Diversity and specialization responses to climate and land use differ between deadwood fungi and bacteria

Climate and land use are major determinants of biodiversity, and declines in species richness in cold and human exploited landscapes can be caused by lower rates of biotic interactions. Deadwood fungi and bacteria interact strongly with their hosts due to long-lasting evolutionary trajectories. However, how rates of biotic interactions (specialization) change with temperature and land-use intensity are unknown for both microbial groups. We hypothesize a decrease in species richness and specialization of communities with decreasing temperature and increasing land use intensity while controlling for precipitation. We used a full-factorial nested design to disentangle land use at habitat and landscape scale and temperature spanning an area of 300 × 300 km in Germany. We exposed four deadwood objects representing the main tree species in Central Europe (beech, oak, spruce, pine) in 175 study plots. Overall, we found that fungal and bacterial richness, community composition and specialization were weakly related to temperature and land use. Fungal richness was slightly higher in near-natural than in urban landscapes. Bacterial richness was positively associated with mean annual temperature, negatively associated with local temperature and highest in grassland habitats. Bacterial richness was positively related to the covariate mean annual precipitation. We found strong effects of host-tree identity on species richness and community composition. A generally high level of fungal host-tree specialization might explain the weak response to temperature and land use. Effects of host-tree identity and specialization were more pronounced in fungi. We suggest that host tree changes caused by land use and climate change will be more important for fungal communities, while changes in climate will affect bacterial communities more directly. Contrasting responses of the two taxonomic groups suggest a reorganization of deadwood microbial communities, which might have further consequences on diversity and decomposition in the Anthropocene

Relationship of insect biomass and richness with land use along a climate gradient

Recently reported insect declines have raised both political and social concern. Although the declines have been attributed to land use and climate change, supporting evidence suffers from low taxonomic resolution, short time series, a focus on local scales, and the collinearity of the identified drivers. In this study, we conducted a systematic assessment of insect populations in southern Germany, which showed that differences in insect biomass and richness are highly context dependent. We found the largest difference in biomass between semi-natural and urban environments (−42%), whereas differences in total richness (−29%) and the richness of threatened species (−56%) were largest from semi-natural to agricultural environments. These results point to urbanization and agriculture as major drivers of decline. We also found that richness and biomass increase monotonously with increasing temperature, independent of habitat. The contrasting patterns of insect biomass and richness question the use of these indicators as mutual surrogates. Our study provides support for the implementation of more comprehensive measures aimed at habitat restoration in order to halt insect declines

Dung‐visiting beetle diversity is mainly affected by land use, while community specialization is driven by climate

Dung beetles are important actors in the self‐regulation of ecosystems by driving nutrient cycling, bioturbation, and pest suppression. Urbanization and the sprawl of agricultural areas, however, destroy natural habitats and may threaten dung beetle diversity. In addition, climate change may cause shifts in geographical distribution and community composition. We used a space‐for‐time approach to test the effects of land use and climate on α‐diversity, local community specialization (H (2)′) on dung resources, and γ‐diversity of dung‐visiting beetles. For this, we used pitfall traps baited with four different dung types at 115 study sites, distributed over a spatial extent of 300 km × 300 km and 1000 m in elevation. Study sites were established in four local land‐use types: forests, grasslands, arable sites, and settlements, embedded in near‐natural, agricultural, or urban landscapes. Our results show that abundance and species density of dung‐visiting beetles were negatively affected by agricultural land use at both spatial scales, whereas γ‐diversity at the local scale was negatively affected by settlements and on a landscape scale equally by agricultural and urban land use. Increasing precipitation diminished dung‐visiting beetle abundance, and higher temperatures reduced community specialization on dung types and γ‐diversity. These results indicate that intensive land use and high temperatures may cause a loss in dung‐visiting beetle diversity and alter community networks. A decrease in dung‐visiting beetle diversity may disturb decomposition processes at both local and landscape scales and alter ecosystem functioning, which may lead to drastic ecological and economic damage

Disentangling effects of climate and land use on biodiversity and ecosystem services - a multi‐scale experimental design

Climate and land-use change are key drivers of environmental degradation in the Anthropocene, but too little is known about their interactive effects on biodiversity and ecosystem services. Long-term data on biodiversity trends are currently lacking. Furthermore, previous ecological studies have rarely considered climate and land use in a joint design, did not achieve variable independence or lost statistical power by not covering the full range of environmental gradients. Here, we introduce a multi-scale space-for-time study design to disentangle effects of climate and land use on biodiversity and ecosystem services. The site selection approach coupled extensive GIS-based exploration (i.e. using a Geographic information system) and correlation heatmaps with a crossed and nested design covering regional, landscape and local scales. Its implementation in Bavaria (Germany) resulted in a set of study plots that maximise the potential range and independence of environmental variables at different spatial scales. Stratifying the state of Bavaria into five climate zones (reference period 1981–2010) and three prevailing land-use types, that is, near-natural, agriculture and urban, resulted in 60 study regions (5.8 × 5.8 km quadrants) covering a mean annual temperature gradient of 5.6–9.8°C and a spatial extent of ~310 × 310 km. Within these regions, we nested 180 study plots located in contrasting local land-use types, that is, forests, grasslands, arable land or settlement (local climate gradient 4.5–10°C). This approach achieved low correlations between climate and land use (proportional cover) at the regional and landscape scale with |r ≤ 0.33| and |r ≤ 0.29| respectively. Furthermore, using correlation heatmaps for local plot selection reduced potentially confounding relationships between landscape composition and configuration for plots located in forests, arable land and settlements. The suggested design expands upon previous research in covering a significant range of environmental gradients and including a diversity of dominant land-use types at different scales within different climatic contexts. It allows independent assessment of the relative contribution of multi-scale climate and land use on biodiversity and ecosystem services. Understanding potential interdependencies among global change drivers is essential to develop effective restoration and mitigation strategies against biodiversity decline, especially in expectation of future climatic changes. Importantly, this study also provides a baseline for long-term ecological monitoring programs

Folgen von Klimawandel und intensiver Landnutzung für Zersetzergemeinschaften und Abbauprozesse

The increase in intensively used areas and climate change are direct and indirect consequences of anthropogenic actions, caused by a growing population and increasing greenhouse gas emissions. The number of research studies, investigating the effects of land use and climate change on ecosystems, including flora, fauna, and ecosystem services, is steadily growing. This thesis contributes to this research area by investigating land-use and climate effects on decomposer communities (arthropods and microbes) and the ecosystem service ‘decomposition of dead material’. Chapter II deals with consequences of intensified land use and climate change for the ecosystem service ‘decomposition of dead organic material’ (necromass). Considering the severe decline in insects, we experimentally excluded insects from half of the study objects. The decomposition of both dung and carrion was robust to land-use changes. Dung decomposition, moreover, was unaffected by temperature and the presence/ absence of insects. Along the altitudinal gradient, however, highest dung decomposition was observed at medium elevation between 600 and 700 m above sea level (although insignificant). As a consequence, we assume that at this elevation there is an ideal precipitation:temperature ratio for decomposing organisms, such as earthworms or collembolans. Carrion decomposition was accelerated by increasing elevation and by the presence of insects, indicating that increasing variability in climate and an ongoing decline in insects could modify decomposition processes and consequently natural nutrient cycles. Moreover, we show that different types of dead organic material respond differently to environmental factors and should be treated separately in future studies. In Chapter III, we investigated land-use and climate effects on dung-visiting beetles and their resource specialization. Here, all beetles that are preferentially found on dung, carrion or other rotten material were included. Both α- and γ-diversity were strongly reduced in agricultural and urban areas. High precipitation reduced dung-visiting beetle abundance, whereas γ-diversity was lowest in the warmest regions. Resource specialization decreased with increasing temperatures. The results give evidence that land use as well as climate can alter dung-visiting beetle diversity and resource specialization and may hence influence the natural balance of beetle communities and their contribution to the ecosystem service ‘decomposition of dead material’. The following chapter, Chapter IV, contributes to the findings in Chapter II. Here, carrion decomposition is not only explained by land-use intensity and climate but also by diversity and community composition of two taxonomic groups found on carrion, beetles and bacteria. The results revealed a strong correlation between bacteria diversity and community composition with temperature. Carrion decomposition was to a great extent directed by bacterial community composition and precipitation. The role of beetles was neglectable in carrion decomposition. With this study, I show that microbes, despite their microscopic size, direct carrion decomposition and may not be neglected in future decomposition studies. In Chapter V a third necromass type is investigated, namely deadwood. The aim was to assess climate and land-use effects on deadwood-inhabiting fungi and bacteria. Main driver for microbial richness (measured as number of OTUs) was climate, including temperature and precipitation. Warmer climates promoted the diversity of bacteria, whereas fungi richness was unaffected by temperature. In turn, fungi richness was lower in urban landscapes compared to near-natural landscapes and bacteria richness was higher on meadows than on forest sites. Fungi were extremely specialized on their host tree, independent of land use and climate. Bacteria specialization, however, was strongly directed by land use and climate. These results underpin previous studies showing that fungi are highly specialized in contrast to bacteria and add new insights into the robustness of fungi specialization to climate and land use. I summarize that climate as well as intensive land use influence biodiversity. Temperature and precipitation, however, had positive and negative effects on decomposer diversity, while anthropogenic land use had mostly negative effects on the diversity of decomposers.Die Zunahme intensiv genutzter Landschaften und der Klimawandel sind direkte und indirekte Folgen menschlichen Handelns, verursacht durch eine wachsende Weltbevölkerung und zunehmende Mengen an Treibhausgasen. Die Zahl der wissenschaftlichen Studien, die sich mit den Veränderungen der Umwelt und den Konsequenzen für Ökosysteme, einschließlich Flora, Fauna und Ökosystemleistungen auseinandersetzen, steigt stetig. Mit dieser Thesis möchte ich meinen Beitrag zu diesem wichtigen und aktuellen Forschungsgebiet leisten. Dazu untersuche ich die Auswirkungen von Landnutzung und Klima auf die Ökosystemleistung „Zersetzung toten organischen Materials“ (Nekromasse) und die Auswirkungen auf die daran beteiligten Arthropoden- und Mikrobengemeinschaften. Kapitel II dieser Thesis setzt sich mit den Konsequenzen von intensiver Landnutzung und Klimawandel für die Ökosystemleistung „Zersetzung toten Materials“ auseinander. Unter Anbetracht des globalen Insektenrückgangs, wurde dieser Aspekt anhand eines Insektenausschluss-Experimentes zusätzlich simuliert. Es stellt sich heraus, dass sowohl der Abbau von Dung als auch von Aas sehr robust gegenüber landschaftlicher Nutzung war. Zudem blieb der Abbau von Dung unberührt von Temperaturänderungen und dem Ausschluss von Insekten. Entlang eines Höhengradienten wurde hingegen ein Trend zu einem unimodalen Muster mit maximaler Zersetzung bei ca. 600-700 m ü.M. beobachtet. Dieser Trend lässt vermuten, dass in dieser Höhe das Verhältnis von Niederschlag und Temperatur ideal für Dung zersetzende Gemeinschaften ist. Aas hingegen wurde in zunehmender Höhe und unter der Beteiligung von Insekten schneller zersetzt, was verdeutlich, dass Klimaänderungen und ein ansteigender Insektenrückgang starke Auswirkungen auf die Zersetzung von Aas und somit auf Nährstoffkreisläufe haben können. Hierbei wurde zudem ersichtlich, dass verschiedene Typen von Nekromasse unterschiedlich auf Umweltparameter reagieren und daher in künftigen Studien und Auswertungen separat betrachtet werden sollten. Kapitel III behandelt die Auswirkungen von Landnutzung und Klima auf die Biodiversität und Spezialisierung von Käfergemeinschaften an Dung. Hierbei wurden sämtliche Käfer berücksichtigt, welche vor allem an Dung, Aas oder sonstigem faulenden Material gefunden werden können. Sowohl α- als auch γ-Diversität von diesen Käfern wurde durch Agrarlandschaften und urbane Gebiete stark reduziert. Hohe Niederschlagsmengen wirkten sich negativ auf die Abundanz von Dungkäfern aus, wohingegen die γ-Diversität in warmen Regionen am niedrigsten war. Der Grad der Spezialisierung von Käfergemeinschaften auf verschiedene Dungressourcen nahm mit abnehmenden Temperaturen zu. Aus den Ergebnissen geht hervor, dass sowohl intensive Landnutzung als auch Klimaveränderungen Auswirkungen auf die Diversität und den Spezialisierungsgrad von Käfergemeinschaften an Dung haben können und somit das ökologische Gleichgewicht der Dungkäfergemeinschaften und ihren Ökosystemfunktionen beeinflussen können. Das darauffolgende Kapitel IV stellt eine Ergänzung zu Kapitel II dar. Hier wird die Zersetzung von Aas nicht nur anhand von Landnutzung und Klima erklärt, sondern auch anhand der α-Diversität und der Artenzusammensetzung von Käfern und Bakterien an Aas diskutiert. Es zeigte sich, dass Abundanz und Artenzusammensetzung der Bakteriengemeinschaft an Aas vor allem von der Temperatur abhingen. Außerdem wurde die Zersetzungsgeschwindigkeit maßgeblich von der Bakteriengemeinschaft und der Niederschlagsmenge bestimmt. Mit dieser Studie konnte ich zeigen, dass Bakterien trotz ihrer mikroskopischen Größe maßgeblich an der Zersetzung von Aas beteiligt sind und diese in Zersetzungsversuchen nicht vernachlässigt werden sollten. Das letzte Kapitel, Kapitel V, befasst sich mit den Konsequenzen von intensiver Landnutzung und Klimawandel auf mikrobielle Gemeinschaften in Totholz. Untersucht wurden hier sowohl Bakterien- als auch Pilzgemeinschaften. Haupttreiber der Artenvielfalt für beide Gruppen (gemessen als Anzahl an OTUs) war das Klima (Niederschlag und Temperatur). Ein wärmeres Klima kam der Vielfalt von Bakterien zugute, wohingegen die Pilzvielfalt nicht tangiert wurde. Außerdem reagierten Pilze negativ auf urbane Landnutzung, Bakterienvielfalt in Totholz war auf Wiesen jedoch höher als im Wald. Vor allem Pilze zeigten eine sehr starke Bindung zu ihrem Wirtsbaum, welche auch von äußeren Einflüssen wie Landnutzung und Klima nicht beeinflusst werden konnte. Die Spezialisierung von Bakterien hingegen wurde stark von Landnutzung und Klima beeinflusst. Diese Ergebnisse untermauern frühere Studien, die besagen, dass Pilze hoch spezialisiert sind und geben neue Erkenntnisse zur Robustheit der Spezialisierung gegenüber Landnutzungsintensität und Klima. Zusammenfassend kann ich sagen, dass sowohl Klima als auch Landnutzung Auswirkungen auf die Biodiversität haben. Während Temperatur und Niederschlag jedoch positive so wie negative Effekte hatten, wirkte sich anthropogene Landnutzung überwiegend negativ auf die Diversität von Zersetzergemeinschaften aus

Climate effects on vertical forest phenology of Fagus sylvatica L., sensed by Sentinel-2, time lapse camera, and visual ground observations

Contemporary climate change leads to earlier spring phenological events in Europe. In forests, in which overstory strongly regulates the microclimate beneath, it is not clear if further change equally shifts the timing of leaf unfolding for the over- and understory of main deciduous forest species, such as Fagus sylvatica L. (European beech). Furthermore, it is not known yet how this vertical phenological (mis)match — the phenological difference between overstory and understory — affects the remotely sensed satellite signal. To investigate this, we disentangled the start of season (SOS) of overstory F.sylvatica foliage from understory F. sylvatica foliage in forests, within nine quadrants of 5.8 × 5.8 km, stratified over a temperature gradient of 2.5 °C in Bavaria, southeast Germany, in the spring seasons of 2019 and 2020 using time lapse cameras and visual ground observations. We explained SOS dates and vertical phenological (mis)match by canopy temperature and compared these to Sentinel-2 derived SOS in response to canopy temperature. We found that overstory SOS advanced with higher mean April canopy temperature (visual ground observations: −2.86 days per °C; cameras: −2.57 days per °C). However, understory SOS was not significantly affected by canopy temperature. This led to an increase of vertical phenological mismatch with increased canopy temperature (visual ground observations: +3.90 days per °C; cameras: +2.52 days per °C). These results matched Sentinel-2-derived SOS responses, as pixels of higher canopy height advanced more by increased canopy temperature than pixels of lower canopy height. The results may indicate that, with further climate change, spring phenology of F. sylvatica overstory will advance more than F. sylvatica understory, leading to increased vertical phenological mismatch in temperate deciduous forests. This may have major ecological effects, but also methodological consequences for the field of remote sensing, as what the signal senses highly depends on the pixel mean canopy height and the vertical (mis)match

Relationship of insect biomass and richness with land use along a climate gradient

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

Earlier flowering of winter oilseed rape compensates for higher pest pressure in warmer climates

Global warming can increase insect pest pressure by enhancing reproductive rates. Whether this translates into yield losses depends on phenological synchronisation of pests with their host plants and natural enemies. Simultaneously, landscape composition may mitigate climate effects by shaping the resource availability for pests and their antagonists. Here, we study the combined effects of temperature and landscape composition on pest abundances, larval parasitism, crop damage and yield, while also considering crop phenology, to identify strategies for sustainable management of oilseed rape (OSR) pests under warming climates. In all, 29 winter OSR crop fields were investigated in different climates (defined by multi‐annual mean temperature, MAT) and landscape contexts in Bavaria, Germany. We measured abundances of adult pollen beetles and stem weevil larvae, pollen beetle larval parasitism, bud loss, stem damage and seed yield, and calculated the flowering date from growth stage observations. Landscape parameters (proportion of non‐crop and OSR area, change in OSR area relative to the previous year) were calculated at six spatial scales (0.6–5 km). Pollen beetle abundance increased with MAT but to different degrees depending on the landscape context, that is, increased less strongly when OSR proportions were high (1‐km scale), interannually constant (5‐km scale) or both. In contrast, stem weevil abundance and stem damage did not respond to landscape composition nor MAT. Pollen beetle larval parasitism was overall low, but occasionally exceeded 30% under both low and high MAT and with reduced OSR area (0.6‐km scale). Despite high pollen beetle abundance in warm climates, yields were high when OSR flowered early. Thereby, higher temperatures favoured early flowering. Only among late‐flowering OSR crop fields yield was higher in cooler than warmer climates. Bud loss responded analogously. Landscape composition did not substantially affect bud loss and yield. Synthesis and applications: Earlier flowering of winter OSR compensates for higher pollen beetle abundance in warmer climates, while interannual continuity of OSR area prevents high pollen beetle abundance in the first place. Thus, regional coordination of crop rotation and crop management promoting early flowering may contribute to sustainable pest management in OSR under current and future climatic conditions

Plant richness, land use and temperature differently shape invertebrate leaf-chewing herbivory on plant functional groups

Higher temperatures can increase metabolic rates and carbon demands of invertebrate herbivores, which may shift leaf-chewing herbivory among plant functional groups differing in C:N (carbon:nitrogen) ratios. Biotic factors influencing herbivore species richness may modulate these temperature effects. Yet, systematic studies comparing leaf-chewing herbivory among plant functional groups in different habitats and landscapes along temperature gradients are lacking. This study was conducted on 80 plots covering large gradients of temperature, plant richness and land use in Bavaria, Germany. We investigated proportional leaf area loss by chewing invertebrates (‘herbivory’) in three plant functional groups on open herbaceous vegetation. As potential drivers, we considered local mean temperature (range 8.4–18.8 °C), multi-annual mean temperature (range 6.5–10.0 °C), local plant richness (species and family level, ranges 10–51 species, 5–25 families), adjacent habitat type (forest, grassland, arable field, settlement), proportion of grassland and landscape diversity (0.2–3 km scale). We observed differential responses of leaf-chewing herbivory among plant functional groups in response to plant richness (family level only) and habitat type, but not to grassland proportion, landscape diversity and temperature—except for multi-annual mean temperature influencing herbivory on grassland plots. Three-way interactions of plant functional group, temperature and predictors of plant richness or land use did not substantially impact herbivory. We conclude that abiotic and biotic factors can assert different effects on leaf-chewing herbivory among plant functional groups. At present, effects of plant richness and habitat type outweigh effects of temperature and landscape-scale land use on herbivory among legumes, forbs and grasses