A comparison of the biogeographical and geomorphological characteristics of gullied and non-gullied valley head mires in eastern Lesotho

摘要

Environmental degradation is a serious problem in Lesotho, Africa. The majority ofudstudies dealing with soil loss and gully erosion have mainly focused on the mechanics ofudthe erosion. However, mountain watersheds are sensitive and vulnerable to degradationudand in so being, have large inherent environmental implications. Gully erosion diversifiesudthe micro-topographical and hydrological environment. The severe changes and eventualudsystem degradation incurred as a result of gullying has rarely been quantified. This paperudspecifically highlights mire phytogeographic responses to valley head degradation atudselected sites in eastern Lesotho by comparing patterns observed in gullied mires to thoseudseen in other non-gullied mires. Soil and vegetation belt transects are set up across fiveudmires (2 gullied) in the highlands of eastern Lesotho. The response of many of the plantudspecies to the overall environmental gradient was asymmetrical and unimodal in pattern.udThe spatial distribution of the soil’s physical properties, topography and vegetationudcommunity patterns were found to reflect the spatial mosaic of the soil moisture gradient.udThe negative impact that gullying has on the ecohydrological regime of the valley headsudis evident and is allowing for shrub encroachment. Both the wetland and drylandudvegetation communities correlate strongly with the changes in the surface soil moistureudgradient. Gully erosion is clearly a threshold phenomenon. Continued grasslanduddegradation, accelerated soil erosion and subsequent gullying of the wetlands will lead toudplant and animal diversity loss, decreased livestock productivity, sediment-laden waterudand shortened dam life-span.