摘要：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,
NDVIpre − leaf), at the point in the growing season when canopy NDVI has
reached half of its maximum growing season value (mid-June,
NDVIdemi − leaf) and during the period of maximum leaf-out (late July,
NDVIpeak − leaf). We found
that: (1) NDVIpre − 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) NDVIpeak − leaf is best suited to capturing variation in deciduous canopy cover; and (3) NDVIdemi − 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.
