Vegetation data with and without experimental warming, collected in Finse in 2000, 2004, 2011, under a project called “Experimental warming in alpine Dryas heath”. The seed-addition and warming experiment was conducted at Finse (60°36′59″N, 07°31′23″E) in the alpine region of southern Norway, established in 2000. During summer, (June–August) Finse has a mean monthly temperature and rainfall of 6.3°C and 89 mm, respectively. The study site is located at approximately 1550 m a.s.l. on an exposed ridge of Mt Sanddalsnuten (peak at 1556 m a.s.l.). The bedrock consists mainly of phyllite, supporting a species rich Dryas heath community. The vegetation is dominated by the dwarf shrub Dryas octopetala, and other common species are Bistorta vivipara, Carex rupestris, Carex vaginata, Saussurea alpina and Thalictrum alpinum.
The experiment was initiated in 2000 to study the relative impacts of seed dispersal and different biotic and abiotic factors on plant species richness. They established 80 main plots, each of which consisted of two 30 × 60 cm split-plots which were further divided into eighteen 10 × 10 cm subplots. One of the split-plots in each main plot was randomly selected for seed addition, while the other was used as a control for natural background recruitment. Seeds and propagules (from here on collectively called seeds) were collected of 27 species at Mt Sanddalsnuten and randomly varied the number of species added to each split-plot to study the effect of seed species richness on community species richness. Each seed-addition plot received 0, 3, 6, 9, 12, 15, 18, 21, 24 or 27 species as seeds, with eight replicates per level of seed-addition. Eleven of the added species were not present in the plots prior to seed addition (Table 1). To examine whether warming affected the relative importance of dispersal and environmental filtering for species richness, open- top chambers (OTCs) open- top chambers (OTCs) were randomly placed upon half of the main plots. OTCs are hexagonal polycarbonate chambers with an inside diagonal of 1 m used for experimental warming of vegetation (see for instance Marion et al. 1997). Collection methods: species abundance by subplot frequency.