Browsing by Author "Moll, Eugene"

Now showing 1 - 9 of 9
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    The ecology and control of typha capensis in the wetlands of the Cape flats, South Africa
    (1993) Hall, Deborah Jane; Davies, Bryan; Moll, Eugene
    Typha capensis is indigenous to the Cape, but is thought to be threatening Cape Flats wetlands through invasion and encroachment. This thesis establishes the extent of such encroachment and investigates aspects of the phenology, life-history, growth, production and decomposition of the species in a Cape Flats wetland. The process of invasion by indigenous species rather than by alien species is discussed and the view that wetlands are threatened by mismanagement rather than by encroachment per se is examined. Finally, control methods particularly suited to local environmental and economic conditions are evaluated. T. capensis was shown to be typical of invasive plant species and is spreading in some wetlands. Encroachment is usually associated with the stabilisation of seasonal water-level fluctuations and under these conditions stands were spreading at 1.5m month. Demographic methods used to measure growth, production and decomposition made it possible to quantify leaf fragmentation and shoot collapse, processes that are generally ignored during decomposition studies. Results showed that the structure of Typha stands is related to flood regime, and that flood regime has an important effect on production, litter formation and decomposition.
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    The natural vegetation of the Robertson Karoo : an evaluation of its conservation status
    (1990) Wood, Julia; Moll, Eugene; McDowell Clive
    The natural vegetation of the Robertson Karoo contains many taxa and vegetation communities worthy of conservation. This thesis is concerned with aiding the future conservation of natural vegetation of the Robertson Karoo by assessing the threats to its survival and identifying priority conservation areas.
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    Pattern and process in South Coast dune fynbos : population, community and landscape level studies
    (1990) Pierce, Shirley M; Moll, Eugene
    The study aimed to explain vegetation dynamics in response to disturbance in a dune landscape comprising a mosaic and admixture of grassland, fynbos and thicket. A hierarchical approach directed investigations at the landscape, community and population levels, with emphasis on seed banks. The study concentrated on fynbos, the predominant vegetation type. At the landscape-level, pattern was attributed to successional processes rather than abiotic factors. Each vegetation was maintained under defined disturbance regimes of fire, grazing and bushcutting. In the absence of disturbance, succession proceeded from grassland, through fynbos, to thicket. The study contributed to existing theory on the effects of disturbance on seed bank size, and the relationship between seed bank composition and its above-ground vegetation. No single model for successional pathways and mechanisms was supported: these differed amongst vegetation types and within fynbos communities.
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    The autecology of Widdringtonia Cedarbergensis in relation to its conservation management
    (1985) Manders, Patrick Timothy; Moll, Eugene
    The Clanwilliam cedar is an endangered tree species confined to the Cederberg mountains in the south-western Cape Province. An assessment of the current status of the species is presented as an introduction to the thesis. In the introduction inferences are made from the available evidence on the previous status of the populations. The present status is inferior to that prior to the influence of European settlers. Theories presented by previous authors to account for the decline are examined • A transition matrix model was developed, based on data from permanent monitoring plots, to model the population dynamics of the species. The methods of dealing with the data and fitting the observations to the transition matrix are presented. An eigenvalue of 1,01444 was calculated for the species, indicating population growth in the absence of fire. Inferences drawn from this model indicate that a minimum interval of 15 to 20 years between fires is necessary for the survival of the species . An analysis of habitat features obtainable from maps was used to define the general distribution range and the actual distribution of cedars within their range. Altitude is the major factor influencing both the general and actual distribution. Indirect evidence is presented in this analysis to indicate that cedars can grow over a far greater area within their present distribution range. Sowing experiments were conducted in the field to determine the effects of season of sowing and site features on germination success and seedling survival. Seeds sown in autumn exhibit the best combination of germination and establishment success. It is concluded that the Clanwilliam cedar can be successfully managed without detriment to the other species in the community and therefore warrants efforts for its conservation. Intervals of 15 to 20 years between prescribed burns are recommended on the grounds that cedar stands will be afforded sufficient time to recover from the mortality of the previous fire, especially with respect to seed production. At the same time, this interval should be short enough to preclude the occurrence of extremely intense wildfires and thus should prevent the associated high cedar mortality. Prescribed burns should be applied in late summer or autumn coinciding with the natural period of seed release. This will maximise the germination and establishment of the seed released from both the survivors and the trees killed. Where deemed necessary in terms of adult mortality or seedling recruitment, seed should be sown on selected sites as soon after a fire as possible. Cedar mortality will depend more on the conditions under which the prescribed burn is applied than on the season in which the burn is carried out.
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    The colonisation of fynbos and disturbed sites by indigenous forest communities in the Southern Cape
    (1980) Van Daalen, Johan Cornelis; Moll, Eugene
    The area covered by indigenous forests in the Southern Cape has been and is still diminishing as a result of 1 road construction (for example, 28 ha of indigenous' forest has recently been clear-felled for a new highway), power lines, settlements, fires (man-made and natural, for example the fires of 1869 and 1964) and agricultural activities. Furthermore, large areas are infested with exotic species such as Acacia melanoxylon ·(blackwood), A. mearnsii (black wattle) and different Eugalyptus and Pinus species. Although these species are useful timber and firewood species, they tend to establish themselves on disturbed patches in the indigenous forest and suppress the surrounding forest • trees. The present policy of the Directorate of Forestry and Environmental Conservation of the Department of Water Affairs, Forestry and Environmental Conservation (hereafter called Forestry) regarding these forests aim at their conservation and the reconstruction of small, damaged forest patches. Reconstruction is one of the five management classes for indigenous forests. The others are production, research, protection, and recreation. Especially during the last decade smaller areas were reconstructed, mainly by planting Podocarpus falcatus (kalander) and Ocotea bullata (stinkwood). Recently, other additional indigenous species are being used. A few experimental reconstruction plots have been laid out, the first one (in 1927) being the Taungya plots at
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    The derivation of fire hazard indices and burning prescriptions from climatic and ecological features of the fynbos biome
    (1985) Van Wilgen, Brian William; Moll, Eugene
    This study deals with the development of fire behaviour prediction and fire danger rating systems, and their potential use in fynbos catchment areas. Fynbos catchments are managed for sustained water yields and for nature conservation. Wildfires have always been a problem in these areas, and early management consisted almost entirely of attempts to protect the vegetation from fire. More recently a policy of prescribed burning has been introduced. The analytical fire modelling approach adopted in the United States of America was identified as having potential for use in the management of catchment areas. This study was aimed at testing a number of hypotheses related to the adoption of this system in the management of fynbos areas. It further aimed to combine practical aspects of burning and fire control with conservation goals to provide meaningful burning prescriptions for the biome. The United States National Fire Danger Rating System (NFDRS) is based on Rothermel's analytical fire model. Vegetation characteristics are summarised in a fuel model and used in the NFDRS together with weather variables to produce fire danger indices. The physical properties of fynbos fuels were determined, and a fuel model was derived. The fuel model was tested in a series of experimental fires where it was found to predict fire behaviour parameters with acceptable accuracy. Climate data from nine weather stations were used in a preliminary study with the NFDRS to examine the variation in fire danger over the fynbos biome and to establish ranges of danger indices. The NFDRS reflected the expected seasonal trends in fire potential accurately, and indices compared well with actual fire occurrence. Recorded weather conditions during eight large wildfires were used to generate fire danger indices to determine the value of the various indices for reflecting fire danger. The energy release component was shown to be the steadiest indicator of high fire danger. The system shows good potential for use in the formal management of fynbos catchment areas. The NFDRS was then used in conjunction with the fynbos fuel model and climate data from 40 weather stations to define five distinct fire climate zones within the fynbos biome. The seasonal cycle of fire danger is pronounced in two inland zones, but mean fire danger shows little seasonal fluctuation in three coastal zones. Fires will occur in the coastal zones under occasional suitable conditions. These zones are useful fire management zones. The response of serotinous Proteaceae to season of fire was examined. Regeneration was best following late summer-early autumn fires, but some geographical variation was noticed, The results were used together with other examples from the fynbos biota to support seasonal, constraints on burning operations in conservation areas. Ecologically acceptable burning seasons coincide with periods of high fire danger, which I complicate the prescribed burning task. The conditions currently favoured by managers for burning operations were determined and used together with the seasonal constraints to define preliminary burning prescriptions. The seasonal occurrence of these prescribed conditions in the different fire climate zones was determined to examine the feasibility of burning in the ecologically acceptable season. While suitable conditions are rare 1n all seasons, it is concluded that burning could feasibly be carried out in ecologically acceptable seasons if an awareness of the conditions leading to safe fires is fostered among managers. The effects of invasion of fynbos by alien shrubs on fire hazard and potential fire behaviour were determined by deriving fuel models for invaded fynbos. Invasion increases fuel loads and changes the nature of fuel beds so that fires become difficult to control under extreme weather conditions. This provides a further argument for the eradication of such weeds from catchment areas. The results of this study can be used to refine fire management policies in fynbos mountain catchment areas. No previous work has quantified the seasonal and absolute variations in the physical fire environment of the fynbos biome or attempted to combine practical aspects of burning and fire control with conservation goals. The study also presents baseline data on fuels, fire behaviour and burning prescriptions. The results therefore represent a contribution to the understanding of fire as a physical factor in the management of catchment areas in the fynbos biome.
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    The derivation of fire hazard indices and burning prescriptions from climatic and ecological features of the fynbos biome
    (1985) Van Wilgen, Brian William; Moll, Eugene
    This study deals with the development of fire behaviour prediction and fire danger rating systems, and their potential use in fynbos catchment areas. Fynbos catchments are managed for sustained water yields and for nature conservation. Wildfires have always been a problem in these areas, and early management consisted almost entirely of attempts to protect the vegetation from fire. More recently a policy of prescribed burning has been introduced. The analytical fire modelling approach adopted in the United States of America was identified as having potential for use in the management of catchment areas. This study was aimed at testing a number of hypotheses related to the adoption of this system in the management of fynbos areas. It further aimed to combine practical aspects of burning and fire control with conservation goals to provide meaningful burning prescriptions for the biome. The United States National Fire Danger Rating System (NFDRS) is based on Rothermel's analytical fire model. Vegetation characteristics are summarised in a fuel model and used in the NFDRS together with weather variables to produce fire danger indices. The physical properties of fynbos fuels were determined, and a fuel model was derived. The fuel model was tested in a series of experimental fires where it was found to predict fire behaviour parameters with acceptable accuracy. Climate data from nine weather stations were used in a preliminary study with the NFDRS to examine the variation in fire danger over the fynbos biome and to establish ranges of danger indices. The NFDRS reflected the expected seasonal trends in fire potential accurately, and indices compared well with actual fire occurrence. Recorded weather conditions during eight large wildfires were used to generate fire danger indices to determine the value of the various indices for reflecting fire danger. The energy release component was shown to be the steadiest indicator of high fire danger. The system shows good potential for use in the formal management of fynbos catchment areas. The NFDRS was then used in conjunction with the fynbos fuel model and climate data from 40 weather stations to define five distinct fire climate zones within the fynbos biome. The seasonal cycle of fire danger is pronounced in two inland zones, but mean fire danger shows little seasonal fluctuation in three coastal zones. Fires will occur in the coastal zones under occasional suitable conditions. These zones are useful fire management zones. The response of serotinous Proteaceae to season of fire was examined. Regeneration was best following late summer-early autumn fires, but some geographical variation was noticed, The results were used together with other examples from the fynbos biota to support seasonal, constraints on burning operations in conservation areas. Ecologically acceptable burning seasons coincide with periods of high fire danger, which I complicate the prescribed burning task. The conditions currently favoured by managers for burning operations were determined and used together with the seasonal constraints to define preliminary burning prescriptions. The seasonal occurrence of these prescribed conditions in the different fire climate zones was determined to examine the feasibility of burning in the ecologically acceptable season. While suitable conditions are rare 1n all seasons, it is concluded that burning could feasibly be carried out in ecologically acceptable seasons if an awareness of the conditions leading to safe fires is fostered among managers. The effects of invasion of fynbos by alien shrubs on fire hazard and potential fire behaviour were determined by deriving fuel models for invaded fynbos. Invasion increases fuel loads and changes the nature of fuel beds so that fires become difficult to control under extreme weather conditions. This provides a further argument for the eradication of such weeds from catchment areas. The results of this study can be used to refine fire management policies in fynbos mountain catchment areas. No previous work has quantified the seasonal and absolute variations in the physical fire environment of the fynbos biome or attempted to combine practical aspects of burning and fire control with conservation goals. The study also presents baseline data on fuels, fire behaviour and burning prescriptions. The results therefore represent a contribution to the understanding of fire as a physical factor in the management of catchment areas in the fynbos biome.
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    Vegetation studies in the Humansdorp region of the Fynbos Biome
    (1982) Cowling, Richard M; Moll, Eugene
    This thesis comprises five papers dealing with syntaxonomy, history, species diversity and growth form distribution in Cape shrublands and non-Cape vegetation types (subtropical thicket, Afromontane forest) in the Humansdorp region of the Fynbos Biome. The first paper is a re-evaluation of vegetation concepts in the study area and, more generally, in the Fynbos Biome and adjacent biomes. Syntaxa are characterized in terms of floristics (including biogeographical affinities and patterns of endemism), structure and dynamics. In the second paper both descriptive and historical approaches are used to generate hypotheses to explain vegetation history during the last glacial to Holocene sequence. The third paper investigates, and seeks explanations for, diversity relations in the vegetation types of the study area. Both historical and ecological factors are used to predict patterns of species diversity. In the fourth paper patterns in the relative importance of structural attributes and growth forms along fynbos and non-fynbos coenoclines are studied. An appendix paper focusses on the distribution of C₃ and C₄ grasses in the Cape shrublands of the study area. It was concluded that descriptive studies such as this have much value in clarifying vegetation concepts and generating hypotheses to explain variations in community structure. However, as management and conservation are the major aims of the Fynbos Biome Project, future studies should concentrate on the reproductive biology and regeneration niches of plants in the fire-prone Cape shrublands. From the results of such studies a predictive knowledge of Cape shrubland dynamics will emerge - the key to judicious management.