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Understanding and modelling plant interactions is an important field in quantitative forest ecology. Many spatially explicit techniques have been devised for shedding light into these processes. One of these methods includes the application of kernel functions, which describe the decay with increasing distance of interaction effects of each plant of a given community on others. In forest inventory, a method referred to as relascope sampling is often applied to collect information on the state and change of tree resources: somewhat unexpectedly, the mathematical principles of this technique have been turned into measures of competition for use in ecological modelling. In this study, we combined methods from quantitative ecology and sampling theory by defining a parameter-parsimonious relascope kernel function, thus generalising the concept of individual-tree basal-area factors. By using both relative and absolute growth rates as response variables in the regression we compared the performance of the relascope kernel with an alternative, the exponential kernel function. Our results indicated that the relascope kernel can indeed be applied to both types of growth rates in individual-based models. Using individual-tree basal-area factors, it is even possible to anticipate the performance of the relascope kernel. In most cases the estimation efficiency was greater, when absolute growth rate was the response variable. The exponential kernel was more efficient than the relascope kernel, but at the expense of parameter parsimony and estimation robustness. Our study has shown that simple, parsimonious models, inspired by another field of natural sciences, such as the relascope kernel, can effectively encapsulate the interaction dynamics of forest ecosystems.

1. When tree‐species mixtures are more productive than monocultures, higher light absorption is often suggested as a cause. However, few studies have quantified this effect and even fewer have examined which light‐related interactions are most important, such as the effects of species interactions on tree allometric relationships and crown architecture, differences in vertical or horizontal canopy structure, phenology of deciduous species or the mixing effects on tree size and stand density. 2. In this study, measurements of tree sizes and stand structures were combined with a detailed tree‐level light model (Maestra) to examine the contribution of each light‐related interaction on tree‐ and stand‐level light absorption at 21 sites, each of which contained a triplet of plots including a mixture and monocultures of Fagus sylvatica and Pinus sylvestris (63 plots). These sites were distributed across the current distribution of these species within Europe. 3. Averaged across all sites, the light absorption of mixtures was 14% higher than the mean of the monocultures. At the whole community level, this positive effect of mixing on light absorption increased as canopy volume or site productivity increased, but was unrelated to climate. At the species population or individual tree levels, the mixing effect on light absorption resulted from light‐related interactions involving vertical canopy structure, stand density, the presence of a deciduous species (F. sylvatica), as well as the effects of mixing on tree size and allometric relationships between diameter and height, crown diameter and crown length. 4. The mixing effects on light absorption were only correlated with the mixing effects on growth for P. sylvestris, suggesting that the mixing effects on this species were driven by the light‐related interactions, whereas mixing effects on F. sylvatica or whole community growth were probably driven by non‐light‐related interactions. 5. Synthesis. The overall positive effect of mixing on light absorption was the result of a range of light‐related interactions. However, the relative importance of these interactions varied between sites and is likely to vary between other species combinations and as stands develop. Czech Republic Ministry of Education, Youth and Sports. Grant Number: COST CZ ‐ LD14063 and and LD14074; COST (European Cooperation in Science and Technology). Grant Number: COST Action EuMIXFOR; German Research Foundation. Grant Number: FO 791/4‐1

The growth effects of mixtures are generally assumed to be a result of canopy structure and crown plasticity. Thus, the distribution of leaf area at tree and stand level helps to explain these mixing effects. Therefore, we investigated the leaf area distribution in 12 stands with a continuum of proportions of European larch (Larix decidua Mill.) and Norway spruce (Picea abies (L.) Karst.). The stands were between 40 and 170 years old and located in the northern part of the Eastern Intermediate Alps in Austria at elevations between 900 and 1300 m a. s. l. A total of 200 sample trees were felled and the leaf area distribution within their crowns was evaluated. Fitting beta distributions to the individual empirical leaf area distributions, the parameters of the beta distributions were shown to depend on the leaf area of the individual trees and, for spruce, on the proportion of spruce in the stands. With the equations determined, the leaf area distribution of all trees in the stand, and thus its distribution in the stands, was calculated by species and in 2 m height classes. For the individual trees, we found that the leaf area distribution of larch is more symmetric, and its peak is located higher in the crown than it is the case for spruce. Furthermore, the leaf area distribution of both species becomes more peaked and skewed when the leaf area of the trees increases. The mixture only influences the leaf area distribution of spruce in such a way that the higher the spruce proportion of the stand, the higher the leaf area is located within the crown. At the stand level, a strong relationship was found between the proportion of spruce and the distance between the peaks of the leaf area distributions of larch and spruce.

An increasing number of investigations into mixed forest stands shows clear interactions between complementarity and stand and site characteristics. One of the least-investigated mixture types are mixed stands of Norway spruce and European larch. We investigated pure and mixed stands of these species in the northern part of the eastern intermediate Alps in Austria, at altitudes between approximately 880 and 1330 m above sea level. In these stands, 12 plots sized between 0.25 ha and 1.6 ha, with varying ages and proportions of Norway spruce, were established. All trees were measured for their coordinates, diameter at breast height, tree height, crown height, and crown projection area. The trees were cored at breast height, and from about 200 felled sample trees, equations for leaf area and for the five-year volume increment were developed. Growth efficiency (volume increment of a species per its fraction of the stand area) exhibited a clear interaction with age: in young mixed stands, spruce as well as larch grew less than the reference from the pure stands, while in the older stands especially spruce grew much better in the mixed stands. When the Clark Evans index was entered into the growth efficiency equations, it could be seen that the spatial distribution of the trees (i) explained more variance than the species proportion and (ii) showed an additional influence of stand density on the complementarity of the species.

The growth and yield of mixed-species stands has become an important topic of research since there are certain advantages of this type of forest as regards functions and services. However, the concepts and methods used to characterize mixed stands need to be understood, as well as harmonized and standardized. In this review we have compiled a set of measures, indices, and methods at stand level to characterize the structure, dynamics, and productivity of mixed stands, and we discuss the pros and cons of their application in growth and yield studies. Parameters for the characterization of mixed stand structure such as stand density, species composition, horizontal (intermingling) and vertical tree distribution pattern, tree size distribution, and age composition are described, detailing the potential as well as the constraints of these parameters for understanding resource capture, use, and efficiency in mixed stands. Furthermore, a set of stand-level parameters was evaluated to characterize the dynamics of mixed stands, e.g. height growth and space partitioning, self- and alien-thinning, and growth partitioning among trees. The deviations and changes in the behaviour of the analysed parameters in comparison with pure stand conditions due to inter-specific interactions are of particular interest. As regards stand productivity, we reviewed site productivity indices, the growth–density relationship in mixed stands as well as methods to compare productivity in mixed versus monospecific stands. Finally, we discuss the main problems associated with the methodology such as up-scaling from tree to stand level as well as the relevance of standardized measures and methods for improving forest growth and yield research in mixed stands. The main challenges are also outlined, especially the need for qualitatively sound data. © 2015, Springer-Verlag Berlin Heidelberg.

We examined the relationship between thinning intensity and volume increment predicted by four commonly used individual-tree growth models in Central Europe (i.e., BWIN, Moses, Prognaus, and Silva). We replicated conditions of older growth and yield experiments by selecting 34 young, dense plots of Norway spruce (Picea abies (L.) Karst.), Scots pine (Pinus sylvestris L.), and European beech (Fagus sylvatica L.). At these plots, we simulated growth, with mortality only, to obtain the maximum basal area. Maximum basal area was then decreased by 5% or 10% steps using thinning from below. Maximum density varied considerably between simulators; it was mostly in a reasonable range but partly exceeded the maximum basal area observed by the Austrian National Forest Inventory or the self-thinning line. In almost all cases, simulated volume increment was highest at maximum basal area and then decreased with decreasing basal area. Critical basal area, at which 95% of maximum volume increment can be achieved, ranged from 0.46 to 0.96. For all simulators, critical basal area was lower for the more shade-tolerant species. It increased with age, except for Norway spruce, when simulated with the BWIN model. Age, where mean annual increment culminated, compared well with yield tables.

Research into mixed-forests has increased substantially in the last decades but the extent to which the new knowledge generated meets practitioners' concerns and is adequately transmitted to them is unknown. Here we provide the current state of knowledge and future research directions with regards to 10 questions about mixed-forest functioning and management identified and selected by a range of European forest managers during an extensive participatory process. The set of 10 questions were the highest ranked questions from an online prioritization exercise involving 168 managers from 22 different European countries. In general, the topics of major concern for forest managers coincided with the ones that are at the heart of most research projects. They covered important issues related to the management of mixed forests and the role of mixtures for the stability of forests faced with environmental changes and the provision of ecosystem services to society. Our analysis showed that the current scientific knowledge about these questions was rather variable and particularly low for those related to the management of mixed forests over time and the associated costs. We also found that whereas most research projects have sought to evaluate whether mixed forests are more stable or provide more goods and services than monocultures, there is still little information on the underlying mechanisms and trade-offs behind these effects. Similarly, we identified a lack of knowledge on the spatio-temporal scales at which the effects of mixtures on the resistance and adaptability to environmental changes are operating. Our analysis may help researchers to identify what knowledge needs to be better transferred and to better design future research initiatives meeting practitioner's concerns. This article is based upon work from COST Action FP1206, EuMIXFOR, supported by COST (European Cooperation in Science and Technology). The authors want to specially thank the large number of forest managers that were involved in the participatory process and kindly responded to the surveys. The first author also thanks the Spanish Ministry of Economy and Competitiveness for funding the project AGL2015-70425-R which partly supported his contribution to this study. MM acknowledges support by grant IUT21-4 of the Estonian Ministry of Education and Research and DS support by project III 43007 (2011–2017) from Ministry of Education, Science and Technological Development of Republic of Serbia.

International audience; An appropriate, common interpretation of stand structure characteristics is a key element to better understand forest ecosystem ecology and dynamics. Standards for characterizing the structure, dynamics and productivity of even-aged pure stands are well developed, but such harmonized concepts and methods for mixed forest stands are lacking. Here we compile a comprehensive set of measures, indices and methods at stand level to characterize and evaluate mixed stands. The chapter is organized according to the main components of the structure of forest stands; hence it includes (1) the most relevant concepts and approaches to describe stand density as a key component of stand structure; (2) stand species composition indicators and the most common species diversity indices used in the science of forest growth and yield; (3) how to describe tree distribution patterns, including horizontal spatial pattern, species intermingling and vertical spatial pattern, as well as species-specific height growth and canopy space partitioning; (4) ways to characterize tree-size distribution and growth partitioning among trees of different sizes; and (5) site productivity indices and methods for the comparison of productivity inmixed vs. monospecific stands. Finally we discuss some of the methodological and application challenges related to the reviewed indices and methods which require further attention.

Currently, about 70% of the forest land in Europe is covered by stands composed of two or more tree species. The similar situation can be found outside Europe too. While forest management of monocultures is well described, multispecies forests still need a better understanding to develop appropriate forest practice. Managing mixed forests can be more complex than managing monocultures because of the need to optimize the provision of multiple benefits according to the societal demands including sustaining biodiversity and ecosystem functioning. In this chapter we are going to present (1) the most important and well-described tree species combinations found in each participating countries taking biogeographical region in Europe into account, (2) the main management objectives of those mixtures, (3) the silvicultural approaches that are available for the particular mixed-species forests and (4) the main challenges experienced in mixed-species forest management. We synthesized information about management of mixed-species forests based on questionnaires received from both European countries and few countries from outside Europe participating in COST Action ‘EuMIXFOR’. The survey revealed that (i) the main management objective in the analysed mixtures is valuable timber production followed by protection of soil and water and protection of forests against disturbances, (ii) the uniform shelterwood is the most widespread regeneration method followed by the clear-cutting and the irregular shelterwood system, (iii) the crown thinning followed by low thinning is the most frequent thinning method, and (iv) the main challenge of management is high game pressure and the lack of management rules covering mixture growth and taking into account both species functional traits and site conditions.

An increasing amount of research is focusing on comparing productivity in monospecific versus mixed stands, although it is difficult to reach a general consensus as mixing effects differ both in sign (over-yielding or under-yielding) and magnitude depending on species composition as well as on site and stand conditions. While long-term experimental plots provide the best option for disentangling the mixing effects, these datasets are not available for all the existing mixtures nor do they cover large gradients of site factors. The objective of this study was to evaluate the effects and uncertainties of tree species mixing on the productivity of Scots pine–European beech stands along the gradient of site conditions in Europe, using models developed from National and Regional Forest Inventory data. We found a positive effect of pine on beech basal area growth, which was slightly greater for the more humid sites. In contrast, beech negatively affected pine basal area growth, although the effects switched to positive in the more humid sites. However, the uncertainty analysis revealed that the effect on pine at mid- and more humid sites was not-significant. Our results agree with studies developed from a European transect of temporal triplets in the same pine–beech mixtures, confirming the suitability of these datasets and methodology for evaluating mixing effects at large scale., This research was partially funded by the COST Action FP1206 through the Short Term Scientific Mission COST-STSM-ECOST-STSM-FP1206-091115-068270. This article is based on work from COST Action FP1206 (EuMIXFOR), supported by COST (European Cooperation in Science and Technology). The authors would like to thank the Spanish Ministry of Economy and Competitiveness for funding the research project AGL2014-51964-C2-2-R, which supported part of this study, and to the project CARE4C (# GA 778322). The authors are also grateful to Bayerische Staatsforsten, BaySF for providing the forest inventory data for Bavaria/Germany and to all those who make the National Forest Inventory possible in the different countries, and to those providing the data used for this study. We also thank the German Science Foundation, DFG, for funding the project PR 292/15-1 “Structure and Dynamics of mixed-species stands of Scots pine and European beech in comparison with mono-specific stands”.

International audience; Key message Competition-density relationships and self-thinning are major principles in forest growth. They are combined, describing self-thinning as a marginal case of the competition-density relationship. Robust estimation techniques allow parameterizing of both from national forest inventory data even for minor species. ContextThe competition-density principle, which can mathematically be described by the competition-density rule, is an important principle in plant ecology. The border line relationship is the self-thinning rule. Despite the importance of both rules for forest management, they have been fit for few species. AimsThe aim of this study is to compare competition-density rule and self-thinning rule in particular with respect to potential density for 15 species from the Austrian National Forest Inventory (ANFI). MethodsThe self-thinning line was estimated using quantile regression. The competition-density rule was fit as four- and as three-parameter model, where the fourth parameter was substituted (a) with a specific slope from the self-thinning line estimated from the ANFI and (b) Reineke’s slope (−1.605). ResultsPotential density was highest for Austrian pine and Norway spruce, followed by silver fir and Scots pine; it was considerably lower for European larch, stone pine and broadleaf species. Species-specific slopes of the self-thinning line ranged between −1.5 and −2.0 and were significantly different from Reineke’s slope for Norway spruce, European larch and European beech. ConclusionsUsing robust estimation techniques, both competition-density rule and self-thinning line can also be fit for minor species, providing an important guide for practical forest management.

There is increasing evidence that species diversity enhances the temporal stability (TS) of community productivity in different ecosystems, although its effect at the population and tree levels seems to be negative or neutral. Asynchrony in species responses to environmental conditions was found to be one of the main drivers of this stabilizing process. However, the effect of species mixing on the stability of productivity, and the relative importance of the associated mechanisms, remain poorly understood in forest communities. We investigated the way mixing species influenced the TS of productivity in Pinus sylvestris L.;Fagus sylvatica L. forests, and attempted to determine the main drivers among overyielding, asynchrony between species annual growth responses to environmental conditions, and temporal shifts in species interactions. We used a network of 93 experimental plots distributed across Europe to compare the TS of basal area growth over a 15-year period (1999–2013) in mixed and monospecific forest stands at different organizational levels, namely the community, population and individual tree levels. Mixed stands showed a higher TS of basal area growth than monospecific stands at the community level, but not at the population or individual tree levels. The TS at the community level was related to asynchrony between species growth in mixtures, but not to overyielding nor to asynchrony between species growth in monospecific stands. Temporal shifts in species interactions were also related to asynchrony and to the mixing effect on the TS. Synthesis. Our findings confirm that species mixing can stabilize productivity at the community level, whereas there is a neutral or negative effect on stability at the population and individual tree levels. The contrasting findings regarding the relationships between the temporal stability and asynchrony in species growth in mixed and monospecific stands suggest that the main driver in the stabilizing process may be the temporal niche complementarity between species rather than differences in species’ intrinsic responses to environmental conditions. © 2016 The Authors. Journal of Ecology © 2016 British Ecological Society

Key message Trees with otherwise equal dimensions have different leaf areas if they are located in different stand types. While leaf area of European larch is affected by mixture proportion, leaf area of Norway spruce is affected by stand density. Context Leaf area is a key parameter for evaluating growth efficiency of trees, and therefore needs to be measured as consistently and accurately as possible. This is even more important when comparing monospecific and mixed stands. Aims The aim of the study is to find combinations of parameters and allometric relationships that can be used to estimate accurately the leaf area of individual trees. Methods Allometries of the measured leaf area of 194 trees in 12 stands were analysed in order to find variables affecting leaf area. Existing functions from the literature were validated. Finally, models were fitted to find the most appropriate method for estimating leaf area of mixed and monospecific stands of Norway spruce and European larch. Results Allometric relationships of leaf area to other measurable characteristics of trees vary in different stand types. Besides individual tree dimensions such as diameter and crown surface area, leaf area of Norway spruce is related to stand density, whereas the leaf area of European larch is dependent on the admixture of Norway spruce in the stand. Conclusion In contrast to models for estimating individual tree leaf area of Norway spruce, models for leaf area of European larch have to consider mixture proportions in order to correctly interpret the growth efficiency of mixed stands.

Key message This data set provides unique empirical data from triplets of Scots pine (Pinus sylvestris L.) and European beech (Fagus sylvatica L.) across Europe. Dendrometric variables are provided for 32 triplets, 96 plots, 7555 trees and 4695 core samples. These data contribute to our understanding of mixed stand dynamics. Dataset access at http://dx.doi.org/10.5061/dryad.8v04m. Associated metadata available at https://metadata-afs.nancy.inra.fr/geonetwork/apps/georchestra/? uuid=b3e098ca-e681-4910-90990e25d3b4cd52&hl=eng.; Key message :This data set provides unique empirical data from triplets of Scots pine (Pinus sylvestris L.) and European beech (Fagus sylvatica L.) across Europe. Dendrometric variables are provided for 32 triplets, 96 plots, 7555 trees and 4695 core samples.These data contribute to our understanding of mixed stand dynamics.Dataset access at http://dx.doi.org/10.5061/dryad.8v04m.Associated metadata available at https://metadata-afs.nancy.inra.fr/geonetwork/apps/georchestra/? uuid=b3e098ca-e681-4910-90990e25d3b4cd52&hl=eng.

Key message Trees with otherwise equal dimensions have different leaf areas if they are located in different stand types. While leaf area of European larch is affected by mixture proportion, leaf area of Norway spruce is affected by stand density. Context Leaf area is a key parameter for evaluating growth efficiency of trees, and therefore needs to be measured as consistently and accurately as possible. This is even more important when comparing monospecific and mixed stands. Aims The aim of the study is to find combinations of parameters and allometric relationships that can be used to estimate accurately the leaf area of individual trees. Methods Allometries of the measured leaf area of 194 trees in 12 stands were analysed in order to find variables affecting leaf area. Existing functions from the literature were validated. Finally, models were fitted to find the most appropriate method for estimating leaf area of mixed and monospecific stands of Norway spruce and European larch. Results Allometric relationships of leaf area to other measurable characteristics of trees vary in different stand types. Besides individual tree dimensions such as diameter and crown surface area, leaf area of Norway spruce is related to stand density, whereas the leaf area of European larch is dependent on the admixture of Norway spruce in the stand. Conclusion In contrast to models for estimating individual tree leaf area of Norway spruce, models for leaf area of European larch have to consider mixture proportions in order to correctly interpret the growth efficiency of mixed stands.

The relation between the growth efficiency of individual trees and stands is critical for scaling up tree-level effects to stand-level phenomena. In this paper, we introduce a new measure of space occupancy – the area exploitation index (AEI), computed as the ratio between the leaf area and the area potentially available (APA) – which has the ability to scale up to the stand area. In this study, efficiency is defined as basal area increment per unit of individual projected tree leaf area (leaf area efficiency; LAE) and as basal area increment per unit of area potentially available for the tree (available area efficiency; AAE). Data were collected from a 28-year-old coast redwood (Sequoia sempervirens [D.Don] Endl.) plantation in California. Thirteen plots with five different treatments and a control were measured two times (2003 and 2007) for diameter, height, sapwood and bark thickness. Leaf area was estimated from the sapwood area of each tree. Using the coordinates of the trees, the area potentially available was calculated, weighted by the individual tree leaf area. A model to estimate leaf area efficiency from the area exploitation index and the leaf area index was developed. Multiplying LAE by AEI results in the efficiency of the area potentially available, which appears to depict a zone of optimal efficiency overAEI.Despitearatherweakcorrelationofthemodel (r = 0.59),anoptimumareaexploitationindex (AEIopt) could be found for coast redwoods depending on LAI, with decreasing LAI leading to increasing AEIopt.

The monitoring of tree diversity and forest structure is a key pre-requisite for understanding and managing forest ecosystems. This paper addresses the question whether and how tree diversity measures can be estimated as extensions of existing forest resource inventories. The sampling simulator Crancod was employed to compare the precision of angle count and fixed radius plot sampling with respect to nine representative diversity indices. The sampling methods were compared (a) in their overall precision in terms of estimating diversity indices and (b) in their ability to provide precise estimations for three different forest types independent of the spatial inventory scale, e.g. inventories at stand or enterprises level or national forest inventories. The results indicated that most of the spatially explicit indices are more precisely estimated by fixed radius plots. Interestingly the superiority of fixed radius plot sampling to angle count sampling increases significantly with increasing diameter differentiation of forests. However, basal area, basal area related diversity indices and Pielou’s segregation index can be estimated by angle count sampling with at least the same precision as from fixed radius plots. This provides options for situations where discarding angle count sampling is not possible because permanent sampling designs are in place or the importance of forestry summary statistics exceeds that of tree diversity by far.

Research highlights ▶ Determination of individual tree leaf area usually is only possible destructively. ▶ Surrogates which can be assessed non-destructively are investigated. ▶ From about 150 trees leaf area is estimated by 3P-branch sampling. ▶ These estimates are best correlated with crown surface area. ▶ Equations to determine individual tree leaf area non-destructively are presented., Since individual tree leaf area is an important measure for productivity as well as for site occupancy, it is of high interest in many studies about forest growth. The exact determination of leaf area is nearly impossible. Thus, a common way to get information about leaf area is to use substitutes. These substitutes are often variables which are collected in a destructive way which is not feasible for long term studies. Therefore, this study aimed at testing the applicability of using substitutes for leaf area which could be collected in a non-destructive way, namely crown surface area and crown projection area. In 8 stands of Norway spruce (Picea abies L. Karst.), divided into three age classes and two thinning treatments, a total of 156 trees were felled in order to test the relationship between leaf area and crown surface area and crown projection area, respectively. Individual tree leaf area of the felled sample trees was estimated by 3P-branch sampling with an accuracy of ±10%. Crown projection area and crown surface area were compared with other, more commonly used, but destructive predictors of leaf area, namely sapwood area at different heights on the bole. Our investigations confirmed findings of several studies that sapwood area is the most precise measure for leaf area because of the high correlation between sapwood area and the leaf area. But behind sapwood area at crown base and sapwood area at three tenth of the tree height the predictive ability of crown surface area was ranked third and even better than that of sapwood area at breast height (R2 = 0.656 compared with 0.600). Within the stands leaf area is proportional to crown surface area. Using the pooled data of all stands a mixed model approach showed that additionally to crown surface area dominant height and diameter at breast height (dbh) improved the leaf area estimates. Thus, taking dominant height and dbh into account, crown surface area can be recommended for estimating the leaf area of individual trees. The resulting model was in line with many other findings on the leaf area and leaf mass relationships with crown size. From the additional influence of dominant height and dbh in the leaf area model we conclude that the used crown model could be improved by estimating the position of the maximum crown width and the crown width at the base of the crown depending on these two variables.

In this study, we present estimated ranges in carbon (C) sequestration per kg nitrogen (N) addition in above-ground biomass and in soil organic matter for forests and heathlands, based on: (i) empirical relations between spatial patterns of carbon uptake and influencing environmental factors including nitrogen deposition (forests only), (ii) 15N field experiments, (iii) long-term low-dose N fertilizer experiments and (iv) results from ecosystem models. The results of the various studies are in close agreement and show that above-ground accumulation of carbon in forests is generally within the range 15–40 kg C/kg N. For heathlands, a range of 5–15 kg C/kg N has been observed based on low-dose N fertilizer experiments. The uncertainty in C sequestration per kg N addition in soils is larger than for above-ground biomass and varies on average between 5 and 35 kg C/kg N for both forests and heathlands. All together these data indicate a total carbon sequestration range of 5–75 kg C/kg N deposition for forest and heathlands, with a most common range of 20–40 kg C/kg N. Results cannot be extrapolated to systems with very high N inputs, nor to other ecosystems, such as peatlands, where the impact of N is much more variable, and may range from C sequestration to C losses.

The spruce-fir-beech dominated forest stands in Litschau in the Austrian part of the Bohemian Massif were converted by former forest management practices into pure Norway spruce stands and are now discussed to be reconverted into the potential natural vegetation type. The targeted potential natural vegetation type is usually defined by experts in vegetation sciences. Because meanwhile individual-tree growth simulators are a well acknowledged tool for predicting fu - ture forest stand development, in this study we investigate if PrognAus can also be used to predict the redevelopment of managed forest ecosystems into natural forest ecosystems regarding species composition. The development of 23 stands in Litschau has been simulated over 1,000 years under the "no-management" option. Generally, the simulated species distri - bution agrees quite well with the expectations of the potential natural vegetation type. However, the predicted amounts of silver fir and maple species are lower than expected, which probably is due to browsing and management effects represented in the parameterization data for PrognAus.

The effects of forest fertilization and Sirococcus shoot blight on growth of mature Norway spruce (Picea abies (L.) Karst.) were studied in a field experiment. The single tree fertilization experiment was established with 144 sample trees in the year 2000. These trees were selected among the dominant and co-dominant trees of the stand in a way that half of the trees exhibited symptoms of Sirococcus shoot blight and the other half did not. One-third of the sample trees were fertilized with dolomitic lime, one-third with kieserite and gypsum and one-third were left unfertilized as control. The treatments were randomly assigned to the sample trees. As the experimental design became unbalanced due to tree mortality caused by bark beetle infestation final analyses were performed with the volume growth data of 125 sample trees only. An analysis of covariance was used to evaluate the effect of fertilization and Sirococcus shoot blight on volume growth. The average volume increment of the period 1977–1980 was used as a covariate attribute, assuming that during this period growth was not yet affected by Sirococcus shoot blight. Indeed an effect of Sirococcus shoot blight on growth turned out to start after 1980 and the analysis revealed that over the whole period 1981–2006 trees with shoot blight symptoms had a significantly lower increment. The increment reduction of the nonfertilized trees by Sirococcus was 7.46 ± 2.90 % in 1981 and was continuously increasing with time to 37 ± 3.78 % by the year 2000. A significant positive effect of fertilization was only found for the kieserite + gypsum variant from 2002 to 2006, with the highest surplus increment in 2004 with 31.6 ± 15.2 %, calculated as average over the diseased and healthy group. However, a mitigation of the Sirococcus-caused increment loss via fertilization with kieserite and gypsum was statistically significant only for the year 2003. A moderate relationship between basal area increment and disease severity was found, indicating decreasing basal area increment with increasing disease severity.

Summary Sampling procedures within stands for species and diversity indices have been widely discussed. However, little attention has been paid to the assessment of such indices within the framework of forest inventories on the management district level. This study deals with such an inventory comprising 245 angle counts in a 750-ha forest management district at the northern fringe of the Austrian Alps. To calculate spatially explicit indices, the nearest neighbours of the angle count in-trees have to be assessed. The distributions of the indices, their correlations and their ability to discriminate between different stand classes are discussed. It is concluded that these indices are meaningful, because they describe the species composition and the structure of the forest district in the expected way and differ signifi cantly and meaningfully among stand classes which have been classifi ed for silvicultural purposes.

To support forest management decisions on converting stands from even-aged to uneven-aged management, tree models are needed that can simulate both options. Therefore, an individual tree model for Pinus halepensis Mill. is compared with the respective yield table. The individual tree model is built from data of two Spanish forest inventories in this province and evaluated with published yield tables, which have been built from permanent observational plots. The individual tree model consists of a basal area increment model and a height increment model, both based on two measurements of about 4,000 trees from single species stands of Aleppo pine. The R² values of 0.362 and 0.107 for the basal area increment model and the height increment model, respectively, are within the range of other published models of this type. Comparing the model with the yield tables for different site indices, we find that our model matches the yield table well. Only in higher ages where the database for the yield table was poor, our model indicates higher basal area growth rates than the yield table.

Scots pine (Pinus sylvestris L.) and European beech (Fagus sylvatica L.) dominate many of the European forest stands. Also, mixtures of European beech and Scots pine more or less occur over all European countries, but have been scarcely investigated. The area occupied by each species is of high relevance, especially for growth evaluation and comparison of different species in mixed and monospecific stands. Thus, we studied different methods to describe species proportions and their definition as proportion by area. 25 triplets consisting of mixed and monospecific stands were established across Europe ranging from Lithuania to Spain in northern to southern direction and from Bulgaria to Belgium in eastern to western direction. On stand level, the conclusive method for estimating the species proportion as a fraction of the stand area relates the observed density (tree number or basal area) to its potential. This stand-level estimation makes use of the potential from comparable neighboring monospecific stands or from maximum density lines derived from other data, e.g. forest inventories or permanent observations plots. At tree level, the fraction of the stand area occupied by a species can be derived from the proportions of their crown projection area or of their leaf area. The estimates of the potentials obtained from neighboring monospecific stands, especially in older stands, were poorer than those from the maximum density line depending on the Martonne aridity index. Therefore, the stand-level method in combination with the Martonne aridity index for potential densities can be highly recommended. The species' proportions estimated with this method are best approximated by the proportions of the species' leaf areas. In forest practice, the most commonly applied method is an ocular estimation of the proportions by crown projection area. Even though the proportions of pine were calculated here by measuring crown projection areas in the field, we found this method to underestimate the proportion by 25% compared to the stand-level approach. The networking in this study has been supported by COST Action FP1206 EUMIXFOR. All contributors thank their national funding institutions to establish, measure, and analyze data from the triplets. The first author thanks the Austrian Science Fund, which supported his work under project number P24433-B16. We also want to thank the two anonymous reviewers for their constructive criticism.

The mixing of tree species with complementary ecological traits may modify forest functioning regarding productivity, stability, or resilience against disturbances. This may be achieved by a higher heterogeneity in stand structure which is often addressed but rarely quantified. Here, we use 32 triplets of mature and fully stocked monocultures and mixed stands of Scots pine (Pinus sylvestris L.) and European beech (Fagus sylvatica L.) located along a productivity and water availability gradient through Europe to examine how mixing modifies the stand structure in terms of stand density, horizontal tree distribution pattern, vertical stand structure, size distribution pattern, and variation in tree morphology. We further analyze how site conditions modify these aspects of stand structure. For this typical mixture of a light demanding and shade tolerant species we show that (i) mixing significantly increases many aspects of structural heterogeneity compared with monocultures, (ii) mixing effects such as an increase of stand density and diversification of vertical structure and tree morphology are caused by species identity (additive effects) but also by species interactions (multiplicative effects), and (iii) superior heterogeneity of mixed stands over monocultures can increase from dry to moist sites. We discuss the implications for analyzing the productivity, for modelling and for the management of mixed species stands. The networking in this study has been supported by COST Action FP1206 EuMIXFOR. All contributors thank their national funding institutions and the woodland owners for agreeing to establish, measure, and analyze data from the triplets. The first author also thanks the Bayerischen Staatsforsten (BaySF) for supporting the establishment of the plots, the Bavarian State Ministry for Nutrition, Agriculture, and Forestry for permanent support of the project W 07 “Long-term experimental plots for forest growth and yield research” (# 7831-22209-2013) and the German Science Foundation for providing the funds for the projects PR 292/12-1 “Tree and stand-level growth reactions on drought in mixed versus pure forests of Norway spruce and European beech”. The second author thanks the COST Action FP1206 EuMIXFOR for funding the STSM FP1206-160714-045064, and the Spanish project AGL2014-51964-C2-2-R.

In this manuscript the prediction of the primary roe deer habitat variables canopy cover, stand structural classes, proportion of evergreen trees and understory vegetation cover (classified according to palatability for roe deer and vegetation height into barren ground, graminoids, Vaccinium spp., herbs, conifers, Rubus spp. ferns deciduous and shrubs) with the growth model PROGNAUS was evaluated for a 10-year period. Canopy cover was calculated as a function of crown radius with a correction for crown overlap and also estimated using multiple linear regression. Using these two methods observed canopy cover was underestimated by 14% and 2%, respectively. Coefficients of correlation between observed and predicted canopy cover were 0.47 and 0.51. Stand structural classes were predicted within 10% of the actual proportion and 68% of all sample plots were assigned to the correct structural class. The proportion of canopy cover of evergreen species was predicted within 1% and was highly correlated ( r = 0.6) to the basal area proportion of the evergreen trees. All understory vegetation classes were predicted within 5% of the actual proportion. 4 were correctly classified into five cover classes (0%, 1–25%, 25–50%, 50–75% and 75–100%) and the proportion of each of these covers classes for each vegetation type was well predicted. A visual comparison showed that observed and predicted spatial patterns were similar. Predictions of both forest growth and understory vegetation models are reasonably accurate for roe deer habitat predictions.

In 25 permanent sample plots in Cupressus lusitanica plantations of the Munesa Shashemene Wood Industry Enterprise, in the Oromia Federal Regional State, Ethiopia, the dominant height growth was observed and site index functions fitted. The plots had been continuously observed from ages 7 (10) to 21 (18) in the Gambo–Shashemene and the Munesa growth districts, respectively. Measurements in each plot were taken 5–8 times, altogether a total of 163 observations were available. Parameterising the general Chapman–Richards function, showed that (i) no point of inflection within the range of the data was found, (ii) the growth rate parameter, k , of the model did not depend on site index, and (iii) the growth rate parameter, k , and thus the shape of the height growth curves differed significantly between the Gambo–Shashemene and Munesa growth districts. Previous site index curves for the same region fitted well for the Gambo–Shashemene district but not so for Munesa. Therefore, it is concluded that when developing and using site index functions, growth districts as a possible reason for different shapes have to be taken into account.

The shape of the diameter distribution is one of the important elements characterising forest stand structure. In this work we present the application of the method of moments for the estimation of the parameters of a 2-parameter Weibull function. Due to its properties, this function is often used for the description of the diameter distribution in forestry. The work analyses the properties of the Weibull function and its application to a data set representing natural (virgin forest Babia hora) and managed forests (Litschau and Forest School Enterprise of Technical University Zvolen). The parameters of the Weibull function are simply and reliably estimated from the basic stand variables, namely the mean diameter and the coefficient of variation of the diameters. The method is general and does not require specific parameterisation, e.g. for the individual tree species. The work also presents a new algorithm for the estimation of parameters in cases, where tree diameters are measured from a certain minimum recording limit. Based on this study, we suggest using the Weibull function in forest stands only for uni-modal diameter distribution with a mean diameter above 7 cm.

An estimate of net carbon (C) pool changes and long-term C sequestration in trees and soils was made at more than 100 intensively monitored forest plots (level II plots) and scaled up to Europe based on data for more than 6000 forested plots in a systematic 16 km x 16 km grid (level I plots). C pool changes in trees at the level II plots were based on repeated forest growth surveys At the level I plots, an estimate of the mean annual C pool changes was derived from stand age and available site quality characteristics. C sequestration, being equal to the long-term C pool changes accounting for CO2 emissions because of harvest and forest fires, was assumed 33% of the overall C pool changes by growth. C sequestration in the soil were based on calculated nitrogen (N) retention (N deposition minus net N uptake minus N leaching) rates in soils, multiplied by the C/N ratio of the forest soils, using measured data only (level II plots) or a combination of measurements and model calculations (level I plots). Net C sequestration by forests in Europe (both trees and soil) was estimated at 0.117 Gton yr(-1), with the C sequestration in stem wood being approximately four times as high (0.094 Gton yr(-1)) as the C sequestration in the soil (0.023 Gton yr(-1)). The European average impact of an additional N input on the net C sequestration was estimated at approximately 25 kg C kg(-1) N for both tree wood and soil. The contribution of an average additional N deposition on European forests of 2.8 kg ha(-1) yr(-1) in the period 1960-2000 was estimated at 0.0118 Gton yr(-1), being equal to 10% of the net C sequestration in both trees and soil in that period (0.117 Gton yr(-1)). The C sequestration in trees increased from Northern to Central Europe, whereas the C sequestration in soil was high in Central Europe and low in Northern and Southern Europe. The result of this study implies that the impact of forest management on tree growth is most important in explaining the C pool changes in European forests.

In plantation forestry, as well as in forests managed according to the single tree selection system (Plenter forest), there are well established methods available to control sustainable management in terms of timber resources. If a shift from even-aged to uneven-aged management is intended, there is usually a lack of a clear, numerically defined aim. Then individual tree growth models help to (i) check if certain aims can be achieved at all and (ii) to define these aims more clearly and numerically, e.g. in terms of structural indices. Regular inventories, based on permanent sample plots, help to determine deviations from these aims. As a feedback of these results, management may be changed or aims may be adjusted. Two forest management districts in Austria were investigated. In one of them, continuous cover forestry was intended where, as soon as regeneration has reached a certain height, the upper layer was removed. In the other case, individual tree harvesting has been performed for 30 years, and a single tree selection system is intended. In both cases, permanent inventories based on angle-count sampling have been installed and re-measured at least once after 10 years. Using the individual tree simulator PrognAus it is shown, that the intended management strategy for the single tree selection system leads to an equilibrium of harvests and growth after about 80 years, accompanied by the intended high structural diversity of the stands, while species diversity and between-stand variation cannot be enhanced by much. In the natural regeneration system without single tree selection, species diversity, structural diversity and between-stand variation is enhanced, but during the 100 years simulated no equilibrium between harvests can be reached. Periods where there is a lack of large timber to be harvested occur regularly. From these examples it is concluded that inventories with permanent sample plots, together with individual tree growth simulators are appropriate tools to evaluate forest management changes.

Crown width is an important feature in describing stand density and individual tree competition. Two different approaches to using crown width in competition measures are reported in the literature: (i) crown width of open-grown trees, assumed to describe the zone of influence, and thus the potentially available stand area attributable to an individual tree and (ii) crown width of stand-grown trees, describing individual tree competition in distance-dependent individual tree growth models. The crown width measurements of the second Spanish National Inventory are used to derive (i) open-grown tree crown width equations and (ii) general tree crown width equations. The results show that the expectation that open-grown tree crown width may be derived as a special case of a general crown width equation is not met. Therefore, the authors sought a method of obtaining “compatible” tree crown width equations (modelled to a specific region and for individual tree species) that cover the range from open-grown to stand-grown trees with acceptable accuracy. As a practical example, the authors’ compatible tree crown width equations with their species-dependent coefficients are then compared for 11 major tree species in Spain in order to see if these equations give the open-grown tree crown width when open-grown tree height diameter ratio is inserted as independent variable. For conifers and for Eucalyptus globulus, the authors’ procedure does indeed provide equations valid for open-grown trees to stand-grown trees with an acceptable loss of efficiency over the range. For the other broad-leaved tree species, no recommendable compatible crown width equation could be derived.

Ten years work of the European Forest Institute on forest resources and information research is reviewed. Two special lines of research are found: research in retrieving and organising data in data bases and information systems, combining and linking them mutually and with other data bases in order to finally end up as a first stop shop for forest and forestry related information. A special diamond in this line is the description of the methods, how to derive a map of forests in Europe combining such different sources like satellite data, forest statistics and national inventories. The second line is a large scale scenario model, with many sub-modules, extensions and applications, covering the whole range of questions from the effects of an increasing proportion of nature oriented forestry in Europe to their effect on carbon trading and different objectives.

Der Beitrag dokumentiert die praktische Relevanz von Wachstumssimulatoren, gibt einen Uberblick uber aktuelle Modellansatze, definiert Standards zur Beschreibung und Evaluierung von Wachstumsmodellen und -simulatoren und weist auf Forschungsbedarf in diesem Bereich hin. Die Empfehlungen sollen Anwendern von Wachstumsmodellen Vertrauen beim Ubergang zu zeitgemasen Prognosesystemen vermitteln und die Akzeptanz neuer Informationstechnologien erhohen. Indem dieses Papier Modellentwicklern Leitlinien fur die Modellbeschreibung, Modellevaluierung und Softwareentwicklung gibt, kann es zu einer effizienten Kooperation aller Beteiligten beitragen.

Summary For determining the amount and structure of the allowable cut in forests in transition (from evenaged to uneven-aged management) the assumptions of the usual formulas for calculating allowable cut no longer apply. In this situation, growth models applied to permanent sample inventories become an important planning tool. This is demonstrated at a forest management district in the Austrian part of the Bohemian Massif, where clearcutting was abandoned 40 years ago. The existing inventory is based on angle counts. The site mapping, performed there in 1963, is translated into the site factors used in the growth simulator PROGNAUS, using a sample of site assessments in the mapped site classes. The simulation results, for four different harvesting regimes over 80 years, are evaluated to find the most appropriate harvesting level.

PROGNAUS is an individual tree growth model, containing a major sub-model which depicts basal area growth as a function of tree size, competition and a set of diagnostic site variables. The coefficients of this model have previously been estimated using the data from the Austrian National Forest (ANF) inventory. The examination of 60 new sample plots in two Austrian growth districts showed that the increment of Norway spruce (Picea abies L. Karst.) in pure spruce stands was overestimated by this model while it was underestimated in mixed species stands with European beech (Fagus sylvatica L.). In order to adapt PROGNAUS to account for this effect, the data of the 60 plots were used to modify PROGNAUS by adding quantitative soil characteristics and the percentage of Norway spruce as variables. The markedly improved model accounts for the effect that in a given stand, below a certain competition level, Norway spruce grows better in the pure stand than in an otherwise comparable mixed species stand. These small spruce trees in mixed stands have a shallow rooting system and therefore suffer from water stress, which is caused by the competing European beech with its higher water consumption, and deeper rooting system. Adding the Norway spruce proportion as an independent variable into the original model and re-parameterising it with the data of the ANF inventory, reveals that this effect can be generalised to some extent, but differs in magnitude depending on the geological substrate.

Highlights ► Absorbed light was only marginally superior to predict volume increment than leaf area. ► Larger trees were consistently more efficient than smaller trees. ► Thinning increased the efficiency of an average tree., Silviculture focuses on establishing forest stand conditions that improve the stand increment. Knowledge about the efficiency of an individual tree is essential to be able to establish stand structures that increase tree resource use efficiency and stand level production. Efficiency is often expressed as stem growth per unit leaf area (leaf area efficiency), or per unit of light absorbed (light use efficiency). We tested the hypotheses that: (1) volume increment relates more closely with crown light absorption than leaf area, since one unit of leaf area can receive different amounts of light due to competition with neighboring trees and self-shading, (2) dominant trees use light more efficiently than suppressed trees and (3) thinning increases the efficiency of light use by residual trees, partially accounting for commonly observed increases in post-thinning growth. We investigated eight even-aged Norway spruce (Picea abies (L.) Karst.) stands at Bärnkopf, Austria, spanning three age classes (mature, immature and pole-stage) and two thinning regimes (thinned and unthinned). Individual leaf area was calculated with allometric equations and absorbed photosynthetically active radiation was estimated for each tree using the three-dimensional crown model Maestra. Absorbed photosynthetically active radiation was only a slightly better predictor of volume increment than leaf area. Light use efficiency increased with increasing tree size in all stands, supporting the second hypothesis. At a given tree size, trees from the unthinned plots were more efficient, however, due to generally larger tree sizes in the thinned stands, an average tree from the thinned treatment was superior (not congruent in all plots, thus only partly supporting the third hypothesis).

Aim of study: The aim of this paper is to compare differences in growth per hectare of species in pure and mixed stands as they result from different definitions of species proportions.Area of Study: We used the data of the Spanish National Forest Inventory for Scots pine and beech mixtures in the province of Navarra and for Scots pine and Pyrenean oak mixtures in the Central mountain range and the North Iberic mountain range.Material and Methods: Growth models were parameterized with the species growth related to its proportion as dependent variable, and dominant height, quadratic mean diameter density, and species proportion as independent variables. As proportions we use once proportions by basal area or by stand density index and once these proportions considering the species specific maximum densities.Main Results: In the pine – beech mixtures, where the maximum densities do not differ very much between species, the mixing effects are very similar, independent of species proportion definitions. In the pine – oak mixture, where the maximum densities in terms of basal area are very different, the equations using the proportions calculated without reference to the maximum densities, result in a distinct overestimation of the mixing effects on growth.Research highlights: When comparing growth per hectare of a species in a mixed stand with that of a pure stand, the species proportion must be described as a proportion by area considering the maximum density for the given species, wrong mixing effects could be introduced by inappropriate species proportion definitions.Keywords: Mixing effects; proportion by area; Stand Density Index; overyielding; Pinus sylvestris L.; Fagus sylvatica L.; Quercus pyrenaica Willd.

The forests of the Schlagl-Monastery in the north-eastern corner of Austria are managed according to Reininger’s [Osterreichischer Agraverlag, Vienna, Austria, 163] idea of target diameter harvesting. Twenty years of observations in a 3.5 ha Norway spruce stand in Schlagl and the first re-observation of a permanent inventory in the nearly 500 ha forest management district (FMD) Sonnenwald are investigated and reveal that indeed small trees make efficient use of the area they gain from the removal of their larger neighbours and that the growth per hectare is not decreased by target diameter harvesting. It seems that over a rather long period in the investigated stand and in all stands above 80 years the number of larger trees removed will be replaced by the growth of smaller ones. Comparing the stem number distribution with Schutz’s [Schweiz. Z. Forstwes. 126 (9) Romandes, 178] equilibrium model shows that the steady state is not yet achieved but is fast approached by target diameter harvesting. Probably the equilibrium stocking volume is somewhat below the current average stocking of 450 m3 ha−1.

Crown-condition assessment, hypothesized to estimate needle losses following damage from several sources, one of which might be air pollution, suffers from the subjective notion of a standard "healthy" tree. On the other hand, the foliage biomass - sapwood area ratios are reported to depend on a number of factors, e.g., site quality, stand density, crown class, and tree ring width conductivity. The authors hypothesize that early sapwood area might help to even better estimate needle biomass of Norway spruce (Picea abies (L.) Karst.) and to help standardize crown-condition assessment. Thirty-six Norway spruce trees at two Austrian sites, from three age-classes, three crown classes, and two crown-condition classes were felled. Needle mass, cross-sectional area, sapwood area, and early sapwood area (i.e., sapwood area excluding latewood) were measured. The results of this study indicate that indeed early sapwood area is a good estimator of foliage, independent of site, age, crown class, and crown condition. The ratio between early sapwood area and cross-sectional area could be a good estimator for crown condition and thus help to standardize crown-condition assessments by different surveyors.

Between 1981 and 1985 the Austrian National Forest Inventory (ANF) established a set of 5500 clusters, each with four permanent plots covering all Austrian forests. After the first remeasurement between 1986 and 1990 models were developed to predict tree growth, mortality and the behavior of forest owners in harvesting timber. A set of logistic equations describes the probability for a given stand to exhibit intermediate harvesting, single-tree selection or final clear cutting. Independent variables were either continuous or categorical, describing: (i) regional units such as provinces, (ii) types of ownership (groups of ownership sizes), (iii) site factors (elevation and slope), and (iv) stand characteristics (species mixture, density, mean diameter). Timber removals on the plots are recorded by five relative diameter at breast height (dbh)-classes. Removal percentages differ by elevation, harvesting categories, and tree species groups. Timber harvest forecasts and their spatial arrangement over Austria in the following four 5-year periods were made available to the public using computer software. In 1997 data of the second inventory remeasurements were available and thus the forecasts for this period could be evaluated. When forecast units are large enough, deviations from the model are either small or can be explained by a different timber market scenario and/or a general socio-economical scenario.

Crown-condition assessment, hypothesized to estimate needle losses following damage from several sources, one of which might be air pollution, suffers from the subjective notion of a standard "healthy" tree. On the other hand, the foliage biomass - sapwood area ratios are reported to depend on a number of factors, e.g., site quality, stand density, crown class, and tree ring width conductivity. The authors hypothesize that early sapwood area might help to even better estimate needle biomass of Norway spruce (Picea abies (L.) Karst.) and to help standardize crown-condition assessment. Thirty-six Norway spruce trees at two Austrian sites, from three age-classes, three crown classes, and two crown-condition classes were felled. Needle mass, cross-sectional area, sapwood area, and early sapwood area (i.e., sapwood area excluding latewood) were measured. The results of this study indicate that indeed early sapwood area is a good estimator of foliage, independent of site, age, crown class, and crown condition. ...