The saproxylic beetle assemblage associated with different host trees in Southwest China

Dead wood is a habitat for many insects and other small animals, some of which may be rare or endangered and in need of effective protection. In this paper, saproxylic beetle assemblages associated with different host trees in the subtropical forests in southwestern China were investigated. A total of 277 species (1 439 specimens) in 36 beetle families were collected from 117 dead wood samples, of which 101 samples were identified and respectively belonged to 12 tree genera. The number of saproxylic beetle species varied greatly among logs of different tree genera, with the highest diversity on logs of Juglans. Generally, broad‐leaved trees had a higher richness and abundance of saproxylic species than coniferous trees. Cluster analysis revealed that assemblages from broad‐leaved tree genera were generally similar (except for Betula) and assemblages from coniferous trees formed another distinct cluster. The subsequent indicator analysis proposed that there are different characteristic species for different cluster groups of host tree genera. In our study, log diameter has no positive influence on beetle species density. Conversely, comparisons of individual‐based rarefaction curves suggested that beetle species richness was highest in the small diameter class both in coniferous and broad‐leaved tree genera. With increased wood decay, proportion of habitat specialists (saproxylic beetles living on one tree genus) decreased, whereas proportion of habitat generalists (living on more than three tree genera) increased. The beetle species density was found to be higher in early stages, and decreased in later stages as well. A negative influence of altitude on saproxylic beetle species richness and abundance was detected. It was indicated that different tree genera and altitudes possibly display cross effects in modulating the altitudinal distribution and host preference of the beetles.     

Spatial and temporal scales relevant for conservation of dead-wood associated species: current status and perspectives

Dead wood is a key substrate for forest biodiversity, hosting a rich and often threatened biodiversity of wood-living species. However, the relationship between the occurrence of dead wood and associated species is modified by several environmental factors. Here we review the present state of knowledge on how dead wood on different spatial and temporal scales affects saproxylic biodiversity. We searched for peer-reviewed studies on saproxylic species that compared dead wood distribution on at least two spatial or temporal scales. We scanned close to 300 articles, of which 34 fit our criteria. 20 studies were directed towards the current amount of dead wood at different scale levels and how this relates to the abundance or occurrence of saproxylic species, embracing scales from 10 m to 10 km. 14 studies compared time-lagged effects of dead wood, covering time-lags from 25 years to more than 200 years. The reviewed articles focused mainly on European forest and addressed invertebrates (mostly beetles), alone or in combination with fungi (27 articles), fungi (six articles), or lichens (one article). Although the significance of dead wood for forest biodiversity is firmly established, the reviewed studies show that we still have limited knowledge of the relationship between saproxylic biodiversity and spatial and temporal scales. Based on the reviewed studies, we conclude that there is large variation in response to spatial and temporal dead wood patterns between different taxa and sub-groups. Still, several of the reviewed papers indicate that time-lagged effects deserve more attention, especially on a landscape scale and for specialized or red-listed species. Further work is required before firm management recommendations can be suggested.     

Boxes mimicking tree hollows can help conservation of saproxylic beetles

Old hollow trees have declined in Europe and many saproxylic (i.e. wood-dwelling) invertebrates living on them are threatened. The aim of this study was to investigate to what extent artificial habitats can be exploited by saproxylic beetles. To mimic the conditions in tree hollows, we constructed wooden boxes filled with different combinations of substrates like oak saw dust, oak leaves, a dead hen (Gallus domesticus), chicken dung, lucerne flour or potatoes and placed them on tree trunks. To investigate the importance of distance from dispersal sources, we placed boxes at different distances (0–1,800 m) from three species-rich sites with high densities of hollow oaks. Over 3 years, 3,423 specimens of 105 saproxylic beetle species were caught in 47 boxes. Among beetles found in hollow oaks that were either tree-hollow species, bird nest species, or wood rot species, 70% were also found in the boxes. A dead hen added to the artificial wood mould gave a higher number of beetle specimens. The number of species associated with tree hollows in oak decreased with distance from sites with hollow oaks. In conclusion, the prospects for using artificial environments for boosting substrate availability, or to fill spatial and temporal gaps therein, for saproxylic beetles are good.     

Saproxylic Beetles in Standing Dead Wood Density in Relation to Substrate Sun-exposure and Diameter

Species-specific densities of saproxylic beetles in cut 4-m high, medium to large diameter stumps of spruce, birch, aspen and oak were monitored for 7 years after cutting, by trapping emerging insects within seasonally applied net enclosures. A total of 47,038 individuals, representing 316 saproxylic beetle species including 40 red-listed species, were recorded. Densities of 86 species were modelled in relation to stump diameter and measured levels of sun-exposure. Two thirds of the species favoured semi- or fully exposed substrates, while one third performed better in shade. Few species seemed to be specifically adapted to semi-exposed conditions. Diameter was generally of less importance than exposure, and similar numbers of species favoured medium and large diameter substrates. Group mean diameter and exposure calculated from means per individual and species were similar for groups of modelled and non-modelled species, and for groups of red-listed and non-red-listed species, respectively. This indicates that the proportions found in the models are representative for the diverse regional fauna of saproxylic beetles that utilise high stumps of spruce, birch, aspen and oak in early stages of decay. The results suggest that sun-exposed dead wood substrates generated and retained in managed forest landscapes are potentially important for many species. However, stands of unmanaged self-thinning successions of deciduous trees, as well as substantial areas of old-growth spruce-forests are also necessary to address the wide spectrum of saproxylic beetles.     

Wood decomposition is more strongly controlled by temperature than by tree species and decomposer diversity in highly species rich subtropical forests

While the number of studies on the role of biodiversity on ecosystem functioning is steadily increasing, a key component of biogeochemical cycling in forests, dead wood decay, has been largely neglected. It remains widely unknown whether and how dead wood decay is affected by diversity loss in forests. We studied the hierarchical effects of tree species diversity on wood decay rates in a subtropical forest landscape in southeast China via its influence on fungal OTU richness and invertebrate diversity using piecewise structural equation models. The experiment was conducted in natural forest plots that span a wide gradient of tree species diversity embedded in a heterogeneous topography. To account for interactions between macro‐invertebrates and fungi, that potentially modify the influence of tree biodiversity and climate on dead wood decay, we compared a macro‐invertebrate exclusion treatment with a control treatment that allowed access to all types of decomposers. Diversity effects of trees on wood decay rates were mostly negative and mediated by the diversity of macro‐invertebrates. However, the effects of tree species diversity or fungal OTU richness and macro‐invertebrate diversity on wood decay rates were comparatively weak. Temperature affected decay rates positively and had the strongest influence in all treatments. While the exclusion of macro‐invertebrates did not lead to a reduction of wood decay rates, our results suggest that they may however have a mediating role in the process. In the presence of invertebrates the predictability of wood decay rates was higher and we observed a tendency of a stronger temperature control. Our results suggest that there is evidence for diversity effects on wood decomposition, but the temperature control is still more important. Thus, an increase in mean annual temperature will increase carbon and nutrient turnover through wood decomposition in subtropical forest irrespective of biotic composition.     

The Biodiversity and Conservation of Saproxylic Diptera In Scotland

Over a ten year period, 1988–1998, over 300 woodlands were visited throughout Scotland and 2061 records of saproxylic Diptera obtained. Of these 1574 were records of early stages; 258 species in 32 families were encountered; 206 species were reared of which 53 were red-listed, 9 were new to Britain and 10 were new to science. Most records came from native boreal trees such as Betula pubescens, Pinus sylvestris and Populus tremula. However, few saproxylic Diptera were specific to tree species, exceptions were 6 red-listed species associated with P. tremula and 5 red-listed species with P. sylvestris. In contrast, most saproxylic Diptera were specific to microhabitat or breeding site. The most important microhabitats were decaying sap under bark and decaying sapwood. Most red-listed species are restricted to Strathspey and north-east Scotland where relatively large stands of native boreal trees exist.     

Fast but ephemeral effects of ecological restoration on forest beetle community

Many protected areas have a long history of human intervention before being protected. In protected forests, the past land use has reduced the amount of natural structures, which are crucial substrates for thousands of species. We evaluate the short-term ecological effect of forest restoration (dead wood creation) on conifer-associated saproxylic (dead-wood dependent) beetles. More specifically, we analyze the effect of dead wood creation on the number of beetle species and individuals 1 and 5 years after restoration in spruce and pine forests, using a large-scale monitoring network over Finland. The number of saproxylic beetle species and individuals was larger at restored than at control plots both 1 and 5 years after restoration in both spruce and pine forests. Community composition in restored plots was different from control plots 1 year after restoration, but had returned towards the control plot composition 5 years after restoration, while control plots remained largely unchanged. Both in spruce and pine forests, there were more red-listed and rare saproxylic beetles in restored than in control plots 1 and 5 years after restoration. Our results indicate that restoration has an overall positive influence on saproxylic beetle diversity immediately after dead wood creation, but this effect is rather short-lived. Long term monitoring of restored dead wood is crucial in investigating successional pathways as well as biotic communities in advanced decay stages, and in fully evaluating the ecological effect of dead wood creation as a forest restoration measure.     

Species richness of phytophagous beetles in the tropical tree Brosimum utile (Moraceae): the effects of sampling strategy and the problem of tourists

Abstract.  1. Phytophagous beetles on six mature living trees and two dead trees of Brosimum utile (Moraceae) were surveyed during 1 year in a tropical wet forest in Panama. The dead trees were surveyed both as suspended in the canopy and after falling down to the understorey.
2. Canopy access was provided by a construction crane and sampling was performed by beating and hand-collecting. The same amount of time was spent on each tree in order to standardise sampling effort. A list of all species associated with the tree is presented.
3. A total of 3009 individuals representing 364 species were collected. Tourists were excluded from the analyses by recording host associations directly and by probability assessments of host associations based on abundance categories. A total of 2603 individuals and 244 species were associated with the tree. The proportion of tourists in the trees increased with sample size.
4. A single mature living tree had on average 58.5 ± 6.5 species. The local species richness of B. utile was estimated as 2.5 times higher than in a single mature tree; however, a substantial increase in species richness was attained when dead wood habitats were included. Saproxylic species made up 82% of the total material.
5. The investigated habitat types of B. utile constituted distinct, complementary species assemblages. Similarity between saproxylic species of dead suspended wood and dead understorey wood of the same tree was 0.2 (Morisita–Horn index), confirming a prominent vertical stratification among this guild.     

Importance of high quality early-successional habitats in managed forest landscapes to rare beetle species

Species adapted to early-successional forest habitats are in managed landscapes largely confined to clearcuts. To improve habitat quality on clearcuts, green tree and dead wood retention is widely applied in forestry; however, its effects on rare early-successional species have rarely been shown. We repeatedly surveyed two red-listed beetle species (Upis ceramboides and Platysoma minus) on clearcuts in a managed boreal forest landscape. We found that U. ceramboides decreased its occupancy over time while P. minus increased, indicating that red-listed species vary in their ability to successfully utilise managed habitats. We found no effect of connectivity on probability of occurrence, colonisation or extinction per clearcut. Trees retained alive improved habitat quality of clearcuts, since both species were more frequent in dead wood of such trees, in comparison to logging residues. We suggest that retention can be improved by protecting and creating dead wood as intact trees during harvesting. Rare specialist species require habitat of high quality, and consequently it is impossible to meet the requirements of these species on every clearcut. To preserve all early-successional species at a regional scale, we recommend focusing retention of green trees and dead wood to one or a few trees species on each clearcut and in each landscape.