Vascular plant biomass and herbivore disturbance, but not summer temperature, explain satellite and drone-based NDVI in High Arctic Svalbard

The normalized difference vegetation index (NDVI) is a critical tool for studying Arctic vegetation patterns and changes, but more knowledge is needed about its links with plant biomass and disturbances, especially in sparsely vegetated habitats in the High Arctic. Here, we investigate the relationship between NDVI and vascular plant biomass, summer temperature, goose disturbance, and winter damage in Dryas ridge and moss tundra habitats on Svalbard, all recorded in the corresponding year across a 5-year time series. We test these relationships using mixed-effect models at two spatial resolutions (10 cm and 10 m) and two extents with data from drone and Sentinel-2 imagery. We found that in our plots, an increase in biomass of 100 g m −2 increased NDVI from drone imagery by 0.08 ± 0.03 (95% CI) for Dryas ridge and by 0.04 ± 0.03 for moss tundra. Despite record-warm summers, temperature of the same summer was not associated with NDVI in our time-series. In moss tundra, severe goose disturbance had a negative relationship with drone NDVI in plots, while in Dryas ridge habitat, winter damage had no clear correspondence with NDVI. Our study provides an example of context dependencies highlighted in remote-sensing literature in the Arctic, encouraging future studies to include effects of disturbance on NDVI and to establish habitat-specific relationships with NDVI.