Indirect climate change impacts on alpine plant communities

Mountains make up 37% of Norway's land area. They hold a distinctive and diverse flora and fauna, and mountain nature also contributes with important benefits and ecosystem services such as carbon storage and flood regulation and areas for game and livestock grazing, berry-picking or hunting, and recreation. However, mountain nature is vulnerable to climate change, and rising temperatures in particular pose an increasing threat to their biodiversity and ecosystems. Climate change can affect mountain species in two different ways, either through direct physiological effects of higher temperature, more rainfall, a longer growing season and/or more droughts, or through indirect effects that occur through changes in species interactions. An example of the latter is changes in competition for light and nutrition between plants. These effects can be particularly large if the mountain plants are exposed to new neighbors, lowland plant species that spread up into the mountains as the climate warms. The aim of the INCLINE project is to investigate and compare such direct and indirect effects of climate change on mountain plants. Experiments are well suited to distinguish different causes and effects, and in INCLINE we used a field experiment where we moved more or less competitive plants from the lowlands up into the mountains, with and without artificial heating. We then measured how these new neighbors affected the mountain plants. In our experiments, we found that the plants we moved from the lowlands managed to grow and establish in the mountains, although especially the most competitive lowland species fared best when they were artificially heated. This may indicate that the current mountain climate is still not quite optimal for these species, but they can still survive in the mountains already, and they will probably be able to spread in the mountains in a warmer future. The mountain plants generally did well under artificial heating alone, but they fared worse if there were neighbors present, and particularly poorly if surrounded by the more competitive new neighbors from the lowlands. In another study, we found that extreme weather, such as drought, can also have negative effects, for example by reducing seed germination and survival. All these negative climate effects were most pronounced in areas with high rainfall, and for species adapted to grow in snow beds. This suggests that mountain plants in high-rainfall regions, such as Western Norway, and adapted to wet habitats, such as snow beds and mountain bogs, may be most vulnerable as climate changes progress. In collaboration with colleagues around the world, we have assembled a database of climate experiments in mountains. We are now investigating whether mountain plants in other climate zones and on other continents are affected by climate change in the same general ways as what we find in Norwegian mountains, and whether we can generalize understanding of how species are affected also in areas where we do not have experiments. One theory is that we can use species’ geographical distributions to predict how they will be affected by climate change. For example: we expect that species that have the coldest part of their distribution in western Norwegian mountains generally will respond positively to warming here, while species that have the main part of their distribution in even colder areas will tolerate warming less well. Similarly, we can use functional traits that characterize species' competitive effects and responses to say something about which species will win and lose under a warmer climate. If such generalizations hold true, we can contribute to better general understanding for how mountain nature and mountain species are affected by climate change. Three PhD students and six Master's students have been associated with the INCLINE project. We have actively participated in dissemination and contributed teaching programs about climate change and mountain nature to university students and pupils at primary and secondary school.

Outcomes: We have conducted a field experiment across four sites over five years and produced 12 different datasets spanning from plant community composition, population dynamics of two alpine species, germination of alpine and lowland species, reflectance (NDVI), ecosystem carbon flux, to microclimate data. We have contributed data to different global meta-analyses. One database of climate change experiments We have published 18 scientific papers, have several manuscripts or papers under review, with more publications planned in the upcoming year. Several papers, under which registered reports, are student led. We have presented 30 scientific talks and 11 posters at scientific conferences. We have 1 completed and 2 ongoing PhDs, 3 completed and 2 ongoing MSc, 9 completed bachelors degrees/ student research projects, and 22 interns from 9 different countries. We have organized a workshop on integral projection models and species distribution models, and a PhD level course on integral projection models. INCLINE has been highly visible in popular and social media, including newspapers, popular science, and five television appearances e.g. documentaries (Norsk hodepine), and a second place in the Bergen finale of Forsker Grand Prix. We have developed knowledge and educational packages for teachers distributed locally and nationally on public broadcast Impacts: INCLINE has generated new knowledge on resource allocation of native alpine and lowland plants in alpine areas, reproduction of alpine plants along climate gradients and under warming, seedling establishment of native alpine and lowland plants in alpine areas under warming in the field, drought tolerance of seedling establishment of native alpine plants, and community and population dynamics of alpine plants under warming and novel biotic interactions from lowland species in alpine vegetation. We are contributing to more realistic incorporation of species interactions in species distribution modeling and ecosystem carbon dynamics. The INCLINE community and population data are currently being used to assess biotic effects under warming in species range dynamics (on-going PhD at UiO) and test functional leaf trait-fitness linkages (on-going MSc UiB). INCLINE has generated data on carbon dynamics of alpine vegetation under both climate warming and invasion from lowland plants(on-going PhD at UiB). INCLINE has contributed to develop the FATES module within the Norwegian Earth System Model norESM, and will generate upscaled information about climate effects of novel species in alpine vegetation (ongoing PhD at UiO). We have trained early-career researchers in climate change experimental ecology, ecological modeling, and plant ecology. We have built and maintained a network of climate change ecologists including previous and new collaborators. INCLINE has actively supported school teacher education locally and nationally

Climate warming is already causing significant alterations in plant communities, including range shifts to higher elevation and latitude and changes in biodiversity and ecosystem functioning. It is unclear, however, to what extent these responses represent direct effects of altered climate, or indirect effects mediated by changing interactions among species. Entirely novel interactions, which arise because species do not migrate in concert, could have especially large impacts on species, community and ecosystem responses to climate change, especially if newly arriving species introduce novel functional traits and trait combinations. This possibility has until now received little attention in climate change ecology. INCLINE focuses on these indirect effects of climate change, and particularly the impact of novel species colonizing upland plant communities. With innovative experimental approaches (WP1) we will be among the first to investigate and disentangle impacts of novel species interactions under climate warming within an ecologically realistic field setting, representing a major advance beyond the current state-of-the-art. In a meta-analysis approach, we will harness existing data from plant community transplant experiments from around the world, and relate patterns of colonisation/extinction to functional traits of the component species (WP2). This will improve our understanding of climate change impacts on mountain vegetation, uncover underlying mechanisms, and explore how these vary with ecological and environmental settings on a global scale. Finally, the results of WP1 and WP2 will be used in developing mechanistic models of species' distributions (WP3), and contributing to the next-generation of predictive models that can incorporate impacts of changing species interactions on range dynamics under climate change.