References of "Claessens, Hugues"
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See detailGrowth partitioning within beech trees (Fagus sylvatica L.) varies in response to summer heat waves and related droughts
Latte, Nicolas ULg; Lebourgeois, François; Claessens, Hugues ULg

in Trees (2016), 30(1), 189-201

To characterize growth partitioning within the tree and its responses to climate, we studied 8 dominant beech trees (Fagus sylvatica L.) of a pure, even-aged 98-year-old stand in Belgium. We sampled 10 ... [more ▼]

To characterize growth partitioning within the tree and its responses to climate, we studied 8 dominant beech trees (Fagus sylvatica L.) of a pure, even-aged 98-year-old stand in Belgium. We sampled 10 disks along the stem from breast height to treetop and examined the inter-annual patterns of, and discrepancies between, ring-area and volume increments by performing detailed stem analysis and dendroecological investigations. Although the common inter-annual variation among all increment series was high, we observed increasing growth variability and climate sensitivity with height, leading to notable bole-crown discrepancies. Both the common inter-annual variation and bole-crown discrepancies were mainly driven by summer heat waves and related droughts of the previous year, and spring droughts of the current year. Despite these discrepancies, the radial growth at breast height can be considered a good estimate of the tree volume increment but not for the purpose of focusing on climatic effects of isolated years. Extreme climatic conditions increase the risk of inaccurate estimations. The results of the present study are discussed in relation to tree ecophysiology hypotheses. [less ▲]

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See detailMapping of riparian invasive species with supervised classification of Unmanned Aerial System (UAS) imagery
Michez, Adrien ULg; Piégay, Hervé; Lisein, Jonathan ULg et al

in International Journal of Applied Earth Observation and Geoinformation (2016), 44

Riparian zones are key landscape features, representing the interface between terrestrial and aquatic ecosystems. Although they have been influenced by human activities for centuries, their degradation ... [more ▼]

Riparian zones are key landscape features, representing the interface between terrestrial and aquatic ecosystems. Although they have been influenced by human activities for centuries, their degradation has increased during the 20th century. Concomitant with (or as consequences of) these disturbances, the invasion of exotic species has increased throughout the world’s riparian zones. In our study, we propose a easily reproducible methodological framework to map three riparian invasive taxa using Unmanned Aerial Systems (UAS) imagery: Impatiens glandulifera Royle, Heracleum mantegazzianum Sommier and Levier, and Japanese knotweed (Fallopia sachalinensis (F. Schmidt Petrop.), Fallopia japonica (Houtt.) and hybrids). Based on visible and near-infrared UAS orthophoto, we derived simple spectral and texture image metrics computed at various scales of image segmentation (10,30, 45, 60 using eCognition software). Supervised classification based on the random forests algorithm was used to identify the most relevant variable (or combination of variables) derived from UAS imagery for mapping riparian invasive plant species. The models were built using 20% of the dataset, the rest of the dataset being used as a test set (80%). Except for H. mantegazzianum, the best results in terms of global accuracy were achieved with the finest scale of analysis (segmentation scale parameter = 10). The best values of overall accuracies reached 72%, 68%, and 97% for I. glandulifera, Japanese knotweed, and H. mantegazzianum respectively. In terms of selected metrics, simple spectral metrics (layer mean / camera brightness) were the most used. Our results also confirm the added value of texture metrics (GLCM derivatives) for mapping riparian invasive species. The results obtained for I. glandulifera and Japanese knotweed do not reach sufficient accuracies for operational applications. However, the results achieved for H. mantegazzianum are encouraging. The high accuracies values combined to relatively light model-inputs needed (delineation of a few umbels) make our approach a serious contender as a cost-effective tool to improve the field management of H. mantegazzianum. [less ▲]

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See detailReview of shrubs and trees in intensive ruminant systems in temperate areas
Vandermeulen, Sophie ULg; Ramìrez-Restrepo, Carlos Alberto; Beckers, Yves ULg et al

Conference (2016, January)

Using shrubs and trees as forage for ruminants is common in extensive production systems in the tropics, as well as the Mediterranean region and mountain areas. In temperate Europe, the intensification of ... [more ▼]

Using shrubs and trees as forage for ruminants is common in extensive production systems in the tropics, as well as the Mediterranean region and mountain areas. In temperate Europe, the intensification of agriculture led to a decline in the numbers of woody perennials on farmlands. A review of the potential uses of shrubs and trees in temperate intensive systems shows that this concept is rather recent. Few studies have been investigating the potential outputs and limitations of shrubs and trees forage in production systems, while in Belgium and other European countries, agro-environmental policies are promoting the establishment of hedgerows and woody strips that provide shelter to animals against variable climate conditions. Furthermore, it has been found that ruminant species browse the plants, or alternatively, the forage is harvested and fed fresh or preserved as hay, silages or pellets. In both cases, consequences on feed intake control, woody plant survival, dry matter (DM) production and forage quality in terms of crude protein content reduction have been documented. In addition, depending on the plant species and the preservation method, bio-active plant metabolites such as condensed tannins (CT) are also present in the range of less than 1 to more than 100 g/kg foliage DM. Overall, CT may reduce ruminal N degradation, methanogenesis and nematode parasites infestation, while enhancing microbial-protein synthesis, feed use efficiency and systemic animal physiology. Planting shrubs and trees into the agricultural landscape (i.e. silvopastoral system) can further improve biodiversity and environmental services. Nevertheless, agronomic practices, farm management or environmental policy limitations may reduce the use of this fodder resource. Therefore, although silvopastoral systems seem promising in temperate ruminant systems, the current knowledge to their introduction and efficient management need to be cautiously considered. [less ▲]

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See detailClassification of riparian forest species and health condition using multi-temporal and hyperspatial imagery from unmanned aerial system
Michez, Adrien ULg; Piégay, Hervé; Lisein, Jonathan ULg et al

in Environmental Monitoring and Assessment (2016), 188(3),

Riparian forests are critically endangered many anthropogenic pressures and natural hazards. The importance of riparian zones has been acknowledged by European Directives, involving multi-scale monitoring ... [more ▼]

Riparian forests are critically endangered many anthropogenic pressures and natural hazards. The importance of riparian zones has been acknowledged by European Directives, involving multi-scale monitoring. The use of this very high resolution and hyperspatial imagery in a multi-temporal approach is an emerging topic. The trend is reinforced by the recent and rapid growth of the use of the unmanned aerial system (UAS), which has prompted the development of innovative methodology. Our study proposes a methodological framework to explore how a set of multi-temporal images acquired during a vegetative period can differentiate some of the deciduous riparian forest species and their health conditions. More specifically, the developed approach intends to identify, through a process of variable selection, which variables derived from UAS imagery and which scale of image analysis are the most relevant to our objectives. The methodological framework is applied to two study sites to describe the riparian forest through two fundamental characteristics: the species composition and the health condition. These characteristics were selected not only because of their use as proxies for the riparian zone ecological integrity but also because of their use for river management. The comparison of various scales of image analysis identified the smallest OBIA objects (ca. 1 m²) as the most relevant scale. Variables derived from spectral information (bands ratio's) were identified as the most appropriate, followed by variables related to the vertical structure of the forest. Classification results show good overall accuracies for the species composition of the riparian forest (five classes, 79.5 and 84.1 % for Site 1 and Site 2). The classification scenario regarding the health condition of the black alders of the Site 1 performed the best (90.6 %). The quality of the classification models developed with a UAS-based, cost-effective, and semi-automatic approach competes successfully with those developed using more expensive imagery, such as multispectral and hyperspectral airborne imagery. The high overall accuracy results obtained by the classification of the diseased alders open the door to applications dedicated to monitoring of the health conditions of riparian forest. Our methodological framework will allow UAS users to manage large imagery metrics datasets derived from those dense time series. [less ▲]

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See detailVegetation classification and biogeography of European floodplain forests and alder carrs
Douda, Jan; Boublik, Karel; Slezak, Michal et al

in Applied Vegetation Science (2016)

Aim: Formalized classifications synthesizing vegetation data at the continental scale are being attempted only now, although they are of key importance for nature conservation planning. Therefore, we aim ... [more ▼]

Aim: Formalized classifications synthesizing vegetation data at the continental scale are being attempted only now, although they are of key importance for nature conservation planning. Therefore, we aim to provide a vegetation classification and to describe the main iogeographical patterns of floodplain forests and alder carrs in Europe. Location: Europe. Methods: A database of more than 40 000 vegetation plots of floodplain forests and alder carrs across Europe was compiled. After geographic stratification, 16 392 plots were available for classification, which was performed using the supervised method Cocktail. We also searched for new associations using semi-supervised K-means classification. The main biogeographic patterns and climate-related gradients in species composition were determined using detrended correspondence analysis and cluster analysis. Results: Thirty associations of floodplain forests and alder carrs were distinguished, which belong to five alliances. The Alnion incanae includes riparian, seepage and hardwood floodplain forests in the nemoral and hemiboreal zones (dominated by Alnus glutinosa and Fraxinus excelsior) and in the boreal zone (dominated by A. incana). The Osmundo-Alnion represents oceanic vegetation dominated by Alnus glutinosa, Fraxinus angustifolia and F. excelsior distributedmostly on the Iberian Peninsula and composed of species with Atlantic distribution and Iberian endemics. The Populion albae comprises floodplain forests frequently dominated by Fraxinus angustifolia, Populus alba and P. nigra that arewidespread in floodplains of large rivers under summer-dry climates in the Mediterranean region. The Platanion orientalis represents easternMediterranean floodplain forests dominated by Platanus orientalis. The Alnion glutinosae includes forest swamps dominated by Alnus glutinosa distributed mostly in the nemoral and hemiboreal zones. The main biogeographic patterns within European floodplain forests and alder carrs reflect the climatic contrasts between the Mediterranean, nemoral, boreal andmountain regions. Oceanic floodplain forests differ fromthose in the rest of Europe. The hydrological regime appears to be themost important factor influencing species compositionwithin regions. Conclusions: This study is the first applying a formalized classification at the association level for a broad vegetation type at the continental scale. The proposed classification provides the scientific basis for the necessary improvement of the habitat classification systems used in European nature conservation. [less ▲]

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See detailDendroécologie du hêtre en forêt de Soignes : Les cernes des arbres nous renseignent sur les changements récents et futurs
Latte, Nicolas ULg; Kint, Vincent; Drouet, Thomas et al

in FORÊT.NATURE (2015), 137(Octobre-Novembre-Décembre), 24-37

La dendroécologie combine la dendrochronologie et l’écologie forestière. Elle a permis d’analyser les cernes des hêtres de la forêt de Soignes et de comparer les tendances dans le contexte plus large des ... [more ▼]

La dendroécologie combine la dendrochronologie et l’écologie forestière. Elle a permis d’analyser les cernes des hêtres de la forêt de Soignes et de comparer les tendances dans le contexte plus large des hêtraies de Belgique. Depuis la fin des années ‘70, le hêtre devient de plus en plus sensible au climat, surtout en Soignes. L’augmentation de la fréquence et de l’intensité des sécheresses printanières et des canicules ont affecté négativement la croissance annuelle des hêtres. Les prévisions climatiques pour le 21e siècle présage une rapide aggravation. Les risques encourus par l’essence aboutissent à de nouvelles réflexions sur la gestion de la hêtraie de Soignes. Pour les peuplements existants : une sylviculture dynamique avec des éclaircies fortes et fréquentes afin de limiter la concurrence pour les ressources et favoriser la croissance individuelle des arbres. Pour la régénération des vieilles hêtraies : les remplacer par d’autres essences plus tolérantes ou favoriser le mélange et confiner le hêtre aux surfaces limitées des stations les plus fraîches. Un risque mesuré pourrait être pris en regard du rôle patrimonial des hêtraies cathédrales en Soignes. Toutefois, ce faciès peut être obtenu avec d’autres essences. [less ▲]

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See detailDosage de la lumière pour maintenir la coexistence d’espèces d’ombre et de demi-ombre dans la régénération de la futaie irrégulière
Ligot, Gauthier ULg; Balandier, Philippe; Courbaud, Benoît et al

in Revue Forestière Française (2015), 3

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See detailDiscrimination of deciduous tree species from time series of unmanned aerial system imagery
Lisein, Jonathan ULg; Michez, Adrien ULg; Claessens, Hugues ULg et al

in PLoS ONE (2015), 10(11),

Technology advances can revolutionize Precision Forestry by providing accurate and fine forest information at tree level. This paper addresses the question of how and particularly when Unmanned Aerial ... [more ▼]

Technology advances can revolutionize Precision Forestry by providing accurate and fine forest information at tree level. This paper addresses the question of how and particularly when Unmanned Aerial System (UAS) should be used in order to efficiently discriminate deciduous tree species. A time series of high resolution UAS imagery was collected to cover the growing season from leaf flush to leaf fall. Full benefit was taken of the temporal resolution of UAS acquisition, one of the most promising features of small drones. The disparity in forest tree phenology is at the maximum during early spring and late autumn. But the phenology state that optimized the classification result is the one that minimizes the spectral variation within tree species groups and, at the same time, maximizes the phenologic differences between species. Sunlit tree crowns (5 deciduous species groups) were classified using a Random Forest approach for monotemporal, two-date and three-date combinations. The end of leaf flushing was the most efficient single-date time window. Multitemporal datasets definitely improve the overall classification accuracy. But single-date high resolution orthophotomosaics, acquired on optimal time-windows, result in a very good classification accuracy (overall out of bag error of 16%). [less ▲]

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See detailLa carte bioclimatique de Wallonie : un nouveau découpage écologique du territoire pour le choix des essences forestières
Van der Perre, Raphaèle; Bythell, Stephen; Bogaert, Patrick et al

in Forêt-Nature (2015), (135), 47-58

Dans le cadre de la révision du Fichier écologique des essences et du Guide de boisement, les deux principaux outils à disposition du gestionnaire pour la bonne adéquation essence-station, un nouveau ... [more ▼]

Dans le cadre de la révision du Fichier écologique des essences et du Guide de boisement, les deux principaux outils à disposition du gestionnaire pour la bonne adéquation essence-station, un nouveau découpage du territoire a été réalisé sur base de données climatiques actualisées et à la lumière des nouvelles connaissances en autécologie des essences. Dans un premier temps, les données de températures, de précipitations et de rayonnement solaire, de 1986 à 2005, ont été rassemblées et spatialisées sur une maille de 500 x 500 mètres. Le croisement de ces données avec les sensibilités écologiques des essences a permis d’aboutir à un nouveau découpage du territoire en dix zones bioclimatiques. Ces dix zones remplacent les territoires écologiques comme porte d’entrée du Guide de boisement. Elles permettent également de proposer des cartes de zones à risques pour les différentes essences en fonction de paramètres climatiques spécifiques et selon les quatre niveaux d’aptitude définis pour le nouveau Fichier écologique des essences (optimum, tolérance, tolérance élargie et exclusion). [less ▲]

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See detailIncreased tree-growth synchronization of beech (Fagus sylvatica L.) in response to climate change in northwestern Europe
Latte, Nicolas ULg; Lebourgeois, François; Claessens, Hugues ULg

in Dendrochronologia (2015), 33

To better understand how the radial growth of beech (Fagus sylvatica L.) high forests has responded to climate change, we selected 12 sites (137 trees) with optimal growing conditions along a W − E ... [more ▼]

To better understand how the radial growth of beech (Fagus sylvatica L.) high forests has responded to climate change, we selected 12 sites (137 trees) with optimal growing conditions along a W − E altitudinal gradient (67–590 m) in Belgium. We evaluated temporal changes in growth response to climate by using pointer year analysis, moving mean sensitivities (1860–2011), and moving bootstrapped correlation coefficients (1952–2011). The strongest driving climatic variables were identified by using the partial least squares method. The common patterns of growth trends, pointer years, and mean sensitivities among sites provided evidences for the impact of environmental changes operating at a regional scale. The results of growth–climate analysis indicated that these changes were strongly influenced by the climatic conditions of the previous year. The climate sensitivity of beech increased progressively in response to more frequent and intense heat waves and warming-related droughts, especially during recent decades, leading to remarkable inter-site synchronization. The changes were much more pronounced for sites located in lowlands (<300 m). The differences in growth responses along the altitudinal gradient and the consequences of warming for beech growth and physiology are discussed. [less ▲]

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See detailEvolution de la chalarose du frêne en Wallonie
Gerarts, Fanny ULg; Chandelier, Anne; Claessens, Hugues ULg et al

in Forêt Wallonne (2015), 134

Depuis quelques années, la maladie du frêne, la chalarose, cause des dégâts catastrophiques dans les frênaies européennes, au point de poser la question de l'avenir du frêne. Avec cet article, l ... [more ▼]

Depuis quelques années, la maladie du frêne, la chalarose, cause des dégâts catastrophiques dans les frênaies européennes, au point de poser la question de l'avenir du frêne. Avec cet article, l'Observatoire wallon de la santé des forêts fait le point sur la situation en Wallonie et propose des voies de gestion des peuplements affectés par cette maladie. [less ▲]

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See detailNote de référence pour la gestion du frêne dans le contexte de la crise liée à la chalarose
Delahaye, Laurence; Herman, Marc; Claessens, Hugues ULg et al

in Forêt.Nature (2015), (136), 54-58

La chalarose, ou maladie du frêne, est présente sur tout le territoire wallon depuis 2012. Les jeunes plantations de moins de 90 cm de circonférence sont les plus touchées. Toutefois, des sujets sains ... [more ▼]

La chalarose, ou maladie du frêne, est présente sur tout le territoire wallon depuis 2012. Les jeunes plantations de moins de 90 cm de circonférence sont les plus touchées. Toutefois, des sujets sains semblent cohabiter avec des arbres atteints. Il importe donc de ne pas les couper prématurément au risque de voir disparaître la sylviculture du frêne en Wallonie. Le champignon responsable de la maladie, Hymenoscyphus fraxineus, provoque des nécroses au collet, causant un affaiblissement important de l'arbre favorable à l'infection des racines par des armillaires présentes dans le sol. Pour le forestier, c'est donc l'état du collet qui prime sur l'état du houppier dans sa décision d'intervenir. L'observatoire wallon de la santé des forêts préconise de garder dans le processus normal des coupes les sujets de plus de 90 cm non atteints au collet afin de maintenir des semenciers susceptibles d'assurer une régénération moins sensible à la chalarose. Les peuplements mélangés sont également à favoriser. Un outil d'aide à la gestion en fonction de la circonférence des arbres, du type de peuplement et des symptômes observés est proposé en fin d'article. [less ▲]

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See detailCharacterization of riparian zones in wallonia (belgium)
Michez, Adrien ULg; Piégay, Hervé; Lejeune, Philippe et al

Conference (2014, June 16)

The present study proposes an innovative approach to automatically extract riparian zone characteristics in order to assess its quality, from pre-determined river management reaches (1-3 km long) to ... [more ▼]

The present study proposes an innovative approach to automatically extract riparian zone characteristics in order to assess its quality, from pre-determined river management reaches (1-3 km long) to regional scale (ca. 13000 km for 1000 management sectors). The aim of this remotely sensed monitoring is to improve the river and riparian zone management and planning by providing some key information for river managers. This first research is exclusively based on data which are available at the regional scale (170000 square km) to develop automated tools to implement the methodology to the whole Walloon river network (13000 km) before 2015 with an update frequency of 3 years (photogrammetric DSM survey frequency). [less ▲]

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See detailForest radiative transfer models: which approach for which application?
Ligot, Gauthier ULg; Balandier, Philippe; Courbaud, Benoît et al

in Canadian Journal of Forest Research = Journal Canadien de la Recherche Forestière (2014), 44(5), 385-397

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See detailLe nouveau fichier écologique des essences. Pourquoi et comment ?
Claessens, Hugues ULg; Bifolchi, Eva; Cordier, Sophie ULg et al

in Forêt Wallonne (2014), (129), 60-70

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See detailLa régénération naturelle des hêtraies-chênaies en lumière : approche expérimentale en forêt ardennaise
Ligot, Gauthier ULg; Claessens, Hugues ULg; Baudry, Olivier et al

in Forêt Wallonne (2014), (129), 19-21

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See detailNouvelles courbes de productivité harmonisées pour le douglas, l'épicéa et les mélèzes en wallonie
Perin, Jérôme ULg; De Thier, Olivier ULg; Claessens, Hugues ULg et al

in Forêt Wallonne (2014), 129(mars/avril),

Les courbes de productivité sont des outils de diagnostic précieux en gestion forestière. Elles permettent d'estimer le potentiel de production d'un peuplement de structure équienne d’âge connu à partir d ... [more ▼]

Les courbes de productivité sont des outils de diagnostic précieux en gestion forestière. Elles permettent d'estimer le potentiel de production d'un peuplement de structure équienne d’âge connu à partir d'une mesure ponctuelle de la hauteur dominante. Une nouvelle génération de modèles de productivité plus fiables ont été développés pour l'épicéa, le douglas et les mélèzes en Wallonie et ont été intégrés au sein d'un outil informatique de diagnostic simple et rapide d'utilisation. [less ▲]

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See detailCharacterization of riparian zones in wallonia (belgium) from local to regional scale using aerial lidar data and photogrammetric DSM
Michez, Adrien ULg; Piégay, Hervé; Lejeune, Philippe et al

in EARSeL eProceedings (2014), 13(2),

The present study proposes an innovative approach to automatically extract riparian zone characteristics in order to assess its quality, from pre-determined river management reaches (1-3 km long) to ... [more ▼]

The present study proposes an innovative approach to automatically extract riparian zone characteristics in order to assess its quality, from pre-determined river management reaches (1-3 km long) to regional scale (ca. 13000 km for 1000 management sectors). The aim of this remotely sensed monitoring is to improve the river and riparian zone management and planning by providing some key information for river managers. The methodology was developed based on two watersheds covering approximately 500 km of river network (ca. 200 management sectors). The riparian zone quality is evaluated through various indicators of its ecological integrity (e.g. longitudinal continuity of riparian forest, mean vegetation height and relative standard deviation), hydromorphological quality and physical settings (e.g. flow channel extent, floodplain width, channel sinuosity). The physical characteristics of the riparian zone are mainly extracted from a high quality Digital Terrain Model (derived from ALS data) while the attributes of the riparian forest are derived from a « hybrid » Canopy Height Model (photogrammetric Digital Surface Model – LiDAR derived DTM). This first research is exclusively based on data which are available at the regional scale (170000 square km) to develop automated tools to implement the methodology to the whole Walloon river network (13000 km) before 2015 with an update frequency of 3 years (photogrammetric DSM survey frequency). Moreover, our approach is based on a photogrammetric Digital Surface Model which is derived from raw images of an orthophoto coverage. As most of European countries are regularly covered by orthophoto surveys, our approach is widely replicable in countries where a quality DTM is available. [less ▲]

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See detailInfluence du changement climatique sur l'accroissement du hêtre en Wallonie
Latte, Nicolas ULg; Claessens, Hugues ULg

Conference (2014, January 28)

Depuis quelques décennies, des signes d’affaiblissement de plus en plus marqués ont été observés sur le hêtre (Fagus sylvatica L.) un peu partout en Europe. L’inquiétude grandissante des gestionnaires ... [more ▼]

Depuis quelques décennies, des signes d’affaiblissement de plus en plus marqués ont été observés sur le hêtre (Fagus sylvatica L.) un peu partout en Europe. L’inquiétude grandissante des gestionnaires forestiers s’inscrit dans la problématique complexe du changement climatique. Une étude dendroécologique a donc été réalisée afin de mieux comprendre la relation entre l’accroissement du hêtre et son environnement. Des mesures de cernes ont été effectuées sur des échantillons de bois issus de 158 hêtres sélectionnés dans douze hêtraies (de 84 à 206 ans) situées le long du gradient climatique de Wallonie (de 67 à 590 m d’altitude). L’analyse de l’évolution temporelle de l’accroissement et de sa relation avec le climat a abouti à 3 résultats majeurs : (1) l’accroissement du hêtre a augmenté à partir des années 30 puis à diminuer de manière soutenue à partir des années 1980, (2) la sensibilité climatique des hêtraies a aussi fortement augmenté et cette augmentation est plus forte pour les peuplements de base altitude, et (3) les températures plus élevées en été et en début d’automne ont un impact négatif de plus en plus prononcé sur l’accroissement. Le réchauffement global rend les arbres de plus en plus dépendants de l’eau disponible (précipitation et sol). Les sécheresses et canicules plus fréquentes et intenses semblent progressivement affaiblir les arbres que puissent de plus en plus dans leur réserve. L’étude comprend une discussion complète intégrant l’interprétation écophysiologique des résultats mis en évidence. [less ▲]

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