (Larrieu et al, 2018; Larsson et al, 2001). A more recent approach has emerged from the concept of tree-related microhabitats (TreMs), based on the observation that trees provide important microhabitats for a wide range of organisms, including insects, vertebrates, arachnids, Diplopoda, collemboles, gastropods, fungi, lichens, bryophytes, vascular plants, nematodes, rotifers and tardigrades (Bütler et al, 2020; Larrieu et al, 2018; Majdi et al, 2024; Martin et al, 2022; Müller et al, 2014; Schauer et al, 2018; Winter and Möller, 2008). TreMs are morphological singularities found on living or standing dead trees and form essential substrates or microhabitats for thousands of species.…”