Fire regimes in eastern coastal fynbos: drivers, ecology and management
- Authors: Kraaij, Tineke
- Date: 2012
- Subjects: Forest fires -- South Africa , Climatic changes , Prescribed burning , Fire ecology -- South Africa
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:10607 , http://hdl.handle.net/10948/d1008047 , Forest fires -- South Africa , Climatic changes , Prescribed burning , Fire ecology -- South Africa
- Description: Conventional knowledge of fynbos fire ecology is based on the summer-autumn fire regimes of the western Cape Floral Kingdom (CFK) where the climate is Mediterranean. However, the climate in the eastern coastal-CFK is milder and rainfall occurs year-round, with presumed effects on fire regimes. The Garden Route National Park (GRNP) has recently been established in the region, in a landscape where indigenous forests, fire-prone fynbos shrublands and fire-sensitive plantations of invasive alien trees are interspersed. The park faces considerable challenges related to the management of fire, including significant pressure from the adjacent plantation industry to reduce wildfire hazard by burning fynbos at short intervals, and high levels of invasion by alien trees (largely Pinus species originating from plantations). This study sought to improve understanding of fire regimes in eastern coastal fynbos shrublands, and to provide guidelines for ecologically sound management of fire in the area. My approach entailed (i) an assessment of the context within which fire management was practiced during the past century; (ii) characterisation of the recent fire history and fire regime (1900–2010); (iii) characterisation of the seasonality of fire weather and lightning; (iv) estimation of minimum fire return intervals (FRIs) from juvenile periods and post-fire recruitment success of overstorey proteoids (non-sprouting, slow-maturing, serotinous Proteaceae); and (v) determination of the ecologically appropriate fire season from post-fire recruitment seasonality of proteoids. I established that historically, plantation protection enjoyed priority over fynbos conservation in the area that is now the GRNP. Fynbos close to plantations has most likely been compromised by frequent and low-intensity burning in the past, as well as by invasion by alien trees. In terms of area burnt (1900–2010), natural (lightning-ignited) fires dominated the fire regime, particularly in the east, whereas prescribed burning was relatively unimportant. Typical fire return intervals (FRIs; 8–26 years; 1980–2010) were comparable to those in other fynbos protected areas and appeared to be shorter in the eastern Tsitsikamma than in the western Outeniqua halves of the study area. Proteaceae juvenile periods (4–9 years) and post-fire recruitment success (following fires in ≥7 year-old vegetation) suggested that for biodiversity conservation purposes, FRIs should be no less than nine years in moist, productive fynbos. Increases in the total area burnt annually (since 1980) were correlated with long-term increases in average fire danger weather, suggesting that fire regime changes may be related to global change. Collectively, findings on the seasonality of actual fires and the seasonality of fire danger weather, lightning, and post-fire proteoid recruitment suggested that fires in eastern coastal fynbos are not limited to any particular season, and for this reason managers do not need to be concerned if fires occur in any season. The ecological requirements for higher fire intensity may nonetheless be constrained by a need for safety. I articulated these findings into ecological thresholds pertaining to the different elements of the fire regime in eastern coastal fynbos, to guide adaptive management of fire in the Garden Route National Park. I also recommended a fire management strategy for the park to address the aforementioned operational considerations within the constraints posed by ecological thresholds. Finally, I highlighted further research and monitoring needs.
- Full Text:
- Date Issued: 2012
- Authors: Kraaij, Tineke
- Date: 2012
- Subjects: Forest fires -- South Africa , Climatic changes , Prescribed burning , Fire ecology -- South Africa
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:10607 , http://hdl.handle.net/10948/d1008047 , Forest fires -- South Africa , Climatic changes , Prescribed burning , Fire ecology -- South Africa
- Description: Conventional knowledge of fynbos fire ecology is based on the summer-autumn fire regimes of the western Cape Floral Kingdom (CFK) where the climate is Mediterranean. However, the climate in the eastern coastal-CFK is milder and rainfall occurs year-round, with presumed effects on fire regimes. The Garden Route National Park (GRNP) has recently been established in the region, in a landscape where indigenous forests, fire-prone fynbos shrublands and fire-sensitive plantations of invasive alien trees are interspersed. The park faces considerable challenges related to the management of fire, including significant pressure from the adjacent plantation industry to reduce wildfire hazard by burning fynbos at short intervals, and high levels of invasion by alien trees (largely Pinus species originating from plantations). This study sought to improve understanding of fire regimes in eastern coastal fynbos shrublands, and to provide guidelines for ecologically sound management of fire in the area. My approach entailed (i) an assessment of the context within which fire management was practiced during the past century; (ii) characterisation of the recent fire history and fire regime (1900–2010); (iii) characterisation of the seasonality of fire weather and lightning; (iv) estimation of minimum fire return intervals (FRIs) from juvenile periods and post-fire recruitment success of overstorey proteoids (non-sprouting, slow-maturing, serotinous Proteaceae); and (v) determination of the ecologically appropriate fire season from post-fire recruitment seasonality of proteoids. I established that historically, plantation protection enjoyed priority over fynbos conservation in the area that is now the GRNP. Fynbos close to plantations has most likely been compromised by frequent and low-intensity burning in the past, as well as by invasion by alien trees. In terms of area burnt (1900–2010), natural (lightning-ignited) fires dominated the fire regime, particularly in the east, whereas prescribed burning was relatively unimportant. Typical fire return intervals (FRIs; 8–26 years; 1980–2010) were comparable to those in other fynbos protected areas and appeared to be shorter in the eastern Tsitsikamma than in the western Outeniqua halves of the study area. Proteaceae juvenile periods (4–9 years) and post-fire recruitment success (following fires in ≥7 year-old vegetation) suggested that for biodiversity conservation purposes, FRIs should be no less than nine years in moist, productive fynbos. Increases in the total area burnt annually (since 1980) were correlated with long-term increases in average fire danger weather, suggesting that fire regime changes may be related to global change. Collectively, findings on the seasonality of actual fires and the seasonality of fire danger weather, lightning, and post-fire proteoid recruitment suggested that fires in eastern coastal fynbos are not limited to any particular season, and for this reason managers do not need to be concerned if fires occur in any season. The ecological requirements for higher fire intensity may nonetheless be constrained by a need for safety. I articulated these findings into ecological thresholds pertaining to the different elements of the fire regime in eastern coastal fynbos, to guide adaptive management of fire in the Garden Route National Park. I also recommended a fire management strategy for the park to address the aforementioned operational considerations within the constraints posed by ecological thresholds. Finally, I highlighted further research and monitoring needs.
- Full Text:
- Date Issued: 2012
Biological control of Pereskia aculeata Miller (Cactaceae)
- Authors: Paterson, Iain Douglas
- Date: 2011
- Subjects: Pereskia -- Biological control -- South Africa Cactus -- Biological control -- South Africa Invasive plants -- Biological control -- South Africa Curculionidae -- South Africa Pyralidae -- South Africa Insects as biological pest control agents -- South Africa
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:5825 , http://hdl.handle.net/10962/d1007653
- Description: Pereskia aculeata Miller (Cactaceae) is an environmental weed that is damaging to natural ecosystems in South Africa. The plant is native to Central and South America and was first recorded in South Africa in a botanical garden in 1858. In this thesis, research into the biological control of P. aculeata was conducted with the intention of improving the control of the weed. A pre-release study of the relationship between P. aculeata density and native plant biodiversity indicated that P. aculeata has a negative impact on native biodiversity. The native plant biodiversity associated with different P. aculeata densities was used to determine threshold values and goals for the control of the weed. A threshold value of 50% P. aculeata density was calculated, indicating that P. aculeata density must be maintained below 50% in order to conserve native plant biodiversity. The ultimate goal of the control programme should be to maintain P. aculeata densities below 30%. At these densities there was no significant difference in native plant biodiversity from if the weed were absent from the ecosystem. The biological control agent, Phenrica guérini Bechyne (Chrysomelidae), has been released in South Africa but the potential of the agent to impact P. aculeata is not known and no post release evaluation has been conducted. Impact assessment studies indicate that P. guérini does not impact P. aculeata, even at high densities, but the results of greenhouse experiments should be interpreted with caution because of problems with extrapolation into the field. Although observations in the field suggest that P. guérini has reduced P. aculeata densities at one site, it is clear that new biological control agents are needed to reduce the weed to acceptable levels. Identifying the origin of the South African P. aculeata population was believed to be important to the biological control programme due to the disjunct native distribution and intraspecific variation of the species. Natural enemies associated with plant genotypes in different parts of the native distribution may have developed specialised relationships with certain intraspecific variants of the plant, resulting in differences in agent efficacy on certain host plant genotypes. A molecular study indicated that the closest relatives to the South African weed population found in the native distribution were in Rio de Janeiro Province, Brazil. A bioassay experiment in which fitness related traits of the biological control agent, P. guérini, were measured on various P. aculeata genotypes was conducted to determine the importance of host plant intraspecific variation. There was little variation in fitness traits between genotypes and no evidence of intraspecific host plant specialization. Although intraspecific variation had no effect on agent efficacy in the case of P. guérini, it is possible that other natural enemies may be more specialized. Genotype matching is expected to be more important when natural enemies likely to be specialised to individual genotypes are considered for biological control. Potential biological control agents were prioritized from data collected on surveys in the native distribution. The most promising of these, based on the presence of feeding, incidence, predicted host range, climatic matching, genotype matching and mode of damage, are two species of Curculionidae, the current biological control agent P. guérini and the stem boring moth, Maracayia chiorisalis Walker (Crambidae). The two curculionid species and M. chlorisalis should be considered priorities for host specificity studies. Releases of P. guérini and any new biological control agents should be made at sites where the pre-release study was conducted so that post-release evaluation data can be compared with the pre-release data and the impact of biological control can be evaluated. Retrospective analyses of biological control programmes provide important ways of improving aspects of biological control programmes, such as methods of agent selection. The evaluation of success in biological control programmes is essential for retrospective analyses because factors that have lead to successes or failures can be analysed. Retrospective analyses of biological control programmes, such as this thesis, may improve weed management, thereby contributing to the conservation of natural resources.
- Full Text:
- Date Issued: 2011
- Authors: Paterson, Iain Douglas
- Date: 2011
- Subjects: Pereskia -- Biological control -- South Africa Cactus -- Biological control -- South Africa Invasive plants -- Biological control -- South Africa Curculionidae -- South Africa Pyralidae -- South Africa Insects as biological pest control agents -- South Africa
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:5825 , http://hdl.handle.net/10962/d1007653
- Description: Pereskia aculeata Miller (Cactaceae) is an environmental weed that is damaging to natural ecosystems in South Africa. The plant is native to Central and South America and was first recorded in South Africa in a botanical garden in 1858. In this thesis, research into the biological control of P. aculeata was conducted with the intention of improving the control of the weed. A pre-release study of the relationship between P. aculeata density and native plant biodiversity indicated that P. aculeata has a negative impact on native biodiversity. The native plant biodiversity associated with different P. aculeata densities was used to determine threshold values and goals for the control of the weed. A threshold value of 50% P. aculeata density was calculated, indicating that P. aculeata density must be maintained below 50% in order to conserve native plant biodiversity. The ultimate goal of the control programme should be to maintain P. aculeata densities below 30%. At these densities there was no significant difference in native plant biodiversity from if the weed were absent from the ecosystem. The biological control agent, Phenrica guérini Bechyne (Chrysomelidae), has been released in South Africa but the potential of the agent to impact P. aculeata is not known and no post release evaluation has been conducted. Impact assessment studies indicate that P. guérini does not impact P. aculeata, even at high densities, but the results of greenhouse experiments should be interpreted with caution because of problems with extrapolation into the field. Although observations in the field suggest that P. guérini has reduced P. aculeata densities at one site, it is clear that new biological control agents are needed to reduce the weed to acceptable levels. Identifying the origin of the South African P. aculeata population was believed to be important to the biological control programme due to the disjunct native distribution and intraspecific variation of the species. Natural enemies associated with plant genotypes in different parts of the native distribution may have developed specialised relationships with certain intraspecific variants of the plant, resulting in differences in agent efficacy on certain host plant genotypes. A molecular study indicated that the closest relatives to the South African weed population found in the native distribution were in Rio de Janeiro Province, Brazil. A bioassay experiment in which fitness related traits of the biological control agent, P. guérini, were measured on various P. aculeata genotypes was conducted to determine the importance of host plant intraspecific variation. There was little variation in fitness traits between genotypes and no evidence of intraspecific host plant specialization. Although intraspecific variation had no effect on agent efficacy in the case of P. guérini, it is possible that other natural enemies may be more specialized. Genotype matching is expected to be more important when natural enemies likely to be specialised to individual genotypes are considered for biological control. Potential biological control agents were prioritized from data collected on surveys in the native distribution. The most promising of these, based on the presence of feeding, incidence, predicted host range, climatic matching, genotype matching and mode of damage, are two species of Curculionidae, the current biological control agent P. guérini and the stem boring moth, Maracayia chiorisalis Walker (Crambidae). The two curculionid species and M. chlorisalis should be considered priorities for host specificity studies. Releases of P. guérini and any new biological control agents should be made at sites where the pre-release study was conducted so that post-release evaluation data can be compared with the pre-release data and the impact of biological control can be evaluated. Retrospective analyses of biological control programmes provide important ways of improving aspects of biological control programmes, such as methods of agent selection. The evaluation of success in biological control programmes is essential for retrospective analyses because factors that have lead to successes or failures can be analysed. Retrospective analyses of biological control programmes, such as this thesis, may improve weed management, thereby contributing to the conservation of natural resources.
- Full Text:
- Date Issued: 2011
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