SUNScholar - Browsing by Author "De Klerk, Helen Margaret"

Browsing by Author "De Klerk, Helen Margaret"

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Avian endemism in northeastern tropical Africa
(Det Kongelige Danske Videnskabernes Selskab, 2001) Fjeldsa, Jon; De Klerk, Helen Margaret
The avian endemism of Ethiopia and the Horn of Africa was analyzed using a database where all bird distributions in Africa south of the Sahara are recorded in a one-degree grid. Applying a hierarchical classification algorithm, the tropical northeastern Subregion of Africa stands out clearly and can be subdivided in all Ethiopian Highlands Province and the Somalia-Masai. Tana-Jubba and Turkana districts and a Danakil Province. The Horn of Africa Province is associated with the Northern Arid (Sahara) Subregion in this hierarchical classification, although this reflects the replacement of savanna with desert birds more than shared endemism. Although most of the Ethiopian Highland endemics are distributed all over the highland, a more complex pattern of local endemics can also be defined, using a complementarity algorithm. Local endemism is very pronounced among the larks, Alaudidae. The majority of endemics belongs to recently radiated groups, and is mainly related to the fauna of East Africa; however, the fauna of the Sidamo district contains relict elements, two of these of a significant evolutionary age. The pattern of endemism in the birds of northeastern tropical Africa has a number of features in common with patterns found in plants.
Biogeographical patterns of endemic terrestrial Afrotropical birds
(Wiley-Blackwell, 2002) De Klerk, Helen Margaret; Crowe, T. M.; Fjeldsa, J.; Burgess, N. D.
Biogeographical zones are described for terrestrial bird species endemic to the Afrotropics using up-to-date distributional data and multivariate statistical techniques. This provides an objective basis for a hierarchy of subregions, provinces and districts, based on a set of rules. Results are compared to previous studies at continental and regional scales. Biogeographical zones for passerines and non-passerines are compared and found to be similar. Peaks of species richness and narrow endemism are described for the six major subdivisions (subregions) identified by the cluster analysis. Coincidence of peaks of species richness and narrow endemism is found to be low, such that areas selected to represent high species richness tallies will often fail to represent narrow endemics. Strong regionalization of Afrotropical birds indicates the need to use a biogeographical framework in conservation priority setting exercises to ensure that unique, but species-poor, avifaunas are not neglected.
Evaluation of satellite-derived burned area products for the fynbos, a Mediterranean shrubland
(CSIRO Publishing, 2011-10-17) De Klerk, Helen Margaret; Wilson, Adam M.; Steenkamp, Karen
Fire is a critical ecological process in the fynbos of the south-western area of South Africa, as it is for all dwarf Mediterranean shrublands. We evaluated the potential of current publicly available MODIS burned area products to contribute to an accurate fire history of the fynbos. To this end, we compared the Meraka Institute’s MODIS burned area product, based on the Giglio algorithm (termed the ‘WAMIS’ product) as well as the standard MODIS MCD45A1 burned area product, based on the Roy algorithm, with comprehensive manager-mapped fire boundary data. We used standard inventory accuracy assessment (number and size of individual burn scars) and confusion matrix techniques. Results showed promise for both burned area products, depending on the intended use. The MCD45A1 had low errors of commission (8.1–19.1%) and high consumer’s accuracy (80.9–91.9%), but relatively common errors of omission, making it useful for studies that need to identify burned pixels with a high degree of certainty. However, the WAMIS product generally had low errors of omission (12.2–43.8%) and greater producer’s accuracy (56.2–87.6%), making it a useful tool for supplementing manager-mapped fire records, especially for fynbos remnants occurring outside protected areas.
Fire‑mediated disruptive selection can explain the reseeder–resprouter dichotomy in Mediterranean‑type vegetation
(Springer, 2014) Altwegg, Res; De Klerk, Helen Margaret; Midgley, Guy F.
Crown fire is a key selective pressure in Mediterranean-type plant communities. Adaptive responses to fire regimes involve trade-offs between investment for persistence (fire survival and resprouting) and reproduction (fire mortality, fast growth to reproductive maturity, and reseeding) as investments that enhance adult survival lower growth and reproductive rates. Southern hemisphere Mediterranean-type ecosystems are dominated by species with either endogenous regeneration from adult resprouting or fire-triggered seedling recruitment. Specifically, on nutrient-poor soils, these are either resprouting or reseeding life histories, with few intermediate forms, despite the fact that the transition between strategies is evolutionarily labile. How did this strong dichotomy evolve? We address this question by developing a stochastic demographic model to assess determinants of relative fitness of reseeders, resprouters and hypothetical intermediate forms. The model was parameterised using published demographic data from South African protea species and run over various relevant fire regime parameters facets. At intermediate fire return intervals, trade-offs between investment in growth versus fire resilience can cause fitness to peak at either of the extremes of the reseeder–resprouter continuum, especially when assuming realistic non-linear shapes for these trade-offs. Under these circumstances, the fitness landscape exhibits a saddle which could lead to disruptive selection. The fitness gradient between the peaks was shallow, which may explain why this life-history trait is phylogenetically labile. Resprouters had maximum fitness at shorter fire-return intervals than reseeders. The model suggests that a strong dichotomy in fire survival strategy depends on a non-linear trade-off between growth and fire persistence traits.
Framing the concept of satellite remote sensing essential biodiversity variables : challenges and future directions
(John Wiley & Sons Ltd., 2016-03) Pettorelli, Nathalie; Wegmann, Martin; Skidmore, Andrew; Mucher, Sander; Dawson, Terence P.; Fernandez, Miguel; Lucas, Richard; Schaepman, Michael E.; Wang, Tiejun; O’Connor, Brian; Jongman, Robert H. G.; Kempeneers, Pieter; Sonnenschein, Ruth; Leidner, Allison K.; Bohm, Monika; He, Kate S.; Nagendra, Harini; Dubois, Gregoire; Fatoyinbo, Temilola; Hansen, Matthew C.; Paganini, Marc; De Klerk, Helen Margaret; Asner, Gregory P.; Kerr, Jeremy T.; Estes, Anna B.; Schmeller, Dirk S.; Heiden, Uta; Rocchini, Duccio; Pereira, Henrique M.; Turak, Eren; Fernandez, Nestor; Lausch, Angela; Cho, Moses A.; Alcaraz-Segura, Domingo; McGeoch, Melodie A.; Turner, Woody; Mueller, Andreas; St-Louis, Veronique; Penner, Johannes; Vihervaara, Petteri; Belward, Alan; Reyers, Belinda; Geller, Gary N.
Although satellite-based variables have for long been expected to be key components to a unified and global biodiversity monitoring strategy, a definitive and agreed list of these variables still remains elusive. The growth of interest in biodiversity variables observable from space has been partly underpinned by the development of the essential biodiversity variable (EBV) framework by the Group on Earth Observations – Biodiversity Observation Network, which itself was guided by the process of identifying essential climate variables. This contribution aims to advance the development of a global biodiversity monitoring strategy by updating the previously published definition of EBV, providing a definition of satellite remote sensing (SRS) EBVs and introducing a set of principles that are believed to be necessary if ecologists and space agencies are to agree on a list of EBVs that can be routinely monitored from space. Progress toward the identification of SRS-EBVs will require a clear understanding of what makes a biodiversity variable essential, as well as agreement on who the users of the SRS-EBVs are. Technological and algorithmic developments are rapidly expanding the set of opportunities for SRS in monitoring biodiversity, and so the list of SRS-EBVs is likely to evolve over time. This means that a clear and common platform for data providers, ecologists, environmental managers, policy makers and remote sensing experts to interact and share ideas needs to be identified to support long-term coordinated actions.
Gaps in the protected area network for threatened Afrotropical birds
(Elsevier, 2004) De Klerk, Helen Margaret; Fjeldsa, J.; Blyth, S.; Burgess, N. D.
Protected areas established for wildlife conservation (IUCN category I–VI protected areas) or for forest and watershed conservation (forest reserves) across mainland sub-Saharan Africa have high biodiversity values. However, they fail to cover over half of the 106 threatened bird species, and thus leave these vulnerable to extinction. An analysis of Red List bird species that are not represented in existing reserves indicates gaps in the current network of protected areas, namely: Mt. Cameroon-Bamenda highlands (Cameroon), the Angolan scarp (Angola), the Drakensberg Highlands (South Africa), the Highveld (South Africa), the Eastern Arc Mountains (Tanzania), the eastern African coastal forest mosaic (Kenya and Tanzania), the Albertine Rift (Uganda, Rwanda, Burundi, eastern Democratic Republic of Congo and western Tanzania), and the Ethiopian Highlands. The addition of Forest Reserves to the existing protected areas closes some of the reservation gaps for threatened birds in Africa. We suggest that these Forest Reserves should be included within official lists of protected areas, and that National forestry authorities be encouraged to manage these areas. Publication of scientific articles showing the conservation value of Forest Reserves is needed to raise local and international support and funding.
Geo-information pyramids for up-to-date and flexible conservation plans : a case study for Transfrontier Conservation Areas
(OpenJournals Publishing, 2007) Smith, Nadia; De Klerk, Helen Margaret
The initiative to link habitat and parks across political borders, to form large Transfrontier Conservation Areas (TFCAs), has gained momentum in Africa and the world. TFCAs hold many advantages, one of them being the restoration of habitat connectivity in order to conserve ecosystem functioning. A feasibility study in 2002 highlighted 22 sites as potential TFCAs in southern Africa, and the Peace Parks Foundation is facilitating the implementation of eight of them. This paper describes a methodological framework with which to map remaining large, natural habitat fragments (or remnants) in southern Africa, the distribution, shape and size of which will provide the foundation and stakeholders with information on possible coarse-scale landscape linkages. This framework, which maps remnants, was designed to be transparent, systematic and dynamic to facilitate easy updating as TFCA projects mature, or updated data become available. This is intended to be the first in a series of studies towards developing an integrated, systematic framework for TFCA planning at a sub-continental scale. It does not aim to prioritize remnants or linkages.
A hierarchical Bayesian model of wildfire in a Mediterranean biodiversity hotspot : implications of weather variability and global circulation
(Elsevier, 2010) Wilson, Adam M.; Latimer, Andrew M.; Silander, John A.; Gelfand, Alan E.; De Klerk, Helen Margaret
In this study we combined an extensive database of observed wildfires with high-resolution meteorological data to build a novel spatially and temporally varying survival model to analyze fire regimes in the Mediterranean ecosystem in the Cape Floristic Region of South Africa (CFR) during the period 1980-2000. The model revealed an important influence of seasonally anomalous weather on fire probability, with increased probability of fire in seasons that are warmer and drier than average. In addition to these local-scale influences, the Antarctic Ocean Oscillation (AAO) was identified as an important large scale influence or teleconnection to global circulation patterns. Fire probability increased in seasons during positive AAO phases, when the subtropical jet moves northward and low level moisture transport decreases. These results confirm that fire occurrence in the CFR is strongly affected by climatic variability at both local and global scales, and thus likely to respond sensitively to future climate change. Comparison of the modeled fire probability between two periods (1951-1975 and 1976-2000) revealed a four year decrease in an average fire return time. If, as currently forecasted, climate change in the region continues to produce higher temperatures, more frequent heat waves, and/or lower rainfall, our model thus indicates that fire frequency is likely to increase substantially. The regional implications of shorter fire return times include shifting community structure and composition, favoring species that tolerate more frequent fires.
Patterns of species richness and narrow endemism of terrestrial bird species in the Afrotropical region
(Wiley-Blackwell, 2002) De Klerk, Helen Margaret; Crowe, Tim M.; Fjeldsa, Jon; Burgess, Neil D.
Geographical patterns and peaks of species richness and narrow endemism (defined by rangerestrictedness and range-size rarity) are described for terrestrial Afrotropical birds and subsets thereof based on residency, endemism, and taxonomy. Species richness for residents and Afrotropical endemics (species globally restricted to sub-Saharan Africa) peaks along the mountains and adjacent lowlands of eastern and southern Africa. Isolated mountains in central and western Africa and the lowlands of the north-eastern Congo Basin (Ituri) are highlighted to a lesser degree. Peaks of narrow endemism occur in these areas as well as in the Ethiopian Highlands (particularly for non-passerines), Somalia (particularly for passerines), and the Angolan Escarpment. Within residents, patterns of species richness vary greatly between Afrotropical endemics (which concentrate in forests on mountains and adjacent lowlands, and the southern Brachystegia woodlands) and non-endemic residents (which concentrate in Sudanian woodlands and the Ethiopian Highlands). Patterns of species richness of residents (species that breed in the Afrotropics) and non-breeding migrants (non-breeding visitors to the Afrotropics) also show notable differences. The latter concentrate in areas close to the Palaearctic, which forms their distributional range centres. Patterns of species richness and narrow endemism for Afrotropical endemics show broad-scale coincidence within mountains or mountain-lowland complexes, particularly the Cameroon-Bamenda Highland system, East African rift system and Eastern Arc mountains. However, fine-scale coincidence of peaks of species richness and narrow endemism within these complexes is low. Narrow endemism peaks occur in areas of topographical complexity, which may have conferred localized climatic stability over short-, medium-, and long-term climatic cycles (sensu Fjeldsa , 1994; Fjeldsa et al., 1997), allowing these areas to act as `species pumps'. Species accumulate in areas of high productivity. Lack of fine-scale coincidence of narrow endemism and species richness peaks have implications for conservation prioritization exercises.
A pragmatic assessment of the usefulness of the MODIS (Terra and Aqua) 1-km active fire (MOD14A2 and MYD14A2) products for mapping fires in the fynbos biome
(CSIRO Publishing, 2008) De Klerk, Helen Margaret
The moderate resolution imaging spectroradiometer (MODIS) fire-affected area data are not currently available for download by the public; therefore, 1-km pixel MODIS active fire data (MOD14A2 and MYD14A2) were assessed as a potential source of fire history data for the fynbos biome. These data mapped between 60.1 and 65.7% of the area within fire boundaries mapped by reserve managers between July 2002 and April 2005. These results should not be taken as a negative reflection on the MODIS team, as active fires do not aim to map fire-affected area. Rather this exercise has helped identify specific limitations in the fynbos, which will provide insight into the fine-tuning of other MODIS fire products for use in the fynbos. Limitations are likely to be primarily due to sun-glint around coastlines; topographic shadows; highly reflective, light soils exposed after a fire; partial burning of pixels; patchy and irregular-shaped fires; and large pixel size. The MODIS active fire data are not sufficient for the purposes of developing a 4-year fire history of the fynbos. The publication of the 500-m MODIS fire-affected area data is eagerly anticipated as a solution.
Revealing unexpected uses of space by wintering Aquila pomarina : how does satellite telemetry identify behaviour at different scales?
(Wiley Online, 2015) Meyburg, Bernd-Ulrich; Mendelsohn, Stephie; Mendelsohn, John; De Klerk, Helen Margaret
Little is understood about the dispersion and movements of Palaearctic migrant raptors while wintering in southern Africa. The high temporal and spatial resolution of GPS telemetry data provided the opportunity to describe how space is used by one such migratory raptor in its wintering range, the lesser spotted eagle Aquila pomarina. Kernel density estimation was used to map the distribution of three individuals at various spatial scales. In addition to their extremely large overall wintering range (up to 112 000 km2), three finer levels of spatial concentration were identified: favoured activity zones where the birds spent much of the winter, smaller core areas to which the birds returned each year, and tiny intensive foraging clusters. Philopatry was demonstrated by one bird which revisited core areas over eight wintering seasons. The same core areas, particularly the Waterberg, Grootfontein (Namibia) and the eastern and western sides of the Okavango Delta (Botswana), were visited by two other eagles in 2012/2013, although not simultaneously. Such results potentially provide important information on areas where conservation activities might be focused to mitigate human degradation of habitat.
Towards a multi-instrument analysis of atmospheric composition in fire driven ecosystems
(2013) Smith, Nadia; De Klerk, Helen Margaret; Schloms, Bennie H. A.; Weisz, Elisabeth; Huang, Allen
Much research has gone into mapping the onset and spatial extent of fires using imager data from space. In addition, much progress has been made in the ability to characterize and trace biomass burning plumes with hyperspectral sounders. In this paper we investigate the feasibility of combining satellite measurements from different instruments to promote an improved and comprehensive understanding of pollution events.
Using remote sensing in support of environmental management : a framework for selecting products, algorithms and methods
(Elsevier, 2016-08) De Klerk, Helen Margaret; Gilbertson, Jason; Luck-Vogel, Melanie; Kemp, Jaco; Munch, Zahn
Traditionally, to map environmental features using remote sensing, practitioners will use training data to develop models on various satellite data sets using a number of classification approaches and use test data to select a single ‘best performer’ from which the final map is made. We use a combination of an omission/commission plot to evaluate various results and compile a probability map based on consistently strong performing models across a range of standard accuracy measures. We suggest that this easy-to-use approach can be applied in any study using remote sensing to map natural features for management action. We demonstrate this approach using optical remote sensing products of different spatial and spectral resolution to map the endemic and threatened flora of quartz patches in the Knersvlakte, South Africa. Quartz patches can be mapped using either SPOT 5 (used due to its relatively fine spatial resolution) or Landsat8 imagery (used because it is freely accessible and has higher spectral resolution). Of the variety of classification algorithms available, we tested maximum likelihood and support vector machine, and applied these to raw spectral data, the first three PCA summaries of the data, and the standard normalised difference vegetation index.We found that there is no ‘one size fits all’ solution to the choice of a ‘best fit’ model (i.e. combination of classification algorithm or data sets), which is in agreement with the literature that classifier performance will vary with data properties.We feel this lends support to our suggestion that rather than the identification of a ‘single best’ model and a map based on this result alone, a probability map based on the range of consistently top performing models provides a rigorous solution to environmental mapping.
Where are the major gaps in the reserve network for Africa's mammals?
(Cambridge University Press (CUP), 2004-01) Fjeldsa, Jon; Burgess, Neil D.; Blyth, Simon; De Klerk, Helen Margaret
The establishment of protected areas for wildlife conservation in Africa was motivated by a number of different reasons (including hunting, recreation and wildlife conservation). The current reserve network provides good coverage of the distributions of the 194 species of larger mammals (> 3 kg) and 51 species of threatened larger mammals. However, it is less effective in covering the distribution of all 197 of Africa's threatened mammal species, which includes >140 smaller bodied species ( <3 kg) often restricted to habitat patches. A fully comprehensive network of areas for the conservation of African mammals, especially those facing extinction, is not yet in place, and further reserves may be needed in the Horn of Africa (Somalia in particular), the Cameroon Highlands, parts of the eastern African coastal forests and Eastern Arc Mountains, and parts of the Albertine Rift Mountains. More and larger reserve areas are also required to adequately cover all the species of South Africa. Parts of these gaps are already covered by government forest reserves, and the importance of this reserve category for the conservation of African mammals, especially threatened species, needs to be better recognized. As many of the gaps in reserve coverage are in areas of high human population and good agricultural potential, conservation goals may be difficult to achieve unless we supplement traditional reserves with novel approaches to maintain natural habitats and wildlife outside reserves.

Browsing by Author "De Klerk, Helen Margaret"

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