Showing papers by "Barend F.N. Erasmus published in 2015"

Systematic land-cover change in KwaZulu-Natal, South Africa: Implications for biodiversity.

Abstract: Land-cover change and habitat loss are widely recognised as the major drivers of biodiversity loss in the world. Land-cover maps derived from satellite imagery provide useful tools for monitoring land-use and land-cover change. KwaZulu-Natal, a populous yet biodiversity-rich province in South Africa, is one of the first provinces to produce a set of three directly comparable land-cover maps (2005, 2008 and 2011). These maps were used to investigate systematic land-cover changes occurring in the province with a focus on biodiversity conservation. The Intensity Analysis framework was used for the analysis as this quantitative hierarchical method addresses shortcomings of other established land-cover change analyses. In only 6 years (2005-2011), a massive 7.6% of the natural habitat of the province was lost to anthropogenic transformation of the landscape. The major drivers of habitat loss were agriculture, timber plantations, the built environment, dams and mines. Categorical swapping formed a significant part of landscape change, including a return from anthropogenic categories to secondary vegetation, which we suggest should be tracked in analyses. Longer-term rates of habitat loss were determined using additional land-cover maps (1994, 2000). An average of 1.2% of the natural landscape has been transformed per annum since 1994. Apart from the direct loss of natural habitat, the anthropogenically transformed land covers all pose additional negative impacts for biodiversity remaining in these or surrounding areas. A target of no more than 50% of habitat loss should be adopted to adequately conserve biodiversity in the province. Our analysis provides the first provincial assessment of the rate of loss of natural habitat and may be used to fulfil incomplete criteria used in the identification of Threatened Terrestrial Ecosystems, and to report on the Convention on Biological Diversity targets on rates of natural habitat loss.

The impacts of changes in land use on woodlands in an equatorial african savanna

Abstract: Savanna landscapes are vitally important in providing both ecological and economic services that sustain local livelihoods and national economies, particularly for sub-Saharan African countries whose economies are mainly agrarian. Development prospects in savanna landscapes are however dependent on actions to avoid and to slow or reverse degradation and that are aided with a clear understanding of trends in land use/cover changes, their causes and implications for conservation. We analysed land use/cover changes based on three Landsat satellite images (1984, 1995 and 2000/2001) and the influence of human utilization on the changes in an equatorial African savanna, central Uganda, for the period 1984–2000/2001. The land cover classification and change analysis clearly identified the dominant land cover types, revealing a severe reduction in woodland cover with dense woodlands decreasing by 64%, over a 17-year period. Consequently, medium woodland, open woodland and cultivation/settlements areas cover increased by 31%, 3% and 80%, respectively. The cover change analysis results were corroborated with interview results that also attributed the woodland cover loss to increasing commercial charcoal production, expanding livestock grazing, subsistence crop cultivation and an insecure land use tenure system. Indeed, the major land use types in the savanna are charcoal production, shifting crop cultivation and livestock rearing. The decreasing woody vegetation cover threatens the savanna's ability to continue providing ecosystems services to support the livelihoods of people who mainly depend on natural resources and are vulnerable to the impacts of climate change. Copyright © 2014 John Wiley & Sons, Ltd.

Biomass Increases Go under Cover: Woody Vegetation Dynamics in South African Rangelands

Abstract: Woody biomass dynamics are an expression of ecosystem function, yet biomass estimates do not provide information on the spatial distribution of woody vegetation within the vertical vegetation subcanopy. We demonstrate the ability of airborne light detection and ranging (LiDAR) to measure aboveground biomass and subcanopy structure, as an explanatory tool to unravel vegetation dynamics in structurally heterogeneous landscapes. We sampled three communal rangelands in Bushbuckridge, South Africa, utilised by rural communities for fuelwood harvesting. Woody biomass estimates ranged between 9 Mg ha -1 on gabbro geology sites to 27 Mg ha -1 on granitic geology sites. Despite predictions of woodland depletion due to unsustainable fuelwood extraction in previous studies, biomass in all the communal rangelands increased between 2008 and 2012. Annual biomass productivity estimates (10–14% p.a.) were higher than previous estimates of 4% and likely a significant contributor to the previous underestimations of modelled biomass supply. We show that biomass increases are attributable to growth of vegetation <5 m in height, and that, in the high wood extraction rangeland, 79% of the changes in the vertical vegetation subcanopy are gains in the 1-3m height class. The higher the wood extraction pressure on the rangelands, the greater the biomass increases in the low height classes within the subcanopy, likely a strong resprouting response to intensive harvesting. Yet, fuelwood shortages are still occurring, as evidenced by the losses in the tall tree height class in the high extraction rangeland. Loss of large trees and gain in subcanopy shrubs could result in a structurally simple landscape with reduced functional capacity. This research demonstrates that intensive harvesting can, paradoxically, increase biomass and this has implications for the sustainability of

Evidence for climate-induced range shift in Brachystegia (miombo) woodland.

Abstract: Brachystegia spiciformis Benth. is the dominant component of miombo, the sub-tropical woodlands which cover 2.7 million km2 of south-central Africa and which is coincident with the largest regional centre of endemism in Africa. However, pollen records from the genus Brachystegia suggest that miombo has experienced rapid range retraction (~450 km) from its southernmost distributional limit over the past 6000 years. This abrupt biological response created an isolated (by ~200 km) and incomparable relict at the trailing population edge in northeast South Africa. These changes in miombo population dynamics may have been triggered by minor natural shifts in temperature and moisture regimes. If so, B. spiciformis is likely to be especially responsive to present and future anthropogenic climate change. This rare situation offers a unique opportunity to investigate climatic determinants of range shift at the trailing edge of a savannah species. A niche modelling approach was used to produce present-day and select future B. spiciformis woodland ecological niche models. In keeping with recent historical range shifts, further ecological niche retraction of between 30.6% and 47.3% of the continuous miombo woodland in Zimbabwe and southern Mozambique is predicted by 2050. Persistence of the existing relict under future climate change is plausible, but range expansion to fragmented refugia in northeast South Africa is unlikely. As Brachystegia woodland and associated biota form crucial socio-economic and biodiversity components of savannas in southern Africa, their predicted further range retraction is of concern.

Modelling the current and future dry-season distribution of the edible stinkbug Encosternum delegorguei in sub-Saharan Africa

Abstract: Rural communities in South Africa, Malawi, and Zimbabwe annually harvest from winter aggregations of the edible stinkbug Encosternum (= Haplosterna) delegorguei Spinola (Hemiptera: Tessaratomidae). Using a regional maximum entropy modelling method (MAXENT) for winter field records of E. delegorguei, current and future climate scenarios were identified. Winter precipitation and to a lesser degree summer precipitation and winter temperature were the climatic variables found to limit the regional distribution of E. delegorguei. The receiver operating characteristic analysis (ROC) yielded an AUC (area under the curve) value of 0.995, indicating a reliable model, although interpretations must consider the influence of elevation for this insect. A testable hypothesis regarding future distribution of E. delegorguei in the face of climate change has been formulated for its winter range. Predator-prey relationships and food source also influence the occurrence of E. delegorguei and may override the influence of climate. The current distribution modelled identifies potential new sites in areas of similar climate which may be unknown to harvesters. Areas for mini-livestock pilot studies provide opportunities for extending commercial potential and ensuring a sustainable, valuable food source during periods of food scarcity.

Observed range dynamics of South African amphibians under conditions of global change

Abstract: Changes in the size and location of species ranges are a recognized response to environmental changes. We assessed recent range dynamics of South African amphibians using data consolidated by the South African Frog Atlas Project, which provided both historical (1905–1995) and recent distribution data (1996–2003). Sampling differences were accounted for using a correction factor and subsampling protocols. Changes to the size of species ranges and shifts in the mean range centre for latitude, longitude and altitude were assessed. Most (70%) of the assessed species showed range contractions. Of the expected climate change predictions, only upslope shifts were supported (mean 47.6 m). There were no significant mean latitudinal shifts for the assessed group of species. Species of the Bushveld region shifted northwesterly and upslope, while species of the Winter Rainfall region also shifted northwesterly. The small, though significant, general taxon-wide trends where minor in comparison to the wide variety of idiosyncratic, species-specific range changes that were observed. The species-specific observed range changes that were documented should be used to further investigate range change drivers on an individual species basis.

What lies beneath: detecting sub-canopy changes in savanna woodlands using a three-dimensional classification method

Abstract: The Carnegie Airborne Observatory is made possible by the Avatar Alliance Foundation, Margaret A. Cargill Foundation, John D. and Catherine T. MacArthur Foundation, Grantham Foundation for the Protection of the Environment, W.M. Keck Foundation, Gordon and Betty Moore Foundation, Mary Anne Nyburg Baker and G. Leonard Baker Jr. and William R. Hearst III. Application of the CAO data in South Africa is made possible by the Andrew Mellon Foundation and the endowment of the Carnegie Institution for Science.

Observing vegetation dynamics at medium spatial scale: Lessons from Africa and Asia

Abstract: In this paper, we drew on experience from current Earth Observation (EO) research in Africa and Asia based on the 250m MODIS vegetation index time series covering large spatial extents. In the first example in the southern Africa, we derived a key set of phenometrics (overall greenness, peak and timing of annual greenness) and analyzed trends in these parameters. In the second example in the eastern Africa, we mapped human-induced vegetation productivity decline. The climate-induced changes in vegetation were largely disentangled from the anthropogenic-driven changes by using rainfall data from radar observations. In the last example, we revealed vegetation dynamic patterns across Central Asia by analyzing trends in overall greenness. The paper concluded on the possibilities and constraints of the available data and methods used to analyze vegetation dynamics at medium spatial resolution in relation to evolving issues in Africa and Asia.