Kurt Bollmann

Global change reshapes arthropod communities, yet long‐term effects on their functional diversity remain unclear. Using a long‐term dataset comprising > 1.3 million individuals of 728 carabid and spider species, we quantified temporal trends in functional diversity across forests, grasslands and croplands. Trajectories diverged strongly among land uses: functional richness increased in forests and grasslands but declined sharply in croplands. In forests, communities became more specialised and less redundant, suggesting increasing niche differentiation, but experienced greater functional richness loss under simulated species extinctions. Cropland assemblages became functionally homogenised. Losses of key effect traits among spiders suggest potential erosion of ecosystem functions in croplands. Moreover, genera dominated by species with unique trait combinations were typically larger‐bodied and less dispersive, and their loss would remove irreplaceable functional strategies from communities. Overall, our study reveals diverging long‐term trajectories of arthropod functional diversity across land uses, indicating potential negative consequences for ecosystem functioning in arable landscapes.

Arthropods drive essential ecosystem processes such as pollination, decomposition, and nutrient cycling and are widely used as indicators of ecosystem condition and function. Among various arthropod-derived metrics, body weight is a key variable in functional ecology and frequently assessed as dry body weight. However, drying arthropod specimens limits the samples’ future potential for research, as it prevents further processing such as trait measurements or species identification. Here, we present AWET (Arthropod Weight Estimation Tool), an open-source application for automated estimation of individual fresh body weight and extraction of morphometric measurements from standardized images of pre-sorted arthropod samples. AWET combines automated image analysis with taxon-specific allometric regression models to estimate fresh body weight while simultaneously quantifying body length, width, area, and specimen abundance. The software operates with standard imaging equipment, requires no machine-learning-based classification or segmentation, and allows users to define taxonomic groupings according to their objectives. By preserving specimens for downstream analyses while processing large numbers of individuals within milliseconds, AWET provides an efficient, non-destructive, and cost-effective workflow for high-throughput arthropod phenotyping. The software is a practical and expandable tool for biodiversity monitoring projects investigating changes in arthropod biomass, abundance and individual morphometric measures.

Forests are vertically structured ecosystems where light attenuation, microclimatic buffering and resource availability occur along continuous gradients from the canopy to the understorey layers. Despite this complexity, studies rarely integrate trophic interactions across vertical layers, overlooking how vertical forest structure shapes consumer communities through abiotic and biotic pathways. In this study, we combined layer-specific measurements of plant diversity, structure and microclimate with arthropod sampling in the canopy and understorey, as well as bird survey data, in a temperate forest. Applying Bayesian structural equation models with explicitly defined directional pathways, we modelled both consumer biomass and abundance across trophic levels and vertical layers. Abundance measures were predominantly filtered by local layer conditions, while biomass responded to conditions across layers, reflecting stand-level energy flow. This suggests that these two metrics capture fundamentally different ecological processes. Canopy conditions consistently predicted understorey arthropod abundance across trophic levels, while the reverse was not observed, suggesting a strong asymmetric downward propagation of canopy-driven effects. Furthermore, trophic interactions between arthropod primary and secondary consumers remained largely stratified within vertical layers, suggesting a vertical food web compartmentalisation rarely shown in structurally complex aboveground systems. Plant diversity, structure and microclimate shaped consumer communities mainly through the modulation of resource availability and plant apparency, with effects varying across vertical layers, trophic levels and taxonomic groups. Through complementary mechanisms, plant diversity likely determined the variability of resources available to consumers at different trophic levels. Structural properties, in contrast, potentially drove the spatial redistribution of these resources through light attenuation and microclimatic buffering, which in turn influenced the physiological capacity of consumers to access and exploit available resources. These findings demonstrate that vertical stratification mediates trophic pathways in a highly directional manner, with canopy characteristics playing a disproportionate role in structuring the forest community across layers. Integrating layer-specific structural and trophic indicators into forest biodiversity assessments and management strategies is therefore essential to fully evaluate biodiversity dynamics and multifunctionality in structurally complex forest ecosystems.

Conservation planning requires prioritizing particular species, habitats, or objectives and handling information gaps. Spatial prioritization analyses apply various weighting schemes, for example assigning relative importance to different biodiversity features, balancing threatened and common species, or trading off ecological objectives against socioeconomic constraints. Such value driven choices may strongly affect conservation outcomes, yet little clarity exists on where and how they are employed. To address this opacity, we developed a comprehensive decision framework that organizes weighting criteria across three dimensions, conservation objectives, socioeconomic considerations, and implementation constraints, operating at species, habitat, and landscape levels. We then confronted 71 systematically chosen spatial prioritization studies with this framework to assess how weighting was considered. Representativeness and conservation urgency were the dominant motivations for weighting. However, ecosystem services were considered in only one study despite their prominence in policy-related discourse. Seventy-two percent of the studies did not explicitly justify their weighting decisions, challenging transparent communication of the underlying rationales. In a final step, we applied the framework in three case studies considering 1,472 species in Switzerland and prioritizing across taxonomic groups, realms, and threat categories to demonstrate the fundamental impact of weighting on conservation outcomes. Our results emphasize why weighting decisions require clear justification and documentation in spatial prioritization. Our framework will help planners make explicit choices that align with their conservation objectives.

Invertebrate herbivory is a key ecological process shaping ecosystem multifunctionality, especially in forest habitats. The vertical stratification of forests is characterised by unique structural niches, microclimatic conditions, the availability of resources for organisms and biotic assemblages. Nevertheless, a comprehensive understanding of the processes driving plant–herbivore interactions across forests' complex three‐dimensional systems remains poorly understood. We selected forest stands along physiological and structural axes and used high‐resolution LiDAR data on stand structure, together with microclimate and biodiversity data, to investigate patterns of invertebrate herbivory on European beech ( Fagus sylvatica ) leaves and herbivore abundance across different spatial scales, in the canopy and understorey of a beech‐dominated forest. Herbivore abundance in the canopy was 67% higher than in the understorey, yet relative herbivory did not differ between layers. This decoupling between herbivore abundance and herbivory suggests a resource dilution effect: greater foliage availability in canopies leads to herbivore aggregation but proportionally dilutes relative leaf damage. We found layer‐specific drivers, with herbivore abundance responding negatively to vertical structure and positively to microclimate in both layers, while woody plant diversity had contrasting effects across layers. Relative herbivory was only influenced positively by woody plant diversity in the understorey. Stand‐specific factors explained substantial variance in both metrics, suggesting that important drivers operate simultaneously across stands and vertical layers. Synthesis . This study shows that the relationship between herbivore abundance and herbivory can be decoupled across vertical forest layers through resource dilution, challenging the assumption that more herbivores result in more per‐leaf damage. The effects of woody plant diversity and structure depend on whether a stratum functions as a resource‐rich or resource‐limited environment for beech leaf herbivores. These findings highlight that understanding the mechanisms of resource availability as drivers of herbivory in forests requires vertically resolved, multi‐scale approaches.

Most studies on insect trends have focused on the past few decades, but major changes could have occurred earlier. If so, shifted baselines can result in misleading conclusions or poor conservation decisions. Here we analyse nine decades of insect trends in Switzerland and relate them to changes in land use and climate. By reconstructing continuous trends in species richness based on 1.2 million records of 595 saproxylic beetle and 216 butterfly species, we find that both groups declined from the 1930s to the 1960s. While saproxylic beetle richness stabilized and subsequently recovered, butterfly richness continued to decline until the 1980s and has not recovered. The strong mid-century decreases were linked to increases in agricultural mechanization, while the subsequent increases were linked to climate warming. Over the entire 90-year period, declines primarily affected specialist and cold-adapted species, while warm-adapted species have increased since the 1980s. Recent gains in saproxylic beetle richness might also reflect increased deadwood availability from windthrow and ‘biodiversity-friendly’ forest management. Our findings suggest that reducing adverse land use is key to maintaining and promoting insect diversity, and that shifted baselines and climate-change effects should be considered when setting restoration goals and priorities.

The microclimate temperature within forests can substantially deviate from measurements outside forests. Yet, the amount and direction of this buffering strongly depend on meteorological conditions outside forests, such as free‐air temperature, wind speed, soil moisture, precipitation and solar radiation. Most studies on microclimate buffering focus on long‐term averages at coarse temporal resolution (e.g., monthly to seasonal), potentially overlooking the impact of daily fluctuations, which are nonetheless critical for many forest species and processes. Here, we linked in situ measured air and soil temperatures, at the daily resolution over a period of more than 5 years across 45 European deciduous forests spanning a 2300‐km latitudinal gradient, to daily variation in weather conditions (i.e., free‐air temperature, precipitation, wind speed, soil moisture, solar radiation, day length and snow cover). We assessed the interactive effects of weather conditions and forest structural complexity (plant area index) and distance to the forest edge on air and soil temperature offsets. Temperature offsets are the difference between understory air or soil temperature and macroclimate reference conditions measured at weather stations in the open field. We show that relative effect sizes of free‐air temperature prevailed over the effects of other weather variables to determine air and soil temperature buffering. In general, higher free‐air temperatures, soil moisture, wind speed and snow cover led to more negative air and soil temperature offsets, with variations depending on forest structural complexity and season. Conversely, slightly increased air and soil temperature offsets were found as precipitation and solar radiation increased. Our study highlights the dominant role of daily free‐air temperature fluctuations outside forests in shaping microclimatic buffering. We emphasize complex interaction paths between daily weather conditions, and forest structure and edge effects, offering valuable insights for next‐generation microclimate models and enhancing our understanding of forest ecosystem responses to environmental change that account for microclimate.

Resource pulses associated with forest disturbances can significantly influence biological communities, with interacting and sometimes lagged effects on species numbers. Among the most common disturbances in temperate forests are bark beetle outbreaks, which represent a resource pulse and initiate additional resource pulses of other insects and of deadwood. Moreover, bark beetle outbreaks are often followed by changes in habitat conditions due to canopy cover loss or salvage logging that can have contrasting effects on co‐occurring forest species. However, the effects of this multi‐resource pulse on forest species have rarely been quantified simultaneously. Here, we investigated if and to what extent changes in woodpecker population density were related to resource pulses, specifically spruce bark beetle and standing dead wood of Norway spruce. We used data from long‐term monitoring projects collected across Switzerland from 1984 to 2020 to build a network model that estimated relationships among species and resources. We built a semi‐mechanistic model that included structured equations of parameters of interest. The equations modelled Norway spruce standing deadwood volume, bark beetle density and density of three woodpecker species as a function of their interactions, as well as climatic, environmental and management variables. The model allowed both same‐year and 1‐year lagged effects. We found weak relationships between bark beetle outbreaks and woodpecker densities, and strong positive relationships between deadwood amount and woodpecker densities. In turn, standing deadwood was strongly linked to bark beetle outbreaks, highlighting the indirect role of bark beetles in promoting woodpecker populations by means of providing deadwood for foraging and nesting. Salvage logging, that is, the removal of trees infested by bark beetles, had only minor effects on bark beetles. Bark beetle outbreaks contributed to the generation of deadwood that ensured the continuity of its associated ecosystem functions, which benefited woodpeckers and, potentially, forest biodiversity as a whole. Large‐scale consequences of these multi‐resource pulses were reflected by species populations over longer time periods than the pulses.