Unprecedented bark beetle outbreaks have been observed for a variety of forest ecosystems recently, and damage is expected to further intensify as a consequence of climate change. In Central Europe, ...the response of ecosystem management to increasing infestation risk has hitherto focused largely on the stand level, while the contingency of outbreak dynamics on large‐scale drivers remains poorly understood. To investigate how factors beyond the local scale contribute to the infestation risk from Ips typographus (Col., Scol.), we analysed drivers across seven orders of magnitude in scale (from 10³ to 10¹⁰ m²) over a 23‐year period, focusing on the Bavarian Forest National Park. Time‐discrete hazard modelling was used to account for local factors and temporal dependencies. Subsequently, beta regression was applied to determine the influence of regional and landscape factors, the latter characterized by means of graph theory. We found that in addition to stand variables, large‐scale drivers also strongly influenced bark beetle infestation risk. Outbreak waves were closely related to landscape‐scale connectedness of both host and beetle populations as well as to regional bark beetle infestation levels. Furthermore, regional summer drought was identified as an important trigger for infestation pulses. Large‐scale synchrony and connectivity are thus key drivers of the recently observed bark beetle outbreak in the area. Synthesis and applications. Our multiscale analysis provides evidence that the risk for biotic disturbances is highly dependent on drivers beyond the control of traditional stand‐scale management. This finding highlights the importance of fostering the ability to cope with and recover from disturbance. It furthermore suggests that a stronger consideration of landscape and regional processes is needed to address changing disturbance regimes in ecosystem management.
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BFBNIB, FZAB, GIS, IJS, KILJ, NLZOH, NMLJ, NUK, OILJ, PNG, SAZU, SBCE, SBMB, UL, UM, UPUK
The majority of wood decomposing fungi are mushroom-forming Agaricomycetes, which exhibit two main modes of plant cell wall decomposition: white rot, in which all plant cell wall components are ...degraded, including lignin, and brown rot, in which lignin is modified but not appreciably removed. Previous studies suggested that brown rot fungi tend to be specialists of gymnosperm hosts and that brown rot promotes gymnosperm specialization. However, these hypotheses were based on analyses of limited datasets of Agaricomycetes. Overcoming this limitation, we used a phylogeny with 1157 species integrating available sequences, assembled decay mode characters from the literature, and coded host specialization using the newly developed R package, rusda.
We found that most brown rot fungi are generalists or gymnosperm specialists, whereas most white rot fungi are angiosperm specialists. A six-state model of the evolution of host specialization revealed high transition rates between generalism and specialization in both decay modes. However, while white rot lineages switched most frequently to angiosperm specialists, brown rot lineages switched most frequently to generalism. A time-calibrated phylogeny revealed that Agaricomycetes is older than the flowering plants but many of the large clades originated after the diversification of the angiosperms in the Cretaceous.
Our results challenge the current view that brown rot fungi are primarily gymnosperm specialists and reveal intensive white rot specialization to angiosperm hosts. We thus suggest that brown rot associated convergent loss of lignocellulose degrading enzymes was correlated with host generalism, rather than gymnosperm specialism. A likelihood model of host specialization evolution together with a time-calibrated phylogeny further suggests that the rise of the angiosperms opened a new mega-niche for wood-decay fungi, which was exploited particularly well by white rot lineages.
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1. The successional dynamics of forests—from canopy openings to regeneration, maturation, and decay—influence the amount and heterogeneity of resources available for forest-dwelling organisms. ...Conservation has largely focused only on selected stages of forest succession (e.g., late-seral stages). However, to develop comprehensive conservation strategies and to understand the impact of forest management on biodiversity, a quantitative understanding of how different trophic groups vary over the course of succession is needed. 2. We classified mixed mountain forests in Central Europe into nine successional stages using airborne LiDAR. We analysed α- and β-diversity of six trophic groups encompassing approximately 3,000 species from three kingdoms. We quantified the effect of successional stage on the number of species with and without controlling for species abundances and tested whether the data fit the more-individuals hypothesis or the habitat heterogeneity hypothesis. Furthermore, we analysed the similarity of assemblages along successional development. 3. The abundance of producers, first-order consumers, and saprotrophic species showed a U-shaped response to forest succession. The number of species of producer and consumer groups generally followed this U-shaped pattern. In contrast to our expectation, the number of saprotrophic species did not change along succession. When we controlled for the effect of abundance, the number of producer and saproxylic beetle species increased linearly with forest succession, whereas the U-shaped response of the number of consumer species persisted. The analysis of assemblages indicated a large contribution of succession-mediated β-diversity to regional γ-diversity. 4. Synthesis and applications. Depending on the species group, our data supported both the more-individuals hypothesis and the habitat heterogeneity hypothesis. Our results highlight the strong influence of forest succession on biodiversity and underline the importance of controlling for successional dynamics when assessing successional stages with highest diversity (early and late successional stages) are currently strongly underrepresented in the forests of Central Europe. We thus recommend that conservation strategies aim at a more balanced representation of all successional stages.
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•Windstorms and bark beetle outbreaks restored natural forests in the Bohemian Forest.•Increased dead wood amount and insolation contributed to increasing biodiversity.•Retention of legacies ...maintains biodiversity in salvage logging.
Severe natural disturbances are common in many forest ecosystems, particularly in the Northern Hemisphere. Attempts to minimize their effects through forest management include salvage logging. In the Bohemian Forest, one of Central Europe’s largest continuous forests, windstorms and bark beetle outbreaks have affected stands of Norway Spruce for centuries. Over the past decades, these natural disturbances and their management in the Bavarian Forest National Park and the adjacent Šumava National Park in the central part of the Bohemian Forest have been scientifically studied. Owing to a benign-neglect strategy, both windstorms and bark beetle outbreaks have increased stand structural heterogeneity, the amount of dead wood and light availability, which contribute to increased populations of nearly-extinct forest specialists. However, the response of a particular taxonomic group or species strongly depends on its relationship to specific legacies that persist after disturbances. Stand climate but not dead wood appears to greatly influence the diversity of epigeal bryophytes, whereas both factors determine the diversity of epixylic bryophytes. Both the amount and heterogeneity of dead wood seems to be more important than stand climate in determining assemblages of wood-inhabiting fungi and lichens. To reduce the population density of bark beetles in the management zones of both national parks, storm-felled spruces are salvage logged, which alters a variety of these legacies and natural successional pathways. Consequently, the numbers of species of wood-inhabiting fungi, saproxylic beetles and epixylic lichens are reduced. Natural levels of biodiversity in salvage-logged areas can be preserved by (1) preserving root plates of storm-felled trees with partly retained trunks; (2) avoiding soil disturbance by using cable yarding instead of harvesters; (3) retaining sun-exposed dry branches of storm-felled trees and snags of beetle-killed spruces; (4) avoiding logging damage of natural regeneration and of large trees that survive disturbances; and (5) bark scratching instead of debarking to avoid bark beetle outbreaks while maintaining biodiversity. Windstorms and bark beetle outbreaks could be utilized to restore intensely managed forests of Central Europe to their natural composition and structure. Furthermore, experimentally mimicked natural disturbances might help in gaining a mechanistic understanding of how natural disturbances affect biodiversity.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK, ZRSKP
The evolutionary split between gymnosperms and angiosperms has far‐reaching implications for the current communities colonizing trees. The inherent characteristics of dead wood include its role as a ...spatially scattered habitat of plant tissue, transient in time. Thus, local assemblages in deadwood forming a food web in a necrobiome should be affected not only by dispersal ability but also by host tree identity, the decay stage and local abiotic conditions. However, experiments simultaneously manipulating these potential community drivers in deadwood are lacking. To disentangle the importance of spatial distance and microclimate, as well as host identity and decay stage as drivers of local assemblages, we conducted two consecutive experiments, a 2‐tree species and 6‐tree species experiment with 80 and 72 tree logs, respectively, located in canopy openings and under closed canopies of a montane and a lowland forest. We sampled saproxylic beetles, spiders, fungi and bacterial assemblages from logs. Variation partitioning for community metrics based on a unified framework of Hill numbers showed consistent results for both studies: host identity was most important for sporocarp‐detected fungal assemblages, decay stage and host tree for DNA‐detected fungal assemblages, microclimate and decay stage for beetles and spiders and decay stage for bacteria. Spatial distance was of minor importance for most taxa but showed the strongest effects for arthropods. The contrasting patterns among the taxa highlight the need for multi‐taxon analyses in identifying the importance of abiotic and biotic drivers of community composition. Moreover, the consistent finding of microclimate as the primary driver for saproxylic beetles compared to host identity shows, for the first time that existing evolutionary host adaptions can be outcompeted by local climate conditions in deadwood.
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FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SBCE, SBMB, UL, UM, UPUK
Abstract
Climate change affects ecosystems worldwide and is threatening biodiversity. Insects, as ectotherm organisms, are strongly dependent on the thermal environment. Yet, little is known about ...the effects of summer heat and drought on insect diversity. In the Mediterranean climate zone, a region strongly affected by climate change, hot summers might have severe effects on insect communities. Especially the larval stage might be sensitive to thermal variation, as larvae—compared to other life stages—cannot avoid hot temperatures and drought by dormancy. Here we ask, whether inter-annual fluctuations in Mediterranean moth diversity can be explained by temperature (T
Larv
) and precipitation during larval development (H
Larv
). To address our question, we analyzed moth communities of a Mediterranean coastal forest during the last 20 years. For species with summer-developing larvae, species richness was significantly negatively correlated with T
Larv
, while the community composition was affected by both, T
Larv
and H
Larv
. Therefore, summer-developing larvae seem particularly sensitive to climate change, as hot summers might exceed the larval temperature optima and drought reduces food plant quality. Increasing frequency and severity of temperature and drought extremes due to climate change, therefore, might amplify insect decline in the future.
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IZUM, KILJ, NUK, PILJ, PNG, SAZU, UL, UM, UPUK
Tree-killing bark beetles are the most economically important insects in conifer forests worldwide. However, despite >200 years of research, the drivers of population eruptions and crashes are still ...not fully understood and the existing knowledge is thus insufficient to face the challenges posed by the Anthropocene. We critically analyze potential biotic and abiotic drivers of population dynamics of an exemplary species, the European spruce bark beetle (ESBB) (Ips typographus) and present a multivariate approach that integrates the many drivers governing this bark beetle system. We call for hypothesis-driven, large-scale collaborative research efforts to improve our understanding of the population dynamics of this and other bark beetle pests. Our approach can serve as a blueprint for tackling other eruptive forest insects.
Bark beetles are currently causing unprecedented damage to European and North American forests.Their population dynamics rarely have been studied in a hypothesis-driven manner incorporating exogenous biotic variables.We propose a conceptual framework to reveal the drivers of bark beetle populations.This approach can be equally applied to other eruptive insect pests.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
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.
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Deadwood is an important structural component in forest ecosystems and plays a significant role in global carbon and nutrient cycling. Relatively little is known about the formation and decomposition ...of CWD by microbial communities in situ and about the factors controlling the associated processes. In this study, we intensively analyzed the molecular fungal community composition and species richness in relation to extracellular enzyme activity and differences in decomposing sapwood and heartwood of 13 temperate tree species (four coniferous and nine deciduous species, log diameter 30-40 cm and 4 m long) in an artificial experiment involving placing the logs on the forest soil for six years. We observed strong differences in the molecular fungal community composition and richness among the 13 tree species, and specifically between deciduous and coniferous wood, but unexpectedly no difference was found between sapwood and heartwood. Fungal species richness correlated positively with wood extractives and negatively with fungal biomass. A distinct fungal community secreting lignocellulolytic key enzymes seemed to dominate the decomposition of the logs in this specific phase. In particular, the relative sequence abundance of basidiomycetous species of the Meruliaceae (e.g. Bjerkandera adusta) correlated with ligninolytic manganese peroxidase activity. Moreover, this study reveals abundant white-rot causing Basidiomycota and soft-rot causing Ascomycota during this phase of wood decomposition.
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Major environmental gradients co-vary with elevation and have been a longstanding natural tool allowing ecologists to study global diversity patterns at smaller scales, and to make predictions about ...the consequences of climate change. These analyses have traditionally studied taxonomic diversity, but new functional diversity approaches may provide a deeper understanding of the ecological mechanisms driving species assembly. We examined lichen taxonomic and functional diversity patterns on 195 plots (200 m²) together with forest structure along an elevational gradient of 1000 m in a temperate low mountain range (Bohemian Forest, Germany). Along this elevation gradient temperature decreased and precipitation increased, two macroclimatic variables critical for lichens. Elevation was more important than forest structure in driving taxonomic and functional diversity. While species richness increased with elevation, functional diversity decreased and revealed that community patterns shift with elevation from random to clustered, reflecting selection for key shared traits. Higher elevations favored species with a complex growth form (which takes advantage of high moisture) and asexual reproductive mode (facilitating establishment under low temperature conditions). Our analysis highlights the need to examine alternative forms of diversity and opens the avenue for community predictions about climate change. For a regional scenario with increasing temperature and decreasing availability of moisture, we expect a loss of specialized species with a complex growth form and those with vegetative organs at higher elevations in low mountain ranges in Europe.
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