The Influence of Recent Climate Change on Tree Height Growth Differs with Species and Spatial Environment

Tree growth has been reported to increase in response to recent global climate change in controlled and semi-controlled experiments, but few studies have reported response of tree growth to increased temperature and atmospheric carbon dioxide (CO2) concentration in natural environments. This study addresses how recent global climate change has affected height growth of trembling aspen (Populus tremuloides Michx) and black spruce (Picea mariana Mill B.S.) in their natural environments. We sampled 145 stands dominated by aspen and 82 dominated by spruce over the entire range of their distributions in British Columbia, Canada. These stands were established naturally after fire between the 19th and 20th centuries. Height growth was quantified as total heights of sampled dominant and co-dominant trees at breast-height age of 50 years. We assessed the relationships between 50-year height growth and environmental factors at both spatial and temporal scales. We also tested whether the tree growth associated with global climate change differed with spatial environment (latitude, longitude and elevation). As expected, height growth of both species was positively related to temperature variables at the regional scale and with soil moisture and nutrient availability at the local scale. While height growth of trembling aspen was not significantly related to any of the temporal variables we examined, that of black spruce increased significantly with stand establishment date, the anomaly of the average maximum summer temperature between May-August, and atmospheric CO2 concentration, but not with the Palmer Drought Severity Index. Furthermore, the increase of spruce height growth associated with recent climate change was higher in the western than in eastern part of British Columbia. This study demonstrates that the response of height growth to recent climate change, i.e., increasing temperature and atmospheric CO2 concentration, did not only differ with tree species, but also their growing spatial environment

Adaptation de la gestion forestière au changement de climat - Biodiversité du sol et fonctionnement de l'écosystème en réponse à la diminution de la densité des peuplements

International audienceGlobal warming induces new constraints on forest ecosystems and requires forest management adaptation. The reduction of stand density is currently debated in France as a potential tool to face increasing climate change-induced tree mortality risk due to summer drought by improving forest resistance to water stress. Our study aimed to assess the potential impact of this forest management adaptation on soil biodiversity, i.e. the detrital food web, and ecosystem functioning, i.e. litter and soil organic matter decomposition processes. We took advantage of a large-scale, multi-site experimental network of long-term forestry trials experimentally manipulating oak stand density through thinning operations in contrasted stand age and local abiotic context. Our results provide evidence that reducing stand density will have substantial impacts on the detrital food web structure, with cascading effects on soil functioning. While microbial biomass had little response, the effect of stand density on microbial-feeding nematodes was much more contrasted. Microarthropods such as collembolan and oribatid mites as well as diplopoda and anecic earthworms were depleted by stand density reduction. In contrast, endogeic earthworms were beneficially affected. Litter quality and decomposability decreased with stand density reduction while standard litter decomposition increased. Therefore, in situ litter decomposition was lower and carbon sequestration higher at intermediate stand density. Exploratory analysis using causal diagrams, i.e. path analyses, highlighted that those changes were mainly related to understory vegetation, microclimate and soil pH conditions alterations Overall, our study emphasizes that managing stand density of oak forests at intermediate level appears as the best way to optimize the trade-off between improving forest resistance to drought and preserving soil biodiversity and ecosystem functioning

Adaptation de la gestion forestière au changement de climat - Biodiversité du sol et fonctionnement de l'écosystème en réponse à la diminution de la densité des peuplements

International audienceGlobal warming induces new constraints on forest ecosystems and requires forest management adaptation. The reduction of stand density is currently debated in France as a potential tool to face increasing climate change-induced tree mortality risk due to summer drought by improving forest resistance to water stress. Our study aimed to assess the potential impact of this forest management adaptation on soil biodiversity, i.e. the detrital food web, and ecosystem functioning, i.e. litter and soil organic matter decomposition processes. We took advantage of a large-scale, multi-site experimental network of long-term forestry trials experimentally manipulating oak stand density through thinning operations in contrasted stand age and local abiotic context. Our results provide evidence that reducing stand density will have substantial impacts on the detrital food web structure, with cascading effects on soil functioning. While microbial biomass had little response, the effect of stand density on microbial-feeding nematodes was much more contrasted. Microarthropods such as collembolan and oribatid mites as well as diplopoda and anecic earthworms were depleted by stand density reduction. In contrast, endogeic earthworms were beneficially affected. Litter quality and decomposability decreased with stand density reduction while standard litter decomposition increased. Therefore, in situ litter decomposition was lower and carbon sequestration higher at intermediate stand density. Exploratory analysis using causal diagrams, i.e. path analyses, highlighted that those changes were mainly related to understory vegetation, microclimate and soil pH conditions alterations Overall, our study emphasizes that managing stand density of oak forests at intermediate level appears as the best way to optimize the trade-off between improving forest resistance to drought and preserving soil biodiversity and ecosystem functioning