Monitoring land Cover Changes and Fragmentation dynamics in the subtropical thicket of the Eastern Cape Province, South Africa

Land cover change trends and fragmentation dynamics in the Great Fish River Nature Reserve (GFRNR) and surrounding settlements were monitored for a period of 38 years, in the intervals of 1972-1982, 1982-1992 and 2002-2010. Gaining an understanding of these trends and dynamics is vital for land management and combating desertification. Monitoring land cover change and fragmentation dynamics was conducted using LandSAT MSS, LandSAT4TM and LandSAT 7ETM and SPOT 5 High-resolution Geometric (HRG) imagery. The objected-oriented supervised approach and cross-classification algorithm were used for classification of the satellite imagery and change detection respectively. Landscape fragmentation was analysed using FRAGSTATS 3.3® class level  land metrics. Overall, a decrease in the land area under intact and transformed thicket was realised. Degraded thicket, grassland and bare surfaces increased over the same period. Landscape metric analyses illustrated an increase in vegetation fragmentation over the 38-year period, as demonstrated by an increase in the number of patches (NP) and a decrease in the Largest Patch Index (LPI), particularly for intact and transformed thicket. Baseline land use/cover maps and fragmentation analyses in a temporal framework are valuable for gaining insights into, among other things, carbon stock change trends.Keywords: Land cover change, fragmentation; remote sensing; Geographic information systems (GIS

Factors affecting the invasion of Pteronia incana (Blue bush) onto hillslopes in Ngqushwa (formerly Peddie) District, Eastern Cape

The factors that influence the invasion of hillslopes by the shrub Pteronia incana in the communal rangelands of Ngqushwa (formerly Peddie) district were investigated. Mgwalana, one of the catchments in the district where encroachment by the species is widespread, was chosen. The study combined field observations with image analysis based on high resolution infrared imagery. The catchment was flown and high resolution infrared images (1mx1m) were taken using a Kodak DCS420 digital, colour-infrared camera. The images were analysed using Idrisi32 and Kilimanjaro GIS versions. The ability of different vegetation indices to separate P. incana from the other cover types was investigated. Field observations of the degree of P. incana invasion in relation to, inter alia, soil surface conditions, slope angle and visible forms of erosion were made. A Digital Elevation Model (DEM) of 20m spatial resolution was used to derive terrain parameters. The presence and absence of P. incana in relation to slope gradient and aspect were determined. The combined influence of the two terrain parameters and land use on the invasion was also investigated. The Topographic Wetness Index (WI), a component of the TOPMODEL was derived from the DEM and its relationship with the spatial distribution of P. incana was explored. Soil moisture dependencies for P. incana and grass species as well as surrogates for runoff under the shrub and adjacent bare areas were determined in the field. A high level of classification accuracy confirmed the reliability of digital camera imagery for spatial analyses. Distinct spectral separability for the surface vegetation cover types was achieved by means of the Perpendicular Vegetation Index (PVI) as opposed to the ratio based vegetation indices (NDVI, SAVI and MSAVI). The absence/presence of P. incana was noted to be strongly influenced by slope angle and aspect. The probability for P. incana occurrence increased with slope steepness and southerly slope orientation. Abandoned and grazing lands were identified as the main invasion hotspots. Blanket invasion of the former signified the high susceptibility of abandoned land to P. incana invasion. The combined influence of land use, slope gradient and aspect was also noted to have promoted the invasion. This is borne out by the concentration of the invasion on abandoned steep slopes with a southerly orientation. Local topographic variations were identified as having a strong bearing on P. incana spatial distribution. The topographically driven WI confirmed this relationship, such that P. incana was associated with the low WI values of convexities. Differences in the moisture dependencies between P. incana and grass species were demonstrated by the greater rooting depth of the former. During field surveys, soil surface crusting was noted as inherent to P. incana patchiness. The coupling between local topography and soil surface crusting underpins soil moisture variability at hillslope and patch scales respectively. This in turn determines the competition between P. incana and grass species and the eventual replacement of the latter by the former. A close spatial correlation between fully established P. incana and severe forms of soil erosion was observed. Loss of patchiness and expansion of inter-patch bare areas promote runoff connectivity erosion. As most of the runoff becomes run out, hillslopes tend towards dysfunctional systems. Greater soil moisture storage after rainstorms under P. incana tussocks than the adjacent bare areas signifies the shrub’s water harvesting capabilities. The tussocks could thus serve as a starting-pointbuilding- block for the rehabilitation of dysfunctional hillslope systems

A reconstruction of the history of land degradation in relation to land use change and land tenure in Peddie district, former Ciskei

A history of land degradation is reconstructed in a part of the dividing ridge between the Great Fish and Keiskamma rivers, in Peddie District, former Ciskei. The study entails a comparative investigation of the progressive changes in land use, vegetation and soil erosion in three tenure units, namely: former commercial farms, traditional and betterment villages. Analysis of the sequential aerial photography of the area for 1938,1954, 1965, 1975 and 1988 is employed. This is backed by groundtruthing exercises. Data thus obtained are quantified, and linkages between degradation, anthropogenic and physical factors are derived using PC ARC/INFO GIS. Differences in land tenure systems emerge as the main controlling factor to variations in land degradation. Confinement of vegetation diminution and erosion to traditional and betterment villages is observed at all dates. Scantily vegetated surfaces and riparian vegetation removal are a characteristic feature of both areas throughout the study period. 'Betterment,' introduced in the early 1960s to curb land degradation is, instead observed to exacerbate it, particularly soil erosion. Trends in land use change are characterised by the abandonment of cultivated land, which is noted to coincide with a sharp rise in population. Erosion intensification into severe forms particularly between 1965 and 1975, coincident with a period of extreme rainfall events, emerges as the most significant degradation trend. A close spatial correlation between abandoned cultivated land and intricate gullies is identified. So is the case between grazing land and severe sheet erosion. Within the grazing lands, an examination of erosion and categories of vegetated surfaces reveals that erosion occurs predominantly on the scanty vegetation category. Such erosion-vegetation interaction largely explains the non-recovery of the scanty vegetation category, even during periods of intense rainfall. Extensive channel degradation is evident along stream courses with scanty riparian vegetation. Physical factors are noted to have a significant bearing on erosion. The high prevalence of erosion on the Ecca group of rocks confirms its erosion-prone nature. Pockets of colluvium and alluvium accumulation in the steep bottomlands are identified as the sites of the most severe gully erosion. Field surveys at some of the sites indicate that a dolerite sill through the area forms a boundary of colluvium accumulation and the upslope limit to gully incision. That these sites are recognised as formerly cultivated land, portrays the interaction between physical and anthropogenic variables with regard to inducing degradation in the area

Use of sediment source fingerprinting to assess the role of subsurface erosion in the supply of fine sediment in a degraded catchment in the Eastern Cape, South Africa

Sediment source fingerprinting has been successfully deployed to provide information on the surface and subsurface sources of sediment in many catchments around the world. However, there is still scope to reexamine some of the major assumptions of the technique with reference to the number of fingerprint properties used in the model, the number of model iterations and the potential uncertainties of using more than one sediment core collected from the same floodplain sink. We investigated the role of subsurface erosion in the supply of fine sediment to two sediment cores collected from a floodplain in a small degraded catchment in the Eastern Cape, South Africa. The results showed that increasing the number of individual fingerprint properties in the composite signature did not improve the model goodness-of-fit. This is still a much debated issue in sediment source fingerprinting. To test the goodness-of-fit further, the number of model repeat iterations was increased from 5000 to 30,000. However, this did not reduce uncertainty ranges in modelled source proportions nor improve the model goodness-of-fit. The estimated sediment source contributions were not consistent with the available published data on erosion processes in the study catchment. The temporal pattern of sediment source contributions predicted for the two sediment cores was very different despite the cores being collected in close proximity from the same floodplain. This highlights some of the potential limitations associated with using floodplain cores to reconstruct catchment erosion processes and associated sediment source contributions. For the source tracing approach in general, the findings here suggest the need for further investigations into uncertainties related to the number of fingerprint properties included in un-mixing models. The findings support the current widespread use of <5000 model repeat iterations for estimating the key sources of sediment samples

Quantifying HIV transmission flow between high-prevalence hotspots and surrounding communities: a population-based study in Rakai, Uganda

Background International and global organisations advocate targeting interventions to areas of high HIV prevalence (ie, hotspots). To better understand the potential benefits of geo-targeted control, we assessed the extent to which HIV hotspots along Lake Victoria sustain transmission in neighbouring populations in south-central Uganda. Methods We did a population-based survey in Rakai, Uganda, using data from the Rakai Community Cohort Study. The study surveyed all individuals aged 15–49 years in four high-prevalence Lake Victoria fishing communities and 36 neighbouring inland communities. Viral RNA was deep sequenced from participants infected with HIV who were antiretroviral therapy-naive during the observation period. Phylogenetic analysis was used to infer partial HIV transmission networks, including direction of transmission. Reconstructed networks were interpreted through data for current residence and migration history. HIV transmission flows within and between high-prevalence and low-prevalence areas were quantified adjusting for incomplete sampling of the population. Findings Between Aug 10, 2011, and Jan 30, 2015, data were collected for the Rakai Community Cohort Study. 25 882 individuals participated, including an estimated 75·7% of the lakeside population and 16·2% of the inland population in the Rakai region of Uganda. 5142 participants were HIV-positive (2703 [13·7%] in inland and 2439 [40·1%] in fishing communities). 3878 (75·4%) people who were HIV-positive did not report antiretroviral therapy use, of whom 2652 (68·4%) had virus deep-sequenced at sufficient quality for phylogenetic analysis. 446 transmission networks were reconstructed, including 293 linked pairs with inferred direction of transmission. Adjusting for incomplete sampling, an estimated 5·7% (95% credibility interval 4·4–7·3) of transmissions occurred within lakeside areas, 89·2% (86·0–91·8) within inland areas, 1·3% (0·6–2·6) from lakeside to inland areas, and 3·7% (2·3–5·8) from inland to lakeside areas. Interpretation Cross-community HIV transmissions between Lake Victoria hotspots and surrounding inland populations are infrequent and when they occur, virus more commonly flows into rather than out of hotspots. This result suggests that targeted interventions to these hotspots will not alone control the epidemic in inland populations, where most transmissions occur. Thus, geographical targeting of high prevalence areas might not be effective for broader epidemic control depending on underlying epidemic dynamics. Funding The Bill & Melinda Gates Foundation, the National Institute of Allergy and Infectious Diseases, the National Institute of Mental Health, the National Institute of Child Health and Development, the Division of Intramural Research of the National Institute for Allergy and Infectious Diseases, the World Bank, the Doris Duke Charitable Foundation, the Johns Hopkins University Center for AIDS Research, and the President's Emergency Plan for AIDS Relief through the Centers for Disease Control and Prevention

A reconstruction of the history of land degradation in relation to land use change and land tenure in Peddie district, former Ciskei

A history of land degradation is reconstructed in a part of the dividing ridge between the Great Fish and Keiskamma rivers, in Peddie District, former Ciskei. The study entails a comparative investigation of the progressive changes in land use, vegetation and soil erosion in three tenure units, namely: former commercial farms, traditional and betterment villages. Analysis of the sequential aerial photography of the area for 1938,1954, 1965, 1975 and 1988 is employed. This is backed by groundtruthing exercises. Data thus obtained are quantified, and linkages between degradation, anthropogenic and physical factors are derived using PC ARC/INFO GIS. Differences in land tenure systems emerge as the main controlling factor to variations in land degradation. Confinement of vegetation diminution and erosion to traditional and betterment villages is observed at all dates. Scantily vegetated surfaces and riparian vegetation removal are a characteristic feature of both areas throughout the study period. 'Betterment,' introduced in the early 1960s to curb land degradation is, instead observed to exacerbate it, particularly soil erosion. Trends in land use change are characterised by the abandonment of cultivated land, which is noted to coincide with a sharp rise in population. Erosion intensification into severe forms particularly between 1965 and 1975, coincident with a period of extreme rainfall events, emerges as the most significant degradation trend. A close spatial correlation between abandoned cultivated land and intricate gullies is identified. So is the case between grazing land and severe sheet erosion. Within the grazing lands, an examination of erosion and categories of vegetated surfaces reveals that erosion occurs predominantly on the scanty vegetation category. Such erosion-vegetation interaction largely explains the non-recovery of the scanty vegetation category, even during periods of intense rainfall. Extensive channel degradation is evident along stream courses with scanty riparian vegetation. Physical factors are noted to have a significant bearing on erosion. The high prevalence of erosion on the Ecca group of rocks confirms its erosion-prone nature. Pockets of colluvium and alluvium accumulation in the steep bottomlands are identified as the sites of the most severe gully erosion. Field surveys at some of the sites indicate that a dolerite sill through the area forms a boundary of colluvium accumulation and the upslope limit to gully incision. That these sites are recognised as formerly cultivated land, portrays the interaction between physical and anthropogenic variables with regard to inducing degradation in the area

Estimation and monitoring of aboveground carbon stocks using spatial technology

Monitoring temporal changes of aboveground carbon (AGC) stocks distribution in subtropical thicket is key to understanding the role of vegetation in carbon sequestration. The main objectives of this research paper were to model and quantify the temporal changes of AGC stocks between 1972 and 2010 in the Great Fish River Nature Reserve and its environs, Eastern Cape Province, South Africa. We used a method based on the integration of remote sensing and geographical information systems to estimate AGC stocks in a time series framework. A non-linear regression model was developed using Normalised Difference Vegetation Index values generated from SPOT 5 High Resolution Geometric satellite imagery of 2010 as an independent variable and AGC stock estimates from field plots as the dependent variable. The regression model was used to estimate AGC stocks from satellite imagery for 1972 (Landsat TM), 1982 (Landsat 4 TM), 1992 (Landsat 7 ETM), 2002 (Landsat ETM+) and 2010 (SPOT 5) satellite imagery. AGC stocks for the respective years were compared by means of change detection analysis at the subtropical thicket class level. The results showed a decline of AGC stocks in all the classes from 1972 to 2010. Degraded and transformed thicket classes had the highest AGC stock losses. The decline of AGC stocks was attributed to thicket transformation and degradation, which were attributed to anthropogenic activities

Estimation and monitoring of aboveground carbon stocks using spatial technology

Monitoring temporal changes of aboveground carbon (AGC) stocks distribution in subtropical thicket is key to understanding the role of vegetation in carbon sequestration. The main objectives of this research paper were to model and quantify the temporal changes of AGC stocks between 1972 and 2010 in the Great Fish River Nature Reserve and its environs, Eastern Cape Province, South Africa. We used a method based on the integration of remote sensing and geographical information systems to estimate AGC stocks in a time series framework. A non-linear regression model was developed using Normalised Difference Vegetation Index values generated from SPOT 5 High Resolution Geometric satellite imagery of 2010 as an independent variable and AGC stock estimates from field plots as the dependent variable. The regression model was used to estimate AGC stocks from satellite imagery for 1972 (Landsat TM), 1982 (Landsat 4 TM), 1992 (Landsat 7 ETM), 2002 (Landsat ETM+) and 2010 (SPOT 5) satellite imagery. AGC stocks for the respective years were compared by means of change detection analysis at the subtropical thicket class level. The results showed a decline of AGC stocks in all the classes from 1972 to 2010. Degraded and transformed thicket classes had the highest AGC stock losses. The decline of AGC stocks was attributed to thicket transformation and degradation, which were attributed to anthropogenic activities

Hydrologic response to land use/cover changes and Pteronia incana shrub invasion in Keiskamma catchment, Eastern Cape Province, South Africa

The Keiskamma catchment has undergone significant land use/cover changes (LUCC) and invasion by Pteronia incana (P. incana) shrub, and the hydrological implications of the phenomena are not fully understood. This study assessed the hydrological response of the catchment using remote sensing per-pixel classification, the SWAT model between 1994 and 2016, and field experiments. Results revealed a significant increase in woody vegetation encroachment and a decrease in mean annual streamflow, runoff, soil water content, evapotranspiration and groundwater. However, high surface runoff, and sediment loss were evident under P. incana invader shrub at hillslope scale. The study concludes that the hydrological response of the catchment was influenced significantly by LUCC in the form of extensive invader shrub encroachment, expansion of exotic forest tree species, impoundments and infestation of riparian zones by invasive vegetation. Control of alien invasive plants and utilization of indigenous forest species are recommended for catchment management

An assessment of the spatial and temporal changes of Mabira tropical forest reserve and its environs, Central Uganda

Uganda’s forest cover has under gone radical changes in the past century with conflicting views being expressed on the ecological benefits versus economic value. This study presents the dynamics of land use/cover changes in and around Mabira Central Forest Reserve (CFR) between the period 1970 and 2015. A series of Landsat TM/ETM+ images were used to characterize ecological changes and socio-economic data was used to assess the dynamics of land use/cover changes. The classification results showed significant losses in wetlands for the period 1975-2000, while for the period between 2000 and 2015, the greatest losses were realized in forest cover. The gain in land use/cover changes occurred in subsistence farmlands between 1975 and 2000 whereas between 2000 and 2015, it was seen in the built-up class. The overall image classification accuracy achieved was 100%, 100%, 79% and 76% for the years 1975, 1986, 2000 and 2015, respectively. The logistic regression results revealed that the significant drivers of land use/ cover changes were: the high household size, perceived loss of soil fertility, poor agricultural practices, establishment of roadside markets, industrialization, and unclear forestry boundaries (P&lt;0.05). The non-significant drivers included the low education levels, establishment of power grids, insecurity, political interference, and weak enforcement of environmental laws. This study is among those that seek to contribute evidence that stakeholders may use to continue to advocate for demarcation of forest boundaries, enforcement of forestry laws and land use planning critical in the sustainable utilization of forest products and biodiversity conservation.Key words: Remote sensing, land use, land cover, change detectio