Climate change is causing shifts in plant species distributions, and nowhere is this being felt more strongly than in alpine regions where short dispersal distances along elevation are less limiting to spread. In the short term, climate change is causing both direct physiological effects on plant species, as well as indirect effects through altered biotic interactions within existing plant communities. However, in the longer term, the upward shift of lowland species distributions will result in novel interactions with higher elevation species, with implications for both plant community structure and ecosystem functioning. To assess the impact of lowland plant expansion into alpine regions, we use plant community composition data from the TransPlant Network, a distributed network of 20 experiments across the northern hemisphere. In these experiments, intact alpine vegetation turfs are transplanted lower in elevation to simulate climate warming. As species originating from lower elevation may possess traits that confer a competitive advantage as compared to alpine species, we coupled this data with functional trait information. We investigate how the functional identity of the colonizers or recipient community mediates establishment success of low elevation origin plants into alpine communities, and whether the same traits drive assembly patterns in different climatic regimes.
Results/Conclusions
We found that over time the composition and functional identity of transplanted alpine turfs converged on that of the low elevation plant communities, often within the first two years of transplantation. However, alpine communities remained distinct from low elevation communities even after 10 years of transplantation. Using null models, we found that colonizing species are not a random subset of the surrounding low elevation community, both in terms of abundance and functional identity. We expected that colonizers with trait values conferring a (local) dispersal advantage (e.g. clonal growth, high fecundity) will more often establish successfully in transplanted alpine turfs. Interestingly, we also found that the suite of traits which predict establishment success of colonizers did not necessarily predict long-term performance (abundance). The results of this study indicate that functional traits can be useful in informing predictions of those lowland species which are more likely to invade into alpine regions. We further demonstrate that lowland species establish and increase in abundance rapidly in alpine turfs, suggesting that the long term impacts of climate change may result in large shifts in the composition and function of alpine communities.