Correspondence between growth, branching and NDVI
Annual variation in C. tetragona shoot-length growth and branching frequency positively related to fluctuations in satellite-observed vegetation greenness over the research area. This suggests that there is, at least to some degree, correspondence in annual variation in community-level vascular plant biomass. This is in line with , who found that annual growth of this species represents annual above-ground tundra vegetation productivity at the local scale. Moreover, the same climate variables, i.e. summer and winter temperatures, as observed for the evergreen dwarf shrub C. tetragona drove year-to-year satellite-observed variation in greenness. The same climate parameters determine growth rates of the co-dominant deciduous dwarf shrub B. nana in the research area in the Blæsedalen valley on Disko Island . Such similarity in climatic drivers of growth patterns between shrub species with contrasting life strategies and NDVI was earlier observed over Arctic-alpine areas in northwest North America . The lack of a link between branch mortality and NDVI may be due to increased branching after winter warming events . Satellite-observed vegetation productivity in the research area did not correlate with early summer precipitation, but there were positive relations with late winter and spring precipitation. Growth and productivity of the shrub-dominated vegetation in the Blæsedalen valley may thus be increasingly moisture-limited. It is, however, not in decline, as observed for B. nana and S. glauca in a warmer and drier area on the mainland of Greenland , approx. 270 km south-southeast of Disko Island. While there was a slight increasing trend in late summer NDVI, there was no trend in NDVImax, which is in line with the widespread vegetation stability observed over large parts of the Arctic .