Integrated assessment to aid mitigation of negative impacts by THREE global change Drivers on alpine biodiversity and ecosystem function

Mountain areas provide important habitats for many plant and animal species, but they also contribute with important ecosystem functions and services such as carbon storage, areas for livestock grazing, and regulation of floods and landslides. At the same time, mountain ecosystems are particularly vulnerable to human made global change. Climate warming, nitrogen deposition and grazing are important global change drivers with impacts on biodiversity and carbon cycling. Both climate warming and nitrogen deposition increase nutrient availability and therefore biomass and plant productivity, often with negative impacts on biodiversity. Further, these drivers can increase carbon storage in the soil because of increased decomposition of organic plant material. Grazing also increases the nutrient input and productivity in ecosystems, but at the same time reduces biomass. The intensity of grazing is however important for how grazing affects biodiversity and carbon storage. The effects of each single driver are quite well understood. But in a natural system, these drivers will interact with complex effects on the ecosystem. In 2019, the field experiment with three sites along an elevational gradient was started. Half of the plots were transplanted to warmer sites to simulate warmer climate. Each year the plots are fertilized (0 – 150 kg N ha-1 y-1) and cut to simulate grazing. For 4 years, we have recorded data on plant species composition, biomass, productivity, decomposition, carbon flux, microclimate data and collected soil samples for pH, soil texture, bulk density, soil nutrients and soil carbon and nitrogen stocks. The results show that warmer climate and fertilization increase vegetation height, biomass, and productivity of graminoids, while biomass and diversity of forbs decrease. Only few adapted species tolerate high levels of nitrogen. The effect of grazing needs further investigation. The results of this experiment will be used in model simulations to predict the consequences of climate and climate change for biodiversity and carbon sequestration on a larger scale and under different future climate scenarios. And will further contribute to increased knowledge and feedbacks between terrestrial ecosystems and the climate system.

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Three global change drivers - climate warming, nitrogen deposition, and grazing - pose major threats to alpine biodiversity. THREE-D will develop a mechanistic experiment-based approach and framework to (i) assess the interactive effects of these three global change drivers on alpine biodiversity and ecosystem function; (ii) explore the circumstances under which grazing can be an effective tool for mitigating the ecological strains on biodiversity and ecosystem functioning caused by climate warming and/or nitrogen deposition; and (iii) develop a management decision-making support tool in collaboration with farmers and local conservation managers. The tool will allow farmers and land managers to estimate the impact of the current level of grazing on biodiversity and ecosystems, and to explore the potential of adapting the grazing regime to meet new pressures and/or optimise ecosystem service delivery. The THREE-D approach to develop a unified framework to assess and mitigate the effects of three global change drivers on ecosystems represents a significant advancement beyond the state-of-the-art. THREE-D brings together an optimal team of researchers with complementary skills and expertise from five world-class institutions in Norway and abroad to develop new approaches in global change, ecosystem, and conservation ecology with important applications and benefits for both basic and applied research. The THREE-D team and the Chinese partner build on an established collaboration, and both have a strong track record in these fields and are uniquely positioned to deliver the important research outcomes and mitigation strategies.