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Global warming and land‐use change are expected to be additive threats to global diversity, to which insects contribute the highest proportion. Insects are strongly influenced by temperature but also require specific habitat resources, and thus interaction between the two factors is likely. We selected saproxylic beetles as a model group because their life cycle depends on dead wood, which is highly threatened by land use. We tested the extent to which higher temperatures compensate for the negative effects of low amounts of dead wood on saproxylic beetle species richness (Temperature–Dead wood compensation hypothesis) on both a macroclimate and a topoclimate scale (north‐ and south‐facing slopes). We analyzed 1404 flight‐interception trap catches across Europe to test for interaction effects of temperature and dead‐wood amount on species richness. To experimentally test our findings from the activity trap data, we additionally reared beetles from 80 bundles of dead wood initially exposed at high and low elevations. At the topoclimate scale, we analyzed trap catches and reared beetles from dead wood exposed in 20 forest stands on south‐facing and north‐facing slopes in one region. On the macroscale, both temperature and dead‐wood amount positively affected total and threatened species richness independently, but their interaction was significantly negative, indicating compensation. On both scales and irrespective of the method, species richness decreased with temperature decline. Our observation that increasing temperature compensates for lower amounts of dead wood has two important implications. First, managers of production forests should adapt their dead‐wood enrichment strategy to site‐specific temperature conditions. Second, an increase in temperature will compensate at least partially for poor habitat conditions in production forests. Such a perspective contrasts the general assumption of reinforcing impacts of global warming and habitat loss on biodiversity, but it is corroborated by recent range expansions of threatened beetle species.

During spring and summer 1999 a ring-test and field-validation study with an open, intact Terrestrial Model Ecosystem (TME) was conducted at four different European sites (Amsterdam, The Netherlands; Bangor, U.K.; Coimbra, Portugal; Flörsheim, Germany). The objective of the study was to establish a standardised method which allows the impact of chemical stressors on terrestrial compartments at ecosystem level to be investigated and possible uses of such data in existing Environmental Risk Assessments (ERAs) for chemicals to be evaluated. This issue of Ecotoxicology presents in a series of papers the results of the TME ring-test and field-validation study. Additionally, results derived from an open-homogeneous terrestrial microcosm (Integrated Soil Microcosm, ISM) are included in this series as a separate paper. In this first paper of the series background information on the planning and organisation of the study are given. The conceptual approach and the design of the study with TMEs are briefly outlined, based on the scientific discussion on the use of terrestrial microcosms in ecology and applied environmental sciences during the last 25 years. Further, some suggestions are presented on the selection of measurement endpoints to quantify structural and functional aspects of terrestrial ecosystems. Finally, the main results of the TME-study are summarised and conclusions are drawn on the technical feasibility of TMEs, their comparability with field studies and the potential use of TMEs in ERA.

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 km ) 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.

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1. European Beech (Fagus sylvatica) is the natural dominant tree species in many forests across Europe. Despite Europe's global responsibility for these forests, the correct conservation strategies are still a matter of debate. In particular, it remains controversial whether high conservation efforts should be directed towards beech forests, owing to the small number of insects that are Fagus specialists, and at what spatial scale conservation should take place.2. To provide evidence for this discussion, we compiled saproxylic beetle data from 1115 flight-interception traps in eight countries and addressed two main questions: (i) what percentage of central European species can be expected in beech-dominated forests? and (ii) which are the important spatial scales for the conservation of biodiversity in beech-dominated forests?3. We included six spatial scales in our analysis: among traps, forest stands, forest sites, low ⁄ high elevations, oligo ⁄ eutrophic soils, and European bioregions. 4. By extrapolating species numbers, we showed that 70% of the central European saproxylic beetle species can be expected in beech-dominated forests. Multiplicative b-diversity partitioning revealed the forest site level as the most important diversity scale for species richness, particularly for red-listed and rare species, followed by elevation and bioregion.5. We conclude that beech-dominated forests form a useful umbrella for the high species diversity of central European saproxylic beetles. Conservation activities, such as protecting areas or increasing dead wood, should be undertaken in as many forest sites as possible, at different elevations, and in different bioregions. For this, the Natura 2000 net may provide the most useful template.

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