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Forests in Central Europe have been used since centuries and were systematically changed by silvicultural practices since the late 1700s. Focusing on possible biodiversity losses, forest stand management primarily impacts on the biodiversity attributes ‘composition, structure and functioning’ that are interlinked and incorporate different organizational and spatial ecosystem levels. Forest stand management can manipulate tree species diversity, which in turn affects stand structure and finally leads to changes in forest functions and services. We used meta-analyses to review 49 papers with 197 comparisons on compositional and structural diversity between unmanaged and managed forests as well as 53 comparisons of biomass productivity between mixed and monoculture forests throughout the temperate biome of Europe. Besides management impacts, for species and structural comparisons, we took time since abandonment of forest stand management into consideration when dealing with unmanaged forests. For species richness and diversity, we could not detect significant management effects; no significant influences of time since abandonment of management could be identified either. Structural attributes partly revealed considerable responses to forest stand management. Importantly, deadwood quantity, the number of microhabitats, and tree size diversity were reduced by forest stand management, while no effect was found for stand basal area and the number of living trees. Some of these effects become more pronounced with increasing time since abandonment. Forest productivity was significantly enhanced by regular moderate thinning compared with untreated stands and by tree species mixing compared with monospecific stands. Based on these results, we discuss the role of direct and indirect silvicultural effects, interactions between biodiversity components, the problem of defining the unmanaged reference state, and perspectives for forest stand management in practice.

Currently the paradigm of sustainable forest management is extended to a broad range of ecological, economic, and social forest functions and services. In particular, biodiversity becomes a more and more important issue in the forest planning processes. However, its quantification, monitoring and assessment still remain complex and difficult although data from regional or national forest inventories might contribute valuable information for quantifying biodiversity. Here, we demonstrate how such data can be tapped and aggregated to different spatial and temporal scales for deriving indicators to support biodiversity assessment and monitoring. By focusing on tree species and structural related indices, our method allows the evaluation of spatial and temporal variation of diversity indicators by using inventory data. We present a practice-oriented approach on how to integrate such indicators into forest planning processes and thereby extend the paradigm of sustainability of forest management. We exemplify our approach by inventory data from the Bavarian State Forest Enterprise to show how inventory data can be utilised to (i) assess biodiversity aspects from stand to landscape scales and (ii) integrate such information into forest management at different spatial and temporal scales. Finally, we discuss how this information extracted from forest inventories may contribute to a more generalised assessment, monitoring and planning of biodiversity in managed forest ecosystems.

Individual tree mortality prediction is a key component of single tree-based stand simulators. However, accurate modeling of long-term research plot data is hampered by rare events, variable lengths of observation, and multiple sources of heterogeneity. This study makes use of a result from medicine that demonstrates the equivalence of logistic and Cox proportional hazards regression for modeling survival data in the case of large sample sizes, rare events, and variable interval periods of observation. Pooled logistic regression models are used to model tree mortality across multiple observation periods with random effects to account for heterogeneity due to plots and calendar year. The models are applied to data from 21,051 observation periods (each approximately 5 years) from 9,292 beech trees in a Bavarian long-term forest research plot network. Among the observation periods studied, 604 (2.9%) resulted in a mortality. Indices measuring competition from light, trees of the same species, conifer trees, and shading are significantly associated with mortality, whereas other variables, including dbh, fail to add additional predictive value. Analytic equations for predicting mortality in new trees are provided and yield an area underneath the receiver operating characteristic curve of 91.5%.

The question how tree species allometry in mixed stands differs from pure stands is approached by analyzing how crown morphology of European beech (Fagus sylvatica L.) behaves in intra- versus interspecific neighborhoods. Based on long-term experimental plots with individual tree records on tree allometry and competition, our results revealed that (i) in pure stands crown allometry of beech is far from constant, but closely related to intraspecific competition, (ii) in mixed stands crown allometry of beech is considerably modified by competition reduction when growing in the vicinity of spruce, oak or pine, and (iii) crown extension due to competition reduction by interspecific neighbors increases with site fertility. Implications for the allometric theory, the stress-gradient hypothesis and a general understanding/conceptual model for mixing reactions are discussed.

The mixture of beech (Fagus sylvatica L.) and oak (sessile oak, Quercus petraea (Matt.) Liebl., and pedunculate oak, Q. robur L.) is of considerable importance in Europe and will probably become even more important under climate change. Therefore, the performance of oak and beech in mixture was compared with the species’ growth in pure stands. Data from 37 long-term mixing experiments in Poland, Germany and Switzerland were pooled for analysis of mixing effects on stand productivity and possible interrelationships with mixing portions or site conditions. We found that on average, mixed stands of oak and beech exceeded biomass productivity in pure stands by 30 % or 1.7 t ha−1 year−1, as the growth of both species was benefitted by the mixture. However, that the interaction actually ranged from facilitation and overyielding on poor sites to underyielding on fertile sites triggered by competition. An empirically derived interaction model showed volume and dry mass growth changing in mixed stands from gains of 50 % to losses of 10 % depending on site conditions. It is concluded that the analysed mixture grows in accordance with the stress-gradient hypothesis and that our results suggest a site-specific relationship between species mixture and biomass productivity. As a consequence, an adequate species mix should result in increased productivity under steady state as well as climate change.

Tropospheric ozone (O3) is a critical threat to forest ecosystems. A stomatal flux-based risk evaluation methodology at the leaf level was established recently in the context of the Convention on Long-Range Transboundary Air Pollution (LRTAP). This study demonstrates improvement and validation of the stomatal flux-effect approach for adult beech with results from the 8-year free-air O3 enrichment experiment at “Kranzberger Forst” (Germany). The risk assessment module of the SVAT model FO3REST, being under development for local scale O3-risk assessment of adult beech stands, was parameterized according to the LRTAP Convention’s Mapping Manual. Mean maximum stomatal conductance for water vapour of 245 mmol H2O m−2 PLA s−1, as suggested in the LRTAP Convention’s Mapping Manual for beech, was affirmed by assessment at “Kranzberger Forst”, resulting in 162 mmol O3 m−2 PLA s−1 upon recommended adjustment of the O3/water vapour diffusivity ratio to 0.663. Based on this ratio, a provisional corrected flux-effect function was deduced. Modelled Phytotoxic O3 Doses (POD 1) and potential O3-caused losses in biomass formation estimated with a site-specific stomatal conductance algorithm differed slightly only from estimates by the original LRTAP parameterisation. Analysis-derived POD 1 target value within the meaning of Article 2 of the European Council Directive 2008/50/EC of 10 mmol O3 m−2 corresponded to potential loss in biomass formation of about 10 % in ambient air relative to “pre-industrial” conditions. However, exceedance occurred by about a factor of two during the study period, indicating high risk at “Kranzberger Forst” under ambient air. Assessment for doubled O3 exposure indicated potential underestimation even of the O3 risk because modelled losses in biomass formation are in the lower range of the standard deviation of the observed ones.

Species mixing is widely held to stabilize productivity, increase resilience and contribute to risk minimization in forest stands in need of special as a result of longevity. However, research on the effects of mixing on productivity and resource consumption so far yielded fairly incoherent results rather than general findings. We focused on the effects of the spatial mixing pattern and the annual climate conditions on the mixing effect, which to date have seldom been considered as modifiers of mixing effects. Nine years of intensive survey of four pure stands of Norway spruce (Picea abies [L.] Karst.) and European beech (Fagus sylvatica [L.]) and two mixed plots with different mixing pattern showed: (1) mixing hardly changed annual net primary productivity at stand level when Norway spruce and European beech are cultivated group-wise but increased by 37 % on account of a higher efficiency of water and light use in individual tree-wise mixture. (2) Favourable climatic conditions increased the superiority of mixed versus pure stands productivity, while, in particular, water stress cancelled the benefit of mixing considerably. (3) An interaction between the spatial pattern and variable climatic conditions was revealed. Both improved light and water use were found in favourable years in close inter-specific intermingling. However, in unfavourable years the spatial pattern played a less pronounced role in terms of productivity.

General scaling rules or constants for metabolic and structural plant allometry as assumed by the theory of Euclidian geometric scaling (2/3-scaling) or metabolic scaling (3/4-scaling) may meet human’s innate propensity for simplicity and generality of pattern and processes in nature. However, numerous empirical works show that variability of crown structure rather than constancy is essential for a tree’s success in coping with crowding. In order to link theory and empiricism, we analyzed the intra- and inter-specific scaling of crown structure for 52 tree species. The basis is data from 84 long-term plots of temperate monospecific forests under survey since 1870 and a set of 126 yield tables of angiosperm and gymnosperm forest tree species across the world. The study draws attention to (1) the intra-specific variation and correlation of the three scaling relationships: tree height versus trunk diameter, crown cross-sectional area versus trunk diameter, and tree volume versus trunk diameter, and their dependence on competition, (2) the inter-specific variation and correlation of the same scaling exponents (\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$ {\upalpha}_{h,d}, {\upalpha}_{{\text{csa,}}d} $$\end{document} and \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$ {{\upalpha}}_{v,d} $$\end{document}) across 52 tree species, and (3) the relevance of the revealed variable scaling of crown structure for leaf organs and metabolic scaling. Our results arrive at suggesting a more extended metabolic theory of ecology which includes variability and covariation between allometric relationships as prerequisite for the individual plant’s competitiveness. Electronic supplementary material The online version of this article (doi:10.1007/s00442-011-2240-5) contains supplementary material, which is available to authorized users.

In a 50- to 70-year-old mixed stand of Norway spruce (Picea abies (L.) Karst.) and European beech (Fagus sylvatica L.) in Germany, tree cohorts have been exposed to double ambient ozone (2xO(3)) from 2000 through 2007 and can be compared with trees in the same stand under the ambient ozone regime (1xO(3)). Annual diameter growth, allocation pattern, stem form, and stem volume were quantified at the individual tree and stand level. Ozone fumigation induced a shift in the resource allocation into height growth at the expense of diameter growth. This change in allometry leads to rather cone-shaped stem forms and reduced stem stability in the case of spruce, and even neiloidal stem shapes in the case of beech. Neglect of such ozone-induced changes in stem shape may lead to a flawed estimation of volume growth. On the stand level, 2xO(3) caused, on average, a decrease of 10.2 m(3) ha(-1) yr(-1) in European beech.

Air pollution and climate change are inherently linked to each other. After introducing into the presently prevalent air pollutants and their relevance for forest tree and ecosystem performance, the account focuses on nitrogen deposition and tropospheric ozone (O3), the latter being regarded as potentially most detrimental to vegetation, and hence, as negating carbon sink strength and storage. Mechanisms of O3 action in trees and stands are highlighted, stressing interactions with other abiotic and biotic factors, including volatile organic compounds, as a fundamental pre-requisite for understanding O3 effects. O3 is emphasized as a globally effective agent of climate change, regarding relevance for forest productivity, in particular, at hot spots of air pollution in the southern hemisphere, prognosticated for the upcoming decades. Adaptation capacities of forest trees are discussed in view of the rapidity in the progression of environmental change.

Rising tropospheric ozone (O3) concentrations pose a critical threat to forest ecosystems. A stomatal flux-based risk evaluation methodology at leaf level was established recently in the context of the Convention on Long-Range Transboundary Air Pollution. This study demonstrates improvement and validation of the stomatal flux–effect approach for European beech and Norway spruce with results from the 8-year free-air O3 enrichment experiment at Kranzberg Forest (Germany). Based on the recommended O3/water vapour diffusivity ratio of 0.663, provisional corrected flux–effect functions for beech and spruce were deduced. Comparison of observed and modelled loss in annual growth under twice-ambient O3 exposure relative to whole-stem productivity under ambient O3 seems to confirm the Convention’s leaf-level stomatal flux approach and the associated response function for Norway spruce up to twice-ambient O3 exposure. For European beech, it must be emphasized that the Convention’s methodology may underestimate the risk for loss in whole-stem productivity.

This chapter starts with the geometric and metabolic scaling theory which predicts stable scaling relations between trunk and crown dimensions for the allometric ideal plant and constant slopes for the self-thinning process on stand level. Empirical works in contrast evidence crown plasticity and species-specific self-thinning slopes. In order to link theory and empiricism we first draw attention on the intra-specific variation of crown scaling exponents in dependency on stand density, intra-, and inter-specific competition, and on relationships between scaling exponents. Second, we analyze the differences of crown scaling between Norway spruce and European beech as well as between the groups of gymnosperm and angiosperm species. Third, we draw attention on the relevance of scaling relationships for space occupation and stand dynamics. Finally we discuss the findings in view of the allometric theory, their implications for space occupation at the individual plant level and for self-thinning at the stand level.

The focus is on the interindividual growth partitioning in forest stands under stress. We use (1) individual tree records of size and growth from about 100 long-term experimental plots under survey since 1871 in forest stands along an ecological gradient through South Germany, (2) annual measurements of the size–growth relationship, including the extremely dry years of 1976 and 2003, from a mixing experiment of spruce and beech, and (3) annual growth rates of spruces and beeches with and without double ambient ozone fumigation between 2000 and 2007. Low stress increases steepness and size-asymmetry of the size–growth relationship, i.e., it favors the superiority of tall trees at the smaller trees’ expense. High stress, no matter whether induced by competition, drought, or ozone, distinctly reduces the superior growth rate of tall trees. The causes for this behavior and the consequences for modeling stand dynamics and silvicultural treatment are discussed.

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 treesoil 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. Empirical proof corroborates substantial mitigation of carbon sequestration in the treesoil system of a forest site under enhanced O3 impact for adult beech.

Against a backdrop of increasing climate change, the effects of site conditions, drought events and ozone stress on the size-growth relationship in Norway spruce (Picea abies [L.] Karst.) and European beech (Fagus sylvatica [L.]) stands are analyzed. The size-growth relationship is represented by a straight line defined by intercept and slope of a simple linear equation with stem diameter at height 1.30 m as independent variable and annual stem diameter increment at height 1.30 as dependent variable. On the basis of 64 long-term experimental plots dating back to 1871 and representing an ecological gradient from fertile to poor sites, it is shown that poorer sites exhibit shallower slopes of the linear size-growth relationships than fertile sites. Annual measurements of the size-growth relationship, including the extremely dry years of 1976 and 2003, also showed that lower stand growth rates result in shallower size-growth relationship slopes. By comparing stands with and without experimental twice-ambient ozone exposure between 2000 and 2007, it was found that ozone stress can significantly reduce the slope of the size-growth relationship. This indicates that limiting site condition, whether acute or chronic in nature, distinctly reduces the superiority of tall trees, and that a lower degree of resource limitation increases the steepness of the size-growth relationship. The causes for this behavior and the consequences for stand dynamics, silvicultural treatment and prognostication by models are discussed.

International audience; Existing growth and yield plots of pure and mixed stands of Norway spruce (Picea abies (L.) H. Karst.) and European beech (Fagus sylvatica L.) were aggregated in order to unify the somewhat scattered sources of information currently available, as well as to develop a sound working hypothesis about mixing effects. The database contains information from 23 long-term plots, covering an ecological gradient from nutrient poor and dry to nutrient rich and moist sites throughout Central Europe.* An empirically formed interaction model showed, that depending on the site conditions, dry mass growth in mixed stands can range from − 46% to +138 % of the growth yielded by a scaled combination of pure stands at equal mixing proportions.* Drawing from the interaction model, overyielding of the mixed stands appears to be triggered by two separate mechanisms. On poor sites, where significant overyielding is commonly found, facilitation by beech offsets nutrient-related growth limitations in spruce. In contrast, overyielding of mixed stands occurs less frequently on rich sites, and appears to be based on an admixture effect, with spruce reducing the severe intra-specific competition common in pure beech stands.* It was concluded that silviculture can accelerate growth of spruce by beech admixtures on poor sites, while growth of beech can be promoted by admixture of spruce, particularly on excellent sites.