Seasonal reflectance factor dynamics in boreal forest clear-cut communities

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Abstract
Seasonal reflectance factor dynamics was studied on a set of boreal forest clear-cut communities in Estonia in 1986–1989. Weekly and more frequent measurements were carried out on permanent sample plots with a ground-based radiometer in the blue (480 nm), green (550 nm), red (675 nm) and near-infrared (NIR) (780 nm) spectral bands over the growing periods. Seasonal curves were calculated from discrete measurements by the cubic spline approximation for all spectral bands and for vegetation indices. The seasonal curve shape types in the NIR band and of vegetation indices form a continuum with high bell-shaped convex curves in fertile mesic and plateau-like curves in poor growing conditions serving as the extremes. The peak of the seasonal reflectance curves in the NIR region and of vegetation indices is gained at the earliest in fertile mesic growing conditions and correspondingly later with the decrease in the site type fertility. Above-ground net primary productivity of communities can be determined by seasonal Peak Greenness value.