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Increasing atmospheric nitrogen deposition and climate change are considered the main factors accelerating the long-term growth of forests. Quantification of changes in growth rate can be extremely useful in monitoring and assessing the impact of climate change on site productivity. In this study, we carried out a country-wide analysis of long-term (100 years) dynamics and changes in the height growth rate and site index (SI) of Scots pine in Poland. To ensure representativeness we used a large sample of stem analysis trees collected on 312 plots selected using stratified sampling. To control the effect of site fertility and thus avoid the over-representation of older stands on infertile sites, we measured a range of soil properties that, together with environmental indicators characterising climatic conditions and topography, were used in growth trend modelling as explanatory variables. We found that trees planted in successive years have grown faster. The SI calculated for individual trees is linearly dependent on the year of germination and with increasing age of germination, the SI at the base age of 100 years has increased by 8.4 cm per year. Despite the differences in the growth dynamics of pines planted in different germination years, tree growth follows the same growth pattern. The observed continuous changes in site productivity correspond to an increase in the SI by over 29% between 1900 and 2000. A consequence of continuous changes in site conditions and height growth rate is ambiguity in derived SI values. Under changing site conditions, SI values calculated based on stand height and age depend not only on site productivity but also the year of germination. As a consequence, stands growing under identical site conditions show different SIs, which should be acknowledged if the SI is to be used in forest management. Therefore, determining the SI of newly established stands based on the SI of older generations requires the application of an amendment to account for stand age. Continuously improving our understanding of potential climate change impacts on forest ecosystems is essential and provide information to support forest managers seeking to develop effective adaptation measures and determine sustainable forestry production. As such, our results provide valuable support when making long-term decisions and developing effective adaptation strategies in forest management.

Tree species mixing has been widely promoted as a promising silvicultural tool for reducing drought stress. However, so far only a limited number of species combinations have been studied in detail, revealing inconsistent results. In this study, we analysed the effect of mixing Scots pine and oak (pedunculate oak and sessile oak) trees on their drought response along a comprehensive ecological gradient across Europe. The objective was to improve our knowledge of general drought response patterns of two fundamental European tree species in mixed versus monospecific stands. We focused on three null hypotheses: () tree drought response does not differ between Scots pine and oak, () tree drought response of Scots pine and oak is not affected by stand composition (mixture versus monoculture) and () tree drought response of Scots pine and oak in mixtures and monocultures is not modified by tree size or site conditions. To test the hypotheses, we analysed increment cores of Scots pine and oak, sampled in mixed and monospecific stands, covering a wide range of site conditions. We investigated resistance (the ability to maintain growth levels during drought), recovery (the ability to restore a level of growth after drought) and resilience (the capacity to recover to pre-drought growth levels), involving site-specific drought events that occurred between 1976 and 2015. In monocultures, oak showed a higher resistance and resilience than Scots pine, while recovery was lower. Scots pine in mixed stands exhibited a higher resistance, but also a lower recovery compared with Scots pine in monocultures. Mixing increased the resistance and resilience of oak. Ecological factors such as tree size, site water supply and site fertility were found to have significant effects on the drought response. In the case of Scots pine, resistance was increased by tree size, while recovery was lowered. Resistance of oak increased with site water supply. The observed mixing effect on the tree drought response of Scots pine and oak was in some cases modified by the site conditions studied. Positive mixing effects in terms of resistance and resilience of oak increased with site water supply, while the opposite was found regarding recovery. In contrast, site fertility lessened the positive mixing effect on the resistance of Scots pine. We hypothesise that the observed positive mixing effects under drought mainly result from water- and/or light-related species interactions that improve resource availability and uptake according to temporal and spatial variations in environmental conditions. This work was supported by the European Union as part of the ERA-Net SUMFOREST project REFORM – Mixed species forest management. Lowering risk, increasing resilience (2816ERA02S, PCIN2017-026) and the Horizon 2020 research and innovation programme under the Marie Skłodowska-Curie grant agreement No 778322. All contributors thank their national funding institutions for supporting the establishment, mensuration and analysis of the studied triplets. The first author wants to thank the German Federal Ministry of Food and Agriculture (BMEL) for financial support through the Federal Office for Agriculture and Food (BLE) (grant number 2816ERA02S), as well as the Bayerische Staatsforsten (BaySF) and Landesbetrieb Forst Brandenburg for providing suitable research sites. Research on the Lithuanian triplets (LT 1, LT 2) was made possible by the national funding institution Research Council of Lithuania (LMTLT) (agreement number S-SUMFOREST-17-1). The French site FR 1 belongs to the OPTMix experimental site (https://optmix.irstea.fr), which is supported annually by Ecofor, Allenvi, and the French national research infrastructure ANAEE-F. A special thank is due to Peter Biber for supporting the statistical analysis.

International audience; Climate change has swept away the former general principles of long-term stability in forest productivity. New types of models are needed to predict growth and to plan forest management under future climate conditions. These models must remain robust for silvicultural practices and variations in climate. In this study, we present a new type of model development to achieve these goals. Our study focused on pure and mixed stands of Quercus petraea and Pinus sylvestris in central France. We used National Forest Inventory (NFI) data: respectively, 525 and 548 pure plots of Quercus petraea and Pinus sylvestris, and 68 plots of mixed species. We also used 108 tree cores from an experimental site of the same species. The cores cover the period from 1971 to 2013, making a total of 4572 individual annual increments. We coupled two types of models. One was developed with NFI data (transversal data). This model takes into account mean diameter and stand density effects on stand growth. It includes a set of biophysical factors accounting for stand fertility. The other one was developed with the data from tree cores (longitudinal data), and provides a climate modulation thanks to the correlation between ring width and yearly climate. The model with tree core data reveals the influence of December to July rainfalls on yearly variability in stand growth for Quercus petraea and of May to August rainfalls for Pinus sylvestris. We obtained a coupled model that allowed us to project growth up to 2100 for all the different IPCC scenarios but one; the model was outside its area of validity beyond 2060 for the RCP 8.5 scenario.

Key message We compared two methods for detailed individual tree measurements: single image photogrammetry (SIP), a simplified, low-cost method, and the state-of-the-art terrestrial laser scanning (TLS). Our results provide evidence that SIP can be successfully applied to obtain accurate tree architectural traits in mature forests. Context Tree crown variables are necessary in forest modelling; however, they are time consuming to measure directly, and they are measured in many different ways. We compare two methods to obtain crown variables: laser-based and image-based. TLS is an advanced technology for three-dimensional data acquisition; SIP is a simplified, low-cost method. Aims To elucidate differences between the methods, and validate SIP accuracy and usefulness for forest research, we investigated if (1) SIP and TLS measurements are in agreement in terms of the most widely used tree characteristics; (2) differences between the SIP traits and their TLS counterparts are constant throughout tree density and species composition; (3) tree architectural traits obtained with SIP explain differences in laser-based crown projection area (CPA), under different forest densities and stand compositions; and (4) CPA modelled with SIP variables is more accurate than CPA obtained with stem diameter-based allometric models. We also examined the correspondence between local tree densities extracted from images and from field measurements. Methods We compared TLS and SIP in a temperate pure sessile oak and mixed with Scots pine stands, in the Orléans Forest, France. Standard major axis regression was used to establish relations between laser-based and image-based tree height and diameter at breast height. Four SIP-derived traits were compared between the levels of stand density and species composition with a t test, in terms of deviations and biases to their TLS counterparts. We created a set of linear and linear mixed models (LMMs) of CPATLS, with SIP variables. Both laser-based and image-based stem diameters were used to estimate CPA with the published allometric equations; the results were then compared with the best predictive LMM, in terms of similarity with CPATLS measurement. Local tree density extracted from images was compared with field measurements in terms of basic statistics and correlation. Results Tree height and diameter at breast height were reliably represented by SIP (Pearson correlation coefficients r = 0.92 and 0.97, respectively). SIP measurements were affected by the stand composition factor; tree height attained higher mean absolute deviation (1.09 m) in mixed stands, compared to TLS, than in pure stands (0.66 m); crown width was more negatively biased in mixed stands (− 0.79 m), than in pure stands (− 0.05 m); and diameter at breast height and crown asymmetry were found unaffected. Crown width and mean branch angle were key SIP explanatory variables to predict CPATLS. The model was approximately 2-fold more accurate than the CPA allometric estimations with both laser-based and image-based stem diameters. SIP-derived local tree density was similar to the field-measured density in terms of mean and standard deviation (9.6 (3.5) and 9.4 (3.6) trees per plot, respectively); the correlation between both density measures was significantly positive (r = 0.76). Conclusion SIP-derived variables, such as crown width, mean branch angle, branch thickness, and crown asymmetry, were useful to explain tree architectural differences under different densities and stand compositions and may be implemented in many forest research applications. SIP may also provide a coarse measure of local competition, in terms of number of neighbouring trees. Our study provides the first test in mature forest stands, for SIP compared with TLS.

International audience; Forecasted climate change impacts on temperate forest ecosystems include increased summer drought. Forest managers can increase the resistance of forest stands against summer drought by reducing stand density and favoring tree species mixtures. These strategies have been studied separately, but their combined effect on increasing forest stand resistance to summer drought is unknown.The main objective of our study was to quantify tree species interaction effects on radial growth during a water stress period and to determine whether these effects changed with different levels of competition reflected by stand density. The study was based in the Orleans state forest (Central France) at a long-term triplet experimental site (OPTMix) with pure and mixed stands of mature Quercus petraea and Pinus sylvestris. The experimental design comprised three repetitions of two densities (low and medium) in each composition (pure oak, mixed stands, pure pine). We monitored tree radial growth with 216 manual dendrometers placed throughout 18 plots, on small, medium and large trees. We analyzed three consecutive years with contrasted water stress: no water stress, a summer stress period, and a late summer stress period. We found that mixture did not improve tree growth of the either species during the summer water stress period. On the other hand, there was a mixture effect during the late summer water stress period but only in medium-density stands inversely for the two species studied. More growth occurred for oaks in mixtures while, inversely, more growth occurred for pines in monocultures. A density effect occurred only for oaks, which grew more in lower-density stands than in medium-density stands. Finally, tree size did not influence seasonal resistance to drought.

International audience; For forest ecosystems, studies dealing with diversity-productivity relationships are often based on diameter increment observations. Studying how height growth is affected by species interactions can provide new insights on this issue. We studied the mixture effect on dominant height growth in order to answer two questions. Do species interactions in mixed forest modify the dominant height growth of species? Does the diversity effect on diameter found in previous studies correspond to actual overyielding, or rather to an effect on allocation of growth between diameter and height? We used the French National Forest Inventory (NFI) data to model the mixture effect on dominant height. We included biophysical factors in the models to compare the dominant height of mixed and monospecific stands, all other parameters being equal. We studied five target species – Quercus petraea (Matt.) Liebl., Fagus sylvatica L., Picea abies (L.) Karst., Abies alba Mill., and Pinus sylvestris L. – in association with sixteen other species. Mixture effects on dominant height were weak, though often significant. They were either positive or negative according to species association. We showed that mixture effect on dominant height corresponds to a leveling process between species: the taller one limits its growth while the smaller one’s growth increases. Furthermore, most of the time, mixture effects on dominant height are in the same direction as those found on diameter, though with a lower magnitude. Our results confirm that tree diversity results in overyielding rather than in a different allocation of volume between the parts of the tree.

International audience; AbstractKey messageStatic site indices determined from stands’ top height are derived from different forest inventory sources with height and age information and thus enable comparisons and modeling of a species’ productivity encompassing large environmental gradients.ContextEstimating forest site productivity under changing climate requires models that cover a wide range of site conditions. To exploit different inventory sources, we need harmonized measures and procedures for the productive potential. Static site indices (SI) appear to be a good choice.AimsWe propose a method to derive static site indices for different inventory designs and apply it to six tree species of the German and French National Forest Inventory (NFI). For Norway spruce and European beech, the climate dependency of SI is modeled in order to estimate trends in productivity due to climate change.MethodsHeight and age measures are determined from the top diameters of a species at a given site. The SI is determined for a reference age of 100 years.ResultsThe top height proves as a stable height measure that can be derived harmoniously from German and French NFI. The boundaries of the age-height frame are well described by the Chapman-Richards function. For spruce and beech, generalized additive models of the SI against simple climate variables lead to stable and plausible model behavior.ConclusionThe introduced methodology permits a harmonized quantification of forest site productivity by static site indices. Predicting productivity in dependence on climate illustrates the benefits of combined datasets.

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.

The IPCC previsions for the upcoming decades include an increase in frequency and intensity of drought events in several regions worldwide, including Northern Europe. Drought significantly affects forest ecosystems through decreased productivity, increased vulnerability to biotic disturbances and increased subsequent mortality. How forest ecosystems maintain resistance and resilience to drought events are important questions. Our study aimed to assess whether species mixture or an individual tree size within a stand alters a given tree’s resilience and resistance to drought. A retrospective study of tree-ring widths allowed us to calculate resistance, resilience and recovery indices for five recent drought events: 1976, the 1990–1992 period, 2003, 2006 and 2010. These drought events were selected based on the SPEI (Standardized Precipitation Evapotranspiration Index) drought index. Our study sample consisted of 108 individual sessile oak ( Quercus petraea (Matt.)) or Scots pine ( Pinus sylvestris L.) trees sampled in 2012 and 2013 (Orleans forest, central France) in pure and mixed stands, divided into three diameter classes corresponding to three sizes: large, medium and small trees. Scots pine performed better than sessile oak during the 1990–1992 and 2010 droughts while the contrary was observed for the 2003 and 2006 droughts. They performed equally in 1976. We suggest that the differing sensitivity of the two species to spring and summer drought explained this result. In our study, stand composition had no effect on resilience or resistance for either species. The size effect in oaks was unclear as small oaks displayed either a better performance or a worse performance than large oaks. Small pines displayed better resistance and resilience than pines of a larger size. This work stressed the importance of taking into account stand composition and trees size as well as soil and climatic conditions for each drought events to achieve a better understanding of the diversity of responses to climatic variations among forest ecosystems.

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”.

The effects of mixed stands on biodiversity are increasingly being studied since they are supposed to offer higher habitat heterogeneity. Nevertheless, for tree-associated diversity, including epiphytes and terricolous species near tree trunks, few studies exist, and still fewer compare mixed stands with each corresponding pure tree species stand. We evaluated and quantified the influence of forest composition on tree-associated bryophyte diversity (species richness, abundance, composition) in mixed and pure oak-pine stands in a French lowland forest. The main explanatory variables for bryophyte diversity at tree-level were the identity of the phorophyte tree species and the mixture type (pure versus mixed). At the plot level, the main explanatory variable was the stand type (pure oak, pure pine and mixed). We also explored the role of other variables including the chemistry of the bryophyte substrates (soil, bark) and water supply (stemflow, throughfall), as well as stand abundance variables (basal area, interfering plant cover). We analyzed data with Generalized Linear Models under Bayesian statistics, to take into account the spatial autocorrelation between plots and any under- or over-dispersion of our data. At the tree-level, bryophyte richness and abundance were higher on oak than on pine. Pine bryophyte richness was higher in mixed compared to pure stands, whereas for oak, mixed stands did not enhance bryophyte richness. At the plot level, mixed stands hosted bryophyte communities of similar richness to those in pure oak stands, whereas pure pine stands were clearly poorer. Our exploratory models suggested strong effects of water supply chemistry (stemflow and throughfall pH or conductivity) and basal area; the latter had a strong quadratic effect on epiphytic richness at the plot level. In terms of composition, three species were more likely to be found on pine phorophytes, seven species clearly occurred more frequently on oaks. Some species were more likely to be associated to pine in mixed than in pure stands, and one species was found more often under pines in pure stands. Therefore, bryophyte diversity at the landscape level should benefit from the simultaneous presence of the three stand composition types – pure oak, pure pine and mixed stands.

Substituting renewable forms of energy for fossil fuels is a real challenge in developed countries and fuel wood will undoubtedly have an important role to play in forested areas. However, fuel wood harvesting may deplete nutrients in forest ecosystems and adversely affect site fertility in the long term. We compared the cost of compensatory fertilising and liming operations between whole-tree harvesting and traditional stem-only harvesting. We worked in beech (Fagus sylvatica L.) stands in eastern France and two site fertility classes (high and low). We used a growth model to calculate the nitrogen, calcium, potassium, magnesium and phosphorus contents of fine woody debris (FWD, diameter < 7 cm) and compared the benefits of selling this fine wood for energy to the cost of compensatory fertilising and liming. We showed that compensating and liming are more expensive than the profits derived from selling fine fuel wood, except when fuel wood prices rise considerably. This was mainly due to the high proportion of bark in FWD compared with other tree compartments. Indeed, bark is especially rich in nutrients such as nitrogen and phosphorus, which were the most costly nutrients to replace. Our study highlights the importance of considering the environmental costs of fuel wood production at the stand scale. Whenever fertilisation or liming is necessary, we recommend compensating at least for calcium and magnesium, two nutrients that account for a very small part of the costs. In any case, fertilisation should only be used if long-term site fertility has been compromised.

Questions: How to evaluate the mixture effect on basal area increment in two-species forest stands? Is a mixed Norway spruce–silver fir stand more productive than pure adjacent stands of either species? How to develop generic modelling approaches to assess mixture effects in forest stands? Location: In addition to a case study on Norway spruce–silver fir stands in French mountain forests, the generic approach used goes beyond local applications. Methods: We took advantage of National Forest Inventory data to develop a unique stand basal-area-increment model for pure and mixed stands of Norway spruce and silver fir that responds to ecological site conditions. The database was made up of 284 pure Norway spruce stands, 196 pure silver fir stands, and 323 mixed stands of these species. Results: Pure silver fir basal area increment is strongly influenced by spring climatic conditions, whereas pure Norway spruce is more influenced by soil conditions. The mixture of these species has a positive effect on silver fir, which decreases as the proportion of fir increases. In contrast, the mixture has no noticeable effect on Norway spruce. Conclusion: We developed a stand basal-area-increment model evidencing an advantage of the mixture on silver fir basal area increment, but not on Norway spruce. The mathematical formulation of the model developed is generic and can be used in all two-species mixture situations. It also makes it possible to compare different mixture situations with each other.

International audience; The main aim of this paper is to illustrate, using a large set of indicators, the consequences of management choices imposed under five socio-economic forward-looking scenarios within a given case study area during the next 60 years. This 101,000 ha case study area is centred around the village of Pontenx-les-Forges in south west France. This paper details this INTEGRAL project case study area and some forest management schemes implemented by forest owners under various scenarios. Using a landscape simulator handling two forest growth models, the evolution of all forest stands in the landscape is simulated using 9 indicators over a 60-year period: growing stock, harvested volume, carbon sequestered in trees, mean tree volume, commercial value of growing stock, susceptibility to wind and fire and biodiversity indexes. One of the main results of this study was to show up the magnitude of effects on growing stock and harvested volumes: according to the scenarios, annual harvesting could vary by 50% as from 2030. As a consequence, other indicators are impacted, such as biodiversity, wind and fire susceptibility. All these changes are observed despite the fact that the dominant species remain the same and that forest owners are considered not very prone to changing their behaviour. In conclusion, options for future improvement are discussed and the opportunities offered by high definition data acquisition from remote sensing are considered.; L'objectif de cette étude est d'illustrer à l'aide d'indicateurs les conséquences de choix de gestion imposés par cinq scénarios socioéconomiques prospectifs appliqués à une large zone forestière pour les 60 prochaines années. Le cas d'étude choisi est la zone centrée sur la commune de Pontenx-les-Forges dans le sud-ouest de la France et couvrant 101000 hectares. Cet article présente une description de la zone d'étude et des itinéraires sylvicoles mis en ½uvre par les propriétaires forestiers selon des scénarios. À l'aide d'un simulateur pilotant deux modèles de croissance, l'évolution de la zone d'étude à l'échelle de chaque parcelle est synthétisée par 9 indicateurs sur une période de 60 ans : le volume sur pied, le carbone sur pied, le volume total exploité, la valeur commerciale sur pied, le volume de l'arbre moyen, la vulnérabilité au vent et au feu, et des indices de biodiversité. Un des principaux résultats de cette étude est de montrer l'amplitude des changements pour la production et le volume sur pied : selon les scénarios les récoltes annuelles peuvent varier de 50 % dès 2030. Par conséquent, d'autres indicateurs sont impactés comme la biodiversité, la vulnérabilité au vent ou au feu. Pourtant, l'espèce dominante est maintenue et le comportement partiellement conservateur des types de propriétaires est pris en compte. En conclusion, des améliorations pour de futures simulations sont envisagées ; dans ce but, des synergies avec la télédétection sont nécessaires pour la collecte des données d'initialisation sur de larges territoires, ce qui permettra d'améliorer la précision des résultats.

The sampling design was based on the OPTMix experimental plots (Irstea Nogent-sur-Vernisson, France); OPTMix provided a part of the soil and dendrometric data as well. We thank Deki Fourcin, Sebastien Mace, Vincent Seigner and Yann Dumas for their help with data collection. We thank Frederic Miller from the INRA Orleans, Pierre Gelhaye and Frederic Mothe from the INRA Champenoux, and Frederic Lagane from the INRA Bordeaux for their help with sample preparations and microdensitometer analyses. We are thankful to Victoria Moore for correcting the English.; Mixing species has been proposed as a forest management option to mitigate the effects of the increase in summer drought episodes predicted by climate change models in temperate zones. Studying how the relationship between tree rings and summer drought episodes is modified by species mixture is of primary importance in this context. Based on a dendroclimatology study, we (i) qualified and quantified the relationship between ring width (RW) or mean ring density (MRD) and soil water deficit (SWD) in a ring-porous species, Quercus petraea, and a coniferous species, Pinus sylvestris, and (ii) determined if the relationships between tree ring characteristics and SWD are modified in mixtures. We found interspecific differences in RW patterns depending on the seasonality of the drought periods: RW in Q. petraea responded mainly to SWD from May to July, and RW in P. sylvestris to SWD from May to September. The ring-width of both species was strongly reduced by SWD; however, inter-specific differences in response to SWD seasonality triggered RW variations of opposite directions between the two species, for several years. In contrast, MRD for both species was dependent on the SWD from June to July. MRD in Q petraea increased slightly with SWD whereas MRD in P. sylvestris decreased strongly with SWD. The relationship between RW and SWD was not modified in mixtures compared to pure stands. We found that the effect of SWD on MRD was stronger in mixtures. The impact of SWD on species may be worsened in mixtures, but mixture of species with different growth sensitivities to the seasonality of the drought periods and to the drought intensity might help to buffer the effects of climatic fluctuations on the overall mixed stands productivity compared to pure stands. (C) 2015 Elsevier B.V. All rights reserved.

Growth compensations following a disturbance have been found in different species communities through experimentation, but there are few results obtained in natural conditions, in particular for forest ecosystems. The objective of this study was to determine whether there was growth compensation in a mixed oak–pine forest following a biotic disturbance: an outbreak of pine sawfly (Diprion pini) that caused massive defoliation of pines in Europe in the early 1980s. The data were collected in mixed oak–pine stands located in the plains of north-central France. We measured the ring widths of 223 oaks and 271 pines in nine mixed stands over a period ranging from 1972 to 2005. We established a model which incorporated climatic effects in order to predict the ring width under undisturbed conditions and to quantify the response of each species to the disturbance. We found that the growth of both species varied synchronously with a positive covariation outside of the disturbance. During the disturbance, the growth of both species covaried negatively especially in the plots where pine had been the most severely affected. For the year following the peak of the defoliations, the reduction in growth for pine was strong and ranged from −27% to −92% depending on the plot. In addition, the more significant the reduction in growth for pine, the more significant the increase in growth for oak. We found that a 100% reduction in pine growth was accompanied by a 61% increase in oak growth for the three years following the most severe defoliation. These results demonstrate that compensation between the two tree species following the insect outbreak did occur. We suggest that growth compensations would especially occur in the case of severe biotic disturbances but probably not in the case of climatic fluctuations.

Cette etude presente un exemple de modeles de biomasse empiriques etablis pour le Hetre et repondant a des caracteristiques d’exhaustivite (prise en compte des branches et des fines decoupes), de performance (evaluation la plus precise possible) et de robustesse (face aux changements de productivite et aux interventions sylvicoles). Ce niveau de precision a pu etre atteint en ajoutant l’âge des peuplements aux variables explicatives traditionnelles des modeles de biomasse (diametre a 1,30 m et hauteur totale de l’arbre), et en adoptant une forme d’equation allometrique permettant de relier les parametres du modele aux phenomenes biologiques regissant la croissance des arbres. Les modeles ont ete appliques a une chronosequence situee en Bretagne. Les resultats obtenus ont ete compares avec ceux des tarifs de Bouchon (1982) actuellement utilises par les gestionnaires forestiers pour les estimations des stocks de biomasse. Il apparait que les outils utilises actuellement dans la pratique sous-estiment fortement les stocks de houppier qui representent pourtant l’essentiel de la biomasse potentiellement utilisable pour satisfaire les besoins en bois energie. Pour l’estimation des stocks de carbone a l’echelle nationale, l’emploi d’equations de biomasse permet d’augmenter la precision des estimations de 10 % par rapport aux calculs successifs d’un volume puis d’une masse.

A base for volume and biomass data of the aerial woody compartments of individual trees was constituted under the ANR EMERGE (French acronym for ‘designing models for a robust, all-purpose estimation of wood energy’) project by seven bodies involved in forest research and management in France (ONF, INRA, Cemagref, IFN, FCBA, CNPF and CIRAD) so as to come up with a robust model of woody resources in forests. These measurements, taken for various logging diameters, sometimes down to the slenderest branches, have been performed since the beginning of the 20th century forming a unique data base in France. The data cover a broad range of age groups, sizes, species, stand structures and environmental factors (soil, climate). Of particular interest is the distribution of the available data in relation to French resources as estimated in the National Forest Inventory so as to use sampling campaigns to collect missing information under the EMERGE project. Another significant feature is the potential for designing robust, all-purpose models of volumes and biomass for various logging diameters depending on species, stage of development, geographic gradients, variations in silvicultural practises and possible effect of date of measurement.

Cet article presente une evaluation des quantites de bois qui pourraient etre exploitables dans les forets francaises, les peupleraies et les haies pendant la periode 2007 a 2020. Dans un premier temps, les quantites disponibles brutes de bois, c’est-a-dire avant deduction des differentes consommations actuelles, ont ete evaluees en appliquant des scenarios sylvicoles de reference a l’ensemble des placettes de l’Inventaire forestier national, en fonction de leurs caracteristiques (essence, structure, fertilite, âge, volume a l’hectare observe). Les consommations actuelles ont ete retranchees a ces quantites. Elles ont ete estimees grâce a l’enquete annuelle de branche « exploitation forestiere » pour l’industrie, et a une estimation de la consommation de bois de feu par les menages. Il en ressort une disponibilite supplementaire de plus de 28 millions de metres cube de bois par an pour la bioenergie ou pour la trituration, et de pres de 15 millions en bois d’oeuvre, majoritairement en feuillus.

Species choice is potentially an important management decision for increasing carbon stocks in forest ecosystems. The substitution of a slow-growing hardwood species (Quercus petraea) by a fast-growing conifer plantation (Pinus nigra subsp. laricio) was studied in central France. Simulations of carbon stocks in tree biomass were conducted using stand growth models Fagacees for sessile oak and PNL for Corsican pine. The changes in soil carbon were assessed using the Century model and data from two European soil monitoring networks: 16 km � 16 km grid and RENECOFOR. Carbon in wood products was assessed with life cycle analysis and lifespan of final products. However, only carbon stocks and their variation were accounted for: effects of energy-consuming materials or fossil fuel substitution are excluded from the analysis. To compare the growth of these two types of forest stands, an important part of the study was to assess the productivity of both species at the same site, using National Forest Inventory data. Simulations showed that (i) this species substitution would lead to an additional carbon storage of 1.6 tC/ha/year with the conifer plantation during its first rotation (64 years) (ii) at steady state, the time- averaged carbon stock of the conifer plantation over the whole rotation would be 42 tC/ha to 47 tC/ha lower than that of the hardwood even-aged forest, depending on applied silvicultural scenarios. The time-averaged carbon stocks including vegetation, soil and wood products are 221 tC/ha for sessile oak, and around 175 tC/ha for Corsican pine. The amount of carbon stored in wood products is low compared to the total carbon stock (5% for sessile oak, 8-8.5% for Corsican pine), mainly due to important losses during early wood processing, and to the short lifespan of wood products compared to the rotation length of forest stands.

International audience; This paper is the outcome of a group discussion held at the Savonlinna meeting Management of forest ecosystems and its impact on the GHG budget'. The aim of this break-out group discussion was to Characterize forest management impacts on the GHG budget of forest ecosystems in different European regions'. In this paper we briefly characterize different options that a forest owner has in order to maintain or maximize forest carbon pools and carbon sequestration. These hectare scale descriptions of measures are then regarded in connection to the current state of European forests and how they can be combined with ongoing management trends and local issues. We point out the various possibilities that exist in European forests, where they are located, and where they could possibly be combined with adaptation. We identify these hotspots for largest growing stocks, largest peat areas, and, e.g. largest risks for loss of carbon due to fire or urban sprawl. We conclude that one common strategy cannot be designed. Within each region, local solutions have to be found that optimize goals and aim at integrated and sustainable land use.

International audience; In order to improve the estimation of carbon stored in the French forest biomass from National Forest Inventory data, we developed six species-specific equations for estimating the total aboveground volume of trees, including merchantable volume, branches and twigs. Equations use circumference at breast height and total height as independent variables. They were built from even-aged forests of the Landes massif, the northern half and the eastern mountain regions of France. The sample was selected within archives of volume measurements taken in growth and yield permanent plots between 1920 and 1955. It is made up of 4619 trees belonging to seven important species: 1222 Sessile Oak, 1293 Common Beech, 347 Douglas Fir, 309 Norway Spruce, 389 Scots Pine, 297 Maritime Pine and 762 Silver Fir. These trees were felled and measured in 26 different forests (62 stands). Tree form factor was analysed, rather than volume, to remove heteroscedasticity, and height was substituted by a hardiness coefficient to remove diameter–height correlation. The analysis identified species-specific modes of variation of tree form with respect to developmental stage and tree hardiness. Maritime and Scots Pine did not differ statistically, despite large differences between ecological and silvicultural situations of both species. This suggests the possibility to use identical volume equations for species belonging to the same genus. Regional variations of tree form were explored by a cross-validation technique. Prediction biases did not exhibit a clear geographic structure. A 5% overestimation for hardwoods in southern sites is possible, and would deserve further testing. The hypothesis that recent growth changes may have slightly altered tree form is also discussed. Finally, a national-scale application provided Biomass Expansion Factors consistent with former studies and suggested that these volume equations behave well in extrapolation to coppices, uneven-aged or mixed stands.

L'article relate une etude des changements de productivite intervenus dans les hetraies regulieres du Nord-Est de la France entre 1900 et 2000. L'etude est basee sur la comparaison retrospective de la croissance de deux generations, structurees en 14 couples de peuplements associant un jeune et un vieux, separes par 75 ans en moyenne et situes a proximite l'un de l'autre, dans la meme foret sur la meme station. Dans chaque peuplement, trois arbres dominants ont ete abattus, dont la croissance en hauteur a ete reconstituee par analyse de tige et la croissance radiale mesuree a 1,30 m. La jeune generation a connu une croissance nettement superieure, la hauteur dominante a 65 ans surclassant de plus de 4 m celle des vieux peuplements adjacents. Une modelisation originale des donnees a permis d'estimer la courbe de tendance de l'accroissement au cours du XXe siecle. Il apparait que l'essentiel de l'acceleration s'est produit entre 1950 et 1980. Integree dans le simulateur de croissance de peuplements forestiers Fagacees, cette tendance a ete utilisee pour comparer deux regimes d'eclaircies, appliques a deux generations nees en 1850 et 1950. Les simulations montrent une tres forte reduction de l'âge d'exploitabilite, pour un meme diametre dominant-objectif de 60 cm : sur station equivalente, la vieille generation conduite en eclaircies faibles est mure a 150 ans, contre 90 ans pour la jeune ayant subi des eclaircies fortes.

International audience; The maximum size-density relationship (MSDR) reflects the boundary site occupancy and the self-thinning line for a given species, being a useful tool in forestry. Studies focusing on the MSDR often do not cover the whole distribution of the studied species, which results in different boundaries for a given species in different regions. A common MSDR is lacking for the increasingly demanded large-scale studies. However, this information is important where silvicultural responses must be prioritized among monospecific stands or where comparisons among maximum and relative stand densities between and within species are required. For the purposes of this study, we used data from 9911 sample plots located in Scots pine and European beech monospecific stands. Both of these species are of considerable importance and widely distributed throughout Europe. The data came from National or Regional Forest Inventories of five European countries (Austria, Germany, France, Spain and Poland) and therefore were distributed across a wide range of climatic conditions. The main aim of this study was to determine whether the MSDR of these species depends on environmental variables and to develop a MSDR model for each species that explain this variability along a climate gradient. The resulting models showed that both parameters of species boundary lines were climate-dependent, but that the pattern of variation differed between species. Hence, the higher the humidity, the steeper the MSDR (more negative exponent) and the higher the intercept for beech, while in the case of pine, the higher the humidity, the straighter the MSDR and the lower the intercept. According to these models, the stand density indices, for a reference diameter of 25 cm, varied with the humidity in a different way for each species. Consequently, the ratio between the two species increases with humidity, although it also depends on stand diameter. These results are in accordance with the yield level theory and could contribute to the development of more precise silvicultural guidelines and growth models based on the self-thinning line. Moreover, they are of particular importance in the discussion of growth and the effects of mixing on mixed species stands.