The role of Functional group interactions in mediating climate change impacts on the Carbon dynamics and Biodiversity of alpine ecosystems

Mountain areas provide important habitats for many plant and animal species, and they also contribute important ecosystem functions and services such as carbon storage, livestock grazing pastures, and regulation of floods and landslides. Mountain ecosystems are particularly vulnerable to climate change, potentially threathening their charactersitic biodiversity and ecosystem services. Alpine vegetation consists of several important groups of organisms; including primary producers such as shrubs, herbs, grasses, mosses, and lichens, and decomposers such as bacteria and fungi. To understand how climate change affects the ecosystem and its functioning we must understand both the direct effects of climate and climate change on each of these groups, and how climate change affects the interactions between them. FunCaB explores these questions using field experiments. We remove one or more of the functional groups graminoids, forbs, and bryophytes from intact alpine grassland vegetation and assess how the remaning groups are responding. We replicate these experiments under different temperature and precipitation conditions so that we can assess climatic context-dependencies of these interactions. The hypothesis is that competition between the different primary producers dominate under relatively warm and productive conditions, while cooperation (facilitation) dominate under cold and unproductive conditions. We also expect mosses to contribute more to productivity and carbon storage, and fungi contribute more to decomposition, under humid conditions. To test these hypotheses, we measure Carbon dynamics, decomposition, and plant community composition, recruitment, and biomass along the climatic gradients and in response to the removal experiments. The results largely confirm our hypotheses; when we removed grasses, forbs in the lowlands grow and survive better, whereas the forbs in the mountains actually perform worse without their grass neighbors. Graminoids are the functional group best able to tolerate, exploit and compensate for the loss of their neighbours. Our studies further show that climate is of major importance for decomposition and carbon sequestration through photosynthesis, both of which are slow in cold, wet climates. At the same time, we also see that the plant community, and especially the functional composition of species, is of great importance for the carbon dynamics. For example, grass and herbs contribute to faster turnover in the ecosystem, while mosses help to stabilize moisture and temperature and thus to slow down carbon sequestration but also slow down decomposition. This means that competition between the species dominate under hot conditions, while cooperation or facilitation is dominant when it is cold. Mosses have an additional role in regulating soil microclimate with consequences for microbial activity and soil moisture content. Such questions about changes in the nature and strength of species interactions along climate gradients can only be investigated by replicating experiments along gradients. FunCaB is an example of a "macro-ecological experiment", a new methodological approach where we borrow strengths by combining experiments and gradient studies. Such approaches will become more important in the future as we urgently need to understand if and how the impacts of climate and environmental change vary across landscapes. The results of the FunCaB experiments are 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. The results will thus contribute to increased knowledge and feedbacks between terrestrial ecosystems and the climate system.

FunCaB contributes new knowledge on biodiversity and ecosystem responses to climate change. Based on our long-term research portfolio in these sites and systems, FunCaB has laid foundations for stronger cooperation with climate researchers enabling exploring key research gaps related to the feedback effects between vegetation and the climate system. The sites are already used for new experiments, and we are committed to ensuring their continued operation. European and international networks are important for promoting collaboration, data utilization, funding, and new studies in the SeedClim sites. FunCaB has generated significant data and we will secure and make this data FAIR and openly available to the research community while heeding research ethics principles, including author rights. We have disseminated results in various user-directed and public forums, and we have been met with interest from industry, management, society and the general public.

Alpine regions contribute important ecosystem functions and services, and are at the same time particularly vulnerable to the ongoing climate change. Recent research, including work by the team behind this proposal, indicates that to understand the impacts of climate and environmental change on alpine ecosystems we urgently need improved knowledge on (i) the effects of both temperature and precipitation change, including disentangling potential interactive effects between these two aspects of climate change, and (ii) the roles of, and interactions between, important functional groups in alpine ecosystems. In particular, to understand alpine biodiversity and carbon ( C) dynamics under climate change, we need to disentangle the roles of and interactions between characteristic and important alpine primary producer (e.g., graminoids, forbs, woody, and non-vascular) and decomposer (e.g., bacteria, fungi) communities under different climatic settings. FunCaB will use an effective combination of gradient studies, field experiments and model simulations. The experiments are targeted specifically at quantifying and disentangling key climatic and biotic controls of alpine biodiversity and C dynamics, whereas the simulations will enable process-level understanding and assessment of larger-scale and longer-term consequences including feedbacks to the climate system. The comparison of the two approaches will contribute to model validation and guide future development of the nationally facilitated Earth system model NorESM (Norwegian Earth System Model). The project will enable better estimates of the current biodiversity and C stocks and dynamics of alpine regions, and establish causal linkages between these key ecosystem functions and services and climate. These results will provide an improved knowledge basis for projecting future climate change impacts and feedbacks between terrestrial ecosystems and the climate system.