132 research outputs found

    Mixture enhances productivity in a two-species forest: evidence from a modeling approach

    Get PDF
    The effect of mixture on productivity has been widely studied for applications related to agriculture but results in forestry are scarce due to the difficulty of conducting experiments. Using a modeling approach, we analyzed the effect of mixture on the productivity of forest stands composed of sessile oak and Scots pine. To determine whether mixture had a positive effect on productivity and if there was an optimum mixing proportion, we used an aggregation technique involving a mean-field approximation to analyze a distance-dependent individual-based model. We conducted a local sensitivity analysis to identify the factors that influenced the results the most. Our model made it possible to predict the species proportion where productivity peaks. This indicates that transgressive over-yielding can occur in these stands and suggests that the two species are complementary. For the studied growth period, mixture does have a positive effect on the productivity of oakpine stands. Depending on the plot, the optimum species proportion ranges from 38 to 74% of oak and the gain in productivity compared to the current mixture is 2.2% on average. The optimum mixing proportion mainly depends on parameters concerning intra-specific oak competition and yet, intra-specific competition higher than inter-specific competition was not sufficient to ensure over-yielding in these stands. Our work also shows how results obtained for individual tree growth may provide information on the productivity of the whole stand. This approach could help us to better understand the link between productivity, stand characteristics, and species growth parameters in mixed forests

    Spatial pattern of trees influences species productivity in a mature oak-pine mixed forest

    Get PDF
    Spatial pattern has a key role in the interactions between species in plant communities. These interactions influence ecological processes involved in the species dynamics: growth, regeneration and mortality. In this study, we investigated the effect of spatial pattern on productivity in mature mixed forests of sessile oak and Scots pine. We simulated tree locations with point process models and tree growth with spatially explicit individual growth models. The point process models and growth models were fitted with field data from the same stands. We compared species productivity obtained in two types of mixture: a patchy mixture and an intimate mixture. Our results show that the productivity of both species is higher in an intimate mixture than in a patchy mixture. Productivity difference between the two types of mixture was 11.3% for pine and 14.7% for oak. Both species were favored in the intimate mixture because, for both, intraspecific competition was more severe than interspecific competition. Our results clearly support favoring intimate mixtures in mature oak-pine stands to optimize tree species productivity; oak is the species that benefits the most from this type of management. Our work also shows that models and simulations can provide interesting results for complex forests with mixtures, results that would be difficult to obtain through experimentation

    HEPPA-II model-measurement intercomparison project : EPP indirect effects during the dynamically perturbed NH winter 2008-2009

    Get PDF
    We compare simulations from three high-top (with upper lid above 120 km) and five medium-top (with upper lid around 80 km) atmospheric models with observations of odd nitrogen (NOx D NO+NO2), temperature, and carbon monoxide from seven satellite instruments (ACE-FTS on SciSat, GOMOS, MIPAS, and SCIAMACHY on Envisat, MLS on Aura, SABER on TIMED, and SMR on Odin) during the Northern Hemisphere (NH) polar winter 2008/2009. The models included in the comparison are the 3-D chemistry transport model 3dCTM, the ECHAM5/MESSy Atmospheric Chemistry (EMAC) model, FinROSE, the Hamburg Model of the Neutral and Ionized Atmosphere (HAMMO-NIA), the Karlsruhe Simulation Model of the Middle Atmosphere (KASIMA), the modelling tools for SOlar Climate Ozone Links studies (SOCOL and CAO-SOCOL), and the Whole Atmosphere Community Climate Model (WACCM4). The comparison focuses on the energetic particle precipitation (EPP) indirect effect, that is, the polar winter descent of NOx largely produced by EPP in the mesosphere and lower thermosphere. A particular emphasis is given to the impact of the sudden stratospheric warming (SSW) in January 2009 and the subsequent elevated stratopause (ES) event associated with enhanced descent of mesospheric air. The chemistry climate model simulations have been nudged toward reanalysis data in the troposphere and stratosphere while being unconstrained above. An odd nitrogen upper boundary condition obtained from MIPAS observations has further been applied to medium-top models. Most models provide a good representation of the mesospheric tracer descent in general, and the EPP indirect effect in particular, during the unperturbed (pre-SSW) period of the NH winter 2008/2009. The observed NOx descent into the lower mesosphere and stratosphere is generally reproduced within 20 %. Larger discrepancies of a few model simulations could be traced back either to the impact of the models' gravity wave drag scheme on the polar wintertime meridional circulation or to a combination of prescribed NOx mixing ratio at the uppermost model layer and low vertical resolution. In March-April, after the ES event, however, modelled mesospheric and stratospheric NOx distributions deviate significantly from the observations. The too-fast and early downward propagation of the NO x tongue, encountered in most simulations, coincides with a temperature high bias in the lower mesosphere (0.2-0.05 hPa), likely caused by an overestimation of descent velocities. In contrast, upper-mesospheric temperatures (at 0.05-0.001 hPa) are generally underestimated by the high-top models after the onset of the ES event, being indicative for too-slow descent and hence too-low NOx fluxes. As a consequence, the magnitude of the simulated NOx tongue is generally underestimated by these models. Descending NOx amounts simulated with mediumtop models are on average closer to the observations but show a large spread of up to several hundred percent. This is primarily attributed to the different vertical model domains in which the NOx upper boundary condition is applied. In general, the intercomparison demonstrates the ability of state-of- the-art atmospheric models to reproduce the EPP indirect effect in dynamically and geomagnetically quiescent NH winter conditions. The encountered differences between observed and simulated NOx, CO, and temperature distributions during the perturbed phase of the 2009 NH winter, however, emphasize the need for model improvements in the dynamical representation of elevated stratopause events in order to allow for a better description of the EPP indirect effect under these particular conditions.Peer reviewe

    Emerging stability of forest productivity by mixing two species buffers temperature destabilizing effect

    Get PDF
    The increasing disturbances in monocultures around the world are testimony to their instability under global change. Many studies have claimed that temporal stability of productivity increases with species richness, although the ecological fundamentals have mainly been investigated through diversity experiments. To adequately manage forest ecosystems, it is necessary to have a comprehensive understanding of the effect of mixing species on the temporal stability of productivity and the way in which it is influenced by climate conditions across large geographical areas. Here, we used a unique dataset of 261 stands combining pure and two-species mixtures of four relevant tree species over a wide range of climate conditions in Europe to examine the effect of species mixing on the level and temporal stability of productivity. Structural equation modelling was employed to further explore the direct and indirect influence of climate, overyielding, species asynchrony and additive effect (i.e. temporal stability expected from the species growth in monospecific stands) on temporal stability in mixed forests. We showed that by adding only one tree species to monocultures, the level (overyielding: +6%) and stability (temporal stability: +12%) of stand growth increased significantly. We identified the key effect of temperature on destabilizing stand growth, which may be mitigated by mixing species. We further confirmed asynchrony as the main driver of temporal stability in mixed stands, through both the additive effect and species interactions, which modify between-species asynchrony in mixtures in comparison to monocultures. Synthesis and applications. This study highlights the emergent properties associated with mixing two species, which result in resource efficient and temporally stable production systems. We reveal the negative impact of mean temperature on temporal stability of forest productivity and how the stabilizing effect of mixing two species can counterbalance this impact. The overyielding and temporal stability of growth addressed in this paper are essential for ecosystem services closely linked with the level and rhythm of forest growth. Our results underline that mixing two species can be a realistic and effective nature-based climate solution, which could contribute towards meeting EU climate target policies.Emerging stability of forest productivity by mixing two species buffers temperature destabilizing effectpublishedVersio

    Emerging stability of forest productivity by mixing two species buffers temperature destabilizing effect

    Get PDF
    The increasing disturbances in monocultures around the world are testimony to their instability under global change. Many studies have claimed that temporal stability of productivity increases with species richness, although the ecological fundamentals have mainly been investigated through diversity experiments. To adequately manage forest ecosystems, it is necessary to have a comprehensive understanding of the effect of mixing species on the temporal stability of productivity and the way in which it is influenced by climate conditions across large geographical areas. Here, we used a unique dataset of 261 stands combining pure and two-species mixtures of four relevant tree species over a wide range of climate conditions in Europe to examine the effect of species mixing on the level and temporal stability of productivity. Structural equation modelling was employed to further explore the direct and indirect influence of climate, overyielding, species asynchrony and additive effect (i.e. temporal stability expected from the species growth in monospecific stands) on temporal stability in mixed forests. We showed that by adding only one tree species to monocultures, the level (overyielding: +6%) and stability (temporal stability: +12%) of stand growth increased significantly. We identified the key effect of temperature on destabilizing stand growth, which may be mitigated by mixing species. We further confirmed asynchrony as the main driver of temporal stability in mixed stands, through both the additive effect and species interactions, which modify between-species asynchrony in mixtures in comparison to monocultures. Synthesis and applications. This study highlights the emergent properties associated with mixing two species, which result in resource efficient and temporally stable production systems. We reveal the negative impact of mean temperature on temporal stability of forest productivity and how the stabilizing effect of mixing two species can counterbalance this impact. The overyielding and temporal stability of growth addressed in this paper are essential for ecosystem services closely linked with the level and rhythm of forest growth. Our results underline that mixing two species can be a realistic and effective nature-based climate solution, which could contribute towards meeting EU climate target policies

    Quel est le niveau de détail pertinent pour modéliser la croissance d'une forêt mélangée ? Comparaison d'une famille de modèles et application aux peuplements mélangés chêne sessile - pin sylvestre

    No full text
    Appropriate tools and models are needed for the management of mixed forests. The aim of this thesis is to show how the construction and the comparison of models with different levels of detail can help us to choose the most appropriate level to model the growth of a mixed stand. We developed a family of models at different levels of detail from data collected in mixed stands of sessile oak (Quercus petraea L.) and Scots pine (Pinus sylvestris L.) : a tree distance independent model (MAID), a tree distance dependent model (MADD), three stand models and an intermediate model bridging the MAID and the MADD. We ensured consistency between models using several approaches in order to make relevant comparisons. These models have given us some knowledge on the growth and dynamics of these forests, in particular on the spatial and temporal interactions between oaks and pines. Thus, we showed a compensatory growth phenomenon between the two species using the MAID. The MADD made it possible to show that, in these stands, the intraspecific competition was stronger than interspecific competition. A stand model developed from the MADD helped us to study the influence of mixing rate on production. To assess the quality of models predictions, we used an independent data set obtained by splitting our data. For example, we have shown that the MAID was more efficient than the MADD to predict individual increments. The models were also compared on examples of applications with short or medium term simulations. The proposed approach is of interest for both understanding the studied phenomenon and developing predictive tools. The different results of this work, allowed us to assess the relevance of a type of model for different contexts of use. This very general approach could be applied to the modeling of other processes such as mortality or regenerationFace à l'intérêt grandissant pour les forêts mélangées, des d'outils et des modèles adaptés à leur gestion sont nécessaires. L'objectif de cette thèse est de montrer comment la construction et la comparaison de modèles ayant différents niveaux de détail peuvent nous aider à choisir le niveau le plus approprié pour modéliser la croissance d'un peuplement mélangé dans un contexte d'application donné. A partir de données récoltées dans des peuplements mélangés chêne sessile (Quercus petraea L.) pin sylvestre (Pinus sylvestris L.), nous avons construit une famille de modèles à différents niveaux de détail : un modèle arbre indépendant des distances (MAID), un modèle arbre dépendant des distances (MADD), trois modèles peuplement et un modèle intermédiaire entre le MAID et le MADD utilisant des distributions de voisinage. Pour que la comparaison de ces modèles soit pertinente, nous avons assuré une cohérence entre les modèles en utilisant plusieurs approches. Ces modèles nous ont permis d'acquérir des connaissances sur la croissance et la dynamique de ces forêts en particulier sur les interactions spatiales et temporelles entre le chêne et le pin. Ainsi le MAID a permis de montrer qu'il peut y avoir des phénomènes de compensation de croissance entre les deux espèces. Le MADD a permis de montrer que dans ces peuplements la compétition intraspécifique est supérieure à la compétition interspécifique. Un modèle peuplement obtenu à partir du MADD a permis d'étudier l'influence du taux de mélange sur la production. Pour évaluer la qualité prédictive des modèles, nous avons utilisé un jeu de données indépendant obtenu en partageant nos données avant la construction des modèles. Nous avons ainsi montré que le MAID était plus performant que le MADD pour prédire les accroissements individuels. Les modèles ont aussi été comparés sur des exemples d'applications mettant en ½uvre des simulations à court ou moyen terme. La démarche proposée présente un intérêt aussi bien pour la compréhension du phénomène étudié que pour sa modélisation dans un but prédictif. En regroupant l'ensemble des résultats acquis, ce travail nous a permis d'apprécier la pertinence d'un type de modèle en fonction du contexte d'utilisation. Cette démarche très générale pourrait être appliquée à la modélisation d'autres processus comme la mortalité ou la régénératio

    Oakpine2 : un modèle arbre qui utilise des distributions de voisinage pour prédire la croissance d'une forêt mélangée

    No full text
    National audienceThis presentation describes the Oakpine2 module of the Capsis software
    • …
    corecore