A COMPARISON OF GREENNESS MEASURES IN 2 SEMIARID GRASSLANDS

A field experiment was conducted during 1988 in a semi-arid grassland along a portion of the U.S./Mexico border in which the utility of NDVI-transformed data for estimating green vegetation amount and cover was explored. Results showed that, although there was significant difference in green and total biomass between the U.S. and Mexico sites, we were unable to find any correlation between either these vegetation parameters and NDVI values calculated from reflectance measurements. Based on these results, it would appear that semi-arid perennial grasslands can pose problems for remote sensing analysis due to their erectophile structure, the likelihood of significant accumulation of senescent biomass, and dominance of soil background in sparsely vegetated areas. Therefore, if remotely-sensed data, and indices derived from them, are to be used in global change models, it is critical to establish if these indices are sufficiently sensitive to distinguish long-term change from the seasonal and spatial variability in vegetation biomass normally found within these perennial grassland communities. © 1990 Kluwer Academic Publishers.