Abstract1 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.2 We compared saproxylic beetle assemblages caught by alcohol‐baited or unbaited window traps in different forest contexts. Considering that trap attractiveness depends on kairomone concentrations, we appraised whether the trap efficiency was influenced by trap environment (openness and local supply of fresh dead wood).3 Saproxylic beetles were sampled using 48 cross‐vane window flight traps, arranged in paired designs (alcohol‐baited/unbaited), in eight ancient and eight recent gaps (open stands), and eight closed‐canopy control stands in an upland beech forest in the French Pyrenees.4 Baited traps were more efficient than unbaited traps in terms of abundance and richness in our deciduous forests. The ethanol lure did not have any repellent effect on the individual response of saproxylic taxa.5 The influence of local environmental conditions on trap attractiveness was observed. Openness had a significant moderate effect on species richness. Trap attractiveness was slightly reduced in the alcohol‐saturated environment of recent gaps probably due to a disruption by local fresh dead‐wood concentrations of the kairomonal response of saproxylic beetles to baited traps (‘alcohol disruption’).6 Because the ethanol lure enhanced the probability of species detection, it may be useful in early‐warning surveillance, monitoring and control of wood borers, despite slight influences of local conditions on baited trap efficiency.
Organisms associated with dead wood (i.e. saproxylic species) are threatened by intensified forest and agricultural management. For a majority of saproxylic beetles the detailed information on their habitat requirements is still lacking, thus hindering efficient conservation information. This also applies to the violet click beetle (Limoniscus violaceus), one of the umbrella species of European saproxylic beetle fauna. This specie needs basal tree hollows for its larval development.
We studied habitat preferences of L. violaceus in basal tree hollows using emergence traps installed on 208 trees located in five sites in France. We used logistic regressions and recursive partitioning methods to understand the species–habitat relationships and to identify key environmental variables to predict the occurrence of L. violaceus.
The probability of occurrence of L. violaceus in basal hollows increases with increased tree circumference at 30 cm above ground and with increased hollow decay stage. The analysis of threshold values shows that the occurrence of the beetle is relatively high in trees that have a circumference greater than 360 cm, uncertain for those between 235 and 360 cm, and improbable for circumferences lower than 235 cm. Similarly, the occurrence of L. violaceus was probable in advanced stages of hollow decomposition and improbable in early stages.
Our results provide non‐specialists with helpful habitat features of an umbrella species which is hard to detect. This will increase the ability of conservation managers to identify sites that deserve protection and better monitor the habitat of many saproxylic species associated with basal hollow trees.
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.
2. We used emergence traps to sample saproxylic beetle assemblages in oak and pine large‐diameter (>20 cm) logs and stumps and compared the assemblages from the two sources.
3. With 64–84.5% of the species pool in oak and pine, respectively, stumps definitely constituted a suitable substratum for many saproxylic species in managed forests. Higher species density suggested that stumps are more diverse habitats than logs. Stumps also host rare species and natural enemies of bark beetles. For both tree species, the assemblage composition was significantly different between logs and stumps. The dissimilarity between substratum types was predominantly due to turnover, especially for oak.
4. Our results revealed that not only do stumps constitute a substitute for some log‐dwelling species; they also provide a suitable breeding substratum for many species that may be at risk in case of massive exportation of stumps for bioenergy purposes.
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