Browsing by Department "Plant Conservation Unit (PCU)"

Now showing 1 - 12 of 12
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    Open Access
    Aloe Pillansii on Cornell's Kop : are population changes a result of intrinsic life history patterns or climate change?
    (2004) Duncan, John A; Hoffmann, Timm
    Aloe pillansii populations in the biodiversity hotspot of the Succulent Karoo in Southern Africa are thought to be under threat of extinction. This study investigated the population at the type locality; Cornell's Kop in the Richtersveld, South Africa. It has been suggested that theft, animal damage and more recently climate change have caused a decline in the population by over 50% in the last decade, however very little is known about this rare species. Repeat photography and surveys were used to analyse life history patterns and dynamics of the population and thus establish what the potential threats to this keystone species actually are. Repeat photography indicates that there have been high rates of adult mortality over the last fifty years (1.8% of the population dies annually), which results in an average predicted lifespan of 39 years for the remaining adult population on Cornell's Kop. However, a recent survey reported that over 40% of the population recorded were seedlings, which weren't found in a 1995 survey, which is indicative of a recent recruitment pulse on Cornell's Kop and that conditions on the hill are still habitable for A. pillansii. Growth analyses suggest that A. pillansii has an average annual growth rate of 20 mm.yr⁻¹, which in tum means that 8 m individuals may be up to 453 years old. This long-lived strategy would require A. pillansii to only recruit infrequently, during periods of high rainfall, in order to sustain a viable population, which is consistent with findings on other large desert succulents. Seedling ages were estimated from their heights and it was found that 50% of the seedlings appear to have germinated five to ten years ago; this is consistent with rainfall records from the area which indicate that rainfall was consistently above the annual average for this same period. The findings indicate that although the adult A. pillansii population is declining, the presence of 30 seedlings suggest that the population is entering a recruitment phase after just coming out of a lengthy senescent phase. Although A. pillansii 's extensive lifespan makes it a potentially useful indicator species of climate change, the evidence presented in this study does not suggest that climate change has affected the dynamics of this population.
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    Blow me down: A new perspective on Aloe dichotoma mortality from windthrow
    (BioMed Central, 2014-03-18) Jack, Samuel L; Hoffman, Michael T; Rohde, Rick F; Durbach, Ian; Archibald, Margaret
    Background: Windthrow, the uprooting of trees during storms associated with strong winds, is a well-established cause of mortality in temperate regions of the world, often with large ecological consequences. However, this phenomenon has received little attention within arid regions and is not well documented in southern Africa. Slow rates of post-disturbance recovery and projected increases in extreme weather events in arid areas mean that windthrow could be more common and have bigger impacts on these ecosystems in the future. This is of concern due to slow rates of post-disturbance recovery in arid systems and projected increases in extreme weather events in these areas. This study investigated the spatial pattern, magnitude and likely causes of windthrown mortality in relation to other forms of mortality in Aloe dichotoma, an iconic arid-adapted arborescent succulent and southern Africa climate change indicator species. Results: We found that windthrown mortality was greatest within the equatorward summer rainfall zone (SRZ) of its distribution (mean = 31%, n = 11), and was derived almost exclusively from the larger adult age class. A logistic modelling exercise indicated that windthrown mortality was strongly associated with greater amounts of warm season (summer) rainfall in the SRZ, higher wind speeds, and leptosols. A statistically significant interaction term between higher summer rainfall and wind speeds further increased the odds of being windthrown. While these results would benefit from improvements in the resolution of wind and substrate data, they do support the hypothesised mechanism for windthrow in A. dichotoma. This involves powerful storm gusts associated with either the current or subsequent rainfall event, heavy convective rainfall, and an associated increase in soil malleability. Shallow rooting depths in gravel-rich soils and an inflexible, top-heavy canopy structure make individuals especially prone to windthrown mortality during storms. Conclusions: Results highlight the importance of this previously unrecognised form of mortality in A. dichotoma, especially since it seems to disproportionately affect reproductively mature adult individuals in an infrequently recruiting species. Smaller, more geographically isolated and adult dominated populations in the summer rainfall zone are likely to be more vulnerable to localised extinction due to windthrow events.
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    Can nitrogen isotopes be used to detect the effects of burning on nitrogen cycling? A study on Pinus resinosa in Minnesota, USA
    (2004) Ballantyne, Fiona; Craine, Joseph
    Pinus resinosa stands in Minnesota, USA were surveyed and fine and coarse roots from stands were analysed for nitrogen isotopes in an attempt to determine if fire effects nitrogen cycling. Fire increased the % nitrogen of coarse roots and changed the ratio of C: N. It may also decrease the depth of the A-horizon. It did not however affect the nitrogen isotope ratio of stands. Isotope values of coarse roots were affected by the depth of the A-horizon, which is consistent with other studies. A correlation between the 15N values of course and fine roots was found however fine roots were enriched proportionately to coarse roots. This suggests that they may be using a more enriched source of nitrogen such as ammonia although this is not conclusive. A PCA performed on site variables and isotope values determined the two major axes for sites were bum history and nitrogen cycle openness but that burning did not affect the second axis. A stepwise backwards regression showed the best predictors of a root's isotope value were, in decreasing order, the isotope value of coarse roots for fine roots and vice versa, the % nitrogen of roots and the age of stands. Coarse and fine roots showed opposite trends with % nitrogen. As the % nitrogen increased, fine roots were more 15 N enriched, again pointing to different nitrogen sources for coarse and fine roots. Older stands do appear to have a more open nitrogen cycle, as roots were 15N enriched in these stands. The availability of different forms of nitrogen may influence the 15N signal of roots especially if fine roots are preferentially using ammonia. Therefore, it is not possible to say if isotope values are due to stand openness, or due to different resources use by roots.
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    Current status and impact (2004-2015) of indigenous ungulate herbivory on the vegetation of Sanbona Wildlife Reserve in the Little Karoo
    (2017) Vorster, Liesl; Todd, Simon W; Hoffmann, Timm
    Game farming is becoming more popular in southern Africa and the introduction of large indigenous ungulates into confined enclosed areas could alter plant communities and ecosystem processes. This is of particular concern in semi-arid rangelands of the Succulent Karoo where the evolutionary history of grazing is not clear and the compatibility of large herbivores in confined areas remains to be demonstrated. The establishment of Sanbona Wildlife Reserve, a 54 000 hectare private game reserve in the Little Karoo, which converted from livestock farming to game farming, allows an opportunity to study the vegetation dynamics in a confined plant-herbivore system. This study investigates the current community structure and the changes in the floral composition and vegetation structure of enclosed and comparable sites subjected to grazing by large herbivores after twelve years (2004-2015). It also determines the relative effect of grazing and rainfall on the observed patterns. Finally, the implications of these findings for management are discussed. Data from drop-point surveys in fenced (exclosure) and unfenced (grazed) plots in the dominant vegetation types as well as annual and seasonal rainfall totals, stocking rates of herbivores and annual game census information, were analysed. These were used in multivariate ordination techniques, regressions and linear mixed-effects models to determine the communities and their relationship with herbivory and rainfall over time and identify a set of indicator species. The annual game census information was used to determine areas of herbivore preference or 'hotspots' and for the identification of highly-utilised areas. Cluster analysis, using the flexible beta method in PC-Ord, was used to determine the current plant communities. Non-metric multidimensional scaling ordination (NMS) was used to determine the relationship of these communities with the environmental variables and illustrate the trajectories in floristic data. Species were also assigned to plant growth forms and examined as communities and growth form types. The Bray-Curtis distance measures were used to investigate the difference between each treatment over time, within each vegetation community and between treatments. Finally, the effects of rainfall and herbivory were examined using linear mixed-effects models of change over time vs the various potential determinants of change using lmer functions in R. Four communities were identified. These communities corresponded well with to the vegetation type descriptions for Western Little Karoo, Little Karoo Quartz Vygieveld and Renosterveld as described in the National Vegetation Map of Mucina and Rutherford (2006). However, the Western Little Karoo was too broad and two communities were recognised within this vegetation type. The finer scale mapping by Vlok et al. (2005) corresponded relatively well to these communities. Results showed an increase in species richness, abundance and cover over time, with the ungrazed plots experiencing more change than the plots exposed to grazing. Most growth forms exhibited an increase in cover, although low leaf succulents declined in both grazed and ungrazed plots. Medium evergreen shrubs declined in the exclosures and stem succulents declined in the grazed plots. The effects were found in both grazed and ungrazed treatments. In addition, many species which declined in abundance were unpalatable or toxic to herbivores. Because of this, the decline in cover of such species was not attributed to grazing, but was instead interpreted as being a response to other disturbance mechanisms, to competitive displacement and to rainfall events. The low stocking rates in the first five years of the study resulted in there being very little difference evident between the treatments. However, once stocking rates increased from 2008, both species richness and cover increased more rapidly in the ungrazed plots, compared to the grazed plots. An increase in palatable and unpalatable species was observed within both ungrazed and grazed plots indicating that grazing did not change the proportion of palatability classes. However, specific plots in the areas of high animal utilisation were more affected as indicated by the response of cover, species richness and palatable species in these specific plots. This suggests that the grazing pressure may be too high within those areas. The linear mixed-effect model supports the argument that grazing pressure is the dominant driver of the community change within grazed plots. Similarly, the results show that rainfall is the primary driver of the vegetation community in the absence of grazing. Timing, amount and intensity of rainfall can mask these impacts. Thus, the contribution of grazing to vegetation change can probably only be detected by tracking the trends over decades or longer. The use of indicators as a management tool is well documented. In order to identify indicators, a theoretical framework for determining indicators species in the different vegetation communities was created. This was based on the correlation between species abundance and sampling period in the different treatments, which identified species that have significantly increased or decreased over time as a result of the change in land use. Species identified as potential indicators were selected on the basis based on their abundance and ranged in lifespans and palatability. The indicators chosen need to be monitored into the future to confirm their utility as indicators. A small but significant difference between grazed and ungrazed plots suggest that herbivore impact is apparent. Identifying this trend indicates that the monitoring programme is providing a useful tool for assessing the impact of herbivores on an ongoing basis. The recovery process following the withdrawal of domestic livestock from Sanbona was much slower in the grazed plots than in the protected plots. Therefore, for the continued recovery of the vegetation to occur and for there to be a sustained increase in cover, active management of animal numbers needs to take place. The results from this study can contribute to future management decisions on the reserve and form a basis for future analyses.
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    The demography of Acacia stands on the Hluhluwe-Umfolozi Game Reserve
    (2003) Mader, André Derek; Midgley, Jeremy J
    Little is known about the demographics of the genus Acacia in Africa, despite its prominence and the economic and environmental importance of this group. The demographics and species composition of stands of four different Acacia species was investigated in the Hluhluwe-Umfolozi Game Reserve in northern Kwazulu-Natal in order to determine whether stands were self-replacing, or whether other Acacia species were invading them. Soil and stand density as well as the density and composition of the grass layer were investigated in order to determine whether any of these affected Acacia demography and species composition. In three out of four cases, the species whose large size class dominated the stand (known as the "stand species") was found to have a strongly bimodal size class distribution, skewed primarily towards the large size class and secondarily towards the small size class. Other Acacia species in the stands, with few or no large individuals present ("nonstand species") tended to have unimodal size class distributions, skewed primarily towards the small size class and secondarily towards the medium size class. Based on the proportion of small to large individuals, non-stand species are more likely to increase in overall numbers in future, suggesting that the species composition of the stands may be in a state of flux. Few relationships were found between stand density, grass density, grass composition and numbers of small and medium acacias. This could be as a result of differentiation between Acacia species, meaning that they cannot be analysed collectively. Furthermore, sample sizes of individual species may have been too small to analyse individually. Alternatively, it could mean that none of these factors have a significant effect on one another and that other explanations need to be found for the demographics of this genus.
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    The distribution and population structure of Aloe pillansii in South Africa, in relation to climate and elevation
    (2004) Bolus, Cosman; Hoffmann, Timm
    South Africa comprises almost 10% of known plant species and also has the only arid zone "hotspot" defined worldwide, namely the succulent Karoo. Anthropogenic climate change predictions for South Africa suggest rapid climate change in the next 50 years will have adverse effects on its vegetation biomes. This study shows how the aborescent succulent, Aloe pillansii, has a limited distribution due significantly to environmental and climatic variables and therefore it is potentially at risk given anthropogenic climate change predictions. The total South African A. pillansii population investigated is made up of 1202 individuals and is found in the Richtersveld, which is part of the Succulent Karoo. The A. pillansii individuals were sampled in terms of their height and geographical position and then defined into subpopulations by a distance of 2 kms of separation. The sub-populations were then evaluated in terms of their respective environmental and climatic variables acquired from a CCWR database for South Africa using Arc View 3.2. The sub-population size class distributions were also constructed so that population dynamics and recruitment could be investigated. The results show how the A. pillansii sub-populations are limited to a specific environmental and climatic range. The sub-populations group along similar environmental and climatic variables with the healthiest sub-populations found at lower elevation, higher temperatures and higher Potential Evapo-Transpiration. The climatic range of A. pillansii is also evident from the range of its environmental and climatic variables and the associated unhealthy sub-populations that lie on the extremes of this range. Recruitment was found to correlate strongly with the environmental and climatic variables, % winter rainfall and elevation, suggesting it is moisture limited. The evidence found in this study of A. pillansii 's specific environmental and climatic distribution may have negative implications for its future survival and conservation especially with present indications of anthropogenic climate change.
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    Ecosystem goods and services in semi-arid lanscape : an examination of the relationship between ecological processes, land-use strategies and biodiversity conservation
    (2005) O'Farrell, Patrick John
    [page 80, 121, 137, x2; 20, 156 missing] Biodiversity loss and the disruption and degradation of ecosystems is proceeding at unprecedented rates. Conservation areas are insufficient to protect all species and there is growing recognition of the need to promote biodiversity conservation on private land, through the adoption of biodiversity-friendly land-use practices. Conservation and ecosystem function are linked to the delivery of ecosystem goods and services, which are processes and conditions of ecosystems that benefit humans and their activities. The research focus on ecosystem goods and services to date has been at global and regional scales, and there is a paucity of research at the fine scale. Benefits need to be measured and evaluated at a fine scale if land-users are to adopt best practices. The central aim of this study was to examine the relationship between commercial agricultural land-use practices and ecosystem goods and services in a biodiversity hotspot in a semi-arid area of South Africa. The approach adopted was based on the premise that to influence management activities and land-use practices it is best to first develop an understanding of what farmers perceive to be the most important ecosystem goods and services and how they manage their landscapes according to these perceptions. Farmers recognise and value a broad range of ecosystem goods and services that they incorporate into their farming practices, and their management framework is structured according to these in an attempt to optimise production. Ecosystem goods and services are perceived according to landscape heterogeneity which provides temporal and spatial opportunities for their exploitation. An exploration of the effects of land-use practices on identified ecosystem goods and services showed these to be highly dependent on the incorporation of natural vegetation and the maintenance of key ecological processes. Natural vegetation is essential for the provision of goods and services related to grazing and livestock production, with different vegetation types providing different goods and services. The maintenance of the service provided by an abundance of small mammals as an alternative source of prey to livestock for medium-sized predators, was demonstrated to be highly dependent upon landscape and vegetation structure, with 82% of all mammals trapped in the most structurally diverse vegetation type, vegetation clearance resulted in a seven fold decrease in small mammal abundance. A detailed examination of rainfall infiltration and erosion in natural, transformed and managed transformed vegetation showed there to be greater infiltration, less run-off, wind speeds reduced four fold, and eight times less soil lost to wind erosion in natural vegetation compared with transformed areas. However, in managed transformed areas, rainfall infiltration was greater than in natural and transformed areas. An examination of the key ecological processes maintaining soil health showed a decline in 1 soil invertebrate activity with increasing distance from natural vegetation remnants. However, under managed transformed conditions earthworm populations were three times greater than in natural vegetation remnants and this may account for greater infiltration rates measured here. An exploration of the potential to develop horticultural products from the species in the area, demonstrated the importance of the retention of natural vegetation as repositories of future-use options. In comparing farmers' perceptions, with analysed ecosystem goods and services, their perceptions were demonstrated to be generally accurate in their identification of ecosystem goods and services. While their perceptions may be correct, the value farmers place on a particular service is often not sufficient to influence fanning practice. Farmers appear to misjudge the degree of magnitude that management effects have on the delivery of ecosystem goods and services. Despite farmers perceiving the general concept of future-use options, they do not perceive the repository potential of their own remnant patches of natural vegetation for ecosystem goods. The broader objective of this thesis has been to consider the role that an understanding of ecosystem goods and services can play in promoting biodiversity conservation on private agricultural land. While scientists grapple with the conceptual issue of how diversity links to ecosystem processes, whether all species are important, and finally how these may benefit humans, farmers work at a mdre intuitive level trying to achieve benefits for themselves based on their experiences and perceptions, which influence land strategies. As a result, understanding farmers' perceptions and testing some of their assumptions can provide a basis for illustrating the links between biodiversity and goods and services at a farm level and in this way offer opportunities for conservation on private land.
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    Land degradation in South Africa
    (2014-09-17) Hoffmann, Timm; Todd, Simon; Ntshona, Zolile; Turner, Stephen
    South Africa has a long history of desertification research which stretches back to the last century. These resources contain literature on water, soil and veld degradation in both commercial and communal areas of South Africa. Also, the most important socio-economic reasons for land degradation are discussed. This resource contains various chapters and factsheets on land degradation in South Africa. A vast amount of data which was generated during the national review of land degradation in South Africa is also available in both GIS and Excel format.
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    Land use and its impact on the Succulent Karoo
    (2004) Jonas, Zuziwe; Hoffmann, Timm; Rouget, Mathieu
    The Succulent Karoo biome (SK biome) is one of the 25 internationally recognized biodiversity hotspots in South Africa with approximately 1940 endemic species. The SK biome is, however, poorly conserved with less than 5% of the area under formal protection. It is also highly threatened by a range of different land use practices. Considering the lack of protected areas and the high levels of endemism (about 40%), which characterize the region, the current and future land use practices are likely to be the key factors in determining the future conservation of the area. Understanding the land use pattern and its drivers that have occurred in the SK biome provides a useful starting point for outlining the future research needs and establishing conservation goals. This project investigates a range of different land use practices such as urban settlement, mining, cropland, conservation and livestock production with their associated environmental drivers. The study used a Geographical Information System (GIS) to map the current extent of land use practices based on available data from different sources in the SK biome. The study also mapped the current extent of livestock density in two land tenure systems (private and communal) of Namaqualand and developed a statistical model to assess the future agricultural potential in the SK biome. The current status of the land use practices in the SK biome shows that most of its area is used for extensive grazing (90%) followed by conservation (4.8%). Due to the aridity of the area, agriculture potential is low. The results confirmed that the conservation status of the SK biome is relatively low but improving, with 4.8% of the biome conserved. Only 3.5%, however, is formally protected in statutory reserves. The remaining conserved area (1.3%) is conserved in non-statutory reserves.
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    Life history traits of South African Encephalartos spp. (Zamiaceae) and their implications for understanding population structure, responses to threats and effective conservation action
    (2016) Konings, Kim Martina; Donaldson, John Sydney; Hoffman, Timm
    Understanding life history traits and how they influence population-level processes under different conditions have been important areas of study in evolution and ecology. One application in ecology has been to determine whether there are general responses that apply to species with similar life history traits, which could provide a predictive understanding of species with shared traits rather than having to adopt a speciesspecific approach to management. In this study, an analysis of life history traits was applied to cycads, the oldest living seeds plants which are at risk of extinction due to vulnerability to illegal wild harvesting and habitat loss. The study focused on South African cycad species within the genus Encephalartos, as well as two species from Swaziland. The first objective was to identify groups of species with similar life histories and to assess whether these groups are aligned with phylogenetic relationships or an association with particular environments. The second objective was to determine whether species with shared suites of life history traits exhibited a similar population stage structure. Hierarchical cluster analysis and Principal Component Analysis (PCA) were used to identify groups based on key life history traits, namely, cone number and coning interval, number of seeds produced, number of stems, stem height and plant habit. Four life history groups emerged, these were: Group 1 with single-stemmed, subterranean species such as E. villosus; Group 2 generally characterised by medium-height species with many stems such as E. lehmannii; Group 3 with the tallest species which generally produce the most cones at the most frequent interval such as E. natalensis; and Group 4 with dwarf-arborescent, multi-stemmed species such as E. horridus. The groups were not found to correspond with the most recent phylogeny for Encephalartos and thus phylogenetic constraints were excluded. An analysis of environmental variables for 193 populations of species in all groups, including maximum and minimum temperatures, mean annual precipitation, moisture index, rainfall co-efficient of variation and fire return frequency, showed that the means per group were not significantly different from each other for most of the variables. However, it was evident that the variable ranges showed clear trends with biological significance. These tended towards more stable, less variable environments with more predictable rainfall for Group 1 species, and less stable, more variable environments with less predictable rainfall for species within Group 4. Groups 2 and 3 showed a large range and overlap in environmental associations with no consistent patterns. Population structure is valuable for determining whether recruitment in a population is adequate for species survival. Static life tables and Chi-Squared analyses were used to test differences in the population structure and survivorship patterns of species between and within the life history groups. If particular demographic patterns were shown to be emergent properties of certain suites of life history traits, autecological studies may be avoided for predictive-ecological conservation frameworks. The results showed that species in Group 1 had populations with a high proportion of juveniles and fewer reproductive adults, indicating high recruitment as well as high juvenile mortality. In contrast, species in Group 4 had populations with a high proportion of adults and fewer juveniles indicating low recruitment and high juvenile mortality with primary investment into adult plant persistence through vegetative suckering. Group 2 consisted mostly of rare species with very small populations and high proportions of adult plants showing evidence of episodic recruitment events. Species in Group 3 showed a similar trend towards intermittent recruitment with adult persistence, however, no explicit population structure emerged. This led to the conclusion that Groups 1 and 4 are relatively consistent and predictable, however, Groups 2 and 3 would better benefit from an autecological approach to management. This study was helpful to assemble life history data for South African Encephalartos, as well as environmental parameters for each species. Ultimately, it has shown that primary investment into seeds versus persistence, or a combination thereof, can influence population structure.
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    A socio-ecological approach for identifying and contextualising spatial ecosystem-based adaptation priorities at the sub-national level
    (Public Library of Science, 2016) Bourne, Amanda; Holness, Stephen; Holden, Petra; Scorgie, Sarshen; Donatti, Camila I; Midgley, Guy
    Climate change adds an additional layer of complexity to existing sustainable development and biodiversity conservation challenges. The impacts of global climate change are felt locally, and thus local governance structures will increasingly be responsible for preparedness and local responses. Ecosystem-based adaptation (EbA) options are gaining prominence as relevant climate change solutions. Local government officials seldom have an appropriate understanding of the role of ecosystem functioning in sustainable development goals, or access to relevant climate information. Thus the use of ecosystems in helping people adapt to climate change is limited partially by the lack of information on where ecosystems have the highest potential to do so. To begin overcoming this barrier, Conservation South Africa in partnership with local government developed a socio-ecological approach for identifying spatial EbA priorities at the sub-national level. Using GIS-based multi-criteria analysis and vegetation distribution models, the authors have spatially integrated relevant ecological and social information at a scale appropriate to inform local level political, administrative, and operational decision makers. This is the first systematic approach of which we are aware that highlights spatial priority areas for EbA implementation. Nodes of socio-ecological vulnerability are identified, and the inclusion of areas that provide ecosystem services and ecological resilience to future climate change is innovative. The purpose of this paper is to present and demonstrate a methodology for combining complex information into user-friendly spatial products for local level decision making on EbA. The authors focus on illustrating the kinds of products that can be generated from combining information in the suggested ways, and do not discuss the nuance of climate models nor present specific technical details of the model outputs here. Two representative case studies from rural South Africa demonstrate the replicability of this approach in rural and peri-urban areas of other developing and least developed countries around the world.
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    Vegetation, diversity and rarity on the Cape Peninsula, South Africa
    (1996) Simmons, Mark T
    The Cape Peninsula, (471 km2 ) with over 2285 vascular plant species, is characterised by the combination of a diversity of habitats supporting a mosaic of vegetation types. This study attempts describe. and explain some of the determinants of species pattern and distribution. The first part of the thesis compares a simple vegetation classification, derived from visual examination of dominant species and environmental characteristics, • with the results of a multivariate classification derived from the analysis of an extensive database (835 plots, 833 species). This rapid system of classification of fynbos showed an 81 % similarity with Two-Way Analysis (fWA) classification. Detrended Correspondence Analysis (DCA) and Canonical Correspondence Analysis (CCA) were used to relate floristic variation to environmental factors. Theses analyses revealed that altitude, rainfall and soil fertility were the principle environmental factors explaining species distribution. The second part of the thesis examined patterns of local ric~ess and turnover (beta and gamma diversity). Similar sized areas in other mediterranean-climate region biodiversity hot-spots support between 4. 7 and 2. 7 times fewer species than the Cape Peninsula. This high plant regional richness is due to the exceptionally high turnover between moderately species-rich sites in along steep environmental gradients .(beta diversity) and between sites in similar habitats along geographical gradients (gamma diversity). Highest beta diversity, encompassing almost complete turnover, was recorded along soil fertility gradients. Although similar patterns for these independent components explain the richness of other regions in the Cape Floristic region, it is the very long and steep habitat gradients of the Cape Peninsula that makes this region exceptionally rich. Furthermore, the flora is characterized by a high degree of rarity, a phenomenon that undoubtedly influences the turnover. Thus, the third part of this thesis analyses the biological and habitat correlates of plant rarity. Given the Jack of any general theory of University of Cape Town iii ' causality, understanding rarity has become a considerable problem for reserve management. To date, there have been no studies which compare the attributes of rare and ' common plant species. There were no strong relationships between rarity status and biological attributes of species. However, rare species occupy wider resource niches as measured in multivariate space. Although some habitats contained a relatively larger proportion of rare plants, most were riot restricted to particular vegetation types and exhibited ~ wide range of habitat infidelity. However, the distribution of many species, particularly those with high fidelity-indices could be successfully modelled regardless of rarity status abundance. Therefore, although rarity is difficult to predict at the phenomenon level, for management purposes, priority habitats can be identified and the distribution of rare species modelled individually. The results of theses studies are discussed in terms of management and conservation of the Cape Peninsula's uniquely high plant diversity