Vegetation change on mountaintops in northern Sweden: Stable vascular‐plant but reordering of lichen and bryophyte communities

Abstract

Alpine ecosystems harbor remarkably diverse and distinct plant communities that are characteristically limited to harsh, and cold climatic conditions. As a result of thermal limitation to species occurrence, mountainous ecosystems are considered to be particularly sensitive to climate change. Our understanding of the impact of climate change is mainly based on vascular plants however, whereas cryptogams (i.e., lichens and bryophytes) are generally neglected or simply considered as one functional group. Here we aimed to improve our understanding of the drivers underlying temporal changes in vegetation of alpine ecosystems. To this end, we repeatedly surveyed the vegetation on four mountain summits along an elevational gradient in northern Sweden spanning a 19‐year period. Our results show that the vascular plant communities remained relatively stable throughout the study period, despite fluctuations in terms of ground cover and species richness of shrubs and graminoids. In contrast, both lichens and bryophytes substantially decreased in cover and diversity, leading to alterations in community composition that were unrelated to vascular plant cover. Thermophilization of the vascular plant community was found only on the two intermediate summits. Our findings are only partially consistent with (long‐term) climate‐change impacts, and we argue that local non‐climatic drivers such as herbivory might offset vegetation responses to warming. Hence, we underline the importance of considering local non‐climatic drivers when evaluating temporal vegetation change in biologically complex systems.

Combining taxonomic, functional and phylogenetic diversity metrics to explain spatiotemporal variation in mountaintop flora

“…Despite the widespread evidence of such trends, local studies also report stable or decreasing plant species richness on mountaintops or an absence of thermophilization (see e.g. Vanneste et al 2017, Hagenberg et al 2022. Moreover, with time this increase in plant richness is likely a transient phenomenon that temporarily masks the accumulation of a so-called extinction debt (Dullinger et al 2012a).…”