AVHRR-LAC estimates of forest area in Madagascar, 1990

Abstract

Three AVHRR-LAC data sets acquired in September 1990 and January 1991 were used to map the forest resources of Madagascar. The island was partitioned into four strata to include: (1) the western hardwoods, (2) the central grasslands, (3) the eastern rainforest, and (4) spiny forest. Each stratum was classified separately using AVHRR-LAC data in conjunction with 1984-1988 Landsat-MSS photoproducts. The results of AVHRR classification indicate that approximately 11 per cent of the island is covered by forest. Approximately 1 per cent of the island was obscured by clouds and could not be enumerated. Estimates of forest area, by stratum, follow: western hardwoods, 6697 km²; central grasslands, 2830km²; eastern rainforest 34167km²; and spiny forest, 17 224 km². The total forest area on the 587041km² island is estimated to be 60918km². The AVHRR forest map was compared to a mid 1970s land cover map which was developed using Landsat-MSS photoproducts. The average class agreement between the mid 1970s ground reference map and the 1990 AVHRR-LAC map was 78-2 per cent, the overall accuracy was 81-1 per cent. Areas identified as forest on the ground reference map on the 1990 AVHRR map agreed only 62 per cent of the time, however, that figure confounds AVHRR misclassifi-cation error with actual forest loss over the decade. Much of the per-pixel disagreement between the ground reference and AVHRR maps involved areas identified as forest in the 1970s and as nonforest in 1990. These results demonstrate that one kilometre spatial resolution satellite data may be used to provide a reconnaissance level survey of the forest resources of a region or subcontinent when used in conjunction with fine resolution data.