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Healthy soils are the second C sink on Earth, and this sink could last for hundreds or even thousands of years as stable soil organic matter (SOM). Forest soils, in particular, have the potential to store significant amounts of C, however, the amount of C sequestered and the carbon-to-nitrogen (C/N) ratio of soil organic matter (SOM) depend on the vegetation influencing the soil. In the last decades, mixed stands have aroused great interest among the scientific community, but it is still necessary to intensify research on its effect on soils and their C storage capacity. In this study, we assess soil C sequestration potential in soil and litter of mixed and pure stands of Scots pine and beech (Pinus sylvestris–Fagus sylvatica). Three triplets (9 forest plots), two located in Southern Poland and one in Southern Germany were studied. A total of 40 circular subplots of 5 m radius were selected within the triplets, covering a wide range of species mixture, and soil and litter were sampled. Data were analyzed at two scales (plot-level and microsite-level) to determine which option is more appropriate when studying the mixing effect on SOM. Cstock in forest floor ranged between 2.5 and 11.1 Mg C ha−1 and in mineral soil between 39.6 and 337.8 Mg ha−1. According to our findings, the percentage of species mixture primarily impacted the forest floor rather than the mineral soil. On the forest floor, stands with 25–50% pine in the mixture were found to have a C/N ratio between 20 and 30, which indicates an equilibrium state between mineralization and immobilization. In the mineral soil, total organic C was the only variable affected by mixture percentage (p < 0.1). Finally, microsite-level scale proved to be the most appropriate when studying tree stand composition effect on SOM, as the plot-level scale diluted or masked some effects. [ABSTRACT FROM AUTHOR]

In the light of ongoing climate change, European beech trees face a loss of vitality due to an expected increase in the frequency of droughts, exacerbated by prolonged periods of high temperatures and solar radiation. Such conditions increase the predisposition to European beech splendour beetle attacks, and trigger sunburn, fungal infections and complex diseases. As a result, European beech forests are seriously threatened by climate change. Following prolonged and repeated periods of exceptional drought since 2018, European beech decline have been observed in several regions of Germany and Europe. Vitality losses, in some cases severe, of due to the extraordinarily warm, dry summers of 2018 and 2019 have been observed and investigated in several regions of Germany. The first symptoms of vitality loss of European beech associated with severe signs of crown dieback were recorded in midsummer 2018. Mortality of branches and individual trees was often associated with sunburn, bark necrosis and bleeding spots of sap flux. The first signs of mortality were observed locally in predisposed stands in autumn 2018. The stem stability and break resistance of affected trees were significantly reduced. To elucidate the complex interactions involved, the occurrence of vitality loss of European beech and associated causative agents were examined in north-western Germany. Disease symptoms of individual trees were studied, associated fungi (endophytes, plant pathogens and saprobes) were isolated and identified. Frequent potentially severe pathogens included Neonectria coccinea, Diplodia corticola and D. mutila. The presented cases of disease were the first, where D. corticola was recorded on beech. In addition, inoculation tests were used to assess the potential roles of Botryosphaeria species in the observed symptomatology. [ABSTRACT FROM AUTHOR]

Earth's forests are increasingly exposed to climate risks through climate change-related drought and heat waves. Here, we review the climate vulnerability of European beech (Fagus sylvatica), the most abundant tree species of Central Europe's temperate forests, and its adaptation potential to a hotter and drier climate in northern Germany, close to the center of the species' distribution range. About two-thirds of the studied beech forests show persistent negative growth trends of their dominant trees since the onset of rapid warming in the early 1980s, driven primarily by long-term deterioration of the climatic water balance (CWB) in summer and, locally, long-term decrease in June precipitation. Lower water storage capacity of the soil increases the climate sensitivity of growth. Even though beech populations of drier sub-regions reveal some acclimation to drought (reduced stomatal conductance, turgor loss point reduction, higher C allocation to roots), they are more climate-vulnerable than populations at moister sites, visible in larger growth decreases and greater CWB sensitivity of growth. Even though beech mortality is still lower in the study region than in other parts of Central Europe, our results identify beech forest regions with <350 mm growing-season precipitation as vulnerable to recent climate conditions, which refers to half of the study region. With further climate warming and aridification, most of northern Germany likely will become unfavorable for beech growth within the next tree generation, which suggests choosing in many production forests alternative, more drought- and heat-resistant timber species. [ABSTRACT FROM AUTHOR]

The onset of the growing season in temperate forests is relevant for forest ecology and biogeochemistry and is known to occur earlier with climate change. Variation in tree phenology among individual trees of the same stand and species, however, is not well understood. Yet, natural selection acts on this inter-individual variation, which consequently affects the adaptive potential to ongoing environmental changes. Budburst dates of 146 mature individuals of Fagus sylvatica , the dominant natural forest tree of central Europe, were recorded over 12 years in one forest stand of 1 ha in the Müritz National Park, Germany. The tree-specific location, topographical differences, as well as social status, were measured to explain the inter-individual variation in budburst. Furthermore, inter-individual differences in bud dormancy were quantified. Additional phenology and weather data across Germany from 405 sites over a 25-year period was used to put the insights from the single stand into perspective. Consistent phenological ranking over the years with respect to early and late flushing trees was observed within the single forest stand, with 23 trees consistently flushing 3–6 days earlier and 22 trees consistently flushing 3–10 days later than the median. Trees flushing consistently early varied most in their spring budburst dates and were less dormant than late-flushing trees already in mid-winter. The higher variation in earlier flushing trees was best explained by a slower warming rate during their budburst period in the observed stand as well as across Germany. Likewise, years with a lower warming rate during the budburst period were more variable in budburst dates. The rate of warming during spring time is crucial to accurately project future within-species variation and the resulting adaptive potential in spring phenology of dominant forest tree species. [ABSTRACT FROM AUTHOR]

Background: Organic carbon stored in forest soils (SOC) represents an important element of the global C cycle. It is thought that the C storage capacity of the stable pool can be enhanced by increasing forest productivity, but empirical evidence in support of this assumption from forests differing in tree species and productivity, while stocking on similar substrate, is scarce. Methods: We determined the stocks of SOC and macro-nutrients (nitrogen, phosphorus, calcium, potassium and magnesium) in nine paired European beech/Scots pine stands on similar Pleistocene sandy substrates across a precipitation gradient (560–820 mm∙yr− 1) in northern Germany and explored the influence of tree species, forest history, climate, and soil pH on SOC and nutrient pools. Results: While the organic layer stored on average about 80% more C under pine than beech, the pools of SOC and total N in the total profile (organic layer plus mineral soil measured to 60 cm and extrapolated to 100 cm) were greater under pine by about 40% and 20%, respectively. This contrasts with a higher annual production of foliar litter and a much higher fine root biomass in beech stands, indicating that soil C sequestration is unrelated to the production of leaf litter and fine roots in these stands on Pleistocene sandy soils. The pools of available P and basic cations tended to be higher under beech. Neither precipitation nor temperature influenced the SOC pool, whereas tree species was a key driver. An extended data set (which included additional pine stands established more recently on former agricultural soil) revealed that, besides tree species identity, forest continuity is an important factor determining the SOC and nutrient pools of these stands. Conclusion: We conclude that tree species identity can exert a considerable influence on the stocks of SOC and macronutrients, which may be unrelated to productivity but closely linked to species-specific forest management histories, thus masking weaker climate and soil chemistry effects on pool sizes. [ABSTRACT FROM AUTHOR]

Similar to soils, tree stems emit and consume nitrous oxide (N 2 O) from the atmosphere. Although tree leaves dominate tree surface area, they have been completely excluded from field N 2 O flux measurements and therefore their role in forest N 2 O exchange remains unknown. We explored the contribution of leaf fluxes to forest N 2 O exchange. We determined the N 2 O exchange of mature European beech (Fagus sylvatica) stems and shoots (i.e., terminal branches) and of adjacent forest floor, in a typical temperate upland forest in Germany. The beech stems, and particularly the shoots, acted as net N 2 O sinks (-0.254 ± 0.827 μg N 2 O m -2 stem area h -1 and -4.54 ± 1.53 μg N 2 O m -2 leaf area h -1 , respectively), while the forest floor was a net source (2.41 ± 1.08 μg N 2 O m -2 soil area h -1 ). The unstudied tree shoots were identified as a significant contributor to the net ecosystem N 2 O exchange. Moreover, we revealed for the first time that tree leaves act as substantial N 2 O sinks. Although this is the first study of its kind, it is of global importance for the proper design of future flux studies in forest ecosystems worldwide. Our results demonstrate that excluding tree leaves from forest N 2 O flux measurements can lead to misinterpretation of tree and forest N 2 O exchange, and thus global forest greenhouse gas flux inventories., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2024 The Authors. Published by Elsevier B.V. All rights reserved.)

Scientists and society are increasingly becoming aware of loss of insect biodiversity and biomass. The level of biodiversity determines the efficiency of ecological communities to capture essential resources, produce biomass, decompose and recycle nutrients. Relationships between plant and insect diversity can be modified by changes in insect abundance. This study determined the associations between microclimate and diversity of forest plants on overall insect abundance and abundances of different insect orders in the canopy of temperate deciduous forests dominated by Fagus sylvatica L. (European beech; Fagaceae) in Central Germany. Following model selection, a linear mixed model was used to analyse the associations between abiotic factors (air temperature and relative humidity) as well as biotic factors (species richness and cover for the ground, shrub and tree layer) and insect abundance and abundances of insect orders. Within similar strength of evidence, best models were chosen as those with a single explanatory parameter. Significant associations were recorded between abundances of Lepidoptera and Neuroptera and relative air humidity, insect abundance and species richness in the shrub layer, and between abundances of Diptera and Psocoptera and percentage cover of shrubs. Trends in associations were detected between the abundance of Hemiptera and species richness recorded in the shrub layer, and between the abundance of Thysanoptera and the species richness in the ground layer. No significant associations with single explanatory parameters were recorded for the abundances of Coleoptera and Hymenoptera. Phytodiversity, especially that in the shrub layer, were more often associated with the abundances of insect orders than microclimatic factors. The potential importance of the association between shrub layer parameters and the abundance of insects might be based on the shrub layer combining the associations with the ground layer (bottom-up processes) and canopy layer (environmental conditions). In addition, associations between phytodiversity and abundance of insects seem to vary most for Coleoptera and Hymenoptera in which there are markedly different functional groups. [ABSTRACT FROM AUTHOR]

• After the 2018–2020 drought, crown condition differed strongly within beech stands. • Growth dynamics and tree genetics of non–/vital individuals were compared. • Long-term growth decline was widespread in both groups. • Climate sensitivity and individual heterozygosity did not consistently differ. • Crown condition after drought is a poorer indicator of tree vitality than ring width. Global warming poses a major threat to forest ecosystems around the world. In Central Europe, vitality losses and tree mortality have already been observed in various regions, especially after extreme drought episodes such as the 2018–2020 drought. European beech (Fagus sylvatica L.), which is the dominating deciduous tree species in large parts of temperate Europe, also suffered from the recent drought. In Germany, for example, losses in crown condition were observed. Within individual stands, however, the crown condition of beech differed strongly from non–/weakly damaged trees (hereafter referred to as vital trees) to severely damaged/dead trees (non-vital trees). Tree characteristics and micro-site conditions were apparently similar. Hence, we checked whether differences in growth behavior exist and (or) developed over time and assessed if observed differences between the non–/vital individuals might be genetically driven. We found that the climate sensitivity as well as the drought resistance of tree growth did not consistently differ between non–/vital trees. In both groups, a growing importance of water availability for tree growth was apparent. Further, long-term growth decline was widespread in both vital and non-vital trees, suggesting severe stress and future risks of tree mortality irrespective of crown condition. Only at one out of nine sites, we found significant differences in individual heterozygosity, signaling potential differences in the adaptation of trees to environmental stress. As a consequence, our study highlights that crown condition after an extreme drought is a poorer indicator of tree vitality than ring width in beech stands in Germany. [ABSTRACT FROM AUTHOR]

Trees concentrate rainfall to near-stem soils via stemflow. When canopy structures are organized appropriately, stemflow can even induce preferential flow through soils, transporting nutrients to biogeochemically active areas. Bark structure significantly affects stemflow, yet bark-stemflow studies are primarily qualitative. We used a LaserBark to compute bark microrelief (MR), ridge-to-furrow amplitude (R) and slope (S) metrics per American Society of Mechanical Engineering standards (ASME-B46.1–2009) for two morphologically contrasting species (Fagus sylvatica L. (European beech), Quercus robur L. (pendunculate oak)) under storm conditions with strong bark water storage capacity (BWSC) influence in central Germany. Smaller R and S for F. sylvatica significantly lowered BWSC, which strongly and inversely correlated to maximum funnelling ratios and permitted stemflow generation at lower rain magnitudes. Larger R and S values in Q. robur reduced funnelling, diminishing stemflow drainage for larger storms. Quercus robur funnelling and stemflow was more reliant on intermediate rain intensities and intermittency to maintain bark channel-dependent drainage pathways. Shelter provided by Q. robur's ridged bark also appears to protect entrained water, lengthening mean intrastorm dry periods necessary to affect stemflow. Storm conditions where BWSC plays a major role in stemflow accounted for much of 2013's rainfall at the nearest meteorological station (Wulferstedt). Editor M.C. Acreman; Associate editor not assigned [ABSTRACT FROM AUTHOR]

In 1990 the Federal State of Hesse (Germany) started a long-term faunistic research programme in selected Strict Forest Reserves. Here we report the results of the inventory of pseudoscorpions from seven reserves: Goldbachs- und Ziebachsrück, Hasenblick, Hohestein, Kinzigaue, Niddahänge east of Rudingshain, Schönbuche and Stirnberg. A total of 4567 specimens (315-1314 per site) belonging to 13 species (4-9 per site) were recorded using a broad spectrum of methods. The bulk of material comes from pitfall traps (83 %), followed by various types of stem eclectors (16 %). The structure and quality of the species assemblage in the oak-dominated flood plain forest of the Kinzigaue differs strongly from those of the remaining reserves, which are all dominated by beech. In the Kinzigaue a species-rich community (9 species) with balanced dominance structure (Shannon-Index 1.67) has been recorded. At this site, rare or moderately common species reach abundance proportions of more than 50 %. Most importantly, two species with strong affinities to pristine forests, Dendrochernes cyrneus and Chernes cimicoides, were exclusively recorded from this reserve. In contrast, the beech-dominated reserves were strongly dominated by a single species, Neobisium carcinoides (59-91 % of the specimens, Shannon-Index < 1), and the abundance proportion of the very common species exceeded 90 % in each of these areas. Temperature and altitude determine the composition of the species communities significantly. Of the recorded species, two will be categorized in the forthcoming Red Lists of pseudoscorpions of Germany and Hesse. Dendrochernes cyrneus (cat. 3 "vulnerable") reached an abundance proportion of 20 % in the reserve Kinzigaue. Dinocheirus panzeri (cat. G "indeterminate risk") has been recorded in single specimens from the reserves Hasenblick, Stirnberg and Niddahänge. The preferred habitat for most of the species is the forest. Species with strong affinities to forests make up more than 95 % of the specimens in all reserves except for Kinzigaue, where this proportion was 89 %. Species richness and abundances were not different between the Strict Forest Reserves (management was stopped at the end of the 1980's) and the reference areas with continued forestry. However, the proportions of rare and moderately common species were higher in the Strict Reserves as compared to the reference areas. [ABSTRACT FROM AUTHOR]

The effects of management on insect communities have been studied in several forest ecosystems, although the consequences for single potential pests are only known for a few species. The present study investigated whether forest management affects the infestation of European beech trees by the beech scale Cryptococcus fagisuga., We assessed the densities of C. fagisuga on a total of 520 trees ( Fagus sylvatica) at 104 forest sites, representing three main types of beech forest management intensity across three regions in Germany., The infestation rates on beech trees were 16% in the South- West, 20% in the Centre and 35% in the North- East of Germany, although the rates per plot did not differ significantly among regions. No significant differences between unmanaged beech, managed even-aged beech and managed uneven-aged beech forests were found because of high variability in beech scale infestation observed among forest sites and within forest management types. Highest infestation rates occurred on widely dispersed mature trees within thickets with shelterwood stage and lowest infestation rates occurred on young beech trees in the thicket stage., The results of the present study suggest that the infestation rates of C. fagisuga on beech depend on tree age and canopy openness rather than on management intensity. [ABSTRACT FROM AUTHOR]

English Ivy (Herdera helix , Araliaceae) is an evergreen woody climbing plant occurring naturally in temperate forests of Europe and as introduced ornamental plant in many parts of the world, becoming invasive in some. Over the last decades an increase of ivy occurrence in middle Europe was observed in forests as well as in urban or rural areas. As a consequence, ivy might also play a larger role in food webs and nutrient and carbon cycling in the future. We followed the decomposition of litter of ivy and compared it to litter of four common host trees species (sycamore, ash, oak, beech) using mesh bags with and without mesofauna access over a period of 10 months. Experiments were set up in nine gardens spread over Germany, involving citizen scientists. In the presence of mesofauna, ivy litter decomposed faster than litter of three of the tree species. The contribution of mesofauna to decomposition followed a similar pattern. In the absence of mesofauna, ivy decomposed faster than two of the tree species. In a changing world where ivy becomes more abundant, and tree species face population decline due to disease or climatic stress, litter composition will also change. Ivy adds medium to fast decaying litter to the ecosystem, and in other seasons than tree species. Conducting experiments with citizen scientist offers the possibility for wide-spread multi-site experiments generating robust data and overcoming local restrictions with low budgets. • In the presence of mesofauna, ivy litter decomposed faster than litter of oak, beech and sycamore. • In the absence of mesofauna, ivy litter decomposed faster than oak and beech litter. • Experiments done by citizen scientist can generate robust data with low budgets. • We did not detect a citizen scientist bias in our data. [ABSTRACT FROM AUTHOR]

Future climate projections for Central Europe indicate a decrease in summer precipitation which might range between 15% and 50%, and equally important, changes in the climate variability, resulting in consecutive years with drought periods. With respect to Central European forests, we asked to which degree realistic drought conditions are tolerated by the recruits of the dominant tree species Fagus sylvatica L . , and how the effects depend on biotic interactions. To test the combined effects of drought, competition and provenance of F. sylvatica recruits we set up a rain shelter experiment at three sites in different regions of Germany. Transposable roof panels allowed a flexible precipitation reduction between 10% and 70% corresponding with a return period of 40 years. We planted F. sylvatica saplings of three provenances, exposed them to drought and competition. We tested if understorey herbaceous competitors have a negative impact on F. sylvatica saplings, and thus, exacerbate drought effects and that F. sylvatica provenances from drier regions are adapted to drought conditions and cope better with drought conditions. Six months after the drought treatment started, we encountered significant drought effects, seen in a reduced leaf stomatal conductance, although there was not yet a response in growth rates. Overall, the site had the greatest impact on phytometer performance, while we found no indication of adaptation to drought of the different provenances. Furthermore, drought effects increased in interaction with site effects, being highest at the driest site. At the driest site, leaf stomatal conductance decreased in the presence of competition but increased in the control subplots, while the site of intermediate moisture conditions showed the opposite pattern and the wettest site displayed no differences. Our results highlight the fact that biotic interactions can mitigate or exacerbate drought effects, depending on regional site conditions. [ABSTRACT FROM AUTHOR]

[Display omitted] • Throughfall volume increased with stem distance in summer, but decreased in winter. • Element concentrations and fluxes in throughfall decreased with stem distance. • Chemistry of soil matrix did not show clear spatial gradients with stem distance. The partitioning of bulk precipitation (PR) in forest ecosystems and its chemical composition depends on both meteorological factors, such as precipitation amount and intensity, evaporation rate, and wind speed, and stand structural factors, such as stand density, canopy structure, bark texture, and spatiotemporal distribution and density of foliage. We analysed fluxes of water and element contained therein of a mature European beech (Fagus sylvatica L.) forest stand on sandy soils in northeastern Germany. We applied a radially symmetrical setup within a stem distance gradient to measure stand precipitation (SP) with its components of throughfall (TF) and stemflow (SF), as well as to measure soil moisture, the chemical composition of the soil solution, the soil chemistry, and the fine root distribution. The chemical analysis of the constituents covered the macroelements (Ca, Mg, K, Na, Al, Fe, Mn, Si, S, P), the cations and anions NH 4 +, NO 3 –, Cl-, SO 4 2-, and a few heavy metals (Cu, Pb, Zn). With an average PR of 620 mm a-1, the partitioning resulted in 79% TF, 6% SF, and 15% canopy interception. TF volume increased with distance to stem during summer, but decreased during winter. Clear spatial gradients with increasing concentrations from PR, to different classes of TF as the distance from the trunk decreased, to SF were observed for nearly all elements. The contact of precipitation with leaves and the canopy structures alters the chemical composition of TF and SF by transferring elements from dry deposition or leaching of intracellular materials from the canopy and leads to the input of larger amounts of macroelements and heavy metals with the SP into the soil. Spatial patterns of canopy structures thus affect the spatial variation of TF and its constituents, which also affects the spatial distribution of roots and, at least in phases, the chemical composition of the topsoil solution. [ABSTRACT FROM AUTHOR]

Highlights: [•] Scots pine has been planted on roughly 5 Mio ha in northern Central Europe replacing beech. [•] Pine plantations had 75% larger organic layer C pools than beech forests. [•] Ancient beech forests stored about 25% more SOC in the mineral soil than pine plantations. [•] The N and Ca, K and Mg pools under beech were even larger as compared to pine stands. [•] Scots pine on sandy soil has a particularly small C accumulation potential. [Copyright &y& Elsevier]

Abstract: The linkage between tree diversity and the soil food web in temperate deciduous forest ecosystems remains uncertain. Using microbial phospholipid fatty acids (PLFAs), we analyzed the effect of tree species composition on microbial communities from topsoil collected in Hainich National Park, Germany. Previous results had shown minimal direct effects of tree species on the microbial community in autumn, most likely due to low plant activity and high nutrient and energy input from litterfall. However, microbial composition was affected indirectly through an influence of tree species on soil pH. In this study, we analyzed PLFA profiles in early summer and compared them with the results from autumn sampling. We hypothesized that plant-based traits would have stronger direct effects on the abundance and structure of the microbial community during the photosynthetically active period. The results showed that the soil microbial community differed more markedly between the tree diversity levels in early summer than in autumn. The acidifying character of the decaying beech litter strongly influenced the soil pH values and structured the soil microbial community indirectly in early summer as it had in autumn. However, the measured differences in the microbial composition in early summer could be attributed primarily to litter quality. This direct influence of plant traits appeared to be eclipsed in autumn because of the high nutrient supply from fresh litter input. Following litter decomposition in the topsoil, however, litter-based plant traits emerged as a factor structuring the soil microbial community in early summer. Our results suggest that the PLFAs i14:0 and i15:0, indicative of Gram-positive bacteria, are strongly involved in decomposition processes and may be promoted by readily available nutrients. Furthermore, our results indicate that a dense root network in association with arbuscular mycorrhizal fungi strongly supported microbial growth in the more diverse forest stands. High proportions of arbuscular mycorrhizal fungi (PLFA 16:1ω5), root-associated microorganisms (PLFAs 16:1ω9, 16:1ω7, 17:1ω8 and 18:1ω7) and bacterial grazers (PLFA 20:5) characterized the microbial community in early summer on these study plots. We conclude that microbial communities are strongly influenced by abiotic controls. However, seasonal differences in litter decomposition rates and root activity should be considered in the analysis of the effects of tree diversity or species on soil microbial communities. [Copyright &y& Elsevier]

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]

Abstract: The rejuvenation ecology of three main tree species in anthropogenic pine (Pinus sylvestris L.) forests is explored in our study. We focus on the scale of micro-plots, which provide the safe sites for tree rejuvenation. We thrive on the multi-factorial relationship of tree establishment and driving ecological factors using a large dataset from pine stands in NE Germany and applying multivariate analyses. The success of the establishment of the investigated focal tree species Fagus sylvatica L., Quercus petraea Liebl. and Pinus sylvestris L. is, on general, mostly affected by three factors, i.e. water balance of the upper soil layers, browsing pressure, and diaspore sources. Our investigations on the micro-plot scale revealed species-specific differences. For beech saplings <50cm growth height, primarily the availability of water, indicated by available water capacity (AWC), thickness, quality, and structure of the organic layer, silt and humus content in the topsoil, and the lack of a dense competitive herb layer, were identified as most important factors. On the contrary, oak seems hardly be restricted by hydrologic and/or trophic deficits in the topsoil or humus layer. In conclusion and comparison to Fagus sylvatica L., we assume for Quercus petraea Liebl. advantages in natural regeneration processes under sub-continental climate conditions and thus under the scenarios of climate change. Pinus sylvestris L. regeneration in our investigation area occurs only in a narrow niche. We conclude with regard to future forest development and the objective of stand conversion with low management intensity that oak should be favoured within natural stand regeneration. [ABSTRACT FROM AUTHOR]

Abstract: This modeling study used recent observations at a temperate broad-leaved forest in Central Germany to calculate water balances of a Fagus sylvatica monoculture and mixed stands of F. sylvatica, Tilia spp., Acer spp., Carpinus betulus, Fraxinus excelsior and Quercus robur. To simulate soil water flow the modeling framework Expert-N was applied which combines models that describe the physiological and hydrological processes of the plant-soil system including models of evapotranspiration (Penman–Monteith equation), interception (revised Gash model) and soil water flow (Richards equation). Measurements of rainfall partitioning, volumetric soil water content, evapotranspiration and tree transpiration provided reliable data for the parameterization and the calibration of the model for three stands of different diversity levels. They allowed to include species specific physiological (transpiration rates, response to dry soil water conditions) and structural (leaf area dynamics) characteristics. During the 3-year long observation period 2005–2007 the mean yearly precipitation was 652mm, the simulated mean yearly interception loss of the three observed forest stands was between 219 and 272mm, the transpiration accounted for 197–225mm, the forest floor evaporation for 96–104mm, the drainage for 16–60mm and the runoff for 13–50mm. The calculations of the water balance were sensitive to the species composition of the forest and showed differences of rainfall interception and root water uptake between the stands. The applied stand-level model was able to simulate the water dynamics of the monospecific and mixed forest stands. It was shown that differences in drought tolerance of tree species can have a strong impact on the simulated soil water extraction during periods when available soil water is low. [ABSTRACT FROM AUTHOR]

Ground-level ozone (O3) has gained awareness as an agent of climate change. In this respect, key results are comprehended from a unique 8-year free-air O3-fumigation experiment, conducted on adult beech (Fagus sylvatica) at Kranzberg Forest (Germany). A novel canopy O3 exposure methodology was employed that allowed whole-tree assessment in situ under twice-ambient O3 levels. Elevated O3 significantly weakened the C sink strength of the tree–soil system as evidenced by lowered photosynthesis and 44% reduction in whole-stem growth, but increased soil respiration. Associated effects in leaves and roots at the gene, cell and organ level varied from year to year, with drought being a crucial determinant of O3 responsiveness. Regarding adult individuals of a late-successional tree species, empirical proof is provided first time in relation to recent modelling predictions that enhanced ground-level O3 can substantially mitigate the C sequestration of forests in view of climate change. [Copyright &y& Elsevier]

To determine which factors contribute most to the stability of species composition in a beech forest after profound disturbance, we made use of a natural experiment caused by a severe windthrow that occurred at a permanent monitoring site in an old beech forest in Lower Saxony (Germany). The floristic composition was recorded for the succeeding five years after the disturbance and used to derive measures of resistance and resilience for plots as well as for individual species. Due to the existence of previously established randomly distributed permanent plots, we had precise information of the pre-disturbance state, including initial cover of the herb layer, species richness, and species composition. Variables describing the floristic change, resistance, and resilience were derived from correspondence analysis allowing for partitioning the effects of variation among plots from those of temporal change. We asked to which degree these variables could be predicted by pre-disturbance state and disturbance intensity. We found that both the pre-disturbance state and the disturbance intensity were good predictors for floristic change and resistance, while they failed to predict resilience. Among the descriptors of the pre-disturbance state the initial cover of the herb layer turned out to be a useful predictor, which is explained by a high vegetation cover buffering against losses and preventing establishment of newcomers. In contrast, species number neither showed a relationship to floristic change nor to resistance. Putative positive effects of species number on stability according to the insurance hypothesis might have been counterbalanced by a disruption of niche complementarity in species-rich communities. Among the descriptors of disturbance intensity, the loss in canopy cover and the change in photosynthetically active radiation after the storm were equally good predictors for the change in floristic composition and resistance. The analysis of the responses of single species on initial vegetation cover and disturbance intensity revealed that a wide range of different mechanisms were involved. Resistance and resilience did not depend on the presence of particular species or on specific traits. [ABSTRACT FROM AUTHOR]

• Scots pine plantations cover 1.7 million hectares in northern Germany. • Pine plantations increase regional climate warming via a reduced canopy albedo. • Pine plantations decrease groundwater recharge by ∼ 70 mm yr−1. • C storage in biomass and soil is markedly lower than under broadleaf forest. • The plantations are neither environmental-friendly nor climate-smart. Increasing temperatures and rising atmospheric vapor pressure deficits are exposing forests around the globe to increasing drought and heat stress, demanding a shift to climate-smart forestry for increasing the stress resistance and resilience of production forests and to enhance their climate change mitigation potential. Based on measurements in paired pine and beech forests and the review of literature data, we analyse the biophysical consequences and the carbon cycle impact of large-scale Scots pine (Pinus sylvestris L.) plantations in northern Germany in the face of a warming and aridifying climate. We quantified canopy surface albedo and surface temperature, evapotranspiration and deep seepage, carbon (C) storage in biomass and soil and annual C sequestration, and soil acidification of pine plantations in comparison to beech forests (Fagus sylvatica L.), the natural forest vegetation. We find that near-infrared (NIR, 700–3000 mn) canopy surface albedo is higher by 5.2 percentage points during summer over beech as compared to pine forest, resulting in a 9 % higher net radiation and a 0.6 K higher surface temperature of the pine canopy. Deep seepage is on average by 68 mm yr−1 smaller under pine than beech forest (66 mm yr−1 vs. 134 mm yr−1) due to the higher evapotranspiration of pine. C storage in biomass and soil is by ∼ 48 Mg C ha−1 higher in beech than pine forests, reflecting the higher productivity of beech, demonstrating an unfavorably low C sequestration potential of Scots pine plantations. We conclude that the large-scale Scots pine plantations in northern Germany (>1.7 million ha) are neither environmental-friendly nor climate smart, given their enhancement of climate-warming, low climate change mitigation potential, and negative effect on groundwater recharge. Replacing pine plantations by beech (or other hardwood) forests in northern Germany and adjacent regions is urgently needed for achieving the goals of climate-smart forestry. [ABSTRACT FROM AUTHOR]

Abstract: A non-papillate, slow-growing Phytophthora species, which could not be assigned to any existing taxon, was isolated from rhizosphere soil of a declining oak in Northeast France, and from the rhizosphere of Phragmites australis at Lake Constance in south-west Germany in 1998 and 2004, respectively. We describe this species, previously informally designated Phytophthora taxon ‘G’, as Phytophthora gallica sp. nov. Morphology, growth rates, and pathogenicity against cuttings of riparian tree species and leaves of reed are described and compared with those of morphologically and phylogenetically similar Phytophthora species. P. gallica produces colonies with limited aerial mycelium and variable growth patterns. Gametangia are not formed in single or mixed cultures with tester strains of known mating types. P. gallica produces globose and elongated irregular chlamydospores, of which a high proportion is abortive. In water culture irregular hyphal swellings and non-papillate persistent sporangia are formed abundantly. P. gallica is moderately aggressive to Alnus glutinosa and Fagus sylvatica, weakly aggressive to Quercus robur and Salix alba and non-pathogenic to Fraxinus excelsior and Phragmites australis. According to ITS and mtDNA sequence data P. gallica belongs to a distinct Phytophthora clade, with P. boehmeriae and P. kernoviae being the closest relatives. The origin of P. gallica and its ecological role in wet ecosystems remain unclear. [Copyright &y& Elsevier]

In this study, we present an approach for the identification of indicators for biodiversity within forest ecosystems. We analyze the data of stands of pure Norway spruce ( Picea abies (L.) Karst) and European beech ( Fagus sylvatica L.), as well as mixed P. abies–F. sylvatica forests in the Solling mountains (NW Germany). The analysis is based on 683 vegetation samples in total. For different plant groups, that is, vascular plants, bryophytes, Red List species, we investigate species numbers as a parameter of biodiversity. Species numbers are differentiated into three classes to describe low to high diversity. Plots are separately examined for the three different forest types. In order to take the species–area relationship into account, we only use relevés with a plot size of 100 m2. Our approach focuses on the probability to be in a defined range of species numbers, that is, class, if a certain species occurs. For the purpose of facilitating the differentiation of the classes, we use the presence values of species in the classes for further characterization of indicators. Few indicators were found for the low ranges of species numbers. In addition, there were only a small number of species groups and stand types having indicators for all three classes. Various species have multiple indicator functions, e.g., with regard to the investigated species groups. The focus on a few of these multi-indicators allows a rapid assessment of forest biodiversity. The catalog of indicators resulting from the investigation helps to facilitate and accelerate biodiversity evaluations of forest stands, in particular with regard to nature conservation and the restoration of natural forests. [ABSTRACT FROM AUTHOR]

Abstract: The responsiveness of adult beech and spruce trees to chronic O3 stress was studied at a free-air O3 exposure experiment in Freising/Germany. Over three growing seasons, gas exchange characteristics, biochemical parameters, macroscopic O3 injury and the phenology of leaf organs were investigated, along with assessments of branch and stem growth as indications of tree performance. To assess response pattern to chronic O3 stress in adult forest trees, we introduce a new evaluation approach, which provides a comprehensive, readily accomplishable overview across several tree-internal scaling levels, different canopy regions and growing seasons. This new approach, based on a three-grade colour coding, combines statistical analysis and the proficient ability of the “human eye” in pattern recognition. [Copyright &y& Elsevier]

Beech forests (Fagus sylvatica L.) represent the natural vegetation cover for the majority of sites in Germany. Although coniferous forests actually dominate, beech is the most important among the deciduous-tree-species in Germany, when considering the area and the economics. While the wood of the younger beech normally shows a whitish colour (white beech), the timber of older beech may form coloured heartwood (facultative). This heartwood is highly variable in its colour. In most cases a reddish colour predominates, but sometimes the heartwood can be brown, grey, green, or even purple. Usually the coloured heartwood is called “red heartwood”. As the uses of beech with “red heartwood” are restricted, mainly for aesthetical reasons, its presence severely reduces the timber quality. However, the existence of “red heartwood” cannot be distinguished until the tree is felled.In this context the paper presents a possible new approach within the “red heartwood” research. The object is to predict the future “red heartwood” formation in beech trees, while they are actually still showing a bright colour. This information is relevant to improve the beech forest management. In order to provide this information the data of 392 felled beech trees were utilised. By means of a logistic regression analysis the probability of the occurrence of “red heartwood” was first analysed. Specific tree characteristics were tested as independent variables (age, diameter at 1.3 m height, crown base height, average diameter increment, injuries to the bark, forking). Transition probabilities (probabilities with which a recent “red heartwood” is formed) were then derived based on the statistical logistic regression function.In order to predict the transition probabilities for still standing beech trees a model was formed comprising of tree characteristics as independent variables, which significantly influenced the “red heartwood” probability. Among the independents the age of the tree and the average diameter growth rate were the most important. The distance to the soil surface at which the heartwood was measured, and the number of injuries to the bark (dead branches, knobs, big scars), through which oxygen may enter the stem significantly influenced the transition probability. The presence or absence of a stem fork was also significant. [Copyright &y& Elsevier]

• New index SHI TLS presented to analyse and monitor forest structural heterogeneity. • Including several individual-tree structural attributes measured at high resolution. • SHI TLS showed different trends in beech-dominated and coniferous stands. • Very large variability of SHI TLS within single age classes per stand type. • Weak correlation between SHI TLS and an existing stand structural complexity index. The maintenance or enhancement of structural heterogeneity (SH) of forest stands is considered a key element of sustainable forest management in central Europe, making the monitoring of stand structure an important task. However, existing approaches that enable the quantification of SH usually neglect the three-dimensional (3D) representation of forest structures. To overcome this limitation, terrestrial laser scanning (TLS) can be applied to provide an efficient, non-destructive and high resolution record of 3D structures. In this study, we present a new structural heterogeneity index (SHI TLS) at the plot level which is based on 3D point clouds of individual trees that were derived from multiple scans. Because tree crowns are of particular importance for the 3D SH of forests, we focus particularly on outer and inner crown attributes. To test the robustness and the explanatory power of our index we sampled data on 84 plots across 12 different forest stand types in two study areas of Germany. We analyzed whether our index is able to explain differences between the different stand types. In addition, we compared our SHI TLS to an existing stand structural complexity index (SSCI) that is based purely on single TLS scans. We found different trends of SHI TLS between stand types dominated by Fagus sylvatica compared to those dominated by coniferous tree species (mainly Picea abies and Pinus sylvestris). Correlation analyses showed a significant, but weak, correlation with SSCI. The advantage of the SHI TLS is the use of multiple scans from several scan positions. Thus, a better and very high resolution coverage of the forest structures is achieved. Due to its TLS-based nature this method provides many benefits in terms of reproducibility, objectivity and simplicity of data evaluation. [ABSTRACT FROM AUTHOR]

• Extensive beech and spruce dieback observed after hot droughts in 2018 and 2019. • Dead and healthy spruce and beech trees from central Germany were investigated. • Ca. 50% (7%) of all sampled spruce (beech) trees already died in 2018. • Drought signal enhanced by edaphic conditions and species-specific responses. • Dying trees showed lower growth and higher drought sensitivity than healthy trees. Anthropogenic climate change pushes forest ecosystems globally beyond their limits. Widespread events of forest die-off have been attributed to direct and indirect impacts of increasingly frequent and intense droughts. Here, we focus on an extensive mortality event in Norway spruce (Picea abies (L.) H. Karst.) and European beech (Fagus sylvatica (L.)) forests in Germany, following the successive 2018 – 2019 hot droughts. To examine whether this die-off indeed attributed to observed trends in drought occurrence and intensity, we sampled 143 beech and 186 spruce trees at three low-elevation sites (Spessart, Hassberge, Fichtelberg) with different edaphic properties in northern Bavaria. We analysed long-term hydroclimatic sensitivity and growth responses to extreme events of five site- and species-specific tree-ring width chronologies, including a reference site for each species. Growth of beech was sensitive to drought in April to June, whereas spruce growth was strongly related to drought during June to August, except at slightly higher elevations at the Fichtelberg site, where a summer temperature signal was observed. Trees at the Spessart and Hassberge sites showed an increased response to hydroclimatic conditions in April following the extreme drought in 1976 and from the 1990s onwards at the Fichtelberg site. Spruce bark beetle (Ips typographus L.) outbreaks during the 2018 drought accelerated the high mortality rates in around 50% of the trees at the Spessart and Hassberge site. In 2018, around 7% of all beech trees died at the Hassberge site, the site with the highest clay content. Our results suggest that these widespread mortality events can be attributed to an increasing drought sensitivity and were accelerated by the consecutive recent drought years. Sustainable forest management practices for these ecologically and economically important tree species are required to mitigate the effects of global warming in the future. [ABSTRACT FROM AUTHOR]

• Fine root biomass is 6.5 times higher in European beech than in Scots pine forests. • Marked plasticity of beech fine roots to soil chemical variation, but not to climate. • Marked plasticity of pine fine roots to climate variation, but not to soil chemistry. Planted forests of Scots pine (P. sylvestris L.) and other Pinus species extend over >1.7 million hectares in the Pleistocene lowlands of northern Germany, replacing former broadleaf forests (primarily European beech, Fagus sylvatica L.). This transformation belongs to the world's largest broadleaf-conifer forest conversions; yet, the belowground consequences of this species shift are poorly studied. Based on root coring, an ingrowth core study and root morphological analyses, we compared (i) the bio- and necromass, productivity and morphology of fine roots in pairs of beech and pine stands and (ii) analyzed the species' fine root system response to variation in soil properties and climatic conditions across a climate continentality gradient. Fine root biomass was on average 6.5 times higher (237 vs. 37 g m−2) and fine root productivity 1.9 times greater (147 vs. 77 g m−2 yr−1, difference not significant) in beech than pine stands. Beech responded with considerable plasticity in fine root system size and fine root morphology to variation in soil acidity and soil fertility and to the contrasting growing conditions in organic layer and mineral soil, but was not responsive to the climatic gradient. In contrast, pine modified fine root biomass and root morphology in response to precipitation and temperature, but did not respond to soil chemistry and fertility. Pine had a somewhat higher mean fine root diameter and also higher specific fine root surface area than beech, while its fine root tip abundance and mean fine root lifespan were lower than in beech (4 vs. 13 months). We conclude that the conversion of broadleaf (beech) to coniferous (pine) forest is accompanied by marked root system changes, notably the reduction of standing fine root biomass and productivity and an apparently contrasting belowground responsiveness to climatic and edaphic changes, with possible consequences for the trees' susceptibility to climate-warming and drought. [ABSTRACT FROM AUTHOR]

Viruses could be demonstrated in 61 cases of 160 samples of beech trees collected from 1982 to 1984 at different sites of the Rhineland area and in Westfalia (Federal Republic of Germany). According to morphological characteristics they are tentatively grouped to the Poty-, Potex- and Tobamoviruses. Two isolates showed spherical particles and maybe Nepoviruses based on indicator plant symptoms. Only viruses which are mechanically transmissible could be found by the methods applied. Their presumable role in the multi-factor complex of the beech decline has been discussed. [ABSTRACT FROM AUTHOR]

In the Central German Uplands, Fagus sylvatica and Picea abies have been particularly affected by climate change. With the establishment of beech forests about 3000 years ago and pure spruce stands 500 years ago, they might be regarded as 'neophytes' in the Hessian forests. Palaeoecological investigations at wetland sites in the low mountain ranges and intramontane basins point to an asynchronous vegetation evolution in a comparatively small but heterogenous region. On the other hand, palynological data prove that sustainably managed woodlands with high proportions of Tilia have been persisting for several millennia, before the spread of beech took place as a result of a cooler and wetter climate and changes in land management. In view of increasingly warmer and drier conditions, Tilia cordata appears especially qualified to be an important silvicultural constituent of the future, not only due to its tolerance towards drought, but also its resistance to browsing, and the ability to reproduce vegetatively. Forest managers should be encouraged to actively promote the return to more stress-tolerant lime-dominated woodlands, similar to those that existed in the Subboreal chronozone. [ABSTRACT FROM AUTHOR]

High N depositions of past decades brought changes to European forests including impacts on forest soil nutrition status. However, the ecosystem responses to declining atmospheric N inputs or moderate N depositions attracted only less attention so far. Our study investigated macronutrient (N, S, Ca2+, Mg2+, K+) pools and fluxes at forest conversion sites over 80 years old in Central Germany with European beech (so-called "Green Eyes" (GE)). The GE are embedded in large spruce and pine stands (coniferous stands: CS) and all investigated forest stands were exposed to moderate N deposition rates (6.8 ± 0.9 kg ha−1 yr−1) and acidic soil conditions (pHH2O < 4.7). Since the understanding of forest soil chemical and macronutrient status is essential for the evaluation of forest conversion approaches, we linked patterns in water-bound nutrient fluxes (2001–2018) and in predicted macronutrient storage in the herbaceous and tree layer to patterns in litter fall (2016–2017) and in forest floor and mineral soil macronutrient stocks at GE and CS assessed in 2018. Our results exhibited 43% (Nt) and 21% (S) higher annual throughfall fluxes at CS than at GE. Seepage water at 100 cm mineral soil depth (2001–2018) of CS is characterized by up to fivefold higher NO3− (GE: 2 ± 0.7 µmolc L−1; CS: 9 ± 1.4 µmolc L−1) and sevenfold higher SO42− (GE: 492 ± 220 µmolc L−1; CS: 3672 ± 2613 µmolc L−1) concentrations. High base cation (∑ Ca2+, Mg2+, K+) concentrations in CS mineral soil seepage water (100 cm depth: 2224 ± 1297 µmolc L−1) show significant positive correlations with SO42−. Tree uptake of base cations at GE is associated especially with a Ca2+ depletion from deeper mineral soil. Foliar litter fall turns out to be the main pathway for litter base cation return to the topsoil at GE (>59%) and CS (>66%). The litter fall base cation return at GE (59 ± 6 kg ha−1 yr−1) is almost twice as large as the base cation deposition (30 ± 5 kg ha−1 yr−1) via throughfall and stemflow. At CS, base cation inputs to the topsoil via litter fall and depositions are at the same magnitude (24 ± 4 kg ha−1 yr−1). Macronutrient turnover is higher at GE and decomposition processes are hampered at CS maybe through higher N inputs. Due to its little biomass and only small coverage, the herbaceous layer at GE and CS do not exert a strong influence on macronutrient storage. Changes in soil base cation pools are tree species-, depth- and might be time-dependent, with recently growing forest floor stocks. An ongoing mineral soil acidification seems to be related to decreasing mineral soil base cation stocks (through NO3− and especially SO42− leaching as well as through tree uptake). [ABSTRACT FROM AUTHOR]

• Green Eyes (GE) were planted in 1920s as groups of beech in coniferous sites (CS). • GE increase organic matter turnover on former coniferous sites. • Organic C translocation from forest floor into topsoil is higher in GE. • For GE, translocation of cations increases forest floor pH but acidifies the subsoil. To reduce the effects of extended coniferous monoculture plantations on forest floor and topsoil processes, like amplified acidification or nutrient immobilization in organic layers, small interspersed groups of European beech were planted at the beginning of the 20th century amid large coniferous stands (CS) in Central Germany. Today, these so-called "Green Eyes" (GE) are 82-year old. In our study we focused on two different timelines to investigate the effects of forest conversion on vegetation composition, forest floor and mineral soil properties, encompassing a long-term (>80 year) comparison from tree planting in the 1930s to 2018 and a shorter timeframe nearly spanning 20 years (1999–2018). Since long-term forest conversion experiments (>60 years) across sites sharing a common forest land-use history are scarce, our study allows to contribute to a better evaluation of the long-term effects on changes in soil properties. We linked standard methods assessing soil pH, organic C and total N concentrations as well as stocks as indicators of soil quality changes in forest floor and mineral soil (down to 40 cm depth) to patterns in ground vegetation dynamics (most GE were characterized only by a few herbaceous species). Our results exhibited an effect of forest conversion on the activation in forest floor turnover resulting in increased turnover rates in the GE (GE contain only half of the forest floor OM of CS), hence forming more bioactive humus forms (mull, moder) and a noticeable higher forest floor pH (+0.6 units) compared to CS. The OC translocation from the forest floor into the topsoil is higher under GE (+0.7% OC content), probably building up a stable SOC pool hence contributing to C sequestration. The positive effects of European beech on forest floor quality are related to a stronger acidification of the subsoil during the past 20 years (-0.5 pH units). The base pump effect (uptake of Ca2+, Mg2+, K+ and assimilation into tree biomass in exchange release of H+) in GE led to more acidic conditions (- 0.2 pH units) in the deeper mineral soil compared to CS. This bio-acidification may serve as one reason for subsoil acidification, as observed in our study, pointing out that mineral soil acidification is still an important issue in central European forests. Future restoration of soil base cation pools will still depend on the rate of bio-acidification, on the amount of acidifying air pollutant (and base cation) depositions and on forest management practices (e.g. intensity of biomass removal, soil regeneration-oriented liming). [ABSTRACT FROM AUTHOR]

• Biomass C storage in European beech forests is twice as high as in Scots pine forests. • Primary productivity is 25% lower in pine forests than in beech forests. • Large-scale forest conversion has reduced aboveground C storage and sequestration. In Europe, production forests with conifers widely replace native broadleaf trees. In the Pleistocene lowlands of northern Germany, > 1.7 million hectares of pine forests (Pinus spp., mostly P. sylvestris) have replaced natural broadleaf forests. We compared aboveground biomass carbon (C) pools and net primary productivity (ANPP) of broadleaf forests with natural development (ND; mostly Fagus sylvatica or Quercus petraea forests; 146 years old on average) to nearby young pine forests (YP; 65 years old on average) and old pine forests (OP; > 90 years) in northern Germany. Study aims where (i) to estimate the aboveground biomass C loss resulting from forest transformation, (ii) to compare the ANPP of broadleaf and pine forests, and (iii) to identify the main factors causing differences in biomass C storage and ANPP between forest types. YP forests stored only half of the biomass C of the ND forests (means: 72 vs. 147 Mg C ha−1); OP stands exceeded YP stands only by ~20% (87 vs. 72 Mg C ha−1). The main factor driving the biomass C pool differences was tree species identity, while stand age was not influential. Mean ANPP was 1.1 Mg C ha−1 year−1 higher in ND forests than in YP stands due to higher litter production, while wood production was similar. We conclude that large-scale forest conversion to Scots pine forests has decreased the aboveground biomass carbon storage by half and the C sequestration potential with aboveground productivity by ~25%; this effect must be assessed together with changes in soil organic carbon stocks. [ABSTRACT FROM AUTHOR]

• Beech and fir are able to use water from depths >0.5 m during drought. • Beech was unable to support transpiration by water contributions of this soil depth. • Firs transpiration remained unaffected due to isohydry and a taproot system. • In mixture, fir outcompeted beech for water in shallow soil after drought. In the present study we investigated water use strategies of mature stands of Fagus sylvatica (European Beech) with and without co-cultivation of Abies alba (Silver fir) during a summer drought and subsequent rewetting through simulated heavy precipitation in a temperate forest in south-west Germany. We used a combination of sap flow analysis, water stable isotope labeling and a simple linear mixing model with physiological restrictions to determine whether both species were able to switch water uptake depths during drought and reverse this switch after restoration of water supply. We showed that both species utilized water from relatively deep soil layers (>0.5 m) during the drought phase, though for beech trees these contributions were not able to support the high transpiration demands. In contrast, the transpiration of firs remained unaffected by drought probably due to a mixture of its isohydric water use strategy and taproot system. The reactions towards high intensity irrigation differed among species but also between beeches of the pure and mixed stands. While beech trees in the pure stand, once water uptake from the topsoil was re-established, used ~70% of water from more shallow soil depths and were able to restore transpiration, beech trees in the mixed stand obtained only 50% and transpiration decreased further. Firs used around 70% of the water in shallow soil layers and transpiration rates again remained unaffected. These differences indicate competition between beech trees and firs in the mixed stand upon drought. We conclude that drought is able to disrupt water relations in mixed temperate forested ecosystems in such a way that facilitation can turn into competition for resources like water. [ABSTRACT FROM AUTHOR]

The functional role of internal water storage is increasingly well understood in tropical trees and conifers, while temperate broad-leaved trees have only rarely been studied. We examined the magnitude and dynamics of the use of stem water reserves for transpiration in five coexisting temperate broad-leaved trees with largely different morphology and physiology (genera Fagus, Fraxinus, Tilia, Carpinus and Acer). We expected that differences in water storage patterns would mostly reflect species differences in wood anatomy (ring vs. diffuse-porous) and wood density. Sap flux density was recorded synchronously at five positions along the root-to-branch flow path of mature trees (roots, three stem positions and branches) with high temporal resolution (2 min) and related to stem radius changes recorded with electronic point dendrometers. The daily amount of stored stem water withdrawn for transpiration was estimated by comparing the integrated flow at stem base and stem top. The temporal coincidence of flows at different positions and apparent time lags were examined by cross-correlation analysis. Our results confirm that internal water stores play an important role in the four diffuse-porous species with estimated 5-12 kg day(-1) being withdrawn on average in 25-28 m tall trees representing 10-22% of daily transpiration; in contrast, only 0.5-2.0 kg day(-1) was withdrawn in ring-porous Fraxinus. Wood density had a large influence on storage; sapwood area (diffuse- vs. ring-porous) may be another influential factor but its effect was not significant. Across the five species, the length of the time lag in flow at stem top and stem base was positively related to the size of stem storage. The stem stores were mostly exhausted when the soil matrix potential dropped below -0.1 MPa and daily mean vapor pressure deficit exceeded 3-5 hPa. We conclude that stem storage is an important factor improving the water balance of diffuse-porous temperate broad-leaved trees in moist periods, while it may be of low relevance in dry periods and in ring-porous species.