In habitats where prey is either rare or difficult to predict spatiotemporally, such as open habitats, predators must be adapted to react effectively to variations in prey abundance. Open-habitat foraging bats have a wing morphology adapted for covering long distances, possibly use information transfer to locate patches of high prey abundance, and would therefore be expected to show an aggregative response at these patches. Here, we examined the effects of prey abundance on foraging activities of open-habitat foragers in comparison to that of edge-habitat foragers and closed-habitat foragers. Bat activity was estimated by counting foraging calls recorded with bat call recorders (38,371 calls). Prey abundance was estimated concurrently at each site using light and pitfall traps. The habitat was characterized by terrestrial laser scanning. Prey abundance increased with vegetation density. As expected, recordings of open-habitat foragers clearly decreased with increasing vegetation density. The foraging activity of edge- and closed-habitat foragers was not significantly affected by the vegetation density, i.e., these guilds were able to forage from open habitats to habitats with dense vegetation. Only open-habitat foragers displayed a significant and proportional aggregative response to increasing prey abundance. Our results suggest that adaptations for effective and low-cost foraging constrains habitat use and excludes the guild of open-habitat foragers from foraging in habitats with high prey abundance, such as dense forest stands.

Climate change is expected to exacerbate the frequency of drought-induced tree mortality world-wide. To better predict the associated change of species composition and forest dynamics on various scales and develop adequate adaptation strategies, more information on the mechanisms driving the often observed patchiness of tree die-back is needed. Although forest-edge effects may play an important role within the given context, only few corresponding studies exist. Here, we investigate the regional die-back of Scots pine in Franconia, Germany, after a hot and dry summer in 2015, thereby emphasizing possible differences in mortality between forest edge and interior. By means of dendroecological investigations and close-range remote sensing, we assess long-term growth performance and current tree vitality along five different forest-edge distance gradients. Our results clearly indicate a differing growth performance between edge and interior trees, associated with a higher vulnerability to drought, increased mortality rates, and lower tree vitality at the forest edge. Prior long-lasting growth decline of dead trees compared to live trees suggests depletion of carbon reserves in course of a long-term drought persisting since the 1990s to be the cause of regional Scots pine die-back. These findings highlight the forest edge as a potential focal point of forest management adaptation strategies in the context of drought-induced mortality.

Changes of the soil chemical status during the recent 22-30 years at two historically degraded forest sites in southern Germany (Pfaffenwinkel, Pustert) stocked with mature Scots pine (Pinus sylvestris L.) stands were studied by repeated soil inventories conducted in 1974, 1982-1984, 1994, and 2004 on replicated control plots of fertilization experiments, allowing a statistical analysis. Additionally, the nutritional status of the stands at all plots was monitored from 1964 until 2004 by annual or bi-annual analysis of current-year foliage, and stand growth was assessed by repeated stand inventories carried out in 3-to 9-year intervals. For both sites, a statistically significant systematic decrease of the forest floor C/N ratio between 1974 and 2004 from 35.4 to 29.2 (Pfaffenwinkel) and from 36.5 to 23.0 (Pustert) was observed. The soils at both sites also showed a considerable accumulation of organic carbon (210 and 400 kg C ha -1 year -1 for Pfaffenwinkel and Pustert, respectively) and nitrogen (13 and 18 kg N ha -1 year -1 ). In addition, the mineral topsoil at both sites has acidified considerably, indicated by significantly decreased pH values (Pustert only; mean decrease 0.1 units per decade), base saturation, and base cation stocks. The trend of N enrichment and base cation loss in the soils is mirrored by the trends of stand nutrition at both sites, which are characterized by improved N nutrition and reduced supply with K, Mg (Pustert only), and Ca. The results confirm findings of other studies indicating a recent N eutrophication and acidification of forest soils in Central Europe and southern Scandinavia. Since soils with historic degradation due to earlier non-sustainable forest utilization are widespread in Central Europe, the results obtained on our study sites probably apply for large forested areas, suggesting a significant potential of Central European forests to sequester atmospheric carbon and nitrogen not only in stand biomass, but also in the soil.

Question: What are the main drivers for tree species distribution in the Bavarian Alps? What are the species-specific habitat requirements? Are predictions in accordance with expert knowledge?Location: Bavarian Alps (Southern Germany).Methods: To describe tree species-environment relationships, we established species distribution models for the 14 most common tree species of the region. We combined tree species occurrence data from forest inventories and a vegetation database with environmental data from a digital elevation model, climate maps and soil maps. For modelling, we used generalized additive models (GAM) combined with techniques to account for spatial autocorrelation and uneven coverage of environmental gradients. We developed parsimonious models to judge whether statistical models correspond to models based on expert knowledge.Results: Conceptual models were generally in accordance with expectations.Variables based on average temperatures were the most important predictors in most models. Proxies for soil properties such as water and nutrient availability were statistically significant and generally plausible, but appeared largely redundant for model performance. Altitudinal limits of tree species were generally well represented by models. Most species responded differently to summer and January temperatures, indicating that temperature variables are proxies not only for energy balance, but also for frost damage and drought. Although model building benefits considerably from collation with expert knowledge, there are limitations.Conclusions: Meaningful species distribution models can be obtained from noisy data sets covering only a small fraction of species ranges. Models calibrated with such data sets benefit from hypothesis-driven model building rather than strict data-driven model building. Hence, misleading explanations and predictions can be avoided and uncertainties identified. Nevertheless, projections based on climate scenarios can be substantially improved only with models calibrated on a wider data set. Ideally, environmental gradients should cover the whole niche space of a species, or at least include regions with analogous climate.