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Fort Beaufort, South Africa

Dreber N.,North West University South Africa | Dreber N.,University of Hamburg | Harmse C.J.,North West University South Africa | Gotze A.,Environment Research Consulting | And 2 more authors.
Rangeland Journal | Year: 2014

Bush encroachment is a serious problem in savanna rangelands of southern Africa. There is a strong interest in practical and reliable assessment methods to quantify related vegetation changes in the woody layer such as the widely applied point-centred quarter (PCQ) methods. Several variations of these distance methods exist but their results differ due to differences in sampling effort and methodological accuracy. The aim of this study was to compare the performance of two recently developed adapted PCQ methods. These methods were used to estimate density, productivity and diversity of the woody layer of a semiarid savanna along a degradation gradient in the Kalahari rangelands. It was found that both adapted PCQ methods (APCQ10 and APCQ20, with the APCQ20 method using less recording points but a larger sampling area and higher sampling intensity per recording point) provided similar results for density, phytomass, available browse and browsing capacity in open, dense and encroached savanna types. Significant differences between the methods were obtained in differentiating height classes, which were, however, largely restricted to the woody layer above 2m in open savanna types. There, applying the APCQ20 method avoided an under-sampling of larger shrubs and trees and increased precision in data assessment. This was confirmed by a better representation of species frequency distributions, as well as the density, phytomass and diversity status of the woody layer. These differences disappeared as the woody vegetation became denser with the APCQ10 method providing similar results to that of the APCQ20 method in densely vegetated and encroached savanna types. From a practical point of view, the APCQ10 method has a range of advantages in dense vegetation, where restricted movement impedes effective data collection. It is concluded that the APCQ20 method should be used to quantify open savanna communities, whereas the APCQ10 method is more suitable in dense stands of >1200 tree equivalents ha-1. Overall, the two APCQ methods were effective for assessing and monitoring woody savanna layers for management purposes but, for research, their accuracy still needs to be investigated in comparison to other assessment methods. © 2014 Australian Rangeland Society. Source


Higgins S.I.,Goethe University Frankfurt | Bond W.J.,University of Cape Town | Combrink H.,University of Cape Town | Craine J.M.,Kansas State University | And 5 more authors.
Journal of Ecology | Year: 2012

Fire is a process that shapes the structure and composition of vegetation in many regions. Species in these regions have presumably evolved life-history strategies that allow success in fire-prone environments. In this study, we examine the extent to which the ecological success of savanna trees is determined by traits that enhance the capacity to tolerate fire and/or traits indicative of an ecophysiological capacity for rapid growth. We define ecological success as the relative change in stem density over the course of a long-term (circa 40 year) fire experiment conducted in the Kruger National Park, South Africa. We first examine the extent to which differences in the capacity of trees to tolerate fire can be explained by allometries describing bark traits and tree size. We then examine whether these differences in fire tolerance traits can explain observed shifts in abundance. We show that species differ in their topkill responses (probability of above-ground mortality) and that these differences are explained in part by differences in bark moisture content and the allometry between height and diameter. Contrary to previous studies, we find no evidence that bark thickness is important in explaining susceptibility to topkill. Synthesis. Fire tolerance traits did explain a significant component of the variance in observed shifts in the abundance of tree species. However, traits related to the carbon economy of photosynthesis were also important. © 2012 The Authors. Journal of Ecology © 2012 British Ecological Society. Source


Africa is often referred to as the Fire Continent, and fire is recognised as a natural factor of the environment due to the prevalence of lightning storms and an ideal fire climate in the less arid regions with seasonal drought. On a global scale, the most extensive areas of tropical savanna, characterized by a grassy under stories that become extremely flammable during the dry season, occur in Africa. The use of fire in Africa to manage vegetation for domestic livestock and indigenous wildlife is widely recognized by both commercial and communal land users. Research on the effects of fire has been conducted throughout the grassland and savanna areas since the early twentieth century, resulting in the development of effective and practical guidelines for prescribed burning for domestic livestock and wildlife management systems. Generally, the reasons for prescribed burning in Africa are similar for both commercial and communal land users, namely, to remove moribund and or unacceptable plant material and to control the encroachment of undesirable plants negatively affecting domestic livestock and wildlife. In addition, commercial operators use fire to manage wildlife conservation areas. Prescribed burning to control ticks is also widely used in communal communities but is generally not recognised in commercial livestock enterprises. However, research has shown that tick populations can be reduced using fire to alter the micro-habitat for these organisms. Until recently, commercial and communal land users held differing views on the appropriate season for prescribed burning, with the former igniting fires shortly after the first spring rains and the latter burning throughout the dry winter period. Subsequent research has shown that both seasons of burn have similar effects; the key requirement being that the grass sward is dormant at the time of burning to minimise the negative effects on the vegetation. A valuable tentative comparison has been made between fire management practices applied by commercial land users and communal land users, and provides an exciting opportunity for further and essential research to be conducted to gain greater insight into how communal African communities use fire. Based on extensive experience, my aim is to provide a personal perspective on the use of fire by commercial and communal land users for managing rangelands in southern and east African regions of the continent. Source


Tedder M.J.,University of KwaZulu - Natal | Kirkman K.P.,University of KwaZulu - Natal | Morris C.D.,University of KwaZulu - Natal | Trollope W.S.W.,Working On Fire International | Bonyongo M.C.,University of Botswana
Koedoe | Year: 2013

The dry woodland and savanna regions of the Okavango Delta form a transition zone between the Okavango Swamps and the Kalahari Desert and have been largely overlooked in terms of vegetation classification and mapping. This study focused on the species composition and height structure of this vegetation, with the aim of identifying vegetation classes and providing a vegetation map accompanied by quantitative data. Two hundred and fifty-six plots (50 m × 50 m) were sampled and species cover abundance, total cover and structural composition were recorded. The plots were classified using agglomerative, hierarchical cluster analysis using group means and Bray-Curtis similarity and groups described using indicator species analysis. In total, 23 woody species and 28 grass species were recorded. Acacia erioloba and Colophospermum mopane were the most common woody species, whilst Urochloa mossambicensis, Panicum maximum, Dactyloctenium gigantium and Eragrostis lehmanniana were the most widespread grasses. Eleven vegetation types were identified, with the most widespread being Short mixed mopane woodland, Tall mopane woodland and Tall mixed mopane woodland, covering 288.73 km2 (28%), 209.14 km2 (20%) and 173.30 km2 (17%) of the area, respectively. Despite their extensive area, these three vegetation types were the least species-rich, whilst Palm thornveld, Short mixed broadleaf woodland and Open mixed Acacia woodland were the most taxonomically variable. By contrast, Closed mixed Acacia woodland and Closed Acacia-Combretum woodland had the most limited distribution, accounting for less than 1% of the mapped area each. Conservation implications: The dry woodland and savanna vegetation of the Okavango Delta comprises a much wider suite of plant communities than the Acacia-dominated and Mopane-dominated classifications often used. This classification provided a more detailed understanding of this vegetation and essential background information for monitoring, management and research. © 2013. The Authors. Source


Trollope W.,Working On Fire International | van Wilgen B.,Stellenbosch University | Trollope L.A.,Working On Fire International | Govender N.,SANParks Kruger National Park | Potgieter A.L.,SANParks Kruger National Park
African Journal of Range and Forage Science | Year: 2014

Few assessments of the effects of fire and grazing on the herbaceous components of savannas have been reported for Africa. In the Kruger National Park, South Africa, range condition was monitored at three savanna sites spanning a rainfall gradient of 450 to 700 mm and subject to grazing by wildlife. The sites were burnt at 1-, 2- and 3-year intervals, in different seasons and included a control treatment excluding fire for >40 years. Initial surveys of the herbaceous vegetation were conducted between 1954 and 1957 and repeated between 1998 and 2001. Grass species were categorised as either decreaser or increaser species, which decline or increase with over- or under-utilisation, respectively, and their potential to provide forage and fuel for fires indicative of range condition were derived. Range condition improved with regular burning in the moist sites, but deteriorated in the arid sites over all seasons and frequencies of burning. It is concluded that the current homogenous approach to burning across the Park needs to be adapted by reducing the frequency of fires at more arid sites and can be achieved by burning according to the proportions of decreaser and increaser species reflecting the ecological status of the herbaceous vegetation. © 2014, Copyright © NISC (Pty) Ltd. Source

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