Assessment of biomass dynamics of a semidesert grassland by remote sensing techniques.

Abstract

In order to study the effect of standing dead biomass on vegetation canopy spectral response, the normalized difference, the soil-adjusted vegetation index, the green vegetation index and the perpendicular vegetation index were used to examine and compare the spectral behavior of a mostly green (regrowth after burning) vegetation canopy to a perennial vegetation stand. Results showed all greenness indicators to be strongly affected by the presence of standing dead vegetation. The burned plots which had less green biomass in the first growing season (February-June) exhibited higher vegetation index values through the entire growing season. The observed discrepancies in the vegetation indices seem to stem from the attenuation of the near-infrared flux combined with a lack of responsivity of the red channel. Overall, there was no correlation between green biomass and greenness measures in the perennial stand. Furthermore, in the perennial environment, a steady increase in "greenness" was observed while the green biomass was actually decreasing. The problem seems to be more of visibility than quantity of green biomass present.