Search

Soil erosion is a global environmental problem and a pervasive form of land degradation that threatens land productivity and food and water security. Some of the biggest sources of sediment in catchments are cultivated and abandoned lands. However, the abandonment of cultivated fields is not well-researched. Our study assesses the level of degradation in cultivated and abandoned lands using a case study in South Africa. We answer three main questions: (1) What is the extent of crop field degradation on used, partly used, and abandoned fields? (2) What are the drivers of field abandonment in relation to land degradation? (3) Can proposed sustainable land management interventions tackle the dynamics of land abandonment and associated degradation? To answer these questions, cultivated and abandoned lands were mapped in a pilot catchment with ArcGIS tools and assigned severity codes and classified according to status, degradation, and encroachment. Systems diagrams were developed to show the interactions between agricultural land use and the level of degradation and leverage points in the system, with interventions assessed via a multi-criteria analysis. The results revealed that 37% of the total mapped area of croplands in the pilot site was abandoned and 20% of those lands were highly degraded. We argue that the innovative application of systems thinking through causal loop diagrams (CLDs) and leverage point analysis, combined with spatial and multi-criteria analyses, can assist with planning SLM interventions in similar contexts in the developing world. [ABSTRACT FROM AUTHOR]

Using an analysis of aerial photographs from 1942, 1985 and 2004 we assessed the impact of changing land tenure and land-use regimes on the cover of thicket vegetation on the Grahamstown commonage. Land-use impacts were examined by comparing plant species composition within three vegetation types between sites incorporated into commonage for different lengths of time and sites outside the commonage. Results showed that thicket cover increased by 87% between 1942 and 1985 but declined by 11% between 1985 and 2004. The increase in thicket cover was highest on land where goat browsing and wood harvesting was excluded. There was a decline in thicket cover when uncontrolled goat browsing and wood harvesting were introduced. An analysis of plant species composition suggests an increase in the impact of livestock in areas closest to the urban area and with time since inclusion into commonage. Such areas exhibited greater cover of Increaser II grasses and dwarf shrubs in the herbaceous layer and lower cover of succulents within subtropical thicket. We interpret the decline in thicket cover and shift to a less palatable and less productive vegetation as resulting from the open-access land use system that has prevailed on the commonage since 1994. [ABSTRACT FROM AUTHOR]

We examined the effect of changes in land use and land tenure on bush encroachment and vegetation condition. An analysis of aerial photographs from three time steps (1949, 1985 and 2004) was used to document changes in woody plant density in different vegetation types on commonage and an adjacent commercial farm in Fort Beaufort, South Africa. Rangeland condition was assessed in different vegetation units of the area and woody plant density was related to distance from urban settlement. Results showed that there has been an increase in woody plant cover in both commonage and commercial farming areas, particularly between 1949 and 1985. However, since 1985, increased rates of urbanisation have stabilised, and in some areas reduced, woody plant thickening, especially at locations closest to urban settlements. Bush encroachment is being controlled to some extent by fuelwood harvesting and goat browsing, resulting in a reduction in height of favoured woody species such asAcacia karroo(Vachellia karroo). There has been a shift to less palatable browse species on the commonage areas and the condition of the grass sward is poor. Change in woody plant cover is significantly influenced by changing patterns of land use and land tenure over time which, in turn, affect rangeland condition. [ABSTRACT FROM AUTHOR]

The West African savanna experiences a prolonged dry season with Harmattan winds which facilitate large and persistent biomass burning from November to April. The fires are mostly caused by humans, mainly in pursuit of the day to day livelihood activities. We examined how fire influences the population structure and abundance of two economically important woody species Vitellaria paradoxa (Shea tree) and Anogeissus leiocarpa (African Birch) in six land use types in the Guinea savanna, Ghana. We calculated the stand basal area, mean densities of juveniles and adult trees, Lorey's mean height of adult trees and Simpson's index of dominance. Eight diameter size classes of each species were analysed by comparing their observed distributions to a three-parameter Weibull distribution across the land use types. A total of 3366 individuals of A. leiocarpa (n = 1,846) and V. paradoxa (n = 1,520) were enumerated. The basal area of A. leiocarpa and V. paradoxa in sacred groves (16.9 m2 ha−1) and unburnt woodlands (20.6 m2 ha−1) was higher than the estimates in the other land use types. High mean densities of A. leiocarpa and V. paradoxa were found in sacred groves (22.7 ± 29.7 stems ha−1) and fallows (15.3 ± 2.2 stems ha−1), respectively. Mean density of juveniles of both A. leiocarpa (248.0 ± 89.1 stems ha−1) and V. paradoxa (68.0 ± 29.7 stems ha−1) were higher in unburnt woodlands than in the other land use types. A. leiocarpa was absent in fallows and burnt crop fields. An inverse J-shaped distribution was found in sacred groves for both species. The absence of A. leiocarpa in burnt crop fields and the decrease of some size classes of V. paradoxa in both burnt and unburnt crop fields indicate the need for sustainable conservation of both species. Furthermore, the inverse J-shape distribution found in sacred groves for both A. leiocarpa and V. paradoxa implies that these species thrive best with minimal anthropogenic disturbances. Although species conservation is achieved through conventional protection, traditional or cultural conservation practices which avoid the indiscriminate use of fire should be highly promoted to ensure sustainable conservation of species. • We examined how fire influences the population structure and abundance of two important woody species in a West African parkland. • High mean densities of A. leiocarpa and V. paradoxa were found in some land use types. • An inverse J-shaped distribution was found in community conserved groves for both species. • Decrease in size classes of V. paradoxa in some land use types are an indication of the need for conservation of species. [ABSTRACT FROM AUTHOR]