Organisation for Tropical Studies

Organisation for, South Africa

Organisation for Tropical Studies

Organisation for, South Africa
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Helm C.,University of Witwatersrand | Wilson G.,University of Cape Town | Midgley J.,University of Cape Town | Kruger L.,Organisation for Tropical Studies | Witkowski E.T.F.,University of Witwatersrand
Austral Ecology | Year: 2011

Sclerocarya birrea ssp. caffra (marula), a typical savanna tree, is vulnerable to the effects of fire, herbivory and their combination. This paper investigated the relative importance of these agents of disturbance, at the level of the individual stem, by specifically focusing on the following questions: (i) What is the greatest cause of mortality in adult marula stems in conservation areas with both elephants and fire? (ii) Does fire interact with bark stripping to cause adult stem mortality and if so what is the dominant mechanism? (iii) At what stem diameter are marulas resistant to fire? Field surveys quantified the extent of damage in marula individuals in the Kruger National Park, South Africa, highlighting the high levels of extreme herbivory such as toppling (7%) and pollarding (8%), relative to bark stripping (only 6% with more than 50% of the circumference stripped). In addition to extreme herbivory, the progression from bark stripping through to invasion of the soft, exposed heartwood by wood borers, often facilitated by fire, through to toppling of the weakened stem after successive fires, appears to be the dominant mechanism by which fire interacts with herbivory to cause adult stem death. Bark stripping and fire manipulation experiments indicated that bark stripping failed to increase the vulnerability of stems to fire directly through transport tissue damage. However, the combination of bark stripping and fire reduced the ability of the stem to regrow bark, increasing the vulnerability of the exposed stem to boring insects and future fires. Fire manipulation experiments were used to identify the minimum stem diameter of resistance to fire. Marula resisted stem death when greater than 3.4cm in basal diameter. This paper emphasizes the importance of both fire and herbivory in the development of woody plant population structure and by extension, the relative proportion of trees and grasses in savanna landscapes. © 2011 The Authors. Journal compilation © 2011 Ecological Society of Australia.

Bouchard E.H.,Wheaton College at Illinois | Little L.E.,University of Washington | Miller C.M.L.,Grinnell College | Rundell S.M.,Yale University | And 3 more authors.
Koedoe | Year: 2015

Encroachment by alien species is the second greatest threat to biodiversity worldwide. As South Africa’s Cape Floristic Region has a botanical endemism of nearly 70%, conservation efforts are a high priority. Estimates suggest that alien species cost the country over R6.5 billion per year. Despite significant research on alien species dispersal, the role of tourists as seed dispersers requires further exploration. To investigate the potential role tourists play in introducing alien seeds into protected areas, long-bristle brushes were used to scrape seeds off the shoes of hikers, dog walkers and cyclists, as well as the wheels of mountain bikes and dogs themselves, upon entering the Silvermine Nature Reserve section of the Table Mountain National Park in the Western Cape province, South Africa. In addition, a vegetation survey was conducted. This comprised 18 transects at various distances from the recreational paths in the park, and used a prioritisation ranking system that identified the alien species of greatest concern. It was concluded that the greatest number of alien plant species could be found along dog paths, in comparison to the hiking trails and cycling trails. This corresponded to the findings that dog walkers had the highest incidence of seeds on their shoes, suggesting that tourists were possibly dispersing seeds from their gardens. Alien species significantly covered more of the vegetation transects closer to the trails than they did in transects further into the matrix. Because more alien species were present in areas susceptible to human disturbance, the data suggest that tourists can act as vectors for alien seed dispersal. These findings emphasise the need for active tourism management in line with the South African National Parks Biodiversity Monitoring Programme in order to prevent the introduction and spread of alien species into South Africa’s protected areas. Conservation implications: Tourism is the main source of revenue for South African National Parks, and one of the organisation’s principal goals is to create a tourism management policy conducive to conservation. This research explores the potential role that tourists may play in the introduction of non-native species into a protected area, thereby providing novel information that could assist managers in the sustainable management of protected areas. © 2015. The Authors. Licensee: AOSIS OpenJournals. This work is licensed under the Creative Commons Attribution License.

Ndlovu M.,University of Witwatersrand | Devereux E.,Organisation for Tropical Studies | Chieffe M.,Organisation for Tropical Studies | Asklof K.,Organisation for Tropical Studies | Russo A.,Organisation for Tropical Studies
South African Journal of Science | Year: 2016

Human settlement expansion into elephant ranges, as well as increasing elephant populations within confined areas has led to heightened levels of human-elephant conflict in southern African communities living near protected areas. Several methods to mitigate this conflict have been suggested including the use of bees as an elephant deterrent. We investigated whether bee auditory and olfactory cues (as surrogates for live bees) could be used to effectively deter elephants. We evaluated the responses of elephants in the southern section of the Kruger National Park to five different treatments: (1) control noise, (2) buzzing bee noise, (3) control noise with honey scent, (4) honey scent, and (5) bee noise with honey scent. Elephants did not respond or displayed less heightened responses to the first four treatments. All elephants exposed to the bee noise with honey scent responded with defensive behaviours and 15 out of 21 individuals also fled. We concluded that buzzing bees or honey scent as isolated treatments (as may be the case with dormant beehives) were not effective elephant deterrents, but rather an active beehive emitting a combination of auditory and olfactory cues was a viable deterrent. However, mismatches in the timing of elephant raids and activity of bees may limit the use of bees in mitigating the prevailing human-elephant conflict. © 2016. The Author(s). Published under a Creative Commons Attribution Licence.

Hempson G.P.,Organisation for Tropical Studies | Hempson G.P.,University of Cape Town | Midgley J.J.,University of Cape Town | Lawes M.J.,Charles Darwin University | And 2 more authors.
Journal of Vegetation Science | Year: 2014

Aims: Bark thickness-stem diameter relationships are non-linear above a stem diameter threshold inmany woody species, whichmakes relative bark thickness measures dependent on the range of stem diameters that are sampled. This influences the appropriateness of differentmethods for comparing fire responses of woody plants across studies. Here we develop a framework for bark thickness comparisons by evaluating relative bark thickness estimates and bark thickness predictions obtained from linear and curved models fitted to raw and log-transformed bark-stem data. We use this framework to contrast bark thickness among fynbos and savanna plant functional groups. Location: Fynbos (17 species) and savanna (21 species) systems in South Africa. Methods: The linear subset of bark-stem data was identified using a three-step procedure. Linear regressions (with and without an intercept) and curved models (allometric and modified exponential models) were fitted to the linear subset and complete raw bark-stem data set, respectively. In addition, linear regression models were fitted to the log-transformed complete bark-stem data set. Regression slopes and bark thickness predictions obtained from these different approaches were compared, to determine which method provides the most robust metric for comparing bark thickness. Bark thickness was compared among fynbos resprouter guilds and acacias fromlow- and high-fire savannas. Results: The slope of the regression model fitted to the linear subset of raw bark-stem data provides a reliable metric for general comparisons of relative bark thickness. Bark thickness predictions from the curved and log models were comparable at 20-cm stem diameter, but the log model underestimated bark thickness at 5 cm for certain species. Relative bark thickness was significantly higher in: (1) fynbos fire resisters and epicormic resprouters than in non-resprouters; and (2) acacias fromhigh- vs low-fire savannas. Conclusions: The slope of the regressionmodel fitted to the linear subset of raw bark-stem data is a useful metric for bark thickness comparisons across studies, and compares favourably with bark thickness predictions derived from models fitted to the complete bark-stem data set. Fynbos and savanna trends support the proposition that relative bark thickness reflects differences in woody plant responses to fire and indicate themodal fire regime of ecosystems. © 2014 International Association for Vegetation Science.

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