Ecological response of tree saplings to simulated climate change along an elevational gradient (CLIMARBRE)

Switzerland will face higher temperature increases than the global average, which will have strong impacts on the mountain ecosystems. How tree species will respond to future climate change scenarios, and what mechanisms will they adopt, remains as a gap of knowledge in ecological research. Foresters will have to make short-term decisions and plan future managements under the great uncertainty of climate change and they demand answers to know if the current species will cope with the predicted climate change and to what extent the ecological goods and services will be affected (e.g. timber industry). The project CLIMARBRE was developed in order to ease and support their decision making by providing an advanced knowledge about the responses of beech and spruce regeneration to simulated climate change (specifically, warmer and drier conditions) in the wooded pastures of the Swiss Jura mountains. This project, which was built on the interface between fundamental research in forestry ecology and applied sciences, should attract the attention of foresters, managers of natural environments and of the general public. By using transplantation along an elevational gradient, in the Jura mountains, ârealisticâ climate conditions were created to specifically simulated three potential future climatic scenarios from the IPCC (from A1B to A2). This space for time approach enabled the assessment of saplingsâ responses to simulated climate change and their acclimation abilities. Saplings adapted to subalpine conditions at 1350 m were collected and transplanted towards lower altitudes exposing them to an average increase of 6.3áµC and a reduction in 30% of precipitation, at the lowest site throughout the study period. The main findings include i) a longer growing season due to induced-elevation warming (downward shift) could not fully account for the species-specific positive growth responses; (ii) the contrasting species growth responses were linked to different sensitivities to elevated vapor-pressure deficits; (iii) models could better account for the growth response to warming after incorporating extreme climatic events and their effects; iv) beech leaves showed an increase of xeromorphism through the increase of the cuticle thickness, vein network and smaller stomata, associated, to a higher leaf area v) which allowed it to grow in warmer conditions while coping with an increase of evaporative; vi) and finally, the linkage between responses at tree, leaf, tissue and soil level, through a multiple level approach, improved the mechanistic understanding of these species capacities to respond to simulated climate change

Vapor-pressure deficit and extreme climatic variables limit tree growth

Assessing the effect of global warming on forest growth requires a better understanding of species-specific responses to climate change conditions. Norway spruce and European beech are among the dominant tree species in Europe and are largely used by the timber industry. Their sensitivity to changes in climate and extreme climatic events, however, endangers their future sustainability. Identifying the key climatic factors limiting their growth and survival is therefore crucial for assessing the responses of these two species to ongoing climate change. We studied the vulnerability of beech and spruce to warmer and drier conditions by transplanting saplings from the top to the bottom of an elevational gradient in the Jura Mountains in Switzerland. We (1) demonstrated that a longer growing season due to warming could not fully account for the positive growth responses, and the positive effect on sapling productivity was species-dependent, (2) demonstrated that the contrasting growth responses of beech and spruce were mainly due to different sensitivities to elevated vapor-pressure deficits (VPD), (3) determined the species-specific limits to VPD above which growth rate began to decline, and (4) demonstrated that models incorporating extreme climatic events could account for the response of growth to warming better than models using only average values. These results support that the sustainability of forest trees in the coming decades will depend on how extreme climatic events will change, irrespective of the overall warming trend

Ecological response of trees to simulated climate change along an altitudinal gradient (CLIMARBRE)

Assessing the impacts of climate change on mountain ecosystems is challenging as it takes several decades to observe an ecological response. Using a transplantation experiment in the Swiss Jura Mountains we study the adaptability of beech and spruce to simulated climate change. In situ ecophysiological measures, e.g. photosynthetic rate at a constant CO2 partial pressure, were undertaken to assess the performance of saplings. Moreover, leaf phenology and growth rate monitoring were performed during the growing season. The main findings include a clear altitudinal effect on growth and photosynthetic capacity of both species and an advanced leaf flushing at lower altitudes

Long-term effects of crop succession, soil tillage and climate on wheat yield and soil properties

International audienceClimate change is increasing crop losses and yield variability with impacts for global food security. In this context, conservation agriculture appears as a potential solution to maintain crop productivity, soil fertility and environmental sustainability. Therefore, understanding the combined effects of soil tillage and crop succession over a long period is of primary interest. In this study, we analyzed data from a 50 year long-term field experiment to assess (i) the change of climatic parameters, wheat yield and soil organic carbon (SOC) content; (ii) the combined effects of crop succession (monoculture vs. crop rotation) and soil tillage system (minimum tillage vs. plough) on wheat yield, SOC content and other soil properties at three soil depths (0-10, 10-20 and 20-50 cm); and (iii) the relative contributions of climatic parameters, wheat phenology and agricultural practices on wheat yield variability. Wheat yield was 16% higher in crop rotation compared to monoculture, while soil tillage system had no significant effect on wheat yield during the period 1977-2016. Despite a SOC content decline over time, which was especially marked during the first ten years of the study, SOC content was 7% higher in the minimum tillage treatment compared to the plough treatment, while crop rotation had no significant effect. In 2016, after 50 years of experimentation, both crop succession and soil tillage systems influenced soil properties. Over the 50-year period, the climatic conditions around the heading phase explained 22% of yield variability, while 18% of this variability was explained by crop succession and 6% by the growing degree days until heading stage. In a context of conservation agriculture promotion, our long-term field experiment provides key evidence that the combination of both minimum soil tillage and crop rotation improves soil fertility and crop productivity

Vapor-pressure deficit and extreme climatic variables limit tree growth

Assessing the effect of global warming on forest growth requires a better understanding of species-specific responses to climate change conditions. Norway spruce and European beech are among the dominant tree species in Europe and are largely used by the timber industry. Their sensitivity to changes in climate and extreme climatic events, however, endangers their future sustainability. Identifying the key climatic factors limiting their growth and survival is therefore crucial for assessing the responses of these two species to ongoing climate change. We studied the vulnerability of beech and spruce to warmer and drier conditions by transplanting saplings from the top to the bottom of an elevational gradient in the Jura Mountains in Switzerland. We (1) demonstrated that a longer growing season due to warming could not fully account for the positive growth responses, and the positive effect on sapling productivity was species-dependent, (2) demonstrated that the contrasting growth responses of beech and spruce were mainly due to different sensitivities to elevated vapor-pressure deficits (VPD), (3) determined the species-specific limits to VPD above which growth rate began to decline, and (4) demonstrated that models incorporating extreme climatic events could account for the response of growth to warming better than models using only average values. These results support that the sustainability of forest trees in the coming decades will depend on how extreme climatic events will change, irrespective of the overall warming trend