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1. Dead wood is a habitat for numerous fungal species, many of which are important agents of decomposition. Previous studies suggested that wood-inhabiting fungal communities are affected by climate, availability of dead wood in the surrounding landscape and characteristics of the colonized dead-wood object (e.g. host tree species). These findings indicate that different filters structure fungal communities at different scales, but how these factors individually drive fungal fruiting diversity on dead-wood objects is unknown. 2. We conducted an orthogonal experiment comprising 180 plots (0.1 ha) in a random block design and measured fungal fruit body richness and community composition on 720 dead-wood objects over the first 4 years of succession. The experiment allowed us to disentangle the effects of the host (beech and fir; logs and branches) and the environment (microclimate: sunny and shady plots; local dead wood: amount and heterogeneity of dead wood added to plot). 3. Variance partitioning revealed that the host was more important than the environment for the diversity of wood-inhabiting fungi. A more detailed model revealed that host tree species had the highest independent effect on richness and community composition of fruiting species of fungi. Host size had significant but low independent effects on richness and community composition of fruiting species. Canopy openness significantly affected the community composition of fruiting species. By contrast, neither local amount nor heterogeneity of dead wood significantly affected the fungal diversity measures. 4. Synthesis. Our study identified host tree species as a more important driver of the diversity of wood-inhabiting fungi than the environment, which suggests a hostcentred filter of this diversity in the early phase of the decomposition process. For the conservation of wood-inhabiting fungi, a high variety of host species in various microclimates is more important than the availability of dead wood at the stand level.

Resource availability and habitat heterogeneity are principle drivers of biodiversity, but their individual roles often remain unclear since both factors are usually correlated. The biodiversity of species dependent on dead wood could be driven by either resource availability represented by dead‐wood amount or habitat heterogeneity characterized by dead‐wood diversity or both. Understanding their roles is crucial for improving evidence‐based conservation strategies for saproxylic species in managed forests. To disentangle the effects of dead‐wood amount and dead‐wood diversity on biodiversity relative to canopy openness (microclimate), we experimentally exposed different amounts of logs and branches of two different tree species representing a gradient of dead‐wood diversity in 190 sunny and shady forest plots. During the 3 years after exposing dead wood, we sampled saproxylic beetles, which are together with fungi the most diverse and important taxonomic group involved in decomposition of wood. The composition of saproxylic beetle assemblages differed clearly between shady and sunny forest plots, with higher richness in sunny plots. Both dead‐wood amount and dead‐wood diversity positively and independently affected species richness of saproxylic beetles, but these effects were mediated by canopy openness. In sunny forest, species richness increased with increasing amount of dead wood, whereas in shady forest, dead‐wood diversity was the prevailing factor. The stepwise analysis of abundance and species richness, however, indicated that effects of both factors supported only the habitat‐heterogeneity hypothesis, as the positive effect of high amounts of dead wood could be explained by cryptic variability of dead‐wood quality within single objects. Synthesis and applications. As canopy openness and habitat heterogeneity seem to be the major drivers of saproxylic beetle diversity in temperate forests, we recommend that managers aim to increase the heterogeneity of dead‐wood substrates under both sunny and shady forest conditions. Intentional opening of the canopy should be considered in anthropogenically homogenized, dense forests. Specifically in temperate mixed montane forests, dead wood should be provided in the form of large logs in sunny habitats and a high diversity of different dead‐wood substrates should be retained or created in shady forests.

The habitat-amount hypothesis challenges traditional concepts that explain species richness within habitats, such as the habitat-patch hypothesis, where species number is a function of patch size and patch isolation. It posits that effects of patch size and patch isolation are driven by effects of sample area, and thus that the number of species at a site is basically a function of the total habitat amount surrounding this site. We tested the habitat-amount hypothesis for saproxylic beetles and their habitat of dead wood by using an experiment comprising 190 plots with manipulated patch sizes situated in a forested region with a high variation in habitat amount (i.e., density of dead trees in the surrounding landscape). Although dead wood is a spatio-temporally dynamic habitat, saproxylic insects have life cycles shorter than the time needed for habitat turnover and they closely track their resource. Patch size was manipulated by adding various amounts of downed dead wood to the plots (∼800 m3 in total); dead trees in the surrounding landscape (∼240 km2) were identified using airborne laser scanning (light detection and ranging). Over 3 yr, 477 saproxylic species (101,416 individuals) were recorded. Considering 20–1,000 m radii around the patches, local landscapes were identified as having a radius of 40–120 m. Both patch size and habitat amount in the local landscapes independently affected species numbers without a significant interaction effect, hence refuting the island effect. Species accumulation curves relative to cumulative patch size were not consistent with either the habitat-patch hypothesis or the habitat-amount hypothesis: several small dead-wood patches held more species than a single large patch with an amount of dead wood equal to the sum of that of the small patches. Our results indicate that conservation of saproxylic beetles in forested regions should primarily focus on increasing the overall amount of dead wood without considering its spatial arrangement. This means dead wood should be added wherever possible including in local landscapes with low or high dead-wood amounts. For species that have disappeared from most forests owing to anthropogenic habitat degradation, this should, however, be complemented by specific conservation measures pursued within their extant distributional ranges.

Standing dead trees (snags) decompose more slowly than downed dead wood and provide critical habitat for many species. The rate at which snags fall therefore influences forest carbon dynamics and biodiversity. Fall rates correlate strongly with mean annual temperature, presumably because warmer climates facilitate faster wood decomposition and hence degradation of the structural stability of standing wood. These faster decomposition rates coincide with turnover from fungal-dominated wood decomposer communities in cooler forests to codomination by fungi and termites in warmer regions. A key question for projecting forest dynamics is therefore whether temperature effects on wood decomposition arise primarily because warmer conditions facilitate faster decomposer metabolism, or are also influenced indirectly by belowground community turnover (e.g., termites exert additional influence beyond fungal-plus-bacterial mediated decomposition). To test between these possibilities, we simulate standing dead trees with untreated wooden posts and follow them in the field across 5 yr at 12 sites, before measuring buried, soil–air interface and aerial post sections to quantify wood decomposition and organism activities. High termite activities at the warmer sites are associated with rates of postfall that are three times higher than at the cooler sites. Termites primarily consume buried wood, with decomposition rates greatest where termite activities are highest. However, where higher microbial and termite activities co-occur, they appear to compensate for one another first, and then to slow decomposition rates at their highest activities, suggestive of interference competition. If the range of microbial and termite codomination of wood decomposer communities expands under climate warming, our data suggest that expansion will accelerate snag fall with consequent effects on forest carbon cycling and biodiversity in forests previously dominated by microbial decomposers.

Coarse woody debris (CWD) is an important pool of carbon in forest ecosystems and is present in all strata as fallen, standing or suspended CWD. However, there are relatively few decomposition studies of CWD in tropical forests compared with temperate forests, and research on suspended CWD in particular has largely not been attempted. Termites are important decomposers in tropical ecosystems yet their role relative to microbial decomposers and the importance of the vertical location of CWD has rarely been considered. For the first time, we examined the relative contribution of macro-invertebrates (predominantly termites) and microbes to the decay of suspended and ground-placed (fallen) CWD in lowland, tropical rainforest. We set up wood baits (Pinus radiata) with and without termite access, and measured wood mass loss after 1 year. Mass loss of ground-placed CWD assays was over four times greater than suspended CWD assays. Termite decomposition was vertically stratified with termites having a large relative contribution to the decomposition of ground-placed CWD and a negligible contribution to the decomposition of suspended CWD. In contrast, the effect of microbes on decomposition was low and not vertically stratified. Although our results support the findings of temperate studies in that decomposition of CWD is dependent on its physical location, we show that in tropical rainforests this is predominantly due to greater termite decomposition on the forest floor. Suspended CWD remains an important carbon sink due to slow microbial decay until it falls to the forest floor where it is more accessible to termites.

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

In the context of global change, a better understanding of the dynamics of wood degradation, and how they relate to tree attributes and climatic conditions, is necessary to improve broad‐scale assessments of the contributions of deadwood to various ecological processes, and ultimately, for the development of adaptive post‐disturbance management strategies. The objective of this meta‐analysis was to review the effects of tree attributes and local climatic conditions on the time since death of coarse woody debris ranging in decomposition states. Results from our meta‐analysis showed that projected warming will likely accelerate wood decomposition and significantly decrease the residence time in decay stages. By promoting such a decrease in residence time, further climate warming is very likely to alter the dynamics of deadwood, which in turn may affect saproxylic biodiversity by decreasing the temporal availability of specific habitats. Moreover, while coarse woody debris has been recognized as a key resource for bioenergy at the global scale, the acceleration of decay‐stages transition dynamics indicates that the temporal window during which dead trees are available as feedstock for value‐added products will shrink. Consequently, future planning and implementation of salvage harvesting will need to occur within a short period following disturbance, especially in warmer regions dominated by hardwood species. Another important contribution of this work was the development of a harmonized classification system that relies on the correspondence between the visual criteria used to characterize deadwood decomposition stages in locally developed systems the literature. This system could be used in future investigations to facilitate direct comparisons between studies. Our literature survey also highlights that most of the information on wood decay dynamics comes from temperate and boreal forests, whereas data from subtropical, equatorial and subarctic forests are scarce. Such data are urgently needed to allow broader‐scale conclusions on global wood degradation dynamics. Using a meta‐analysis, we reviewed the effects of tree attributes and local climate on the time‐since‐death of coarse woody debris ranging in decomposition states. Our results suggest that warming will accelerate wood decomposition and significantly decrease the residence time in decay stages, leading to a decreased temporal window during which dead trees are available as feedstock for value‐added products. We also developed a harmonized classification system which could be used to facilitate comparisons between further studies and enable broader‐scale conclusions on global wood degradation dynamics.

Aim: Climate change is expected to have major impacts on terrestrial biodiversity at all ecosystem levels, including reductions in species-level distribution and abundance. We aim to test the extent to which land use management, such as setting-aside forest from production, could reduce climate-induced biodiversity impacts for specialist species over large geographical gradients. Location: Sweden. Methods: We applied ensembles of species distribution models based on citizen science data for six species of red-listed old-forest indicator fungi confined to spruce dead wood. We tested the effect on species habitat suitabilities of alternative climate change scenarios and varying amounts of forest set-aside from production over the coming century. Results: With 3.6% of forest area set-aside from production and assuming no climate change, overall habitat suitabilities for all six species were projected to increase in response to maturing spruce in set-aside forest. However, overall habitat suitabilities for all six species were projected to decline under climate change scenario RCP4.5 (intermediate-low emissions), with even greater declines projected under RCP 8.5 (high emissions). Increasing the amount of forest set-aside to 16% resulted in significant increases in overall habitat suitability, with one species showing an increase. A further increase to 32% forest set-aside resulted in considerably more positive trends, with three of six species increasing. Main conclusions: There is interspecific variation in the importance of future macroclimate and resource availability on species occurrence. However, large-scale conservation measures, such as increasing resource availability through setting aside forest from production, could reduce future negative effects from climate change, and early investment in conservation is likely to reduce the future negative impacts of climate change on specialist species.

Due to global change, temperate forests are expected to face growing threats to forest health (e.g. insects/disease) and increasing probabilities of severe disturbances (e.g. wildfires), which may result in amplified tree mortality against a backdrop of a changing climate and associated ecosystem/atmospheric feedbacks (i.e. increased rates of dead wood decay/combustion). Despite these expectations, we lack a fundamental understanding of current forest biomass trends among live and dead components across large spatial and temporal domains. The goal of this study was to examine changes in forest biomass components (downed dead wood (DDW), standing dead trees (SDs), and live trees) across coterminous US forests using a nation-wide, multi-decade (∼2006–2010 to ∼2015–2019) repeated forest inventory at the scale of regional ecosystems. It was found that the total biomass stocks of DDW, standing dead, and live trees all increased (18.3%, 14.7%, and 3.9%, respectively) with biomass accumulation in large live trees coupled with increases in the biomass of smaller sized down dead wood illustrating the influence of stand development across US forests at the scale of individual forest ecosystems (i.e. self-thinning). Coupled with this observation, tremendous positive skew of biomass change across all biomass components and size classes demonstrates the ability of severe but episodic disturbance events to produce substantial biomass inputs to SD and DDW pools with legacy effects exceeding the period of this study. Overall, against a backdrop of expected future global change and growing interest in the maintenance of the terrestrial forest carbon pool, the incorporation of dead wood-focused analytics such as decay-related functional traits, microbial/fungal community assessments, or dead/live biomass relationships into broader forest carbon/biomass monitoring efforts is essential.

The Middle-spotted Woodpecker is an indicator of structurally complex deciduous forests, typically associated with mature oak stands but occasionally found in beech dominated forests, including at elevations exceeding 1,000 m. Although standing dead wood is often used for nesting and foraging, its necessity for the species’ occurrence remains debated. This study examined the relationship between D. medius presence and standing dead wood characteristics in beech-dominated low-mountain forests of the Perșani Mountains, central Romania. Standardized national woodpecker monitoring protocols were applied at 25 fixed points. Standing dead wood variables (density, diameter at breast height (DBH), height, volume, and basal area) were measured across three habitat categories: all forest types, mature and old stands (> 70 years), and stands containing at least 10% oak. Snag density did not differ significantly between plots with and without Middle-spotted Woodpecker, yet occupied plots contained taller and thicker snags, with predicted occurrence probabilities highest at DBH > 60 cm and height > 25 m. No significant differences were found for basal area or volume. In predominantly beech stands, the species’ presence appeared to be influenced by the availability of standing dead wood and the presence of rough-barked species. These findings confirm the species’ strong association with mature deciduous forests, particularly where oak is present. The increasing probability of occurrence with higher oak proportions in standing dead wood underscores the ecological importance of conserving large, old trees and mixed forest structures for Middle-spotted Woodpecker persistence.