Remote sensing of Arctic percent vegetation cover and fAPAR on Baffin Island, Nunavut, Canada

Percent vegetation cover (PVC) and the fraction of absorbed photosynthetically active radiation (fAPAR) are important functional variables for assessing Arctic vegetation density and vigor. In this study, field measures of PVC, fAPAR and normalized difference vegetation index (NDVI) were collected from July 5 to August 8, 2015 (i.e., summer season) along a moisture gradient in the Apex River Watershed (ARW) (63 degrees 45'N, 68 degrees 30'W), Baffin Island, Nunavut, Canada. Two field methods for estimating PVC (i.e., the point-frame and image classification methods) were examined and it was determined that the image classification approach provided a suitable alternative to the point-frame method, especially for detecting changes in Arctic PVC. Meanwhile, fAPAR was measured based on the method presented by Tagesson et al. (2012): f APAR = (1 -PAR(Reflected)/PAR(incoming)) x PVC. The spatial and temporal patterns of PVC and fAPAR in the context of NDVI derived from remote sensing data were examined. For this site, vegetation types exhibited contrasting patterns of PVC as a result of differing moisture regimes: (1) vegetation types with saturated soils (e.g., sedge dominated) exhibited a continuous increase in PVC throughout the growing season; (2) mesic vegetation types with moderate soil moisture (e.g., mosses dominated with a mixture of sedges and shrubs) exhibited an increase in PVC from July to early August followed by a decline in mid-August; and (3) semi-desert vegetation types that tended to dry early in the growing season (e.g., dominated by prostrate dwarf shrubs, herb tundra and large areas of bare soil and rock) exhibited little variation in PVC. Field measures of PVC and fAPAR demonstrated strong relationships to field NDVI data and the vegetation indices (VIs) derived from 2 m-resolution WorldView-2 data, thereby providing further evidence that VIs are well-suited for modelling PVC and fAPAR of Arctic vegetation.