Vincent Boulanger

The indicator side of tree microhabitats: A multi‐taxon approach based on bats, birds and saproxylic beetles

National and international forest biodiversity assessments largely rely on indirect indicators, based on elements of forest structure that are used as surrogates for species diversity. These proxies are reputedly easier and cheaper to assess than biodiversity. Tree microhabitats—tree‐borne singularities such as cavities, conks of fungi or bark characteristics—have gained attention as potential forest biodiversity indicators. However, as with most biodiversity indicators, there is a lack of scientific evidence documenting their quantitative link with the biodiversity they are supposed to assess. We explored the link between microhabitat indices and the richness and abundance of three taxonomic groups: bats, birds and saproxylic beetles. Using a nation‐wide multi‐taxon sampling design in France, we compared 213 plots located inside and outside strict forest reserves. We hypothesized that the positive effect setting aside forest reserves has on biodiversity conservation is indirectly due to an increase in the proportion of large structural elements (e.g., living trees, standing and lying deadwood). These, in turn, are likely to favour the quantity and diversity of microhabitats. We analysed the relationship between the abundance and species richness of different groups and guilds (e.g., red‐listed species, forest specialists, cavity dwellers) and microhabitat density and diversity. We then used confirmatory structural equation models to assess the direct and indirect effects of management abandonment, large structural elements and microhabitats on the biodiversity of the target species. For several groups of birds and bats, the indirect effect of management abandonment and large structural elements on biodiversity was mediated by microhabitats. However, the magnitude of the link between microhabitat indices and biodiversity was moderate. In particular, saproxylic beetles’ biodiversity was poorly explained by microhabitats, large structural elements or management abandonment. Synthesis and applications. Tree microhabitats may serve as indicators for bats and birds, but they are not a universal biodiversity indicator. Rather, compared to large structural elements, they most likely have a complementary role to biodiversity. In terms of forest management and conservation, preserving diversity of microhabitats at the local scale benefits several groups of both bats and birds.

IMPACT DE L’ARRÊT D’EXPLOITATION FORESTIÈRE SUR LA STRUCTURE DENDROMÉTRIQUE DES HÊTRAIES MÉLANGÉES EN FRANCE

Based on a comparison between managed and unmanaged forests, the aim of our study is to provide managers with a tentative quantitative analysis of the structural differences between managed and unmanaged mixed beech forests in France from a sample of 213 plots located in 15 lowland and mountain forests. Most structural descriptors were significantly higher in unmanaged forests. There were more very large living trees (+ 105 %) in unmanaged than in managed forests. These trees were also bigger (+ 145 %). The volume of dead wood was four times higher in unmanaged forests. Because of its nationwide scope, our investigation is a first French benchmark study for biodiversity-oriented forest policy, and contributes additional knowledge to a poorly researched area in France

Network connectivity value

In order to unveil the value of network connectivity, we formalize the construction of ecological networks in forest environments as an optimal control dynamic graph-theoretic problem. The network is based on a set of bioreserves and patches linked by ecological corridors. The node dynamics, built upon the consensus protocol, form a time evolutive Mahalanobis distance weighted by the opportunity costs of timber production. We consider a case of complete graph, where the ecological network is fully connected, and a case of incomplete graph, where the ecological network is partially connected. The results show that the network equilibrium depends on the size of the reception zone, while the network connectivity depends on the environmental compatibility between the ecological areas. Through shadow prices, we find that securing connectivity in partially connected networks is more expensive than in fully connected networks, but should be undertaken when the opportunity costs are significant.

Nothing else matters? A nationwide study of microhabitats drivers at the tree scale

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.Managing forest structure to preserve biodiversity requires a good knowledge of the elements that actually support biodiversity as well as the driving factors of their dynamics. Tree-related microhabitats (cavities, cracks, conks of fungi) are tree-borne features that are reputed to support specific biodiversity, linked to microhabitats for at least a part of their life cycle. 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 range. Here, we used a nationwide database of forest natural reserves comprising more than 22000 trees where microhabitats have been inventoried since 2005. We analysed the effect of tree diameter and live status (alive or dead) on microhabitat number and occurrence per tree, taking into account biogeoclimatic variables and tree genus. We confirmed that larger trees as well as dead trees bore more microhabitats than their smaller or alive counterparts, and extended these results to a wider range of tree genus and conditions. Contrary to expectations, these relationships varied neither much with tree genus, with slightly higher accumulation levels for broadleaves than for conifers, nor with biogeographical context. We observed these results both for the total number of microhabitats per tree and for the occurrence of individual microhabitat types. However they were more marked 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 seems a good and quite universal way to promote microhabitats and enhance potential substrates to support specific biodiversity. In addition, a better understanding of the drivers of microhabitats at the tree scale may help to better define them as biodiversity indicators for large scale monitoring.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 (cavities, cracks, conks of fungi) are tree-borne features that are reputed to support specific biodiversity for at least a part of species9 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. Contrary to 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. 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 an interesting, and nearly universal, way to favour microhabitats and enhance the substrates needed to support specific biodiversity. In addition, 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.

Pollen limitation as a main driver of fruiting dynamics in oak populations

In many perennial wind-pollinated plants, the dynamics of seed production is commonly known to be highly fluctuating from year to year and synchronised among individuals within populations. The proximate causes of such seeding dynamics, called masting, are still poorly understood in oak species that are widespread in the northern hemisphere, and whose fruiting dynamics dramatically impacts forest regeneration and biodiversity. Combining long-term surveys of oak airborne pollen amount and acorn production over large-scale field networks in temperate areas, and a mechanistic modelling approach, we found that the pollen dynamics is the key driver of oak masting. Mechanisms at play involved both internal resource allocation to pollen production synchronised among trees and spring weather conditions affecting the amount of airborne pollen available for reproduction. The sensitivity of airborne pollen to weather conditions might make oak masting and its ecological consequences highly sensitive to climate change.

Une approche multiacteur et multidisciplinaire pour innover dans les pratiques de plantation forestière

La plantation forestiere est un outil majeur pour l’adaptation des forets aux changements globaux. Les echecs parfois recurrents dans certains contextes, les couts associes a la plantation, la penibilite du travail pour les ouvriers forestiers ainsi que les impacts environnementaux parfois negatifs sont autant de facteurs qui freinent le recours a la plantation et peuvent ainsi limiter la capacite d’adaptation des forets. Un ensemble de travaux ont ete menes pour repondre aux besoins en innovation technique sur les methodes de plantation exprimes par les praticiens. Ces travaux portent sur le processus d’innovation en sylviculture et sur l’amelioration technique des methodes de plantation. L’analyse du processus d’innovation indique une faiblesse des reseaux sociotechniques associee a un mauvais partage des connaissances entre acteurs et une reticence a l’investissement dans du nouveau materiel, dans un contexte economique percu comme incertain. Ces observations suggerent qu’un des principaux leviers possibles serait une meilleure mise en reseau des acteurs, a travers differents liens fonctionnels : partage d’information, echanges de services, construction de partenariats economiques. Des exemples de methodes innovantes pour realiser chacune des differentes etapes de l’itineraire de plantation (preparation du site, plantation, entretiens), repondant aux besoins d’innovation technique exprimes par les praticiens, sont ensuite presentes.

Les dispositifs de type enclos-exclos : des outils au service de la gestion et de la recherche

Suite aux fortes augmentations des populations d’ongules sauvages, l’equilibre foret-grands herbivores est devenu un enjeu majeur de la gestion durable des forets. Intuitivement, les forestiers ont illustre les effets des herbivores en installant des placettes cloturees, suggerant indirectement une comparaison entre une vegetation en presence et en l’absence d’herbivores. De nouveaux projets d’implantation de placettes cloturees se profilent, notamment dans des massifs ou la pression des cervides est jugee preoccupante. Cet article propose un rappel sur la notion d’enclos (placettes cloturees) ainsi qu’une presentation des applications potentielles comme dispositif de recherche et outil pour les gestionnaires. Afin de tirer le meilleur de ces installations, nous presentons des recommandations essentielles lors de la mise en place et pendant la duree des mesures, garantes d’un suivi rigoureux et pertinent. / The balance between wild ungulates and the forest they inhabit has become a major issue for sustainable forest management as a result of recent increases in animal populations. Intuitively, forest managers have resorted to the use of fenced plots (exclosures) indirectly suggesting a comparison between vegetation subjected to herbivory and vegetation that is not. Numerous plans to set up fenced plots are in the pipeline, particularly in forested areas where deer densities are a cause of concern. This article discusses the concept of using fenced plots to study ungulate impacts. We present possible applications for research and management. In order to make the best use of these experimental facilities, we make some recommendations on how to set up and operate these monitoring systems so that they yield precise and relevant results.