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Forest decline caused by climate change has been a growing challenge for European foresters for decades. The accumulation of tree-related microhabitats (TreMs) and deadwood during decline can enhance stand structural heterogeneity and provide crucial habitat features for many forest ecological guilds. We analysed changes in deadwood and TreM assemblages using a trait-based approach in three case studies: drought-induced decline in highland Pyrenean fir and lowland oak forests, and windstorm/pest-induced dieback in highland Bavarian spruce forests. Decline caused significant changes in deadwood and TreM characteristics and composition in three forest contexts. However, tree density with cavities, exudates, or crown deadwood was not linked to decline intensity. Declining conifer forests had more large deadwood and downed woody debris, and their TreM assemblages were more saproxylic, less epixylic, and included more cracks and exposed sapwood. TreM assemblages in drought-declining forests had higher diversity, functional richness, and more dead tops than healthy stands. In Bavarian spruce forests, there was more decayed downed deadwood, and the TreM assemblages were more associated with the base of the tree, snags, and logs. Overall, forest decline significantly boosts ecological niche resources, typically scarce in managed forests, which could benefit many forest biodiversity groups. Though post-disturbance management should respect tree species-dependent economic balance and avoid phytosanitary risks, it should also consider the ecological benefits of decline-induced heterogeneity. [ABSTRACT FROM AUTHOR]

Despite its importance as a key element for forest biodiversity and ecosystem functioning, uncertainties remain on how deadwood may change due to increasing forest dieback and subsequent management. The opportunistic cross-analysis of two large-scale, never-before-crossed forest databases, based on the spatially representative 16 × 16 km European grid, provided a dataset of 1804 plots in 17 countries with 10-year time series of annual measurements of tree defoliation followed by punctual assessment of deadwood volumes. Generalized linear mixed models and magnitude analyses quantified the relative influence of site environmental factors and 16 metrics of the current, recent and mid-term dynamics of local decline severity on plot-level deadwood volumes across European forests. The average level of dieback over the last five years and, to a lesser extent, the time elapsed since the last peak defoliation, were more important for deadwood stocks than were older levels of defoliation, the intensity or the frequency of extreme past declines. In Europe overall, total deadwood volume was 33% higher when the average level of decline over the previous five years increased by 10%. The significance and magnitude of the effects of past defoliation on deadwood were stronger in lowland forests than in upland forests, in coniferous forests than in broadleaf forests, in young stands than in mature stands, and for standing deadwood than for total deadwood, and varied with management. Retaining small, declining patches, excluded from salvage or sanitary logging within managed forests, could be an integrative opportunistic forestry tool for spontaneous restoration of deadwood. [Display omitted] • How deadwood amount may respond to global change in the future is questionable. • We analyze two large-scale, never-before-crossed European forest databases. • The effects of recent defoliation on deadwood vary with forest context across Europe. • Recent forest dieback is a more important predictor of deadwood volume than past diebackRetaining declining patches as a biodiversity-friendly tool for deadwood restoration. [ABSTRACT FROM AUTHOR]

Increasing the density of natural reserves in the forest landscape may provide conservation benefits for biodiversity within and beyond reserve borders. We used 2 French data sets on saproxylic beetles and landscape cover of forest reserves (LCFR) to test this hypothesis: national standardized data derived from 252 assessment plots in managed and reserve stands in 9 lowland and 5 highland forests and data from the lowland Rambouillet forest, a forested landscape where a pioneer conservation policy led to creation of a dense network of reserves. Abundance of rare and common saproxylic species and total saproxylic species richness were higher in forest reserves than in adjacent managed stands only in highland forests. In the lowland regional case study, as LCFR increased total species richness and common species abundance in reserves increased. In this case study, when there were two or more reserve patches, rare species abundance inside reserves was higher and common species richness in managed stands was higher than when there was a single large reserve. Spillover and habitat amount affected ecological processes underlying these landscape reserve effects. When LCFR positively affected species richness and abundance in reserves or managed stands, >12-20% reserve cover led to the highest species diversity and abundance. This result is consistent with the target of 17% forested land area in reserves set at the Nagoya biodiversity summit in 2010. Therefore, to preserve biodiversity we recommend at least doubling the current proportion of forest reserves in European forested landscapes. [ABSTRACT FROM AUTHOR]

The extrapolation of metapopulation concepts to saproxylic insects suggests that the occupancy of forest patches and the colonization of ephemeral deadwood substrates are driven by micro-evolutionary processes that are related to adaptive plasticity and intraspecific sex-dependent polymorphism of dispersal traits. We hypothesized that forest fragmentation could favor more mobile individuals within populations, but little empirical data have been published on the potentially sex-biased response of insect populations to habitat availability. We selected 88 fragmented woodlots in two European agricultural landscapes to cover different degrees of spatio-temporal fragmentation, from small, isolated and recently established woodlots to large, inter-connected ancient woodlots. In line with our hypothesis, the average wing loading (WL), used as a proxy for dispersal ability, for each of nine flight-dispersing saproxylic beetle species should be lower in recent, small, isolated woodlots than in ancient, large, inter-connected woodlots, respectively (i.e. ancient vs. recent, small vs. large, isolated vs. connected). Forest patch size did not significantly influence the average dispersal ability of beetle colonizers. However, WL of one-third of the tested species did significantly respond to forest ancientness or connectivity. Significant patterns were sex-biased, probably due to the contrasting role of males and females in species colonization dynamics. WL was lower in recent than in ancient forest plots for Melandrya barbata males, and it was lower in isolated than in connected woodlots for Tetratoma ancora and Phymatodes testaceus males. Contrary to expectations, we did not observe any decrease in polymorphism of dispersal abilities with decreasing woodlot size or increasing isolation. Our findings give support to the usefulness of gender consideration in insect conservation ecology studies. [ABSTRACT FROM AUTHOR]

Monitoring saproxylic beetle diversity, though challenging, can help identifying relevant conservation sites or key drivers of forest biodiversity, and assessing the impact of forestry practices on biodiversity. Unfortunately, monitoring species assemblages is costly, mainly due to the time spent on identification. Excluding families which are rich in specimens and species but are difficult to identify is a frequent procedure used in ecological entomology to reduce the identification cost. The Staphylinidae (rove beetle) family is both one of the most frequently excluded and one of the most species-rich saproxylic beetle families. Using a large-scale beetle and environmental dataset from 238 beech stands across Europe, we evaluated the effects of staphylinid exclusion on results in ecological forest studies. Simplified staphylinid-excluded assemblages were found to be relevant surrogates for whole assemblages. The species richness and composition of saproxylic beetle assemblages both with and without staphylinids responded congruently to landscape, climatic and stand gradients, even when the assemblages included a high proportion of staphylinid species. At both local and regional scales, the species richness as well as the species composition of staphylinid-included and staphylinid-excluded assemblages were highly positively correlated. Ranking of sites according to their biodiversity level, which either included or excluded Staphylinidae in species richness, also gave congruent results. From our results, species assemblages omitting staphylinids can be taken as efficient surrogates for complete assemblages in large scale biodiversity monitoring studies. [ABSTRACT FROM PUBLISHER]

The decline of many saproxylic species results from the decrease in old-growth structures in European harvested forests. Among conservation tools, protected reserves withdrawn from regular harvesting and extended rotations have been employed to restore old-growth attributes in structurally simplified managed forests, even if the effects of such management actions on forest habitats and biodiversity remain largely unknown. In this study, we compared structural stand features and saproxylic beetle assemblages in two stand classes - recently harvested stands and long-established reserves, where less or more than 30 years had elapsed since last harvest. Habitat and saproxylic beetle data were collected according to standardized protocols in 153 plots in seven lowland deciduous forests. Tangible contrasts in stand features were found between long-established reserves and recently harvested plots. Indeed, most higher-value densities and volumes were found in unharvested areas. The difference was weaker for microhabitat-bearing tree density than for deadwood; some deadwood features, such as volume of large downed and standing deadwood showed a very pronounced difference, thus indicating a marked deleterious effect of forest harvesting on these elements. Deadwood diversity, on the other hand, was only slightly affected and the level of stand openness did not change. The response of saproxylic beetles to delayed harvesting was weaker than the structural changes in deadwood features. Indeed even if only some guilds weakly increased in non-harvested plots, harvesting classes significantly affected the abundance of a quarter of the species tested. Our results tend to question measures such as rotating and temporarily ageing patches. We argue in favor of permanent strict fixed-location reserves. Future work should examine how stands recover old-growth forest attributes and how the associated saproxylic fauna colonizes in the long term. [ABSTRACT FROM AUTHOR]

Highlights: [•] Key saproxylic features derived from rapid habitat assessment to monitor biodiversity. [•] Snags, tree microhabitats and openness are key features for saproxylic beetles. [•] No robust structural biodiversity indicator in deciduous or coniferous temperate forests. [•] Deadwood and microhabitats effects are affected by meso/micro-climatic features. [Copyright &y& Elsevier]

1 Subsequent to the diversity of saproxylic beetles being proposed as a management tool in forestry, more explicit knowledge about the efficiency and selective properties of beetle sampling methods is needed. 2 We compared saproxylic beetle assemblages caught by alcohol-baited or unbaited window traps in different forest contexts. Considering that trap attractiveness depends on kairomone concentrations, we appraised whether the trap efficiency was influenced by trap environment (openness and local supply of fresh dead wood). 3 Saproxylic beetles were sampled using 48 cross-vane window flight traps, arranged in paired designs (alcohol-baited/unbaited), in eight ancient and eight recent gaps (open stands), and eight closed-canopy control stands in an upland beech forest in the French Pyrenees. 4 Baited traps were more efficient than unbaited traps in terms of abundance and richness in our deciduous forests. The ethanol lure did not have any repellent effect on the individual response of saproxylic taxa. 5 The influence of local environmental conditions on trap attractiveness was observed. Openness had a significant moderate effect on species richness. Trap attractiveness was slightly reduced in the alcohol-saturated environment of recent gaps probably due to a disruption by local fresh dead-wood concentrations of the kairomonal response of saproxylic beetles to baited traps (‘alcohol disruption’). 6 Because the ethanol lure enhanced the probability of species detection, it may be useful in early-warning surveillance, monitoring and control of wood borers, despite slight influences of local conditions on baited trap efficiency. [ABSTRACT FROM AUTHOR]

In most temperate deciduous forests, windstorm is the main source of dead wood. However, the effects of this natural disturbance on ambrosia and bark beetle communities are poorly known. In managed oak-hornbeam forests storm-damaged in France in 1999, we sampled ambrosia (and second bark beetles) by ethanol-baited window-flight traps in 2001. By comparing uncleared gaps, undisturbed closed-canopy controls and seedling-sapling stands, we investigated the short-term effects of gap formation, gap size and surrounding landscape to provide a snapshot of scolytid response. Contrary to expectations, neither the abundance nor the richness of ambrosia beetle species was significantly higher in gaps than in undisturbed stands. Few responses in abundance at the species level and only a slight difference in assemblage composition were detected between gaps and closed-canopy controls. Gaps were more dissimilar from seedling-sapling stands, than from closed-canopy controls. More scolytid individuals and species were caught in gaps than in seedling-sapling stands. Mean local and cumulative richness peaked in mid-size gaps. Only mid-size gaps differed from closed-canopy controls in terms of species composition. We identified generalist gap species ( Xyleborus saxesenii, X. cryptographus), but also species significantly more abundant in mid-size gaps ( Platypus cylindrus, Xyloterus signatus). The faunistic peculiarity of mid-size gaps seemed to be partly related to a bias in oak density among gap size classes. Few landscape effects were observed. Only the scolytids on the whole and X. dispar were slightly favoured by an increasing density in fellings at the 78 ha scale. We did not find any correlation between scolytid abundance and the surrounding closed-forest percentage area. We confirmed that temperate, deciduous, managed stands did not come under threat by ambrosia and bark beetle pests after the 1999 windstorm. Nonetheless, our data stressed the current expansion in Western Europe of two invasive species, X. peregrinus and especially X. germanus, now the predominant scolytid in the three oak forests studied. [ABSTRACT FROM AUTHOR]

Forest decline and dieback are growing phenomena worldwide, resulting in severe, large‐scale degradation of the canopy. This can profoundly alter the provision of trophic resources and microhabitats for canopy‐dwelling arthropods.In 2019, we assessed the effect of oak decline on the community of canopy‐dwelling Hymenoptera. We selected 21 oak stands and 42 plots, located in three forests in France, presenting contrasting levels of decline. Insects were sampled at the canopy level with green multi‐funnel and flight‐interception traps.We collected a particularly diverse community of 19,289 insect individuals belonging to 918 taxa, 10 larval trophic guilds and 7 nesting guilds.Oak decline had no effect on the abundance or richness of the overall community but significantly reshaped the community assemblages. Decline had contrasting effects depending on the taxa and guilds considered. Specialist parasitoids were more abundant at intermediate levels of decline severity while generalists were negatively affected. Taxa depending on ground‐related resources and microhabitats were promoted. Saproxylic taxa were more abundant while xylophagous insects were negatively impacted.Reduced leaf area index promoted several guilds and the diversity of the overall community. While an increasing tree mortality rate enhanced the abundance and diversity of deadwood resources, it had negative impacts on several Hymenoptera guilds. Our results suggest that micro‐environmental changes at the ground level due to canopy decline have major cascading effects on the communities of canopy‐dwelling Hymenoptera.Our study highlights the relevance of studying Hymenoptera communities to investigate the outcomes of disturbances on forest biodiversity. [ABSTRACT FROM AUTHOR]

Stump harvesting after clear-felling may be detrimental for species’ landscape-scale persistence. Sensitivity to it is most likely due to reductions in habitat density, resulting in a non-linear relationship between population size and total habitat amount (i.e. fragmentation effects). Here we summarize theoretical expectations and empirical findings on fragmentation effects in stumps and other types of dead wood in disturbed forest habitats and draw conclusions about the consequences of stump harvesting. Within disturbed patches, some negative fragmentation effects have been observed for beetles and lichens, but most studies have found a linear relationship between habitat amount and population size. At landscape scale, evidence of fragmentation effects in disturbed forest habitats has been detected in some published investigations, but none of them focused on stumps. Thus, although organisms associated with disturbed forest habitats are assumed to be strong dispersers, they may still be sensitive to habitat fragmentation. We conclude that stump harvesting at a moderate level is not likely to increase risks for landscape-scale species extinctions markedly, despite clearly negative local effects. However, due to large uncertainties, adaptive management with monitoring of dead wood-dependent species should be applied wherever stump harvesting is more extensive. [ABSTRACT FROM PUBLISHER]

In most European temperate forests, the heavy harvesting of low-quality wood for energy, a low minimum harvest diameter and a short rotation period, result in the limited deadwood resources. However, areas are being set aside in managed forests to restore deadwood levels. Coppice-with-standards is a silvicultural method characterized by periodic logging which clear-cuts coppice trees and removes some standard trees. We studied the deadwood profile (i.e., both amount and diversity) in oak-beech coppice-with-standards over time-since-the-last-harvest in order to evaluate how long it takes to recover significantly high amounts and diversity of deadwood substrates. A total of 282 circular 500-m2 plots were set up in 24 forests in southwestern France. We sampled five time-since-harvest classes within 80 years of the time elapsed since the last harvest. At the plot level, we used Generalized Linear Mixed Models to compare both deadwood volume and diversity among time classes. Diversity was also compared within time classes through accumulation curves. Deadwood legacies were very scarce after harvesting, both for volume and diversity. It took more than 70 years for deadwood amounts to become significantly higher than just after harvest; deadwood diversity was significantly higher only 30-50 years after harvesting due to quick snag recruitment. Crown deadwood, a particularly specialized resource rarely recorded, provided roughly 10-20% of the total deadwood amount throughout the study period and should be systematically recorded in further studies. Time-since-the-last-harvest was the best explanatory variable for both deadwood volume and diversity. We therefore recommend installing permanent set-aside areas to ensure deadwood conservation. [ABSTRACT FROM AUTHOR]

Abstract: Aim: Biodiversity monitoring and conservation are extremely complex, and surrogate taxa may represent proxies to test methods and solutions. However, cross‐taxon correlations in species diversity (i.e., cross‐taxon congruence) may vary widely with spatial scale. Our goal is to assess how cross‐taxon congruence varies with spatial scale in European temperate forests. We expect that congruence in species diversity increases when shifting from fine to coarse spatial scales, with differences between species richness and composition, and across pairs of taxonomic groups. Location: European temperate forests. Time period: Present. Major taxa studied: Vascular plants, bryophytes, birds, epiphytic lichens, saproxylic beetles and wood‐inhabiting fungi. Methods: We used field data (354 plots across 23 sites) encompassing Italy, France and Hungary, with species information for six taxonomic groups. We accounted separately for spatial grain (the size of elementary sampling unit) and extent (the geographical area included in the survey) and evaluated the relationships within all the possible pairs of taxa. Results: Although no pair of taxa had its species richness consistently correlated across scales, we found no changes in the direction of correlations when analysing species composition. However, when increasing grain and extent, we did find a general increase in the magnitude of correlations in species composition and partial changes in significance, with plants having the highest number of significant correlations. Main conclusions: Species richness congruence among taxa is strongly scale dependent owing to differences in the relative contribution of large‐ and small‐scale processes across taxa. Cross‐taxon congruence in species composition is scale dependent only for its magnitude, because life‐history traits of individual species make responses to environmental factors similar across scales. Forest monitoring should consider multi‐taxon sampling and limit the use of surrogates at specific spatial scales, especially for species richness. Sampling plant species composition in scattered plots across different sites may effectively summarize the whole community composition. [ABSTRACT FROM AUTHOR]