Key message
An influence of the recent changes in temperature or rainfall was demonstrated, increasing background tree mortality rates for 2/3 of the 12 studied tree species. Climate change-induced ...tree mortality was exacerbated towards the warm or dry limits of the species ranges, suggesting in these areas a progressive replacement by more xeric species.
Context
Despite the identification of climate change effects on tree mortality in various biomes, the characterization of species-specific areas of vulnerability remains poorly understood.
Aims
We sought to assess if the effects of temperature and rainfall changes on background tree mortality rates, which did not result from abrupt disturbances, were linked to climate change intensity only, or if they also depended on the tree’s location along climatic gradients.
Methods
We modelled background mortality for 12 of the most common European tree species using 265,056 trees including 4384 dead trees from the French national forest inventory. To explain mortality, we considered variables linked to tree characteristics, stand attributes, logging intensity and site environmental characteristics, and climate change effects.
Results
We found an influence of temperature and rainfall changes on 9 species out of 12. For 8 of them, climate change-induced tree mortality was exacerbated towards the warm or dry limits of the species ranges.
Conclusion
These results highlight that tree mortality varies according to the climate change intensity and the tree location along temperature and rainfall gradients. They strengthen the poleward and upward shifts of trees forecasted from climate envelope models for a large number of European tree species.
Key message
Decreasing stand density increases resistance, resilience, and recovery of
Quercus petraea
trees to severe drought (2003), particularly on dry sites, and the effect was independent of ...tree social status.
Context
Controlling competition is an advocated strategy to modulate the response of trees to predicted changes in climate.
Aims
We investigated the effects of stand density (low, medium, high; relative density index 0.20, 0.53, 1.04), social status (dominant, codominant, suppressed), and water balance (dry, mesic, wet; summer water balance − 182, − 126, − 96 mm) on the climate-growth relationships (1997–2012) and resistance (Rt), resilience (Rs), and recovery (Rc) following the 2003 drought.
Methods
Basal area increments were collected by coring (269 trees) in young stands (28 ± 7.5 years in 2012) of sessile oak (
Quercus petraea
) in a French permanent network of silvicultural plots.
Results
We showed that the climate-growth relationships depend on average site-level water balance with trees highly dependent on spring and summer droughts on dry and mesic sites and not at all on wet sites. Neither stand density nor social status modulated mean response to climate. Decreasing stand density increased Rt, Rs, and Rc particularly on dry sites. The effect was independent of tree social position within the stand.
Conclusion
Reducing stand density mitigates more the effect of extreme drought events on drier sites than on wet sites.
Les effets de la densité du peuplement, du statut social et des conditions locales de bilan hydrique estival ont été analysés sur la résistance (Rt), la récupération (Rc) et la résilience (Rs) à la ...sécheresse de 2003. La croissance radiale a été étudiée sur 269 jeunes chênes sessiles échantillonnés dans le réseau d’expérimentations sylvicoles du GIS Coop. Il apparaît une interaction forte entre les conditions locales de bilan hydrique et la densité : diminuer la densité augmente la résistance, la récupération et la résilience des arbres particulièrement sur les sites secs. Cet effet est indépendant du statut social.
Messages clés :• Les peuplements en situation hydrique favorable ont été les plus exposés à la sécheresse de 2003.• Diminuer la densité a augmenté la résistance, la récupération et la résilience des chênes sessiles.• L’effet a été particulièrement fort dans les conditions stationnelles les plus sèches.
To improve our understanding of species range limits by studying how height growth, a trait related to plant survival, varies throughout the geographic range of Fagus sylvatica L. in France. The ...geographic range of beech in France, representing the western area of its European distribution, within which this species exhibits range distribution limits in both plains and mountainous areas. A generalized linear regression model was used to link beech growth performance to environmental variables using data from 819 plots of the French National Forest Inventory (IFN) database. This model was applied to predict potential growth on 97,281 IFN plots covering the geographic range of beech in France. A kriging technique was used to interpolate estimated growth potential. Finally, the performance of plot-based predictions of potential growth from the map (i.e. map quality) was evaluated against an independent data set. The beech growth performance model highlighted the major impact of climate on potential tree growth at a broad spatial scale. The relevant climatic factors were related mainly to spring cold, summer heat, and winter temperatures and rainfall. The study also revealed the predictive power of soil parameters, which explained a large proportion of the variation in potential beech growth (c. 30%). Analyses of height growth patterns near the boundary of the species range in France showed that the limit only partly coincides with the growth decline caused by climatic and soil factors. Along parts of the range limit, the predicted potential for growth was high, suggesting that in these areas the limit of the range could be explained by other factors, such as competition or constraints on reproduction. The spatial variation in the potential height growth of Fagus sylvatica can be explained by environmental factors and is partly correlated with its regional range limits. By identifying areas where growth potential constrains the geographic range of species, environmental growth models can help to improve our knowledge of the spatial drivers of species geographic range limits and shed light on their response to future environmental changes.
The effects of population density and summer drought were analysed by means of diameter and height growth in sessile oaks (Quercus petraea) on the stand and individual tree scales. Dendrometric ...inventory data collected from two networks of silvicultural experimentation were used (LERFOB and GIS Coop networks, 9 sites, 31 plots, 99 inventories, ages from 10 to 120 years). These networks study the effects of a broad range of densities, from freely growing trees (relative density index, or RDI, close to 0) to maximum density situations where self-thinning occurs (RDI equal to or in excess of 1). Climate conditions vary from 660 to 850 mm per year with a heat gradient of 9.5 to 11.5 °C (average 1990-2010). Generally speaking, density very strongly affects tree and stand growth, with drought playing a secondary role that is nonetheless significant. Overtopped trees contribute very little to the growth of the stand, particularly when the stand is dense. Drought reduces growth, particularly that of non-dominant trees. Density and drought therefore have the same effect: they accentuate growth differences between trees when stresses are greater. By allocating more resources to diameter growth as compared to height growth, trees in open stands are more “stocky”. In contrast, in densely populated stands, there is “a race for light” making for greater height growth, especially that of overtopped trees. In all cases, drought has a greater effect in reducing height growth than in reducing diameter growth. Finally, following a particularly severe drought (1976), trees recovered most quickly at the drier sites (recovery in 2 years) while the overtopped trees in the higher density stands recovered very little (still no recovery 7 years later). These results suggest that sessile oak adapts better in drier conditions.
Les effets de la densité du peuplement et de la sécheresse estivale ont été analysés sur la croissance en diamètre et en hauteur du Chêne sessile (Quercus petraea) à l’échelle du peuplement et de l’arbre. Les données des inventaires dendrométriques issues de deux réseaux d’expérimentations sylvicoles ont été utilisées (réseaux LERFOB et GIS Coop, 9 sites, 31 placettes, 99 inventaires, âges de 10 à 120 ans). Ces réseaux étudient les effets de larges gradients de densité, depuis des arbres en croissance libre (relative density index, ou RDI, proche de 0) jusqu’à des situations de densité maximale avec des phénomènes d’autoéclaircie (RDI supérieur ou égal à 1). Les conditions climatiques varient de 660 à 850 mm par an pour un gradient thermique de 9,5 à 11,5 °C (moyenne 1990-2010). D’une façon générale, la densité module très fortement la croissance des arbres et du peuplement, la sécheresse jouant un rôle secondaire mais néanmoins significatif. Les arbres dominés participent peu à la croissance du peuplement et ceci est d’autant plus vrai que le peuplement est dense. La sécheresse réduit la croissance et ceci particulièrement pour les arbres non dominants. Ainsi densité et sécheresse ont le même effet, c’est-à-dire qu’elles accentuent les différences de croissance entre arbres quand les contraintes augmentent. En allouant davantage de ressources à leur croissance en diamètre par rapport à leur croissance en hauteur, les arbres dans les peuplements ouverts sont « trapus ». Au contraire, dans les peuplements denses, c’est la « course à la lumière » avec une croissance en hauteur accrue et ceci d’autant plus que l’arbre est dominé. Dans tous les cas, la sécheresse réduit davantage la croissance en hauteur que la croissance en diamètre. Enfin, après une sécheresse exceptionnelle (1976), la récupération des arbres a été la plus rapide sur les sites les plus secs (récupération après 2 ans) et elle fut très faible pour les arbres dominés dans les peuplements les plus denses (toujours pas de récupération après 7 ans). Ces résultats suggèrent une meilleure adaptation des chênes sessiles dans les conditions plus sèches.
•We study tree-ring responses to climate of Abies alba and Fagus sylvatica.•We consider competition at stand and individual tree levels.•Climatic drivers are different between both ...species.•Competition at stand level prevails on competition at tree level.•Sensitivity to summer drought increases with dominancy in high stand basal area.
The aim of the study was to assess the effects of competition at both stand and tree levels on climate tree-growth relationships of 414 Abies alba and 243 Fagus sylvatica trees growing in 2 contrasting ecological conditions (north- and south-facing) under mountainous continental climate (mean altitude: 886m). Stand level competition was considered through three stand basal area (SBA) modalities (Low: 32m2/ha, Medium: 41 and High: 49) while tree level competition was assessed through three social statuses (SST, Dominant, Codominant and Suppressed trees). A strong specific response to climate was pointed out with different key periods; growth of Abies being mainly driven by previous and current late summer temperatures, while that of Fagus was controlled by April and June ones. No obvious difference between facing sides was evidenced. Competition at stand level prevailed on competition at tree level. In Low and Medium SBA, trees exhibited similar responses to climate whatever their social statuses. On the opposite, sensitivity to summer drought increased with dominancy in high SBA. Inter-specific differences and consequences for forest management are discussed.
Increases in tree mortality rates have been highlighted in different biomes over the past decades. However, disentangling the effects of climate change on the temporal increase in tree mortality from ...those of management and forest dynamics remains a challenge. Using a modelling approach taking tree and stand characteristics into account, we sought to evaluate the impact of climate change on background mortality for the most common European tree species. We focused on background mortality, which is the mortality observed in a stand in the absence of abrupt disturbances, to avoid confusion with mortality events unrelated to long-term changes in temperature and rainfall. We studied 372 974 trees including 7312 dead trees from forest inventory data surveyed across France between 2009 and 2015. Factors related to competition, stand characteristics, management intensity, and site conditions were the expected preponderant drivers of mortality. Taking these main drivers into account, we detected a climate change signal on 45% of the 43 studied species, explaining an average 6% of the total modelled mortality. For 18 out of the 19 species sensitive to climate change, we evidenced greater mortality with increasing temperature or decreasing rainfall. By quantifying the mortality excess linked to the current climate change for European temperate forest tree species, we provide new insights into forest vulnerability that will prove useful for adapting forest management to future conditions.
Changes in forest growth have been found in European forests and worldwide. However most observations have been derived from samples of restricted size, whose representativeness at a regional forest ...scale is questionable. National forest inventories provide an interesting perspective for both regional scale assessment of these trends and the investigation of their variations over environmental gradients, but have been little used.
The aim of our work was to carry out an exploratory modelling analysis of productivity changes, based on the French national forest inventory data. The objectives were: (i) to assess recent trends in forest productivity and to investigate a possible recent decline as found in previous studies; and (ii) to investigate trend variations relative to site fertility factors. We focused on pure and even-aged stands of common beech (
Fagus sylvatica L.) in north-eastern France, already documented from previous studies based on retrospective data.
The dataset consisted of 925 temporary plots inventoried between 1979 and 2007. We developed two regression models of stand basal area increment (
BAI) against stand developmental stage (dominant height), site fertility (site index in the
SI model, environmental indicators in the
EI model) and stand density (relative density index). The effect of calendar date was tested in order to investigate possible historical trends. Site fertility–date interactions were also tested to investigate the site-dependence of trends.
The fitted models showed a high goodness of fit (adj.
R
2 over 0.69). We showed an increase in stand
BAI of 27.8% between 1977 and 1987, (10.4% between 1979 and 1987). Stand
BAI then decreased by approximately 5% between 1987 and 2004. We thus confirmed the hypothesis of a recent decline in common beech vitality in its temperate range. The chronologies clearly depicted the effect of severe drought events (1976 and 2003), pointing out the predominant role of water availability in the changes observed. No significant site-dependence of the trend was identified.
•Large-scale model or map performance significantly decreases above 1 km resolution.•Fine resolution is more accurate for heterogeneous landscapes and for reduced extents.•Aggregation of the cell ...values of predictive maps can improve their precision.•Different spatial resolution levels should be compared before soil mapping.
The important development of digital soil mapping (DSM) these last decades has led to a large number of maps of soil properties with increasingly finer raster size. Map resolution is mostly determined by expert knowledge or by matching with the resolution of existing data, while scale is recognized as a major issue. Using the pH and the C/N ratio describing the surface horizon of forest soils and estimated by bioindication, we evaluated the effect of resolution changes on model and map performance for different geographical extents. Using 40,663 plots from the national forest inventory and 25 environmental variables calculated at eight different spatial resolution levels (50, 100, 250, 500, 1000, 8000, 16,000, and 50,000 m), we modeled and mapped pH and C/N over a vast and diversified area of 91,000 km2 in the north-east of France. The models highlighted the importance of geology in pH and C/N spatial variations, and to a lesser extent the importance of stand type, climate and topography, with a slight influence of data resolution on predictor selection. On the contrary, the accuracy of model or map performance decreased significantly above 1000 m resolution. Significant performance differences were observed according to the location and the size of the geographical extent. Globally, the more heterogeneous environmental characteristics and the smaller the geographical extent, the better fine spatial resolution performed. In addition, the aggregation of fine-resolution pH or C/N maps at a coarser cell size improved map performance as compared to the direct use of the coarse-resolution predictors. The impact of resolution changes on map accuracy varies according to the mapping procedure, the local environment, and the geographical extent, and should be evaluated in DSM studies to optimize map accuracy.
•Tree competition, stand structure and composition mainly drive tree mortality.•Recent climate change increase tree mortality for the main European tree species.•This over-mortality was greater for ...suppressed than for small or large dominant trees.•Over-mortality of suppressed trees was mainly related to temperature increase.•Over-mortality of large dominant trees was mainly related to rainfall decrease.
Changes in temperature and rainfall linked to recent climate change increase the mortality rates of European temperate tree species. The economic importance of trees and the ecosystem services they provide differ according to their social status (dominant or suppressed trees) and their size. The extent to which climate change impacts these different categories in different ways remains little explored.
Ecophysiological differences between tree size and status suggest different sensitivities to climate change. Dominant trees are exposed to more evapotranspiration than suppressed trees that benefit from buffered climatic conditions. Large trees are able to develop a network of fine roots that allow deeper water and nutrient uptake during water shortage periods, but that have higher water requirements and more physical constraints than small trees due to the fact that they must lift water to greater heights.
We used 207,100 trees from the French forest inventory data (including 3,514 dead trees), representing eight common European tree species. For each species, we separated the tree population into three subsets of suppressed, small dominant and large dominant trees. For each subset, we modelled the mortality observed in a stand in the absence of disturbances (background mortality), with a focus on the differences in sensitivity to recent changes in temperature and rainfall.
After having taken the main mortality drivers related to competition into account, as well as stand characteristics including logging intensity effect, we assessed the over-mortality linked to the recent changes in temperature and rainfall for each of the three subsets.
When considering both changes in temperature and rainfall, the climate change related to over-mortality was greater for suppressed than for small or large dominant trees, for all the species. Over-mortality of suppressed trees was related to temperature increase, whereas a maximum vulnerability related to rainfall decrease was observed for large dominant trees.
Over-mortality driven by climate change not only concerns large and dominant trees, but small and especially suppressed ones as well. These results suggest that in addition to wood production, forest renewal and ecosystem services associated with understorey vegetation are threatened by the recent changes in temperature and rainfall in European temperate forests.
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