Saproxylic Beetle Biodiversity Research Articles

A decadal study reveals that restoration guided by an umbrella species does not reach target levels

AbstractMaintaining structural and functional elements of ecosystems are essential in order to preserve biodiversity and ecosystem function. As a means of guiding conservation work, the umbrella species concept was developed. In Sweden, one putative umbrella species, the white‐backed woodpecker, has guided conservation and restoration of deciduous forests for two decades.Here, we evaluate the decadal effects of restoration aimed at the white‐backed woodpecker on biodiversity of saproxylic beetles. We compare stands that were restored 12 to 21 years ago to non‐restored stands and historical white‐backed woodpecker habitats acting as restoration target stands.Restored stands contained higher deciduous deadwood volumes than non‐restored stands but lower volumes than restoration target stands. The deadwood in restored stands was concentrated in later decay stages, whereas target stand deadwood was more evenly distributed across decay stages.Restored stands had similar species richness and abundance of most groups of saproxylic beetles compared with non‐restored stands while not reaching the levels of restoration target stands. Species assemblages differed among all stand types with restored stands supporting late decay stage and generalist species while target stands supported more deciduous associated and threatened species.Synthesis and applications: We conclude that after one to two decades, restoration improve stand structure and benefit beetle diversity but that target levels are not yet reached. Thus, only partial restoration is achieved. Our results stress that for restoration to be successful both continuous and repeated restoration efforts are needed and that it is important to identify target levels of important habitat characteristics when assessing restoration outcome.

Forest age drives saproxylic beetle biodiversity in the southeastern United States

Old forests are valuable for biodiversity conservation because they provide uninterrupted forest cover over time and late-successional habitat, promoting low-mobility and late-successional species. However, forest age may be less important in highly forested landscapes because dispersal limitation is reduced. We investigated how species richness and community composition of saproxylic beetles (Coleoptera) are influenced by forest age and the surrounding landscape in the southeastern United States (Georgia). Forests in this region are highly fragmented and dominated by early-successional stands. We sampled beetles in 20 old forests (mature in 1938) and 20 young forests (originating after 1938), located along a landscape forest cover (LFC) gradient. Old and young forests were structurally similar but tree communities differed along a Quercus (old) to Pinus (young) gradient. Regional diversity of saproxylic beetles was higher in old forests, and high species turnover between forest age groups suggests they both help to maintain regional biodiversity. Two models of local richness had near equal merit: one showed higher richness in old forests regardless of LFC, while the other showed higher richness in old forests at high LFC. Contrary to expectations, neither model supports old forests losing importance in highly forested landscapes. Higher richness in old forests is likely due to temporal stability and late-successional habitat, promoting low-mobility and specialist species. Because the land area of young forests exceeds that of old forests, old forests are disproportionately important for saproxylic biodiversity in the region.

Canopy openness as the main driver of aculeate Hymenoptera and saproxylic beetle diversity following natural disturbances and salvage logging

Forests are increasingly affected by natural disturbances like fires, insect outbreaks, and windstorms. Such disturbances are commonly followed by salvage logging. Disturbance and salvage logging affect biodiversity by altering microclimate, habitat structure, and deadwood amount. To mitigate possible negative effects of salvage logging on biodiversity, ecologists often recommend the retention of disturbance-created structures. However, the mechanisms through which retained structures affect biodiversity remain largely unknown. We analysed 9,602 individuals of saproxylic beetles belonging to 268 species and 3,172 individuals of aculeate Hymenoptera belonging to 68 species of cavity-nesters and 126 species of non-cavity-nesters over two years in a wind-disturbed beech forests with various intensity of salvage logging. We quantified the relative importance of canopy openness and deadwood amount. Our final dataset consisted of 268 saproxylic beetle species and 194 species of aculeate Hymenoptera out of which 68 were cavity-nesters and 126 non cavity-nesters. Generalized linear mixed effect models showed the lowest number of Hymenoptera and beetle species in undisturbed forest. Permutational analysis of variance revealed that treatment and canopy openness drive community composition of both taxa. Increased canopy openness was the main factor positively affecting numbers of species of aculeate Hymenoptera and saproxylic beetles in the first two years after the disturbance. Deadwood amount only affected community composition of saproxylic beetles. However, gamma diversity and community composition of saproxylic beetles indicated that disturbed and extensively logged plots resembled disturbed unlogged plots rather than disturbed and intensively logged plots. Our findings suggest that at least some timber might be extracted from disturbed areas, without major losses of biodiversity of saproxylic beetles and aculeate Hymenoptera.

Heritage Trees as an Important Sanctuary for Saproxylic Beetles in the Central European Landscape: A Case Study from Litovelské Pomoraví, Czech Republic

Intensive forest and agroforestry management has greatly reduced the biodiversity of saproxylic organisms. Large trees are one of the most important refuges of saproxylic beetles. These large trees that grow outside and inside the forest are declining in the wider landscape. Heritage trees are one of the essential groups of beneficial trees in the landscape. We investigated saproxylic beetles associated with 35 selected oak heritage trees in Litovelské Pomoraví in the eastern Czech Republic. The study aimed to investigate the distribution of saproxylic beetles on trees growing inside or at the edge of forest stands, or on free-growing heritage trees. The other studied variables were the height, DBH, and light condition (sunny or shady) of heritage trees. The results showed that sunny habitats were the only significant factor found for all saproxylic species. However, the significance of increasing tree trunk dimension was found for the endangered species. Diversity indices q = 0 (species richness) and q = 1 (exponential of Shannon entropy index) were also higher for sunny trees, while solitary trees showed a high Shannon index value despite the low number of samples. Redundancy analysis of saproxylic species showed that the preferred habitats of most species were sunny massive solitary oaks. The results indicated that strictly protected heritage trees scattered in the landscape are crucial sanctuaries for many species—especially in landscapes where there are not enough suitable habitats for saproxylic beetles. Finding, conserving, and protecting these rare types of massive trees in the landscape has a significant impact on the conservation of saproxylic beetle biodiversity.

How to Increase Biodiversity of Saproxylic Beetles in Commercial Stands through Integrated Forest Management in Central Europe

Due to traditional forest management, the primary goal of which is the production of raw wood material, commercial forest stands are characterized by low biodiversity. At the same time, commercial forests make up the majority of forests in the Central European region, which means a significant impact on the biodiversity of the entire large region. Saproxylic species of organisms are a frequently used criterion of biodiversity in forests. Based upon the analysis of 155 scientific works, this paper defines the fundamental attributes of the active management supporting biodiversity as well as the preservation of the production function. Using these attributes, a model management proposal was created for three tree species, which takes into account the results of research carried out in the territory of the University Forest Enterprise of the Czech University of Life Sciences Prague, since 2019. The optimum constant volume of deadwood in commercial stands was set at 40–60 m3/ha, 20% of which should be standing deadwood. The time framework is scheduled for an average rotation period of the model tree species, while the location of deadwood and frequency of enrichment must comply with the rate of decomposition, the requirement for the bulkiest dimensions of deadwood possible, and the planned time of tending and regeneration operations in accordance with the models used in the Czech Republic. The goal of active management is to maintain the continuity of suitable habitats for sensitive and endangered species. The estimates of the value of retained wood for decomposition can be as high as 45–70 EUR/ha/year for spruce and beech, and about 30 EUR /ha/year for oak.

Effects of Environmental Traits and Landscape Management on the Biodiversity of Saproxylic Beetles in Mediterranean Oak Forests

This study assesses the effects of environmental traits and landscape management on the biodiversity of saproxylic beetles from “dehesas” located in Sierra Morena Mountains (Córdoba, Southern Iberian Peninsula). The dehesa is an open savanna-like landscape with mature/old trees scattered on a pasture cover where both living and dead wood are of great importance for the maintenance of macroinvertebrate fauna. The study was carried out in five plots, with different environmental features and management. A total of 137 branches belonging to the four main tree species present in the area were collected, classified, and kept under four different thermal conditions. From January to June 2019, the adult emergences were followed. A total of 466 saproxylic specimens of 31 species were obtained, 5 of them included in red lists of protected fauna. Two Bostrichidae species (Lichenophanes numida Lesne and Scobicia pustulata Fab.) and two Cerambycidae (Chlorophorus ruficornis Oliv. and Trichoferus fasciculatus Faldermann) are included in the “European Red List of Saproxylic Beetles”; and the Clerid Tillus ibericus Bahillo de la Puebla, López–Colón and García–Paris, is included in the “Red Book of Invertebrate of Andalucía”. Differences were observed regarding the diversity and abundance among the plots and among the tree species from which the beetles emerged. Simple regression analyses revealed negative relationships between tree density/Buprestidae, livestock/Bostrichidae, and land use/Cerambycidae. Multivariant logistic regression analysis did not find significant relationships among environmental traits and saproxylic diversity. Results confirmed that dry wood was a main resource for the maintenance dehesas’ biodiversity because it constitutes an ecological niche exploited by a significant set of saproxylic beetles belonging to the Bostrichidae, Buprestidae, and Cerambycidae families, in addition to other guilds of species, mainly Carabidae and Cleridae, which feed on the above-mentioned groups. Our results also support that increasing environmental temperature accelerates the development of Buprestidae, but this effect was not evident for the Bostrichidae species.

Saproxylic beetles in tropical and temperate forests – A standardized comparison of vertical stratification patterns

Forests are complex three-dimensional ecosystems, but little is known about the influence of vertical stratification of forest structure on biodiversity and species turnover. Saproxylic beetles make a substantial contribution to forest biodiversity and ecosystem functions such as nutrient cycling. Management measures aimed at supporting saproxylic biodiversity are becoming an integral part of sustainable forest management practices. Yet, monitoring is carried out under the assumption that saproxylic activity at ground level will be a realistic reflection of saproxylic biodiversity in the forest as a whole.To investigate the validity of this assumption we compare vertical stratification and composition of saproxylic beetle assemblages between three forest types of varying altitude and latitude, including a tropical lowland forest in Panama, a temperate lowland forest and a temperate montane forest, both in the eastern Czech Republic. Beetles were sampled following a standardized sampling protocol using flight intercept traps arranged in vertical transects.Overall, the tropical forest was estimated to harbour two to three times more saproxylic beetle species than the temperate lowland and the montane forest, respectively. However, point richness estimates within vertical strata were remarkably similar between biomes. Species richness was similar in the understorey of all three forests. It peaked in the canopy of the tropical forest but in the understorey of temperate forests. So, while the beetle assemblages were clearly vertically stratified in all three forest types, stratification patterns varied markedly between tropical and temperate forests. This trend is driven primarily by the high richness of saproxylic beetles in the tropical forest canopy. However these richness differences belie the strong similarities in stratification of feeding guild composition observed all three forest types. This would tend to suggest that similar trophic structuring forces might operate across very different forest biomes of the world.Similarities in feeding guild composition suggest that management measures aiming at conserving biodiversity of saproxylic beetles are likely to be effective across different forest types. The differences in vertical stratification, however, suggest that understorey monitoring alone will be insufficient to understand management effects on saproxylic biodiversity. In the tropics, in particular, more emphasis will need to be placed on managing the diverse, three-dimensional structure of forest canopies as habitat for saproxylic beetles.

Defining stump harvesting retention targets required to maintain saproxylic beetle biodiversity

Stumps comprise up to 80% of the residual deadwood following clear cutting and are a significant source of biomass for bioenergetic applications. However, stump harvesting may pose significant conservation risks for saproxylic organisms that occur in residual deadwood. To define retention targets for stump harvesting operations, we compared abundance and species richness of saproxylic beetles within individual stumps as well as species accumulation curves in replicated pairs of clear cuts with and without stump harvesting in northern Sweden. Using 20 stands, we sampled 1049 stumps using eclector traps and collected 9821 beetles representing 253 species with known saproxylic biology. Nineteen of these species were red-listed in Sweden. We hypothesized that individual stumps left following stump harvesting would contain higher densities and species richness than in clear cuts without stump removal due to crowding of beetles into increasingly limited habitats. However, we found no difference in density or richness within individual stumps between control clear cuts and stumped stands. We also compared species richness between control and stumped treatments using rarefaction within individual stands and across all stands and found no difference. As with density and richness, beetle composition at the stand-level did not differ between control and stumped stands. Thus, the density of surrounding stumps within a stand had very little effect on beetle assemblages in residual stumps. We estimated the effect of stump harvest on species richness at the stand level by combining all samples and extrapolating a rarefaction curve derived from the landscape-level species pool to an accumulated sample volume of 48m3 which corresponds to the total volume of stumps on average-sized clear cuts in Northern Sweden. Using this curve, we compared differences in species richness in average-sized clear cuts with 100% (48m3) and 25% (12m3) stump retention and found that stump harvest resulted in a 26% (95% C.I. 7–41%) loss of species. While the absolute scaling of the landscape-derived rarefaction does not reflect species loss at the stand-level because the combined curve reflects all rare species in the landscape, the relative species loss derived from this curve may serve as credible benchmark for species loss at the stand level following current stump harvesting practices. This benchmark may be further calibrated with additional information on number of singleton species and estimates of maximum species richness.

Effect of sun exposure on saproxylic beetle assemblages may change with topoclimate in a subtropical forest of east China

Sun exposure is an important determinant of diversity and distribution of saproxylic beetles. However, the sun requirement of saproxylic beetles in forests outside of Europe is still poorly known. In this study, we explored the effect of sun exposure on the biodiversity of saproxylic beetles in a subtropical forest of east China. Beetles were sampled from 64 newly cut boles of Pinus taiwanensis and Cryptomeria fortunei which were equally distributed across high-exposed and low-exposed sites on a warm south-facing and a cold north-facing slope (×4 replicates) during 2 years by, respectively, using flight intercept and emergence traps. It was suggested that sun exposure had no significant effect on species richness of saproxylic beetles. Its effect on beetle abundance changed over the season and significantly varied with topoclimate in the colder months of April and May. Species richness and abundance of beetles associated with different trees did not respond differently to sun exposure. Significantly more beetle individuals were trapped on the warm south-facing slope than on the cold north-facing slope, but aspect had no detectable effect on beetle species richness. Beetle assemblages were significantly affected by sun exposure, but tended to be more similar among low-exposed sites across different slopes. In general, our results indicated that sun exposure is not a sufficient indicator of species richness of saproxylic beetles, but may play an important role in retaining the integrity of saproxylic fauna in subtropical forests. The effect of sun exposure on biodiversity of saproxylic beetles is affected by topoclimate variations.

La magia de los insectos en México: la singular historia del “Maquech” (Zopherus chilensis Gray, 1832)

Zopherus chilensis Gray, 1932 (Coleoptera: Zopheridae), is a small size saproxylic beetle called “Maquech”. This Neotropical specie has peculiar connotations into Maya´s culture. In this paper we show the ornamental use of Z. chilensis and our ultimate goal is to claim for a comprehensive conservation of biodiversity of saproxylic beetles from Mexico.

Key features for saproxylic beetle diversity derived from rapid habitat assessment in temperate forests

Managing and monitoring forest biodiversity is challenging and rapid habitat assessment protocols should be developed to provide us with general key features based on field data.A rapid habitat assessment protocol was implemented over a wide forest gradient in France to analyze surrogacy patterns and performance consistency of presumed key attributes for saproxylic beetle diversity (large trees, microhabitat-bearing trees with trunk cavities, fruiting bodies of saproxylic fungi, tree crown deadwood and sap runs, large logs and snags) and of stand openness. Data compiled in this study include standardized deadwood and window-flight trapped beetle data from 313 plots in oak, lowland and highland beech, lowland pine, highland spruce–fir and mixed temperate forests throughout France.The most structuring factors for species richness and composition of saproxylic beetles were the density of cavity- or fungus-bearing trees and of snags, as well as the degree of openness in the 1-ha surrounding the stand. These key habitat features were nevertheless inconsistent over the different types of temperate forests, and for rare species vs. all species combined. No one variable robustly explained variations in species richness in the deciduous or conifer forest types.The influence of deadwood and “habitat trees” was affected by meso- and micro-climatic features. A significant effect of stand openness on saproxylic beetles was observed both in deciduous and in conifer forests, but only in lowlands. Effects on species richness due to an interaction between substrate availability and openness were observed in montane forests only.Our results point toward the relevance of ecological attributes in tracking changes in saproxylic beetle biodiversity in specific forest contexts, but our study failed to identify any universal structural biodiversity indicators which could be surveyed in part with data from national forest inventories and used to track progress in sustainable forest management or in the protection of sensitive areas.

The effects of forest age on saproxylic beetle biodiversity: implications of shortened and extended rotation lengths in a French oak high forest

Abstract In French oak high forests, current silvicultural trends include two seemingly opposed practices: shortening the forestry cycle, which contributes to forestry intensification, and lengthening rotations in temporary set‐aside stands, called ‘ageing islands’, to favour biodiversity and high‐quality large‐diameter tree production. To derive the potential effects of these two trends, we studied habitat structure and saproxylic beetles biodiversity along an age gradient in a French oak high forest. Four age classes were surveyed: premature (i) 160/180 years and (ii) 180/200 years, (iii) mature 200/220 years, and (iv) overmature 300‐year‐old stands. Structural features were noted: deadwood volumes, density of large trees with or without microhabitats, number of cavities, presence of dead large canopy branches, sap droppings and sporophores of saproxylic fungi. Results showed that beetle species richness was positively related to stand age. Globally, overmature stands differed significantly from younger premature and mature forests in species composition and structure. Younger stands tended to show both fewer structural features and lower levels of saproxylic biodiversity. As the forest aged, the overall structural complexity and saproxylic biodiversity increased. However, no individual stand characteristic influenced preferentially biodiversity, and stand age was the best explaining factor. In conclusion, we discuss how (i) shorter rotations in the high forest production cycle and (ii) temporary set‐aside forest islands affect forest structure and deadwood‐associated assemblages. Shortening rotation length in oak high forests may negatively impact saproxylic biodiversity, whereas temporary set‐asides may play a key role for biodiversity conservation in a managed forest matrix.

A test for assessment of saproxylic beetle biodiversity using subsets of “monitoring species”

In European forests, large scale biodiversity monitoring networks need to be implemented – networks which include components such as taxonomical groups that are at risk and that depend directly on forest stand structure. In this context, monitoring the species-rich group of saproxylic beetles is challenging. In the absence of sufficient resources to comprehensively survey a particular group, surrogates of species richness can be meaningful tools in biodiversity evaluations. In search of restricted subsets of species to use as surrogates of saproxylic beetle richness, we led a case study in Western Europe.Beetle data were compiled from 67 biodiversity surveys and ecological studies carried out from 1999 to 2010 with standardised trapping methods in France and Belgium. This large-scale dataset contains 642 forest plots, 1521 traps and 856 species. Twenty-two simplified species subsets were identified as potential surrogates, as well as the number of genera, a higher taxonomic level, taking into account, for each surrogate, the effort required for species identification, the practical monitoring experience necessary, the species conservation potential or the frequency of species occurrence. The performance of each surrogate was analyzed based on the following parameters: overall surrogacy (correlation between subset richness and total species richness), surrogacy vs. identification cost balance, surrogacy variation over a wide range of ecological conditions (forest type, altitude, latitude and bio-geographical area) and consistency with spatial scale. Ecological representativeness and ability to monitor rare species were supplementary criteria used to assess surrogate performance.The subsets consisting of the identifiable (or only easy-to-identify species) could easily be applied in practice and appear to be the best performing subsets, from a global point of view.The number of genera showed good prediction at the trap level and its surrogacy did not vary across wide environmental gradients. However, the subset of easy-to-identify species and the genus number were highly sensitive to spatial scale, which limits their use in large-scale studies. The number of rare species or the species richness of single beetle families (even the best single-family subset, the Cerambycidae) was very weak surrogates for total species richness. Conversely, the German list of monitoring species had high surrogacy, low identification costs and was not strongly influenced by the main geographical parameters, even with our French and Belgian data.In European-wide monitoring networks, such internationally validated subsets could be very useful with regard to the timing and cost-efficiency of field inventories.

Coppice-with-standards with an overmature coppice component enhance saproxylic beetle biodiversity: A case study in French deciduous forests

Until its replacement by high forest systems in the 19th centuries, coppicing had been practiced in the deciduous broad-leaved forests of Central Europe for many centuries, serving as a source of fuel wood, charcoal and tan-bark for the local populations. Nowadays, some coppice-with-standards (CWS) stands have been converted to high forest by singling (sprout thinning), but many others were simply abandoned, resulting in CWS stands with an overmature coppice component. Little knowledge exists on the biodiversity hosted by such abandoned CWS. In this study, we compared stand features and saproxylic beetle biodiversity in CWS stands with a mature (20-year-old) coppice component to those in stands with an overmature (60-year-old) coppice component. For our study area, we selected 29 plots in 12 oak-hornbeam forests in five regions in northern France. We show that extending rotation age increases the amount of woody debris and alters the deadwood profile. The older the trees and the stands, the more coarse woody debris was created; this includes debris resulting from natural disturbance events. We demonstrated that overmature CWS stands have a higher saproxylic beetle richness than mature CWS. Moreover, even though we found few red-listed beetle species, their number tended to increase in the overmature CWS stands. These results are in line with the observed shift in deadwood profile. Indeed, the increase in deadwood volume along the maturity gradient seems to positively affect saproxylic beetle diversity. Consequently, we conclude that conserving CWS stands with an overmature coppice component can be a useful tool in biodiversity restoration management, in addition to set aside areas.

Saproxylic beetle biodiversity in old‐growth forests of the south‐east of France

This study compared the richness of saproxylic beetle species and the composition of species assemblages between the major forests types of the south‐east of France. The forests differed by their geographical position and their composition in tree species. The results confirmed the existence of a clear local identity of the saproxylic beetles communities. This identity combined three geographical and ecological factors: the geographical position, the altitude and the dominant species of trees. Surprisingly, the period length since the last important perturbation of the stand was not a determinant factor to explain the composition of the saproxylic communities. Selective logging and deadwood retention favoured the increase of the diversity of saproxylic species. This diversity reached a maximum during the first 10 years following the perturbation, was the lowest 30 years after the stand perturbation, but increased again after 50 years with a different species composition.