Abstract Smaller insect species are routinely described later than larger species, perpetuating the Linnean shortfall. Using 425 saproxylic beetle species from 28 veteran oak sites, we test whether body size varied with year of description and earliest georeferenced record year, and whether body length predicted detection probability. Linear models show a significant negative relationship between body length and both year of description ( β = −0.00063 ± 0.00021 SE, p = 0.003) and earliest georeferenced year ( β = −0.00057 ± 0.00024 SE, p = 0.016). Single‐season occupancy models reveal only a marginal size effect on detection ( β = −0.021, p = 0.055); instead, the trophic group drives variation, with sapro‐xylophagous species detected most readily. Fourteen species remain undescribed, and 29% lack any georeferenced record, highlighting combined Linnean and Wallacean shortfalls. Historical taxonomic bias towards conspicuous species and methodological undersampling of specific trophic guilds together impede accurate biodiversity assessment. We recommend integrated taxonomic revision, diversified trapping protocols and trait‐based occupancy models to rectify these biases and improve conservation planning.

Boreal forests are important carbon sinks and host a diverse array of species that provide important ecosystem functions. Boreal forests have a long history of intensive forestry, in which even-aged management with clear-cutting has been the dominant harvesting practice for the past 50-80 years. As a second cycle of clear-cutting is emerging, there is an urgent need to examine the effects of repeated clear-cutting events on biodiversity. Clear-cutting has led to reduced numbers of old and large trees, decreased volumes of dead wood of varied decay stages and diameters, and altered physical and chemical compositions of soils. The old-growth boreal forest has been fragmented and considerably reduced. Here, we review short- and long-term (≥50 years) effects of clear-cutting on boreal forest biodiversity in four key substrates: living trees, dead wood, ground and soil. We then assess landscape-level changes (habitat fragmentation and edge effects) on this biodiversity. There is evidence for long-term community changes after clear-cutting for several taxa: epiphytic lichens; saproxylic fungi, bryophytes and insects; epigeic bryophytes; and soil snails, bacteria, and ectomycorrhizal fungi. Long-term declines in species richness were found for saproxylic fungi, bryophytes and true flies. However, for the majority of taxa, long-term effects of clear-cutting are not well understood. On the landscape level, reduced connectivity to old-growth forests has negative effects on several species of fungi, lichens, bryophytes and insects, notably among Red-Listed species. Furthermore, altered microclimate near clear-cut edges negatively affects epiphytic lichens and epigeic arthropods, implying complex effects of habitat fragmentation. Repeated cycles of clear-cutting might pose even stronger pressures on boreal forest biodiversity due to continued fragmentation of old-growth forests and accumulation of extinction debts. Examining the broad effects of forestry on biodiversity across the boreal biome is crucial: (i) to increase our knowledge of long-term and landscape-level effects of former clear-cutting; and (ii) to gain a better understanding of how forestry will affect biodiversity and, subsequently, ecosystem functioning, with repeated cycles of clear-cutting.

The widespread introduction of clear-cutting to Fennoscandia in the 1950s led to fundamentally altered forest structure and reduced volume and quality of deadwood-a key resource for saproxylic organisms. As previously clear-cut forests now approach economic maturity, the long-term ecological effects of this management practice on saproxylic beetle communities become measurable. We sampled beetles using flight interception traps in 12 paired Norway spruce forest stands in southeastern Norway: one previously clear-cut and approaching maturity, and one never clear-cut (near-natural), but with otherwise similar conditions. We found that clear-cutting negatively impacted the richness and abundance of red-listed species. In addition, we found weak evidence for the effect on species composition. The total saproxylic beetle richness, abundance and within-stand beta diversity were similar in the two forest management types. Both red-listed and total saproxylic beetle richness were positively associated with deadwood diversity at the stand scale. Our findings underscore the importance of preserving near-natural forests as refugia for red-listed saproxylic beetles, while highlighting the need to enhance deadwood diversity and structural complexity in managed forest stands to better support saproxylic biodiversity.

Beetles (Coleoptera) are one of the most diverse insect groups, playing vital roles in ecosystem functions such as decomposition and pollination. Despite their ecological importance, their immense diversity is often under-sampled due to inconsistent and non-standardised sampling methodologies. We assessed the sampling efficiency of flight interception traps using six trap designs that differed in shape and panel material in a hemiboreal, mixed deciduous forest. We compared the designs in terms of overall coleopteran species richness, abundance, and diversity, as well as saproxylic coleopteran species richness. Trap efficiency was evaluated using species accumulation curves. We collected a total of 457 beetle species (8552 individuals) from 51 families, including 272 saproxylic species. Although species accumulation curves showed signs of flattening, significant differences were observed among trap designs. Panels made of soft plastic (polyethylene) outperformed those made of hard plastic (polycarbonate) in terms of species diversity and the proportion of red-listed species captured. No differences in body size were detected among the trap catches. Our results highlight an overlooked yet significant effect of panel material in sampling beetle communities. The combination of soft plastic panels with a triangular trap design significantly improved trap efficiency. This improvement not only enhanced the capture of common beetle species but also resulted in a higher sampling rate of those of conservation concern. These findings underscore the importance of selecting appropriate trap designs to increase the accuracy of biodiversity assessments to make better-informed conservation decisions. A standardised trap design would enhance comparability across studies, improving ecological inferences.

The history of forestry in Fennoscandia spans five centuries, with clear-cutting being the dominant practice since the mid-20th century. This has led to a significant transformation of the forest landscape. In this study we investigated long-term effects of clear-cutting on forest structure and dead wood volumes. We established twelve pairs of spruce forest sites in southeastern Norway, each pair constituting of a mature, previously clear-cut stand and its near-natural counterpart with similar edaphic factors. The near-natural stands had 2.8 times higher volumes of dead wood and a larger proportion of dead wood in late stages of decay. The near-natural stands had on average 36.8 f 9.1 m(3) ha(-1) of downed dead wood and 24.1 f 6.2 m(3) ha(-1) of standing dead wood. Corresponding numbers for the previously clear-cut stands were 10.2 f 2.8 m(3) ha(-1) and 11.9 f 3.7 m(3) ha(-1). Forests with lower volumes of dead wood often also had lower connectivity of old spruce forests, which potentially have further negative effects on biodiversity. Furthermore, near-natural stands displayed greater tree size heterogeneity, resulting in a wider variation in light conditions. While no difference was observed in living tree volume, we found only weak evidence for higher basal area in the previously clear-cut stands, which had a higher stem density with more slender stems and shorter crowns. Our findings suggest that managed forests do not develop structures typical of near-natural forests before they become mature for logging. We stress the importance of a thorough site selection for studies of management effects, as forest management history may be confounded with productivity and other edaphic factors. Experimental designs like ours are vital for testing how differences in structure and deadwood volumes, driven by forest management, translate into variations in biodiversity, carbon sequestration and ecosystem functioning in future studies.

The role of insects in the transfer of radionuclides has received little attention, despite their key role in nutrient cycling within ecosystems. In this study, we investigated the trophic food chain transfer of radiocaesium (137Cs) from reindeer meat to the blowfly Calliphora vicina (Robineau-Desvoidy) (Diptera: Calliphoridae) and further from blowfly pupae to the parasitoid wasp Nasonia vitripennis (Walker) (Hymenoptera: Pteromalidae). Radiocaesium was transferred to blowfly larvae during their feeding stage, with the highest whole-organism to food source concentration ratios (CRwo-fs) being found in actively feeding third instar blowfly larvae, with CRwo-fs in the range of 0.68-0.90. CRwo-fs in blowfly larvae at later developmental stages (i.e., post-feeding stage, prepupal stage, pupal stage, and adult stage) were significantly lower, with CRwo-fs in adult flies in the range of 0.07-0.10. Modelling of the data indicated that >70 % of the radiocaesium present in third instar feeding stage larvae was removed exponentially with excreta prior to pupariation. Furthermore, on average 49 % of the radiocaesium activity concentration assimilated in the metamorphing blowfly pupa was retained in the pupal case after the adult blowfly had emerged. When blowfly pupae were parasitised by parasitoid wasps, a greater proportion of radiocaesium was retained in the parasitised pupal case, with only 2-3 % of the activity concentration in the meat being found in the wasps, providing further evidence to support that radiocaesium is biodiluted in insect food chains. Our results indicate that carcass decomposition driven by insects directly affects the fate of radiocaesium retained in vertebrate carcasses and we discuss these findings in connection to radiocaesium cycling and dispersion in terrestrial ecosystems.

The species-energy hypothesis predicts increasing biodiversity with increasing energy in ecosystems. Proxies for energy availability are often grouped into ambient energy (i.e., solar radiation) and substrate energy (i.e., non-structural carbohydrates or nutritional content). The relative importance of substrate energy is thought to decrease with increasing trophic level from primary consumers to predators, with reciprocal effects of ambient energy. Yet, empirical tests are lacking. We compiled data on 332,557 deadwood-inhabiting beetles of 901 species reared from wood of 49 tree species across Europe. Using host-phylogeny-controlled models, we show that the relative importance of substrate energy versus ambient energy decreases with increasing trophic levels: the diversity of zoophagous and mycetophagous beetles was determined by ambient energy, while non-structural carbohydrate content in woody tissues determined that of xylophagous beetles. Our study thus overall supports the species-energy hypothesis and specifies that the relative importance of ambient temperature increases with increasing trophic level with opposite effects for substrate energy.

Abstract Forests contribute to numerous ecosystem functions and services and contain a large proportion of terrestrial biodiversity, but they are being negatively impaced by anthropogenic activities. Forests that have never been clear‐cut and have old growth characteristics, termed “near‐natural,” often harbor different and richer species assemblages than managed forests. Alternative management strategies may be able to balance the needs of biodiversity with the demands of forestry, but evaluation efforts are limited by the challenges of measuring biodiversity. Species richness is frequently used as a simple measure of biodiversity, but research indicates that it may not adequately capture community‐level changes. Alternatively, trait‐based measures of biodiversity may prove to be useful, but research is lacking. In this paper, we use a large dataset that includes 339 obligate saproxylic beetle species collected over a decade in the boreal region throughout southern Norway to: (1) establish if there is a difference in beetle community composition between near‐natural and managed forests; and (2) determine which measures of beetle biodiversity best indicate forest naturalness. We arranged the sites in an ordination space and tested for differences in community composition between these forest types. We also tested different measures of biodiversity to determine which were the most predictive of forest naturalness. We found a clear difference in community composition between near‐natural and managed forests. Additionally, three measures of biodiversity were most predictive of forest naturalness: proportional abundance of predators, community weighted mean (CWM) of wing length, and CWM of body roundness. The probability that a forest was near‐natural increased with the proportional abundance of predators but decreased with CWM wing length and body roundness. Although species richness was higher in near‐natural forests, the effect was not significant. Overall, our findings underscore the conservation value of near‐natural forests and highlight the potential of several measures of biodiversity for determining forest quality.

Abstract Functional trait approaches are common in ecology, but a lack of clear hypotheses on how traits relate to environmental gradients (i.e., trait–niche relationships) often makes uncovering mechanisms difficult. Furthermore, measures of community functional structure differ in their implications, yet inferences are seldom compared among metrics. Community‐weighted mean trait values (CWMs), a common measure, are largely driven by the most common species and thus do not reflect community‐wide trait–niche relationships per se. Alternatively, trait–niche relationships can be estimated across a larger group of species using hierarchical joint species distribution models (JSDMs), quantified by a parameter Γ. We investigated how inferences about trait–niche relationships are affected by the choice of metric. Using deadwood‐dependent (saproxylic) beetles in fragmented Finnish forests, we followed a protocol for investigating trait–niche relationships by (1) identifying environmental filters (climate, forest age, and deadwood volume), (2) relating these to an ecological function (dispersal ability), and (3) identifying traits related to this function (wing morphology). We tested 18 hypothesized dispersal relationships using both CWM and Γ estimates across these environmental gradients. CWMs were more likely than Γ to show support for trait–niche relationships. Up to 13% of species' realized niches were explained by dispersal traits, but the directions of effects were consistent with fewer than 11%–39% of our 18 trait–niche hypotheses (depending on the metric used). This highlights the difficulty in connecting morphological traits and ecological functions in insects, despite the clear conceptual link between landscape connectivity and flight‐related traits. Caution is thus warranted in hypothesis development, particularly where apparent trait–function links are less clear. Inferences differ when CWMs versus Γ estimates are used, necessitating the choice of a metric that reflects study questions. CWMs help explain the effects of environmental gradients on community trait composition, whereas the effects of traits on species' niches are better estimated using hierarchical JSDMs.

Wood decay fungi are considered to be dispersed by wind, but dispersal by animals may also be important, and more so in managed forests where dead wood is scarce. We investigated whether beetles could disperse spores of the keystone species Fomitopsis pinicola . Beetles were collected on sporocarps and newly felled spruce logs, a favourable habitat for spore deposition. Viable spores (and successful germination) of F. pinicola were detected by dikaryotization of monokaryotic bait mycelium from beetle samples. Viable spores were on the exoskeleton and in the faeces of all beetles collected from sporulating sporocarps. On fresh spruce logs, nine beetle species transported viable spores, of which several bore into the bark. Our results demonstrate that beetles can provide directed dispersal of wood decay fungi. Potentially, it could contribute to a higher persistence of some species in fragmented forests where spore deposition by wind on dead wood is less likely.

Biological communities within living organisms are structured by their host's traits. How host traits affect biodiversity and community composition is poorly explored for some associations, such as arthropods within fungal fruit bodies. Using DNA metabarcoding, we characterized the arthropod communities in living fruit bodies of 11 wood-decay fungi from boreal forests and investigated how they were affected by different fungal traits. Arthropod diversity was higher in fruit bodies with a larger surface area-to-volume ratio, suggesting that colonization is crucial to maintain arthropod populations. Diversity was not higher in long-lived fruit bodies, most likely because these fungi invest in physical or chemical defences against arthropods. Arthropod community composition was structured by all measured host traits, namely fruit body size, thickness, surface area, morphology and toughness. Notably, we identified a community gradient where soft and short-lived fruit bodies harboured more true flies, while tougher and long-lived fruit bodies had more oribatid mites and beetles, which might reflect different development times of the arthropods. Ultimately, close to 75% of the arthropods were specific to one or two fungal hosts. Besides revealing surprisingly diverse and host-specific arthropod communities within fungal fruit bodies, our study provided insight into how host traits structure communities.

DATA FROM: Burner, R., J. Åstrom, T. Birkemoe, A. Sverdrup-Thygeson. 2021. Flattening the curve: approaching complete sampling for diverse beetle communities. Insect Conservation and Diversity https://doi.org/10.1111/icad.12540 ACKNOWLEDGEMENTS This research was funded by the Norwegian Environment Directorate as part of an ‘Agreement on monitoring hollow oaks and insects in hollow oaks’. The Norwegian University of Life Sciences (NMBU) workshop designed and produced the cross-pane flight intercept traps. Thanks to Sindre Ligaard for identifying the beetle species, and to Lindsay Burner, Ruben Roos, and Ross Wetherbee for assistance in the field. High-performance computing resources were provided by Frederick H. Sheldon and Louisiana State University (LSU HPC). INFORMATION This dataset contains all data necessary to reproduce the analysis in the resulting manuscript. Briefly, 110 insect traps were set for 3 months in a single forest stand in Ås, Norway in 2020. This dataset includes trap locations, number of individuals of each species captured in each trap, trap type, and forest covariates collected around the traps. For more detailed information see manuscript and README file. From abstract of manuscript: Insects are a hyper diverse and ecologically important group. Their high diversity, however, presents challenges in sampling methodology, because rare species are unreliably detected with low sampling effort. However, the relationship between effort and species detections, critical for effective monitoring and evaluation of population trends, is too seldom quantified. We sampled forest beetles for three months in a 4-ha stand of mixed deciduous forest in southeastern Norway using 110 flight intercept (four types) and Malaise traps, the highest trap density (29 traps/ha) that we have seen reported. We examined species accumulation curves to quantify the benefits of each additional trap, compared capture rates among several trap designs and trap emptying frequencies, and tested for spatial autocorrelation. In total we captured 566 beetle taxa (19,854 individuals) from 52 families, yet our species accumulation curve was only beginning to flatten. Trap types differed considerably in their effectiveness. Nevertheless, twenty of our most effective window traps detected 75% of all taxa in our dataset. We found no evidence of spatial correlation within the scale of the study (100 m radius), nor did trap-level forest covariates (5 m radius) explain much variation. This implies that low to moderate sampling effort dramatically underestimates species richness, but that a limited number of effective traps can nonetheless achieve relatively thorough sampling for some applications. Immediate trap surroundings and spacing appeared unimportant. But, insect ecologists should take particular care in selecting trap types and be cautious comparing studies that employed different trap types.

Climate, topography and the 3D structure of forests are major drivers affecting local species communities. However, little is known about how the specific functional traits of saproxylic (wood-living) beetles, involved in the recycling of wood, might be affected by those environmental characteristics.Here, we combine ecological and morphological traits available for saproxylic beetles and airborne laser scanning (ALS) data in Bayesian trait-based joint species distribution models to study how traits drive the distributions of more than 230 species in temperate forests of Europe.We found that elevation (as a proxy for temperature and precipitation) and the proportion of conifers played important roles in species occurrences while variables related to habitat heterogeneity and forest complexity were less relevant. Furthermore, we showed that local communities were shaped by environmental variation primarily through their ecological traits whereas morphological traits were involved only marginally. As predicted, ecological traits influenced species' responses to forest structure, and to other environmental variation, with canopy niche, wood decay niche and host preference as the most important ecological traits. Conversely, no links between morphological traits and environmental characteristics were observed. Both models, however, revealed strong phylogenetic signal in species' response to environmental characteristics.These findings imply that alterations of climate and tree species composition have the potential to alter saproxylic beetle communities in temperate forests. Additionally, ecological traits help explain species' responses to environmental characteristics and thus should prove useful in predicting their responses to future change. It remains challenging, however, to link simple morphological traits to species' complex ecological niches. Read the free Plain Language Summary for this article on the Journal blog.

Recent progress in the taxonomy of flat bark beetles (Cucujidae), specifically, in the genus Cucujus, has revealed great diversity in subtropical Asia, but the seemingly well-known temperate and boreal taxa need further attention because of their conservation status. Here, we used an integrative approach using morphology, DNA, and species distribution modelling to disentangle phylogenetic relations, verify the number of species, and understand the historical biogeography of Palearctic and Nearctic Cucujus beetles, particularly the C. haematodes species group. Species distinctiveness was supported for C. cinnaberinus, but present-day C. haematodes turned out to be a species complex made up of separate lineages in the western, middle and eastern parts of its Palearctic range. Cucujus muelleri was a member of that complex, being sister to Asian C. haematodes. Moreover, C. haematodes caucasicus was found to be phylogenetically closely related to Italian C. tulliae, and both to be sister to European C. haematodes. North American C. clavipes clavipes and C. c. puniceus resulted to be enough divergent to be considered different species. Interestingly, western American C. puniceus turned out to be closely related to the C. haematodes complex, whereas eastern American C. clavipes constituted a separate lineage, being distantly related to both C. puniceus and C. cinnaberinus. These patterns suggest former trans-continental connections among the ancestors of extant flat bark beetle species. Moreover, a divergent lineage of C. cinnaberinus was found in Calabria, which should be regarded at the very least as a subspecies. The ancestor of C. hameatodes group originated in mid-Miocene, and next, ca. 6.2 Mya, a line leading to C. cinnaberinus had split. Speciation of the American lineages occurred during Pliocene (4.4 Mya for C. clavipes and 3.3 Mya for C. puniceus). Species classified as C. haematodes, C. tulliae and C. muelleri, as well as distinct lineages within C. cinnaberinus split during mid Pleistocene (ca. 1.5 Mya). A comparison of species climatic requirements and their present distribution allowed to identify glacial refugia in south-eastern areas of North America (C. clavipes), south-western areas of North America (C. puniceus), and the Mediterranean and Caspian Sea Basins (European Cucujus species), or south-eastern areas of Asia and the foothills of the central Asian mountains (eastern C. haematodes). Subsequent climatic changes in the Holocene forced these beetles to move their ranges northwards along the coasts of the Pacific (C. puniceus) or Atlantic (C. clavipes), north-eastwards to central, northern, and eastern Europe (C. cinnaberinus and European C. haematodes) or Siberia (Asian C. haematodes). The combined use of molecular, morphological and climatic data allows a comprehensive understanding of the phylogenetic relations and past distributions of Cucujus beetles, highlighting the complexity of C. haematodes species group evolution.

Fungi are the main decomposers of litter and wood, driving carbon and nutrient cycles. Despite a large number of studies, fungal community composition is remarkably difficult to predict. In the present study, we explore the importance of secondary metabolites and nutrient content in wood and bark as determinants of fungal community composition. We used aspen (Populus tremula) logs of similar size, from one location, and measured concentrations of carbon, nitrogen and secondary metabolites in bark and wood sampled shortly after felling. Fungal DNA was extracted from logs directly after felling and after two seasons of decomposition, and the fungal communities were assessed using DNA-metabarcoding. Concentrations of metabolites varied considerably between individual trees, and we also observed significant differences within single trees. Plant metabolites and nitrogen concentrations significantly affected fungal community composition. For the overall fungal communities and for wood saprotrophic fungi, the explanatory power of wood and bark metabolites was highest in logs decomposed over two seasons. In recently felled trees however, concentration of metabolites had a stronger effect on plant pathogens and endophytes. We conclude that secondary metabolites represent an overlooked, but important niche dimension for fungal communities in both functional sapwood and dead wood.

Biodiverse communities have been shown to sustain high levels of multifunctionality and thus a loss of species likely negatively impacts ecosystem functions. For most taxa, however, roles of individual species are poorly known. Rare species, often most likely to go extinct, may have unique traits and functional roles. Alternatively, rare species may be functionally redundant, such that their loss would not disrupt ecosystem functions. We quantified the functional role of rare species by using captures of wood-living (saproxylic) beetle species, combined with recent databases of morphological and ecological traits, from three regions in central and northern Europe. Using a rarity index based on species' local abundance, geographic range, and habitat breadth, we used local and regional species removal simulations to examine the contributions of both the rarest and the most common beetle species to three measures of community functional structure: functional richness, functional specialization, and functional originality. Both regionally and locally, all three measures declined more rapidly when rare species were removed than under common (or random) species removal scenarios. These consistent patterns across scales and among forest types give evidence that rare species provide unique functional contributions, and their loss may disproportionately impact ecosystem functions. This implies that conservation measures targeting rare and endangered species, such as preserving intact forests with dead wood and mature trees, can provide broader ecosystem-level benefits. Experimental research linking functional structure to ecosystem processes should be prioritized to increase understanding of the functional consequences of species loss and to develop more effective conservation strategies.

During decomposition of organic matter, microbial communities may follow different successional trajectories depending on the initial environment and colonizers. The timing and order of the species arrival (assembly history) can lead to divergent communities through priority effects. We explored how assembly history and resource quality affected fungal communities and decay rate of decomposing wood, 1.5 and 4.5 years after tree felling. Additionally, we investigated the effect of invertebrate exclusion during the first two summers. We measured initial resource quality of bark and wood of aspen (Populus tremula) logs and surveyed the fungal communities by DNA metabarcoding at different times during succession. We found that gradients in fungal community composition were related to resource quality and we discuss how this may reflect different fungal life history strategies. As with previous studies, the initial amount of bark tannins was negatively correlated with wood decomposition rate over 4.5 years. The initial fungal community explained variation in community composition after 1.5, but not 4.5, years of succession. Although the assembly history of initial colonizers may cause alternative trajectories in successional communities, our results indicate that the communities may converge with the arrival of secondary colonizers. We also identified a strong legacy of invertebrate exclusion on fungal communities, even after 4.5 years of succession, thereby adding crucial knowledge on the importance of invertebrates in affecting fungal community development. By measuring and manipulating aspects of assembly history and resource quality that have rarely been studied, we expand our understanding of the complexity of fungal community dynamics.

Old veteran trees function as biodiversity hotspots in both forests and open landscapes, and protecting such trees is an important measure to halt loss of biodiversity. Nevertheless, the number of veteran trees continues to decline worldwide, although estimates of this decline mainly stem from geographically restricted case studies. In Norway, veteran oak trees have received special protection since 2011 through the Norwegian Biodiversity Act, however, there is a lack of knowledge on status and trends for these trees. A national monitoring program was started in 2012, using a random, stratified sampling procedure. We use the data from the baseline survey and the first monitoring revisit to estimate the total number as well as mortality trends of veteran oaks in Norway. Further, we assess recruitment potential (in the baseline survey) and changes in variables describing ecological state such as regrowth.The monitoring area covered the geographical distribution of oaks in Norway and was divided into > 200 000 plots of 500 x 500 m. A set of 500 monitoring plots were randomly selected from two strata: High probability plots (n = 100; plots with high probability of occurrence of veteran oaks), and Low probability plots (n = 400), using existing knowledge and databases. Plots were surveyed over a five year-period (2012-2016), with 20 HighProb-plots and 80 LowProb-plots each year. All veteran oaks that were observed during the baseline survey were revisited in 2019, three to seven years after they were initially registered. Tree absence and cause of death/ change of ecological status was recorded. We estimated a total of 138 100 veteran oaks in Norway based on the baseline survey, of which 25 000 could be denoted "top quality oaks". Based on the revisit, we estimated a loss of 7 600 veteran trees, i.e., an annual mortality rate of 1.2%. Recruitment oaks were present in most plots with veteran oaks, but recruitment into the veteran oak category is slow and unlikely to balance out the mortality rate. More precise estimates of recruitment should be prioritized in future monitoring. The estimate of 138 000 vet-eran oaks far exceeds the appr. 10 000 trees registered in the national database, and clearly demonstrates the need for continued mapping and monitoring to improve the foundation for a knowledge-based land manage-ment. Further, this short-term monitoring demonstrates the decline of this biodiversity hotspot and pivotal source of ecosystem functions, despite increased protection in recent years. Our results and conclusions are relevant also for veteran trees of other species than oak.

Veteran trees are keystone structures and play vital roles in ecosystems. Tree hollows, which are filled with a mix of leaves and wood that is transformed by the biotic community into wood mould, represent an important microhabitat. Tree hollow communities consist of three major groups of organisms: microbes, mesofauna (nematodes, mites and springtails) and macrofauna (beetles, millipedes and other insects). Little is known about the interplay between associated biota and their importance for decomposition and wood mould production. The aim of this study was to test how initial food web complexity in artificial tree hollows influences community structure, decomposition, and wood mould production. We used large wooden boxes to imitate natural hollows, and mounted them on 20 veteran oaks in Southern Norway. The food webs were manipulated into three levels: (i) a complex community with macrofauna and mesofauna, (ii) a simple community without macrofauna, and (iii) only the defaunated material. Three boxes (one of each treatment, N = 60 boxes) were mounted on each oak and left in the field from May 2017 to October 2019 (28 months). After the field experiment, macrofauna and mesofauna were collected and identified, mass loss in the boxes was determined, and nitrogen and phosphorus concentrations in the wood mould were measured. We found that the complex community treatment had the greatest diversity of beetles and the highest number of predatory macrofauna. The nematodes within the complex community treatment had greater trophic structuring with K-selected species associated with stable conditions. The nematodes communities also indicated that the complex community had a balanced decomposition pathway, while the simple community was dominated by fungi and the defaunated community by bacteria. Lastly, we found that the boxes with the complex community treatment had the highest overall rate of mass loss, and greater amounts of wood mould with higher concentrations of nitrogen and phosphorus. Our results indicate that macrofauna in artificial hollows increase trophic structuring, enhance decomposition rates and wood mould production, and mediate the decomposition pathway. These findings highlight the importance of food web complexity for promoting biodiversity and ecosystem functioning in veteran tree hollows. Read the free Plain Language Summary for this article on the Journal blog.

Sustainable nature management and ecosystem conservation depends critically on scientifically sound and stakeholder-relevant analytical frameworks for monitoring and assessing ecological condition. Several general frameworks are currently being developed internationally, including the Essential Biodiversity Variables (EBV), and the UN's SEEA EEA Ecosystem Condition Typology (ECT). However, there has so far been few attempts to develop empirical implementations of these general frameworks, or to assess their applicability for environmental decision-making at national or regional scales. In this paper, we aim to fill this implementation gap by demonstrating a practical application of an empirically-based ecological condition assessment framework, the Index-Based Ecological Condition Assessment (IBECA). IBECA defines seven major classes of indicators of ecological condition, representing distinct ecosystem characteristics, and empirically synthesizes indicators for each of these characteristics from various monitoring data. We exemplify and explore the utility and robustness of IBECA using a case study from forest and alpine ecosystems in central Norway, and we investigate how IBECA aligns with the two international frameworks EBV and ECT. In particular, we analyze how the different approaches to categorize indicators into classes affect the assessment of ecological condition, both conceptually and using the case study indicators. We used eleven indicators for each of the two ecosystems and assessed the ecological condition according to IBECA for i) each individual indicator, ii) the seven ecosystem characteristics (indicator classes), and iii) a synthetic ecological condition value for the whole ecosystem. IBECA challenges key concepts of the international frameworks and illustrates practical challenges for national or regional level implementation. We identify three main strengths with the IBECA approach: i) it provides a transparent and management-relevant quantitative approach allowing assessment of spatio-temporal variation in ecological condition across indicators, characteristics and ecosystems, ii) the high degree of flexibility and transparency facilitates updating the ecological condition assessments, also back in time, as improved data and knowledge of indicators emerge, and iii) the quantitative and flexible procedure makes it a cost-effective approach suitable for fast management implementations. More generally, we stress the need for carefully choosing appropriate classification and aggregation approaches in ecological condition assessments, and for transparent and data-driven analytical approaches that can be adjusted as knowledge improves.