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Browsing by Author "Asner, GP"

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An above-ground biomass map of African savannahs and woodlands at 25m resolution derived from ALOS PALSAR

Author: Bouvet, A ; Mermoz, S ; Le Toan, T ; Villard, L ; Mathieu, Renaud SA ; Naidoo, Laven ; Asner, GP Date: Mar 2018 Savannahs and woodlands are among the most important biomes in Africa: they cover half of sub-Saharan Africa, provide vital ecosystem services to the rural communities, and play a major part in the carbon budget. Despite their importance and ... Read more
Assessing degradation across a land-use gradient in the Kruger National Park area using advanced remote sensing modalities

Author: Van Aardt, JAN ; Mathieu, Renaud SA ; Cho, Moses A ; Wessels, Konrad J ; Erasmus, B ; Asner, GP ; Smit, IPJ Date: 2011 Land degradation is regarded as one of the most important environmental issues facing sub-Saharan Africa and is especially relevant in the former communal ‘homeland’ areas of South Africa. Although it has been a topic of intense research, ... Read more
The assessment of data mining algorithms for modelling Savannah woody cover using multi-frequency (X-, C- and L-band) synthetic aperture radar (SAR) datasets

Author: Naidoo, Laven ; Mathieu, Renaud SA ; Kleynhans, W ; Wessels, Konrad J ; Asner, GP ; Leblon, B Date: Jul 2014 The woody component in African Savannahs provides essential ecosystem services such as fuel wood and construction timber to large populations of rural communities. Woody canopy cover (i.e. the percentage area occupied by woody canopy or CC) ... Read more
Assessment of the mapping of fractional woody cover in southern African savannas using multi-temporal and polarimetric ALOS PALSAR L-band images

Author: Urbazaev, M ; Thiel, C ; Mathieu, Renaud SA ; Naidoo, Laven ; Levick, SR ; Smit, IPJ ; Asner, GP ; Schmullius, C Date: Sep 2015 Woody vegetation cover affects several ecosystem processes including carbon and water cycling, energy fluxes, and fire regimes. In order to understand the dynamics of savanna ecosystems, information on the spatial distribution of woody ... Read more
Biomass increases go under cover: woody vegetation dynamics in South African rangelands

Author: Mograbi, PJ ; Erasmus, BFN ; Witkowski, ETF ; Asner, GP ; Wessels, Konrad J ; Mathieu, Renaud SA ; Knapp, DE ; Martin, RE ; Mathieu, Renaud SA Date: May 2015 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 ... Read more
Comparing parametric and non-parametric classifiers for remote sensing of tree species across a land use gradient in a Savanna landscape

Author: Cho, Moses A ; Naidoo, Laven ; Mathieu, Renaud SA ; Asner, GP ; Ramoelo, Abel Date: Nov 2012 Several classification techniques have been used to map vegetation communities or land cover types using remote sensing data including maximum likelihood (ML), discriminant analysis and spectral angle mapper classifiers. ML classifier is a ... Read more
Environmental change in Bushbuckridge

Author: Erasmus, BFN ; Coetzer, K ; Mambo, J ; Archer, Emma RM ; Fisher, JT ; Asner, GP Date: May 2011 Bushbuck Ridge is a typical cultural landscape where the interdependency of people and the environment shape the savanna ecosystem goods and services upon which many people are dependent. The forced resettlement of people in the apartheid ... Read more
Extracting structural land cover components using small-footprint waveform LDAR data

Author: McGlinchy, J ; Van Aardt, J ; Rhody, H ; Kerekes, J ; Ientiluci, E ; Asner, GP ; Knapp, D ; Mathieu, Renaud SA ; Kennedy-Bowdoin, T ; Erasmus, BFN ; Wessels, Konrad J ; Smit, IPJ ; Wu, J ; Sarrazin, D Date: Jul 2010 Previous work has shown the ability of waveform LiDAR sensors to accurately describe various land cover types and biomass estimates made in the field. What is lacking, however, is a way to describe the different structural components that are ... Read more
Human-modified landscapes: patterns of fine-scale woody vegetation structure in communal savannah rangelands

Author: Fisher, T ; Witkowski, ETF ; Erasmus, BFN ; Van Aardt, J ; Asner, GP ; Wessels, Konrad J ; Mathieu, Renaud SA Date: Nov 2011 Despite electrification, over 90% of rural households in certain areas of South Africa continue to depend on fuelwood, and this affects woody vegetation structure, with associated cascading effects on biodiversity within adjacent lands. To ... Read more
Humans and elephants as treefall drivers in African savannas

Author: Mograbi, PJ ; Asner, GP ; Witkowski, ETF ; Erasmus, BFN ; Wessels, Konrad J ; Mathieu, Renaud SA ; Vaughn, NR Date: Jan 2017 Humans have played a major role in altering savanna structure and function, and growing land-use pressure will only increase their influence on woody cover. Yet humans are often overlooked as ecological components. Both humans and the African ... Read more
Hyper-temporal c-band SAR for baseline woody structural assessments in deciduous savannas

Author: Main, Russell S ; Mathieu, Renaud SA ; Kleynhans, W ; Wessels, Konrad J ; Naidoo, Laven ; Asner, GP Date: Aug 2016 Savanna ecosystems and their woody vegetation provide valuable resources and ecosystem services. Locally calibrated and cost effective estimates of these resources are required in order to satisfy commitments to monitor and manage change ... Read more
Impact of communal land use and conservation on woody vegetation structure in the Lowveld savannas of South Africa

Author: Wessels, Konrad J ; Mathieu, Renaud SA ; Erasmus, BFN ; Asner, GP ; Smit, IPJ ; Van Aardt, JAN ; Main, Russell S ; Fisher, J ; Marais, W ; Kennedy-Bowdoin, T ; Knapp, DE ; Emerson, R ; Jacobson, J Date: Jan 2011 Millions of people rely on savannas for ecosystem services, such as the provision of grazing and fuel wood, so it is important to determine the extent to which utilization affects woody vegetation resources. Using airborne LiDAR from the ... Read more
Impact of communal land use and conservation on woody vegetation structure in the Lowveld savannas of South Africa – Lidar results

Author: Wessels, Konrad J ; Mathieu, Renaud SA ; Erasmus, BFN ; Asner, GP ; Smit, IPJ ; Van Aardt, JAN ; Main, Russell S ; Fisher, J Date: Apr 2011 People in the rural, communal areas of South Africa rely on live fuel wood for more than 90% of their energy requirements. Using airborne lidar from the Carnegie Airborne Observatory (CAO) the authors compared tree canopy cover and height ... Read more
Impacts of communal fuelwood extraction on lidar-estimated biomass patterns of savanna woodlands

Author: Wessels, Konrad J ; Erasmus, BFN ; Colgan, M ; Asner, GP ; Mathieu, Renaud SA ; Twine, W ; Van Aardt, JAN ; Smit, I Date: Jul 2012 Approximately 54% of rural households in South Africa continue to use wood as their main source of energy, mainly for cooking and heating. The provision of biomass by savanna woodlands is thus of considerable value to rural households and ... Read more
On using discrete return LIDAR distributions as a proxy for waveform LIDAR signals when modeling vegetation structure

Author: Van Aardt, JAN ; Wu, J ; McGlinchy, J ; Wessels, Konrad J ; Mathieu, Renaud SA ; Kennedy Bowdoin, T ; Knapp, DE ; Asner, GP Date: Jul 2012 The goals of the study were to (i) determine if there is a direct relationship between waveform LiDAR intensity-by-height and discrete return frequency-by-height (do the distributions match?) and (ii) assess the impact of scale (does this ... Read more
Optimizing tree-species classification in hyperspectal images

Author: Barnard, E ; Cho, Moses A ; Debba, Pravesh ; Mathieu, Renaud SA ; Wessels, Konrad J ; van Heerden, C ; Van der Walt, Christiaan M ; Asner, GP Date: Nov 2010 The authors investigate the classification of eight prominent savanna tree species, based on hyperspectral reflectance data. Although two principal components account for 95% of the variance of the data, up to 20 components are found to be ... Read more
Remote sensing research for spatial assessment of woody structure in African savannahs & woodlands –past, on-going, and future work by the CSIR

Author: Mathieu, Renaud SA ; Naidoo, Laven ; Cho, Moses A ; Wessels, Konrad J ; Asner, GP Date: Apr 2011 Appropriate techniques are needed to monitor woody vegetation cover, biomass and carbon stocks. Light Detection and Ranging (LiDAR) & Synthetic Aperture Radar (SAR) interact with vegetation morphology and structure. The aim of this study is ... Read more
Savanna woody vegetation classification – now in 3-D

Author: Fisher, JT ; Erasmus, BFN ; Witkowski, ETF ; Van Aardt, J ; Wessels, Konrad J ; Asner, GP Date: May 2013 The co-existence of woody plants and grasses characterize savannas, with the horizontal and vertical spatial arrangement of trees creating a heterogeneous biotic environment. To understand the influence of biogeophysical drivers on the spatial ... Read more
Toward structural assessment of semi-arid African savannahs and woodlands: The potential of multitemporal polarimetric RADARSAT-2 fine beam images

Author: Mathieu, Renaud SA ; Naidoo, Laven ; Cho, Moses A ; Leblon, B ; Main, Russell S ; Wessels, Konrad J ; Asner, GP ; Buckley, J ; Van Aardt, J ; Erasmus, BFN ; Smit, IPJ Date: Nov 2013 Woody vegetation structure affects wildlife habitat selection and species diversity for a wide range of taxa, and at a variety of scales. Indicators of woody structure can indicate the spatio-temporal variability of biodiversity, species ... Read more
Unsustainable fuelwood extraction from South African savannas

Author: Wessels, Konrad J ; Colgan, MS ; Erasmus, BFN ; Asner, GP ; Twine, WC ; Mathieu, Renaud SA ; Van Aardt, JAN ; Fisher, JT ; Smit, IPJ Date: Jan 2013 Wood and charcoal supply the majority of sub-Saharan Africa’s rural energy needs. The long-term supply of fuelwood is in jeopardy given high consumption rates. Using airborne light detection and ranging (LiDAR), we mapped and investigated ... Read more

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