Nothing else matters? Tree diameter and living status have more effects than biogeoclimatic context on microhabitat number and occurrence: An analysis in French forest reserves

Abstract

Managing forests to preserve biodiversity requires a good knowledge not only of the factors driving its dynamics but also of the structural elements that actually support biodiversity. Tree-related microhabitats (e.g. cavities, cracks, conks of fungi) are tree-borne features that are reputed to support specific biodiversity for at least a part of species’ life cycles. While several studies have analysed the drivers of microhabitats number and occurrence at the tree scale, they remain limited to a few tree species located in relatively narrow biogeographical ranges. We used a nationwide database of forest reserves where microhabitats were inventoried on more than 22,000 trees. We analysed the effect of tree diameter and living status (alive or dead) on microhabitat number and occurrence per tree, taking into account biogeoclimatic variables and tree genus. We confirmed that larger trees and dead trees bore more microhabitats than their smaller or living counterparts did; we extended these results to a wider range of tree genera and ecological conditions than those studied before. Contrary to our expectations, the total number of microhabitat types per tree barely varied with tree genus–though we did find slightly higher accumulation levels for broadleaves than for conifers–nor did it vary with elevation or soil pH, whatever the living status. We observed the same results for the occurrence of individual microhabitat types. However, accumulation levels with diameter and occurrence on dead trees were higher for microhabitats linked with wood decay processes (e.g. dead branches or woodpecker feeding holes) than for other, epixylic, microhabitats such as epiphytes (ivy, mosses and lichens). Promoting large living and dead trees of several tree species may be a relevant, and nearly universal, way to favour microhabitats and enhance the substrates needed to support specific biodiversity. In the future, a better understanding of microhabitat drivers and dynamics at the tree scale may help to better define their role as biodiversity indicators for large-scale monitoring.

Contribution of European forests to safeguard wild honeybee populations

“…Surprisingly, the larger hotspots have been predicted in low cavity density, but well‐connected forest areas, such as in Sweden and Finland where conifers are dominant (except for some birch— Betula spp.—and aspen— Populus tremula —dominated forests). As expected, other important hotspots were detected in areas of unmanaged forests allowing high cavity densities (Kozák et al., ; Paillet et al., , ), for which wild honeybees should be added to the list of unmanaged forest‐dependent species. It is important to note that our estimates do not include other determinants of wild honeybee population densities, particularly the flower resource quality of forests, which is mainly unknown for European forests.…”

“…Our results showed that conifer‐dominated forests are generally poorer in microhabitats, especially in tree cavities (see also Paillet et al., ). This is likely related to the foraging and nesting habits of cavity excavators, which tend to prefer broadleaved trees (e.g., Kosinski et al., ; Rolstad, Rolstad, & Saeteren, ), as well as to the higher persistence of decayed cavities on broadleaved trees (Paillet et al., ; Wesołowski, ). Unsurprisingly, unmanaged forests displayed significantly higher cavity densities than their managed counterparts, due to the higher occurrence of large trees and snags in these forests (Kozák et al., ; Paillet et al., ).…”

“…However, the current availability of tree cavities is limited by production‐oriented forest management in Europe (Bütler, Lachat, Larrieu, & Paillet, ; Paillet et al., ). Across the main European forest types, unmanaged areas generally host far more tree cavities than their managed counterparts (Kozák et al., ; Paillet et al., , ). Records of wild honeybee colonies in tree cavities are mainly restricted to Northern Poland (Oleksa et al., ) and central Germany (Kohl & Rutschmann, ).…”

How much does it take to be old? Modelling the time since the last harvesting to infer the distribution of overmature forests in France

“…Appendix S2: Protocol for the French nature forest reserves stand structure description On each circular plot, forest stand structure was characterized using the following protocol (Paillet et al, 2015(Paillet et al, , 2019:…”

Diversity of saproxylic beetle communities in chestnut agroforestry systems

“…The relationships between species diversity and forest complexity have been investigated by estimating the species richness (Moning & Müller 2009). Management types strongly influence the occurrence and abundance of microhabitats (MHs), in turn the diversity of coexisting species (Paillet et al 2019, Parisi et al 2020. Microhabitats occurring on living or standing dead trees constitute a particular and essential substrate or life site for species or communities to develop, feed, shel-ter or breed, during at least a part of their life cycle (Larrieu et al 2018).…”