J. Wellens, RANGELAND VEGETATION DYNAMICS AND MOISTURE AVAILABILITY IN TUNISIA - AN INVESTIGATION USING SATELLITE AND METEOROLOGICAL DATA, Journal of biogeography, 24(6), 1997, pp. 845-855
Improved knowledge of the interactions between regional climatic patte
rns and vegetation dynamics are necessary for predicting the future im
pacts of climate change on vegetation and biogeochemical processes. Th
is paper describes how Normalized Difference Vegetation Index (NDVI) i
mages generated from Advanced Very High Resolution Radiometer (AVHRR)
satellite data were used to investigate the dynamics of rangeland vege
tation in Tunisia. The NDVI images provided information about intra-an
d inter-annual variations in vegetation over nine growing seasons (198
3-1992). Comparison of the NDVI data with field-collected ecological p
arameters for nine individual field sites indicated a strong relations
hip between the NDVI and percentage vegetation cover. The relationship
between biomass measurements and NDVI was, however, less strong. Rain
fall and NDVI data for each field site were compared, and significant
relationships were found between the two. These indicated that there w
as a delay in the vegetation response to rainfall. In addition, the ND
VI data showed that the vegetation at some of the field sites remained
active throughout the summer although there was no rainfall during th
is period. TuMERT (Tunisian Model to Estimate Rangeland Transpiration)
, a simple water-balance model, was developed to estimate the amount o
f rainfall available for use by the vegetation during transpiration. T
he estimates of actual transpiration derived from TuMERT were found to
be more strongly correlated with the AVHRR-NDVI measurements than the
rainfall data.