Long-term experimental warming in an alpine heath : decrease in cover of the most abundant bryophytes
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- Master’s theses (MINA) 
Alpine ecosystems have shown to be sensitive to climate warming. Bryophytes are particularly important in alpine ecosystems and are known to support ecosystem services such as water regulation, nitrogen fixation and carbon storage. However, few studies have investigated the effects of long-term warming on alpine bryophytes at species level or genus level. The aim of this thesis is to investigate how global warming will affect community structure for alpine bryophytes. I hypothesize that the consequences of climate warming will be: (I) A decrease in cover of bryophytes. (II) A shift towards decreased richness and decreased evenness of bryophytes – where a few species will increase their cover, and the majority will decrease in cover. (III) A stronger decrease in cover of acrocarpous mosses than in cover of pleurocarpous mosses. I also explore the role of water availability and competition with vascular plants. For this I collected data from an on-going, 18-year old, warming experiment that uses open top chambers, in an alpine heath at Finse. To test the effects of warming on cover, evenness and richness of bryophytes, I performed linear regression models. To test and visualize the effects of warming on species composition, I used non-metric multidimensional scaling (NMDS). To test if acrocarpous mosses decreased more in cover than pleurocarpous mosses, I used linear regression models including an interaction between growth-form and warming. Warming had a negative effect on cover of bryophytes and a positive effect on evenness and richness. Species composition was significantly changed – the abundant species decreased while the less abundant species showed an increasing trend. Acrocarpous mosses did not decrease more than pleurocarpous mosses. Increased competition with vascular plants and decreased moisture availability seemed to be important variables driving the change in the community structure of bryophytes. Different taxa were associated with different environmental variables, such ass moisture and cover of litter. This study underlines that the effects of warming on bryophyte communities depend on the physical and biological environment and the species which make up the community. How global warming will affect community structure for alpine bryophytes remain an un answered question, as these results may not be applicable to other sites and because global warming is likely to be followed by changes in other aspects of the climate. Nevertheless, this thesis show how sensitive bryophyte communities can be to elevated temperatures. A potential decrease in cover of bryophytes and a shift in species composition may greatly impact the alpine ecosystems.