Influence of sampling effort on saproxylic beetle diversity assessment: implications for insect monitoring studies in European temperate forests

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Diameter of downed woody debris does matter for saproxylic beetle assemblages in temperate oak and pine forests

Deadwood is widely recognized to be an important issue for biodiversity conservation in forest ecosystems. Establishing guidelines for its management requires a better understanding of relationships between woody debris characteristics and associated species assemblages. Although deadwood diameter has been identified as an important factor predicting occurrence of many saproxylic species, the boundary between small and large diameter has not yet been precisely defined. In commercial forests, it is also of critical importance to know which diameter is large enough to host the beetle species associated with large logs in order to ensure cost-effectiveness of biodiversity conservation measures. We investigated the differences in saproxylic beetle assemblages among four different diameter classes of downed woody oak and maritime pine debris, in France. Beetles were sampled using in situ emergence traps. The diameter of deadwood pieces ranged from 1 to 40 cm. No patterns of nestedness associated with the gradient of diameter size were identified for either tree species. More indicator saproxylic species were observed in large logs and branches than in small logs. A clear distinction appeared in assemblage composition around the 5-cm diameter threshold whereas no similar pattern occurred around the 10 cm value, i.e. the classical threshold used in forestry to distinguish fine woody debris from coarse woody debris. For both tree species, the mean body length of beetles increased with the diameter of deadwood suggesting that the quantity of available resources per piece may constitute a limiting factor for large beetle species. This study confirms that not only large deadwood pieces are relevant for saproxylic biodiversity conservation but also the smallest pieces. Therefore, forest managers would be well advised to maintain a high diversity of deadwoods to maintain saproxylic biodiversity.     

Old park trees as habitat for saproxylic beetle species

Very old trees harbour a diverse fauna of saproxylic insects, many of which are classified as threatened due to the scarcity of this kind of habitat. Parks, which often contain many old trees, are therefore considered to be important sites for this fauna. However parks are intensively managed and dead wood is often removed. Therefore this study compares if the saproxylic beetle fauna in parks is as diverse as it is in more natural stands. Eight ‘Park’ sites at manor houses around lake Mälaren, Sweden were compared with trees in wooded meadows: eight grazed sites, here termed ‘Open’, and 11 sites regrown with younger trees, termed ‘Re-grown’. The comparison was made on lime trees (Tilia spp.): one of the most frequent tree species in old parks which host a diverse beetle fauna. Beetles were sampled with window traps, which in total caught 14,460 saproxylic beetles belonging to 323 species, of which 50 were red-listed. When comparing all saproxylic species, ‘Park’ sites had significantly fewer species than ‘Open’ sites. However, for beetles in hollow trees and for red-listed species there was no significant difference, the number in ‘Park’ being intermediate between ‘Open’ and ‘Re-grown’. Species composition differed between sites, but only marginally so. Therefore, the conclusion is that old park trees on average are as valuable for faunal diversity as trees in more natural sites. Large conservation benefits can be obtained by combining cultural and conservational values in the management of park habitats.     

Intra-annual patterns of saproxylic beetle assemblages inhabiting Mediterranean oak forests

The temporal factor has been widely neglected in studies related to species distribution. However, knowing the species phenology throughout the year could be a key element in ecological studies, more so considering the current climate change framework. The intra-annual temporal patterns of the saproxylic beetle assemblage inhabiting the oak forests in the western Iberian Peninsula were evaluated in terms of species richness and composition. Moreover, we analysed the temporal patterns of species richness and body size, with respect to the abiotic factors of temperature and relative humidity. The marked seasonality of the Mediterranean weather governed, to a great extent, the temporal patterns of the assemblage, as both species richness and body size showed a positive correlation with temperature and a negative correlation with relative humidity. The high temperatures reached in August limited the activity of certain species, causing a marked decrease in species richness. The results revealed that species body size decreased in the colder months of the year and vice versa, which could fit with the inverse of Bergmann’s rule; nevertheless, studies are needed to address the contribution of species physiology and autoecology to the observed temporal patterns. Regarding species composition, the partition of beta diversity in its two components showed a constant process of species turnover throughout the year. We conclude that, due to global warming, the study of temporal patterns of assemblages is becoming all the more important, since it could significantly affect the spatio-temporal distribution of species and the interactions between them.     

Species coexistence in temperate, mixed deciduous forests

The response of tree life-history traits to community profiles (horizontal and vertical heterogeneity, disturbances and biotic interactions) determines community assembly rules, which are currently a hot issue in community ecology. Important mechanisms of coexistence differ throughout the developing stages of tree life history. Many processes of niche partitioning and tradeoffs that potentially enable tree coexistence have been reported to be present in temperate forests, although some of these life-history traits are either correlated with each other or are not independent. Not all of the proposed mechanisms explain coexistence equally well; some could predominate in determining the community organization of forest communities. Population studies need to concentrate more on the component species of a target community to detect the ecological assembly rule. These approaches can also address how chance factors contribute to the composition of temperate tree communities, which might be less dependent on chance than are tropical ones.     

Explaining the saproxylic beetle diversity of a protected Mediterranean area

Saproxylic beetle diversity is high at the Cabañeros National Park (central Spain), where woodland habitats exhibit remarkable heterogeneity. Our aim was to explain the diversity of saproxylic beetles, focusing on species turnover among mature woodland types. We surveyed five woodland types that represented the heterogeneity of the park’s woodland habitats. Beetles were collected using window traps over a period of 20 months. The Jaccard Similarity Index was used as indirect value of beta diversity among woodlands and to test the relation between species turnover and geographical distance. We also identified the contribution of species turnover to landscape diversity by using a partitioning model. Moreover, the presence of mixed woodlands (more than one tree species) allowed us to attempt to valorise the effect of tree species (coupled with their historical management) on species turnover among woodlands. Finally, we looked for different saproxylic beetle preferences for habitat and tree species using an indicator value method. We found that saproxylic beetle species composition varied significantly among the studied woodlands. The variation in species turnover was independent from the distance among woodlands, which suggested that beetle dispersal abilities could not explain this high turnover. Tree species within woodlands were a key factor that increased diversity turnover in woodlands and, consequently, the diversity of the park. Moreover, we found saproxylic beetle species that had different habitat and tree species preferences. We conclude that woodland heterogeneity (highly affected by woodland composition) seems to be the driving force for saproxylic beetle diversity in this protected area.     

In search of the best correlates for local organismal biodiversity in cultivated areas

Based on a transect consisting of 19 identical trap stations in cultivated areas and seminatural habitats, the correlation of species numbers of higher taxonomic groups with total species numbers of flowering plants and arthropods per trap site was calculated. A total of 191214 invertebrate specimens and 2221 species of plants and animals were analysed. Considering the value of the correlation coefficient R2 as well as the effort for sorting and identification, a top twenty list of indicator groups favours Heteroptera, flowering plants, Symphyta and aculeate Hymenoptera as the best choice for biodiversity evaluation. In general, flight traps rated better than pitfall traps. In most taxonomic groups, diversity indices such as the Shannon and the Simpson index were only weakly correlated with local species diversity.     

Plant species diversity in abandoned coppice forests in a temperate deciduous forest area of central Japan

We investigated plant species diversity as it related to stand structure and landscape parameters in abandoned coppice forests in a temperate, deciduous forest area of central Japan, where Fagus crenata was originally dominant. The species occurring in the study plots were classified into habitat types based on a statistical analysis of their occurrence bias in particular habitats (e.g., primary forest, coniferous plantation) in the landscape studied. The relationships between stand structure, which reflected the gradient of management, and forest floor plant species diversity (H and J) and richness (number of species per unit area) were not significant. However, these factors did influence the forest floor plant composition of the different types of habitat. According to the multiple regression analysis, species diversity and the richness of forest floor plants was affected by landscape parameters rather than by stand structure. For trees, species richness was mainly affected by the relative dominance of F. crenata, which is one of the stand structure parameters that decreases with intensive management. This is probably because many of the tree species that are characteristic of coppice forests increase after F. crenata have been eliminated by management; these species are not dominant in the original forest, where they are suppressed by F. crenata, the shade-tolerant dominant species. The species diversity (H and J) of trees was positively correlated with some landscape parameters, including the road density around the study plot, which may be associated with the intensity of management activity. The number of disturbance-tolerant species increased with increasing road density. Stand structure mainly affected disturbance-intolerant forest floor plant species and disturbance-tolerant tree species. Thus, the species diversity responses differed between forest floor plants and trees. The impact of forest management on species diversity was more prominent for forest floor plants.     

Seed banks of temperate deciduous forests during secondary succession

Question: (i) How does former land use and land use intensity affect seed bank development during post‐agricultural succession? (ii) How does time since the last clear‐cut change seed bank composition during post‐clear‐cut succession? Methods: One data set was compiled per succession type using the following selection criteria: (i) the data set included a successional series, (ii) plots were located in mesotrophic forest plant communities and (iii) vegetation data were available. The post‐agricultural succession data set comprised 76 recent forest plots (eight studies); the post‐clear‐cut succession data set comprised 218 ancient forest plots (three studies). Each data set was analysed separately using either linear mixed models or generalized linear models, controlling for both environmental heterogeneity and variation between study locations. Results: In the post‐agricultural succession data set, land use and time significantly affected nearly all the studied seed bank characteristics. Seed banks on former arable land recovered poorly even after 150 year of restored forest cover, whereas moderate land use intensities (grasslands, heathlands) yielded more rapid seed bank recovery. Time was a significant determinant of all but two soil seed bank characteristics during post‐clear‐cut succession. Seed banks in managed ancient forest differed strongly in their characteristics compared to primary forest seed banks. Conclusions: Forest seed banks bear the marks of former land use and/or forest management and continue to do so for at least 150 years. Nevertheless, time since the last major disturbance, being either former land use or clear‐cutting, remains a significant determinant of the seed bank.     

Species diversity in North American temperate forests

Summary Samples from temperate forest communities across the North American continent were analysed for correlations of plant species diversity with environment and community structure.Alpha diversity relationships are complicated by different vegetation patterns and community history. The differences in community diversity patterns may be due to the independent evolution of communities in different regions.Results of analyses were: 1) on a continental scale plant species diversity is related to mean annual temperature, but not precipitation; 2) diversity is substantially greater in continental climates than in maritime regions; 3) diversity-community structure relationships are generally weak, except 4) there is an inverse relationship between diversity and abundance of conifer tree species. Attempts to relate diversity to environmental parameters with multiple regression techniques met with only moderate success.I thank R. H. Whittaker, R. K. Peet and H. G. Gauch, Jr., for their help and comments. I am especially grateful to R. H. Whittaker for making his data available to me. Computation was supported in part by N.S.F. grant No. GB-30679. I was supported by a Nat. Inst. of Health Traineeship during part of this study.     

Effects of habitat quality and landscape structure on saproxylic species dwelling in boreal spruce-swamp forests

Intensive forest management has caused loss and fragmentation of old‐growth forests and reduced the amount of dead wood throughout northwest Europe. Changes in habitat availability are reflected in occurrence patterns of habitat‐specialist species only after a certain time lag. Here we analyse the responses of wood‐decomposing fungi and saproxylic beetles inhabiting patches of spruce‐swamp forest to habitat quality, loss and isolation at three different spatial scales in eastern Finland and adjacent Russian Karelia, where forestry has been very marginal until recently. Both rare specialist species and common generalist species were included in the study to reveal whether their occurrence patterns differ. Variables describing habitat quality (density and continuity of host trees, patch area) turned out significant in explaining species' incidences (proportion of occupied host trees) in only a few cases, probably because of the relatively high quality of all study patches. Despite this fact, and consistent with our hypothesis, incidences of all the eight specialist species were higher in Russia than Finland, and the difference was significant in the two most strict habitat specialists, Pytho kolwensis and Phlebia centrifuga. In contrast, incidences of three out of four generalist species were higher in Finland than in Russia, and the difference was significant in Rhagium inquisitor. In a subset of 21 patches in Finland, we used a metapopulation model to predict the probability of each patch to be currently occupied by a species given the known spatiotemporal distribution of suitable forest stands during the last 50 years. The degree of isolation alone explained significantly the incidences of five species. However, including habitat variables into the models altered some of the effects. Moreover, inconsistent with our hypothesis, isolation appeared to also negatively affect some very common generalist species. Inclusion of these species in the study disclosed that apparently significant effects of spatiotemporal isolation should be interpreted cautiously.     

Fruit fall in tropical and temperate forests: implications for frugivore diversity

There have been few attempts to compare fruit productivity throughout the world, although this is indispensable for understanding the global variations in frugivore diversity. The purposes of this study are (1) to reveal the patterns in fruit fall in tropical and temperate forests, (2) to examine the environmental factors (location, climate, and total litterfall) affecting these patterns, and (3) to assess the effect of fruit fall on frugivore diversity by using bird and primate data. Fruit fall was compared among 53 forests, from around the equator to the cool-temperate zone at 62°N, in Asia, Africa, North and South America, and Australia. Average ± SD of fruit fall (kg/ha/year) was 454 ± 258 in tropical, and 362 ± 352 in temperate forests. Fruit fall was exceptionally high in Australia (812 ± 461). When Australia was excluded, fruit fall significantly decreased with increasing absolute latitude and altitude, and fruit fall in tropical forest was 1.7 times larger than that in temperate forests (265 ± 227). Total litterfall affected fruit fall significantly, explaining 32, 28, and 64% of the variations of fruit fall in the entire data, tropical data, and temperate data, respectively. The fruit fall/litterfall ratio did not differ between temperate and tropical forests but was significantly higher in Australia than in other regions. Among climatic parameters (annual temperature, precipitation, actual evapotranspiration), a positive relationship was found between temperature and fruit fall in the entire dataset and within temperate forests. Fruit fall seemed to explain the temperate/tropical difference in frugivorous primate diversity to some extent, but not for frugivorous bird diversity. This study shows that the difference in fruit fall in tropical and temperate forests is smaller than that in frugivore diversity, and that it could explain at least part of the frugivore diversity.     

Soil microbial responses to elevated phosphorus and pH in acidic temperate deciduous forests

Although northern temperate forests are generally not considered phosphorus (P) limited, ecosystem P limitation may occur on highly weathered or strongly acidic soils where bioavailable inorganic P is low. In such environments, soil organisms may compensate by increasing the utilization of organic P via the production of extracellular enzymes to prevent limitation. In this study, we experimentally increased available P and/or pH in several acidic eastern deciduous forests underlain by glaciated and unglaciated soils in eastern Ohio, USA. We hypothesized that where inorganic P is low; soil microbes are able to access organic P by increasing production of phosphatase enzymes, thereby overcoming biogeochemical P limitations. We measured surface soil for: available P pools, N mineralization and nitrification rates, total C and N, enzymes responsible for C, N, and P hydrolysis, and microbial community composition (PLFA). Increasing surface soil pH a whole unit had little effect on microbial community composition, but increased N cycling rates in unglaciated soils. Phosphorus additions suppressed phosphatase activities over 60% in the unglaciated soils but were unchanged in the glaciated soils. All treatments had minimal influence on microbial biomass, but available pools of P strongly correlated with microbial composition. Microbes may be dependent on sources of organic P in some forest ecosystems and from a microbial perspective soil pH might be less important overall than P availability. Although our sampling was conducted less than 1 year after treatment initiation, microbial community composition was strongly influenced by available P pools and these effects may be greater than short-term increases in soil pH.     

Importance of the understory stratum to entomofaunal diversity in a temperate deciduous forest

The vertical stratification of lepidopteran and coleopteran communities in a cool-temperate deciduous forest in Japan was examined to evaluate the hypothesis of an expected uniform distribution of mobile flying insects between the canopy and understory of temperate forests. Lepidopteran and coleopteran insects were trapped using light traps at three sites in each of the canopy and understory for three consecutive nights each month from April to October 2001. For Lepidoptera, species richness, abundance, and family richness were significantly higher in the understory than in the canopy. For Coleoptera, only abundance was larger in the canopy relative to the understory; species and family richness did not differ between the strata. The beta diversity of the lepidopteran community was larger between the strata than among sites, but the coleopteran community showed an inverse pattern. These results imply the presence of vertical stratification within the lepidopteran community, but not within the coleopteran community, in the temperate forest. The understory contributes more than the canopy to lepidopteran diversity in the temperate forest, although this stratification may be relatively weak because, in contrast to the situation in tropical forests, the canopy and understory assemblages share many species.     

Simulation and scaling of temporal variation in gross primary production for coniferous and deciduous temperate forests

Observations of ecosystem net carbon dioxide exchange obtained with eddy covariance techniques over a 4‐year period at spruce, beech and pine forest sites were used to derive time series data for gross primary production (GPP) and ecosystem respiration (R_eco). A detailed canopy gas exchange model (PROXEL_NEE) was inverted at half‐hour time step to estimate seasonal changes in carboxylation capacity and light utilization efficiency of the forest canopies. The parameter estimates were then used further to develop a time‐dependent modifier of physiological activity in the daily time step gas exchange model of Chen et al. (1999) , previously used for regional simulations in BOREAS. The daily model was run under a variety of assumptions and the results emphasize the need in future analyses: (1) to focus on time‐dependent seasonal changes in canopy physiology as well as in leaf area index, (2) to compare time courses of physiological change in different habitats in terms of recognizable cardinal points in the seasonal course, and (3) to develop methods for utilizing information on seasonal changes in physiology in regional and continental carbon budget simulations. The results suggest that the daily model with appropriate seasonal adjustments for physiological process regulation should be an efficient tool for use in conjunction with remote sensing for regional evaluation of global change scenarios.     

Phylogenetic and functional diversity area relationships in two temperate forests

Phylogenetic diversity (PD, the diversity of lineages) and functional diversity (FD, the diversity of functional traits or groups in a biological community) reflect important yet poorly understood attributes of species assemblages. Until recently, few studies have examined the spatial variation of PD and FD in natural communities. Yet the relationships between PD and FD and area (termed PDAR and FDAR), like the analogous species–area relationship (SAR), have received less attention and may provide insights into the mechanisms that shape the composition and dynamics of ecological communities. In this study, we used four spatial point process models to evaluate the likely roles of the random placement of species, habitat filtering, dispersal limitation, and the combined effects of habitat filtering and dispersal limitation in producing observed PDARs and FDARs in two large, fully mapped temperate forest research plots in northeast China and in north‐central USA. We found that the dispersal limitation hypothesis provided a good approximation of the accumulation of PD and FD with increasing area, as it did for the species area curves. PDAR and FDAR patterns were highly correlated with the SAR. We interpret this as evidence that species interactions, which are often influenced by phylogenetic and functional similarity, may be relatively unimportant in structuring temperate forest tree assemblages at this scale. However, the scale‐dependent departures of the PDAR and FDAR that emerged for the dispersal limitation hypothesis agree with operation of competitive exclusion at small scales and habitat filtering at larger scales. Our analysis illustrates how emergent community patterns in fully mapped temperate forest plots can be influenced by multiple underlying processes at different spatial scales.