A thesis submitted to the Faculty of Science, University of the Witwatersrand, Johannesburg, in fulfillment of the requirements for the degree of Master of Science. Johannesburg 1990. / No abstract provided.

Open grassy environments in Africa have been key landscapes for the development and evolution of humans and our hominid ancestors for millions of years. These environments have not been static, however, as global climate changes have strongly shaped their nature and location over time. In the modern, at least 80 million people living in Sub-Saharan Africa rely on agriculture and pastoralism within the grasslands and savannas of the Sahel region alone for food security. Devastating droughts and associated famine in the region over the past several decades have highlighted this region’s potential vulnerability to future climate change. Wildfires play a unique and critical role in maintaining Africa’s grasslands and savannas, especially in the Sahel region. Emissions from these fires have additional ramifications for the Earth’s radiative balance and global cycles of carbon and nutrients. As populations in Africa rise over the coming century from ~1.3 billion to 4 billion people by 2100, increasing demand for food, rising temperatures, and highly uncertain changes in rainfall and wildfire patterns are poised to put the people and ecosystems of this region in jeopardy. In the face of potentially novel environmental conditions resulting from anthropogenic climate change, this research aims to better understand the long-term interconnections of climate, ecology, and human presence in Northwest Africa and how these linkages may vary under broad shifts in climate. Accurate projections of future climate and ecosystem change not only require the mechanistic understanding of climate forcings and climate-ecosystem interactions that can be gleaned from modern relationships, but also information about how these interactions may vary as a function of changes in the background climate state itself (on centennial to million year timescales). Highly spatially-resolved satellite measurements relevant for asking such questions only extend back a few decades and thus only provide a limited perspective on whether or not modern climate-ecosystem interactions are stationary through time. This thesis is focused on developing and applying paleoclimate reconstruction techniques to generate new records of hydroclimate, ecosystem structure, and fire activity in Northwest Africa over a broad set of time scales. These new records are used to assess the governing controls of climate variability and evaluate the evolution of climate-ecosystem interactions across a diversity of background climate states. We seek specifically to (1) improve our understanding of the natural climate forcings that dictate changes in Northwest African monsoon rainfall, (2) evaluate how changes in rainfall and other climate parameters––namely atmospheric CO₂ concentrations––together affect ecosystem distributions and compositions in Northwest Africa, (3) ground-truth the use of increasingly popular molecular proxies of fires applied to marine sediment archives, (4) assess the relative environmental and human controls on fires in Northwest African savannas over time, and (5) develop interpretive frameworks for understanding multiproxy records of environmental changes in Northwest Africa to draw conclusions about how climate-ecosystem interactions may have evolved over time. To address these goals, this dissertation is broken down into four chapters. The first two chapters focus on the orbital-scale to multimillion year forcings in the climate system that control the strength and tempo of the Northwest African monsoon and how these changes impact the distributions and compositions of ecosystems in the region over time. In both Chapters 1 and 2, we develop new reconstructions of hydroclimate using the hydrogen isotopic composition of plant-waxes and extraterrestrial 3He normalized dust fluxes from marine sediment core MD03-2705 taken off the coast of Mauritania along the Northwest African margin. We further reconstruct ecosystem change using the carbon isotopic composition of plant-waxes. Chapter 1 is centered on the late-Pleistocene while Chapter 2 takes a wider perspective and explores long-term trends in Northwest African hydroclimate and vegetation structure from the Pliocene to the late-Pleistocene. In the second half of this work, the focus is narrowed to center the role of fire in Northwest African savannas and how the nature of burning in this region has changed since the last glacial maximum. In Chapter 3, we use atmospheric back trajectory modeling and a transect of marine core sediments taken aboard the research vessels Vema and Conrad that spans the southern European to southern west African margin to test if molecular biomarkers of vegetation (plant-wax n-alkanes and pentacyclic triterpene methyl ethers) and fires (pyrosugars and polycyclic aromatic hydrocarbons) preserved in marine sediment archives capture modern distributions of ecosystems and biomass burning on the landscape. In Chapter 4, we generate new records of the fire history of Northwest Africa from the last glacial maximum to the late-Holocene from marine sediment core OCE 437-7 GC68. We compare the relative influences of changes in rainfall, ecosystem structure and human activities on fire across the most recent deglaciation and ‘Green Sahara’ period. From these new records, we are able to draw several conclusions. In Chapter 1 we find that the location, timing, and intensity of northwest African monsoon rainfall is controlled by low-latitude insolation gradients and that while increases in precipitation are associated with the expansion of grasslands into desert landscapes, changes in pCO2 predominantly drive the C3/C4 composition of savanna ecosystems. In Chapter 2 we observe that low latitude insolation gradients best explain both the tempo and amplitude of orbital scale variations in Northwest African rainfall over the last five million years, however strengthening sea surface temperature gradients in the Atlantic Ocean during the mid-Pleistocene likely led to a precipitous and sustained decline in monsoon strength ~900 thousand years ago independent of any change to orbital insolation forcing. Furthermore, changes in the relationship between rainfall and vegetation in Northwest Africa can be used to track changes in the northward extent of ecosystems, augmenting previous pollen-based reconstructions, which together show shifts in ecosystem distributions over the Plio-Pleistocene likely related to changes in ecosystem disturbances and climate-vegetation interactions. In Chapter 3 we show that by accounting for the effects of long-range transport of biomarkers, good agreement is found between ecosystem composition and biomass burning patterns on the African continent and the distribution of terrestrial plant and fire biomarkers in marine core top sediments. This provides strong justification for applying molecular indicators of fires to the paleorecord. In Chapter 4, we show that rainfall is the dominant natural control on the amount of biomass burned in Northwest African savannas, but increased human presence and land-use change during the mid- to late-Holocene likely fundamentally changed the fire regime of Northwest Africa to this day.

As samambaias do gênero Pteridium caracterizam-se pelas largas frondes e por um sistema de rizomas subterrâneos que possibilita sua rápida expansão. Apresentam elevada produção de biomassa ao longo do ano, que aumenta a incidência de incêndios, e ainda liberam substâncias químicas consideradas alelopáticas. Atualmente, são conhecidas como plantas-problema, pois vêm se expandindo e ocupando grandes áreas em diversas partes do mundo, causando impacto econômico e ecológico. Nesse contexto, este estudo teve por objetivo geral a compreensão do impacto da invasão por Pteridium arachnoideum sobre a vegetação de cerrado e a elucidação dos mecanismos por meio dos quais vem sendo lentamente revertido o processo de invasão na área de estudo. Para tanto, analisamos áreas de cerradão invadidas há mais de quatro décadas na Estação Ecológica de Assis (EEcA), no sudoeste do estado de São Paulo. Analisamos a composição florística e estrutura da comunidade em uma área invadida dentro da EEcA. Avaliamos os componentes do estrato arbóreo e regenerante da comunidade, a fim de verificar quais as espécies que conseguiram ultrapassar as barreiras físicas e químicas impostas pela presença da samambaia. Para tanto, comparamos a vegetação da área invadida com uma área adjacente não invadida, com ambiente e histórico de perturbações semelhantes. Utilizamos 100 pontos quadrantes para amostragem da composição florística e, para caracterização da estrutura da comunidade, alocamos 15 parcelas de 10 m x 30 m para amostrar o estrato superior, dentro das quais foram instaladas sub-parcelas de 2 m x 30 m para o estrato intermediário e de 2 m x 2 m para o estrato inferior. Medimos a cobertura das copas das árvores dentro das parcelas e estimamos a porcentagem de cobertura do solo por Pteridium. As espécies que conseguiram ocupar a área no início da invasão são tolerantes à sombra e com ritmo de crescimento rápido, características que possibilitaram que tais espécies ultrapassassem a barreira de samambaia e se estabelecessem na área. Já as espécies do estrato inferior se assemelham às da área não invadida, indicando que está havendo uma substituição das espécies na comunidade vegetal. A baixa densidade das árvores na área invadida diminui a competição entre os indivíduos, que, por sua vez, investem em aumento de tamanho, sendo consideravelmente maiores do que as árvores do cerradão não invadido. Essas árvores, que formam o estrato arbóreo atualmente, estão facilitando a regeneração natural de espécies arbóreas nativas e, assim, revertendo, lentamente, o processo de invasão. Testamos quais variáveis, relacionadas às funções ecológicas e aspectos estruturais das árvores de grande porte que se estabeleceram nas áreas invadidas, estão favorecendo as plantas em regeneração sob suas copas. Para tanto, amostramos os indivíduos maiores que 50 cm sob a copa de árvores sistematicamente selecionadas, segundo atributos funcionais e estruturais. Verificamos que as árvores que possuem copas mais densas e perenifólias apresentaram mais regenerantes sob suas copas. A resiliência característica do cerrado tem possibilitado que as áreas invadidas consigam se recuperar, podendo se assemelhar futuramente às áreas de cerradão da EEcA, porém muito lentamente. Ações de manejo que almejam a restauração dessas áreas mais rapidamente devem focar seus esforços na eliminação do Pteridium e/ou na introdução de espécies que possuam as características das árvores que atuam como facilitadoras da regeneração. / The genus Pteridium comprises bracken species recognized by large fronds and a rhizome system that allows their fast expansion. Bracken presents an elevated biomass production throughout the year, that increases fire occurrence and release chemical compounds that are considered allelopathic. Nowadays, species of the genus Pteridium are well known as problem-species, due to their expansion and occupation of large areas around the world, causing great economic and ecological impacts. Aiming at the comprehension of bracken invasion over cerrado vegetation, we studied its impact over the plant community and, also, the slow natural regeneration process of cerrado recovery after invasion. We analyzed savanna woodland areas that have been invaded for over four decades, at Assis Ecological Station (EEcA), in southwestern São Paulo State. We analyzed the floristic composition and the plant community structure in an invaded area, compared to a non invaded patch of savanna vegetation. Components of the arboreal and regeneration strata were analyzed, in order to verify which species managed to pass by the physical and chemical barrier imposed by bracken. We assessed 100 points to assemble the floristic composition, using the quarter method, and for the community structure we used 15 plots of 10 m x 30 m to assemble the superior strata. The intermediate layer was assessed by sub-plots of 2 m x 30 m and the inferior strata using 2 m x 2 m sub-plots. We measured the canopy cover and also bracken cover inside the plots. The arboreal species first occupying the invaded area are shadow tolerant and fast growing, attributes which allowed them to overtake the bracken layer and establish. Nowadays, the invasive species has been replaced by a high number of arboreal species, the inferior strata being floristically similar to the area not invaded. The low density of adult trees in the invaded area reduce the competition among individuals that end up investing in growth, with greater size compared to those trees in the non invaded area. These large trees function as nurse trees, facilitating other species to establish under their canopies. We tested which variables related to the ecological functions and tree structure are favouring the understory, in order to comprehend the ecological processes and interactions that regulate the assembly rules of the invaded community being recovered. We assembled all individuals from arboreal species over 50 cm high growing under the projection of nurse trees canopy. These nurse trees were systematically selected, for the basis of functional and structural attributes. Understory density and richness were higher under trees with dense and permanent shadow, and that was the attribute better explaining the recovery process. The high resilience of savanna have helped the recovery of invaded areas. This process, however, has been very slow. Interventions whiling to restore those areas should be focused on bracken eradication and/or introduction of those species that can facilitate the natural regeneration.

Savannas are globally important ecosystems characterized by the coexistence of trees and grasses. Woody plants, which are slow-growing dominant life forms, influence the physiognomic structure and function of savanna ecosystems. Their density and distribution provides sustenance to a vast and unique savanna biodiversity, by forming a major source of food material to large mammalian herbivores, sheltering them and through their facilitation of diverse plant species. Savanna tree existence is strongly affected by factors that determine their sapling recruitment. We defined „sapling‟ as a young tree, in the first season of its growth, which does not depend on cotyledonary reserves (=seedling stage) and relies on external resources to grow further. Sapling recruitment may strictly be defined as the progression of a young plant from seedling to sapling stage. However, we believe that savanna tree saplings, present within the grass layer in the initial years of their growth, are equally vulnerable to environmental stresses. This study examines the factors affecting tree sapling establishment in a humid savanna (1250 mm mean annual precipitation). Additionally, the effects of fire were tested in a greenhouse experiment. Dominant species from humid savannas (> 1000 mm MAP), Acacia karroo, Acacia sieberiana, Schotia brachypetala and Strychnos spinosa, and mesic savannas (approx. 750 mm MAP), Acacia nigrescens, Acacia tortilis, Colophospermum mopane and Combretum apiculatum, were studied. In this thesis I examined the effects of resource availability (water, nutrients and light), disturbances (fire and herbivory) and competition (grass) on the sapling ecology of these species. Sapling recruitment and growth were assessed in terms of survival and aboveground growth responses, i.e. total biomass, stem growth rates (used as proxy measures for assessing persistence) and leaf biomass proportion (important for producing root reserves necessary to resprout). I studied the effects of fire and a nutrient gradient on survival and growth of four Acacia species in the presence of grass competition, in a controlled greenhouse experiment. Generally, Acacias invest in defenses after herbivory. I also determined their physical and chemical defense investments in this experiment. Sapling survival was not influenced by nutrients but highly varied among the species due to fire, indicating that fires may have a differential effect on species composition at a landscape scale. Intermediate levels of nutrients were found to be beneficial for sapling growth than high and low levels. This may be due to an increase in grass competition at higher levels of nutrients. Fires did not have a positive influence on sapling defence investment. To evaluate the relative importance of resource availability on sapling tree recruitment and its interactions with grass competition, I tested the effects of water (frequent irrigation vs. rainfall), shade (presence vs. absence), nutrients (addition vs. no addition) and grass competition (presence vs. absence) on sapling survival and growth under controlled field conditions in a humid South African savanna. Treatments did not have an effect on sapling survival, indicating that mortality is not defined by resource availability and grass competition in humid savannas. Shade had the greatest negative effect on sapling growth, suppressing the beneficial effects of nutrients and absence of grass competition. Nutrient limitation and grass competition had a relatively small influence on savanna sapling growth. Frequency of water availability had no effect on sapling growth, perhaps owing to high rainfall experienced over the experimental period. Therefore, canopy shade can be considered to be an important driver of tree dynamics in humid savannas with some degree of influence by nutrient availability and grass competition. The effects of clipping (i.e. simulated herbivory of grass and tree saplings) as influenced by nutrient availability and grass competition were examined on sapling survival and growth of all study species in a humid savanna. None of the treatments had an effect on sapling survival. This signifies that herbivory alone cannot significantly decrease plant density in humid savannas. However, tree saplings grew taller with a reduction in diameter and overall biomass, implying that saplings may become more susceptible to fires after herbivory. Nutrient addition and grass competition in general had a positive and negative effect, respectively, on sapling growth. This response was prominent in the stem length growth rates of defoliated saplings of one humid and two mesic species. These results imply that clipping (or herbivory) is the major factor reducing sapling vigour to establish, but is affected by both grass competition and nutrient availability. This study shows that fire has a differential effect on sapling survival of different species, particularly between humid savanna species. Light interception among all other resources limits the recruitment of saplings into adult size classes. Clipping, nutrient availability and grass competition had a relatively small direct effect, but may interact with other factors to alter sapling establishment dynamics. Wet-season droughts in humid savannas are not a hindrance to tree establishment because sapling survival was not dependent on frequency of rainfall. Thus, in humid savannas, fires can have a major impact on tree species density and composition while canopy shade has a very high potential to alter tree distribution. / Thesis (Ph.D.)-University of KwaZulu-Natal, Pietermaritzburg, 2013.

Considerable understanding of the functioning of semi-arid systems is still needed to enable range managers to formulate management policies, with a degree of confidence. Long term data sets that encompass a wide range of interactions between the various major components of a semi-arid system (vegetation, herbivory, animal performance, landscape and rainfall), are unfortunately rare but essential to provide sufficient depth of data to adequately test various hypotheses about rangeland dynamics. This study comprises an analysis of a ten year data set derived from two cattle stocking rate trials in the semi-arid savanna of KwaZulu/Natal. Statistical analysis revealed that the most pronounced and rapid compositional change was due to rainfall, but that stocking rates between 0.156 and 0.313 AU ha ¯¹ had an important effect as well. Sites on steeper slopes with heavy stocking rates, exhibited the greatest amount of compositional change between 1986 and 1996 (40 Euclidean points in heavy stocking rate treatments on slopes vs 21-24 Euclidean points in heavy stocking rate treatments on flatter land, or 11-24 Euclidean points in low stocking rate treatments). Heavy stocking rates in conjunction with low rainfall tended to cause decreases in densely tufted perennial grasses and increases in annuals and weakly tufted perennials. Multiple regression analysis revealed that seasonal peak grass production (measured as disc height) declined between 1986 and 1996 only at those sites on steeper slopes with heavy stocking rates. The camps that declined in productivity also underwent the greatest degree of compositional change. The decline in grass productivity in certain high stocking rate camps did not translate into a decline in cattle performance. Depending on rainfall, cattle gained on a seasonal basis between 112 and 241 kg at low stocking rates, 82 and 225 kg at medium stocking rates and 84 and 217 kg at high stocking rates Rainfall, compared with stocking rate, accounted for the greatest amount of variance in seasonal peak grass production and cattle performance. Cattle performance had a strong curvilinear response to rainfall, which also proved to be a better predictor of cattle performance than grass biomass. There were no clear trends in soil physical and chemical characteristics between low and high stocking rates that could provide convincing evidence that loss of soil nutrients was an important mechanism of range degradation. The total standing crop of plant nitrogen but not of phosphorus tended to decline at high stocking rates. Plant nutrient and van Soest analyses suggested that forage quality was higher at heavy stocking rates. The results of this study generally supported traditional concepts of rangeland dynamics with regard to rainfall and grazing effects on compositional change and seasonal grass production. The results were important in being able to show quantitatively that heavy stocking rates result in a decline in grass production and that this effect is dependent on an interaction between stocking rate and landscape position or slope, and that there is a link between a decline in seasonal grass production and compositional change. The results also highlighted areas for future research that would be useful for furthering our understanding of various aspects of rangeland dynamics and mechanisms of degradation. / Thesis (M.Sc.)-University of Natal, Pietermaritzburg, 1998.

Savanna degradation is an environmental problem occurring in most countries around the world and it poses threats to biodiversity conservation, the food industry, and other economic sectors. According to FAO, South Africa’s rangelands exhibit the highest rate of fragmentation in comparison to range ecosystems in neighbouring countries including Lesotho and Swaziland, and consensus among researchers is that communal rangelands are more degraded than commercial rangelands. Although researchers and communities have identified the occurrence of land degradation in communal savannas at a local scale, land degradation has been poorly estimated because little has been done to quantify the extent and dynamics of perceived and observed changes associated with land degradation. The main goal of this study is to provide empirical insights on the direction of changes in the communal savannas of Nkonkobe Local Municipality in order to inform policy formulation and implementation. Additional to the communal sites is a private farm included for comparative analysis of trends in communal and commercial savannas. Landsat imagery was used to map, assess, and quantify the extent of land degradation in Nkonkobe Local Municipality, over a period of 30 years between 1984 and 2014. Field investigations were undertaken in June 2015 to acquire reference data to guide supervised classification of Landsat images. Three algorithms (Mahalanobis-distance, Minimum-distance, and Maximum likelihood classification) were compared to identify a classifier that produced the best results. The maximum likelihood classifier produced the best results with classification accuracy levels of 95.24 percent, 89.66 percent, and 95.65 percent for Honeydale Farm, Thyume, and Sheshegu respectively. Regression analysis revealed that both communal and private lands have experienced statistically significant increases in bush encroachment and decreases in surface water. Communal savannas have been confronted more by expansion of built-up area, decrease in open grassland, abandonment of arable land, soil erosion, and a steady invasion by Acacia Karroo compared to the privately owned commercial farm. The land cover changes measured through this investigation suggest an environmental shift that threatens biodiversity and agricultural activity. The study provides empirically informed insights about the direction to which these savannas are changing with the hope that the findings will prompt formulation and implementation of effective policies.

As samambaias do gênero Pteridium caracterizam-se pelas largas frondes e por um sistema de rizomas subterrâneos que possibilita sua rápida expansão. Apresentam elevada produção de biomassa ao longo do ano, que aumenta a incidência de incêndios, e ainda liberam substâncias químicas consideradas alelopáticas. Atualmente, são conhecidas como plantas-problema, pois vêm se expandindo e ocupando grandes áreas em diversas partes do mundo, causando impacto econômico e ecológico. Nesse contexto, este estudo teve por objetivo geral a compreensão do impacto da invasão por Pteridium arachnoideum sobre a vegetação de cerrado e a elucidação dos mecanismos por meio dos quais vem sendo lentamente revertido o processo de invasão na área de estudo. Para tanto, analisamos áreas de cerradão invadidas há mais de quatro décadas na Estação Ecológica de Assis (EEcA), no sudoeste do estado de São Paulo. Analisamos a composição florística e estrutura da comunidade em uma área invadida dentro da EEcA. Avaliamos os componentes do estrato arbóreo e regenerante da comunidade, a fim de verificar quais as espécies que conseguiram ultrapassar as barreiras físicas e químicas impostas pela presença da samambaia. Para tanto, comparamos a vegetação da área invadida com uma área adjacente não invadida, com ambiente e histórico de perturbações semelhantes. Utilizamos 100 pontos quadrantes para amostragem da composição florística e, para caracterização da estrutura da comunidade, alocamos 15 parcelas de 10 m x 30 m para amostrar o estrato superior, dentro das quais foram instaladas sub-parcelas de 2 m x 30 m para o estrato intermediário e de 2 m x 2 m para o estrato inferior. Medimos a cobertura das copas das árvores dentro das parcelas e estimamos a porcentagem de cobertura do solo por Pteridium. As espécies que conseguiram ocupar a área no início da invasão são tolerantes à sombra e com ritmo de crescimento rápido, características que possibilitaram que tais espécies ultrapassassem a barreira de samambaia e se estabelecessem na área. Já as espécies do estrato inferior se assemelham às da área não invadida, indicando que está havendo uma substituição das espécies na comunidade vegetal. A baixa densidade das árvores na área invadida diminui a competição entre os indivíduos, que, por sua vez, investem em aumento de tamanho, sendo consideravelmente maiores do que as árvores do cerradão não invadido. Essas árvores, que formam o estrato arbóreo atualmente, estão facilitando a regeneração natural de espécies arbóreas nativas e, assim, revertendo, lentamente, o processo de invasão. Testamos quais variáveis, relacionadas às funções ecológicas e aspectos estruturais das árvores de grande porte que se estabeleceram nas áreas invadidas, estão favorecendo as plantas em regeneração sob suas copas. Para tanto, amostramos os indivíduos maiores que 50 cm sob a copa de árvores sistematicamente selecionadas, segundo atributos funcionais e estruturais. Verificamos que as árvores que possuem copas mais densas e perenifólias apresentaram mais regenerantes sob suas copas. A resiliência característica do cerrado tem possibilitado que as áreas invadidas consigam se recuperar, podendo se assemelhar futuramente às áreas de cerradão da EEcA, porém muito lentamente. Ações de manejo que almejam a restauração dessas áreas mais rapidamente devem focar seus esforços na eliminação do Pteridium e/ou na introdução de espécies que possuam as características das árvores que atuam como facilitadoras da regeneração. / The genus Pteridium comprises bracken species recognized by large fronds and a rhizome system that allows their fast expansion. Bracken presents an elevated biomass production throughout the year, that increases fire occurrence and release chemical compounds that are considered allelopathic. Nowadays, species of the genus Pteridium are well known as problem-species, due to their expansion and occupation of large areas around the world, causing great economic and ecological impacts. Aiming at the comprehension of bracken invasion over cerrado vegetation, we studied its impact over the plant community and, also, the slow natural regeneration process of cerrado recovery after invasion. We analyzed savanna woodland areas that have been invaded for over four decades, at Assis Ecological Station (EEcA), in southwestern São Paulo State. We analyzed the floristic composition and the plant community structure in an invaded area, compared to a non invaded patch of savanna vegetation. Components of the arboreal and regeneration strata were analyzed, in order to verify which species managed to pass by the physical and chemical barrier imposed by bracken. We assessed 100 points to assemble the floristic composition, using the quarter method, and for the community structure we used 15 plots of 10 m x 30 m to assemble the superior strata. The intermediate layer was assessed by sub-plots of 2 m x 30 m and the inferior strata using 2 m x 2 m sub-plots. We measured the canopy cover and also bracken cover inside the plots. The arboreal species first occupying the invaded area are shadow tolerant and fast growing, attributes which allowed them to overtake the bracken layer and establish. Nowadays, the invasive species has been replaced by a high number of arboreal species, the inferior strata being floristically similar to the area not invaded. The low density of adult trees in the invaded area reduce the competition among individuals that end up investing in growth, with greater size compared to those trees in the non invaded area. These large trees function as nurse trees, facilitating other species to establish under their canopies. We tested which variables related to the ecological functions and tree structure are favouring the understory, in order to comprehend the ecological processes and interactions that regulate the assembly rules of the invaded community being recovered. We assembled all individuals from arboreal species over 50 cm high growing under the projection of nurse trees canopy. These nurse trees were systematically selected, for the basis of functional and structural attributes. Understory density and richness were higher under trees with dense and permanent shadow, and that was the attribute better explaining the recovery process. The high resilience of savanna have helped the recovery of invaded areas. This process, however, has been very slow. Interventions whiling to restore those areas should be focused on bracken eradication and/or introduction of those species that can facilitate the natural regeneration.

Spiders were sampled at Mpala Research Centre, Laikipia, Kenya by pitfall-trapping and sweep-netting from May 2001 to July 2002, at a Kenyan Long-term Exclosure Experiment. The aim was to establish species composition, checklist and examine spider responses to disturbances caused by cattle, megaherbivores (giraffe and elephants) and mesoherbivores (other ungulates) by looking at three levels of resolution, namely the overall community, guilds and individual species. This is the first controlled replicated experimental study on the effects on invertebrates (spiders) by different land uses (access by large herbivores). A total of 10,487 individuals from 132 species belonging to 30 families were recorded. The family Salticidae had the highest number of species (24), followed by Gnaphosidae (20), Araneidae and Lycosidae (15 each), Theridiidae and Thomisidae (8 each) and Zodariidae (4). Most of the other families had fewer than 4 species. Throughout the study period, species not previously sampled emerged after rainfall peaks. Exclosure treatments affected plant cover, spider diversity and total species mainly through the effects of cattle, whose presence significantly reduced relative vegetation cover. An increase in vegetation cover significantly increased the diversity, total species and species evenness of the overall spider community (total samples data set). Megaherbivores and mesoherbivores had no effects on overall spider diversity. Relative vegetation cover explained approximately 20-30% of variation in community diversity, species richness and species evenness. At the guild level of resolution, the exclosure treatments had no significant effects on diversity, species richness and species evenness of web builders, plant wanderers and ground wanderers. Plant wanderers were significantly and positively correlated with relative vegetation cover, which explained 17% of variation in their diversity. Six individual species responded strongly and in contrasting ways to the same environmental variables, indicating that this level was more sensitive to environmental changes than guilds or the overall spider community. Spider diversity, relative vegetation cover and rainfall varied at a temporal scale of months and not at a spatial scale of hundreds of metres. Only species diversity and species richness from sweep-netting samples and total species from pitfall-trapping varied significantly at a spatial scale of hundreds of metres. Ordination analysis revealed that sweep-netting samples were a better indicator of grazing impacts than pitfalltrapping or combined samples and grouped to reflect cattle grazing, non-cattle grazing and to a small extent the control treatments. Other ordination analyses showed that only samples from sweep-netting and not from pitfall-trapping, were spatially partitioned at a scale of hundreds of metres. This study concludes that the spider fauna of black cotton soil habitats is rich and useful for environmental monitoring and that monitoring of several individual species as indicator of grazing impacts in savanna could be useful and relatively easy.

The savanna is an important biome, which is under threat from land transformation, and it is therefore a focus for conservation planning. Yet, the invertebrate fauna of this biome is poorly documented and hence there is a need to provide baseline data for this component of biodiversity. This project aimed to provide relevant information that can be used by conservation planners and ecologists, by recommending a sampling strategy for the collection of specific taxa for savanna invertebrate surveys. The effectiveness and efficiency of a sampling strategy using passive and active sampling methods was assessed to provide recommendations for a multi-taxa approach to sampling invertebrates in a savanna ecosystem. In the collection of data, volunteers assisted and they were evaluated in comparison with experienced researchers to assess the effectiveness, efficiency and benefits of using volunteers to carry out multi-taxa invertebrate surveys. In addition, cross-taxon congruency and congruency across taxonomic levels were assessed between nine invertebrate taxa, to select potential surrogates to reduce biodiversity survey costs for conservation planning. Fieldwork was carried out in the Mkhuze Game Reserve (27.67°S:32.27°E, 400km2 ), Phinda Private Game Reserve (27.78°S:32.35°E, 140km2 ) and False Bay Park (27.94°S:32.38°E, 25km2 ) in north-eastern Kwazulu-Natal, South Africa. Forty-three different sites were sampled between November 2002 and March 2005 (summer months). Twenty of these sites were re-sampled across years and in different months during the summer season, giving 77 sampling events. Fifty-four volunteers recruited by the Earthwatch Institute assisted in the collection of data. Lepidoptera, Hymenoptera (Apoidea), Diptera (Asilidae, Bombyliidae), Neuroptera, Odonata, Hemiptera (Cicadellidae), Coleoptera (Cetoniinae, Scarabaeinae), Orthoptera, Blattodea, Isoptera, Araneae (Araneidae, Thomisidae, Oxyopidae), Scorpionida, Myriapoda (Diplopoda, Chilopoda), Mollusca and Annelida were sampled using four active searching methods (transects, tree beating, leaf litter and sweep sampling) and two passive methods (pan traps and baited traps). In its entirety, this project sampled 50 558 individuals from 797 invertebrate species and an extensive database consisting of 33 257 records now exists. A standardised sampling protocol is described for the effective sampling of multiple invertebrate taxa in a savanna biome and recommendations are made for improving the efficacy and completeness of invertebrate surveys based on the application of species accumulation models. Restrictive active searching methods (quadrats) were found to be more effective for sampling epigaeic invertebrates and should be used in conjunction with leaf litter samples. Flying and plant-dwelling invertebrates should be sampled using a range of sampling methods which include baited, malaise and pan traps, active searching along transects and vacuum sampling. I suggest over 75% of the Lovel/, s.1. - MSc. Thesis i ii total estimated fauna to be a satisfactory and realistic level of inventory completeness for making valid comparisons between regions and across sites. Volunteers sampled lower rates of species accumulation, species richness and unique species when using timed, active search methods. Nevertheless, volunteers and researchers were shown to perform equally well when using un-timed, active searching methods. Previous experience or knowledge of scientific method was beneficial when researchers assessed the perceived usefulness of volunteers to researchers for carrying out fieldwork. The project experience raised the volunteers' environmental awareness, knowledge about biodiversity, invertebrates and conservation research, and enabled volunteers to participate in or design locally relevant conservation based projects on their return home. Cross-taxon congruencies were observed. However, relationships were weak and potential surrogates could not be selected. The use of higher taxonomic levels to represent species shows good potential as a surrogate but only in species-poor genera or families. The use of species density to determine congruency and select surrogates is likely to produce different results to those produced by community similarity. Furthermore, when selecting surrogates from congruency assessments an optimal p-value greater than 0.75 should be required. Below this value, the relationship is likely to be weak and if used as a surrogate misinterpretation may occur. / Thesis (M.Sc.)-University of KwaZulu-Natal, Pietermaritzburg, 2006.

A thesis submi.tted to the Faculty of Science, University of the witwatersrand, Johannesburg I in the fulfillmen,,;"o:f' 't\ :he requirements of the Degree of Magister Scienta~. June 1992 / The present study was undertaken; withirl the South African " savannas, to provide "insight into a j;unctional classification of aavanna plants using ecophY$iologiLcal charact~:t's.THe pri.mary r.:>bjective of this study Was to investigate the vari.ation of these tt'aits throughout: the savanna, aridto relate this variation to plant avail.able moisture and nU~l'ie~~s• !t was conclu.ded that~ 1) no formal or specialized strategies have evolved within a number of the study sites, .2) unlike the woody component I neither divergellce nor convergence was demonstrated within the grass layer, c' 3) plant aVailable nutrients did not appear to be a major determinant of either component. Although plant available moistur~ proved to be unimportant in the woody layer, it did playa role as a determinant of the grass layer, and 4) constancy of the plant traits was not demonstrated to \": OCCllr over the gr~~ing season. A succeisf',\lclassification' would require the components to be separat~pl specific determinan.ts be identified for each component, and an element of time be included into both edaphic and biotic measurements.