OpenUCT :: Browsing by Author "Cowling, Richard M"

Browsing by Author "Cowling, Richard M"

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Current patterns of habitat transformation and future threats to biodiversity in terrestrial ecosystems of the Cape Floristic Region, South Africa
(2003) Rouget, Mathieu; Richardson, David M; Cowling, Richard M; Lloyd, J Wendy; Lombard, Amanda T
The formulation of an effective strategic plan for biodiversity conservation in the Cape Floristic Region (CFR) requires an assessment of the current situation with regard to habitat transformation, and an explicit framework for predicting the likelihood of remaining habitat (i.e. that potentially available for conservation) being transformed. This paper presents the results of a detailed assessment of the current and future extent of three important factors that threaten biodiversity in the CFR: cultivation for intensive agriculture (including commercial forestry plantations), urbanisation, and stands of invasive (self-sown) alien trees and shrubs. The extent of habitat transformation was mapped at the scale of 1:250,000, using primarily satellite imagery. We compared models derived from a rule-based approach relying on expert knowledge and a regression-tree technique to identify other areas likely to be affected by these factors in future. Cultivation for agriculture has transformed 25.9% of the CFR and dense stands of woody alien plants and urban areas each cover 1.6%. Both models predict that at least 30% of the currently remaining natural vegetation could be transformed within 20 years. There was an overall accuracy of 73% between both models although significant differences were found for some habitat types. Spatial predictions of future agriculture threats derived from the rule-based approach were overestimated relative to the statistical approach, whereas future alien spread was underestimated. Threat assessment was used to derive conservation targets for subsequent stages of conservation planning for the CFR. The importance of integrating vulnerability knowledge into conservation planning is discussed. The choice of vulnerability analysis (future habitat degradation and/or impact on biological entities) and methods will depend on the complexity of the threatening processes and the availability of spatial data.
Open Access
Determinants of pattern in fynbos vegetation: physical site factors, disturbance regime, species attributes and temporal change
(1998) Privett, Sean David John; Cowling, Richard M
This study set out to explore the patterns and determinants of contemporary species distribution in a fynbos landscape based on information on 1) physical habitat characteristics, 2) past disturbance regime, 3) intrinsic properties of individual species and 4) temporal change in communities. The body of the thesis is divided into four parts covering each of these aspects individually. Each chapter has been written up as an individual paper and thus includes some repetition as well as cross-referencing. Each chapter includes a detailed rationale for the study in the introduction, as well as methods, results and a discussion of the findings. Chapter 2 describes the patterns of vegetation units in the Cape of Good Hope Nature Reserve and provides a quantitative assessment of the importance of physical site features as determinants of these units. These results are compared with the vegetation classifications of the area derived in earlier studies by Taylor (1984b) and Cowling et al. (1996a). Chapter 3 is the first study in fynbos to partition the variance in vegetation pattern into that explained by physical site factors and that explained by the recent disturbance regime. The study explores the role of 30 years of fire and alien plant infestations in influencing species distribution at the community and landscape scale. While a number of studies have explored spatial determinants of diversity and pattern in fynbos, temporal change within communities has been neglected. High levels of species turnover through time, as a result of colonisation and extinction, could be an important component of diversity at the landscape scale. Hence Chapters 4 and 5 both explore aspects of temporal dynamics in fynbos. The objectives of Chapter 4 are to determine the stability of populations at the landscape scale over a 30-year period and to establish the determinants of local extinction of species. Information on the stability of species over time and the attributes which enable species to persist or go extinct are important for understanding potential impacts of management practices as well as the importance of temporal dynamics in influencing spatial patterns. This is especially appropriate in the context of the results of Chapter 3, which suggest that a high proportion of the variance in species composition is unexplained despite the inclusion of physical factors, and past disturbance regime. The fifth chapter provides a descriptive account of the change in vegetation composition over a 30-year period. It is recommended that those readers not familiar with the fynbos system read it as it provides an overview of a variety of aspects of fynbos dynamics. Its objective is to show how the various components of the disturbance regime, as well as fluctuations in abundance of overstorey Proteaceae and their resultant competitive effects can influence community composition. The final chapter is a general discussion that summarises the major findings of the study.
Open Access
An ecological and conservation planning study of the plant biodiversity on natural and semi-natural remnants on the Cape Flats, South Africa
(2002) Golding, Janice S; Cowling, Richard M
The Cape Flats (Western Cape Province, South Africa) is situated on the low-lying sandy plain immediately adjacent to the Cape Peninsula, and is part of the mediterranean-climate Cape Floristic Region. Fire-dependant Sand Plain Fynbos, Strandveld and West Coast Renosterveld exist on natural and semi-natural remnants interpersed in a hostile landscape. The Cape Flats, its botanical attributes and the threatening processes that prevail in its densely populated urban matrix are introduced. Broad overviews of aspects of the biophysical environment, the flora, land transformation, the socio-political and institutional environment, and conservation initiatives are presented. This chapter provides a framework for the general approach and the methodologies used in the studies contained in this thesis.
Open Access
The ecology of invasions by Pinus (pinaceae) and Hakea (proteaceae) species, with special emphasis on patterns, processes and consequences of invasion in mountain fynbos of the southwestern Cape Province, South Africa
(1989) Richardson, David Mark; Cowling, Richard M
The fire-prone mountain fynbos of the southwestern Cape Province of South Africa has been severely invaded by introduced trees and shrubs. These invasions have transformed fynbos shrublands to dense thickets of trees and shrubs in many parts of the region, thus disrupting various natural ecosystem processes. The ecology of invasions by species of Pinus and Hakea (the most successful genera) was studied using a series of natural experiments in conjunction with autecological studies. The study was divided into main four parts: (i) case studies to elucidate major patterns and processes of invasion; (ii) studies of the life history and population ecology of selected invaders; (iii) studies of the determinants of invasibility; and (iv) assessments of the consequences of invasion and of control programmes. Bibliography: pages 235-272.
Open Access
The effects of fragmentation of South Coast Renosterveld on vegetation patterns and processe
(1997) Kemper, Jessica; Cowling, Richard M; Richardson, David Mark
This thesis investigates the effects of fragmentation on vegetation patterns and processes of South Coast Renosterveld at three hierarchical levels. South Coast Renosterveld is a grassy shrubland derived from shales on the coastal forelands of the Western Cape Province, South Africa. The area forms part of the Cape Floristic Region. It occurs on fine-grained, moderately fertile soils. Thus, most South Coast Renosterveld has been replaced by agriculture. This vegetation type is particularly rich in geophytes, many of which have highly localised distributions. Almost no research has been carried out on the composition and structure of South Coast Renosterveld. However, fragmentation theory suggests that the fragmentation process iof South Coast Renosterveld would cause a loss of biodiversity. Although South Coast Renosterveld is one of the most threatened vegetation types in South Africa, only 0.8% of its area is formally conserved.
Open Access
Evolution and diversification in the Cape flora
(1978) Cowling, Richard M
Open Access
The general continuum model for structured populations, with two case studies in plant ecology
(1994) Laurie, Henri De Guise; Reddy, B Daya; Cowling, Richard M
The broad aim of this thesis is to investigate the formulation and usefulness of a very general model for plant population dynamics. In chapter 1, the goal of generality is discussed, particularly in the light of the lack of interaction between field and experimental population studies on the one hand and theoretical population dynamics on the other hand. A distinction is ma.de between descriptive and axiomatic theories, and it is suggested that they serve different purposes. The advantages of a. rigorous framework are pointed out and the basic elements of the continuum approach are introduced. In chapter 2, the model is proposed, the existence and uniqueness of solutions to its equations is proved, and an algorithm for numerically -approximating transient solutions is discussed. The question of generality is addressed in two places, and it is argued that the basic framework presented here is in principle adequate to model the processes of plant population dynamics in full detail, though the existence proof cannot to accommodate all possible models. In particular, models with time lags are excluded. Further limitations of the existence proof ill terms of constitutive relations are pointed out. In consequence, the theory here presented does not fully exploit the possibilities for generality inherent in the basic equations. In chapter 3, the question of what data would allow identification of factors determining somatic growth and mortality is investigated computationally. It is shown that using only the average size is insufficient. A class of models which includes all possible combinations of three types of size dependence in somatic growth and mortality is formulated. Qualitative parameter estimation for the various models yields size distributions that can be classified into the following biologically meaningful groups: group (i) has no models that use dependence on relative size; group (ii) has all the models in which somatic growth depends on relative size group (iii) has the models where only mortality depends on relative size. Thus it appears that size distribution may be used to distinguish various forms of size dependence in somatic growth and mortality. In chapter 4, a lottery model criterion for coexistence of plants with disjoint generations is developed, which is shown to require relative density dependence. Computer simulations aiming to initiate the use of exploratory calculations in studies of coexisting serotinous proteoids in fynbos indicate that the aspect of plant population dynamics most sensitive to density dependence is seed production, then somatic growth, while mortality is least sensitive to density dependence.
Open Access
Host specificity in the Rhizobium symbioses of two Aspalathus species and an invasive alien legume, Acacia saligna
(1988) Richards, Michael Bruce; Deignan, M T; Cowling, Richard M
The symbiotic specificity of Aspalathus capensis and A. carnosa in relation to their geographical distribution, was investigated by growing plants in soil and in tubes containing soil solutions plus nitrogen-free nutrient solutions. Soila were collected from three sites within their distribution and two from 90km outside. Both species formed nodules in all three soils from within their distribution and A. capensis in one from outside. A. carnosa did not survive in tube culture. The possible role of hostspecificity in the distribution of A. capensis and A. carnosa is discussed. A widespread invasive alien legume, Acacia saligna . was grown in the same soils and soil solutions. It formed nodules only in the three soils from within the distribution of Aspalathus capensis. The degree of nodulation varied between these soils. The possible importance of host-strain specificity in the invasive ability of alien legumes is discussed.
Open Access
An investigation of land-use practices on the Agulhas Plain (South Africa), with emphasis on socio-economic and conservation issues
(1999) Heydenrych, Barry John; Cowling, Richard M; Turpie, Jane
An investigation of land-use practices was undertaken on the Agulhas Plain, a species-rich area at the southern tip of Africa. Data were collected from landowners and visitors using questionnaire surveys. Further information was obtained by means of a literature search and interviews with key informants. A historical background of land use in the area is given. Although the area has been utilized since the Earlier Stone Age (>200000 years BP), the most dramatic changes to the landscape have occurred post 1850, with the large transformation of indigenous veld into cultivated lands. Four categories of farms were identified: livestock farms, fynbos farms, mixed farms and conservation farms. Livestock farms covered the largest surface area. Cereal crops cultivated on these farms provided a net income of R 918 OOO/y. Grazing provided a net income of R 7.3 million/yon cultivated land and R 2.3 million/y was attributed to indigenous veld. This latter figure highlights the importance of natural veld for grazing, but for certain vegetation types, stocking rates were above the recommended norms. Fynbos flower farms had the second largest surface area of the four categories of farms. Fynbos wildflowers were found to be the largest single agricultural sector on the Agulhas Plain, yielding an estimated net income of R 8.55 million/y. Most harvesting from the wild takes place from Acid Sand Fynbos, which is relatively common, and there appears to be potential for wildflower harvesting to be compatible with biodiversity conservation, if managed correctly. Cultivated fynbos flowers yielded a net income of R 1.5 million/y. Cultivation of land for fynbos flowers is on the increase, and pristine fynbos is primarily being targeted for this practice, thereby threatening the biodiversity of these areas. Many landowners are involved with mixed farming practices and there are a small number of conservation farms, generally situated at the coast, which rely on outside funding for their management.
Open Access
Life history and reproductive ecology of selected proteaceae in the mountain Fynbos Vegetation of the South-Western Cape
(1999) Le Maitre, David; Cowling, Richard M; Bond, William J
The studies in this thesis recognise the key role of fire as a factor which has shaped the life-histories of plants in fire-prone Mediterranean shrublands. Fire regimes are not simply products of the abiotic elements of climate and ignition sources. The biotic component makes a significant contribution because community structure and processes like litter fall determine fuel loads, and fuel distribution, and will determine properties such as fire recurrence intervals and shapes and patchiness of fires. Another key factor in the evolution of the traits of fynbos plants is plant-animal interactions involving seed and seedling predators or pathogens and herbivory. Because fires have a significant random component (for example in the timing of ignition, the position of the ignition point in the landscape and in relation to the wind movements and post- and pre-fire rainfall patterns), each fire is a unique event. These random factors are overlaid on the probability distributions of the other, more predictable factors. For example both fire recurrence intervals and the seasonal fire frequencies follow predictable patterns and therefore provide a basis for natural selection. Life-history theory links the evolutionary perspective - why organisms have evolved to be the way they are - and the ecological perspective - how traits function in the current environment. The primary selective pressures in the fynbos environment are nutrient-poor soils, winter rainfall and summer drought, recurrent fires and biotic interactions. The study can be divided into four sections: (1) patterns in reproductive maturation and mortality, (2) seed bank dynamics and pre-dispersal predation by insects, (3) seed germination and seedling mortality, and (4) an analysis of the relationship between plant life-histories and fire frequency distributions. In the first study, mortality rates of Pro tea neriifolia, P. lacticolor and Leucadendrofl xanthoconus varied from 13 to 40% from the age of 1-10 years. Mortality rates from 20-30 years of age were similar in all species and significantly higher than for younger plants, providing some support for the idea that these species undergo senescence. The removal of up to 90% of the inflorescences of Pro tea lacticolor and P. nerizJolia by baboons or rodents reduced seed banks of the proteas but not LeucadendrOll xanthoconus. Seed banks at the age of 10 years, in terms of seeds per shrub were adequate for population replacement except for P. lacticolor. The studies in the second part found that the dynamics of the seed banks of Protea neriifolia and P. repens differ markedly. The number of full seeds (with a firm white embryo) declines with age in both species. Protea repens had many full seeds per inflorescence in the youngest age class, but few full seeds in older inflorescences because of seed predation by insects. Protea neriifolia had few full seeds per infloreseence but there was a slow rate of decline in the number of seeds per inflorescence. Although the number of seeds per shrub of both species declined with increasing stand density, the number of seeds per square metre increased, more than compensating for the decline in unit output. Inflorescences of P. repens experience higher levels of seed predation by insects than those of P. neriifolia. Insect infestation levels increased rapidly with increasing age in P. neriifolia but were lower in mature plants than in the co-occurring P. repens. Low and unpredictable seed set may limit the effects of seed-eating insects on the seed yield of P. neriifolia when compared with co-occurring P. repens. The third section examined the germination of planted seeds in a 28-year old shrub land. Germination and establishment before a fire in March 1987 was similar to that after the fire but seedling mortality was higher before the fire. Seedling mortality during the first summer after the fire (October to March) was significantly correlated with planting date, in contrast to the findings of a similar study in the southern Cape. Simulations using a simple empirical model based on indexes of the daily soil moisture balance and temperature showed that a reduction of 10 or 20% in daily rainfall will have little impact on the germination of seeds released in late-summer or autumn in the western Cape, because of the long wet winter period. An increase in daily temperatures could have a more significant impact as it may reduce the length of the favourable period for germination. The final study compared the life-history traits in seeders and a sprouter. Many studies have identified distinct patterns in the demography and resource alIocation patterns of seed-regenerating and sprouting plants which are analogous to the patterns predicted for semelparous and iteroparous species by life-history theory. But there are several ways in which the demography of plants in fire¬ prone environments violates the assumptions of classical life-history theory. A new approach has been developed which explicitly accommodates these deviations and provides models which predict direct relationships between the probability distribution of fires (in time) and the reproductive maturation, mortality rates and lifespans of seeders and sprouters. A test of these models using data on fire frequencies and the demography of a seed regenerating and a sprouting species of Protea shows that they appear to apply to fynbos as well. This opens the door to the development of quantitative models that can provide a consistent theoretical framework for predicting and interpreting the relationships between fire regimes and life-history traits. It also supports arguments that regeneration exclusively from seeds and by sprouting (and from seeds), and the related suites of traits, are expressions of distinct and divergent life history strategies. Why is it important to understand life-history strategies? Life-history theory is about how organisms maximise their evolutionary fitness and thus is about organisms allocate their limited resources to survival and reproduction to maximise reproductive success. The theory also provides a link between understanding what an organism is doing and when as is typically documented in demographic studies - and why it is doing that - which gives a deeper level of insight. There have been numerous studies and reviews of life-history theory which have covered a wide variety organisms, but somehow most of these studies have been based, explicitly or implicitly, on the highly simplified r-K selection models. The studies in Chapter 6 were based on an alternative model which offers new insights into the life-histories of plants in fire prone environments. The current approach to managing fynbos (e.g. how often to burn) is based on observations of plant maturation and recruitment success which are used to determine the desired intervals between fires. Studies of fire¬ frequencies also have shown that fire intervals follow a definite distribution in time. The intervals determined by these two different approaches are about the same but there has been no direct link. The new life-history based approach makes that link explicit and direct and gives us insights into why there should be a link and what the implications are. For example, what is the likely reproductive success over a range of fire frequencies. The approach still needs further development but it definitely merits further studies.
Open Access
Light microsite requirements of seedlings of some Afromontane forest tree species: the role of canopy gaps promoting regeneration
(1989) Van Coller, Alan; Cowling, Richard M
Predictions of microsite requirements for seven common Afromontane forest tree species were made by testing above ground relative growth rate (RGR) and photosynthetic response of seedlings of the respective species under different light intensities. Virgilia oroboides and Halleria lucida, with either a very high photosynthetic rate or RGR, were regarded to be pioneer species. Podocarpus latifolius was regarded to be a deep shaded species due to its low photosynthetic and RGR's. Rapanea melanophloeos, Ilex mitis, Olea capensis sub Ssp. macrocarpa and Kiggelaria africana either had moderately high RGR or photosynthetic rate and were regarded to be light shaded species. Predictions were tested in Grootvadersbosch (34ᵒ05's,20ᵒ50'E) forest, where frequency of seedlings beneath the canopy and under a canopy gap were recorded and tested using a x²-goodness of fit test, against the null hypothesis that there are equal frequencies of seedlings beneath the canopy and canopy gaps. Results confirmed predictions made for latifolius, O. capensis sub sp. macrocarpa, and R. melanophloeos. Low seedling frequencies for the other species, either due to a restricted distribution of adult trees (e.g. V. oroboides) or high levels of herbivore attack, made it difficult to test predictions. Significantly higher frequencies of seedlings of P. latifolius and O. capensis sub sp. macrocarpa beneath the canopy than in the gap of dry forest suggest that gaps in drier forests are stressful sites for regeneration. This led to the hypothesis of expecting a greater dominance of shade tolerant species in the canopy of dry forests than in moist forests. McKenzie's (1978) findings support this hypothesis. It was concluded that Afromontane forests are largely made up of deep or light shaded tree species, with pioneer species confined to forest margins. The role of canopy gaps can be seen to play a minor role promoting regeneration.
Open Access
Livestock impact assessment and restoration strategies in the semi-arid Karoo
(1999) Beukes, Petrus Cornelius; Cowling, Richard M
Karoo rangelands exhibit spatial and temporal patterns that have important implications for the livestock industry. Spatially, there are gradients, often abrupt, in ecosystem structure and functioning, while plant composition and productivity are highly variable over time. A predictive understanding of these patterns, and the processes that cause them, is a prerequisite for developing appropriate restoration strategies. This thesis comprises several studies that attempt to relate vegetation patterns and processes to restoration strategies in southern Africa's Succulent- and Nama karoo ecosystems. One hypothesis is that small-scale changes in soil physical and chemical properties are responsible for the fine-scale patterning evident in winter-rainfall Succulent karoo ecosystems. Alternatively, these patterns could be the result of area-selective grazing by livestock. To evaluate these hypotheses, plant and soil data were collected along soil- and grazing gradients radiating from a watering point in a Succulent karoo landscape. Results indicated that properties inﬂuencing soil hydrology and nutrient status are important determinants of pattern, and that long-term area-selective grazing can permanently change some of these properties. The hypothesis that the stasis of severely degraded patches in this biosphere is a consequence of poor water inﬁltration and seed limitation was tested in a restoration experiment. It appeared that natural seed availability is not limiting, but water inﬁltration has to be improved to initiate the restoration process. Removal of shrub material in long-ungrazed and moribund areas on the outer perimeter of the biosphere, had a positive impact in releasing resources for more seedlings and young growth, but did not alter plant species richness. Stocking rate, composition and management of livestock profoundly inﬂuence the dynamics and composition of summer-rainfall Nama karoo vegetation. Proponents of non-selective grazing (NSG) argue that the periodic concentration in high densities of livestock in small areas, followed by long resting periods, improves vegetation composition as a consequence of low grazing selectivity, and enhances vegetation productivity and soil ecosystem processes as a result of intense hoof-action, dunging and urination impacts. Despite its application in farming systems, no studies have yet tested the predictions of NSG. I evaluated the effects of NSG on the soils and vegetation of Nama karoo rangeland in a fully replicated experiment. NSG did not alter the fertile-patch matrix, but improved soil infiltration. Plant compositional and cover changes could not be related to NSG. Rainfall was a much stronger driving force. I also explored the economics of NSG at the farm scale under different rainfall and stocking scenarios. An ecological-economic model predicted that NSG would be a viable option in higher rainfall (>200mm) areas because of the forage buffering capacity which enables the manager to maintain livestock through unpredictable droughts. Restoration strategies for the Succulent Karoo have to focus on the resource-retention capacity of the soils. Livestock can reduce this capacity; low-stocking, ﬂexible farming systems are therefore recommended for these more fragile ecosystems. Livestock in the more resilient Nama Karoo can be managed in a NSG system that can lead to an improvement in ecosystem functioning and maintain productivity in times of drought.
Open Access
Modelling the current and potential distribution of woody plants, with special emphasis on the importance of spatial scale and environmental factors
(2002) Rouget, Mathieu; Richardson, Dave; Cowling, Richard M; Lavorel, Sandra; Milton, Suzanne Jane
The relationship between species distribution and environment has always been a central issue in ecology. The primary aim of this thesis is to explore the role of abiotic and biotic factors in mediating the distribution of woody plants, particularly invasive alien species. Predictions of the future distribution of invasive species are required for management, conservation actions, and legislation. Using predictive geographical modelling, this thesis assesses the role of spatial scale in understanding the determinants of species distribution, modelling invasion spread, and taking conservation decisions. The species distribution databases were collated in a Geographic Information System from various sources (from field mapping to remote-sensing data), and at various spatial scales (from local to sub-continental). Classification and regression trees, a ﬂexible non-parametric statistical technique, were developed for each case study. I show that static modelling approaches, such as classification trees, are appropriate for modelling species distribution at regional to sub-continental scales. More mechanistic approaches, which include biological attributes, are required for accurate modelling of species abundance at local scale. A hierarchy of environmental factors was observed. Abiotic factors such as climate were more important for modelling species distribution at broad scales, whereas biotic factors were the fine-scale drivers of species distribution and abundance. This highlights the scale- dependence of prediction accuracy and of environmental drivers. Predictive habitat modelling was also applied to modelling future land use changes (including invasive alien species) in the context of conservation planning for the Cape Floristic Region. Effective conservation planning requires a detailed assessment of current land use patterns and future land use scenarios. Conservation planning is generally derived at regional scale but implementation takes place at finer scales. I investigated the transition from broad-scale planning to fine-scale implementation. This work emphasises the importance of diverse and fragmented habitats in measuring conservation value. This thesis concludes by linking predictive habitat modelling, species determinants, and application types to the spatial scale analysed.
Open Access
Neglected pollinator syndromes in seasonally inundated Renosterveld
(1996) Goldberg, Karen; Picker, Michael D; Cowling, Richard M
A range of fairly common plants were investigated in Darling in the Western Cape, to determine their pollinator syndromes, and to evaluate the relative importance of monkey beetles (Scarabaeidae: Rutelinae: Hopliini) and relatively short-tongued horseflies (Tabanidae) in their pollination. Detailed observations showed that all the plants investigated are visited by more than one insect species. Visitation rates and pollen loads of all insects found on the plants were used to assess their pollination efficiency. For all plants investigated, only a subset of the visitor-suite was found to contribute to the plant's reproductive success. Geissorhiza radians (Thunb.) Goldblatt and Wachendorfia paniculata L. seem to have specialized pollinator systems, both relying on tabanids for their pollination, while Heliophila coronipifolia, L. Monsonia speciosa, L.f. Ornothogalum thyrsoides, Jacq. Romulea hirsuta (Klatt) Baker and Ursinia anthemoides (L.) Poir. appear to have more generalized pollinator syndromes. Monkey beetles were the predominant and generally the most efficient pollinators for all these species. It is therefore concluded that these two insect groups are important pollinators of the plants investigated and probably play a part in the pollination of several other plants in the community. An evaluation of the larval requirements of pollinators revealed that although some species show clear patterns in terms of what types of soil conditions they prefer, successful emergence of insect species is generally not limited by a shortage of suitable habitats. Environmental variability may therefore play the largest role in determining the emergence and abundance of pollinators. This has implications for plants reliant on insects for their pollination, especially for species with specialized pollinator syndromes. Fluctuations in the environment may be a partial explanation for the prevalence of the generalized pollination syndromes observed.
Open Access
Phytogeography, endemism and diversity of the fynbos of the southern Langeberg
(1995) McDonald, David Jury; Cowling, Richard M; Boucher, Charles
The thesis presents a multi-faceted investigation of aspects of phytogeography, endemism and species diversity in the rich fynbos flora of the southern Lange berg, Cape, South Africa. The basis was a survey of the fynbos vegetation of the southern Langeberg carried out following the Braun-Blanquet or Zurich-Montpellier approach. Forty-six plant communities were described which were ultimately synthesized into 14 'community groups'. The core of the study consisted of three parts: (I) A multivariate analysis of vegetationenvironment relationships where questions concerning the distribution of fynbos communities and environmental controls were addressed. It was found that mean annual precipitation was the most important abiotic variable, apart from fir determining distribution of fynbos communities. A model was developed whereby distribution of floristically determined 'community groups' could be predicted from combinations of environmental variables. (2) The southern Langeberg is rich in endemic species and patterns of endemism were investigated using (a) two-way contingency table analysis and (b) generalised linear modelling. From the contingency table approach it was found that endemism is not randomly distributed taxonomically, in terms of biological attributes of species and with respect to the montane habitats where they occur. The majority of endemic species are restricted to 6.7% of the plant families represented and were significantly over-represented in high-altitude wet habitats. The use of generalised linear modelling was a new approach and extension of the contingency table method. It allowed numerical estimation of the probability that a species with a given set of attributes would be endemic. Seven inferences were made from the model but most importantly, an ant-dispersed, non-sprouting low shrub has the largest probability of being endemic. (3) Species diversity in the southern Langeberg flora was analysed firstly in terms of species richness (α diversity) and rarity and secondly with respect to turnover on ecological gradients (β diversity) and geographical gradients (γ diversity). The patterns of species diversity observed are related more to high turnover of sparsely distributed (rare) species on ecological and geographical gradients than to levels of a diversity.
Open Access
Plant ecology of the Namaqualand Strandveld : community structure and dynamics in a winter-rainfall desert
(2000) Eccles, Neil Stuart; Cowling, Richard M; Esler, Karen
The Strandveld forms the western coastal margin of the arid Namaqualand system. As a whole, Namaqualand has a very unusual diversity of plant life. Firstly it is unusually diverse in the most basic sense - there are lots of species, and many of them are endemic. Secondly, the ratio of species diversity to functional diversity is very high (i.e. there appears to be a great deal of functional overlap). Thirdly, in the speciﬁc case of the Strandveld, this diversity exists in a very homogeneous abiotic context. This leads to a challenging theoretical question: how does this diversity persist at a local scale? Although fundamental in nature, the answer to this question has many applied implications in terms of how we might manage the system, and how we might rehabilitate areas that have been damaged by activities such as mining. In order to begin to address this question, I set out to explore the spatial end temporal structure of selected Strandveld communities. This strategy has proved fruitful in many other systems and was in keeping with prevailing conceptual model for Namaqualand. My earliest observation in these communities was that the majority of perennial plants assemble into cosmopolitan vegetation clumps. This led me to postulate that communities are shaped by a positive feedback between seed dispersal strategies that promote the recruitment into clumps and general physical beneﬁts associated with micro-habitat modiﬁcation and mutual protection. Aspects of this postulate were tested with a combination of manipulative and sampling experiments. The results from a removal experiment suggested that interactions between individuals and their neighbours in clumps are in fact more complex than initially thought. Both negative and positive interactions were evident when different variates were considered, indicating that a balance between positive and negative interactions exists. This result was further supported by the obscuration that the spatial distribution of below-ground biomass does not mirror the highly clumped above ground pattern, suggesting that competition for water is a likely possibility. Despite this evidence that interactions between individuals may shape the spatial structure of these communities, I could ﬁnd little evidence that the interactions between individuals of particular species result in any deterministic outcome. There was certainly no evidence for any deterministic competitive exclusion. The species make-up of the vegetation clumps suggests that a large element of chance is involved in the assembly of clumps, and the lack of any strong relationships in populations between the size of individuals and their biotic neighbourhoods further supports this suggestion. The implication of this is that these Strandveld communities may be examples of communities with stochastic domination where species coexistence occurs, not in spite of, but because they are functionally equivalent generalists. Together, this understanding of the forces shaping the spatial structure of Strandveld communities, and the suggestion that Strandveld communities may be characterized by stochastic domination constitutes a very valuable contribution to the conceptual framework that has emerged to explain Namaqualand's unique plant diversity.
Open Access
Predicting the distribution of thickets and forests on the Cape Peninsula, Cape Province using linear regression analyses
(1993) Simmons, Mark T; Cowling, Richard M
Forest and thicket communities are distributed throughout fynbos. The species constituents exhibit life history characteristics significantly different from fynbos species, in that reproductive biology and recruitment are not coupled to fire. The limited occurrence of forests and thickets suggest that there may be specific abiotic factors which limit their distribution. In an attempt to determine which factors are significant in prediction, data from 600 plots covering a substantial part of the Cape Peninsula was analyzed using linear regression models. Although trends in predictive variables were detected for both forest and thickets, the models were largely unsuccessful. This was due both to the lack of inclusion or poor transformation of certain factors and the fact that not all potential forest and thicket sites are filled. The role of fire as the stochastic element in the system as well as the significance of measured environmental variables in determining forest and thicket location is discussed.
Open Access
The reconstruction of late quaternary vegetation and climatic patterns on the Cape West Coast, using a charcoal sequence from Elands Bay Cave
(1998) Allsopp, Janet Christine Natalie; Cowling, Richard M; Parkington, John; Richardson, David Mark
A taxonomically well resolved sequence of charcoal spanning the past 40 000 years from the Elands Bay Cave was used in this thesis to achieve two main objectives: firstly to determine the plant communities which occurred in the past to compare these to extant communities, and secondly to predict past climates by using extant species-climate relationships. This quantitative approach in predicting past climates is novel in the western Cape. Two scales of study were used, a local and a regional scale. The study area used in the local approach was a block of land in the surrounds of the cave where the present-day distributions of the species (that occurred in the charcoal) could be sampled. A larger study area including the whole of South Africa was also used as a study area so as to determine the distribution of species that do not occur on the Cape west coast today, and also to sample a wider suite of climatic conditions. A classification of the past, present and combined data was conducted in order to document the change in communities over time. Ordination techniques were used to asses the environmental variables controlling the distribution of species in the landscape.
Open Access
The relationships between forest and mountain fynbos communities in the southwestern Cape Province of South Africa
(1991) Manders, Patrick Timothy; Cowling, Richard M; Bond, William J; Stock, William D
Evergreen forests are believed to be restricted to moist sites in the southwestern Cape because of seasonal drought and high fire frequency in adjacent fynbos shrublands. However, soil moisture has not been demonstrated as the controlling factor. Succession to forest has been observed in some areas and not all forest trees in the fynbos are killed in some fires. This thesis determines whether forest and fynbos communities are separated by habitat factors or whether they are different successional stages of the same vegetation type. The effects of fire on forests, regeneration processes and habitat factors were studied in Swartboskloof, near Stellenbosch. Establishment requirements of forest seedlings were investigated in nearby Assegaiboschkloof. The effects of habitat factors on germination, establishment, growth and competitive abilities of forest and fynbos species were determined in controlled growth experiments. Established forest stands in Swartboskloof were stable in response to fire. Studies on the relationship between plant size and ability to survive fire showed fire intensity to be the overriding factor. Unlike regeneration in fynbos, regeneration of forest species is not coupled to disturbance. Forests had smaller soil seed banks than nearby fynbos but had the same set of species. Dispersal of ·forest species seeds into fynbos occurs immediately after fire for wind- and bird-dispersed species. Therefore colonization of fynbos by forest species soon after fire is not limited by seed dispersal. Evidence of facilitation of forest development was found in mature fynbos. Forest seedlings were associated with tall vegetation, high cover and deep litter layers as well as proximity to perches. Facilitation is enhanced in nuclei of forest species within fynbos communities. These studies refute the concept of forest and fynbos as distinct vegetation types. The relationships between forest and fynbos are explained on the basis of successional processes. Germination of forest species may occur in post-fire conditions, but establishment is unlikely until habitat amelioration occurs. Soil moisture and nutrients affect the rate of forest development. It is the frequency of fire, in relation to the rate of forest development, which determines the extent of forest development.
Open Access
Seed and seedling ecology of four Agulhas Proteaceae
(1991) Mustart, Penny; Cowling, Richard M
Serotinous (canopy-stored seed) Proteaceae, Protea obtusifolia and Leucadendron meridianum occur on shallow, alkaline soils overlying limestone, and P.susannae and L.coniferum on adjacent, deep, weakly acidic sands, in fire-prone fynbos. Seed reciprocal transplants were used to test whether regeneration niche requirements were determinants of adult distributions. There were no germination niche differences, but limestone species showed greater seedling mortality on the transplanted colluvial sands than limestone. There were also greater relative growth rates of seedlings on their own soil than counterparts on transplanted soil.