Relationship between herbaceous biomass and 1km (2) advanced very high resolution radiometer (AVHRR) NDVI in Kruger National Park, South Africa

Abstract

The relationship between multi-year (1989-2003), herbaceous biomass and 1-km(2) Advanced Very High Resolution Radiometer (AVHRR) Normalized Difference Vegetation Index (NDVI) data in Kruger National Park (KNP), South Africa is considered. The objectives were: (1) to analyse the underlying relationship between NDVI summed for the growth season (Sigma NDVI) and herbaceous biomass in field sites (n=533) through time and (2) to investigate the possibility of producing reliable herbaceous biomass maps for each growth season from the satellite Sigma NDVI observations. Landsat Enhanced Thematic Mapper Plus (ETM+) and Thematic Mapper (TM) data were used to identify highly heterogeneous field sites and exclude them from the analyses. The average R-2 for the Sigma NDVI-biomass relationship at individual sites was 0.42. The growth season mean biomass and Sigma NDVI of most landscape groups were strongly correlated with rainfall and each other. Although measured tree cover and MODIS estimates of tree cover did not have a detectable effect on the Sigma NDVI-biomass relationship, other observations Suggest that tree cover should not be ignored. The Sigma NDVI was successful at estimating inter-annual variations in the biomass at single sites, but on an annual basis the relationship derived from all the sites was not strong enough (average R-2 = 0.36) to produce reliable growth season biomass maps. This was mainly attributed to the fact that the biomass data were sampled from very small field sites that were not fully representative of 1-km (2) AVHRR pixels. Supplementary field surveys that sample a larger area for each field site (e.g. 1 km (2) or larger) should account for the variability in biomass and may improve the strength of Sigma NDVI-biomass relationships observed in a single growth season.