• Energy Research

AbstractSemi‐natural mountain grasslands are increasingly exposed to environmental stress under climate change. However, which are the environmental factors that limit plants in these grasslands? Also, is the present management effective against these changes? Fitness‐related functional traits may offer a way to detect changes in performance and provide new insights into their vulnerability to climate change. We investigated changes in performance and variability of functional traits of the mountain grassland target species Arnica montana along a climate gradient in Central German low mountain ranges. This gradient represents at its lower end climate conditions that are expected at its upper end under future climate change. We measured vegetative, generative, and physiological traits to account for multiple ways of plant responses to the environment. Using mixed effects and multivariate models, we evaluated changes in trait values among individuals as well as the variability of their populations in order to assess performance under changing summer aridity and different management regimes. Fitness‐related performance of most traits showed strongly positive associations with reduced summer aridity at higher elevations, while only specific leaf area and leaf dry matter content showed no association. This suggests a higher performance level at less arid montane sites and that the physiological traits are less sensitive to this climate change factor. The coefficient of variation of almost all traits declined steadily with decreasing site aridity. We suggest that this reduced variability indicates a lower environmental stress level for A. montana toward its environmental optimum at montane elevations, especially because the trait performance increased simultaneously. Surprisingly, management factors and habitat characteristics had only low influence on both trait performance and variability. In summary, summer aridity had a stronger effect to shape the trait performance and variability of A. montana under increased environmental stress than management and other habitat characteristics.

ABSTRACT The establishment and survival of seedlings are critical stages in the life cycle of plants and therefore usually well timed to humid and favourable conditions. Climate projections suggest that the threatened mountain grassland species Arnica montana may be increasingly exposed to drought stress. However, studies that focus on the species’ early development are missing. We evaluated impacts of drought‐induced stress on A. montana seedlings in their early establishment phase and identified traits that could cause the species’ fitness to decline. In a greenhouse experiment, we tested the response of A. montana seedlings to different drought levels (moderate, strong, extreme). To assess their fitness under increasing drought, we evaluated survival of the seedlings based on four senescence stages and measured the performance of above‐ and belowground morphological and physiological functional traits. Arnica montana seedlings showed high resistance to drought. Senescence accelerated and survival declined only under strong and extreme drought conditions. However, the seedlings’ vegetative performance decreased even with moderate drought, as indicated by smaller values of most leaf traits and some root traits. Physiological trait response was less sensitive. Drought stress hinders the establishment and survival of A. montana seedlings. Following the functional trait responses to drought and their association with survival, we suggest declining leaf length, leaf width, and leaf number are sensitive traits that can lead to a decline in performance.

Questions Mountain grasslands can be strongly affected by extreme droughts such as those related to climate change. What are the impacts of extreme droughts on community composition, diversity, Ellenberg indicator scores and species groups in oligotrophic montane Nardus grasslands, and what are the associated mechanisms of vegetation change? Location Rh��n Mountains, Germany Methods In three consecutive years, we investigated the effects of yearly droughts (April-August) in an experimental setup with rainout shelters. Due to the coincidence of ambient extreme dry conditions in those years and our artificial rainfall reduction, we evaluated the contribution to community change of ambient drought conditions and the treatments. We analysed community composition changes by applying redundancy analysis to species differences in comparison with the pre-treatment year, and used mixed-effects models to test for changes in community-weighted means of Ellenberg indicator scores, sociological, and functional groups. Results We found significant changes in species abundances and community structures in response to drought. Evenness increased, but species richness remained rather stable over time. Ellenberg indicator scores for temperature and nitrogen increased, while the score for moisture decreased. Simultaneously, dominant species declined and subdominants increased. Changes occurred with a time lag and were largely driven by the high ambient drought level and less by the artificial treatments. Conclusions Our results show that drought-related community composition changes in Nardus grasslands occur across community structures, characteristic species, and species groups. The post-drought recovery of the community is shaped by community filters, which particularly allow subdominants to take advantage of newly available niches in the matrix, even if they lack strong drought tolerance. Our findings indicate a certain resilience of the community to climate-change-related droughts, which suggests that the observed changes should not lead to an accelerated short-term decline of these grasslands, but that this cannot be excluded in the long term.

AbstractQuestionsMountain grasslands can be strongly affected by extreme droughts such as those related to climate change. What are the impacts of extreme droughts on community composition, diversity, Ellenberg indicator scores and species groups in oligotrophic montane Nardus grasslands, and what are the associated mechanisms of vegetation change?LocationRhön Mountains, Germany.MethodsOver three consecutive years, we investigated the effects of yearly droughts (April–August) in an experimental setup with rainout shelters. Owing to the coincidence of ambient extreme dry conditions in those years and our artificial rainfall reduction, we evaluated the contribution to community change of ambient drought conditions and the treatments. We analysed changes in community composition by applying redundancy analysis to species differences in comparison with the pretreatment year, and used mixed‐effects models to test for changes in community‐weighted means of Ellenberg indicator scores, sociological and functional groups.ResultsWe found significant changes in species abundance and community structures in response to drought. Evenness increased, but species richness remained rather stable over time. Ellenberg indicator scores for temperature and nitrogen increased, whereas the score for moisture decreased. Simultaneously, dominant species declined and subdominants increased. Changes occurred with a time lag and were driven largely by the high ambient drought level and less by the artificial treatments.ConclusionsOur results show that drought‐related changes in community composition in Nardus grasslands occur across community structures, characteristic species, and species groups. The post‐drought recovery of the community is shaped by community filters, which in particular allow subdominants to take advantage of newly available niches in the matrix, even if they lack strong drought tolerance. Our findings indicate a certain resilience of the community to droughts related to climate change, which suggests that the observed changes should not lead to an accelerated short‐term decline in these grasslands, but that this cannot be excluded in the long term.

Semi-natural mountain grasslands are increasingly exposed to environmental stress under climate change. However, which are the environmental factors that limit plants in these grasslands? Also, is the present management effective against these changes? Fitness-related functional traits may offer a way to detect changes in performance and provide new insights into their vulnerability to climate change. We investigated changes in performance and variability of functional traits of the mountain grassland target species Arnica montana along a climate gradient in Central German low mountain ranges. This gradient represents at its lower end climate conditions that are expected at its upper end under future climate change. We measured vegetative, generative and physiological traits to account for multiple ways of plant response to the environment. Using mixed effects and multivariate models, we evaluated changes in trait values among individuals as well as the variability of their populations in order to assess performance under changing summer aridity and different management regimes. Fitness-related performance of most traits showed strongly positive associations with reduced summer aridity at higher elevations, while only specific leaf area and leaf dry matter content showed no association. This suggests a higher performance level at less arid montane sites and that the physiological traits are less sensitive to this climate change factor. The coefficient of variation of almost all traits declined steadily with decreasing site aridity. We suggest that this reduced variability indicates a lower environmental stress level for A. montana towards its environmental optimum at montane elevations, especially because the trait performance increased simultaneously. Surprisingly, management factors and habitat characteristics had only low influence on both trait performance and variability. In summary, summer aridity had a stronger effect to shape the trait performance and variability of A. montana under increased environmental stress than management and other habitat characteristics. The plant functional trait data of Arnica montana (individuals and populations) and data about the populations site and habitat characteristics. Modification date: 03/03/2020 Temporal coverage: Measurements taken in June 2019 Spatial Coverage: East Hesse (Vogelsberg, Spessart, Rhön Mountains) / North-East Bavaria (Rhön Mountains), Germany CSV separator: Semicolon

The establishment and survival of seedlings are critical stages in the life cycle of plants and therefore usually well timed to humid and favourable conditions. Climate projections suggest that the threatened mountain grassland species Arnica montana may be increasingly exposed to drought stress. However, studies that focus on the species’ early development are missing. We evaluated impacts of drought-induced stress on A. montana seedlings in their early establishment phase and identified traits for the species’ fitness decline. In a greenhouse experiment, we tested the response of A. montana seedlings to different drought levels (moderate, strong, extreme). To assess their fitness under increasing drought, we evaluated the survival of the seedlings based on four senescence stages and measured the performance of above- and belowground morphological and physiological functional traits. Arnica montana seedlings showed high resistance to drought. Senescence accelerated and survival declined only under strong and extreme drought conditions. However, the seedlings’ vegetative performance decreased even with moderate drought, as indicated by smaller values of most leaf traits and some root traits. Physiological trait response was less sensitive. Drought stress hinders the establishment and survival of A. montana seedlings. Following the functional trait responses to drought and their associations with survival, we suggest declining leaf length, leaf width, and leaf number as sensitive traits that can lead to a decline performance.