Hervé Brustel

Current Near‐to‐Nature Forest Management Effects on Functional Trait Composition of Saproxylic Beetles in Beech Forests

With the aim of wood production with negligible negative effects on biodiversity and ecosystem processes, a silvicultural practice of selective logging with natural regeneration has been implemented in European beech forests (Fagus sylvatica) during the last decades. Despite this near-to-nature strategy, species richness of various taxa is lower in these forests than in unmanaged forests. To develop guidelines to minimize the fundamental weaknesses in the current practice, we linked functional traits of saproxylic beetle species to ecosystem characteristics. We used continental-scale data from 8 European countries and regional-scale data from a large forest in southern Germany and forest-stand variables that represented a gradient of intensity of forest use to evaluate the effect of current near-to-nature management strategies on the functional diversity of saproxylic beetles. Forest-stand variables did not have a statistically significant effect on overall functional diversity, but they did significantly affect community mean and diversity of single functional traits. As the amount of dead wood increased the composition of assemblages shifted toward dominance of larger species and species preferring dead wood of large diameter and in advanced stages of decay. The mean amount of dead wood across plots in which most species occurred was from 20 to 60 m(3) /ha. Species occurring in plots with mean dead wood >60 m(3) /ha were consistently those inhabiting dead wood of large diameter and in advanced stages of decay. On the basis of our results, to make current wood-production practices in beech forests throughout Europe more conservation oriented (i.e., promoting biodiversity and ecosystem functioning), we recommend increasing the amount of dead wood to >20 m(3) /ha; not removing dead wood of large diameter (50 cm) and allowing more dead wood in advanced stages of decomposition to develop; and designating strict forest reserves, with their exceptionally high amounts of dead wood, that would serve as refuges for and sources of saproxylic habitat specialists.

Species variables or environmental variables as indicators of forest biodiversity: a case study using saproxylic beetles in Maritime pine plantations

Abstract• To assess the sustainability of plantation forest management we compare two types of biodiversity indicators. We used the species richness of saproxylic beetles as a case study to test the “species” and “environmental” indicator approaches. We compared single species abundance or occurrence and deadwood volume or diversity as predictor variables.• Beetles were sampled with flight interception traps in 40 Maritime pine plantation stands. The volume and diversity of deadwood was estimated with line intersect and plot sampling in the same stands. Predictive models of species richness were built with simple linear or Partial Least Square regressions.• Deadwood variables appeared to be good predictors of saproxylic beetle richness at the stand-scale with at least 75% of variance explained. Deadwood diversity variables consistently provided better predictive models than volume variables. The best environmental indicator was the diversity of deadwood elements larger than 15 cm in diameter.• By contrast, the use of “species variables” appeared to be less relevant. To reach the quality of prediction obtained with “environmental variables”, the abundance or occurrence of 6 to 7 species — some of which are difficult to identify — had to be used to build the indicator.Résumé• Pour améliorer le suivi de la gestion durable des forêts de plantation, nous avons cherché à développer des indicateurs de biodiversité en prenant pour exemple la richesse en Coléoptères saproxyliques. Nous avons comparé l’approche directe, basée sur l’abondance ou l’occurrence de certaines espèces de coléoptères saproxyliques, et l’approche indirecte, basée sur les caractéristiques du bois mort comme variables prédictives.• Les Coléoptères ont été inventoriés à l’aide de pièges à interception dans 40 peuplements de pin maritime. Le volume et la diversité des pièces de bois mort ont été estimés à l’aide d’un échantillonnage par transects ou par placettes dans les mêmes plantations. Les modèles prédictifs ont été construits à l’aide de régressions linéaires simples ou PLS.• Les variables locales de bois mort apparaissent comme de bons prédicteurs de la richesse spécifique en coléoptères saproxyliques, avec jusqu’à 75% de la variance expliquée. Les variables de diversité du bois mort semblent de meilleurs prédicteurs que les variables volumiques. Le meilleur indicateur « indirect » pourrait être la diversité des pièces de bois mort de diamètre supérieur à 15 cm.• En revanche, le recours à des indicateurs « directs » semble moins prometteur. Pour obtenir une qualité de prédiction équivalente à l’approche indirecte, il faudrait prendre en compte l’abondance ou l’occurrence d’au moins 6 ou 7 espèces dont certaines sont difficilement identifiables.

Evaluation of window flight traps for effectiveness at monitoring dead wood-associated beetles: the effect of ethanol lure under contrasting environmental conditions.

1 Subsequent to the diversity of saproxylic beetles being proposed as a management tool in forestry, more explicit knowledge about the efficiency and selective properties of beetle sampling methods is needed.

Implications from large‐scale spatial diversity patterns of saproxylic beetles for the conservation of European Beech forests

Abstract.  1. European Beech (Fagus sylvatica) is the natural dominant tree species in many forests across Europe. Despite Europe’s global responsibility for these forests, the correct conservation strategies are still a matter of debate. In particular, it remains controversial whether high conservation efforts should be directed towards beech forests, owing to the small number of insects that are Fagus specialists, and at what spatial scale conservation should take place.

Emergence trap, a new method to survey Limoniscus violaceus (Coleoptera: Elateridae) from hollow trees

The study of insects inhabiting basal hollow trees presents a methodological challenge inducing the fact that there is very little research done on fauna of this habitat. Many endangered saproxylic species only develop in cavities located at ground level. One of the most emblematic species of the kind is the Violet Click Beetle (Limoniscus violaceus), included in Annex II of the UE “Habitats” Directive. Surveys have been conducted in five Natura 2000 areas using a new method to monitor L. violaceus: the emergence traps. A total of 376 beetle species, including 239 saproxylics, have been identified. Five are considered threatened and are registered on the European Red List of saproxylic beetles and three are included in Annex II of the “Habitats” Directive. Among 191 trees studied, 33 revealed the presence of L. violaceus. Sampling efforts required to detect at least one specimen have been evaluated. Our results show that sampling a minimum of 20 hollow trees in April and May with emergence traps is recommended to obtain a meaningful survey on the presence of the Violet Click Beetle.

Saproxylic beetles (Coleoptera) and hoverflies (Diptera: Syrphidae) from a Mediterranean forest: towards a better understanding of their biology for species conservation

This report represents the first integrative study on saproxylic Coleoptera and Diptera Syrphidae from a representative Mediterranean forest in Cabañeros National Park in Central Spain. We collected 107 beetles, representing 32 families, and 25 species of hoverfly. Two undescribed and numerous rare beetle species were recorded, as were four hoverflies considered to be threatened species in Europe. We compiled biological information for all of the taxa encountered and recorded new data on their feeding habits, breeding microsites, and known tree associations. We found that the saproxylic biodiversity in this National Park was characterized by a significant number of Central European and North African species. Our results on the saproxylic assemblage, comprising many rare and poorly known species, of a typical Mediterranean forest represent a first step toward improved understanding of the saproxylic community and establishing the basis for conservation strategies in this region.

Breaking down Complex Saproxylic Communities: Understanding Sub-Networks Structure and Implications to Network Robustness

Saproxylic insect communities inhabiting tree hollow microhabitats correspond with large food webs which simultaneously are constituted by multiple types of plant-animal and animal-animal interactions, according to the use of trophic resources (wood- and insect-dependent sub-networks), or to trophic habits or interaction types (xylophagous, saprophagous, xylomycetophagous, predators and commensals). We quantitatively assessed which properties of specialised networks were present in a complex networks involving different interacting types such as saproxylic community, and how they can be organised in trophic food webs. The architecture, interacting patterns and food web composition were evaluated along sub-networks, analysing their implications to network robustness from random and directed extinction simulations. A structure of large and cohesive modules with weakly connected nodes was observed throughout saproxylic sub-networks, composing the main food webs constituting this community. Insect-dependent sub-networks were more modular than wood-dependent sub-networks. Wood-dependent sub-networks presented higher species degree, connectance, links, linkage density, interaction strength, and were less specialised and more aggregated than insect-dependent sub-networks. These attributes defined high network robustness in wood-dependent sub-networks. Finally, our results emphasise the relevance of modularity, differences among interacting types and interrelations among them in modelling the structure of saproxylic communities and in determining their stability.

The “dehesa”, a key ecosystem in maintaining the diversity of Mediterranean saproxylic insects (Coleoptera and Diptera: Syrphidae)

The “dehesa” is a traditional Iberian agrosilvopastoral ecosystem characterized by the presence of old scattered trees that are considered as “keystone-structures”, which favor the presence of a wide range of biodiversity. We show the high diversity of saproxylic beetles and syrphids (Diptera) in this ecosystem, including red-listed species. We analyzed whether saproxylic species distribution in the “dehesa” was affected by tree density per hectare, dominant tree species or vegetation coverage. Species diversity did not correlate with tree density; however, it was affected by tree species and shrub coverage but in a different way for each taxon. The highest beetle diversity was linked to Quercus pyrenaica, the most managed tree species, with eight indicator species. In contrast, Q. rotundifolia hosted more species of saproxylic syrphids. Regarding vegetation coverage, shrub coverage was the only variable that affected insect richness, again in a different way for both taxa. In contrast, beetle species composition was only affected by dominant tree species whereas syrphid species composition was not affected by tree species or shrub coverage. We concluded that the high diversity of saproxylic insects in the “dehesa” is related to its long history of agrosilvopastoral management, which has generated landscape heterogeneity and preserved old mature trees. However, the richness and composition of different taxa of insects respond in different ways to tree species and vegetation coverage. Consequently, conservation strategies should try to maintain traditional management, and different saproxylic taxa should be used to monitor the effect of management on saproxylic diversity.

Are stumps important for the conservation of saproxylic beetles in managed forests? – Insights from a comparison of assemblages on logs and stumps in oak-dominated forests and pine plantations

Abstract.  1. The expanding interest in harvesting stumps for bioenergy may represent a potential threat to forest biodiversity. Whereas stumps are common in managed stands, knowledge of their associated saproxylic assemblages is still incomplete.

Are biodiversity patterns of saproxylic beetles shaped by habitat limitation or dispersal limitation? A case study in unfragmented montane forests

Understanding the processes that shape biodiversity patterns is essential for ecosystem management and conservation. Local environmental conditions are often good predictors of species distribution and variations in habitat quality usually positively correlate to species richness. However, beside habitat limitation, species presence-absence may be constrained by dispersal limitation. We tested the relative importance of both limitations on saproxylic beetle diversity, using forest continuity as a surrogate for dispersal limitation and stand maturity as a surrogate for habitat limitation. Forest continuity relies on the maintenance of a forest cover over time, while stand maturity results in the presence of old-growth habitat features. Forty montane beech-fir forests in the French pre-Alps were sampled, under a balanced sampling design in which forest continuity and stand maturity were crossed. A total of 307 saproxylic beetle species were captured using flight-interception traps and Winkler–Berlese extractors. We explored the response of low- versus high-dispersal species groups to forest continuity and stand maturity. Saproxylic beetle diversity increased significantly with stand maturity and was mostly influenced by variables related to deadwood diversity at the stand scale and suitable habitat availability at the landscape scale. Surprisingly, no evidence of dispersal limitation was found, as diversity patterns were not influenced by forest continuity and associated variables, even for low-dispersal species. Our study demonstrates that in an unfragmented forest landscape, saproxylic beetles are able to colonize recent forests, as long as local deadwood resources are sufficiently diversified (e.g. tree species, position, diameter and/or decay stage).