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Aim: Species' biogeographical patterns are already being altered by climate change. Here, we provide predictions of the impacts of a changing climate on species' geographical ranges within high-latitude mountain flora on a sub-continental scale. We then examined the forecasted changes in relation to species' biogeographic histories. Location: Fennoscandia, Northern Europe (55-72 degrees N). Methods: We examined the sensitivity of 164 high-latitude mountain species to changing climate by modelling their distributions in regard to climate, local topography and geology at a 1 km(2) resolution. Using an ensemble of six statistical modelling techniques and data on current (1981-2010) and future (2070-2099) climate based on three Representative Concentration Pathways (RCPs 2.6, 4.5, 8.5), we developed projections of current and future ranges. Results: The average species richness of the mountain flora is predicted to decrease by 15%-47% per 1 km(2) cell, depending on the climate scenario considered. Arctic flora is projected to undergo severe range loss along with non-poleward range contractions, while alpine flora is forecasted to find suitable habitat in a warmer North. A substantial majority (71%-92%) of the studied species are projected to lose more than half of their present range by the year 2100. Species predicted to lose all suitable habitat had ranges centred in the northernmost (>68 degrees N) part of continental Europe. Main conclusions: Climate change is predicted to substantially diminish the extent and richness of Europe's high-latitude mountain flora. Interestingly, species' biogeographic histories affect their vulnerability to climate change. The vulnerability of true Arctic and endemic species marks them as highly important for conservation decisions.

Refugia, the sites preserving conditions reminiscent of suitable climates, are projected to be crucial for species in a changing climate, particularly at high latitudes. However, the knowledge of current locations of high-latitude refugia and particularly their ability to retain suitable conditions under future climatic changes is limited. Occurrences of refugia have previously been mainly assessed and modelled based solely on climatic features, with insufficient attention being paid to potentially important landscape-scale factors. Here, climate-only models and full' models incorporating topo-edaphic landscape-scale variables (radiation, soil moisture and calcareousness) were developed and compared for 111 arctic-alpine plant species in Northern Fennoscandia. This was done for both current and future climates to determine cells with resilient climatic suitability harbouring refugia. Our results show that topographic and edaphic landscape-scale predictors both significantly improve models of arctic-alpine species distributions and alter projections of refugia occurrence. The predictions of species-climate models ignore landscape-scale ecological processes and may thus provide inaccurate estimates of extinction risk and forecasts of refugia where species can persist under a changing climate.

Determining the drivers, patterns and hotspots of biodiversity can be of critical importance in supporting regional conservation planning. However, as biodiversity hotspots can be described with several different metrics, it is important to investigate their congruence as well as the spatial overlap of hotspots with protected areas. Here, by using extensive data on climate, topography, soil characteristics and vascular plants combined with boosted regression tree models, we determine the patterns and key drivers of plant diversity hotspots along broad environmental gradients in northernmost Europe spanning from taiga landscapes to treeless tundra. We assess plant diversity with four metrics – species richness, range-rarity richness, threatened species richness, and local contribution to beta diversity – and examine their congruence with each other as well as with contemporary conservation areas. We found that climate plays an important role in governing species diversity, though topo-edaphic are highlighted alongside climatic predictors in determining the diversity patterns of many threatened, near-threatened, and range-restricted species. Importantly, the different diversity metrics have contrasting drivers and, overall, their hotspots have low congruence. Furthermore, existing protected areas appear to offer limited coverage for hotspots of vascular plant diversity. Modelling the various facets of diversity and their drivers, such as the topo-edaphic setting, may provide useful information to help conserve diversity in a changing climate. Projected patterns of different aspects of diversity and their congruency can provide insights into the processes underlying biodiversity and be employed to assess the representativeness of protected area networks.

Projected climatic warming calls for increased attention to the identification of suitable refugia for the preservation of biota and ecosystems in changing high-latitude environments. One such way is the development of models for drivers of refugia. Here, we investigate the distribution and species richness of Arctic-alpine vascular plant species' refugia. The study is carried out in an environmentally variable area in N Europe, encompassing the northern boreal to the Arctic-alpine zone. We defined refugia as isolated 1 km x 1 km grid cells with multiple Arctic-alpine plant species occurrences outside their main distribution area and assessed the main environmental factors underlying their distribution and richness using cross-validated boosted regression tree modelling. In the modelling, we examined the effects of climatic, topographic, and geologic factors, and the connectivity of sites with refugia incrementally, i.e. first modelling climatic impact alone, then with separate additions of topographic, geologic and connectivity variables, concluding with a model including all predictor variables. The inclusion of slope and connectivity significantly improved model performance. Although climate has a central role in controlling the occurrence of refugia, topography provides important clues for recognizing heterogeneous locations that harbour refugia with suitable local thermal and moisture conditions. Results suggest considering refugia as, on the one hand, isolated pockets of suitable habitat, but on the other hand as potentially interconnected habitat networks. In general, our study demonstrates that the spatial patterns of refugia can be successfully modelled, but emphasizes a need for high-quality data sampled at resolutions reflecting significant environmental gradients.