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Aboveground biomass density models for NASA’s Global Ecosystem Dynamics Investigation (GEDI) lidar mission
(2022-03) Duncanson, L; Kellner, JR; Armston, J; Dubayah, R; Minora, DM; Hancock, S; Healey, SP; Patterson, PL; Main, Russell S; Naidoo, Laven
NASA’s Global Ecosystem Dynamics Investigation (GEDI) is collecting spaceborne full waveform lidar data with a primary science goal of producing accurate estimates of forest aboveground biomass density (AGBD). This paper presents the development of the models used to create GEDI’s footprint-level (~25 m) AGBD (GEDI04_A) product, including a description of the datasets used and the procedure for final model selection. The data used to fit our models are from a compilation of globally distributed spatially and temporally coincident field and airborne lidar datasets, whereby we simulated GEDI-like waveforms from airborne lidar to build a calibration database. We used this database to expand the geographic extent of past waveform lidar studies, and divided the globe into four broad strata by Plant Functional Type (PFT) and six geographic regions. GEDI’s waveform-to-biomass models take the form of parametric Ordinary Least Squares (OLS) models with simulated Relative Height (RH) metrics as predictor variables. From an exhaustive set of candidate models, we selected the best input predictor variables, and data transformations for each geographic stratum in the GEDI domain to produce a set of comprehensive predictive footprint-level models. We found that model selection frequently favored combinations of RH metrics at the 98th, 90th, 50th, and 10th height above ground-level percentiles (RH98, RH90, RH50, and RH10, respectively), but that inclusion of lower RH metrics (e.g. RH10) did not markedly improve model performance. Second, forced inclusion of RH98 in all models was important and did not degrade model performance, and the best performing models were parsimonious, typically having only 1-3 predictors. Third, stratification by geographic domain (PFT, geographic region) improved model performance in comparison to global models without stratification. Fourth, for the vast majority of strata, the best performing models were fit using square root transformation of field AGBD and/or height metrics. There was considerable variability in model performance across geographic strata, and areas with sparse training data and/or high AGBD values had the poorest performance. These models are used to produce global predictions of AGBD, but will be improved in the future as more and better training data become available.
The Circular Economy as Development Opportunity: Exploring Circular Economy Opportunities across South Africa’s Economic Sectors
(CSIR, 2021-12) Godfrey, Linda K; Nahman, Anton; Oelofse, Suzanna HH; Trotter, Douglas; Khan, Sumaya; Nontso, Zintle; Magweregwede, Fleckson; Sereme, Busisiwe V; Okole, Blessed N; Gordon, Gregory ER; Brown, Bernadette; Pillay, Boyse; Schoeman, Chanel; Fazluddin, Shahed; Ojijo, Vincent O; Cooper, Antony K; Kruger, Daniel M; Napier, Mark; Mokoena, Refiloe; Steenkamp, Anton J; Msimanga, Xolile P; North, Brian C; Seetal, Ashwin R; Mathye, Salamina M; Godfrey, Linda K
The intention of this book is to present the CSIR’s position and interpretation of the circular economy, and to use it to drive discussions on where immediate circular economy opportunities are achievable in South Africa. Opportunities that can be harnessed by business, government and civil society. These circular economy opportunities are framed in this book within the context of the current challenges facing various economic sectors. The CSIR has selected seven, resource intensive sectors – mining, agriculture, manufacturing, human settlements, mobility, energy and water – for further assessment. Many of these economic sectors have seen significant declines over the past years, with agriculture, manufacturing, transport and construction all showing negative growth pre-COVID. These are all sectors under economic stress and in need of regeneration. South Africa stands on the threshold of profound choices regarding its future development path. Transitioning to a more circular economy provides the country with the opportunity to address many national priorities including manufacturing competitiveness, food security; sustainable, resilient and liveable cities; efficient transport and logistics systems; and energy and water security, while at the same time decarbonising the economy. The transition to a circular economy provides the country with an opportunity for green and inclusive development to be the cornerstone of a post-COVID economic recovery. The titles of this book chapters are the following: Chapter 1: Driving economic growth in South Africa through a low carbon, sustainable and inclusive circular economy. Chapter 2: Placing the South African mining sector in the context of a circular economy transition. Chapter 3: Supporting food security and economic development through circular agriculture. Chapter 4: Supporting the development of a globally competitive manufacturing sector through a more circular economy. Chapter 5: Creating resilient, inclusive, thriving human settlements through a more circular economy. Chapter 6: Facilitating sustainable economic development through circular mobility. Chapter 7: Decoupling South Africa’s development from energy demand through a more circular economy. Chapter 8: Decoupling South Africa’s development from water demand through a circular economy.
Dammarane-type triterpenoids with anti-cancer activity from the leaves of Cleome gynandra
(2021-06) Mzondo, Buntubonke; Dlamini, Nomusa; Malan, FP; Labuschagne, Philip W; Bovilla, VR; Madhunapantula, SV; Maharaj, V
Three dammarane-type triterpernoids including two new ones, cleogynones A and B (1 and 2), were isolated from the leaves of Cleome gynandra. The structures of the new triterpenoids were elucidated by spectroscopic data analysis and confirmed by single crystal X-ray crystallography. All three compounds showed moderate cytotoxicity against breast cancer (MDA-MB-468), cleogynone B (2) and compound (3) further showed cytotoxicity against colorectal cancer (HCT-116 & HCT-15). Cleogynone B was also moderately active against lung cancer (A549).
Determining the wetland-dryland boundary of depressions using littoral gradient analysis of soil edaphic factors
(2021-08) Nondlazi, Basanda X; Cho, Moses A; Van Deventer, Heidi; Sieben, EJ
Depressional wetlands are highly vulnerable to changes in land surface temperature and rainfall but little is known about their responses to future climate change. This study assessed the variation in edaphic factors between wetlands and along their littoral gradients to detect the boundary between the endorheic wetlands and upland zones. A sample of 202 paired measurements of three edaphic factors were collected (Soil Moisture Content – SMC-g/g, Bulk Density – BD-g/cm 3 and Salinity as Electrical Conductivity – EC-dS/m) in 10 m plots along 14 belt transects in eight representative wetlands in the Mpumalanga Lake District, South Africa. In general, there were significant differences between the eight wetlands for SMC and BD but not for EC.SMC and BD generally showed negative trends along the littoral gradients. The trends occurred over short distances, ranging from 30 to 70 m, reflecting the extent of the wetlands. Understanding of the spatial variation of edaphic factors helps in the management and monitoring of depressional wetlands under a changing climate. In addition, the study showed that the current wetland buffer zone stipulated in local legislation was too narrow and recommended that this be extended to 100 m.
Distinguishing tree species from in situ hyperspectral and temporal measurements through ensemble statistical learning
(2023-08) Dudeni-Tlhone, Nontembeko; Mutanga, O; Debba, Pravesh; Cho, Moses A
Hyperspectral sensors capture and compute spectral reflectance of objects over many wavelength bands, resulting in a high-dimensional space with enough information to differentiate between spectrally similar objects. Due to the curse of dimensionality, high spectral dimensionality can also be difficult to handle and analyse, demanding complex processing and the use of advanced analytical techniques. Moreover, when hyperspectral measurements are taken at different temporal frequencies, separation is likely to improve; however, additional complexities in modelling time variability concurrently with this high spectral dimensionality may be created. As a result, the applicability of ensemble-based techniques suitable for high-dimensional data is examined in this research, together with the statistical evaluation of time-induced variability, since spectral measurements of tree species were taken at different time periods. Classification errors for the stochastic gradient boosting (SGB) and random forest (RF) methods ranged between 5.6% and 13.5%, respectively. Differences in classification accuracy or errors were also accounted for in the assessment of the models, with up to 46% of variation in classification error due to the effect of time in the RF model, indicating that measurement time is important in improving discrimination between tree species. This is because optical leaf characteristics can vary during the course of the year due to seasonal effects, health status, or the developmental stage of a tree. Different spectral properties (assumed from relevant wavelength bands) were found to be key factors impacting the models’ discrimination performance at various measurement times.
Estimating South African maize biomass using integrated high-resolution UAV and sentinel 1 and 2 datasets
(2021-07) Naidoo, Laven; Main, Russell S; Cho, Moses A; Madonsela, Sabelo; Majozi, Nobuhle, P
Sentinel-1 and Sentinel-2 have provided consistent hyper-temporal information (5–7 days or earlier) at high spatial resolutions (10m) on biophysical composition, structural and physiological conditions of crops in a variety of environments. Unmanned aerial vehicles (UAVs) can provide sufficient calibration and validation data for model upscaling and regional extrapolation. Of the numerous maize crop parameters which require regular and accurate modelling, maize above ground biomass (AGB) is important for yield estimates. The aim of this study was to evaluate the Random Forest modelling performance of Sentinel 1 SAR C-band and Sentinel 2 multispectral imagery for maize AGB estimation whilst utilising UAV-derived maize AGB for model upscaling. Results illustrated that Sentinel 2 reflectance bands predicted more accurate estimates of maize AGB than the VV and VH polarisation bands of Sentinel 1 (R2 = 0.91; RMSE = 355.11g/m 2 ; rRMSE = 21.28% versus R2 = 0.31; RMSE = 974.72g/m 2 ; rRMSE = 59.04%).
Ethnomedicinal and phytochemical properties of sesquiterpene lactones from Dicoma (Asteraceae) and their anticancer pharmacological activities: A review
(2021-09) Mangisa, Mandisa; Peter, Xolani K; Khosa, Mbokota; Fouche, Gerda; Nthambeleni, Rudzani; Senabe, Jeremiah V; Tarirai, C; Tembu, VJ
Dicoma species belonging to the Asteraceae family are commonly utilized as traditional medicine in Southern Africa. Dicoma anomala, Dicoma capensis, Dicoma schinzii and Dicoma zheyeri are the most common ethnomedicinal plant species used in Southern Africa. The plant species of Dicoma genus are identified as the main source of sesquiterpene lactones. Dicoma species are associated with pharmacological properties such as antiviral, antibacterial, antihelminthic, antispasmodic antiplasmodial, as analgesic, antiinflammatory, anticancer, and wound healing properties. The plant species of Dicoma genus are identified as the main source of sesquiterpene lactones. In this review, the authors report the ethnomedicinal and phytochemical properties, and pharmacology of sesquiterpene lactones from the genus Dicoma from 1978 to 2020. There are over eighty (80) reported sesquiterpene lactones isolated from Dicoma species including, germacronolides, eudesmanolides, melampolides, guaianolides and pseudoguaianolides. Sesquiterpene lactones possess antimalarial, anticancer and antiinflammation activities due to their structural diversity. The diagnostic search on phytochemistry of sesquiterpene lactones from Dicoma carried out in the 70’s has limited pharmacological screening activities; hence these may need to be revisited and explored. Furthermore, the literature search conducted in this review showed that out of the 35 Dicoma species, seven species were investigated, and their medicinal uses, pharmacology and photochemistry reported. The recommendation drawn is that Dicoma species that are not investigated and not fully exploited should be studied for their phytochemicals and efficacy. The information compiled in this review on the pharmacological, phytochemistry and ethnomedicinal activities of genus Dicoma was obtained from relevant literature sources, including books, book chapters, websites, theses, reviews and research articles from databases such as Web of Science, Scopus, Science Direct, BioMed Central, Springer link, PubMed, and Google Scholar.
Exploring the utility of Sentinel-2 for estimating maize chlorophyll content and leaf area index across different growth stages
(2021-12) Madonsela, Sabelo; Cho, Moses A; Naidoo, Laven; Main, Russell S; Majozi, Nobuhle P
This study investigated the utility of Sentinel-2 spectral data for estimating leaf area index (LAI), leaf and canopy chlorophyll content of maize at different growth stages. Vegetation indices based on the visible-near infrared and red-edge regions of the spectrum were computed from Sentinel-2 imagery acquired within one or two days of field data collection. Results showed that green chlorophyll index (CIgreen) and red-edge chlorophyll index (CIred-edge), using the red-edge variant centred at 705 nm, consistently showed higher relationship to maize LAI with r2 of 0.65 and 0.63 during the early stages of growth, respectively, and an r2 of 0.79 and 0.81 during tassel stage, respectively. Regarding canopy chlorophyll content the results indicated the spectral advantage of the Sentinel-2 sensor with the presence of two red-edge bands for continuous monitoring of maize chlorophyll content. Overall, the results indicated that maize biophysical variables can be monitored at satellite level using Sentinel-2 data.
Geospatial analysis of meteorological drought impact on Southern Africa biomes
(2021-01) Cho, Moses A; Chirwa, PW; Marumbwa, FM
Within Southern African biomes, droughts are recurrent with devastating impacts on ecological, economic, and human wellbeing. In this context, understanding the drought impact on vegetation is of extreme importance. However, information on drought impact on natural vegetation at the biome level is scanty and remains poorly understood. Most studies of drought impact on vegetation have largely focussed on crops. The few existing studies on natural vegetation are based on experiments and field measurements at individual tree level which are not representative of biomes. In this study, we mapped the spatial extent and severity of drought using the Standardized Precipitation Evapotranspiration Index (SPEI) and then quantified the drought impact on Southern African biomes using the Vegetation Condition Index (VCI) for the period 1998 to 2017. To compare drought impact across the biomes, we computed the percentage area of the biome with seasonal VCI <30. The drought trend for each biome was computed for each pixel using a linear regression model in R software using the seasonal VCI images from 1998 to 2017. Our result showed that extreme drought impact on vegetation was mainly confined to the southwestern biomes (i.e. the Nama karoo and desert biomes) with most drought occurring during the first half of the season. We also observed an increasing trend of VCI (1998 to 2017) across all biomes and this increasing VCI trend might be explained by woody encroachment which is prevalent in the Savannah and Grassland biomes. The results of this study provide baseline information on drought hotspots.
Immunogenic profile of a plant-produced nonavalent African horse sickness viral protein 2 (VP2) vaccine in IFNAR-/-mice
(2024-04) O’Kennedy, Martha M; Roth, Robyn; Ebersohn, K; Du Plessis, LH; Mamputha, Sipho; Rutkowska, Daria A; Du Preez, Ilse; Verschoor, JA; Lemmer, Yolandy
A safe, highly immunogenic multivalent vaccine to protect against all nine serotypes of African horse sickness virus (AHSV), will revolutionise the AHS vaccine industry in endemic countries and beyond. Plant-produced AHS virus-like particles (VLPs) and soluble viral protein 2 (VP2) vaccine candidates were developed that have the potential to protect against all nine serotypes but can equally well be formulated as mono- and bi-valent formulations for localised outbreaks of specific serotypes. In the first interferon a/ß receptor knock-out (IFNAR-/-) mice trial conducted, a nine-serotype (nonavalent) vaccine administered as two pentavalent (5 µg per serotype) vaccines (VLP/VP2 combination or exclusively VP2), were directly compared to the commercially available AHS live attenuated vaccine. In a follow up trial, mice were vaccinated with an adjuvanted nine-serotype multivalent VP2 vaccine in a prime boost strategy and resulted in the desired neutralising antibody titres of 1:320, previously demonstrated to confer protective immunity in IFNAR-/- mice. In addition, the plant-produced VP2 vaccine performed favourably when compared to the commercial vaccine. Here we provide compelling data for a nonavalent VP2-based vaccine candidate, with the VP2 from each serotype being antigenically distinguishable based on LC-MS/MS and ELISA data. This is the first preclinical trial demonstrating the ability of an adjuvanted nonavalent cocktail of soluble, plant-expressed AHS VP2 proteins administered in a prime-boost strategy eliciting high antibody titres against all 9 AHSV serotypes. Furthermore, elevated T helper cells 2 (Th2) and Th1, indicative of humoral and cell-mediated memory T cell immune responses, respectively, were detected in mouse serum collected 14 days after the multivalent prime-boost vaccination. Both Th2 and Th1 may play a role to confer protective immunity. These preclinical immunogenicity studies paved the way to test the safety and protective efficacy of the plant-produced nonavalent VP2 vaccine candidate in the target animals, horses.
In vitro study on efficacy of PHELA, an African traditional drug against SARS-CoV-2
(2022-06) Matsabisa, MG; Alexandre, Kabamba B; Ibeji, CU; Tripathy, S; Erukainure, OL; Malatji, Kanyane; Chauke, Sipho H; Okole, Blessed N; Chabalal, HB
In 2019, coronavirus has made the third apparition in the form of SARS-CoV-2, a novel strain of coronavirus that is extremely pathogenic and it uses the same receptor as SARS-CoV, the angiotensin converting enzyme 2 (ACE2). However, more than 182 vaccine candidates have been announced; and 12 vaccines have been approved for use, although, even vaccinated individuals are still vulnerable to infection. In this study, we investigated PHELA, recognized as an herbal combination of four exotic African medicinal plants namely; Clerodendrum glabrum E. Mey. Lamiaceae, Gladiolus dalenii van Geel, Rotheca myricoides (Hochst.) Steane & Mabb, and Senna occidentalis (L.) Link; as a candidate therapy for COVID-19. In vitro testing found that PHELA inhibited> 90% of SARS-CoV-2 and SARS CoV infection at concentration levels of 0.005 mg/ml to 0.03 mg/ml and close to 100% of MERS-CoV infection at 0.1 mg/ml to 0.6 mg/ml. The in vitro average IC50 of PHELA on SARS-COV-2, SARS-CoV and MERS-COV were ~ 0.01 mg/ml. Secondly in silico docking studies of compounds identifed in PHELA showed very strong binding energy interactions with the SARS-COV-2 proteins. Compound 5 showed the highest afnity for SARS-COV-2 protein compared to other compounds with the binding energy of - 6.8 kcal mol-1. Our data showed that PHELA has potential and could be developed as a COVID-19 therapeutic.
Indigenous knowledge on the uses, sustainability and conservation of African ginger (Siphonochilus aethiopicus) among two communities in Mpumalanga province, South Africa
(2022-03) Seile, BP; Bareetseng, Andries S; Koitsiwe, MT; Aremu, AO
Harvesting of medicinal plants in the wild has an impact on sustainability of medicinal plants, which leads to the need for intervention in terms of conservation strategies. Siphonochilus aethiopicus, commonly known as African ginger or wild ginger is used to cure a variety of health conditions/illnesses, such as coughs, colds, asthma, nausea, headaches and pains. This study explored the potential role of indigenous knowledge on the uses, sustainability, and conservation strategies for African ginger among two communities in Mpumalanga province. Qualitative method entailing in-depth interviews were used for this research. We used a non-probability sample (snowballing) to recruit ten (10) participants that comprised of four traditional health practitioners, four knowledge holders and two herbalists, considered as experts on African ginger in the study area. The data was analysed using thematic analysis. The diverse indigenous knowledge on the uses of African ginger were divided into two categories (diseases and spiritual/cultural purposes) among the local communities. African ginger is indigenous to South Africa and the plant species in the wild is mainly lost to commercial trade. As revealed by the participants, the multiple uses of African ginger are major contributing factors exacerbating the demands for the plant. The uses of African ginger have resulted in the scarcity and possibly extinction of this plant species in the wild, which remain a major concerns to several stakeholders especially traditional health practitioners. Harvesting of the rhizomes of African ginger is recommended instead of the root given the relative ease and higher chances for survival and regeneration. To ensure the sustainable utilisation of African ginger, its cultivation was recommended by the participants. However, there is a need for further intervention to assess how the community members can be assisted with developing and adopting indigenous conservation protocols for the continuous sustainability of African ginger. In addition, it is pertinent to strongly discourage the indiscriminate destruction of natural habitats and create more awareness on the importance of designating protected areas among local communities.
Investigating the relationship between tree species diversity and landsat-8 spectral heterogeneity across multiple phenological stages
(2021-06) Madonsela, Sabelo; Cho, Moses A; Ramoelo, Abel; Mutanga, O
The emergence of the spectral variation hypothesis (SVH) has gained widespread attention in the remote sensing community as a method for deriving biodiversity information from remotely sensed data. SVH states that spectral heterogeneity on remotely sensed imagery reflects environmental heterogeneity, which in turn is associated with high species diversity and, therefore, could be useful for characterizing landscape biodiversity. However, the effect of phenology has received relatively less attention despite being an important variable influencing plant species spectral responses. The study investigated (i) the effect of phenology on the relationship between spectral heterogeneity and plant species diversity and (ii) explored spectral angle mapper (SAM), the coefficient of variation (CV) and their interaction effect in estimating species diversity. Stratified random sampling was adopted to survey all tree species with a diameter at breast height of > 10 cm in 90 × 90 m plots distributed throughout the study site. Tree species diversity was quantified by the Shannon diversity index (H'), Simpson index of diversity (D2) and species richness (S). SAM and CV were employed on Landsat-8 data to compute spectral heterogeneity. The study applied linear regression models to investigate the relationship between spectral heterogeneity metrics and species diversity indices across four phenological stages. The results showed that the end of the growing season was the most ideal phenological stage for estimating species diversity, following the SVH concept. During this period, SAM and species diversity indices (S, H', D2) had an r2 of 0.14, 0.24, and 0.20, respectively, while CV had an r2 of 0.22, 0.22, and 0.25, respectively. The interaction of SAM and CV improved the relationship between the spectral data and H' and D2 (from r2 of 0.24 and 0.25 to r2 of 0.32 and 0.28, respectively) at the end of the growing season. The two spectral heterogeneity metrics showed differential sensitivity to components of plant diversity. SAM had a high relationship with H' followed by D2 and then a lower relationship with S throughout the different phenological stages. Meanwhile, CV had a higher relationship with D2 than other plant diversity indices and its relationship with S and H' remained similar. Although the coefficient of determination was comparatively low, the relationship between spectral heterogeneity metrics and species diversity indices was statistically significant (p < 0.05) and this supports the assertion that SVH could be implemented to characterize plant species diversity. Importantly, the application of SVH should consider (i) the choice of spectral heterogeneity metric in line with the purpose of the SVH application since these metrics relate to components of species diversity differently and (ii) vegetation phenology, which affects the relationship that spectral heterogeneity has with plant species diversity.
Investigating the toxicity of compounds yielded by staphylococci on Vero cells
(2022-10) Modimola, MS; Green, E; Njobeh, P; Senabe, Jeremiah V; Fouche, G; McGaw, L; Nkadimeng, SM; Mathiba, Kgama; Mthombeni, J
Bacterial secondary metabolites play a major role in the alleviation of diseases; however, the cytotoxicity of other metabolites cannot be ignored as such metabolites could be detrimental to human cells. Three Staphylococci strains Staphylococcus aureus, staphylococcus epidermidis and staphylococcus saprophyticus were used in the experiments. These strains are well known to cause hospital and community-acquired infections. Secondary metabolites from S. aureus isolated from milk of cows with clinical features of mastitis (swollen udders and the production of watery clotted milk), S. saprophyticus (ATCC 35552), and S. epidermidis (ATCC 51625) were exposed to a minimal medium then screened using Gas Chromatography High-Resolution Time-of-flight Mass Spectrometry (GC-HRTOF-MS) and identified with Nuclear Magnetic Resonance (NMR). From S. epidermidis, two compounds were isolated: oleamide and methyl palmitate; three from S. aureus, including fluoranthene, 3-methyl-2-phenyl-1H-pyrrole, and cyclo(L-Leu-L-Propyl); while S. saprophyticus yielded succinic acid, 1,2,6-hexantriol, veratramine, and 4-methyl-pentyl-amine. The secondary metabolites were tested for cytotoxicity using the Vero cell line. Fluoranthene exhibited toxicity with an LC50 of 0.0167 mg/mL to Vero cells, while the other metabolites did not. Methyl palmitate was the least toxic of all of the metabolites. The results imply that none of the compounds, except fluoranthene, pose any danger to human cells.
Land tenure conflict and agribusiness development in sub-Saharan Africa
(2021-06) Effossou, KA; Cho, Moses A
There is a growing demand of land by multinational commercial agribusinesses to meet the increasing demand for food in sub-Saharan Africa (SSA) and the export market. Land tenure system is identified as one of the factors stymieing the growth of agribusinesses in SSA. The difficulties involved in land tenure for agribusinesses have been frequently attributed to the co-existence of conflicting customary and statutory tenure . However, there is paucity of literature on the variability in land tenure across SSA and their impacts on agribusinesses. This paper reviews the literature on different land tenure and their implication for the growth in agribusiness across SSA. The method used for the literature review involved an analysis of published literature accessed from credible online sources. The analysis reveals that differences between the land tenure systems have varying impacts on agribusinesses across SSA. The study also found that the lack of compatibility between the statutory and customary laws generates resistance by some local community members against agribusiness investors particularly when members of the local communities feel side-lined in the land negotiation processes. The paper therefore articulates a compelling need for SSA countries to harmonize the existing land tenure systems to foster the development of agribusiness sectors.
Land use induced land cover changes and future scenarios in extent of Miombo woodland and Dambo ecosystems in the Copperbelt province of Zambia
(2021-08) Malunga, MM; Cho, Moses A; Chirwa, PW; Yerokun, OA
The pattern of Miombo woodland conversion to other land uses and the attendant impacts on vital Miombo ecosystems such as dambos is not well understood. Using the Copperbelt province of Zambia as a case study, we assessed the spatio-temporal patterns of Miombo woodland and dambo conversion to other land uses between 1984 and 2016 and predicted the changes to 2050. The effects of land use land cover change (LULCC) on the extent of Miombo woodlands and dambos was determined by intersecting layers of croplands, settlements, plantations, grasslands and barelands on woodland and dambo pixels. Prediction of future LULCC was done using the land change modeller (LCM) in TerrSet. It was observed that in the period between 1984 and 2016, woodlands decreased by 17.9% while dambos increased by 4.9%. The two classes were predicted to lose 26.4% and 2.0%, respectively, by 2050. Conversion to cropland was the highest contributor to woodland loss, accounting for 57.5% of total loss by 2016, and projected to reach 67.6% by 2050. Similarly, establishment of cropland was shown to result into 53.5% (2016) and 58.9% (2050) of loss of dambos. Expansion of croplands caused a decline in woodlands and dambos. Therefore, sustainable agriculture should be adopted.
Mapping weed infestation in maize fields using Sentinel-2 data
(2024) Mkhize, Yoliswa; Madonsela, Sabelo; Cho, Moses A; Nondlazi, Basanda X; Main, R; Ramoelo, A
Weed management in maize farms is a time-specific activity and requires timely detection of weed infestations. The challenge to early detection of weeds is that many dicotyledonous crops and broad-leaved weeds often display similar reflectance profile in the early growth stage and requires hyperspectral data to detect them. However, the advent of Sentinel-2 sensor series, with enhanced spectral configuration featuring red-edge bands that are known for species-level discrimination of plants, presents an affordable opportunity to detect weeds using multispectral data. The present study explores the question of whether Sentinel-2 sensor with its advanced spectral configuration can differentiate weeds from maize (Zea mays) in the early growth stages of maize. The study recorded 165 GPS points of weeds, maize, and mixed class in six maize farms during the early stages of maize growth. These GPS points were overlaid on Sentinel-2 images acquired within two days of field data gathering to guide the collection of spectral signatures of the maize, mixed, and weed classes. Spectral signatures were divided into training (70%) and validation (30%) data in a Random Forest (RF) model with S-2 spectral bands and vegetation indices as predictor variables. Spectral signatures were firstly tested for spectral separability between classes using ANOVA. The results of spectral analysis showed that the weed class had higher interclass variability from the maize and mixed class particularly in the red-edge and NIR regions of Sentinel-2. The classification matrix consistently showed that weeds were detected with high user and producers’ accuracy of 95%. These results indicate the utility of the enhanced spectral configuration of Sentinel-2 data in the early detection of weeds in maize farms.
Predicting land degradation using Sentinel-2 and environmental variables in the Lepellane catchment of the Greater Sekhukhune District, South Africa
(Elsevier, 2020-09) Nzuza, P; Ramoelo, Abel; Odindi, J; Mwenge Kahinda, Jean-Marc; Madonsela, Sabelo
Land degradation is defined as the reduction of biological and economic productivity, which impedes the capacity of the land to provide ecosystem services. There is a need to move towards near real-time monitoring of land degradation using new sensors to detect degraded landscapes. Recently launched Sentinel-2 sensor presents the opportunity to collect high-resolution data regularly. Multi-temporal datasets provide crucial information to isolate evidence of land degradation from temporal changes in vegetation cover incurred as a result of climatic and phenological variability. This study applied an integrated approach involving multi-seasonal Sentinel-2 data with environmental variables (i.e. soil moisture, rainfall, slope, evapotranspiration, elevation, soil temperature, rainfall, soil temperature, aspect and albedo). A stratified random sampling approach based on dominant land cover types were used to assess land degradation. Field plots of 20 m × 20 m were setup with three 50 cm × 50 cm quadrants inside. In each quadrant, the percentage estimation of vegetation cover and Leaf Area Index was measured. The model training and validation was implemented using the Random Forest algorithm based on default parameters. The pooled model represents the dry and wet seasons combined. Results showed that pooled model had higher accuracies for Photosynthetic vegetation (PV) (R2 of 0.89, RMSE-11.46%, relRMSE-8.7%), Non-Photosynthetic Vegetation (NPV) (R2 of 0.93, RMSE-5.64%, relRMSE% 17.72) and Bare Soil (BS) (R2 of 0.92, RMSE 8.7% and relRMSE 11.46%). The pooled environmental model achieved accuracy of PV (R2 of 0.42, RMSE-20.67%, relRMSE 4.83%), NPV (R2 of 0.90, RMSE 6.50% and relRMSE 15%) and (BS R2 of 0.85, RMSE 8.64% and relRMSE% 11.5) in estimating vegetation cover.
A radar and LiDAR-based earth observation system for monitoring savanna woody structure in southern Africa
(2018-04) Mathieu, Renaud; Wessels, Konrad; Main, Russell S; Naidoo, Laven; Van der Bergh, Frans; Erasmus, Barend
In southern Africa, landscapes are dominated by savannas, i.e., mixed tree-grass communities. These savannas are threatened by land clearing and degradation, as well as the densification of woody plants, a process known as bush encroachment. There is, however, very limited spatial information on woody cover distribution and changes. Here, we report on the development of an operational system designed to map and monitor woody vegetation cover at a regional scale. This system is based on the combined use of freely available airborne light detection and ranging (LiDAR) data and synthetic aperture radar (SAR) satellite imagery. The integration of these two datasets provides an effective solution for assessing woody fractional cover in southern Africa beyond the level of details and accuracy previously available. Woody fractional cover was mapped at a national scale for South Africa and Namibia in 2010 and 2015 at 1 ha (100 × 100 m) pixel size.
Spatio-temporal analysis of built-up impervious surface area and interplay with land surface temperature in Pretoria, South Africa
(2021-09) Adeyemi, A; Ramoelo, Abel; Cho, Moses A; Strydom, J
Evaluating changes in built-up impervious surface area (ISA) to understand the urban heat island (UHI) extent is valuable for governments in major cities in developing countries experiencing rapid urbanization and industrialization. This work aims at assessing built-up ISA spatio-temporal and influence on land surface temperature (LST) variability in the context of urban sprawl. Landsat-5 Thematic Mapper (TM) and Landsat-8 OLI (Operational Land Imager) and TIRS (Thermal Infrared Sensor) were used to quantify ISA using built-up Index (BUI) and spatio-temporal dynamics from 1993–2013. Thereafter using a suitable analytical sampling scale that represents the estimated ISA-LST, we examined its distribution in relation to elevation using the Shuttle Radar Topography Mission (SRTM) and also create Getis-Ord Gi* statistics hotspot maps to display the UHI extent. The BUI ISA extraction results show a high predictive accuracy with area under the receiver operating characteristic curve, AUROC = 0.8487 for 1993, AUROC = 0.8302 for 2003, AUROC = 0.8790 for 2013. The ISA spatio-temporal changes within ten years interval time frame results revealed a 14% total growth rate during the study year. Based on a suitable analytical scale (90 × 90) for the hexagon polygon grid, the majority of ISA distribution across the years was at an elevation range of between >1200 m–1600 m. Also, Getis-Ord Gi* statistics hotspot maps revealed that hotspot regions expanded through time with a total growth rate of 19% and coldspot regions decreased by 3%. Our findings can represent useful information for policymakers by providing a scientific basis for sustainable urban planning and management.

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