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Highlights • High structural heterogeneity reduces the diurnal temperature range (DTR). • Effects of stand structure on DTR are more pronounced in regions with low precipitation. • DTR is lower in unmanaged than in managed uneven-aged and even-aged stands. • Terrestrial laser scanning based approaches explain 79.4% of variance in DTR. Abstract The microclimate in forest ecosystems can be altered by modifications of stand structure due to forest management or natural forest development. Current forest management practices in Central Europe and North America aim to promote structural heterogeneity and maintain forest canopy cover, which is known to be a major driver of forest microclimate. Here, we investigated the impacts of forest management and structural heterogeneity on the diurnal temperature range (DTR) in 128 managed forest stands in three climatically different locations (Swabian Alb, Hainich-Dün and Schorfheide-Chorin) in Central Europe. Increasing structural heterogeneity by promoting tree size diversity and differentiation increased vertical stratification and resulted in an impaired DTR during the vegetation period. Linear regression models with geographic location, elevation above sea level, canopy openness and measures of structural heterogeneity as explanatory variables explained 79.4–80.9% of variance in DTR. However, the overall effect of structural heterogeneity on DTR was small. Differences in DTR between plots of different main tree species could be attributed to differences in canopy openness and light transmission, whereas tree species diversity had no significant effect on DTR. Unmanaged forests were characterized by a significantly lower DTR than managed, even-aged forests. DTR in uneven-aged stands managed under single tree selection was comparable to unmanaged stands. Terrestrial laser scanning (TLS) derived measures of canopy openness and vertical structure allowed to explain 79.4% of variance in DTR considering geographic location and elevation, which can also be assessed by TLS with integrated GPS and an altimeter. We conclude that structural characteristics of forest stands other than canopy openness contribute marginally to variation in forest microclimate. However, the analyses of structure-microclimate analyses indicate that effects of stand structure on DTR might be more pronounced in regions with low precipitation during the vegetation period. [ABSTRACT FROM AUTHOR]

Highlights • SSCI of beech-dominated forests was highest in primary forests. • SSCI in thickets with shelterwood trees is nearly as high as in primary forests. • Lowest SSCI was found in National Parks with management ceased 30 yrs ago. • SSCI varied significantly across typical age classes in managed forests. Abstract The high structural heterogeneity of primary forests is assumed to positively affect various ecosystem traits and functions, e.g. biodiversity, resilience and adaptability. Against this background, old-growth forest structures are emulated in many managed forests. To properly emulate such structures, quantitative reference values are required, through which primary forests are characterized. In this study, we used the stand structural complexity index (SSCI), derived from terrestrial laser scanning (TLS), to characterize and compare the structures in European beech (Fagus sylvatica L.) dominated forests along a management gradient, ranging from differently managed stands, over formerly managed but now unmanaged stands to primary forests, which have never been managed. The study objective was to quantify and compare the structural complexity of these forests to give insight into possible reference points for an improved prospective handling of managed forests. The highest stand structural complexity was found in primary forests. While there were no significant structural differences between the managed forests, they were more complex in structure than formerly managed forests that have been set aside as National Parks now. The results also showed that structural complexity significantly differed between the investigated stand age classes. Next to primary forests, thickets growing below sheltering overstory trees in managed forests resulted in high structural complexity values. The findings suggest that specific silvicultural management practices can increase the structural complexity in beech forests. This study may facilitate a 'management for complexity' in silvicultural practice and might lead the way towards a more precise promotion of three dimensional forest structures that are associated with specific forest functions as part of the stand management objectives. [ABSTRACT FROM AUTHOR]

The position and size of trees is basic information available for most forest-research sites. Based on such information, various stand structural indices and measures can be calculated that describe the two-dimensional or three-dimensional forest structure. We used fractal analysis to calculate the box-dimension (D b ) as a measure of structural complexity that can be derived from stem positions and stem diameters. D b is supposed to combine information on tree size, tree distribution and stem density in a single meaningful measure. We wanted to know how powerful the method is if applied to two-dimensional stem distribution maps. Based on 125 research plots (coniferous, deciduous and mixed stands) we found that across typical forest systems in Germany there is no benefit from using the box-dimension. Stem number and mean tree diameter determined D b values and there was almost no sensitivity observed for existing differences in stem distribution pattern. We conclude that D b is a measure of stand density but, for the investigated forests, it does not provide information on tree distribution pattern if applied to the stem base maps. [ABSTRACT FROM AUTHOR]

Animal-vehicle collisions (AVCs) pose a serious threat to human and animal welfare, and result in increasing costs for society. Mitigation efforts have been in the focus of research for decades but have revealed only few generalities on where and why AVCs occur. Uncertainty therefore remains on how to make decisions regarding nature conservation, wildlife and transportation management. In our study, we used GPS data on almost 1000 AVCs between October 2014 and October 2016 involving roe deer ( Capreolus capreolus L.) in the administrative district of Göttingen, Germany, to identify accident hotspots based on Kernel Density analysis. We then used information from a mapping campaign of trees outside forests (TOF), including hedges, bushes, groves, isolated trees and other non-forest vegetation to investigate whether TOF abundance is larger near accident hotspots when compared to areas showing no hotspots (assumed as reference area). We found that near hotspots, TOF are significantly more abundant than in the remaining reference area. We conclude that future transportation management should consider TOF management as a possible indicator for AVCs. [ABSTRACT FROM AUTHOR]

Silvicultural success in achieving, among other management goals, maximum productivity strongly depends on knowledge of the relationship between stand density and the resulting growth response of a stand. However, there are still controversial discussions whether wood production can be enhanced by silvicultural thinning or reaches its maximum in unmanaged forest stands if time plays no role. Moreover there is no universal answer whether structural diversity promotes or reduces productivity. In the present study we applied terrestrial laser scanning (TLS) to investigate the relationship between three-dimensional space filling, forest management intensity, productivity and conventional measures of structural diversity. We examined 35 beech-dominated forest plots along a gradient of management intensity in three regions of Germany. We found that space filling in leaf-on condition increased with management intensity, particularly in the shaded crown. Increased space filling in the shaded crown due to tree removals also resulted in higher stand productivity. We conclude that an increased space filling in the shaded canopy of managed European beech stands is responsible for the compensation of production losses in the upper canopy due to thinning activities. Conventional measures of structural diversity were not sensitive to the applied silvicultural activities. We also found no relationship between structural diversity described by conventional measures and stand productivity. [ABSTRACT FROM AUTHOR]

Efficient quantification of the three-dimensional forest structure is of increasing importance for our understanding of forest functions and services, but it remains challenging with conventional methods. We used a single-scan ground-based laser approach in stands with a known difference in management history and associated differences in structures. The data were used to test whether the measurement approach could distinguish various structural measures among the stands, including overall density, vertical structure, competitive conditions for regeneration, horizontal visibility, and three-dimensional structural variability. In general, our data reflected known differences in stand structure. However, in some cases the different measures showed contradicting results, highlighting the limited information represented in each measure when considered in isolation. At the same time, our results suggested that all components of stand structure do not develop in sync. The variability of horizontal and vertical structural heterogeneity appears to be a good indicator of structural elements typically found in old-growth forests, i.e., spatially homogenous (scale independent) horizontal structural variability in combination with a scale-dependent vertical structural variability. In addition, our results provided information with direct management implications. For example, gap creation, a prominent practice in restoration treatments in the region, increased spatial variability, but the hard edges and removal of all trees inside the gap, are not reflecting structural conditions found in our old-growth stand. In summary, our results suggest that this new technology can efficiently provide objective and holistic inventories of stand structures. However, more work is needed to fully understand the implications of the novel structural measures for ecosystem processes and services. [ABSTRACT FROM AUTHOR]

The relevance of stand structural heterogeneity for biodiversity conservation is increasingly recognized and efficient tools for its measurement are demanded. Here, we quantified forest structure by calculating the effective number of layers (ENL) for different Hill Numbers (0D, 1D, 2D) as a measure of vertical structure of a subplot. We than use sampling techniques to cover the horizontal structural variability within study plots. ENL describes the vertical structure based on the occupation of 1 m wide vertical layers by tree components relative to the total space occupation of a stand. Space occupation was quantified by a voxel-model obtained from terrestrial laser scanning (TLS) on 150 forest plots in Germany. We used a single scan approach, which requires less field work and post-processing compared to multiple-scans. Single-scan derived mean ENL and its coefficient of variation successfully differentiated forest structures over a wide range of even-aged, uneven-aged and unmanaged broadleaved and coniferous stands. ENL was correlated to the stand summary measures basal area, quadratic mean diameter and stem density as well as stand age. ENL can be used to describe structural heterogeneity and proved to be efficiently assessable by TLS. [ABSTRACT FROM AUTHOR]

• Forest structure, spatial patterns and productivity in lenga forests were studied in three precipitation sites. • Forest structure, spatial patterns and productivity were influenced by precipitation. • Single tree selection silviculture can be implemented in humid and mesic site. • Transition adaptation strategies may be needed to sustain forest functions in the dry site. Climate is a critical variable in determining the productivity and structural complexity of forest ecosystems. Under similar temperature regimes and other site conditions, precipitation becomes fundamental for forest regeneration and growth, and eventually for the development of structural complexity and patterns in forest productivity. Empirical quantification for this expected response to varying precipitation is needed, especially to provide conservation and management strategies under current and future climate change impacts. To address this need, we evaluated the effects of varying annual precipitation regimes (dry, mesic, and humid sites; all with similar temperature regimes) on three key forest attributes and processes; 1) size and age structure, 2) tree spatial point patterns, and 3) forest stand productivity based on the normalized difference vegetation index (NDVI), in three old-growth lenga (Nothofagus pumilio) forests in western Patagonia. Tree-size and age structure were irregular in the humid and mesic sites, and regular (unimodal) in the dry site (based on Weibull probability function). The relationship between tree diameter and age was strongest in the humid site (r2 = 0.86), and weakest in the dry site (r2 = 0.36). Forest stand productivity was significantly higher in the humid site (mean NDVI = 0.73, vs. 0.68 and 0.63 in the mesic and dry sites, respectively). Univariate spatial-point patterns showed that the humid site had the strongest clumped pattern for live trees along all distances analyzed (i.e., 20 m), while the dry site had a fully random pattern for live and dead trees along all distances analyzed. Collectively, these results illustrate different challenges for silviculture in these forests: 1) The multi-aged structure, plus clumped spatial patterns of small trees (following partial overstory disturbance) in the humid and mesic sites, reflect a gap-based regeneration mode, which consequently suggests the feasibility of implementing uneven-aged silviculture in these sites; 2) Dry sites, close to the forest-steppe ecotone (dry, cool and windy) may require a focus on silviculture for adaptation to cope with expected declines in precipitation and to potentially avoid the loss of these ecosystems to woodlands; 3) Dieback of larger trees in mesic sites (presumably due to xylem cavitation) is a reflection of climate change impacts and a warning to implement strategies that may adapt these forests to new climate conditions (transition to dry condition). Consideration of the great variation in structure and productivity in Patagonian lenga forests due to differences in precipitation regimes, is urgently needed to guide the development of site-specific management approaches for this forest type, particularly given expected future declines in precipitation. [ABSTRACT FROM AUTHOR]

Silvicultural regimes that aim at an increased stand structural diversity typically promote small-scale heterogeneity in horizontal and vertical structures, e.g. through the creation of gaps. We used terrestrial laser scanning (TLS) to investigate impacts of altered growing conditions on trees adjacent to artificial gaps as compared to responses of trees in a regularly spaced, thinned forest interior. Based on the TLS-based point clouds we calculated a number of structural tree crown properties that were hypothesized to be sensitive to spatial variability in growing conditions. We found several significant differences between structural properties of trees in the two growing conditions. Compared to trees in regular spacing, border trees near gaps had a lower crown base height (CBH) and a lower height of maximum crown projection. Crown surface area and crown volume of border trees were significantly larger than those of trees growing in a regular spacing. Also, the asymmetry of entire tree crowns of border trees, and in particular of the lower third of crowns, was directed towards the gap center, reflecting the increased light level in the gap. Our results raise concerns that the economic value of border trees is negatively affected by gap creation. These trees had shorter branch free boles and additionally, due to horizontal branch elongation, larger knots. Conversely, the overall increase in structural variability contributed by the border trees in stands with artificial gaps is likely to positively affect several ecosystem functions as well as biodiversity. [ABSTRACT FROM AUTHOR]

Competition for canopy space is a key process in forest dynamics, but the underlying mechanisms are not well understood in old-growth forests. We combined laser-based canopy structural analysis and length-increment measurements of canopy branches for studying lateral and vertical crown expansion in four temperate broad-leaved tree species ( Fagus sylvatica , Fraxinus excelsior , Carpinus betulus , Tilia cordata ) in an old-growth temperate mixed forest. Using a 30 m-tall mobile canopy lift for accessing the canopy contact zone between different pairs of species, we were able to analyse the growth dynamics of more than 230 branches in their dependence on local light availability and neighbour species identity. The minimum distance between neighbouring crowns (crown shyness) was also determined for different species pairs. Contrary to expectation, lateral branch increment in the contact zone was not dependent on light availability for three species; a positive relationship existed only for Fraxinus . More than 50 percent of the lateral branches of Fagus , Carpinus and Tilia were broken due to mechanical abrasion at least once within the last six years prior to our measurements (2006–2011). Only the thicker more robust branches of Fraxinus showed minor damages. Mechanical interaction in allospecific neighbourhood was highly asymmetric for the species combinations Fraxinus–Tilia , Fraxinus–Carpinus , Fagus–Tilia , and partly asymmetric in the pair Fraxinus–Fagus (lower damage in the respective first species). Crown shyness was highest in the Fagus–Fraxinus neighbourhood (average minimum distance: 1.0 m), intermediate in Carpinus–Fagus pairs (0.6 m), and low in Fagus–Fagus (0.2 m) and Fagus–Tilia pairs (0 m; direct contact). We conclude that the dynamics of lateral canopy expansion in this mixed forest are mainly determined by mechanical interactions and not by competition for light. Interactions were in many cases asymmetric and depended on the species. This has important implications for forest dynamics modelling and forest management in mixed stands. [ABSTRACT FROM AUTHOR]

Highlights: [•] Terrestrial laser scanning can be used to quantify canopy space filling. [•] Space filling is not related to tree diversity per se. [•] Space filling is not related to NPPa. [•] Tree species identity has a significant effect on canopy space filling. [Copyright &y& Elsevier]

Highlights: [•] TLS-based competition indices were highly correlated with target tree growth. [•] All indices ascribed the highest competitive strength to intraspecific competition. [•] Growth response of the target trees reflected the strength in competition. [Copyright &y& Elsevier]

• Belowground biomass equations for 14 juvenile tree species. • Estimators of root biomass based on tree sapling height, diameter, aboveground biomass. • Broadleaf species with higher root biomass for a given dimension. • Trend of increasing relative belowground biomass with increasing light availability. • Height to diameter ratio (HD ratio) negatively correlated to relative belowground biomass. Just as the aboveground tree organs represent the interface between trees and the atmosphere, roots act as the interface between trees and the soil. In this function, roots take-up water and nutrients, facilitate interactions with soil microflora, anchor trees, and also contribute to the gross primary production of forests. However, in comparison to aboveground plant organs, the biomass of roots is much more difficult to study. In this study, we analyzed 19 European datasets on above- and belowground biomass of juvenile trees of 14 species to identify generalizable estimators of root biomass based on tree sapling dimensions (e.g. height, diameter, aboveground biomass). Such estimations are essential growth and sequestration modelling. In addition, the intention was to study the effect of sapling dimension and light availability on biomass allocation to roots. All aboveground variables were significant predictors for root biomass. But, among aboveground predictors of root biomass plant height performed poorest. When comparing conifer and broadleaf species, the latter tended to have a higher root biomass at a given dimension. Also, with increasing size, the share of belowground biomass tended to increase for the sapling dimensions considered. In most species, there was a trend of increasing relative belowground biomass with increasing light availability. Finally, the height to diameter ratio (H/D) was negatively correlated to relative belowground biomass. This indicates that trees with a high H/D are not only more unstable owing to the unfavorable bending stress resistance, but also because they are comparatively less well anchored in the ground. Thus, single tree stability may be improved through increasing light availability to increase the share of belowground biomass. [ABSTRACT FROM AUTHOR]

Abstract: Methods for estimating the biomass potential of dense coppice in coppice-with-standard forests in a fast and objective way are currently rare. We adapted existing methodical approaches for biomass estimations from terrestrial laser scanning developed for mature stands in order to perform single scan measurements of diameter at breast height in extremely dense coppice with a stem density of 30,000 ha−1. Diameter was then used as input for allometric regression models for estimations of the dry weights. As a tribute to the dense stocking on the investigated stands study plots were smaller than in previous studies focusing on mature forests. Results were found to be sound with a mean absolute error of about 6.9 kg which is equal to a relative error of 11.1%. With respect to the strongly reduced amount of field work the method is therefore of high efficiency. With the new approach reliable assessments of the bioenergy potentials become possible for coppice stands, which might play an important role in future tasks of mitigating climate change. [Copyright &y& Elsevier]

Abstract: Interspecific competition is a key process determining the dynamics of mixed forest stands and influencing the yield of multispecies tree plantations. Trees can respond to competitive pressure from neighbors by crown plasticity, thereby avoiding competition. We employed a high-resolution ground-based laser scanner to analyze the 3-dimensional extensions and shape of the tree crowns in a near-natural broad-leaved mixed forest in order to quantify the direction and degree of crown asymmetry of 15 trees (Fagus sylvatica, Fraxinus excelsior, Carpinus betulus) in detail. We also scanned the direct neighbors and analyzed the distance of their crown centres and the crown shape with the aim to predict the crown asymmetry of the focal tree from competition-relevant attributes of its neighbors. It was found that the combination of two parameters, one summarizing the size of the neighbor (DBH) and one describing the distance to the neighbor tree (HD), was most suitable for characterizing the strength of the competitive interaction exerted on a target tree by a given neighbor. By summing up the virtual competitive pressure of all neighbors in a single competitive pressure vector, we were able to predict the direction of crown asymmetry of the focal tree with an accuracy of 96° on the full circle (360°). The competitive pressure model was equally applicable to beech, ash and hornbeam trees and may generate valuable insight into competitive interactions among tree crowns in mixed stands, provided that sufficiently precise data on the shape and position of the tree crowns is available. Multiple-aspect laser-scanning proved to be an accurate and practicable approach for analyzing the complex 3-dimensional shape of the tree crowns, needed to quantify the plasticity of growth processes in the canopy. We conclude that the laser-based analysis of crown plasticity offers the opportunity to achieve a better understanding of the dynamics of canopy space exploration and also may produce valuable advice for the silvicultural management of mixed stands. [Copyright &y& Elsevier]

[Display omitted] • Compared ALS, TLS, and ground data in 52 tree islands in an oil palm landscape in Sumatra. • ALS and TLS similarly capture canopy gaps and tree height metrics. • LiDAR complements ground data, enhancing 3D vegetation structural characterization. Vegetation structural complexity is an important component of forest ecosystems, influencing biodiversity and functioning. Due to the heterogeneous distribution of vegetation elements, structural complexity underpins ecological dynamics, species composition, microclimate, and habitat diversity. Field measurements and Light Detection and Ranging (LiDAR) data, such as airborne (ALS) and terrestrial (TLS), can assess structural characteristics of forest and agroforestry systems at various spatial scales. This assessment is urgently needed for monitoring ecosystem restoration in degraded lands (e.g., in oil palm landscapes), where it is not well-known how structural measures derived from these different approaches relate to each other. Here, we compared the degree of correlation between individual and multivariate datasets of vegetation structural complexity metrics derived from ALS, TLS, and ground-based inventory approaches. The study was conducted in a 140 ha oil palm monoculture, enriched with 52 plots in the form of tree islands representing agroforestry systems of varying sizes and planted diversity levels in Sumatra, Indonesia. Our datasets comprised 25 ALS, five TLS, and nine ground-based inventory metrics. We studied correlations among metrics related to traditional stand summary, heterogeneity, and vertical and horizontal stand structure. We used principal component analysis for data dimensionality reduction, correlation analysis to quantify the strength of relationships between metrics, and Procrustes analysis to investigate the agreement between datasets. Significant correlations were found between ALS and TLS metrics for canopy density (r = 0.79) and maximum tree height (r = 0.58) and between ALS and ground-based inventory measures of stand heterogeneity and height diversity (r between 0.60 and −0.63). Further, we observed significant agreements between the ordinations of multivariate datasets (r = 0.56 for ALS − TLS; and r = 0.46 for ALS – ground-based inventory). Our findings underline the ability of ALS to capture structural complexity patterns, especially for canopy gap dynamics and vegetation height metrics, as captured by TLS, and for measures of heterogeneity and vertical structure as captured by ground-based inventories. Our study highlights the strength of each approach and underscores the potential of integrating ALS and TLS with ground-based inventories for a comprehensive characterization of vegetation structure in complex agroforestry systems, which can provide guidance for their management and support ecosystem restoration monitoring efforts. [ABSTRACT FROM AUTHOR]

• Canopy habitats require more attention in times of global biodiversity loss. • Using LiDAR and canopy fogging, we link canopy structure and arthropod communities. • We use machine learning regression to select variables driving arthropod communities. • Canopy structure drives arthropod communities stronger than tree species identity. • Structural complexity and variability of inter and intra-canopy gaps are key drivers. Forest canopies host an abundant but often neglected diversity of arthropods, which requires careful attention in times of ongoing biodiversity loss. Yet, how tree species composition interacts with canopy structure in shaping arthropod communities remains largely unknown. Here, by combining mobile laser scanning and insecticidal fogging with a machine learning algorithm, we studied which canopy architectural properties affect canopy arthropod communities in monospecific and mixed stands of broadleaved European beech and the coniferous Norway spruce and non-native Douglas fir in Germany. Evaluating the abundances and ecological guild diversity of ∼ 90,000 arthropods and 27 partly novel high-resolution structural variables, we identified vegetation volume and tree species identity as weak predictors of arthropod abundance and ecological guild diversity. In contrast, structural heterogeneity, i.e. structural complexity, vertical layering and variability of canopy gaps—which were highest in coniferous stands—were strong positive drivers. Despite this, arthropod ecological guild diversity was lower in non-native Douglas fir. Mixed stands had intermediate arthropod abundance and ecological guild diversity. Our study shows that habitat heterogeneity and tree species-identity are closely interlinked in shaping associated canopy arthropod communities. Positive effects of habitat heterogeneity on arthropod ecological guild diversity were often uncoupled from resource availability, and the key role of our novel intra-canopy gap indices suggests that they should be considered as indicators in future research on forest heterogeneity-diversity relationships. Broadleaf-conifer mixtures may be suitable to mediate negative tree-species identity effects when adapting forests to global change. [ABSTRACT FROM AUTHOR]

• We measured structural complexity in a biodiversity enrichment experiment in oil palm. • Mixed-species tree planting rapidly enhanced structural complexity. • Species identity was a strong driver of structural complexity–diversity relationship. • Structural complexity of mixed-species plots remains much lower than that of forests. Conversion of structurally complex rainforests into simplified oil palm monocultures leads to dramatic losses of biodiversity and ecosystem functioning. To alleviate negative ecological impacts, enrichment with native tree species may rapidly restore structural complexity in existing oil palm plantations. However, the mechanisms underlying the recovery of structural complexity in mixed-species tree plantings remain poorly understood. We measured structural complexity from terrestrial laser scanning in a biodiversity enrichment experiment with multiple tree species planted in an oil palm monoculture, forming agroforestry plots of varying tree species diversity and plot size. We find that three years after tree planting, structural complexity in oil palm increased by one third, representing 25% of the increase needed to restore the structural complexity of tropical forests. Changes in structural complexity were associated with denser and more complex filling of three-dimensional space, whereas vertical stratification was mainly influenced by oil palm. Furthermore, structural complexity increased with tree species diversity in the agroforestry plots. This relationship was mainly due the presence of well-performing species that contributed to higher levels of structural complexity. However, interactions among multiple species independently from the species identity were also detected. Finally, increasing plot size had a positive effect on a scale-independent measure of structural complexity. Our results provide evidence that planting multiple tree species in large agroforestry plots is a suitable strategy to rapidly enhance structural complexity in oil palm plantations. [ABSTRACT FROM AUTHOR]

Abstract Functionally, ectomycorrhizal (ECM) and saprotrophic (SAP) fungi belong to different guilds, and they play contrasting roles in forest ecosystem C-cycling. SAP fungi acquire C by degrading the soil organic material, which precipitates massive CO 2 release, whereas, as plant symbionts, ECM fungi receive C from plants representing a channel of recently assimilated C to the soil. In this study, we aim to measure the amounts and identify the drivers of ECM and SAP fungal biomass in temperate forest topsoil. To this end, we measured ECM and SAP fungal biomass in mineral topsoils (0–12 cm depth) of different forest types (pure European beech, pure conifers, and mixed European beech with other broadleaf trees or conifers) in a range of about 800 km across Germany; moreover, we conducted multi-model inference analyses using variables for forest and vegetation, nutritive resources from soil and roots, and soil conditions as potential drivers of fungal biomass. Total fungal biomass ranged from 2.4 ± 0.3 mg g−1 (soil dry weight) in pure European beech to 5.2 ± 0.8 mg g−1 in pure conifer forests. Forest type, particularly the conifer presence, had a strong effect on SAP biomass, which ranged from a mean value of 1.5 ± 0.1 mg g−1 in broadleaf to 3.3 ± 0.6 mg g−1 in conifer forests. The European beech forests had the lowest ECM fungal biomass (1.1 ± 0.3 mg g−1), but in mixtures with other broadleaf species, ECM biomass had the highest value (2.3 ± 0.2 mg g−1) among other forest types. Resources from soil and roots such as N and C concentrations or C:N ratios were the most influential variables for both SAP and ECM biomass. Furthermore, SAP biomass were driven by factors related to forest structure and vegetation, whereas ECM biomass was mainly influenced by factors related to soil conditions, such as soil temperature, moisture, and pH. Our results show that we need to consider a complex of factors differentially affecting biomass of soil fungal functional groups and highlight the potential of forest management to control forest C-storage and the consequences of changes in soil fungal biomass. Highlights • Saprotrophic and ectomycorrhizal fungal biomass vary with forest tree composition. • Nutritive resources from soil and roots are the main drivers of fungal biomass. • Forest-related factors primarily influence the saprotrophic fungal biomass. • Soil conditions mainly influence ectomycorrhizal fungal biomass. [ABSTRACT FROM AUTHOR]

Abstract: In temperate deciduous forests, the herb layer contributes most to total vascular plant species richness. The diversity of the tree layer can influence herb layer diversity by modifying resource availability and environmental conditions relevant to herb layer plants. Here, we explore the relationship between tree layer diversity and herb layer species richness and cover. Also, we address the question how different environmental factors that are potentially modified by the tree layer influence herb layer characteristics. Our study area is located in the Hainich National Park, one of the largest continuous stretches of broad-leaved deciduous forest in Central Europe. We recorded herb and tree layer composition on 79 plots selected along a tree diversity gradient ranging from two to nine tree species. In addition, canopy cover, soil pH, mass of the humus layer, soil C:N ratio, soil moisture and distance to the forest edge were determined. We used generalized least square models to analyse effects of tree diversity, environmental variables, and spatial plot positions on herb layer species richness and cover. Species richness and cover of the herb layer increased with increasing tree diversity. In addition, both species richness and cover showed a negative response to increasing canopy cover and mass of the humus layer. Herb layer species richness was also positively related to increasing soil pH and the distance to the forest edge. The proportion of forbs increased with increasing tree diversity, whereas the proportion of tree saplings decreased and the proportion of graminoids was not affected. The proportion of true forest species increased with increasing canopy cover. We conclude that forest stands with a high tree diversity feature a more diverse herb layer and a higher herb cover. Furthermore, the environmental variables humus layer mass, light availability and pH also strongly affect herb layer species richness and cover. [Copyright &y& Elsevier]