No abstract

Climate change is affecting the composition and functioning of ecosystems across the globe. Mountain ecosystems are particularly sensitive to climate warming since their biota is generally limited by low temperatures. Cryptogams such as lichens and bryophytes are important for the biodiversity and functioning of these ecosystems, but have not often been incorporated in vegetation resurvey studies. Hence, we lack a good understanding of how vascular plants, lichens and bryophytes respond interactively to climate warming in alpine communities. Here we quantified long-term changes in species richness, cover, composition and thermophilization (i.e. the increasing dominance of warm-adapted species) of vascular plants, lichens and bryophytes on four summits at Dovrefjell, Norway. These summits are situated along an elevational gradient from the low alpine to high alpine zone and were surveyed for all species in 2001, 2008 and 2015. During the 15-year period, a decline in lichen richness and increase in bryophyte richness was detected, whereas no change in vascular plant richness was found. Dwarf-shrub abundance progressively increased at the expense of lichens, and thermophilization was most pronounced for vascular plants, but occurred only on the lowest summits and northern aspects. Lichens showed less thermophilization and, for the bryophytes, no significant thermophilization was found. Although recent climate change may have primarily caused the observed changes in vegetation, combined effects with non-climatic factors (e.g. grazing and trampling) are likely important as well. At a larger scale, alpine vegetation shifts could have a profound impact on biosphere functioning with feedbacks to the global climate.Keywords Alpine vegetation AE Climate change AE Resurvey study AE Thermophilization AE CryptogamsThe original version of this article was revised due to a retrospective Open Access.Electronic supplementary material The online version of this article

Aim Disjunctly distributed peatmosses (Sphagnum) have been found to exhibit little genetic structure over regional and intercontinental scales, mainly caused by high ability for transoceanic long-distance dispersal. Although, most Northern Hemisphere peatmoss species have wide circumboreal/nemoral ranges, little is known about the magnitude and effects of long-distance dispersal and barriers in shaping the genetic structure of such species. We investigate whether high dispersal capacity has caused genetic homogeneity across broad areas of the Northern Hemisphere, or whether barriers act to shape genetic structure across different species with similar distributional ranges.Location Northern Hemisphere.Methods We studied genetic variation and structure in six Sphagnum species using 19 microsatellite loci.Results Four out of six species were genetically structured in similar ways; with mainly one Beringian and one Atlantic group. Overall, both the North American and Eurasian continents seemed to act as a barrier to gene flow in several species. However, the most abrupt breakpoint between genetic groups was found in south-east Alaska. Main conclusionsWe found evidence for extensive gene flow between regions across the Northern Hemisphere among peatmosses, with oceans seemingly acting as weaker barriers to gene flow than landmasses. Plants from the amphi-Atlantic and amphi-Beringian regions of several species were genetically differentiated. Similar genetic structuring across several species, indicate that spore-producing species do not disperse freely across their entire distributional range, but are likely limited by wind directions, landmass barriers and/or habitat availability.

Spore-producing organisms have small dispersal units enabling them to become widespread across continents. However, barriers to gene flow and cryptic speciation may exist. The common, haploid peatmoss Sphagnum magellanicum occurs in both the Northern and Southern hemisphere, and is commonly used as a model in studies of peatland ecology and peatmoss physiology. Even though it will likely act as a rich source in functional genomics studies in years to come, surprisingly little is known about levels of genetic variability and structuring in this species. Here, we assess for the first time how genetic variation in S. magellanicum is spatially structured across its full distribution range (Northern Hemisphere and South America). The morphologically similar species S. alaskense was included for comparison. In total, 195 plants were genotyped at 15 microsatellite loci. Sequences from two plastid loci (trnG and trnL) were obtained from 30 samples. Our results show that S. alaskense and almost all plants of S. magellanicum in the northern Pacific area are diploids and share the same gene pool. Haploid plants occur in South America, Europe, eastern North America, western North America, and southern Asia, and five genetically differentiated groups with different distribution ranges were found. Our results indicate that S. magellanicum consists of several distinct genetic groups, seemingly with little or no gene flow among them. Noteworthy, the geographical separation of diploids and haploids is strikingly similar to patterns found within other haploid Sphagnum species spanning the Northern Hemisphere. Our results confirm a genetic division between the Beringian and the Atlantic that seems to be a general pattern in Sphagnum taxa. The pattern of strong genetic population structuring throughout the distribution range of morphologically similar plants need to be considered in future functional genomic studies of S. magellanicum.