Showing papers by "Volkmar Wolters published in 2014"

Interannual variation in land-use intensity enhances grassland multidiversity.

Abstract: Although temporal heterogeneity is a well-accepted driver of biodiversity, effects of interannual variation in land-use intensity (LUI) have not been addressed yet. Additionally, responses to land use can differ greatly among different organisms; therefore, overall effects of land-use on total local biodiversity are hardly known. To test for effects of LUI (quantified as the combined intensity of fertilization, grazing, and mowing) and interannual variation in LUI (SD in LUI across time), we introduce a unique measure of whole-ecosystem biodiversity, multidiversity. This synthesizes individual diversity measures across up to 49 taxonomic groups of plants, animals, fungi, and bacteria from 150 grasslands. Multidiversity declined with increasing LUI among grasslands, particularly for rarer species and aboveground organisms, whereas common species and belowground groups were less sensitive. However, a high level of interannual variation in LUI increased overall multidiversity at low LUI and was even more beneficial for rarer species because it slowed the rate at which the multidiversity of rare species declined with increasing LUI. In more intensively managed grasslands, the diversity of rarer species was, on average, 18% of the maximum diversity across all grasslands when LUI was static over time but increased to 31% of the maximum when LUI changed maximally over time. In addition to decreasing overall LUI, we suggest varying LUI across years as a complementary strategy to promote biodiversity conservation.

Mass‐flowering crops increase richness of cavity‐nesting bees and wasps in modern agro‐ecosystems

Abstract: Considerable uncertainties exist on how increased biofuel cropping affects biodiversity. Regarding oilseed rape, the most common biofuel crop in the EU, positive responses of flower-visiting insects to plentiful nectar and pollen seem apparent. However, previous investigations on this insect guild revealed conflicting results, potentially because they focused on different taxonomic groups representing a narrow range of ecological traits and considered only short time periods. Here, using trap nests in landscapes with independent gradients in area of oilseed rape and seminatural habitats, we assessed the whole community of cavity-nesting bees and wasps, including early- and late-emerging species. Our study's temporal resolution allowed determination of flowering and postflowering effects of oilseed rape on these species' richness, abundance, and mortality. Species richness of cavity-nesting bees and wasps significantly increased with oilseed rape, although nesting activity was considerably higher after mass flowering. In addition to increasing richness independently of oilseed rape, the amount of seminatural habitat in the landscape was the sole positive driver of insect abundance once the community's dominant species was accounted for as a covariate. Thus, growth of the co-occurring species' community is not stimulated by the resource pulse provided by oilseed rape early in the year, but by persistent resources provided by seminatural habitats after mass flowering. Early individuals of bivoltine species' first generations accumulated in seminatural habitats when these habitats were scarce, but became increasingly diluted when habitat availability increased. Once established, later foraging females generally benefited from the resource availability of seminatural habitats when initializing the second generation. We conclude that mass-flowering crops, despite covering only a short interval of the community's main activity phase, benefit bee and wasp species richness. However, seminatural habitats are crucial in maintaining viable communities of flower-visiting insects at the landscape scale, mitigating potential negative effects of high land-use intensities in modern agro-ecosystems.

Increased energy maize production reduces farmland bird diversity

Abstract: Producing energy crops as an alternative to fossil fuels in order to reduce CO2 emissions will lead to large-scale changes in agricultural landscapes. Here, we quantify the potential impact of an increase in maize fields on the diversity of farmland birds by means of high resolution (25 9 25 m) land-use scenarios. We generated scenarios in which the area of maize production in Germany increases from presently 2.6 to 2.9, 3.6 and 4.3 million ha, corresponding to the energy crop production targets of the German Renewable Energy Act for the years 2020, 2035 and 2050. To test the mitigating potential of conservation measures, each scenario was generated in a standard version and a landscape protection version, with the latter excluding valuable farmland areas from being converted into maize fields. Nine species of farmland birds belonging to the governmental indicator scheme for sustainable land-use in Germany were modelled for the six nation-wide scenarios. The models predicted that only the Northern Lapwing and the Little Owl might profit from extended maize production. Despite this, the total number of breeding pairs of the indicator species was predicted to decline by about 0.4 million breeding pairs in the most intensive scenario. Protection of valuable farmland did not mitigate these negative effects in the models. Our findings suggest that increased production of energy crops conflicts with conservation of biological diversity.

Grassy margins along organically managed cereal fields foster trait diversity and taxonomic distinctness of arthropod communities

Abstract: It is not known if grassy margins contribute to the conservation of biodiversity if situated along organically managed cereal fields as the contrast in environmental conditions between fields and margins may be too small in absence of pesticide applications. Communities of spiders, ground beetles, true bugs and aphids were sampled in 2years along transects from the centre of organically managed cereal fields into adjacent grassy margins. Based on species richness, abundances, ecological and body size traits of species and taxonomic distinctness between species, communities were compared between organically managed cereal fields and their grassy margins. The species richness, abundance and variation in taxonomic distinctness of true bugs were significantly higher in grassy margins. For spiders and ground beetles, these metrics were either higher in cereal fields or did not differ significantly. At the species level, spiders living under stones or in soil crevices, as well as phytophagous ground beetles and true bugs that overwinter as eggs benefited from grassy margins. True bug communities in cereal fields were dominated by a few abundant species, whereas communities in margins were rather dominated by a few large species. Our comprehensive analyses highlight the importance of accounting for species identities and biology in biodiversity studies. The traits that characterised arthropod species that benefited from margins are not characteristic for pest species. Grassy margins along organic fields therefore represent an important agri-environmental scheme for the conservation of several arthropod taxa and margins should not be removed to increase the crop production area in organically managed cereal fields. (Less)

Assessing spider diversity on the forest floor: expert knowledge beats systematic design

Abstract: The design of sampling schemes affects the results of biodiversity inventories. As an approach for quantifying the implications of such effects, we compared data on spider communities sampled in a beech-dominated forest floor habitat by 1) a regular grid of pitfall traps (systematic design) and 2) an expert-based distribution of traps (stratified design). We tested whether the two designs would lead to similar conclusions about the diversity and composition of ground-dwelling spider communities. Estimates of species richness, rarefied species richness and activity density calculated per trap were significantly higher in the stratified than in the systematic design. The community composition based on the presence or absence of sampled species or based on log-transformed activity densities differed significantly. Most of the dissimilarity between the community estimates of the two designs was attributable to three species, with Pardosa saltans Topfer-Hofmann 2000 being more common in traps of the stratified design and Tenuiphantes zimmermanni (Bertkau 1890) and Walckenaeria cuspidata Blackwall 1833 being more frequently observed in traps of the systematic design. Our study suggests that a stratified sampling design is better suited for inventory surveys of spider communities of forest-floor habitats, as trap locations of this design reflect specific habitat needs. It is important to note that inventories are a major field for the application of such designs and that greater care is needed for the application of inferential statistics. For example, the non-randomness that is caused by expert selection of sampling sites may violate fundamental assumptions of simple linear models.

Sustainable and resource efficient intensivation of crop production - Perspectives of agro-ecosystem research Policy paper of the DFG Senate Commission on Agroecosystem Research

Abstract: Mit dem vorliegenden Grundsatzpapier zeigt die Senatskommission fur Agrarokosystemforschung Perspektiven fur die Grundlagenforschung zur nachhaltigen Erhohung der Kulturpflanzenproduktion auf. Agrarsysteme stehen im Spannungsfeld zwischen steigendem Bedarf an landwirtschaftlichen Produkten, der Verknappung der Ressourcen, dem Verlust der Biodiversitat und dem Klimawandel. Die fur das Jahr 2050 prognostizierte notwendige Ertragssteigerung zur Sicherstellung des Bedarfs an Nahrungsmitteln kann, ohne die Belastbarkeitsgrenzen okologischer Systeme zu uberschreiten,nur durch wissenschaftlichen Fortschritt bewaltigt werden (Abb. 1), der eine nachhaltige und ressourcen­effiziente Steigerung der Agrarproduktion ermoglicht (FAO,2011;Dobermann und Nelson,2013). Die nachhaltige Intensivierung stellt die Agrarwissenschaften vor neue Aufgaben, die weit uber ihre klassischen Grenzen hinausgehen. Die Senatskommission pladiert daher fur eine Erweiterung der agrarwissenschaftlichen Perspektive. Die meist auf einzelne Feldfruchte bezogene Bewertung der Rela­tion zwischen Input und Ertrag muss erganzt werden um die Optionen, die sich aus der raumlichen und zeitlichen Diversifikation der Produktionssysteme unter Einbeziehung der standortlichen Eigenschaften, des Landschaftskontextes sowie des Klimawandels ergeben. Um Okosystemleistungen einzubeziehen, mussen Produktionsstrategien entwickelt werden, die sich auf ganze Landschaften und Regionen richten und auch entsprechende sozio­oko­no­mische und agrarpolitische Rahmenbedingungen berucksichtigen. Vor diesem Hintergrund schlagt die Senatskommission drei interdisziplinare Forschungsschwerpunkte zur ressourceneffizienten Erhohung der Flachenproduktivitat vor: (1) Ausnutzung des Potentials von Kulturpflanzen zur umweltschonenden Ertragssteigerung im Kontext oko­systemarer Bedingungen. (2) Nachhaltige Steigerung der Pflanzenproduktion im Landschaftskontext. (3) Okonomische, gesellschaftliche und politische Dimensionen der Ertragssteigerung von Kulturpflanzen.

Feldversuchsinfrastrukturen - Status quo und Perspektiven, Positionspapier der DFG Senatskommission für Agrarökosystemforschung

Abstract: Gros angelegte und langfristig etablierte Feldversuche sind ein zentrales Element der standortbezogenen Agrarwissenschaften. Die Erarbeitung des Grundlagenwissens zu standortangepassten bzw. regional spezifischen Produktivitatspotentialen von Pflanzenbestanden sowie die Entwicklung von okologisch vertretbaren, innovativen Produktionssystemen mit hoher Produktivitat und Resi­lienz erfordern leistungsfahige Forschungsinfrastrukturen, die relevante Gradienten an Klima- und Bodenfaktoren abdecken und den interdisziplinaren Dialog fordern. Das Positionspapier der Senatskommission fur Agrar­oko­systemforschung der Deutschen Forschungsgemeinschaft stellt den Status quo und die zukunftigen Anforderungen an Feldversuchseinrichtungen dar. Zur Optimierung des agrarwissenschaftlichen Feldversuchswesens wird angeregt, in einem Netzwerk aus Versuchseinrichtungen Landschaftsfunktionen prototypisch abzubilden, um in einem interdisziplinaren Ansatz Flachenproduktivitat, Resilienz und Ressourceneffizienz landschaftsspezifisch untersuchen zu konnen. Des Weiteren ist es erforderlich, der wissenschaftlichen Community standardisierte Daten in Datenrepositorienzur Verfugung zu stellen.