Patterns and mechanisms of stem mortality in Acacia nigrescens induced by elephants and fire

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dc.contributor.advisorMidgley, Jeremy Jen_ZA
dc.contributor.advisorKruger, Laurence Men_ZA
dc.contributor.authorMoncrieff, Glennen_ZA
dc.date.accessioned2017-12-14T12:21:42Z
dc.date.available2017-12-14T12:21:42Z
dc.date.issued2007en_ZA
dc.date.updated2017-02-09T13:24:38Z
dc.description.abstractIncreasing elephant populations have been implicated in the decline of woody vegetation throughout Africa. The problem is particularly relevant to the Kruger National Park in South Africa, where elephant populations have almost doubled in the last 10 years. One manner in which elephants utilize trees is by stripping their bark. The role of bark stripping in increasing stem vulnerability to fire and the mechanism through which fire damage is mediated were investigated by experimentally removing bark and burning Acacia nigrescens stems. Field surveys were conducted in order to investigate patterns of bark stripping in relation to mortality patterns of large trees occurring subsequent to natural fires. In the experimental study, an increasing probability of mortality was associated with increasing amount of bark removed when trees were burnt. However, when trees were stripped but not burnt, simulating damage to cambium and phloem, none died in the 4-month period over which the experiment ran. This was taken as evidence that fire-induced xylem damage causes stem mortality. However, fire did kill a greater proportion of the remaining stem cambium around the circumference when bark had been removed. The field surveys indicate that bark stripping by elephants is frequent on large stems (44%) and that larger trees are more heavily impacted. The only variable measured that explained mortality patterns well was the percent of bark removed around the stem circumference up to 3m (p = 0.0076). These results indicate that damage to xylem is important in determining post-fire survival and that bark stripping by elephants increases the vulnerability of stems to fire. This increased vulnerability is a result of both increased damage to cambium and damage to exposed xylem. The high proportion of trees stripped by elephants and the increase in vulnerability to mortality associated with bark stripping suggests that unless elephant population growth is curbed, large Acacia nigrescens trees will eventually be eliminated from this ecosystem.en_ZA
dc.identifier.apacitationMoncrieff, G. (2007). <i>Patterns and mechanisms of stem mortality in Acacia nigrescens induced by elephants and fire</i>. (Thesis). University of Cape Town ,Faculty of Science ,Department of Biological Sciences. Retrieved from http://hdl.handle.net/11427/26666en_ZA
dc.identifier.chicagocitationMoncrieff, Glenn. <i>"Patterns and mechanisms of stem mortality in Acacia nigrescens induced by elephants and fire."</i> Thesis., University of Cape Town ,Faculty of Science ,Department of Biological Sciences, 2007. http://hdl.handle.net/11427/26666en_ZA
dc.identifier.citationMoncrieff, G. 2007. Patterns and mechanisms of stem mortality in Acacia nigrescens induced by elephants and fire. University of Cape Town.en_ZA
dc.identifier.ris TY - Thesis / Dissertation AU - Moncrieff, Glenn AB - Increasing elephant populations have been implicated in the decline of woody vegetation throughout Africa. The problem is particularly relevant to the Kruger National Park in South Africa, where elephant populations have almost doubled in the last 10 years. One manner in which elephants utilize trees is by stripping their bark. The role of bark stripping in increasing stem vulnerability to fire and the mechanism through which fire damage is mediated were investigated by experimentally removing bark and burning Acacia nigrescens stems. Field surveys were conducted in order to investigate patterns of bark stripping in relation to mortality patterns of large trees occurring subsequent to natural fires. In the experimental study, an increasing probability of mortality was associated with increasing amount of bark removed when trees were burnt. However, when trees were stripped but not burnt, simulating damage to cambium and phloem, none died in the 4-month period over which the experiment ran. This was taken as evidence that fire-induced xylem damage causes stem mortality. However, fire did kill a greater proportion of the remaining stem cambium around the circumference when bark had been removed. The field surveys indicate that bark stripping by elephants is frequent on large stems (44%) and that larger trees are more heavily impacted. The only variable measured that explained mortality patterns well was the percent of bark removed around the stem circumference up to 3m (p = 0.0076). These results indicate that damage to xylem is important in determining post-fire survival and that bark stripping by elephants increases the vulnerability of stems to fire. This increased vulnerability is a result of both increased damage to cambium and damage to exposed xylem. The high proportion of trees stripped by elephants and the increase in vulnerability to mortality associated with bark stripping suggests that unless elephant population growth is curbed, large Acacia nigrescens trees will eventually be eliminated from this ecosystem. DA - 2007 DB - OpenUCT DP - University of Cape Town LK - https://open.uct.ac.za PB - University of Cape Town PY - 2007 T1 - Patterns and mechanisms of stem mortality in Acacia nigrescens induced by elephants and fire TI - Patterns and mechanisms of stem mortality in Acacia nigrescens induced by elephants and fire UR - http://hdl.handle.net/11427/26666 ER - en_ZA
dc.identifier.urihttp://hdl.handle.net/11427/26666
dc.identifier.vancouvercitationMoncrieff G. Patterns and mechanisms of stem mortality in Acacia nigrescens induced by elephants and fire. [Thesis]. University of Cape Town ,Faculty of Science ,Department of Biological Sciences, 2007 [cited yyyy month dd]. Available from: http://hdl.handle.net/11427/26666en_ZA
dc.language.isoengen_ZA
dc.publisher.departmentDepartment of Biological Sciencesen_ZA
dc.publisher.facultyFaculty of Scienceen_ZA
dc.publisher.institutionUniversity of Cape Town
dc.subject.otherBotanyen_ZA
dc.titlePatterns and mechanisms of stem mortality in Acacia nigrescens induced by elephants and fireen_ZA
dc.typeBachelor Thesis
dc.type.qualificationlevelHonours
dc.type.qualificationnameBSc (Hons)en_ZA
uct.type.filetype
uct.type.filetypeText
uct.type.filetypeImage
uct.type.publicationResearchen_ZA
uct.type.resourceThesisen_ZA
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