Browsing by Author "Stock, WD"

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    Atmospheric deposition of combined nitrogen in the Cape Metropolitan Area: a threat to a species rich ecosystem?
    (2008) Wilson, Daniel; Stock, WD
    In this project. two broad approaches were used in order to gauge levels of atmospheric N deposition to the natural vegetation of the Cape Metropolitan Area (CMA). In the first approach, bulk collectors were constructed and set up at five sites around the CMA in order to trap atmospheric deposition for chemical analysis. In the second approach, moss samples collected from different parts of the CMA during various historical periods, were analysed for N concentration, C: N ratio and 15N/14N isotope ratio in order to investigate the increase in N deposition over the past 100 years and the primary source of this increase.
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    Attributes that make Acacia karroo dominant : stable N and C isotope analysis of nine Acacia species from KwaZulu-Natal (South Africa)
    (2006) Mgidi, Theresa Nobuhle; Midgley, Jeremy J; Stock, WD
    This study focuses on nine Acacia species from Hluhluwe-Imfolozi Park in KwaZulu-Natal, South AFrica. The study was motivated by the need to understand the dominance of legumes in the process of bush encroachment in Southern Africa. A. karroo has been identified as a particularly invasive species in HUP, and determining what makes this Acacia species and any of the other acacias in HUP invasive formed the foundation of this study.
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    Decomposition of grasses in a South African savanna
    (2007) Masubelele, Mmoto Leonard; Bond, William J; Stock, WD
    Tropical and subtropical grasslands ecologists have ignored decomposition, because of the important role it plays in nutrient cycling, in terms of understanding how grass litter gets to the soil during the dry season. The major flaw is in the methods employed to investigate decomposition. In the prairies and steppes, litterbag methods employed investigate decomposition when litter is on the soil, even though the importance of carryover from standing litter is recognized. Standing litter results in high carryover which slows down decomposition thereby hindering productivity in the next growing season. I therefore decided to investigate the processes of photodegradation and microbial decomposition, as well as carryover and also how these processes differ between mesic and semi-arid grasslands. Since previous studies suggest that tallgrass prairies experience more carryover and slower decomposition than shortgrass prairies, I therefore hypothesized in this thesis that mesic grasslands will experience carryover and slower decomposition than semi-arid grasslands.
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    Decomposition of grasses in a South African savanna
    (2007) Masubelele, Mmoto Leonard; Bond, WJ; Stock, WD
    Tropical and subtropical grasslands ecologists have ignored decomposition, because of the important role it plays in nutrient cycling, in terms of understanding how grass litter gets to the soil during the dry season. The major flaw is in the method~ employed to l investigate decomposition. In the prairies and steppes, litterbag methods employed investigate decomposition when litter is on the soil, even though the importance of carryover from standing litter is recognized. Standing litter results in high carryover which slows down decomposition thereby hindering productivity in the next growing season. I therefore decided to investigate the processes of photodegradation and microbial decomposition, as well as carryover and also how these processes differ between mesic and semi-arid grasslands. Since previous studies suggest that tallgrass prairies experience more carryover and slower decomposition than shortgrass prairies, I therefore hypothesized in this thesis that mesic grasslands will experience more carryover and slower decomposition than semi-arid grasslands. Results from this thesis showed that standing litter decomposition was slower than surface soil decomposition; hence photodegradation was slower than microbial decomposition. Photodegradation was important in controlling the rate of decomposition among the different grass species standing litter. Different grass species decomposed at different rates. Different plant traits were responsible for decomposition rates of standing litter and surface soil litter. Tensile strength and polyphenolic content were important during initial and final decomposition of standing litter whereas for the surface soil litter the same factors together with CIN ratio and lignin were important. Carryover existed in mesic grasslands but not so much in semi-arid grasslands. This implies that mesic grasslands are phylogenetically designed to bum while semi-arid grasslands are controlled by herbivory.
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    The ecological effects of grazing by the White Rhino (Ceratotherium simum simum) at a landscape scale
    (2005) Waldram, Matthew; Bond, William J; Stock, WD
    In this thesis I generated hypotheses concerning the top down effect of grazing ungulates on grass communities and fire behavior from work done within grazing exclosures in Hluhluwe iMfolozi Park. White Rhino had a large influence in controlling grass biomass in Hluhluwe, a high rainfall mesic savanna. Other smaller species of grazers could not replicate the effect of White Rhino when their grazing was removed. In Umfolozi, a semi-arid savanna, other species of grazer could replace the effect of White Rhino grazing and exert a controlling influence on grass biomass. Hence the relative importance of different species of grazers changed along a rainfall gradient. When examined at a larger spatial scale I found that the removal of White Rhino led to a detectable change in grass biomass and in the grazing behavior of other species in the area of the removal. The effect that herbivores exerted on the grass layer also had consequences for the movement of fire through the landscape by reducing fuel loads. Burnt areas were larger and less patchy in areas from which White Rhino had been removed in comparison to control areas. This effect was larger in Hluhluwe but still significant in Umfolozi. I suggest that both fire and grazing are in competition for the same resource, grass, and that each results in conditions favorable to the recurrence of that event (fire or grazing). This allows the system to switch between mammal and fire dominated states. Rainfall shifts the balance of this competition and in mesic savannas White Rhino appear to be the only animal capable of competing successfully with fire. This work has application for the management of ecosystems that are influenced by top down control and for the maintenance of heterogeneity in mesic savannas.
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    The ecology and nitrogen-fixing ability of selected Aspalathus spp. in fynbos ecosystems
    (1994) Cocks, Martin; Stock, WD
    Aspects of the ecology of selected species of Aspalathus spp. (Fabaceae) were investigated to elucidate the role that this genus may play in the nitrogen economy and ecology of fynbos ecosystems. From the literature it is argued that fire plays a pivotal role in these ecosystems as decomposition is very slow. Decomposition returns nutrients trapped in the vegetation back to the soil. However, nitrogen is lost via volatilisation during fires and as deposition of nitrogen in precipitation is low, symbiotic and non-symbiotic nitrogen-fixation may be of importance in replacing lost nitrogen. The influence of soil total nitrogen and phosphorus on the occurrence of dense stands of Aspalathus plants in vegetation of different ages was investigated. Soil of young vegetation containing stands of Aspalathus plants had the same or higher concentration of phosphorus as nearby older vegetation which lacked stands of Aspalathus. Total nitrogen however showed no trends. Nodulation of 15 Aspalathus spp. at 11 study sites showed varying amounts of nodulation although all these species nodulated well under pot culture. Nodulation of three Aspalathus spp. at three seasonal study sites was followed over the course of one year. A. carnosa showed peak nodulation in the late winter months but A. retroflexa and A. abietina displayed no similar trends. Across the three seasonal sites, which had very similar soil, nodulation was positively correlated with soil total phosphorus and negatively correlated with soil total nitrogen in a multiple regression analysis. The ratio of soil total nitrogen to phosphorus was negatively correlated with nodulation. The opposite correlations for soil total nitrogen and phosphorus were found across all 11 study sites. Differences in soil types and organic content may be responsible for this apparent contradiction. Other soil factors such as pH, temperature and moisture were not correlated with nodulation. Total organic content, however, was negatively correlated with nodulation across the geographic survey study sites.
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    Ecology of the (Brady)rhizobium symbiotic relationship with Fabaceae in the south-western Cape
    (1996) Marumo, Moscow; Stock, WD; Dakora, Felix D
    The mediterranean ecosystems of the south-western Cape, South Africa occur mainly on nutrient-poor acid sands and less often on limestone and mixed limestone soil types which support a high species diversity of Fabaceae. This species richness and diversity is suggested to be a result of a high incidence of microsymbiont/host specificity among the fynbos Fabaceae (Cowling et al. 1990). This hypothesis by Cowling et al. (1990) has ignored other factors which may possibly play a major role in microsymbiont/host relationships in the Cape Floristic Region, such as soil conditions, and bacterial strain competition which may also influence patterns of nodulation in the region. Cowling et al.'s (1990) hypothesis was speculative and was without any experimental basis. In this thesis investigations were carried out to assess the applicability of this hypothesis to fynbos, while at the same time other factors that could affect the microsymbiont/host relationship in fynbos were investigated. In order to test Cowling et al.'s (1990) hypothesis, various complementary methods were used to assess the nodulation patterns of several indigenous fynbos species. Extracts from a range of soils differing in chemical and physical properties were used to inoculate test species, and their nodulation parameters observed. However, a second more specific approach was used to confirm the results of the previous study. This method involved cross-inoculation of indigenous test species used in the previous study with nodule homogenates prepared from other fynbos species originating from various sites within the Cape Floristic Region.
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    Ecosystem level impacts of annual and perennial N2-fixing invasive alien plants in the fynbos vegetation of South Africa
    (2000) Yelenik, Stephanie; Stock, WD; Richardson, David Mark
    In the nutrient-poor fynbos, changes in soil nutrients can affect species composition and community structure. The N2-fixing ability of invasive alien plants, therefore, may have impacts on ecosystem and community functioning within the fynbos vegetation type. This study investigated changes in fynbos N cycling regimes with the invasion of two different N2-fixing invasive alien plants, Acacia saligna and Lupinus luteus.
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    The effect of simulated nitrogen deposition on growth and ecosystem functioning of managed P. patula plantation ecosystems in South Africa
    (2001) Jacobs, Shayne Martin; Stock, WD; Dye, Peter
    The purpose of this study is to investigate the effects of future NO₃ and NH₄ deposition on growth and nutrient cycling in P. patula plantations growing on shale-derived soil. This study consists of a field and pot-grown seedling experiments, the former commencing in November 1995 and the latter in August 1996.
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    Effects of defoliation on regrowth and carbon budgets of three semi-arid Karoo shrubs
    (1992) Van der Heyden, Francois; Stock, WD; Lewis, O A M
    Plant regrowth, nonstructural carbohydrate utilization patterns, photosynthesis and the partitioning of photosynthetic products in response to foliage removal were studied for the following karoo shrubs: Osteospermum sinuatum, a dwarf deciduous shrub with fleshy leaves, Pteronia pallens, a dwarf evergreen shrub with sclerophyllous leaves and Ruschia spinosa, a dwarf evergreen shrub with succulent leaves. Defoliation adversely affected both vegetative growth and reproductive output for periods up to 26 weeks following foliage removal. A gradient of increasing regrowth capacity with decreasing defoliation intensity and frequency was observed in all species. In terms of biomass production, defoliation was the least detrimental to the deciduous shrub, O. sinuatum, and the evergreen shrub, P. pallens, and the most injurious to the succulent shrub, R. spinosa. All species regrew better during spring and autumn, and no regrowth was recorded in the moderate (40%) or intensely (80%) defoliated plants during summer and winter over the 6-week monitoring periods. Spatial patterns of carbohydrate accumulation were the same for all species, with most of the total nonstructural carbohydrates (TNC) being stored in the twigs and stems. Karoo shrubs can be divided into two distinct groups based on the primary nonstructural polysaccharides accumulated in their plant parts. The Asteraceous plants, O. sinuatum and P. pallens, accumulate predominantly fructans. In contrast, the succulent species, R. spinosa, accumulate starch and fructans in equal proportions. Differences among species in terms of seasonal changes in TNC levels of undefoliated plants reflect the extent to which different species are dependent on stored carbohydrates or photosynthesis for normal vegetative growth processes. Repeated defoliations at a moderate frequency (26-week interval) resulted in the elevation of TNC concentrations of O. sinuatum and P. pallens. In contrast, defoliations at heavy or at leniant frequencies caused decreases in TNC concentrations in all plant parts of Ruschia spinosa. Restoration of plant storage TNC levels in excess of undefoliated plant TNC levels occurred prior to complete vegetative regrowth in the two Asteraceous shrubs which suggests that some factor(s) other than the carbon resource was limiting vegetative regrowth in karoo shrubs. Analyses of short-term changes (2-weekly) in TNC levels in response to defoliation demonstrated the elevation in TNC concentrations of Pteronia pallens plant parts only during the periods when no regrowth was recorded. This phenomenon illustrates that on a short-terms basis, regrowth and over-replenishment of reserves represent two alternate responses to defoliation. However, during periods when regrowth was recorded for P. pallens (autumn and spring), and during all seasons of the year for O. sinuatum and R. spinosa, depressions in TNC concentrations were observed in most plant parts up to six weeks following defoliation. This illustrates the large dependence these shrubs have on stored carbohydrates following defoliation. Defoliation had no effect on the photosynthetic rates of karoo shrubs for at least 11 days following defoliation. Foliage removal resulted in the redistribution of photoassimilates in all plant species. These changes in the allocation of newly produced photosynthates appear to be associated largely with the replenishment of carbohydrate reserves following the initial TNC utilization caused by foliage removal. Comparison of TNC utilization patterns, following defoliation of O. sinuatum in the dark (no photosynthesis) and in the light resolved the question of the relative importance of reserve carbohydrates and photosynthates following defoliation. Reserve carbohydrates were used only for the first 2 weeks following defoliation for respiratory functions while photoassimilates were used for the production of new foliage. The magnitude of nonstructural carbohydrate utilization in the absence of photosynthesis emphasized the importance of continuing photosynthesis to the survival of defoliated karoo shrubs. The differences among species in terms of the timing and the extent of changes (elevations or decreases) in TNC levels in response to defoliation are interpreted as being the result of alterations in plant chemistry which in turn are governed by species specific physiological adaptations to environmental constraints. Rangeland management guidelines are recommended within the framework of the observed short-term and long-term defoliation effects on karoo shrub plant production.
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    The effects of elevated atmospheric CO2 on below ground processes in fynbos and C4 ecosystems
    (2002) Morrow, Carl Dylan; Stock, WD
    This thesis investigated ways in which elevated atmospheric carbon dioxide (CO2) concentrations influence the plant: soil interface and soil biological processes. The studies focused on microbial populations associated with the plant rhizosphere, and how these responses could feed into changes in the soil carbon pool.
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    The effects of size and habitat on δ N-15 of carnivorous plants (Drosera spp.)
    (1999) Mgidi, Theresa Nobuhle; Midgley, Jeremy J; Stock, WD
    The δ N-15 natural abundance method was used to investigate the role of nutrient-poor habitats in carnivorous Drosera capensis and Drosera aliciae, and how that role changes under sunny and shady environmental conditions. The main purpose of the study was to evaluate Givnish's (1984) cost/benefit model used to explain the evolution of carnivory in nutrient-poor, sunny and moist habitats. δ N-15and total nitrogen values of the Drosera species were compared against each other, as well as against the non-carnivorous reference plants collected from each of the two habitats. Generally, data indicated significant differences between the carnivorous plants and their reference plants in terms of δ N-15 values. However, there was no significant difference between plants collected from the shade and those collected from the sun for both Drosera species. Total nitrogen results revealed higher values for Drosera plants from Camp's Bay than those from Table Mountain did. This indicated that there was a bigger source of insect nitrogen at that site, meaning more insects were available and being caught by the plants at Camp's Bay. Further investigations were performed on the two Drosera species in order to find the influence of altitude, leaf-size and plant form, on the degree of carnivory. There was an overall, higher degree of carnivory at Camp's Bay where it is, seasonally wet and the plants have longer leaves and a stem-like rosette. On Table Mountain it is cooler, waterlogged, and the plants have short leaves and ground-level rosettes therefore, the degree of carnivory there was lower. Lastly, chlorophyll and anthocyanin contents were measured and compared between the sun and shade collected D. capensis plants, with tentacles intact and with them removed. Chlorophyll investigations showed significant differences between sun and shade collected D. capensis plants but these were not affected by the removal of tentacles. Alternatively, anthocyanin measurements indicated that sun and shade collected D. capensis plants have similar amounts of anthocyanins, but the removal of tentacles results in a decrease (about four times lower) in the anthocyanin content.
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    The embryology, seed coat, and conservation of some Kenyan species of the orchidaceae
    (2000) Ochora, John; Stock, WD; Linder, Peter; Newton, Len
    Aspects of embryology, seed morphological features and symbiotic seed germination of the Kenyan orchid species of the subfamily Epidendroideae were examined critically in order to elucidate their development and importance in conservation. The embryology of ca. 70 species was studied by clearing-squash techniques and differential-interference-contrast optics and seeds of ca. 50 species were studied by scanning electron microscopy to determine their variations.
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    An investigation of the duration of phosphorous fertilization effects on phosphorous and nitrogen cycling patterns of Pinus elliottii plantations in the southern Cape
    (1992) Wienand, Karen Tania; Stock, WD
    The effects of phosphorus fertilization and its duration of impact on nutrient cycling patterns in Pinus elliottii plantations were investigated by examining soil phosphorus and nitrogen turnover and litterfall in a 8, 20 and 25 year old plantation age sequence. Each stand contained plots fertilized with between 30-60 kg ha-1 superphosphate at establishment and an equal number of control (unfertilized) plots. At the oldest stand there were additional variables, namely timing of fertilizer application (at establishment versus 10 years after establishment) and fertilization frequency (double application, at establishment and 10 years later). Phosphate fertilization produced a significant increase in soil phosphorus availability at the 8 and 20 year old stands. At the 25 year old stand, increased phosphorus availability was only significant in the plots fertilized twice. It was only at these latter plots that a significant increase in soil annual net phosphorus turnover with fertilization was evident. Thus, only with a double application of phosphate will increased phosphorus availability and turnover be maintained up to 25 years. Phosphate fertilization significantly reduced soil nitrogen availability and soil annual nitrogen turnover at all the stands. This was ascribed to inorganic nitrogen being immobilized by the large microbial population supported by the increased phosphorus availability. This contention is supported by the investigation of the factors influencing nutrient mineralization - while fertilization was the most significant factor determining phosphorus mineralization, nitrogen mineralization was shown to be strongly controlled by environmental factors, indicating the role of micro-organisms in this process. Thus phosphorus release is mainly a physiochemical phenomenon while nitrogen turnover is biologically controlled. The reduction of nitrogen turnover rates with phosphate fertilization intensified with increasing age, presumably as the nitrogen became bound in biomass which decomposes slowly.
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    An investigation of the limited distribution of the grazing lawns in Hluhluwe-Umfolozi Park, South Africa
    (2002) Swemmer, Anthony Michael; Bond, William J; Stock, WD
    The grasslands and savannas of the Hluhluwe-Umfolozi Park (HUP), South Africa contain unusual 'grazing lawn' communities dominated by short, grazing tolerant grasses. These grazing lawns appear to be highly productive, and support high densities of grazers during the late summer and early winter, but have a very limited distribution within HUP. A review of the grazing literature indicates a similar pattern at the global scale, with grazing lawns absent or rare in almost every grass-grazer system described. Resource limitations responsible for the limited distribution of grazing lawns were investigated. A conceptual model of key processes considered necessary for the formation and persistence of lawns in HUP was developed. Key processes include both frequent and non-selective grazing during the growing season Based on observations that the distribution of grazing lawns within HUP is strongly related to rainfall, it was hypothesized that further key processes control are involved. In areas of lowest rainfall grazing lawns are replaced by a sparse cover of forbs and unpalatable grass species. It was hypothesized that a shortage of mineral nitrogen (N) and / or water are key processes excluding grazing lawn grasses in these environments. In areas of highest rainfall grazing lawns do not form, even where grass communities have been heavily grazed for a year or more. It was hypothesized that below-ground competition for N by the dominant grasses (bunch grasses) prevent the establishment of grazing lawn grasses in these environments.
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    The long-term effect of elevated COâ‚‚ on grassland biomass production
    (1996) Asary, Melanie; Stock, WD
    This study investigates the influence of elevated CO₂ on grassland biomass production at a naturally elevated CO₂ spring situated on the Bongwan gas fault in Natal. The effect of elevated CO₂ on monocotyledenous (C₄) and dicotyledenous (C₃) above ground plant biomass production and their dominance patterns along a CO₂ gradient were studied. Three 7x7m plots were located 18m, 39m and 73m away from the elevated CO₂ spring. The 18m site was the experimental site, while the other two sites were the controls. The primary focus of the study was to determine the biomass production of monocotyledenous and dicotyledenous plants at the above-mentioned distance from the spring. However, to ascertain possible factors that could influence the increase in biomass production with distance from the CO₂ source, plant nutrient analyses (N and P), soil moisture contents (which could have an effect on plant wateruse efficiency) and carbon isotope discrimination values were determined at the three sites. The results show that elevated CO₂ had a significant effect on the monocotyledenous dry matter production, but had no significant effect on any of the other plants or soil. It was also shown that elevated CO₂ increased the soil water retention capacity as one moves toward the spring, however this result is not confirmed.
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    Phylogenetic and functional growth from diversification in the Cape grass genus Ehrharta Thunb
    (2000) Verboom, George Anthony; Linder, Peter; Stock, WD
    This thesis uses phylogenetic and comparative data to test an hypothesis of adaptive radiation in the Cape grass genus Ehrharta Thunb. sensu stricto. Morphological data and sequence data from two noncoding regions of DNA (lTS1 and trnL-F) are used to produce a phylogenetic hypothesis for the tribe Ehrharteae. Combined analysis of these data sets resolves four principal clades that approximate the genera Ehrharta s. s., Micro/aena, Tetrarrhena and Zotovia and this result thus supports a four-genus classification. Poor resolution and a reduction in branch length at the base of a clade nested within Ehrharta s. s. suggests past radiation. Parsimony-based reconstruction of ancestral habitats and growth form attributes indicates that such radiation is associated with a historical transition to seasonallydrier but more fertile habitats, and the coincident or subsequent evolution of several growth form novelties (e.g. buried and swollen culm bases and annualness). These traits are interpreted to reflect divergent strategies for surviving seasonal drought (Le. via seed or storage). Much higher transpiration rates in summer-deciduous leaves than in perennating culms of two species suggest that the evolution of summer-deciduous foliage was important in the occupation of seasonally-arid habitats. Controlled growth experiments are used to test the hypothesis that divergence in persistence traits is associated with differences in seedling biomass allocation and relative growth rate (RGR). Ehrharta s. s. shows wide variation in seedling RGR and regressions based on phylogenetically independent contrasts suggest that differences are better explained by early biomass allocation than leaf area indices. Species with a high allocation to leaves grow faster and flower sooner, so these traits are typical of seeding species.
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    Response of Cynodon dactylon (L.) Pers. to ammonium and nitrate nutrition
    (1999) Mafa, Paseka; Stock, WD
    Plants that come early in succession predominantly prefer_ ammonium form of nitrogen than nitrate. The hypothesis that Cynodon dactylon (L.) Pers., a grass in the primary succession stage would respond well when supplied with ammonium than nitrate fertiliser was tested. Seedlings of Cynodon dactylon were grown in culture solution and fertilised with either ammonium sulphate or potassium nitrate at ~ continuous concentrations of 200 ppm, 400 ppm and 600 ppm in the growth chamber. In support of my hypothesis, growth of Cynodon dactylon was greater from ammonium than nitrate nutrition in terms of aboveground and total plants yields at 200 ppm and 400 ppm and this was associated with efficient utilisation of this form of nitrogen by this species. Production from the nitrate treatments was restricted and showed no change with increase in external nitrogen supply. Decreased dry weights from the ammonium nutrition at 600 ppm were associated with toxicity of ammonium ions in plant tissues. High levels of nitrogen measured from the nitrate treatments were associated with the soluble nitrogen that was not assimilated for yield increase by this grass, Uptake of ammonium ion was shown to result· in high of uptake phosphorus. This study shows that Cynodon dactylon has the capacity for increased growth under ammonium nutrition while this was limited in the nitrate nutrition. However, response is restricted when excessively fertilised with ammonium nitrogen.
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    Soil factors and competition as determinants of fynbos plant species distributions in the South-western Cape, South Africa
    (1993) Richards, Michael Bruce; Cowling, Richard M; Stock, WD
    The Cape Floristic Region is one of the most species-rich regions of the world. Fynbos, the Mediterranean climate shrubland which comprises the largest part of this region, is characterized by high beta diversity and high edaphic endemism. However, very few quantitative studies of the factors controlling species turnover and community boundaries exist. I used an integrated approach of broad correlation techniques and detailed field experiments, to investigate this. The study site was a landscape on the southern slopes of the Soetanysberg hills, near Cape Agulhas. This area is exceptional in its floristic and edaphic complexity. The first part of this work involved an investigation of the patterns of soil characteristics and the relationship between these and the vegetation patterns. This showed a strong vegetation-environment correlation, particularly with regard to communities. Community boundaries were strongly related to patterns of soil nutrients and physical factors (relating to moisture availability). The second part consisted of detailed studies of the factors controlling the distribution of three pairs of key species (all Proteaceae). Each species is dominant in part of the landscape and, for each species pair, the replacement of one species by the other across the study site, is very distinct. Protea susannae and P. compacta occur in deep and shallow sands respectively. Root morphology, water relations and phenology of adult ( 15 yr-old) plants were studied over two years in the field. Differences between these species constituted habitat-specialization for soils of different depth. A laboratory study of seedling morphology and water-use showed that species differences also exist at the seedling stage and these would be important in determining distribution patterns. Very little is known about the importance of interspecific competition in fynbos communities. A three-year field experiment was set up to investigate its role in determining species distribution patterns across community boundaries and soil gradients. Each of the three pairs of Proteaceae species was grown from seed in cleared plots at three sites along a transect crossing a community boundary. Their growth and survival were studied in relation to site (soil factors), density and interspecific competition (monoculture/mixture). For all species, site factors had an overriding influence on survival. Average individual biomass was determined primarily by site for three species and, for the other species, by density (irrespective of monoculture or mixture). It was concluded that soil factors are a major influence on the distribution of these species and that, while competition has an important role in determining spacing patterns within communities, it has a minor role in determining species distributions.
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    Why is Chasmanthe spp. absent from the archaeological record of the south-western Cape?
    (1999) Hesse, Heidi; Parkington, John; Stock, WD
    In the archaeological record of the south-western Cape one finds corm residues in deposits mostly in the form of the netting which surrounds the corm. These plant residues seem to be a widespread feature in the archaeological record of Later Stone Age sites in Southern Africa. Corm residues nave been identified as mainly representative of the Iridaceae family. The most common geophyte corms identified are those of Watsonia, Babiana, Hexaglottis, Moreae and Gladiolus. Interestingly, Chasmanthe spp. commonly found growing on the west coast, have not been found in archaeological deposits of this area. The carbohydrate-rich corms follow seasonal growth patterns and mainly flowering in spring and early summer and growing during the winter months. Hunter-gatherers must have been familiar with their growth patterns and their palatability so that they could exploit these plants when corms were at their optimum and harvest them before the stored carbohydrates were used up by the plant. Utility plant indices for varying plant-resource components and mineral content analysis for N, P and total non-structural carbohydrates of the corms were calculated. From the results it appears that the reason for Chasmanthe spp. not appearing in the archaeological record is due to choices made by foragers regarding field processing of low utility plant parts (i.e. plant waste), rather than its relative importance or more precisely lack thereof, in the diets of early foragers.