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The massive declines in terrestrial arthropods reported across Europe call for effective methods to monitor and promote biodiversity in human-dominated landscapes. Previous studies vary in their support for the suitability of plants as indicators of arthropod diversity, while the potential of subsets of conservation-relevant plant species to estimate arthropod richness remains to be tested. Moreover, the relative importance of plant species richness compared to other factors driving arthropod richness, such as land-use intensity, habitat amount and landscape configuration, is poorly understood. We conducted a multi-scale field study in Southern Germany, sampling vascular plants and terrestrial arthropods in four local land-use types (forest, grassland, arable field, settlement) across large-scale gradients of climate and land-use intensity. We obtained an extensive arthropod dataset using Malaise traps as sampling method and DNA metabarcoding for species identification. We compared the correlation of three sets of plant species richness (total, red-listed and biotope-indicator plants) with arthropod richness, including different trophic and taxonomic groups. Using mixed-effect models, we assessed the partial effects of plant species richness, habitat amount and landscape configuration on local arthropod richness while controlling for climate and land-use effects, and explored the environmental drivers of plant species richness. Arthropod species numbers of all trophic groups strongly responded to species numbers of plants that indicate protected habitats, while red-listed plant species richness was a key determinant for the richness of red-listed arthropods and butterflies. In most cases, plant species richness and temperature were stronger drivers of arthropod richness than the amount of surrounding semi-natural habitat and landscape configuration. While total plant species richness was highest in settlements, the richness of biotope-indicator plants was highest in forests and positively influenced by the amount of semi-natural habitat and edge density. The number of red-listed plant species increased with edge density at the landscape scale but was independent of habitat amount. We conclude that the richness of conservation-relevant plant species provides a powerful indicator of arthropod diversity, and underpins the potential of such plant lists for monitoring habitat quality. Our study highlights the importance of openings in forests for conservation of plants and arthropods as well as of preserving and restoring fragments of high-quality biotopes in agricultural and urban areas where the amount of semi-natural habitat is limited.

Land use is a key control of insect communities. Here the authors investigate relationships of insect biomass and richness with land use along a climate gradient, finding evidence of urbanisation and agriculture as drivers of decline, and of biomass and species richness not being suitable as mutual surrogates.

Arthropod predators are important for ecosystem functioning by providing top-down regulation of insect herbivores. As predator communities and activity are influenced by biotic and abiotic factors on different spatial scales, the strength of top-down regulation ('arthropod predation') is also likely to vary. Understanding the combined effects of potential drivers on arthropod predation is urgently needed with regard to anthropogenic climate and land-use change. In a large-scale study, we recorded arthropod predation rates using artificial caterpillars on 113 plots of open herbaceous vegetation embedded in contrasting habitat types (forest, grassland, arable field, settlement) along climate and land-use gradients in Bavaria, Germany. As potential drivers we included habitat characteristics (habitat type, plant species richness, local mean temperature and mean relative humidity during artificial caterpillar exposure), landscape diversity (0.5-3.0-km, six scales), climate (multi-annual mean temperature, 'MAT') and interactive effects of habitat type with other drivers. We observed no substantial differences in arthropod predation rates between the studied habitat types, related to plant species richness and across the Bavarian-wide climatic gradient, but predation was limited when local mean temperatures were low and tended to decrease towards higher relative humidity. Arthropod predation rates increased towards more diverse landscapes at a 2-km scale. Interactive effects of habitat type with local weather conditions, plant species richness, landscape diversity and MAT were not observed. We conclude that landscape diversity favours high arthropod predation rates in open herbaceous vegetation independent of the dominant habitat in the vicinity. This finding may be harnessed to improve top-down control of herbivores, e.g. agricultural pests, but further research is needed for more specific recommendations on landscape management. The absence of MAT effects suggests that high predation rates may occur independent of moderate increases of MAT in the near future.

Because of some land-use practices (such as overstocking with wild ungulates, historical clear-cuts for mining, and locally persisting forest pasture), protective forests in the montane vegetation belt of the Northern Limestone Alps are now frequently overaged and poorly structured over large areas. Windthrow and bark beetle infestations have generated disturbance areas in which forests have lost their protective functions. Where unfavorable site conditions hamper regeneration for decades, severe soil loss may ensue. To help prioritize management interventions, we developed a geographic information system-based model for assessing sensitivity to site degradation and applied it to 4 test areas in the Northern Limestone Alps of Austria and Bavaria. The model consists of (1) analysis of site conditions and forest stand structures that could increase sensitivity to degradation, (2) evaluation of the sensitivity of sites and stands, and (3) evaluation and mapping of mountain forests' sensitivity to degradation. Site conditions were modeled using regression algorithms with data on site parameters from pointwise soil and vegetation surveys as responses and areawide geodata on climate, relief, and substrate as predictors. The resulting predictor–response relationships were applied to test areas. Stand structure was detected from airborne laser scanning data. Site and stand parameters were evaluated according to their sensitivity to site degradation. Sensitivities of sites and stands were summarized in intermediate-scale sensitivity maps. High sensitivity was identified in 3 test areas with pure limestone and dolomite as the prevailing sensitivity level. Moderately sensitive forests dominate in the final test area, Grünstein, where the bedrock in some strata contains larger amounts of siliceous components (marl, mudstone, and moraines); degraded and slightly sensitive forests were rare or nonexistent in all 4 test areas. Providing a comprehensive overview of site and forest stand structure sensitivity to site degradation, our sensitivity maps can serve as a planning instrument for the management and protection of mountain forests.

Ordination and calibration (indicator species analysis) are based on the taxonomic composition and richness of communities. How strongly does the performance of a widely used method like weighted averaging of Ellenberg indicator values depend on the completeness of samples? Based on a stratified random sample of coincident phytosociological relevés of forest understorey and environmental measurements (overstorey cover, elevation, moisture index, pH and C/N-ratio in topsoil) indicator values for light, temperature, moisture, soil acidity and nitrogen were tested. To simulate reduced sampling effort and uncomplete representation of plant diversity, the original compositional matrix was reduced by randomly deleting 1, 10, 20, 40 and 80% of species records with low abundance. The relationship between indicator values based on the full matrix and environmental variables was closest for temperature (R2 = 0.53) and lowest for soil nitrogen (R2 = 0.28). Deletion of low-abundance species records affected the correlations only weakly. With as little as 20% of the original species records (or 40% of gamma- and 20% of alpha-diversity) explained variance was still in a range of 0.26 to 0.37. The overall multivariate association between species composition and environment, as measured by Mantel statistics, was more strongly affected by the ommission of species records than the Ellenberg method. The relative resilience of Ellenberg indicator values to incomplete sampling is attributed to its predominant reliance on coarse structural information, i.e. the dominance pattern of relatively few plant species. Finely-tuned local indicator systems perform better by exploiting the idiosyncratic information of rare species. Choosing an optimal sampling scale involves a tradeoff between noise and completeness, an issue that has been largely neglected by environment-composition studies. Ordination und Zeigerwertanalyse basieren auf der taxonomischen Zusammensetzung und Vielfalt von Lebensgemeinschaften. Welche Bedeutung hat die Vollständigkeit der Erhebung für das Funktionieren der weithin benutzten gewichteten Mittelwertbildung von Ellenberg-Zeigerwerten? An Hand einer stratifizierten Zufallsstichprobe von Aufnahmen der Waldbodenvegetation und Umweltmessungen (Baumschichtdeckung, Meereshöhe, Wasserhaushalt, Bodenreaktion und C/N-Verhältnis) wurden die Zeigerwerte für Licht, Temperatur, Feuchte, Reaktion und Nährstoffe überprüft. Reduzierte Aufnahmeintensität und unvollständige Erfassung der pflanzlichen Artenvielfalt wurden durch Löschen von 1, 10, 20, 40 und 80% der Nennungen von Arten mit geringem Deckungsgrad aus der ursprünglichen Artenmatrix simuliert. Die Zeigerwert-Umwelt-Korrelation war für den Temperaturwert am höchsten (R2 = 0.53) und für den Nährstoffwert am geringsten (R2 = 0.28). Das Löschen von Nennungen verringerte diese Korrelationen nur geringfügig: Mit nur 20% der Originaldaten (oder 40% der gamma- und 20% der alpha-Diversität) wurden noch Bestimmtheitsmaße zwischen 0.26 und 0.37 erzielt. Dagegen sank die Gesamtbeziehung zwischen Artenzusammensetzung und Umwelt deutlich und gleichmäßig ab, wenn Artnennungen weggelassen wurden. Die verhältnismäßige Unempfindlichkeit des Ellenberg-Systems wird seiner Abhängigkeit von grober struktureller Information zugeschrieben. Fein abgestimmte lokale Zeigersysteme verdanken ihre Überlegenheit der zusätzlichen Einbeziehung idiosynkratischer Information seltener Arten. Die Frage nach dem optimalen Aufnahmemaßstab als Kompromiss zwischen Rauschen und Vollständigkeit ist bislang im Studium des Zusammenhangs zwischen Umwelt und Artenzusammensetzung vernachlässigt worden. [ABSTRACT FROM AUTHOR]