Land degradation in Lesotho : a synoptic perspective

[摘要] Land degradation in Lesotho is undermining the finite resource on which peopledepend for survival. Use of satellite imagery has been recommended for monitoringland degradation because remotely sensed data enable monitoring of large areas atmore frequent intervals than intensive ground based research. Various techniqueshave been developed for land cover change detection. In the present study, vegetationchanges were identified by image differencing, which involved finding the differencebetween the earlier date NDVI image and the later date image. NDVI images areamong products that are generated from the NOAA AVHRR sensor to provideinformation about the quantity of biomass on the earth's surface. The resulting NDVIchange data showed land areas that had experienced vegetation loss, which wereidentified as potentially degraded. The change data were combined with other datasets to determine how potentially degraded areas were influenced by differentenvironmental variables and population pressure. These data sets included land cover,ecological zones, elevation, soil and human and livestock populations. By integratingNDVI data with ancillary data, land degradation was attributed to both demographicpressure and biophysical factors. Widespread degradation was detected on the arableparts of the Lowlands where cultivation was intensive and human settlements wereextensive. Signs of grassland depletion and forest decline were also evident and wereattributed to population expansion, overgrazing and indiscriminate cutting of trees andshrubs for firewood. Extensive biomass decline was also associated more with soils inthe lowlands derived from sedimentary rocks than soils of basalt origin that occurmostly in the highlands. Significant degradation was evident on gentle slopes whereland uses such as cultivation and expansion of settlements were identified as the maincauses of the degradation. There was evidence of greater vegetation depletion onnorth and east-facing slopes than on other slopes. The depletion was attributed to thefragility of ecosystems resulting from intense solar radiation. The study demonstratedthat NOAA AVHRR NDVI images could be used effectively for detecting land coverchanges in Lesotho. However, future research could focus on obtaining and usinghigh resolution data for detailed analysis of factors driving land degradation.

[发布机构] Stellenbosch University