Does NDVI reflect variation in the structural attributes associated with increasing shrub dominance in arctic tundra?: Fid-Bau Portal

Does NDVI reflect variation in the structural attributes associated with increasing shrub dominance in arctic tundra?

Natalie T Boelman / Laura Gough / Jennie R McLaren / Heather Greaves

This study explores relationships between the normalized difference vegetation index (NDVI) and structural characteristics associated with deciduous shrub dominance in arctic tundra. Our structural measures of shrub dominance are stature, branch abundance, aerial per cent woody stem cover (deciduous and evergreen species), and per cent deciduous shrub canopy cover. All measurements were taken across a suite of transects that together represent a gradient of deciduous shrub height. The transects include tussock tundra shrub and riparian shrub tundra communities located in the northern foothills of the Brooks Range, in northern Alaska. Plot-level NDVI measurements were made in 2010 during the snow-free period prior to deciduous shrub leaf-out (early June, NDVI_{pre − leaf}), at the point in the growing season when canopy NDVI has reached half of its maximum growing season value (mid-June, NDVI_{demi − leaf}) and during the period of maximum leaf-out (late July, NDVI_{peak − leaf}). We found that: (1) NDVI_{pre − leaf} is best suited to capturing variation in the per cent woody stem cover, maximum shrub height, and branch abundance, particularly between 10 and 50 cm height in the canopy; (2) NDVI_{peak − leaf} is best suited to capturing variation in deciduous canopy cover; and (3) NDVI_{demi − leaf} does not capture variability in any of our measures of shrub dominance. These findings suggest that in situ NDVI measurements made prior to deciduous canopy leaf-out could be used to identify small differences in maximum shrub height, woody stem cover, and branch abundance (particularly between 10 and 50 cm height in the canopy). Because shrubs are increasing in size and regional extent in several regions of the Arctic, investigation into spectrally based tools for monitoring these changes are worthwhile as they provide a first step towards development of remotely sensed techniques for quantifying associated changes in regional carbon cycling, albedo, radiative energy balance, and wildlife habitat.