Bavarian Forest National Park

Abstract Centuries of timber production have homogenized many forests by reducing variation in canopy density and deadwood availability, with far‐reaching consequences for biodiversity and trophic interactions. Recent studies indicate that increasing structural heterogeneity through canopy gap creation and deadwood enrichment can promote biodiversity and support tree regeneration. These management practices may also influence tree performance, among others assessed by folivory and leaf fluctuating asymmetry, which indicate how well trees resist leaf damage and maintain developmental stability under environmental stress. However, it remains unknown whether such management enables trees to mitigate folivory and developmental instability, especially across macroclimatic gradients such as elevation. We conducted a large‐scale experiment in Germany across 11 pairs of forests: one structurally homogeneous control forest and one experimentally heterogenized forest, where canopy gaps and deadwood were created to increase between‐patch structural heterogeneity. The forests spanned an elevation gradient from 38 to 1143 m. Across all forest pairs, we sampled 19,656 leaves from 1404 European beech ( Fagus sylvatica L.) trees. We quantified folivory, leaf fluctuating asymmetry, microclimatic conditions (temperature, vapour pressure deficit) and biotic pressures (predation, parasitism, competition). Experimental enhancement of structural heterogeneity reduced folivory overall but increased leaf fluctuating asymmetry. Folivory increased with elevation, while leaf fluctuating asymmetry declined, producing an inverse relationship: At low elevations, structural enhancement reduced folivory but increased asymmetry, whereas at high elevations it increased folivory but reduced asymmetry. Microclimatic variables explained variation in both folivory and leaf asymmetry more consistently than biotic pressures. These findings extend the stress‐gradient framework by showing that identical management interventions can yield opposite outcomes depending on the macroclimatic gradient associated with elevation. Thus, integrating elevation and climate context into forest management seems to be crucial for maintaining the resilience of temperate forests under global change. Read the free Plain Language Summary for this article on the Journal blog.

Abstract Animals adjust behavior to changes in perceived predation risk, even when risk is non-consumptive, as is the case for human recreation. However, individuals within populations can differ greatly in their plasticity toward perceived risk, especially when antipredator responses incur fitness costs via lost foraging opportunities. Therefore, risk-benefit trade-offs are usually made at the individual level. We test whether red deer (Cervus elaphus) inhabiting the Bavarian Forest National Park show individual variation in behavioral plasticity toward human disturbance. We measured human disturbance as the number of recreationists on the closest trail on a given day and used random regression to dissolve movement responses, measured as hourly step-length, of 63 GPS-collared red deer females to fine scale spatio-temporal variation in disturbance. We quantified behavioral state-specific between-individual variation along the disturbance gradient. At the population level, red deer responded to recreational disturbance during the middle of the day only, and reduced movement in response to recreation. However, population patterns masked strong between-individual variation in plasticity to recreational disturbance during the morning, midday, and evening, such that some deer reacted with increased or decreased movement rates while others responded little. Behavioral responses were mediated by vegetation cover with stronger responses in more open habitat. Flight responses are costly due to lost foraging opportunities. A shift in risk-benefit tradeoffs when risk is non-lethal, as is the case for recreation in many national parks, may favor more human-tolerant individuals over time.

Abstract Although habitat heterogeneity is known to enhance local species diversity, the effects of management-driven structural heterogeneity on understorey plant communities across spatial scales remain poorly understood, despite their crucial role for forest biodiversity and ecosystem functioning. To analyse how forest understorey plant communities respond to an enhancement of structural heterogeneity in managed forests, we established 11 experimental sites consisting of two paired forest landscapes, an untreated homogenous control and a treatment district (ESBC). In treatment districts, structural heterogeneity was enhanced through different combinations of local patch-scale manipulations of light and deadwood features, leading to greater between-patch heterogeneity at the landscape scale. We performed a meta-analysis across these 11 sites using a Hill-Chao number and sample coverage standardisation framework. Gamma diversity increased across taxonomic, functional and phylogenetic facets in structurally heterogeneous forests (ESBC districts) via higher alpha diversity. This effect was positively associated with heterogeneity in light availability between forest patches, but not with their mean light availability. In contrast, we found no support that species turnover among patches (i.e., beta diversity) significantly contributes on average to the observed increase in gamma diversity. However, both the direction and magnitude of beta diversity responses varied substantially among landscapes. On average, structurally heterogeneous forests supported higher species richness for both open and closed forest habitat species. Synthesis and applications: Our findings highlight the benefits of enhancing structural heterogeneity for understorey plant diversity in managed forest landscapes. Specifically, management strategies that create a spatial mosaic of interventions, such as combining single-tree removal with group felling, can increase the variety of light niches among forest patches, thereby supporting the conservation of a wide range of understorey plant species, including forest specialists.

Fine woody debris (FWD; deadwood < 10cm diameter) is a crucial but often overlooked component of forest ecosystems. It provides habitat for microbial communities and enhances soil fertility through nutrient cycling. This role is especially important in managed forests, which typically have limited deadwood stocks. Climate change is increasing forest disturbances and expanding early successional forests with low canopy cover, yet the effects on microbial communities and related processes remain poorly understood. In a ten-year canopy manipulation experiment, we examined the decomposition of FWD of Fagus sylvatica and Abies alba. Increased canopy openness significantly decreased bacterial diversity in decomposing FWD and altered the community composition in surrounding soil. Decomposition time was the main factor shaping bacterial community structure in FWD, with tree species and canopy cover also contributing. We identified bacterial groups involved in carbohydrate degradation, fungal biomass breakdown, and nitrogen fixation. Importantly, bacterial communities in fully decomposed FWD remained distinct from soil communities. Deadwood decomposition and nutrient cycling are driven by complex ecological interactions. Microbial community dynamics are influenced by the interplay of FWD decomposition stage, tree species, and microclimatic conditions. Bacterial communities, although less frequently studied in this context, appear more stable over time than previously studied fungi. This stability may help sustain decomposition processes and nutrient turnover under the environmental variability associated with global change.

Properly managing forests requires tools that offer up-to-date information on forest dynamics.

Fungi represent a significant portion of Earth's biological diversity and are essential for ecosystem functions like organic matter decomposition and nutrient cycling. While fungi associated with plant roots have been extensively studied, our understanding of fungi in the forest canopies remains limited. To investigate the landscape-scale variation in the canopy mycobiome of temperate beech and spruce forest stands in the Bavarian Forest National Park (Germany), we examined the influence of geophysical conditions and host traits. We found that elevation significantly influenced fungal diversity and composition, with distinct effects observed in both beech and spruce stands. Moreover, canopy water content, a key indicator of tree vitality, was also strongly associated with changes in the canopy fungi community, suggesting a potential link between forest water stress and the forest canopy mycobiome. Our differential abundance analysis further identified a total of 41 fungal families as potential bioindicators: 17 families in beech stands and 9 in spruce stands were significantly associated with elevation, while 9 families in beech stands and 6 in spruce stands were linked to variations in leaf water content. These findings enhance our understanding of the spatial patterns of forest canopy microbial biodiversity and species distributions.

Forest soils are substantial sinks for carbon, yet the effectiveness of management practices such as strict conservation to sequester more soil organic carbon is unknown. A complication is the increase in forest disturbance due to climate change, key to which is the loss of canopy cover. We sampled paired control-canopy gap plots in drought-sensitive Norway spruce stands on Stangosols developed on Buntsandstein in the Black Forest National Park (2000 mm MAP, 5.5&amp;#176;C MAT). Three pairs are located within the management zone with sanitation logging of beetle infestations (gaps &lt; 5 years old with little deadwood), and three more are in the core zone without logging since 1911 (gaps &lt; 15 years old with moderate deadwood).In the management zone, canopy gaps had warmer and slightly wetter forest floors (+0.45 &amp;#176;C and +1.7 % Vol), but thickness, carbon stocks and C/N ratios in the forest floor did not differ between canopy treatments. In the core zone by comparison, circa 50 Mg ha-1 more carbon was found under closed canopies than canopy gaps as well as both canopy types in the management zone. Density fraction revealed most changes occurred in the free and occluded light fractions, which constituted circa 50 and 40% of SOC, respectively, in the core zone.Lignin-derived phenols were extracted with cupric oxide oxidation to trace the source of soil organic matter (SOM). Lignin markers in the forest floor came mostly from coniferous wood and at times was less oxidized in canopy gaps. Additionally, subsoil horizons exhibited surprisingly little lignin oxidation regardless of canopy treatment, resulting in lignin-derived phenols constituting up to circa 20% of SOM. This applied to other CuO-extractable phenols, which in subsoil accounted for a further 10% of SOM.The increase in core zone SOC stock is of a similar magnitude to accumulated deadwood if averages of 10 m3 ha-1 year-1 annual growth increment and 33% mortality are assumed. Wood-derived lignin absent in canopy gaps likely underwent less-oxidative photodegradation and leaching both deeper into mineral soil and laterally into catchments. Sequestration of wood-derived particulate SOM is thus possible in moist, acidic sandy soils, but such SOM is sensitive to disturbance-driven microclimatic changes.

Export of dissolved organic carbon (DOC) from catchments to streams has increased in the last decades in many catchments across the Northern hemisphere. Mobilisation of DOC from riparian soils and wetlands is highly dependent on discharge and is triggered by storm events. In many cases a very strong correlation between DOC and Fe concentrations during storm events can be observed in the streams suggesting joint source areas and mobilisation mechanisms. In this contribution we will discuss causes and mechanisms of Fe transfer from catchments into aquatic systems. Analyses of Fe species from a 40-years sample archive from the Gro&amp;#223;e Ohe Catchment in the Bavarian Forest National Park indicated that between 60 and 100 % of the dissolved Fe determined were in the reduced form Fe(II). Thus, a substantial amount of redox equivalents will thus be exported from catchments, and the implications for e.g. the oxygen budget of streams will be discussed.