Grassland rehabilitation after alien invasive tree eradication: landscape degradation and sustainability in rural Eastern Cape

[摘要] ENGLISH ABSTRACT: Rehabilitating grassland, a threatened biome, requires a comprehensive management approach that integrates the environmental, economic and social matters in sustaining this system. In the Eastern Cape of South Africa, three Quaternary catchments (QCs) (T35B, T12A & S50E) have been severely invaded by Invasive Alien Plants (IAPs) as well as altered by agrarian intensification and human development. Working for Water (WfW) Alien Plant Clearing Programme have been clearing IAPs in these catchments for the past twelve years. The current research aimed at establishing various degradation gradients occurring in the QCs. This was done by conducting land cover classification and change analysis over time, evaluating soil quality and assessing the success of the WfW program by quantifying the net primary production (NPP) and evapotranspiration (ET) trends on the cleared areas. A novel management scheme for decision makers, driver-pressure-state-impact-response (DPSIR) framework, was therefore suggested for managing these QCs sustainably.The soil analysis showed that phosphorus (P) levels are significantly different (P<0.05) between invaded, cleared and natural sites. High nitrogen (N) and pH were associated with Acacia proliferation in acidic soils. Object based image analysis (GEOBIA) was used for the land use land cover (LULC) classification using Landsat 8 OLI & TIRS imagery. LULC change analyses were carried out on two reference bases [National land cover (NLC) 2000 & Edited NLC (ENLC) 2000]. Land cover change analysis was facilitated by using a framework introducing labels to describe land cover change. Annual MODIS ET (MOD16)/NPP (MOD17) data were used to evaluate the rehabilitation progress in T12A using WfW clearing data. A DPSIR management framework, structuring the sustainable indicators at the QCs in a logical manner, was developed for decision and policy makers for dealing with management issues related to land use, water resources and soil quality management.The present research recommends that additional soil samples need to be collected for validation of soil nutrients status. Medium resolution Landsat imagery used for the LULC mapping provided accuracies of greater than 80%, but could not differentiate between invasive and indigenous trees. Hyperspectral or higher resolution imagery should be explored for mapping and delineating IAPs. Using coarse resolution MODIS products to model ET/NPP did not provide adequate detail of the cleared patches to describe the actual status of WfW clearings and their rehabilitation progress.

[发布机构] Stellenbosch University