Saproxylic Beetle Communities Research Articles

Restoration‐oriented forest management affects community assembly patterns of deadwood‐dependent organisms

Abstract Land‐use intensification leads to loss and degradation of habitats and is thus a major driver of biodiversity loss. Restoration strategies typically focus on promoting biodiversity but often neglect that land‐use intensification could have changed the underlying mechanisms of community assembly. Since assembly mechanisms determine the diversity and composition of communities, we propose that evaluation of restoration strategies should consider effects of restoration on biodiversity and community assembly. Using a multi‐taxon approach, we tested whether a strategy that promotes forest biodiversity by restoring deadwood habitats also affects assembly patterns. We assessed saproxylic (i.e. deadwood‐dependent) beetles and fungi, as well as non‐saproxylic plants and birds in 68 beech forest plots in southern Germany, 8 years after the commencement of a restoration project. To assess changes in community assembly, we analysed the patterns of functional–phylogenetic diversity, community‐weighted mean (CWM) traits and their diversity. We hypothesized that restoration increases habitat amount and heterogeneity of deadwood and reduces canopy cover and thereby decreases the strength of environmental filters imposed by past silvicultural intensification, such as a low amount in deadwood. With the restoration of deadwood habitats, saproxylic beetle communities became less functionally–phylogenetically similar, whereas the assembly patterns of saproxylic fungi and non‐saproxylic taxa remained unaffected by deadwood restoration. Among the traits analysed, deadwood diameter niche position of species was most strongly affected indicating that the enrichment of large deadwood objects led to lower functional–phylogenetical similarity of saproxylic beetles. Community assembly and traits of plants were mainly influenced by microclimate associated with changes in canopy cover. Synthesis and applications. Our results indicate that the positive effects of deadwood restoration on saproxylic beetle richness are associated with an increase in deadwood amount. This might be linked to an increase in deadwood heterogeneity, and therefore decreasing management‐induced environmental filters. Deadwood enrichment can thus be considered an effective restoration strategy which reduces the negative effects of intense forest management on saproxylic taxa by not only promoting biodiversity but also by decreasing the environmental filters shaping saproxylic beetle communities, thus allowing the possibly for more interactions between species and a higher functional diversity.

Diversity and conservation of saproxylic beetles in 42 European tree species: an experimental approach using early successional stages of branches

ABSTRACTTree species diversity is important to maintain saproxylic beetle diversity in managed forests. Yet, knowledge about the conservational importance of single tree species and implications for forest management and conservation practices are lacking.We exposed freshly cut branch‐bundles of 42 tree species, representing tree species native and non‐native to Europe, under sun‐exposed and shaded conditions for 1 year. Afterwards, communities of saproxylic beetles were reared ex situ for 2 years. We tested for the impact of tree species and sun exposure on alpha‐, beta‐, and gamma‐diversity as well as composition of saproxylic beetle communities. Furthermore, the number of colonised tree species by each saproxylic beetle species was determined.Tree species had a lower impact on saproxylic beetle communities compared to sun exposure. The diversity of saproxylic beetles varied strongly among tree species, with highest alpha‐ and gamma‐diversity found inQuercus petraea. Red‐listed saproxylic beetle species occurred ubiquitously among tree species. We found distinct differences in the community composition of broadleaved and coniferous tree species, native and non‐native tree species as well as sun‐exposed and shaded deadwood.Our study enhances the understanding of the importance of previously understudied and non‐native tree species for the diversity of saproxylic beetles. To improve conservation practices for saproxylic beetles and especially red‐listed species, we suggest a stronger incorporation of tree species diversity and sun exposure of into forest management strategies, including the enrichment of deadwood from native and with a specific focus on locally rare or silviculturally less important tree species.

Forest management, canopy cover and geographical distance affect saproxylic beetle communities of small-diameter beech deadwood

Beetles (Coleoptera) are the most diverse and species-rich insect order in saproxylic communities, and play a key role in forest dynamics. To prioritize conservation measures, a clear understanding is needed of what habitat features are the most important for beetles that depend on deadwood. Here, we investigate (i) how the assemblages of saproxylic beetles emerging from small-diameter beech deadwood (Fagus sylvatica L.) are influenced by several environmental factors and type of forest management, and (ii) if geographical distance of the investigated sites influences the similarity of these saproxylic beetle assemblages. We visited 10 high beech forest stands along a latitudinal gradient from northern to southern Italy, and collected 200 logs of 50 cm length, 12 ± 2 cm diameter, and Hunter’s decay class 2, from deadwood lying on the forest floor. Logs were stored in ex-situ emergence traps, in common garden conditions, from April to September, and individuals emerging from the deadwood were collected weekly. A total of 2571 beetles were collected, including several species which were either threatened, firstly recorded or endemic. We found that, compared to even-aged stands, forests managed to increase structural heterogeneity (uneven-aged high forests, and former coppice stands converted to high forest), with closed canopy, were colonized by the richest and most abundant saproxylic beetle assemblages. Additionally, we observed distance decay of similarity between sites, indicating geographical structure in community composition. Our findings have important implications for biodiversity conservation in beech forests: (1) small-diameter deadwood hosts a rich biodiversity of Coleoptera and should therefore be left on the ground; (2) forest management practices should aim at preserving or restoring structural heterogeneity and closed canopies; (3) these conservation measures should be carried out along the entire area of occurrence of beech forests, due to turnover in species composition with geographical distance.

Historical Disturbances Determine Current Taxonomic, Functional and Phylogenetic Diversity of Saproxylic Beetle Communities in Temperate Primary Forests

The expected future intensification of forest disturbance as a consequence of ongoing anthropogenic climate change highlights the urgent need to more robustly quantify associated biotic responses. Saproxylic beetles are a diverse group of forest invertebrates representing a major component of biodiversity that is associated with the decomposition and cycling of wood nutrients and carbon in forest ecosystems. Disturbance-induced declines or shifts in their diversity indicate the loss of key ecological and/or morphological species traits that could change ecosystem functioning. Functional and phylogenetic diversity of biological communities is commonly used to link species communities to ecosystem functions. However, our knowledge on how disturbance intensity alters functional and phylogenetic diversity of saproxylic beetles is incomplete. Here, we analyzed the main drivers of saproxylic beetle abundance and diversity using a comprehensive dataset from montane primary forests in Europe. We investigated cascading relationships between 250 years of historical disturbance mechanisms, forest structural attributes and the taxonomic, phylogenetic and functional diversity of present-day beetle communities. Our analyses revealed that historical disturbances have significant effects on current beetle communities. Contrary to our expectations, different aspects of beetle communities, that is, abundance, taxonomic, phylogenetic and functional diversity, responded to different disturbance regime components. Past disturbance frequency was the most important component influencing saproxylic beetle communities and habitat via multiple temporal and spatial pathways. The quantity of deadwood and its diameter positively influenced saproxylic beetle abundance and functional diversity, whereas phylogenetic diversity was positively influenced by canopy openness. Analyzing historical disturbances, we observed that current beetle diversity is far from static, such that the importance of various drivers might change during further successional development. Only forest landscapes that are large enough to allow for the full range of temporal and spatial patterns of disturbances and post-disturbance development will enable long-term species coexistence and their associated ecosystem functions.

Near-natural forests harbor richer saproxylic beetle communities than those in intensively managed forests

Globally, boreal forests cover 33 percent of Earth's forested area, constitute the largest terrestrial carbon source, and house an important biodiversity of forest-dependent species, many of which are saproxylic taxa reliant on a wide variety of dead wood. This dead wood is most prevalent in old-growth forest, yet intensive management means that little old growth is left, and the remaining forests rarely attain the necessary age and structure to resemble these original forests. There is increasing recognition, however, that forests that have not been subjected to modern, stand-replacing harvest methods (like clear-cutting), and in which management activities are no longer occurring, may be able to provide habitat similar to old-growth forest for many species (older mean age, higher deadwood volumes, and more age-class heterogeneity). These are called ‘near-natural’ forests.We use linear mixed models and redundancy analysis (RDA) to compare beetle species richness and community composition using a large, mixed data set, containing more than one third of all beetle species known from Norway, from window trap records in three types of forest: intensively managed mature stands, recent clear-cuts, and ‘near-natural forests’.Even though location, study substrate and other sampling details vary substantially between sites, the signal from management still comes out as a significant factor explaining the patterns on beetle diversity. We find that species richness of saproxylic, natural-forest indicator, and red-listed beetle species is higher in both near-natural forests and recent clear-cuts than in managed mature forests. Community composition also differs significantly between the three forest types, and these differences are correlated with forest age and volume at the landscape (1 km radius) level.These findings provide support for the idea that near-natural forests provide habitats that are distinct from those in managed forests and which are important for species of conservation concern. Clear-cuts briefly harbor some of these same species, probably due to the sun-exposed coarse woody debris (CWD) that is available immediately after felling, but this effect is transient. Conservation of existing near-natural forests, many of which are currently without legal protection, should therefore be prioritized.

Diversity and deadwood-based interaction networks of saproxylic beetles in remnants of riparian cloud forest.

We studied the saproxylic beetle community inhabiting deadwood in remnants of riparian cloud forests in “La Antigua” basin, in central Veracruz (Mexico). We assessed the influence of deadwood features (tree species, trunk position, trunk diameter, trunk volume and decomposition stages) on saproxylic beetle diversity. In order to assess the stability of beetle species-deadwood interactions, we also analyzed the ecological networks structure. A total of 63 deadwood trunks, belonging to four tree species, were sampled by standardized hand-collection throughout well-preserved remnants of riparian cloud forest. We found that tree species and deadwood decay stage are the main drivers that determine the diversity and stability of saproxylic beetle species interactions. Our results indicate that Quercus corrugata is the main tree species in terms of maintaining the significantly highest saproxylic beetle diversity, but with no stable interactions (saproxylic beetle-deadwood). A nested network structure was detected for Clethra mexicana and Liquidambar styraciflua, with a pool of core (generalist) saproxylic beetle species. We observed that beetle diversity from the early and late deadwood stages comprises distinct assemblages and the four stages of decomposition showed a nested network structure. During deadwood succession, community composition and guilds changed among networks; the early successional stage had more specialized xylophagous beetles, while other guilds (mycophagous, saprophagous and zoophagous) arrive later and become the core species in the advanced stages of decomposition networks. Heliscus tropicus (Passalidae) is a key species constituting the core of all of the networks and could be considered an ecosystem engineer in cloud forests. By exploring links between saproxylic beetles and deadwood characteristics, we can further our understanding of species interaction in order to develop management strategies oriented towards the protection of species and their habitats in this threatened ecosystem.

Increasing influence of the surrounding landscape on saproxylic beetle communities over 10 years succession in dead wood

Studies of the spatial scale to which saproxylic beetles respond to the surrounding landscape have generated varied results. We tested how the relationship between beetle fauna and variables describing the landscape changed over ten years of succession. We hypothesized that the relationship to the nearby landscape would be stronger when the wood was in a later successional stage. This is because habitat predictability is higher in the later stages, as they have a longer turnover time of beetle assemblages than early stages. With higher predictability of the habitat, theory expect lower dispersal capacity of hosted species, and thereby higher relation to landscape on smaller scale. The saproxylic beetles were sampled on the same wood objects (high stumps) in three time steps over ten years in 20 clear-cuts in south Sweden. In accordance with our expectations, the nearby (<5 km radius) forest-landscape variables explained more of the species composition of the saproxylic beetles later in the succession. The first- and third-years geographical location (longitude and latitude) were more important and explained, for three different subsets of beetle species, 21%, 4% and 25% of the fauna composition. At this time, the forest-landscape variables explained almost nothing. After ten years the pattern was the opposite, with surrounding forest explaining up to 27% of the variation, and regional factors almost nothing. We showed that this was related to a shift in the species assemblage after ten years, with an increasing share of species associated with more decayed wood. Our results suggest that successional stage of the dead wood helps explain at what scale saproxylic species respond. Several of the surrounding forest variables were associated with biodiversity hotspots, which thus seem to exist also for species associated with abundant wood types. Later-successional species are more indicative of hotspots than earlier-successional species.

Decadal effects of landscape‐wide enrichment of dead wood on saproxylic organisms in beech forests of different historic management intensity

AbstractAimEuropean temperate forests have lost dead wood and the associated biodiversity owing to intensive management over centuries. Nowadays, some of these forests are being restored by enrichment with dead wood, but mostly only at stand scales. Here, we investigated effects of a seminal dead‐wood enrichment strategy on saproxylic organisms at the landscape scale.LocationTemperate European beech forest in southern Germany.MethodsIn a before–after control–impact design, we compared assemblages and gamma diversities of saproxylic organisms in strictly protected old‐growth forest areas (reserves) and historically moderately and intensively managed forest areas before and a decade after starting a landscape‐wide strategy of dead‐wood enrichment.ResultsBefore enrichment with dead wood, the gamma diversity of saproxylic organisms in historically intensively managed forest stands was significantly lower than in reserves and historically moderately managed forest stands; this difference disappeared after 10 years of dead‐wood enrichment. The species composition of beetles in forest stands of the three historical management intensities differed before the enrichment strategy, but a decade thereafter, the species compositions of previously intensively logged and forest reserve plots were similar. However, the differences in fungal species composition between historical management categories before and after 10 years of enrichment persisted.Main conclusionsOur results demonstrate that intentional enrichment of dead wood at the landscape scale is a powerful tool for rapidly restoring saproxylic beetle communities and for restoring wood‐inhabiting fungal communities, which need longer than a decade for complete restoration. We propose that a strategy of area‐wide active restoration combined with some permanent strict refuges is a promising means of promoting the biodiversity of age‐long intensively managed Central European beech forests.

Spatial patterns of saproxylic beetles in a relic silver fir forest (Central Italy), relationships with forest structure and biodiversity indicators

The conservation of biological diversity is one of the main goals for managing forests in an ecologically sustainable way. Presence and abundance of microhabitats, such as tree cavities or bark pockets, can be conveniently used as indicators to evaluate the effectiveness of sustainable forest management measures. In Mediterranean forest ecosystems, the relationships between stand-structure attributes and species-diversity indicators are still poorly studied.We described the structural attributes, deadwood characteristics and microhabitat occurrence in a silver fir forest of Central Apennines (Italy), which has not been submitted to silvicultural interventions for several decades. We assessed linkages between these characteristics and the abundance, distribution and diversity of saproxylic beetle fauna. A systematic aligned sampling method was conduced on 240ha, examining 50 plots of 530m2 each. Saproxylic beetles were sampled using window flight traps and emergence traps in relation to abundance and species richness at the plot level, but also on decaying deadwood. The heterogeneity in types and frequencies of microhabitats, and the link between structural attributes associated with stand complexity and saproxylic species, were also analysed. With the aim of describing the complex saproxylic ecological network, beetle species were classified according to the type of interactions with wood and other insects fauna, but also in relation to the trophic guilds. Linear regressions were conducted for highlighting metric variability and relationships between parameters, while geostatistical analyses were used to describe the spatial variability of structural features and the spatial pattern of beetle distributions.Results of linear regression and geostatistical analysis showed how the saproxylic beetle community is influenced by the amount, type and stage of decay of deadwood, but also by the forest structural complexity and the occurrence of microhabitats. Gap dynamics and natural disturbances had effects on deadwood amounts and microhabitat abundance, which was significantly higher than in managed and structurally simplified forest stands. Most of the entomological variables (namely, Families, Species, Total individuals, Saproxylic individuals, Staphylinidae, Elateridae, Nothodes parvulus, Curculionidae, Ernoporus fagi, Phyllobius emery) were clumped, highlighting the existence of aggregation areas in the sampled forest. In several cases the insect distribution was linked to the spatial pattern of forest attributes, particularly deadwood components.

Saproxylic beetles in non-intervention and coppice-with-standards restoration management in Meerdaal forest (Belgium): an exploratory analysis

Abstract: For many centuries, coppice-with-standards management was applied in the mixed oak stands of Meerdaal forest (Belgium). Over the last century, these stands were gradually converted to high forest. On an area of 20 ha, the coppice-with-standards management is being restored, with specific adaptations for biodiversity (conservation of dead wood and veteran trees). A survey of saproxylic beetles was performed at 8 locations in the forest, including one site within the coppice-with-standards restoration. This survey not only allowed an evaluation of the saproxylic beetle richness of the forest complex, but also made exploratory observations on the effect of this type of management, as compared to non-intervention, on species richness and composition of saproxylic beetles. The results show that the overall species richness in the forest complex was quite high and comparable to forest reserves in Germany. Both coppice-with-standards and high forest options appear to be equally species-rich, but consist of different communities, both containing specific, rare and notable species, with more thermophilous and light-demanding species in the coppice-with-standards plot. Based on these observations we suggest that a diversified management approach may be the most suitable to conserve and enhance diverse saproxylic beetle communities in formerly intensively managed semi-natural woodlands. This could include areas of active conservation management aimed at producing open-canopy stands with considerable amounts of sun-exposed deadwood, combined with areas of non-intervention in a matrix of multifunctional forests, where conservation of dead wood and veteran trees is fully incorporated in the management.

Unraveling cryptic species diversity in an aposematic sap beetle genus (Coleoptera: Nitidulidae: Cryptarchinae) from northern Europe

The saproxylic sap beetleGlischrochilus(Glischrochilus)quadripunctatus(Linnaeus, 1758), is associated with subcortical habitats of coniferous trees. This species is widely distributed across Europe and Siberia, and is the best known and largest European nitidulid species. A closely related cryptic species,G.(G.)tremulaesp. nov.has been discovered in a xerothermic area of SE Finland in association with old aspens. The two species exhibit a sympatric occurrence in SE Finland, on their respective host trees. We analyze the COI barcode region to compareG.(G.)quadripunctatus,G.(G.)tremulaesp. nov., andG. (Librodor) hortensis(Fourcroy, 1785). Morphological, ecological, and molecular data confirm the presence in SE Finland of twoGlischrochiluss.str. species. We provide a description of the new species. The newGlischrochilusapparently represents a relictual taxon associated with old hollow aspens, and should be considered a species with inherent conservation value within European saproxylic beetle communities.

Saproxylic Beetle Biodiversity in Golf Course Habitats

Saproxylic beetles are a diverse group of insects that use deadwood as food or habitat at some stage of their life. While a few species of saproxylic beetles are considered to be pests, the majority of species perform important ecological roles such as decomposition, nutrient recycling, pollination in the mobile adult form, or act as food sources for other organisms. Their diversity and variable responses make them good biological indicators. Promoting biodiversity in managed areas, such as golf courses, may be relatively easy by creating saproxylic habitat. We examined the influence on saproxylic beetle communities of habitat type, log type, and distance from a fairway. Sentinel logs were provided for colonization for one season, and emergence was monitored over the following 2 years. We found that beetle species richness increased with log volume but did not change with distance from the fairway playing surface. Our findings suggest that although species richness may be low compared with that in less fragmented habitats, a diverse assortment of saproxylic beetles can be supported in golf course wooded habitats. This may be accomplished by leaving fallen trees in place when they do not pose a hazard or interfere with play. In particular, the provision of large woody debris that is more difficult to remove may maximize the benefit to superintendents and the saproxylic beetle community. Findings also support the idea that golf courses containing woody patches may increase habitat connectivity for these insects, and possibly other organisms, in otherwise highly fragmented urban areas.

Forest management and regional tree composition drive the host preference of saproxylic beetle communities

Summary Among saproxylic beetles, many early colonizers prefer particular host species. Ranking of preferred hosts of local saproxylic beetle communities is critical for effective dead‐wood management in forests, but is rarely done because experiments with numerous tree species are labour and cost intensive. We analysed the host preference of local saproxylic beetle communities on logs of 13 tree species in relation to management (unmanaged and managed beech stands, conifer plantations on natural beech sites) in three regions of Germany during the most critical period for host specificity, that is the first two years after harvesting. Hosts were ranked quantitatively based on the ordinal ranking of hosts by single beetle species, which in turn was based on the variation in beetle abundance. First, we employed a Bradley–Terry model in which ranking was derived from paired comparisons of host trees. Then, a model‐based recursive partitioning of the Bradley–Terry model tested whether host preference of beetle communities is affected by stand management, region and decay progress of dead wood. Our results indicated that beetle communities overall avoided logs of Fraxinus, Pseudotsuga, Larix and Tilia, and Carpinus ranked highest in preference. Carpinus also ranked highest for communities of broadleaf specialists; Picea abies ranked highest for communities of conifer specialists. Model‐based recursive partitioning revealed that ranking of local hosts in conifer stands differed from that of broadleaf stands, and that ranking of hosts in broadleaf stands differed between regions, but only in the first year for both. Synthesis and applications. Early‐colonizing saproxylic beetle communities vary locally in their choice of host trees. Therefore, forest managers should focus on the enrichment of dead wood of regional tree species and tree species of the local stand to successfully promote early‐colonizing beetle.

Numerical responses of saproxylic beetles to rapid increases in dead wood availability following geometrid moth outbreaks in sub-arctic mountain birch forest.

Saproxylic insects play an important part in decomposing dead wood in healthy forest ecosystems, but little is known about their role in the aftermath of large-scale forest mortality caused by pest insect outbreaks. We used window traps to study short-term changes in the abundance and community structure of saproxylic beetles following extensive mortality of mountain birch in sub-arctic northern Norway caused by an outbreak of geometrid moths. Three to five years after the outbreak, the proportion of obligate saproxylic individuals in the beetle community was roughly 10% higher in forest damaged by the outbreak than in undamaged forest. This was mainly due to two early-successional saproxylic beetle species. Facultative saproxylic beetles showed no consistent differences between damaged and undamaged forest. These findings would suggest a weak numerical response of the saproxylic beetle community to the dead wood left by the outbreak. We suggest that species-specific preferences for certain wood decay stages may limit the number of saproxylic species that respond numerically to an outbreak at a particular time, and that increases in responding species may be constrained by limitations to the amount of dead wood that can be exploited within a given timeframe (i.e. satiation effects). Low diversity of beetle species or slow development of larvae in our cold sub-arctic study region may also limit numerical responses. Our study suggests that saproxylic beetles, owing to weak numerical responses, may so far have played a minor role in decomposing the vast quantities of dead wood left by the moth outbreak.

EPURAEA DEUBELI REITTER, 1898, A CONFIRMED SAPROXYLIC SAP BEETLE FOR THE ITALIAN FAUNA (Coleoptera, Nitidulidae)

During ecological investigations on saproxylic beetle communities at Monte Baldo (Veneto, Verona province), two specimens of &lt;em&gt;Epuraea&lt;/em&gt; &lt;em&gt;deubeli&lt;/em&gt; Reitter, 1898 (Coleoptera, Nitidulidae) were recently collected. It is the first known sure record of this species in Italy (previously known from Northern, Eastern, and Central Europe, southwards to Austria, and from Western Siberia).

Seeing the trees for the wood – beech (Fagus sylvatica) decay fungal volatiles influence the structure of saproxylic beetle communities

Abstract Two experiments were conducted to investigate the role of basidiomycetes and volatiles in the ecology of saproxylic Coleoptera. Volatile organic compounds (VOCs) were sampled from beech (Fagus sylvatica) logs experimentally inoculated with the basidiomycetes Stereum hirsutum, Coriolus versicolor, Phanerochaete velutina, Hypholoma fasiculare, Bjerkandera adusta both singly and in various combinations. Volatile emissions were found to be in accordance with amounts detectable to insects suggesting that in a natural decay situation, saproxylic volatiles are readily available as insect semiochemicals. Furthermore, fungal community structure was found to significantly affect the volatile profile of decaying wood, with specific VOCs associated with particular fungal treatments. Thus, volatiles of fungal origin are a strong potential source of semiochemicals for those insects utilising the saproxylic habitat and their natural enemies. Beetles were reared from logs inoculated with the same basidiomycete treatments as described earlier and a total of 604 individuals comprising 84 species were obtained. Eleven species (Cis boleti, C. micans, Dacne bipustulata, Latridius consimilis, Mycetophagus atomarius, M. quadripustulatus, Octotemnus glabriculus, Platystomus albinos, Ptilinus pectinicornis, Stictoleptura scutellata, Tomoxia bucephala) exhibited significant associations with one or more fungal treatments. Explanations are provided for the various beetle–fungus associations observed. The data set is notable for the presence of various wood boring species that tend to be absent in experiments where volatiles from fungi are presented in isolation. Coarse woody debris (CWD) and its interaction with fungi CWD, are shown to give off VOCs of varying degrees of specificity. These VOCs are potential semiochemicals for saproxylic insects and may mediate fungus/CWD‐specific interactions. We conclude that future work in this direction would be profitable.

In search of the best local habitat drivers for saproxylic beetle diversity in temperate deciduous forests

Deadwood-associated species are increasingly targeted in forest biodiversity conservation. In order to improve structural biodiversity indicators and sustainable management guidelines, we need to elucidate ecological and anthropogenic drivers of saproxylic diversity. Herein we aim to disentangle the effects of local habitat attributes which presumably drive saproxylic beetle communities in temperate lowland deciduous forests. We collected data on saproxylic beetles in 104 oak and 49 beech stands in seven French lowland forests and used deadwood, microhabitat and stand features (large trees, openness) as predictor variables to describe local forest conditions. Deadwood diversity and stand openness were consistent key habitat features for species richness and composition in deciduous forests. Large downed deadwood volume was a significant predictor of beetle species richness in oak forests only. In addition, the density of cavity- and fungus-bearing trees had weak but significant effects. We recommend that forest managers favor the local diversification of deadwood types, especially the number of combinations of deadwood positions and tree species, the retention of large downed deadwood and microhabitat-bearing trees in order to maximize the saproxylic beetle diversity at the stand scale in deciduous forests. To improve our understanding of deadwood-biodiversity relationships, further research should be based on targeted surveys on species-microhabitat relationships and should investigate the role of landscape-scale deadwood resources and of historical gaps in continuity of key features availability at the local scale.

Effect of dead wood enrichment in the canopy and on the forest floor on beetle guild composition

In managed forests, the abundance and diversity of saproxylic insect species and beetles in particular has been argued to be primarily limited by the amount of dead wood while the importance of other factors for community composition of this functional group has been largely neglected. It has also been argued that management regimes that lead to increasing amounts of dead wood in forests will increase the abundance and diversity of saproxylic species, but experimental evidence for this assumption is rare. We studied the importance of dead wood and a number of abiotic and biotic factors for community composition of saproxylic species in a range of managed forests in Germany for 2years and found that the total amount of dead wood in the forests only played a minor role in explaining the composition of the saproxylic beetle community compared to other factors such as precipitation, temperature, tree species and vertical stratum. We then tested for eight forest plots whether dead wood experimentally exposed in the canopy and forest floor is attractive to saproxylic beetles. We found that a high diversity and abundance of beetles of various habitat and feeding guilds, were attracted to fresh dead wood, many more than in control areas without dead wood manipulation. Thus, in managed forests where abundance and diversity of saproxylic beetles is low, enrichment of dead wood resulted in an immediate increase of species and a change of guild composition particularly in the canopy. Our results suggest that the amount of ground dead wood is by itself not a sufficient measure for the local diversity of saproxylic beetles. We conclude that dead wood enrichment in managed forests is an effective strategy to promote saproxylic beetle diversity. Changes in the functional composition are expected to be large enough to influence ecosystem processes such as decomposition of dead wood or the control of herbivores.

Impact of salvage logging on stand structure and beetle diversity in boreal balsam fir forest, 20 years after a spruce budworm outbreak

Spruce budworm outbreaks represent the most important natural disturbance in the boreal balsam fir (Abies balsamea (L.) Mill.) forest of Canada, killing trees over wide areas and thus generating large amounts of dead wood. This disturbance is part of the dynamic processes occurring within balsam fir forests, and its effects on biodiversity need to be understood in order to move closer towards sustainable forest management. We described stand structure and used beetles as biodiversity indicators to compare the ecological value of salvaged stands, managed afterwards with three different silvicultural treatments, with unsalvaged stands, 20years after the last spruce budworm outbreak. Our experimental design involved five replicated stands of each of the four disturbance types for a total of 20 stands. A total of 3124 Coleoptera belonging to 47 families and 269 taxa were captured over 3months of sampling. Results showed that habitat attributes still differed 20years after a spruce budworm outbreak between unsalvaged and treated salvaged stands, such as more abundant and diverse dead wood in unsalvaged stands. Salvage logging and silvicultural treatments led to different beetle communities than in unsalvaged stands, even though abundance and richness did not change significantly. Most indicator species identified were saproxylic and associated with unsalvaged stands, suggesting salvage logging generated the largest changes to the original ecosystem while additional effects of the silvicultural treatments were less pronounced. This may result from the 67% reduction in downed dead wood volumes (e.g., 138m3/ha in unsalvaged stands vs 46m3/ha in managed stands). Even if this volume of dead wood is still relatively high, it is less diverse than in unsalvaged stands and includes almost no recent dead wood. Salvage logging affected saproxylic beetle communities, suggesting that the retention of naturally disturbed stands may help in implementing ecosystem management in boreal balsam fir forest and move closer towards sustainable management.

High within‐ and between‐trunk variation in the nematoceran (Diptera) community and its physical environment in decaying aspen trunks

Abstract Dead wood is a primary habitat for a large number of insects, including species from many nematoceran (Diptera) groups. The species living in dead wood must be adapted to the ephemeral and ever‐changing nature of their substrate. There is a growing body of knowledge about the effects of dead wood quality and the surrounding landscape on the saproxylic beetle community, but we know very little about the other saproxylic insects. Moreover, we know only very little about the variation in the insect community between different parts of decaying wood pieces. Using emergence traps, we studied the saproxylic nematoceran communities occupying different parts of decaying fallen aspen trunks in a boreal forest. To explain the variation in the detected assemblages, we also studied the variation in the physical environment in different parts of one of the studied trunks during the season. We found out that the overall variation in assemblages was very high and also the similarity between the base and top of the same trunk was usually low. Dissimilarity arose more from differences in species richness than from species turnover. The greatest contrasts in the physical conditions of the study trunk were between the inside and the upper and lower surface of the trunk base. Due to high variation within the trunks and especially between the trunks, the sampling effort in studies on the ecology of saproxylic insects should be high to have a reliable estimate of the local community.