The influence of rainfall seasonality and climate change on the demography of Aloe Dichotoma, a long-lived succulent tree from semi-arid southern Africa

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dc.contributor.advisorHoffman, Timmen_ZA
dc.contributor.advisorRebelo, Anthony Gen_ZA
dc.contributor.advisorJack,Samen_ZA
dc.contributor.authorGallaher,Kirsten Sarah Leilanien_ZA
dc.date.accessioned2015-07-08T06:22:11Z
dc.date.available2015-07-08T06:22:11Z
dc.date.issued2014en_ZA
dc.descriptionIncludes bibliographical references.en_ZA
dc.description.abstractIn the arid and semi-arid western parts of southern Africa, Aloe dichotoma Masson, a long-lived succulent tree species, is thought to be responding to anthropogenic climate change. However, differences in response across its distribution are likely to be related to rainfall seasonality. This study investigated change in ten Aloe dichotoma populations within winter and summer rainfall zones in South Africa and southern Namibia. Using repeat photography over a timespan of approximately 30 years, demographic patterns, population dynamics (including mortality, recruitment and overall population change) and growth were assessed and modelled with climatic variables. Long-term patterns of recruitment and longevity were also investigated by using individual plant growth data to reconstruct recruitment histories for each population. Finally, the influences of climatic conditions on recruitment were evaluated by superimposing historical rainfall and temperature data. Differences in response between rainfall zones are clearly evident throughout. Generalised linear models revealed lower mortality, higher recruitment and positive population change at winter rainfall sites, while summer rainfall sites showed negative population change. Growth data revealed more rapid growth in height of juveniles than adults, and slower growth in height in the winter rainfall zone, most likely related to differences in tree architecture. It is evident that biotic and anthropogenic factors such as herbivory, nurse plants and theft are likely to moderate observable patterns as opposed to driving them. Recruitment modelling suggested that A. dichotoma attains a maximum age of 300 to 350 years, and revealed recent recruitment peaks in the winter rainfall zone and peaks around the turn of the 19th century in the summer rainfall zone. Changes in temperature and rainfall are likely to be the main drivers. Rising temperatures within the last century may have driven increased recruitment and low mortality in the cold-limited winter rainfall zone, while decreasing rainfall within the summer rainfall zone, combined with increasing temperatures, may explain this region's low recruitment and high mortality. The advancement of knowledge of broad spatial and temporal patterns in A. dichotoma and the likely causes, coupled with fine-scale future studies, will enable more detailed prediction of the species' response to future global change.en_ZA
dc.identifier.apacitation (2014). <i>The influence of rainfall seasonality and climate change on the demography of Aloe Dichotoma, a long-lived succulent tree from semi-arid southern Africa</i>. (Thesis). University of Cape Town ,Faculty of Science ,Percy FitzPatrick Institute of African Ornithology. Retrieved from http://hdl.handle.net/11427/13388en_ZA
dc.identifier.chicagocitation. <i>"The influence of rainfall seasonality and climate change on the demography of Aloe Dichotoma, a long-lived succulent tree from semi-arid southern Africa."</i> Thesis., University of Cape Town ,Faculty of Science ,Percy FitzPatrick Institute of African Ornithology, 2014. http://hdl.handle.net/11427/13388en_ZA
dc.identifier.citation 2014. The influence of rainfall seasonality and climate change on the demography of Aloe Dichotoma, a long-lived succulent tree from semi-arid southern Africa. Thesis. University of Cape Town ,Faculty of Science ,Percy FitzPatrick Institute of African Ornithology. http://hdl.handle.net/11427/13388en_ZA
dc.identifier.ris TY - Thesis / Dissertation AU - Gallaher,Kirsten Sarah Leilani AB - In the arid and semi-arid western parts of southern Africa, Aloe dichotoma Masson, a long-lived succulent tree species, is thought to be responding to anthropogenic climate change. However, differences in response across its distribution are likely to be related to rainfall seasonality. This study investigated change in ten Aloe dichotoma populations within winter and summer rainfall zones in South Africa and southern Namibia. Using repeat photography over a timespan of approximately 30 years, demographic patterns, population dynamics (including mortality, recruitment and overall population change) and growth were assessed and modelled with climatic variables. Long-term patterns of recruitment and longevity were also investigated by using individual plant growth data to reconstruct recruitment histories for each population. Finally, the influences of climatic conditions on recruitment were evaluated by superimposing historical rainfall and temperature data. Differences in response between rainfall zones are clearly evident throughout. Generalised linear models revealed lower mortality, higher recruitment and positive population change at winter rainfall sites, while summer rainfall sites showed negative population change. Growth data revealed more rapid growth in height of juveniles than adults, and slower growth in height in the winter rainfall zone, most likely related to differences in tree architecture. It is evident that biotic and anthropogenic factors such as herbivory, nurse plants and theft are likely to moderate observable patterns as opposed to driving them. Recruitment modelling suggested that A. dichotoma attains a maximum age of 300 to 350 years, and revealed recent recruitment peaks in the winter rainfall zone and peaks around the turn of the 19th century in the summer rainfall zone. Changes in temperature and rainfall are likely to be the main drivers. Rising temperatures within the last century may have driven increased recruitment and low mortality in the cold-limited winter rainfall zone, while decreasing rainfall within the summer rainfall zone, combined with increasing temperatures, may explain this region's low recruitment and high mortality. The advancement of knowledge of broad spatial and temporal patterns in A. dichotoma and the likely causes, coupled with fine-scale future studies, will enable more detailed prediction of the species' response to future global change. DA - 2014 DB - OpenUCT DP - University of Cape Town LK - https://open.uct.ac.za PB - University of Cape Town PY - 2014 T1 - The influence of rainfall seasonality and climate change on the demography of Aloe Dichotoma, a long-lived succulent tree from semi-arid southern Africa TI - The influence of rainfall seasonality and climate change on the demography of Aloe Dichotoma, a long-lived succulent tree from semi-arid southern Africa UR - http://hdl.handle.net/11427/13388 ER - en_ZA
dc.identifier.urihttp://hdl.handle.net/11427/13388
dc.identifier.vancouvercitation. The influence of rainfall seasonality and climate change on the demography of Aloe Dichotoma, a long-lived succulent tree from semi-arid southern Africa. [Thesis]. University of Cape Town ,Faculty of Science ,Percy FitzPatrick Institute of African Ornithology, 2014 [cited yyyy month dd]. Available from: http://hdl.handle.net/11427/13388en_ZA
dc.language.isoengen_ZA
dc.publisher.departmentPercy FitzPatrick Institute of African Ornithologyen_ZA
dc.publisher.facultyFaculty of Scienceen_ZA
dc.publisher.institutionUniversity of Cape Town
dc.subject.otherConservation Biologyen_ZA
dc.titleThe influence of rainfall seasonality and climate change on the demography of Aloe Dichotoma, a long-lived succulent tree from semi-arid southern Africaen_ZA
dc.typeMaster Thesis
dc.type.qualificationlevelMasters
dc.type.qualificationnameMScen_ZA
uct.type.filetypeText
uct.type.filetypeImage
uct.type.publicationResearchen_ZA
uct.type.resourceThesisen_ZA
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