Tree-related microhabitats (TreMs) as key elements for forest biodiversity

Tree-related microhabitats (TreMs) are specific above-ground morphological singularities borne by standing living or dead trees. They are regularly observed and are crucial issues for forest management in such a way that standards are currently negotiated (e.g. PEFC, FSC, N2000). TreMs depend on tree characteristics. The largest trees play a pivotal role in TreM supply and only the largest trees bear all the TreM types. Living and dead trees are complementary in their supply of TreM types. For instance, cracks and fungus sporocarps are rather borne by snags than by living trees. TreMs distribution patterns are very different in old-growth forests or in managed stands. As «ephemeral resource patches », TreMs host a wide diversity of taxa and play a wide range of pivotal biological roles. Certain Trems, like dendrothelms, host poor but very specific species assemblages. Other TreMs are composite habitats and host several communities. TReMs participate in a complex functional habitat network in species life cycles. How TReMs contribute to local biodiversity depends both on forest type and taxon conservation status. Positive relationships between TReMs density and local species richness are sometimes thresholded. Practical considerations for forest management integrating TreMs include the search for quantitative thresholds. Set-aside areas more than 20 ha in area are needed in mixed forest to conserve TreMs diversity. After a drastic harvesting, the recovery of TreMs needs decades and TreM-associated taxa may have a delayed response. A hierarchical typology is now available as a reference for TreM recording in temperate and Mediterranean European forests. The modelling of TreM ontogenesis is at work, as well as simulation models evaluating long-term effects of management scenarii

Modeling the dynamics of microhabitats

The Integrate+ Conference took place in the Steigerwald Centre near Ebrach, Bavaria from 26 – 28 October 2016 and gathered nearly 80 participants with various professional backgrounds. Those included silviculture trainers, forest ecologists, conservation biologists, forest scientists and representatives from forest administrations and forest managers. The conference invited the participants to discuss and exchange on the project results, its extensive network activities and most importantly reflect on viable options on how to continue what has been initiated by Integrate+ beyond 2016

Comparaison entre l'interception de la lumière et l'endroit où se trouvent les bouquets pour prédire la croissance des arbres

International audienceFor the past few decades, empirical and process-based tree growth models have been developed concurrently, although few comparisons have been made of growth predictions obtained using both approaches. One main difference is the explicit quantification of foliage biomass as a key variable of process-based models. The aim of this work was to test if this difference has a significant impact on models behavior, especially when they are used to simulate new silviculture practices like intensive thinning.In the first part of the study, we developed a method to evaluate leaf area and light interception of the mean tree of an even-aged stand from the data of a yield table. Two cases were distinguished : in closed stand, leaf area was limited by a maximum Leaf Area Index, whereas in open stands, leaf area was limited by the height of the crown base. For the data set we used, a yield table for Norway spruce in the French Northern Alps, these situations complemented well, the first one adapting to young, dense stands and the second one to old, clearer ones. Light interception was then calculated using an interpolation between the situation of a closed stand (Beer-Lambert law) and an isolated tree (light interception proportional to leaf area).In the second part, we used this approach to build a growth model in which competition was described by the ratio of the light intercepted by a mean tree of the stand to the light intercepted by a tree of equivalent size in free growth.Pendant ces dernières décennies, les modèles de croissance des arbres empiriques et basés sur les processus ont été développés de manière concurrentielle, bien que quelques comparaisons de prédiction de croissance aient été effectuées en utilisant les deux approches. Une des principales différences est la quantification explicite de la biomasse des feuillages comme une variable clé des modèles basés sur les processus. Le but de ce travail était de tester si cette différence a un impact significatif sur le comportement des modèles, spécifiquement quand ils sont utilisés pour simuler de nouvelles pratiques de sylviculture telles que l'élagage intensif. Dans la première partie de l'étude, nous avons développé une méthode pour évaluer les zones des feuilles et l'interception de la lumière de l'arbre principal de bouquets d'âge équitable. Deux cas se distinguaient : en bouquet fermé, les zones de feuillages étaient limitées par un Index maximum de Zone de Feuillage, tandis qu'en bouquet ouvert, la zone de feuillage était limitée par la hauteur du pied principal. Pour l'ensemble des données que nous avons utilisé et qui provenait d'épicéas Norway dans les Alpes françaises du nord, ces situations se complémentaient bien, la première étant adaptée aux bouquets jeunes et denses et le second aux vieux et plus parsemés. L'interception de la lumière était alors calculée en utilisant une interpolation entre la situation d'un bouquet fermé (Beer Lambert bas) et un arbre isolé (interception de la lumière proportionnelle à la zone de feuillage). Dans la seconde partie, nous avons utilisé cette approche pour construire un modèle de croissance dans lequel la compétition était décrit par le ratio de la lumière interceptée par un arbre moyen du bouquet sur la lumière interceptée par un arbre de taille équivalente en croissance libre

The effect of colonization and competition processes on the relation between disturbance and diversity in plant communities

Many theoretical and field studies have emphasized the impact of disturbance in the dynamics and diversity of sessile organism communities. This view is best reflected by the Intermediate Disturbance Hypothesis (IDH), which states that a maximum of diversity is found in ecosystems or communities experiencing intermediate disturbance regimes or at an intermediate stage of development since the last major disturbance event. Although theoretical models based on competitive interactions tend to validate this hypothesis, a recent meta-analysis of field experiments revealed that the mono-modal relationship between disturbance and diversity might not be a general pattern. In this article, we investigate the relationship between disturbance and diversity through the study of patch models, combining two types of competitive interactions: with or without competitive hierarchy, with two mechanisms influencing colonization: negative frequency dependence in colonization rates and immigration. These combinations led to various disturbancediversity patterns. In the model without competitive hierarchy (founder effect model), a decreasing relationship appeared to be the rule as mentioned in previous studies. In the model with competitive hierarchy, the IDH pattern was obtained for low frequency dependence and low immigration. Nevertheless, high negative frequency dependence in colonization rates led to a decreasing relationship between disturbance and diversity. In contrast, high immigration led to an increasing relationship. The coexistence window (the range of disturbance intensity allowing coexistence) was the widest for intermediate immigration rates. For random species assemblages, patterns with multiple peaks were also possible. These results highlight the fact that the mono-modal IDH pattern should not be considered a rule. Competition and colonization mechanisms have a profound impact on the relationship between disturbance and diversity