Question: How can we derive baseline/reference situations to evaluate the impact of global change on terrestrial ecosystem functioning?
Location: Main biomes (steppes to rain forests) of Argentina.
Methods: We used AVHRR/NOAA satellite data to characterize vegetation functioning. We used the seasonal dynamics of the Normalized Difference Vegetation Index (NDVI), a linear estimator of the fraction of the photosynthetic active radiation intercepted by vegetation (fPAR), and the surface temperature (Ts), for the period 1981–1993. We extracted the following indices: NDVI integral (NDVI-I), NDVI relative range (Rrel), NDVI maximum value (Vmax), date of maximum NDVI (Dmax) and actual evapotranspiration.
Results: fPAR varied from 2 to 80%, in relation to changes in net primary production (NPP) from 83 to 1700 g.m–2.yr–1. NDVI-I, Vmax and fPAR had positive, curvilinear relationships to mean annual precipitation (MAP), NPP was linearly related to MAP. Tropical and subtropical biomes had a significantly lower seasonality (Rrel) than temperate ones. Dmax was not correlated with the defined environmental gradients. Evapotranspiration ranged from 100 to 1100 mm.yr−1. Interannual variability of NDVI attributes varied across the temperature and precipitation gradients.
Conclusions: Our results may be used to represent baseline conditions in evaluating the impact of land use changes across environmental gradients. The relationships between functional attributes and environmental variables provide a way to extrapolate ecological patterns from protected areas across modified habitats and to generate maps of ecosystem functioning.
Abbreviations: CV = Coefficient of variation; Dmax = Date of maximum NDVI; e = Light use efficiency; Et = Evapotranspiration; fPAR = Fraction of photosynthetic active radiation intercepted by vegetation; MAP = Mean annual precipitation; MAT = Mean annual air temperature; NDVI = Normalized difference vegetation index; NDVI-I = NDVI integral; NPP = Net primary production; PAL = Pathfinder AVHRR Land; PUE = Precipitation use efficiency; Rrel = NDVI relative range; Ts = Surface temperature; Vmax = NDVI maximum value
