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While foliar photosynthetic relationships with light, nitrogen, and water availability have been well described, environmental factors driving vertical gradients of foliar traits within forest canopies are still not well understood. We, therefore, examined how light availability and vapour pressure deficit (VPD) co-determine vertical gradients (between 12 and 42 m and in the understorey) of foliar photosynthetic capacity (Amax), 13C fractionation (∆), specific leaf area (SLA), chlorophyll (Chl), and nitrogen (N) concentrations in canopies of Fagus sylvatica and Abies alba growing in a mixed forest in Switzerland in spring and summer 2017. Both species showed lower Chl/N and lower SLA with higher light availability and VPD at the top canopy. Despite these biochemical and morphological acclimations, Amax during summer remained relatively constant and the photosynthetic N-use efficiency (PNUE) decreased with higher light availability for both species, suggesting suboptimal N allocation within the canopy. ∆ of both species were lower at the canopy top compared to the bottom, indicating high water-use efficiency (WUE). VPD gradients strongly co-determined the vertical distribution of Chl, N, and PNUE in F. sylvatica, suggesting stomatal limitation of photosynthesis in the top canopy, whereas these traits were only related to light availability in A. alba. Lower PNUE in F. sylvatica with higher WUE clearly indicated a trade-off in water vs. N use, limiting foliar acclimation to high light and VPD at the top canopy. Species-specific trade-offs in foliar acclimation to environmental canopy gradients may thus be considered for scaling photosynthesis from leaf to canopy to landscape levels.

The structure of the soil food web in two beech (Fagus sylvatica) forests, the Gottinger Wald and the Solling forest (Northern Germany), was investigated using variations in tissue 15N concentrations of animal species or taxa. The Gottinger Wald is located on a limestone plateau and characterized by mull humus with high macrofauna activity, particularly of Lumbricidae, Diplopoda and Isopoda. In contrast, the Solling forest is located on a sandstone mountain range and characterized by moder humus. The soil fauna of this forest is dominated by mesofauna, particularly by Collembola, Enchytraeidae and Oribatida. In June 1995 soil fauna was sampled using heat extraction. Three soil layers were analysed at each of the sites. 15N/14N ratios of bulk material increased strongly with soil depth in both forests. This also applied to the water-soluble fraction at the Gottinger Wald, but not at the Solling. Generally, the water-soluble fraction was more enriched in 15N than the bulk materials. For most animals studied 15N/14N ratios varied little with soil depth. In both forests soil animals could be classified either as saprophages, including microphytophages, or predators. On average, the δ15N of predatory taxa (Chilopoda, Araneida, Gamasina, Staphylinidae) exceeded that of saprophagous or microphytophagous taxa (Lumbricidae, Isopoda, Diplopoda, Collembola, Oribatida, Enchytraeidae) by 4.4 and 3.9‰ for the Gottinger Wald and the Solling, respectively. We assume that most of the saprophagous or microphytophagous taxa studied consist of primary and secondary decomposers and hypothesize that predators prey more on secondary than primary decomposers. Generally, average δ15N values differed little between saprophagous (Lumbricidae, Diplopoda, Isopoda) and microphytophagous taxa (Collembola, Oribatida). The variations in δ15N values of species within these taxa consistently exceeded the variation between them, indicating that the species of each of these taxa form a continuum from primary to secondary decomposers. Also, variations in δ15N values within predatory taxa in most cases exceeded that between taxa excluding top predators like Sorex. We conclude that using higher taxonomic units in soil food web analysis is problematic and in general not consistent with nature. Higher taxonomic units may only be useful for depicting very general trophic groupings such as predators or microbi-detritivores.

Fruiting is typically considered to massively burden the seasonal carbon budget of trees. The cost of reproduction has therefore been suggested as a proximate factor explaining observed mast-fruiting patterns. Here, we used a large-scale, continuous (13)C labeling of mature, deciduous trees in a temperate Swiss forest to investigate to what extent fruit formation in three species with masting reproduction behavior (Carpinus betulus, Fagus sylvatica, Quercus petraea) relies on the import of stored carbon reserves. Using a free-air CO2 enrichment system, we exposed trees to (13)C-depleted CO2 during 8 consecutive years. By the end of this experiment, carbon reserve pools had significantly lower δ(13)C values compared to control trees. δ(13)C analysis of new biomass during the first season after termination of the CO2 enrichment allowed us to distinguish the sources of built-in carbon (old carbon reserves vs. current assimilates). Flowers and expanding leaves carried a significant (13)C label from old carbon stores. In contrast, fruits and vegetative infructescence tissues were exclusively produced from current, unlabeled photoassimilates in all three species, including F. sylvatica, which had a strong masting season. Analyses of δ(13)C in purified starch from xylem of fruit-bearing shoots revealed a complete turn-over of starch during the season, likely due to its usage for bud break. This study is the first to directly demonstrate that fruiting is independent from old carbon reserves in masting trees, with significant implications for mechanistic models that explain mast seeding.

We hypothesised that the decomposition rates of leaf litter will increase along a gradient of decreasing fraction of the European beech (Fagus sylvatica) and increasing tree species diversity in the generally beech-dominated Central European temperate deciduous forests due to an increase in litter quality. We studied the decomposition of leaf litter including its lignin fraction in monospecific (pure beech) stands and in stands with up to five tree genera (Acer spp., Carpinus betulus, Fagus sylvatica, Fraxinus excelsior, Tilia spp.) using a litterbag approach. Litter and lignin decomposition was more rapid in stand-representative litter from multispecific stands than in litter from pure beech stands. Except for beech litter, the decomposition rates of species-specific tree litter did not differ significantly among the stand types, but were most rapid in Fraxinus excelsior and slowest in beech in an interspecific comparison. Pairwise comparisons of the decomposition of beech litter with litter of the other tree species (except for Acerplatanoides) revealed a “home field advantage” of up to 20% (more rapid litter decomposition in stands with a high fraction of its own species than in stands with a different tree species composition). Decomposition of stand-representative litter mixtures displayed additive characteristics, not significantly more rapid than predicted by the decomposition of litter from the individual tree species. Leaf litter decomposition rates were positively correlated with the initial N and Ca concentrations of the litter, and negatively with the initial C:N, C:P and lignin:N ratios. The results support our hypothesis that the overall decomposition rates are mainly influenced by the chemical composition of the individual litter species. Thus, the fraction of individual tree species in the species composition seems to be more important for the litter decomposition rates than tree species diversity itself. peerReviewed

International audience; Increasing atmospheric CO(2) and temperature are predicted to alter litter decomposition via changes in litter chemistry and environmental conditions. The extent to which these predictions are influenced by biotic factors such as litter species composition or decomposer activity, and in particular how these different factors interact, is not well understood. In a 5-week laboratory experiment we compared the decomposition of leaf litter from four temperate tree species (Fagus sylvatica, Quercus petraea, Carpinus betulus and Tilia platyphyllos) in response to four interacting factors: elevated CO(2)-induced changes in litter quality, a 3 degrees C warmer environment during decomposition, changes in litter species composition, and presence/absence of a litter-feeding millipede (Glomeris marginata). Elevated CO(2) and temperature had much weaker effects on decomposition than litter species composition and the presence of Glomeris. Mass loss of elevated CO(2)-grown leaf litter was reduced in Fagus and increased in Fagus/Tilia mixtures, but was not affected in any other leaf litter treatment. Warming increased litter mass loss in Carpinus and Tilia, but not in the other two litter species and in none of the mixtures. The CO(2)- and temperature-related differences in decomposition disappeared completely when Glomeris was present. Overall, fauna activity stimulated litter mass loss, but to different degrees depending on litter species composition, with a particularly strong effect on Fagus/Tilia mixtures (+58%). Higher fauna-driven mass loss was not followed by higher C mineralization over the relatively short experimental period. Apart from a strong interaction between litter species composition and fauna, the tested factors had little or no interactive effects on decomposition. We conclude that if global change were to result in substantial shifts in plant community composition and macrofauna abundance in forest ecosystems, these interacting biotic factors could have greater impacts on decomposition and biogeochemical cycles than rising atmospheric CO(2) concentration and temperature.

Tree species-rich forests are hypothesised to be less susceptible to insect herbivores, but so far herbivory–diversity relationships have rarely been tested for tree saplings, and no such study has been published for deciduous forests in Central Europe. We expected that diverse tree communities reduce the probability of detection of host plants and increase abundance of predators, thereby reducing herbivory. We examined levels of herbivory suffered by beech (Fagus sylvatica L.) and maple saplings (Acer pseudoplatanus L. and Acer platanoides L.) across a tree species diversity gradient within Germany’s largest remaining deciduous forest area, and investigated whether simple beech or mixed stands were less prone to damage caused by herbivorous insects. Leaf area loss and the frequency of galls and mines were recorded for 1,040 saplings (>13,000 leaves) in June and August 2006. In addition, relative abundance of predators was assessed to test for potential top-down control. Leaf area loss was generally higher in the two species of maple compared to beech saplings, while only beech showed a decline in damage caused by leaf-chewing herbivores across the tree diversity gradient. No significant patterns were found for galls and mines. Relative abundance of predators on beech showed a seasonal response and increased on species-rich plots in June, suggesting higher biological control. We conclude that, in temperate deciduous forests, herbivory–tree diversity relationships are significant, but are tree species-dependent with bottom-up and top-down control as possible mechanisms. In contrast to maple, beech profits from growing in a neighbourhood of higher tree richness, which implies that species identity effects may be of greater importance than tree diversity effects per se. Hence, herbivory on beech appeared to be mediated bottom-up by resource concentration in the sampled forest stands, as well as regulated top-down through biocontrol by natural enemies. Electronic supplementary material The online version of this article (doi:10.1007/s00442-009-1304-2) contains supplementary material, which is available to authorised users.

Seed dispersal patterns were studied in a north-western Spain temperate forest community to assess the performances of alternative dispersal kernels during two years with ecologically contrasting scenarios; a non-mast year, and a mast year of the dominant canopy species, beech Fagus sylvatica. Dispersal kernels were fitted under a Bayesian modeling framework. Both simple and mixture kernels were considered for the five more abundant tree species (Corylus avellana, Crataegus monogyna, F. sylvatica, Ilex aquifolium and Taxus baccata). Mixture kernels provided a better fit for almost all species, and the log-normal performed best for T. baccata. No relationship between dispersal syndromes and the best dispersal kernel function emerged. However, we found temporal changes in the shape of the dispersal kernels that seemed to be related to variation in relative fruit production among species and the resulting changes in the responses of dispersal vectors. This reveals a potential role for disperser-mediated indirect effects in terms of introducing temporal variation in species spread. In this sense, our results highlight the need to consider single species seed dispersal as a community process.

Motivated by decreasing foliar phosphorus (P) concentrations in Fagus sylvatica L. forests, we studied P recycling depending on P fertilization in mesocosms with juvenile trees and soils of two contrasting F. sylvatica L. forests in a greenhouse. We hypothesized that forests with low soil P availability are better adapted to recycle P than forests with high soil P availability. The P resorption efficiency from senesced leaves was significantly higher at the P-poor site (70 %) than at the P-rich site (48 %). P fertilization decreased the resorption efficiency significantly at the P-poor site to 41 %, while it had no effect at the P-rich site. Both acid and alkaline phosphatase activity were higher in the rhizosphere of the P-poor than of the P-rich site by 53 and 27 %, respectively, while the activities did not differ in the bulk soil. Fertilization decreased acid phosphatase activity significantly at the P-poor site in the rhizosphere, but had no effect on the alkaline, i.e., microbial, phosphatase activity at any site. Acid phosphatase activity in the P-poor soil was highest in the rhizosphere, while in the P-rich soil, it was highest in the bulk soil. We conclude that F. sylvatica resorbed P more efficiently from senescent leaves at low soil P availability than at high P availability and that acid phosphatase activity in the rhizosphere but not in the bulk soil was increased at low P availability. Moreover, we conclude that in the P-rich soil, microbial phosphatases contributed more strongly to total phosphatase activity than plant phosphatases.

The objectives of this study were to investigate how different soil types and elevated N deposition (0.7 vs 7 g N m–2a–1) influence the effects of elevated CO2 (370 vs 570 µmol CO2 mol–1) on soil nutrients and net accumulation of N, P, K, S, Ca, Mg, Fe, Mn, and Zn in spruce (Picea abies) and beech (Fagus sylvatica). Model ecosystems were established in large open-top chambers on two different forest soils: a nutrient-poor acidic loam and a nutrient-rich calcareous sand. The response of net nutrient accumulation to elevated atmospheric CO2 depended upon soil type (interaction soil × CO2, P

To maximize fitness, many animals must trade off their need to forage efficiently against their need to avoid predators. We studied such a trade-off in four species of tits (Paridae) in a forest near Oxford, UK. During winter, tits form flocks which increase feeding efficiency and reduce predation risk. These flocks feed extensively on beech (Fagus sylvatica) seeds, the abundance of which may be critical for winter survival. Because these seeds drop to the ground, where birds are exposed to sparrowhawk (Accipiter nisus) attack, tits need to trade off their need to find seeds against the proximity to protective cover, provided by dense clusters of hawthorn (Crataegus spp.). The quality of the beech crop differs markedly between trees and years. During a year of abundant beechmast, most tits searched for seeds close to protective cover. This 'safety-first' strategy precluded visits to superabundant food patches if they were too far from protective cover. Among beech trees near to cover, tits tended to prefer those with high seed density. Tits benefited from foraging under trees with high seed density because this correlated significantly with seed mass per square metre and because mean search times decreased with increasing seed density. Finally, we show experimentally that great tits, Parus major, can discriminate between edible (viable) and inedible (empty) seeds.

The mechanisms for species-specific growth responses to changes in atmospheric CO2 concentration within narrow ecological groups of species, such as shade-tolerant, late-successional trees, have rarely been addressed and are not well understood. In this study the underlying functional traits for interspecific variation in the biomass response to elevated CO2 were explored for seedlings of five late-successional temperate forest tree species (Fagus sylvatica, Acer pseudoplatanus, Quercus robur, Taxus baccata, Abies alba). The seedlings were grown in the natural forest understorey in very low and low light microsites (an average of 1.3% and 3.4% full sun in this experiment), and were exposed to either current ambient CO2 concentrations, 500, or 660 µl CO2 l–1 in 36 open-top chambers (OTC) over two growing seasons. Even across the narrow range of successional status and shade tolerance, the study species varied greatly in photosynthesis, light compensation point, leaf dark respiration (Rd), leaf nitrogen concentration, specific leaf area (SLA), leaf area ratio (LAR), and biomass allocation among different plant parts, and showed distinct responses to CO2 in these traits. No single species combined all characteristics traditionally considered as adaptive to low light conditions. At very low light, the CO2 stimulation of seedling biomass was related to increased LAR and decreased Rd, responses that were observed only in Fagus and Taxus. At slightly higher light levels, interspecific differences in the biomass response to elevated CO2 were reversed and correlated best with leaf photosynthesis. The data provided here contribute to a mechanistic process-based understanding of distinct response patterns in co-occurring tree species to elevated CO2 in natural deep shade. I conclude that the high variation in physiological and morphological traits among late-successional species, and the consequences for their responses to slight changes in resource availability, have previously been underestimated. The commonly used broad definitions of functional groups of species may not be sufficient for the understanding of recruitment success and dynamic changes in species composition of old-growth forests in response to rising concentrations of atmospheric CO2.

Insect herbivore enemies such as parasitoids and predators are important in controlling herbivore pests. From agricultural systems we know that land-use intensification can negatively impact biological control as an important ecosystem service. The aim of our study was to investigate the importance of management regime for natural enemy pressure and biological control possibilities in forests dominated by European beech. We hypothesize that the volatile blend released from herbivore-infested beech trees functions as a signal, attracting parasitoids and herbivore enemies. Furthermore, we hypothesize that forest management regime influences the composition of species attracted by these herbivore-induced beech volatiles. We installed flight-interception traps next to Lymantria dispar caterpillar-infested young beech trees releasing herbivore-induced volatiles and next to non-infested control trees. Significantly more parasitoids were captured next to caterpillar-infested trees compared to non-infested controls, irrespective of forest type. However, the composition of the trophic guilds in the traps did vary in response to forest management regime. While the proportion of chewing insects was highest in non-managed forests, the proportion of sucking insects peaked in forests with low management and of parasitoids in young, highly managed, forest stands. Neither the number of naturally occurring beech saplings nor herbivory levels in the proximity of our experiment affected the abundance and diversity of parasitoids caught. Our data show that herbivore-induced beech volatiles attract herbivore enemies under field conditions. They further suggest that differences in the structural complexity of forests as a consequence of management regime only play a minor role in parasitoid activity and thus in indirect tree defense.

We measured the effect of elevated atmospheric CO(2) on atmospheric nitrogen (N(2)) fixation in the tree species Alnus glutinosa growing in monoculture or in mixture with the non-N(2)-fixing tree species Betula pendula and Fagus sylvatica. We addressed the hypotheses that (1) N(2) fixation in A. glutinosa will increase in response to increased atmospheric CO(2) concentrations, when growing in monoculture, (2) the impact of elevated CO(2) on N(2) fixation in A. glutinosa is the same in mixture and in monoculture and (3) the impacts of elevated CO(2) on N cycling will be evident by a decrease in leaf δ(15)N and by the soil-leaf enrichment factor (EF), and that these impacts will not differ between mixed and single species stands. Trees were grown in a forest plantation on former agricultural fields for four growing seasons, after which the trees were on average 3.8 m tall and canopy closure had occurred. Atmospheric CO(2) concentrations were maintained at either ambient or elevated (by 200 ppm) concentrations using a free-air CO(2) enrichment (FACE) system. Leaf δ(15)N was measured and used to estimate the amount (N(dfa)) and proportion (%N(dfa)) of N derived from atmospheric fixation. On average, 62% of the N in A. glutinosa leaves was from fixation. The %N(dfa) and N(dfa) for A. glutinosa trees in monoculture did not increase under elevated CO(2), despite higher growth rates. However, N(2) fixation did increase for trees growing in mixture, despite the absence of significant growth stimulation. There was evidence that fixed N(2) was transferred from A. glutinosa to F. sylvatica and B. pendula, but no evidence that this affected their CO(2) response. The results of this study show that N(2) fixation in A. glutinosa may be higher in a future elevated CO(2) world, but that this effect will only occur where the trees are growing in mixed species stands.

Elucidating the function of and patterns among plant traits above ground has been a major research focus, while the patterns and functioning of belowground traits remain less well understood. Even less well known is whether species differences in leaf traits and their associated biogeochemical effects are mirrored by differences in root traits and their effects. We studied fine root decomposition and N dynamics in a common garden study of 11 temperate European and North American tree species (Abies alba, Acer platanoides, Acer pseudoplatanus, Carpinus betulus, Fagus sylvatica, Larix decidua, Picea abies, Pseudotsuga menziesii, Quercus robur, Quercus rubra and Tilia cordata) to determine whether leaf litter and fine root decomposition rates are correlated across species as well as which species traits influence microbial decomposition above versus below ground. Decomposition and N immobilization rates of fine roots were unrelated to those of leaf litter across species. The lack of correspondence of above- and belowground processes arose partly because the tissue traits that influenced decomposition and detritus N dynamics different for roots versus leaves, and partly because influential traits were unrelated between roots and leaves across species. For example, while high hemicellulose concentrations and thinner roots were associated with more rapid decomposition below ground, low lignin and high Ca concentrations were associated with rapid aboveground leaf decomposition. Our study suggests that among these temperate trees, species effects on C and N dynamics in decomposing fine roots and leaf litter may not reinforce each other. Thus, species differences in rates of microbially mediated decomposition may not be as large as they would be if above- and belowground processes were working in similar directions (i.e., if faster decomposition above ground corresponded to faster decomposition below ground). Our results imply that studies that focus solely on aboveground traits may obscure some of the important mechanisms by which plant species influence ecosystem processes.

Forest hydrologists have hypothesised that canopy transpiration (E(c)) of European temperate forests occurs at rather similar rates in stands with different tree species and hydrologic regimes. We tested this hypothesis by synchronously measuring xylem sap flow in four mature stands of Fagus sylvatica along a precipitation gradient with the aim (1) of exploring the regional variability of annual canopy transpiration (E(c(t))) in this species, and (2) of analysing the relationship between precipitation (P) and E(c(t)). E(c(t)) rates of 216, 225, 272 and 303 mm year(-1) corresponded to precipitation averages of 520, 710, 801 and 1,040 mm year(-1) in the four stands. We explored the regional variability of E(c(t)) in Central European colline to sub-montane beech stands in two meta-analyses based on (1) existing sap flow data on beech (n=5 observations), or (2) all canopy transpiration data on beech obtained by different techniques (sap flow, micrometeorological or soil water budget approaches, n=25). With a coefficient of variation (CV) of 20%, the regional variability of E(c(t)) (213-421 mm year(-1)) was smaller than the variation in corresponding precipitation (550-1,480 mm year(-1)). The mean E(c(t)) for beech was 289 (+/-58) mm year(-1) (n=25). A humped-shaped relationship between E(c(t)) and P, with a broad transpiration maximum in the precipitation range from ca. 700 to 1,000 mm year(-1), was found which may indicate soil moisture limitation of transpiration for Pca. 700 mm year(-1), and reduced transpiration by increased cloudiness or leaf wetness for P1,000 mm year(-1). Thus, the precipitation level significantly influences canopy transpiration of humid temperate forests; however, the size of the P influence on E(c(t)) and, in part, the direction of its effect differ from forests in semi-arid or arid climates. European beech has the capacity to maintain high E(c) rates in both humid and partly dry summer climates (P550 mm year(-1)).

In Central Europe, Fagus sylvatica and Picea abies represent contrasting extremes in foliage type, crown structure and length of growing season. In order to examine the competitive strategies of these two co-occurring species, we tested the following hypotheses: (1) the space occupied by the foliage of sun branches is characterized by greater foliar mass investment compared to shade branches, (2) the carbon (C) gain per unit of occupied space is greater in sun than in shade branches, and (3) annual C and water costs of the foliage for sustaining the occupied space are low, wherever C gain per unit of occupied space is low. These were investigated in a mature forest in Southern Germany. The examination was based on the annual assessment of space-related resource investments and gains of the foliage. The foliated space around branches was regarded as the relevant volume with respect to aboveground resource availability. Occupied crown space per standing foliage mass was higher in shade compared to sun branches of beech, whereas no difference existed in crown volume per foliage mass between sun and shade branches of spruce (hypothesis 1 accepted for beech but rejected for spruce). However, beech occupied more space per foliage mass than spruce. The C gain per occupied crown volume was greater in sun than in shade branches (hypothesis 2 accepted) but did not differ between species. The amount of occupied space per respiratory and transpiratory costs did not differ between species or between sun and shade branches. In beech and spruce, the proportion of foliage investment in the annual C balance of sun and shade branches remained rather stable, whereas respiratory costs distinctly increased in shade foliage. Hence, shade branches were costly structures to occupy space, achieving only low and even negative C balances (rejection of hypothesis 3), which conflicts with the claimed C autonomy of branches. Our findings suggest that competitiveness is determined by the standing foliage mass and the annual branch volume increment rather than annual investments in foliage. Expressing competitiveness in terms of space-related resource investments versus returns, as demonstrated here, has the potential of promoting mechanistic understanding of plant–plant interactions.

Ash (Fraxinus excelsior L.) and beech (Fagus sylvatica L.) seedlings were grown in the field under three levels of natural light: (1) open, (2) gap and (3) shade. Light acclimation of photosynthesis was characterized by means of modulated chlorophyll a fluorescence of intact leaves and growth parameters were measured at the end of the growing season. Measurements of maximum photochemical efficiency (F v/F m) of dark-adapted leaves at intervals through the day showed that ash had a higher F v/F m than beech in open and gap plots but not in shade plots. This indicated a larger build-up of photoinhibition in beech under gap and open conditions. Steady-state light response curves of the operating efficiency of PSII (F′ q/ F′m), the electron transport rate (ETR) and the photochemical efficiency factor (F′q/F′v) showed greater variability across light treatments in ash than in beech. Both species exhibited similar responses of non-photochemical quenching (NPQ) to light. When the data were normalized to the mean maximum irradiance in the growth environment, all photochemical parameters showed a reduction in variation across treatments, indicating that light acclimation in the two species occurred primarily through adjustments in rates of photochemistry. Adjustments in thermal heat dissipation were small in both species. This pattern was stronger in ash, suggesting a greater degree of phenotypic plasticity in photosynthetic capacity in this earlier successional species. Contrary to our expectations, the build-up of photoinhibition in beech did not appear to have a negative effect on total biomass accumulation relative to ash.

We enriched in CO2 the canopy of 14 broad-leaved trees in a species-rich, ca. 30-m-tall forest in NW Switzerland to test whether elevated CO2 reduces water use in mature forest trees. Measurements of sap flux density (JS) were made prior to CO2 enrichment (summer 2000) and throughout the first whole growing season of CO2 exposure (2001) using the constant heat-flow technique. The short-term responses of sap flux to brief (1.5-3 h) interruptions of CO2 enrichment were also examined. There were no significant a priori differences in morphological and physiological traits between trees which were later exposed to elevated CO2 (n=14) and trees later used as controls (n=19). Over the entire growing season, CO2 enrichment resulted in an average 10.7% reduction in mean daily JS across all species compared to control trees. Responses were most pronounced in Carpinus, Acer, Prunus and Tilia, smaller in Quercus and close to zero in Fagus trees. The JS of treated trees significantly increased by 7% upon transient exposure to ambient CO2 concentrations at noon. Hence, responses of the different species were, in the short term, similar in magnitude to those observed over the whole season (though opposite because of the reversed treatment). The reductions in mean JS of CO2-enriched trees were high (22%) under conditions of low evaporative demand (vapour pressure deficit, VPD

Little is known about below-ground competition between different tree species in mixed forests. We investigated the evidence for asymmetric competition between fine roots (

The effect of processing of beech leaf litter (Fagus sylvatica L.) of different ages by the diplopodGlomeris marginata (Villers) on status and turnover of microorganisms was investigated in the laboratory. Microbial biomass, basal respiration and metabolic quotient of litter-material from three different beechwood sites of a basalt hill forming a gradient from basalt (upper part of the hill) to limestone (lower part of the hill) were determined each season (February, May, August and November). The same microbial parameters were also measured after these litter materials had been processed byG. marginata (faecal pellets of an average age of 4 days). Short-term changes in microbial biomass and respiration in leaf material and faecal pellets from February and August were investigated after 1, 2, 5, 10, 20 and 40 days of incubation. The ergosterol content of August samples was determined. Processing of beech leaf litter byG. marginata increased microbial biomass in February and May but reduced microbial biomass in August and November. It was concluded that processing of litter materials in February and May increased accessibility of carbon resources to microorganisms by fragmentation. In contrast, in litter materials from August and November carbon resources were depleted and fragmentation by diplopods did not increase availability of carbon resources. Addition of carbon (glucose) and nutrients (nitrogen and phosphorus) to litter and faecal pellets indicated that processing of beech litter reduced nutrient deficiency of the microflora. Ergosterol content in faecal pellets was reduced strongly after beech leaf litter processing byG. marginata, indicating a decrease in fungal biomass. Presumably, in faecal pellets bacteria flourished at the expense of fungi.

Xylem embolism in winter and spring as well as the occurrence of positive xylem pressure were monitored in several diffuse-porous and one ring-porous tree species (Fraxinus excelsior). In Acer pseudoplatanus and Betula pendula embolism reversal was associated with positive (above-atmospheric) xylem pressures that frequently occurred during a 2-month period prior to leaf expansion. In Acer high stem pressures were occasionally triggered on sunny days after a night frost. The other species investigated showed no positive xylem pressure during the monitoring period in 1995. Populus balsamifera exhibited a complete embolism reversal in 1994, but, like Fagus sylvatica, recovery was slow and incomplete in 1995. Fraxinus did not refill embolized vessels, but relied entirely on the production of new earlywood conduits in May. Populus × canadensis Moench “robusta” did not recover from embolism during the monitoring period. Under a simulated root pressure of 20 kPa however, excised branches of Populus × canadensis restored maximum hydraulic conductance within 2 days, illustrating the great influence of even small positive pressures on cnductivity recovery in spring. In the absence of positive pressure there was no substantial refilling of embolized vessels within a rehydration period of 9 days.

The physiological activity and C and N allocation of beech seedlings planted in two different beech forest soils (acid brown earth, rendzina) were studied over 80 days. One adult earthworm Octolasion lacteum (Orley) was placed in half of the containers. Transpiration, CO2, assimilation, chlorophyll synthesis and N incorporation were higher in the acid brown earth than in the rendzina. Fine root production was also higher in the acid brown earth. Production of stems and total N incorporation were higher in the O. lacteum treatments than in the controls. Burrowing activity of O. lacteum did not affect total root production but stimulated the transfer of C and N towards aboveground parts of the plants and shifted the large root to fine root ratio towards large roots. O. lacteum effects were similar in both soils. It is concluded that endogeic earthworms significantly affect resource allocation patterns of beech seedlings over a wide range of soils. This effect can be partly explained by an increased availability of N in soils worked by earth-worms.

Changes in the carbon, hydrogen, nitrogen and polyphenol content of chestnut and beech leaves were measured during the first year after fall. Chestnut leaves had an initial carbon, hydrogen and nitrogen content (by weight) of 48.71%, 5.56% and 0.77% respectively; beech had a similar carbon and hydrogen content (47.77% and 5.36%) but less nitrogen (0.56%). Both leaf litter types showed percentage increases in nitrogen content during the study period but only the beech showed absolute increases in nitrogen content of up to 66.7% of the initial weight present in the leaves. The percentage increases in the nitrogen content of chestnut litter were largely attributable to more rapid losses of non-nitrogenous leaf constituents while the weight of nitrogen present in the leaves remained relatively constant. The percentage carbon and hydrogen contents of the chestnut and beech litter showed changes of less than 1% throughout the year, indicating that carbohydrate losses were directly proportional to weight losses. Soil animals fed on chestnut leaves to a far greater extent than beech leaves; this difference did not appear to be directly attributable to differences between the nitrogen contents or C/N ratios of the two leaf litter species. The gross polyphenol contents of chestnut and beech litter showed an intraspecific inverse correlation with the feeding activities of soil animals on the leaves, but did not account for interspecific differences in leaf palatability since chestnut leaves were eaten when they contained higher polyphenol concentrations than beech leaves. However, there was an interspecific negative correlation between palatability and the presence of protocatechuic and gallic acids.

In a montane beech (Fagus sylvatica) forest the influence of the climatic factors, light and temperature, on net photosynthesis and on the CO2 balance of the ground vegetation was investigated. The total turnover of carbon was calculated. Species studied included: Athyrium filix-femina, Oxalis acetosella, Luzula luzuloides, Deschampsia flexuosa and young plants of Fagus sylvatica. 1. The light compensation point in all spp. is between 300 and 500 lux except for D. flexuosa where it is 2 klx. Light saturation is attained at 2-3 klx for A. filix-femina, at 5-6 klx for O. acetosella, and at 6-7 klx for L. luzuloides and F. sylvatica. The net photosynthesis of D. flexuosa increases linearly upto 12 klx. This plant, therefore, is more closely related to plants with high light requirements than all the other species under experiment. 2. The maximum rates of net photosynthesis in O. acetosella and A. filix-femina are higher than in all the other plants, independent of the reference system. Per unit dry weight they even attain rates of CO2 uptake (22-27 mg CO2/gdw·h) known from herbs under the much better light conditions of an open habitat. F. sylvatica and L. luzuloides exhibit per unit dry weight only 30% of this rate and D. flexuosa 25%. On a leaf surface area and chlorophyll content basis differences are smaller: F. sylvatics attains 75%, L. luzuloides reaches 50% and D. flexuosa only 30% of the maximal rates of net photosynthesis of O. acetosella and A. filix-femina. The higher CO2 uptake of O. acetosella and A. filix-femina points to a better adaptation of their photosynthetic apparatus in comparison to all the other species of the same habitat. 3. At light saturation the temperature optimum of A. filix-femina and O. acetosella covers a smaller range at lower temperatures than was found in the other species. These attain almost maximal rates of net photosynthesis over the whole range of temperatures of their natural habitat. At decreasing light intensities the temperature optimum of O. acetosella changes from 13-18° C at 8-12 klx to a range of even lower temperatures (9-12° C at 1 klx). 4. The respiration of the rhizome and the roots of O. acetosella is per unit dry weight 40% of the dark respiration rate in the above ground material. 5. The daily gain of net photosynthesis per unit dry weight of O. acetosella and A. filix-femina is 4 times as high as in L. luzuloides and in F. sylvatica and 7 times as high as in D. flexuosa. Per unit of surface area and chlorophyll content differences are smaller. The sequence in all cases remains the same. During the night D. flexuosa has the highest relative respiratory loss. Its CO2 gain over 24 hours is very small. 6. The importance of sun flecks on the CO2 balance is small in all species except D. flexuosa. More important is the mean light intensity and the rate of net photosynthesis which is attained under these conditions. The amount of CO2 photosynthetically bound in sun flecks is 6% of the daily balance in A. filix-femina, 16-19% of the daily balance in O. acetosella, L. luzuloides and F. sylvatica, and 27% of the daily balance in D. flexuosa. The existence of D. flexuosa is dependent on the occurrence of sun flecks on the forest floor. The ecological significance of the relative light intensity in the mosaic-like distribution of plants on the forest floor is discussed. 7. The varying success in adaptation to the conditions of the habitat becomes even more evident when compared with the primary production of the beech crown. The daily gain of net photosynthesis of O. acetosella and A. filix-femina per unit dry weight is much larger than in either the sun or shade leaves in the canopy of the same stand. Per unit surface area of the leaves they attain 18-20%, per unit chlorophyll content 32% (L. luzuloides and the young plants of F. sylvatica 16-27%, D. flexuosa 4%) of the gain of net photosynthesis in the beech sun leaves. 8. A comparison with a model of primary production (maximal rates of net photosynthesis under experimentally optimal conditions over the whole day = 100%) shows what effect the different climatic factors of the natural habitat have in limiting the CO2 balance, and to what extend the actual CO2 gain reaches the physiological optinum. On the forest floor the rate of net photosynthesis is reduced primarily through the intense shade of the beech canopy and by dawn and dusk (reduction of the maximal CO2 gain in O. acetosella and in A. filix-femina ca. 50%, in L. luzuloides and F. sylvatica ca. 60% and in D. flexuosa ca. 86%). The effect of additional clouds is smaller (reduction of the maximal CO2 gain in all species 4-6%, maximal 19%). The effect of temperature is very small for L. luzuloides, F. sylvatica and D. flexuosa. Corresponding to the low temperature optimum the influence of the prevailing temperatures is much higher in O. acetosella and A. filix-femina (4-6% reduction of the maximal CO2 gain through temperatures above optimum). 9. For an assessment of the competition potential of O. acetosella compared to L. luzuloides and F. sylvatica for the vegetation period of April to August, the carbon balances of the whole plants were estimated. These are compared with the dry weight increase. Among the three life forms of the rhizome geophyte (Oxalis), the hemicryptophyte (Luzula) and the phanerophyte (Fagus) there are striking differences in the use and in the distribution of the CO2 gain. L. luzuloides invests 65% of the net photosynthetic gain as dry weight increment (O. acetosella only 44%, F. sylvatica 40%). Moreover, the growth of L. luzuloides takes place primarily above ground with the establishment of new leaves. The relative proportion of the growth above ground to the total dry weight increment is for L. luzuloides 63%, as against 57% in F. sylvatica and only 42% in O. acetosella. In respect to the total carbon balance the better use of the CO2 gain gives L. luzuloides in this habitat a higher competition potential than the photosynthetically more active O. acetosella. The constitutional differences in the photosynthetic activity are compensated for by the distribution of the assimilates to shoot and root.

The thermal properties of four different types of bark were investigated on twentyfour central European tree species using thermocouples. Tree species with white bark avoid overheating of their surface by reflection of the radiation. Species with fissured and scaly barks shade inner parts of their bark. Some tree species with fissured barks show high insulation across the bark. Smooth and thin barks show no adaptation to avoid overheating. These tree species (in central Europe e.g. Fagus sylvatica) have to form closed stands and are not able to occur in open stands as tree species with structured or white bark types.The arthropod fauna of the same bark types was studied on six tree species using three collecting methods. The microclimate on the bark determines the number per cm2 of some species, some are active during winter, and other tend to aptery and reproduce parthenogenetically. On smooth bark one species dominates, whereas a highly diverse fauna lives on fissured barks. The occurrence of species on bark is determined by the microstructure, microclimate and consistence of the epiphyts. If tree species alter within forest ecosystems the dominant species on bark will persist. Specialists of fissured barks will die out if tree species with smooth bark (Fagus sylvatica) form the central European forest.

In a 10-year study period, outbreaks of the bank vole, Clethrionomys glareolus, Schreber only occurred in years following huge seed production of European beech, Fagus sylvatica. Intensive winter reprodution preceded the outbreaks, in contrast to a normal breeding season from April through September. No winter reproduction occurred in nearby populations from habitats without mast production. During the winter, the average weight of C. glareolus remained high in the mast forests and the age structure resembled that of a summer breeding population. Despite excess energy requirements of winter breeding, survival rates were similar to that of non-breeding winter populations. In mast years, rodent consumption in the beech forest was estimated as 1.0–10.3% of endosperm production available to postdispersal seed predators. Between mast years rodent consumption made up 30–100% of endosperm production available. Mast years occurred at irregular intervals and seed production seems to be synchronized between individual trees over large areas and induced by climatic events. These phenomena lead to seed predator satiation.