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Patterns and mechanisms of stem mortality in Acacia nigrescens induced by elephants and fire
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 tree...
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| Format: | Thesis |
| Language: | English |
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Department of Biological Sciences
2017
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| _version_ | 1867613310331912192 |
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| access_status_str | Open Access |
| author | Moncrieff, Glenn |
| author2 | Midgley, Jeremy J |
| author_browse | Midgley, Jeremy J Moncrieff, Glenn |
| author_facet | Midgley, Jeremy J Moncrieff, Glenn |
| author_sort | Moncrieff, Glenn |
| collection | Thesis |
| description | 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. |
| format | Thesis |
| id | oai:open.uct.ac.za:11427/26666 |
| institution | University of Cape Town (South Africa) |
| language | eng |
| last_indexed | 2026-06-10T12:34:06.076Z |
| license_str | Not specified — see source repository |
| provenance_str_mv | Harvested via OAI-PMH from UCTD — University of Cape Town Open Access Repository |
| publishDate | 2017 |
| publishDateRange | 2017 |
| publishDateSort | 2017 |
| publisher | Department of Biological Sciences |
| publisherStr | Department of Biological Sciences |
| record_format | dspace |
| source_str | UCTD — University of Cape Town Open Access Repository |
| spelling | oai:open.uct.ac.za:11427/26666 Patterns and mechanisms of stem mortality in Acacia nigrescens induced by elephants and fire Moncrieff, Glenn Midgley, Jeremy J Kruger, Laurence M Botany 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. 2017-12-14T12:21:42Z 2017-12-14T12:21:42Z 2007 2017-02-09T13:24:38Z Bachelor Thesis Honours BSc (Hons) http://hdl.handle.net/11427/26666 eng application/pdf Department of Biological Sciences Faculty of Science University of Cape Town |
| spellingShingle | Botany Moncrieff, Glenn Patterns and mechanisms of stem mortality in Acacia nigrescens induced by elephants and fire |
| thesis_degree_str | Bachelor's / Honours |
| title | Patterns and mechanisms of stem mortality in Acacia nigrescens induced by elephants and fire |
| title_full | Patterns and mechanisms of stem mortality in Acacia nigrescens induced by elephants and fire |
| title_fullStr | Patterns and mechanisms of stem mortality in Acacia nigrescens induced by elephants and fire |
| title_full_unstemmed | Patterns and mechanisms of stem mortality in Acacia nigrescens induced by elephants and fire |
| title_short | Patterns and mechanisms of stem mortality in Acacia nigrescens induced by elephants and fire |
| title_sort | patterns and mechanisms of stem mortality in acacia nigrescens induced by elephants and fire |
| topic | Botany |
| url | http://hdl.handle.net/11427/26666 |
| work_keys_str_mv | AT moncrieffglenn patternsandmechanismsofstemmortalityinacacianigrescensinducedbyelephantsandfire |