Browsing by Author "Moll, Eugene J"

Now showing 1 - 17 of 17
  • Thumbnail Image
    Item
    Open Access
    Aspects of coastal fynbos phenology
    (1983) Sommerville, Jacqueline Elizabeth Melville; Moll, Eugene J
    This thesis comprises three papers on different aspects of the phenology of several south western Cape coastal fynbos species, with a general introduction and conclusion I inking the three. The introduction discusses factors relating to the occurrence of summer growth in some Australian heath and Cape fynbos species. The first paper deals with the responses of the stem xylem pressure potential of two species to seasonal moisture changes in three soils. The results show that L. parile experienced little or no water stress throughout the investigation. The decreasing spring-summer potentials measured in T. punctatus suggest considerable water stress in this species. The observed differences can be explained in terms of species rooting depth and soil water-holding capacity. The second paper investigates patterns of seasonal shoot or culm growth in 11 species, in relation to past and present climatic factors and seasonal nutrient availability. The results show that other factors such as root depth and extent, plant age and water-use, and soil water-holding capacity affect the timing of shoot or culm growth in some species. In the final paper the seasonality of reproductive activity is discussed in relation to the seasonality of vegetative growth and to biotic and abiotic environmental factors. Reproductive activity appears to have little effect on the growth of individual shoots or culms. More research is needed to determine the effects of biotic pollinators, dispersers and predators as well as temperature, photoperiod and soil moisture on the seasonality of reproductive activity. In the conclusions summer growth is discussed in relation to water stress, seasonal availability of nutrients and to plant characteristics such as root depth and age.
  • Thumbnail Image
    Item
    Open Access
    Aspects of plant dispersal in the southwestern Cape with particular reference to the roles of birds as dispersal agents
    (1988) Knight, Richard Spencer; Knight, Richard Spencer; Siegfried, Roy; Moll, Eugene J
    The dispersal of plants with particular attention to the roles birds play as dispersal agents was studied in the southwestern Cape, South Africa from 1983 to 1985. The research was organized as ten inter-related studies, each with an independent data base. Each chapter focused on a different scale of plant dispersal processes ranging from regional assemblages of plant species to individual species. At the largest scale, the seven vegetation types commonly occurring in the southwestern Cape were examined for incidence of vertebrate-dispersed plants. Coastal Thicket and Afromontane Forest were found to be the richest in these species. The colonization of vertebrate-dispersed plants was examined in an artificially cleared area of Mountain Fynbos vegetation. Enhanced densities of vertebrate-dispersed species were found in areas where perches had been provided. The seasonal availability of vertebrate-dispersed species was found to be most continuous in Coastal Thicket vegetation. Fruit displays of vertebrate-dispersed indigenous plants were found to vary from those that were sporadic and inconspicuous, to those that were conspicuous and predictable, whereas those of alien plants were usually large and conspicuous. Avian use of these fleshy fruits in Coastal Thicket was examined and found to be proportional to their availability. A study of fruit presentation in relation to leaf number and stem thickness suggested that sessile, stem attached fruits have fewer local leaves at time of ripening than fruits which are presented in panicles. This may enhance accessibility and conspicuousness of stem attached fruits for dispersal by birds. Four autecological studies tested certain predictions arising from models developed to describe fruit/frugivore interactions. The dispersal of the alien Acacia cyclops seeds by the indigenous Black Korhaan Eupodotis afra suggested that successful fruit/frugivore relationships are not necessarily the product of reciprocal evolution. The study on Chrysanthemoides monilifera found that efficient dispersal systems are not limited to plants producing small quantities of lipid-rich fruits and to dispersal by obligate frugivores. The abiotic dispersal of Quercus robur was found to be efficient in relation to vertebrate-dispersal. The study on Protasparagus aethiopicus found that the morphology of fleshy fruits may also reflect attempts to overcome the effects of non-dispersing seed predators. 1It is concluded that a gradient from a predictable to unpredictable fruit availability provides a better basis for studying fruit/frugivore interactions than the coevolutionary models. previously presented.
  • Thumbnail Image
    Item
    Open Access
    Aspects of the revegetation of mountain fynbos vegetation of the south western Cape, South Africa
    (1989) Romoff, Natalie; Moll, Eugene J
    The revegetation of severely, disturbed areas using indigenous vegetation forms the topic of this thesis. Mountain Fynbos was chosen for the study because of its importance as a unique vegetation-type worthy of conservation. Unfortunately, this vegetation faces long-term threats associated with escalating development pressures, which include the demand for improved infrastructures. These factors are discussed and a process is developed for using indigenous vegetation to revegetate severely disturbed areas. This use of indigenous vegetation represents a significant and innovative move away from the traditional use of commercially available grasses in South Africa. Fynbos is adapted to periodic droughts and nutrient poor soils and as such has practical advantages over artificial plant covers in terms of its low maintenance requirements for long term establishment. Theoretical perspectives of disturbance and succession are contrasted with the requirements for revegetation as observed in the field.
  • Thumbnail Image
    Item
    Open Access
    Commercial wildflower production in the fynbos biome and its role in the management of land-use
    (1990) Davis, George William; Moll, Eugene J
    The wildflower industry of the Cape, South Africa, utilizes ecosystems and vegetation of the Fynbos Biome either directly by harvesting of natural plant populations, or indirectly by land transformation for agro-horticultural production. This thesis reports on a study of conservation and management issues arising from: (a) direct veld-harvesting; and (b) primary annexation of land for controlled production of material. A review of the industry's structure and the controlling legislation, indicated a need for integration of current management strategies. A potential means of anticipating population degradation and local extinction of plant species through over-utilization was investigated by construction of a computer model. Lack of data describing the flow of material and revenue was highlighted as an impediment to resource management by means if modelling. Experimental work investigated the effects of marginal cultivation on mountain fynbos ecosystems as utilized by the industry. Work was conducted at a site in the Highlands Forest Reserve in the south-western Cape. This experimental system was cleared by burning, and tilled as if for commercial production. Disturbance effects on system parameters were monitored. These included energy and water regimes, aspects of community structure, plant growth, and water relations of the natural vegetation. Results showed that tillage altered the system during the dry summer months by increasing reflectivity of the soil surface to solar radiation, reducing soil temperatures, and increasing soil water content. Response of the vegetation included reduction of species richness and diversity, a reduction in projected foliar cover, and an increase in the productivity of some, but not all, of the naturally occurring dominant species. Two commercially favoured species of Protea were also introduced to the site. Survival and productivity of these populations were monitored as responses to substrate disturbance. Results showed that the treatment was significantly associated with better survival for P. cynaroides, but better productivity for P. repens. A concluding review suggests that there are general paradigmatic blocks between the economic and ecological facets of natural resource utilization which prevent implementation of optimal environmental management strategies. The wildflower industry is nominated as a small bridge for that gap.
  • Thumbnail Image
    Item
    Open Access
    A comparative study of the seed bank dynamics of two congeneric alien invasive species
    (1989) Holmes, P M; Moll, Eugene J
    The unique vegetation in the lowlands of the fynbos biome is threatened by alien Acacia encroachment. The seed bank dynamics of the two most widespread invaders in the region, Acacia saligma and A. cyclops, was studied to elucidate those factors contributing most to their invasive success. This information was then used to assist in developing optimal control methods. On the basis of information available prior to this study, it was predicted that both species would have large, persistent seed banks in the so.il, and that seed bank processes would provide the - key to invasive success: namely, high seed longevity and heat-stimulated germination. Seed banks were monitored for several years following clearing of the parent stand, using either sites sampled in an earlier study, or sites providing chronosequences of clearing dates. Concurrently, a demographic study of the species' seed banks, including processes from seed rain through to seedling emergence and survival, was done in dense Acacia stands and in fynbos vegetation. Acacia saligma seed banks conformed to predictions, being large and persistent owing to high percentage viability and water-impermeable dormancy. Seed banks accumulate rapidly under dense stands and are "disturbance-coupled" as they have potentially high longevity unless stimulated to germinate by fire. Although A. cyclops seed banks also may be large and long-lived, they display variable percentage viability and dormancy, with the majority of a seed cohort surviving less than a year. Acacia cyclops seed banks do not respond to heat treatment and appear to be "disturbance-uncoupled".
  • Thumbnail Image
    Item
    Open Access
    The dynamics of the Afromontane forest remnants in the Southwestern Cape
    (1990) Masson, Peta Helen; Moll, Eugene J
    This thesis identifies the major forest types present in the southwestern Cape and investigates the floristic and structural changes in vegetation composition across the indigenous forest ecotone. The dynamics of forest-fynbos boundaries of differing post-fire age are compared and patterns of vegetation change from forest to fynbos are related to environmental constraints and disturbance history. Riparian forest and Scree forest were identified, and differences in the structure a.nd composition of the two forest types and their ecotonal communities were evident at both the recently burnt site of Swartboskloof and the fire-protected catchment of Orange · Kloof. Soil moisture, soil depth and the amount of rock cover were. key factors influencing the dynamics of the forest-fynbos ecdtone, with fbrest composition and the consequent availability of seed also important. The analysis of post-fire regeneration strategies indicated that seedling production and coppice growth were best represented in the igirnediate post-fire condition, thus supporting the initial floristic composition (IFC) hypothesis. This implies that coppice production is an immediate, reactionary mode of regeneration following disturbance, and that most seedling establishment and subsequent growth of saplings occurs soon after the disturbance event. The absence of seedlings in scree fynbos areas at Orange Kloof suggests an episodic recruitment strategy which is influenced by local species composition and seed production.
  • Thumbnail Image
    Item
    Open Access
    Ecological aspects of the substrate and water relations of deciduous and evergreen plant forms in the western Karoo
    (1989) Midgley, Guy F; Moll, Eugene J; Rutherford, MC
    The principle aim of this work was to ascertain the relative importance of water and nutrient supply in determining the success of deciduous and evergreen plant forms on two main substrate types in the Worcester-Robertson valley, situated in the Succulent Karoo Biome. The substrate types selected for study represent soils of zoogenic soil mounds (locally termed "heuweltjies", and often referred to in the literature as "Mirna-like" mounds), and soils immediately adjacent to and surrounding the soil mounds. The distribution of deciduous and evergreen plant forms in the Worcester-Robertson valley was analys~d relative to the selected substrate types. Foliar elemental concentrations of four selected species growing on both substrates at five separate sites within the valley were determined. Also, the patterns of seasonal water stress exhibited by three deciduous and five evergreen non-succulent woody perennials growing in both substrates were investigated on high radiation (equator-facing) and low radiation (pole-facing) slopes at one intensive study site, the Worcester Veld Reserve.
  • Thumbnail Image
    Item
    Open Access
    Environmental and biogeographic influences on the distribution and composition of the southern Cape forests (Veld type 4)
    (1989) Geldenhuys, Coert Johannes; Moll, Eugene J
    This study aims at explaining the distribution and composition of the southern Cape forests, the largest forest complex in southern Africa. These are the only forests in southern Africa which are actively and scientifically managed for their products and values. Population growth due to forestry, agricultural and economic development and a growing tourism industry exerts increasing pressures on the natural environment of the southern Cape coast and therefore affect the dynamics and conservation of the forests. Conservation and sustained utilization of the forests require a sound knowledge of the composition, structure and dynamics of the forests. This study was aimed at an understanding of the biogeography of the forests at the landscape level in order to isolate those variables which contributed to the present distribution and composition of the forests. Determinants of the forest location pattern in the southern Cape were identified as rainfall above 500 mm, which determines the potential limits of the forests, and the bergwind fire pattern, which determines the actual forest distribution. Fires driven by the hot, dry, northwesterly, föhnlike bergwinds interacted with the terrain physiography since prehistorical times and the forests persisted in topographic shadow areas. The largest forests in the area therefore occur on the coastal platform at the foot of the mountains, in the river valleys and on the coastal scarp. Forests in the mountains, with high rainfall, are small and scattered. The results have shown that the bergwind driven fires control the distribution of forests which have important implications for the understanding of forest dynamics and for conservation management of forests in multiple-use management systems. Forest composition at the landscape level was studied by means of plant species lists. A species list for the southern Cape forests was annotated with information on the growth form, breeding system, propagule type, forest type, moisture tolerance, abundance and spread in the study area, and the distribution range in southern Africa, of each species. Analyses of the list showed that the species/family ratios for the southern Cape forest flora are very low, that woody plants have mostly fleshy propagules and herbaceous plants mostly dry propagules, and that several species have adaptations to adverse conditions. The species richness and composition, and floristic similarity and relationships were compared between the southern Cape forest flora and the floras of 13 other forests representing particular geographic regions in southern Africa. Forest size explained relatively little of the variation in species richness of the forests. Stepwise multiple regression analyses indicated that the number of dispersal corridors, the proximity to other forests and mean altitude explained most of the variation in number of woody species, whereas the number of landscape types and dispersal corridors explained most of the variation in number of herbaceous species. The high similarity between the southern Cape forest flora and those of the forests along the escarpment from the eastern Cape to northern Transvaal, and the southern attenuation of species suggest that the forests were once continuous. It is suggested that the Sundays river valley east of Port Elizabeth isolated the southern Cape forests from those to the east already during the Pliocene or earlier.
  • Thumbnail Image
    Item
    Open Access
    An evaluation of Landsat MSS data for ecological land classification and mapping in the Northern Cape
    (1989) Gubb, Andrew Alan; Moll, Eugene J; Liversidge, Richard
    This paper examines the issues that arise in the use of visual interpretation of Landsat data during the analysis, classification and mapping of the natural vegetation of the semi-arid Northern Cape. Initial research involved the classifying and mapping of the vegetation using conventional methods. A vegetation map, accompanying legend and descriptive key were produced. The problems encountered during this process, and the constraints of manpower, time and funds, stimulated the investigation of Landsat imagery as a means of improving the speed and accuracy of vegetation classification and mapping. A study area comprising one Landsat scene and which met certain requirements was selected: a) The area had already been surveyed and mapped at a scale of 1:250 000. b) As many vegetation units as possible were included. c) There was maximum diversity, complexity and variability in terms of soil, geology and terrain morphology. Initially a suitable mapping scale was selected, viz. 1:250 000, as it met the requirements of nature conservation authorities and agricultural planners. The scales of survey and remote sensing were based on this. The basic unit of survey was the 1:50 000 topographical map and satellite imagery at a scale of 1:250 000 was found to meet the requirements of reconnaissance level mapping. The usefulness of Landsat imagery was markedly affected by the quality of image production and enhancement. Optimum image production was vitally important and to this end, interaction between the user and the operations engineer at the Satellite Applications Centre, Hartebeeshoek was essential. All images used, were edge-enhanced and systematically corrected. While these procedures were costly, they proved to be fundamental to the success of the investigation. Precision geometric correction was not required for reconnaissance level investigation. The manual superimposition of the UTM grid, using ground control points from 1:250 000 topographical maps, proved to be accurate and convenient. Pattern recognition on single-band, panchromatic imagery was difficult. The scene lacked crispness and contrast, and it was evident that black and white imagery did not satisfy the objectives of the study. Three-band false colour composite imagery was superior to single-band imagery in terms of clarity and number of cover classes. The addition of colour undoubtedly facilitated visual interpretation. False colour composite imagery was investigated further to establish which year, season and possibly time of season would best suit the objectives of the investigation. It was found that the environmental parameters affecting reflectance are relatively stable over time and it was not necessary to acquire imagery of the same year as field surveys. However, the year of imagery should be chosen so that similar climatic conditions prevail. While, in certain instances, imagery captured during winter had advantages in separating complex mosaics, summer imagery was superior in most respects. Furthermore, given "normal" climatic conditions, the ideal period during which there was maximum contrast between and within ground classes, and thus spectral classes, was narrowed to mid-January to mid-April. Units which were acceptably heterogeneous (relatively homogeneous) in terms of reflectance levels were delineated manually on the image. This delineation was done at three levels of complexity and the units were compared with the vegetation map. A series of field trips aided the interpretation of the images, especially where discrepancies occurred between the map and the image. In general, there was a close degree of correspondence between the prepared vegetation map and the delineated image. Field investigation revealed the image units to be more accurate than those on the vegetation map, and the image served to highlight the inadequacies inherent in classifying and mapping vegetation of extensive areas with limited resources.
  • Thumbnail Image
    Item
    Open Access
    An evaluation of the importance of plant resources to rural communities - a case study of Heuningvlei in the Cederberg
    (1991) Reay, Nicky; Moll, Eugene J
    Within the framework of living resource conservation as advocated by the world Conservation Strategy, this case study investigates the utilitarian value of indigenous plant resources as a supplementary or "hidden" income for a rural community at Heuningvlei. The objectives of the study were to document the rapidly disappearing customary knowledge regarding the utilisation of plant resources, to gain an indication of whether a sustainable method of utilisation exists within the case study community, and to interpret the results in terms of conservation objectives.
  • Thumbnail Image
    Item
    Open Access
    The feasibility of using remote sensing and field-based checks to monitor the impact caused by collection of wood in the Eastern Cape/Ciskei forest and thicket formations
    (1989) Lane, Karl; Moll, Eugene J
    A variety of studies have shown the problems of energy supply faced by low-income communities in southern Africa. Most of these communities are dependent upon indigenous fuelwood supplies. In addition, many of these communities use indigenous wood for construction. This largely uncontrolled utilisation imposes severe threats on woody vegetation communities. The Eastern Cape/Ciskei region is an area where energy supply problems are particularly severe and impacts on woody vegetation correspondingly severe. This study aimed to investigate the feasibility of using remote sensing techniques to monitor the the impact caused by collection of wood in the Eastern Cape/Ciskei forest and thicket communities. A variety of remote sensing techniques for landcover analysis were investigated. In all cases, visual interpretation was used because it is considerably cheaper and demands less technical expertise than would computer processing. In addition, many studies have shown visual interpretation to be superior. Maps were drawn from multitemporal aerial photograph sequences and from Landsat and SPOT satellite images. These maps showed that there has been relatively little change in area of woody vegetation in the study area since 1956. However, field studies showed that vegetation community structure had been degraded as a result of intense and sustained human impact. This qualitative decline also reflected a decline in usefulness of the woody vegetation of the area to local communities. This substantial degradation was not visible on any of the remote sensing imageries. This emphasises that field-based checks to monitor human impacts on forest and thicket formations are essential. Strategies for reducing the dependence of low-income communities on indigenous vegetation for energy supplies and constructional timber have been reviewed from the literature and these are descibed in Appendix 1. Most successful strategies in other parts of the world have been the result of a national commitment to tree planting, recognition of a multiplicity of constraints and the voluntary involvement of the communities the strategies are intended to assist.
  • Thumbnail Image
    Item
    Open Access
    Investigation into the plant ecology of the Karstland area in Namibia : with particular reference to the proposed large-scale abstraction of groundwater
    (1992) Chivell, Eleanor Heather; Moll, Eugene J; Bond, William J
    The planned large-scale abstraction of groundwater from the Karst area in northern Namibia prompted concern with respect to possible negative effects on the plant ecology of that area. Although it was thought improbable that the lowering of the groundwater table would result in the deterioration of the vegetation, it was considered necessary to examine the existing vegetation status in order to establish a pre-abstraction baseline datum. It was thus important to establish a broad overview of the current vegetation, any changes in its condition within a two years period, and also the prevailing environmental factors in the Karst area. This was achieved through both manual and photographic monitoring of selected representative transects within the proposed abstraction area during 1986 and 1987. The manual monitoring exercise included the usual measures of density cover and frequency of all species, whereby a full inventory of the transects was established. The environmental conditions were assessed through the collection and evaluation of data on rainfall, groundwater levels and soil conditions, both within the transects and for the area as a whole. Below average rainfall during and prior to the baseline study years, resulting in poor recharge to the groundwater table, was recorded for most of the karst area. Both the vegetation and environmental data were utilized in two ways. Firstly, the 1986 and 1987 vegetation data were analysed, and those aspects indirectly related to the vegetation's vitality status, were then evaluated. A comparison of the parameters such as the quantity of dead material, and the number of standing dead trees, reflected a general decline in vitality over the two year period. In view of the poor rainfall conditions, this decline was interpreted as that which can be expected under natural adverse climatic conditions. Secondly, in order to establish and critically examine the possible relationships between the vegetation data and components of the environmental data, a Canonical Correspondence Analysis was performed. Despite a large amount of "noise" caused by the broad nature of the environmental data, it was possible to identify a number of species which occur within precisely defined environmental conditions. A change in abundance or distribution of these species can in the future first be investigated in terms of their defined vegetation-habitat relationships, and thereafter in terms of any other introduced factors which may be suspected of having an influence. Infra-red aerial photography was another monitoring technique used to obtain a pre-abstraction record of the vitality status of the vegetation. Two surveys were carried out during the baseline period and counts made of stressed and dead trees. A comparison of the counts reflected an increase in stress within the vegetation over this period, thus supporting the findings of the manual surveys. Selected sections of vegetation at various points of interest within the transects, were monitored using fixed point photography on a bi-annual basis. Although these photographic records ret1ected small changes, these were not considered significant. The main purpose of this method is to provide a pre-abstraction record of vegetation at potentially "sensitive" points with which future surveys .could be compared. The usefulness and cost-effectiveness of the three central monitoring methods were evaluated, and an indication provided of how monitoring may continue in the long term as large-scale abstraction goes ahead.
  • Thumbnail Image
    Item
    Open Access
    A preliminary study of the vegetation of Piketberg mountain, Cape Province
    (1976) Linder, Hans Peter; Moll, Eugene J
    A vegetation survey of the Piketberg has been undertaken. with the aim of laying the basis for a more detailed survey. The mountain ranges from 300 m to 1500 m and lies near the north-western edge of the Cape Fynbos. The vegetation was classified using the phytosociological methods of the Zurich- Montpellier school. Vegetation forms were described with particular attention to the vegetation continua within the groups. Extensive data were collected on climatic and edaphic factors, and these were correlated to the vegetation forms and continua. This, it is hoped, will create the frame- work for the study of the ecological and evolutionary dynamics of the system. A check-list was compiled, and the flora analysed and compared to other known floras.
  • Thumbnail Image
    Item
    Open Access
    Seed biology of a recently introduced species, Myoporum laetum in comparison to a successful invasive alien, Acacia cyclops, in the southwestern Cape, South Africa
    (1988) Richards, Michael Bruce; Knight, Richard Spencer; Moll, Eugene J
    The invasive potential of Myoporum laetum, a tree recently introduced into the southwestern Cape, South Africa, was evaluated, by comparing various aspects of its seed biology with those of another bird-dispersed alien, Acacia cyclops which is a successful invader in this region. M. laetum has higher annual seed production, but lower soil-stored seed banks than A. cyclops. Both experience high seed predation, especially under parent canopies. M. laetum has a more persistant seed store and is able to germinate and establish in shade. Germination of untreated A. cyclops seeds was 23.3% and this increased to 47.4% after mild heat treatment. Untreated M. laetum seeds were completely dormant, but 3.3% germinated after acid treatment. The high seed production, bird dispersal, persistant seed banks and ability to establish in shade, suggest that M. laetum could become invasive in thickets, such as existing acacia stands.
  • Thumbnail Image
    Item
    Open Access
    Some effects of fire frequency on fynbos at Jonkershoek, Stellenbosch, South Africa
    (1980) Van Wilgen, Brian William; Moll, Eugene J
    A short literature review on fynbos ecology, with special reference to fire, is presented as an introduction to the thesis. Three post-fire ages of fynbos were studied at the Jonkershoek Forest Reserve, with the aim of determining the effects of fire frequency on the vegetation. The three frequencies investigated were short (about six year) rotation burning, normal rotation burning (about 15 to 20 years) and protection from fire for 37 years. Aerial plant biomass was determined for the three post-fire ages of vegetation. Total (live plus dead) biomass amounted to 6,5 tonnes ha⁻¹ for four year old vegetation, 50 tonnes ha⁻¹ for 21 year old vegetation 75 tonnes ha⁻¹ for 37 year old vegetation. Live biomass apparently increases to an age of roughly 30 years, whereafter it declines, whereas the total mass of dead plus live material showed an increase right up to 37 years of age.
  • Thumbnail Image
    Item
    Open Access
    A study of certain ecological aspects pertaining to a Leucadendron laureolum community at the Silver Mine Nature Reserve, South Africa
    (1981) Kathan, Louis; Moll, Eugene J
    This survey was conducted in three phases, viz. 1. The Braun-Blanquet phytosociological technique was used to describe the vegetation of the study area and adjacent areas. Two major communities, based on plant community structure environmental factors and floristics, are recognised. 2. A determination of phytomass was obtained from five sites in the study area by means of clip-plots from a plant community of post-fire ages of about twenty years, ten years and one year. In this study three structural elements of the fynbos were distinguished viz. proteoid, restioid and "remainder". It was established that the average growth rate for the approximately 20 year old proteoid community was 656 kg/ha/yr and for the ten year old community it was 309,2 kg/ha/yr. The marked difference in growth rate of the proteoid element is due to a slow growth rate until the community is some ten years old and thereafter there is a rapid increase in growth. The restioid component tended to show a decrease in phytomass with increasing age viz. 225, 123,4 and 207,3 kg/ha for one year, ten and approximately twenty year post-fire ages. For th e "remainder" it was found that this also decreased with increasing age viz. 380, 54,5 and 25,5 kg/ha for one year, ten and approximately twenty year post fire ages. 3. The effect of the June fire on the bush-cut vegetation of the study area in the Silver Mine Nature Reserve is discussed. The regeneration of plant species was monitored for twelve months in five randomly selected, permanently marked plots. Field observation revealed that 65,1% of the species regenerated from underground organs, such as rhizomes and corms, and the remaining 34,9% of the plant species regenerated from seed. Based on the phytomass study and rate of regeneration of the plant species in the area it appears that an approximate 15 year fire interval is the most acceptable. Bibliography: pages 104-119.
  • Thumbnail Image
    Item
    Open Access
    A study of the interactions between C₃ and C₄ grasses on Signal Hill, Cape Town
    (1990) Ligavha, Maanda Solomon; Bond, William J; Moll, Eugene J
    Current concerns with reference to global climate change can help us to focus on the competitive interaction of grasses with different photosynthetic pathways. The dominance of eight different common grass species occurring on Signal Hill was investigated, and three species which occurred in localized dense stands were suitable for detailed investigation. Distribution patterns of the three selected grass species, Hyparrhenia hirta (L.) Stapf (C₄), Merxmuellera disticha (Nees) Conert (C₃) and Themeda triandra Forsskal (C₄) were interpreted using a dispersion index (R). Regularity in dispersion of individual grasses was quite common, whilst aggregated and random dispersion was not. Potential competitive interactions between those grasses (perennial) on the east- and west-facing slopes of Signal Hill ·were then described. Using nearest-neighbour analysis it was possible to show that both inter- and intra-specific competition was occurring between the grass species investigated. Pattern analysis was supported by removal experiments and it was possible to infer that the three grass species are competing for water and space. The measurements of carbon dioxide fixation rates under greenhouse conditions demonstrated that C₄ grasses were more competitive, relative to C₃ grass and responded more strongly to changes in soil moisture status. Species with the C₄ pathway showed substantial increase in photosynthetic rate in response to an increase in soil moisture content whilst a C₃ grass' carbon dioxide assimilation rate at those moisture content was relatively lower. Seedling transplant experiments showed that monospecificity of patches could chiefly be attributed to familial clumping, limited seed dispersal, and vegetative reproduction. Phenological aspects like growth, production, and reproduction in terms of flowering tillers of neighboured and non-neighboured individuals, and of individuals one year and two years after fire, were studied to assess the importance of competitive interactions and fire. The results of this study posed the following question: In the light of the global warming effect, which grass species (representing C₃ and C₄ pathways) are likely to prevail in different parts of the world?