Browsing by Author "Gillson, Lindsey"

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    Benchmarks for the future: long-term vegetation change derived form palaeoecological techniques in West-Coast Renosterveld, South Africa
    (2014) Forbes, Cherie Janine; Gillson, Lindsey; Hoffman, Timm
    This study focuses on long-term vegetation changes in West-Coast Renosterveld in the winter rainfall zone of the Cape Floristic Region (CFR), Western Cape, South Africa. Renosterveld is an evergreen, fire-prone Mediterranean-type shrubland consisting of asteraceous elements, grasses and geophytes. It is restricted to fertile, fine-grained soils and more than 90% of this vegetation type has been transformed by agriculture. High richness of endemic geophytes in particular gives remaining fragments an irreplaceable conservation value. Future climate projections for the region suggest a general warming of 1.5-3.5 °C, a 30-50% decrease in precipitation, an increase in drought periods and shorter rainy seasons with important consequences for the vegetation of the CFR. There is limited information regarding the response of Renosterveld to past climate change and land-use disturbance and there is much debate about the pristine composition of Renosterveld vegetation. The lack of Renosterveld environmental history with appropriate pre-colonial or pre-Iron age benchmarks makes it difficult to build evidence-based arguments for conservation management and restoration. Studying the history of Renosterveld in the late Holocene may provide information on responses to past warmer climates, and the more recent effects of anthropogenic disturbance. The aim of the present study was to reconstruct vegetation change, fire regime and changes in herbivory over the past ca. 1300 years at a West-Coast Renosterveld site in the Western Cape and to interpret these findings in light of known climate history and land-use change with a specific focus on the effects of disturbance by fire and herbivory. Findings were explored in relation to resilience theory, and the implications for conservation management and restoration. The following research questions were investigated. How has vegetation, fire and herbivory changed over time in West-Coast Renosterveld vegetation? How do changes in vegetation relate to climate and land-use disturbance and what are the main drivers of change? What are the links to theoretical frameworks such as resilience theory? Are recent changes unprecedented and is there evidence of a threshold response to climate and disturbance? (4) What are the implications of these findings for conservation management and restoration such as present day management of fire and herbivores?
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    Ecological resilience at semi-arid and temperate boundaries of the Mediterranean-type Fynbos Biome, South Africa, during the Holocene
    (2016) Macpherson, Allan J; Gillson, Lindsey; Hoffman, Timm
    Mediterranean-type ecosystems are amongst the most vulnerable to global change. Threats from desertification are projected due to rapid expansion of adjacent semiarid systems. Changes in fire frequency and intensity can alter ecosystem composition and structure, and potentially facilitate transitions between alternative stable states. Given the outstanding biodiversity of the Mediterranean-type fynbos biome in the Greater Cape Floristic Region (GCFR) of South Africa, understanding of the longterm impacts of global change are particularly important. In this study, palaeoecological data are used to assess the effects of changes in climate, fire and land use on vegetation at the semi-arid and temperate margins of the fynbos biome. Previous palaeoecological studies have shown stable fynbos during the recent geologic past, which restricts interpretation of the long-term ecological processes that determine biome resilience. This study sourced sediment cores directly from presentday fynbos-succulent karoo (semi-arid) and fynbos-afrotemperate forest biome boundaries to emphasise ecological dynamics. Fossil pollen, spores and charcoal were extracted from radiocarbon dated sediment cores to provide proxies for vegetation, hydrology, large herbivore abundance and fire. Constrained hierarchical clustering (CONISS), optimal sequence splitting by least-squares, and Non-metric Multidimensional Scaling (NMDS) was applied to the fossil data to identify distinct assemblages in the record, and to further elucidate ecosystem trajectories through time. At the semi-arid boundary at Groenkloof (5,500 cal yrs BP - near present), decreased moisture and fire from 4,000-735 cal yrs BP allowed colonisation of fynbos by a possible 'no-analogue' community dominated by Asteraceae and Poaceae. From 735 cal yrs BP however, climatic amelioration allowed fynbos to re-establish. The system can therefore be viewed as resilient through a capacity for 'recovery' and persistence through turnover in internal composition of fynbos taxa. This sensitive response to climatic forcing reflects the dominant influence of physiological stress at the semiarid limits of Mediterranean-type ecosystems, as well as a Gleasonian type community composition with loose species associations. In contrast, ecosystem
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    Exploring the significance of land-cover change in South Africa
    (2012) Gillson, Lindsey; Midgley, Guy F; Wakeling, Julia L
    Changing land cover is a phenomenon that is growing in magnitude and significance, both globally1 and in South Africa2 . Changes in land cover include the conversion of natural vegetation to agricultural crops and forest plantations, changes to natural vegetation through bush encroachment and overgrazing, soil erosion, invasion by alien plant species, and accelerating urbanisation. Land-cover changes increasingly relate to climate and atmospheric changes in ways that are currently poorly understood but potentially significant, especially in terms of compromising or enhancing the delivery of vital ecosystem services from rangelands, agricultural croplands, water catchments and conservation areas. Land-cover change is being studied in different ways, and at different scales, by ecologists, plant physiologists, applied biologists and social scientists. A core group of scientists has recently formed the Land Cover Change Consortium (LCCC), which aims to begin integrating the results of the varied approaches to studying land-cover change, and to guide future research directions, with a view to building a better science base for informing policy and management decision-making in conservation, agriculture and environmental management. The group has developed a simple conceptual outline that links field experiments, observation and monitoring, modelling and prediction of land-cover change (Figure 1), and is currently developing a funding base to support collaboration in addressing fundamental questions about how ecosystems might change in the coming decades, in training new graduates, and in communicating effectively with policymakers. The LCCC hopes to provide a theoretical and practical multidisciplinary platform for scientific collaboration on global change issues that also includes different stakeholder groups and contributes to policy and decision-making. Multidisciplinary collaboration is notoriously challenging, but holds great promise for novel insights.
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    Extinctions: Past and Present Week 5 - Ecosystem pressures
    (2017-03-17) Chinsamy-Turan, Anusuya; Gillson, Lindsey
    In this video, Professor Anusuya Chinsamy-Turan interviews Professor Lindsey Gillson, an ecologist studying the long-term conservation of ecosystems, about her concerns regarding the Anthropocene. She explains that extinctions of modern biota are being caused by many different factors.
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    Holocene vegetation history and environmental change in the forest-grassland mosaic of the Central Highlands of Madagascar
    (2022) Razafimanantsoa, Andriantsilavo Hery Isandratana; Gillson, Lindsey; Bond, William John
    The origin and classification of open and mosaic ecosystems, particularly in the tropics and subtropics, have led to controversy worldwide. This has affected biodiversity conservation and, in some cases, promoted the establishment of afforestation projects based on the assumption that open and mosaic ecosystems are degraded forests. Although this initiative can have benefits in terms of carbon storage and climate mitigation if carefully planned and managed, it can also cause biodiversity loss and degradation when afforestation takes place in areas that were previously open ecosystems, or where unsuitable species are used. Madagascar, a world biodiversity hotspot, is one of the countries targeted for the implementation of afforestation projects. The Central Highlands of Madagascar, dominated by grassland matrix with forest patches, is the main region targeted. The nature and origin of the landscape are hotly debated, however, and it is not clear whether these open ecosystems are ancient or anthropogenically derived. Understanding of landscape history is therefore required to identify and conserve ancient open ecosystems, and to distinguish them from areas that have been deforested by people. This research aims to reconstruct the vegetation history and environmental change in the Central Highlands of Madagascar during the Holocene using palaeoecological methods, in order to inform appropriate conservation and management plans. We provide new records of vegetation, hydrological change, fire and herbivory activities by using a multiproxy approach, which includes fossil pollen, stable carbon isotopes, diatoms, charcoal and coprophilous spores, that allows for a comprehensive investigation into the history and drivers of vegetation change. Sediment cores were collected from two sites, Tampoketsa-Ankazobe wetland and Lake Dangovavy, located in the eastern and western slopes of the highlands, respectively. Results indicated that the surrounding area of both sites was composed of mosaic ecosystems, comprising of forest patches of variable extent in a matrix of open grassland and ericoid shrubland vegetation, at least from the Early and Mid-Holocene to ca. 1000 cal years BP, driven mainly by climate variability and fire occurrence. In Tampoketsa-Ankazobe wetland (eastern slopes), the vegetation was characterised by a mosaic of ericoid shrubland and mid-elevation forest taxa, between ca. 11 200 and 8300 cal years BP, under warm/wet period and low fire occurrence. The vegetation in the area changed to a mosaic of ericoid shrubland with more dominance of high-elevation forest from ca. 8300 to 1000 cal years BP under a drier climate and consistent low fire occurrence. The abundance of shrubs and trees during those two periods were confirmed by the dominance of C3 plants as reflected by the stable carbon isotopes results, and coincided with low herbivory activities in the TampoketsaAnkazobe site from ca. 11 200 to 1000 cal years BP. In parallel, the pollen record from Lake Dangovavy (western slopes), between ca. 6200 and 5400 cal years BP, suggests a mosaic ecosystem, dominated by more C3 montane grass, ericoid shrubland and high elevation forest patches promoted by cool/dry climate with low fire occurrence and herbivory activities. Between ca. 5400 and 4200 cal years BP, vegetation in the area was dominated by a mosaic of ericoid shrubland and mid-elevation forest under a wetter period, moderate fire occurrence, and herbivory activities. This mosaic was controlled by climate, fire refugia and herbivory feedbacks. The vegetation changed into a forest-savanna mosaic with an abundance of grassland and pioneer/fire-resistant trees between ca. 4200 and 3000 cal years BP. The period was characterised by an initial increase of local fire followed by a regional drought event. This suggests that a threshold might have been reached, with a resulting shift in vegetation composition. Between ca. 3000 and 1000 cal years BP, reoccurrence of ericoid shrubland with woodland savanna taxa was recorded in the area. The vegetation was conditioned by variation of climate from wet (until ca. 2000 cal years BP) to dry period (ca. 2000–⁠1000 cal years BP) with moderate fire occurrence and herbivory activities. In addition, stable carbon isotope results show that between ca. 6200 to 1000 cal years BP, the site was characterised by C3 plants. During the last ca.1000 cal years BP, pollen records from both sites in the Central Highlands of Madagascar showed a shift to a more open landscape dominated by grassland. Trees and shrubland in the highlands experienced a massive decrease and this correlated with an abundance of C4 plants associated with reduced diversity. The shift of vegetation during this period was likely a result of a centennial severe drought period at ca. 950 cal years BP, as recorded in the literature and confirmed by the peak in aerophilous taxa in our diatom record. The drought was followed by a dramatic increase of fire occurrence and herbivory activities in the region, as recorded in the charcoal and spore records from both sites, indicating human activities at ca. 700 and 500 cal years BP for Lake Dangovavy and Tampoketsa-Ankazobe wetland, respectively. Though the vegetation at both sites in Central Highlands of Madagascar was very dynamic until ca. 1000 cal years BP, complex interactions between climate and fire allowed the forest and ericoid elements to persist, consistent with a heterogeneous mosaic landscape. This changed from 1000 years ago with the occurrence of a regional severe drought event followed by an increase in human activities leading to an increase of grass, a decline in forest and ericoid elements. Our findings suggest that although, the eastern and western slopes in Madagascar might have different vegetation histories over time as a response to the complex climatic-fire drivers at least until ca. 1000 cal years BP, they both: a) Contained ancient open ecosystems such as grasslands and/or ericoid shrubland, and a mosaic landscape which should be considered typical of the highland region. b) Experienced a loss of forest, woodland and mosaic elements, a trend that is consistent with the anthropogenic conversion of some forests to grasslands since ca. 1000 cal years BP. Such findings have implications in terms of conservation, fire management and afforestation projects in the Central Highlands, and provide additional knowledge that contributes to the understanding of its ecological processes and history prior to human arrival on the island. Indeed: 1) Ancient grasslands and ericoid shrubland need to be identified and conserved because of their antiquity and unique biodiversity. To date, there has been some focus on ancient grasslands, but the presence of ancient heathlands has not been discussed. 2) It is important to distinguish ancient from derived grasslands and to target the latter for reforestation, using species that are typical of the remaining forest patches. 3) Fire management should be conducted at a local scale and should incorporate the landscape fire history, considering, for example, the differences between two slopes in the Central Highlands.
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    How has woody vegetation changed in north-east Namibia in response to land use, climate and fire?
    (2020) Eastment, Conor; Gillson, Lindsey; Humphrey, Glynis; Hoffman, Timm
    Bush encroachment or the thickening of woody vegetation is a phenomenon occurring throughout savannas, which tends to be more pronounced in small protected areas. The consequences of bush encroachment are often negative for the conservation of biodiversity, for the promotion of tourism and the prevention of wildfires. Hence, effective monitoring of woody vegetation and the factors which influence its spread are essential. This is particularly the case for protected areas such as that of Bwabwata National Park (BNP) in north-east Namibia. With a complex land use history and different fire management approaches being adopted throughout the area, the effect of fire on woody vegetation in BNP is currently poorly understood. This study used a 20-year-old repeat photography monitoring project and satellite-based remote sensing products to explore woody cover dynamics in BNP. Results revealed that woody cover has increased by 13% since 1999 in BNP. Furthermore, the results show differences in the structure of woody vegetation. Repeated late dry season fires in the west of the park have driven an increasing dominance of 3m in eastern sections of the park. This influence of different fire regimes spatially across BNP, suggests that local fire management is a significant determinant of woody vegetation change. Woody vegetation change differs spatially across BNP due to frequent late dry season fires prevailing in the west and less frequent earlier season fires occurring in the east. Therefore, in order to reduce the mortality of woody species and conserve heterogenous height structure in the west, a reduction of frequent late dry season fires is required. Early dry season fires are shown to reduce the rate of increasing total woody cover change and, therefore, this fire management strategy arguably contributes towards the reduction of wildfire risk, conservation of biodiversity and promotion of tourism.
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    Identifying long term patterns and drivers of vegetation structure in an African savanna using stable carbon and nitrogen isotopes
    (2010) Ghaui, Mark; Gillson, Lindsey
    Savanna systems are complex and dynamic in space and time. Climate, fire, herbivory and nutrients have been identified as structuring agents of savanna form and function, but their interactions and feedbacks with one another and vegetation are poorly resolved. Increasing the spatial and temporal scope of studies will help to improve this situation, as demonstrated in recent studies in the spatial dimension in particular. This study aims to investigate vegetation and Nitrogen cycling changes over time in a diverse patch mosaic landscape in Hluhluwe-iMfolozi Park to identify drivers of vegetation structure and their dynamism over time. Sediment from a 150cm core (taken using a Russian corer) was analyzed for stable ¹³C and ¹⁵N isotope abundances, and C:N ratio of soil organic matter. The base of the core was dated at 2380±40cal.Yr.BP. δ¹³C, δ¹⁵N and C:N of soil organic matter was found to be variable over time. δ¹³C followed a pattern of stable periods of distinct abundance separated by abrupt changes; δ¹⁵N and C:N underwent changes over the same periods as δ¹³C. Vegetation follows a pattern of phase and transition as predicted by resilience theory. An aquatic vegetation phase persists around 2000cal.Yr.BP to about 500cal.Yr.BP, coinciding with a warm, wet period (including the Medieval Warm Period) with an open Nitrogen cycle. A C₄ grassland phase follows alter a transition to cool, dry conditions coinciding with the Little Ice Age, and decreasing openness of the N cycle. Recent increasing C₃ vegetation and N-openness were attributed to atmospheric CO₂ increase and Nitrogen deposition respectively. Climate is concluded to be the major driver of vegetation at this site, and a combination of climate and vegetation are responsible for changes in Nitrogen availability. Findings are discussed in relation to landscape management. Multi-proxy evidence in future studies would be useful in validating the findings of this study.
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    Impact of human land-use and rainfall variability in tropical dry forests of southwest Madagascar during the late Holocene
    (2019) Razanatsoa, Estelle; Gillson, Lindsey; Woodborne, Stephan; Virah-Sawmy, Malika
    Over the last 2000 years, climatic and anthropogenic factors have influenced vegetation in Madagascar, but the contribution of these two factors has been the subject of intense debate, a debate hampered by the scarcity of palaeoecological studies on the island. Southwest Madagascar is semi-arid and comprises fragmented tropical dry forests where human subsistence strategies are diverse. Therefore, it provides a perfect setting to generate new palaeoecological records and investigate vegetation response to changes in human land-use and rainfall variability. The aim of this thesis is to understand how and when land-use changed, and rainfall variability impacted the landscape in the southwest region, using dendroclimatological and palaeoecological approaches. Carbon isotopes in the rings of four baobab trees (Adansonia spp.), were compared with pre-existing palaeoclimate data to produce rainfall records for the past 1700 years. Pollen, carbon isotopes, and charcoal in sediment cores from two lakes namely Lake Longiza and Lake Tsizavatsy (located in the northern and southern sites respectively in southwest Madagascar) were analysed to produce vegetation and fire records during the late Holocene in the region. Combination of the four baobab isotope records yields a new 700-year record for the southwest, which suggests an aridity trend over time, associated with a long-term reduction and increase in the duration of wet and dry periods respectively. Drying was more pronounced for the southern site than the northern site. A comparison with a high-resolution record from the northwest region allowed the rainfall of the southwest to be extended back to the last 1700 years as follows: from AD 300-500, the southwest region experienced a dry period which was followed by a wet period until AD 1000. Subsequently, there was a dry period from AD 1000-1250, followed by a wet period in the southwest. The period from AD 1300-1400 represented the wettest period in the record, followed by a decreasing wet period until AD 1600. The period between AD 1600 and 1800 represented the driest period, peaking around AD 1700. This was followed by a relatively wet period of about 50 years and another 100-year dry period. The last period assessed, from AD 1985 to 2000, was a relatively wet period. Such variability of the rainfall might have affected ecosystems and human land-use in the region. The tropical dry forest biome of southwest Madagascar has taxa from the dry forest, riparian forest and savanna woodland in the pollen records of both sites. In the core from the northern site (Lake Longiza), the pollen record suggests a heterogeneous mosaic of dry forest and riparian forest that was present over the last 2400 years. In the earliest part of the record, the community was dominated by trees from both the dry forest and riparian ecosystems. The onset of changes was recorded around AD 420, with a decrease in dry forest and riparian trees and an increase in grasses and xerophytics, possibly driven by dry conditions. This was followed by a short recovery of trees and C3 plants around AD 870 punctuated by a decrease in dry forest taxa around AD 980, possibly associated with the suggested expansion of pastoralism. After this period, the landscape became more open and grassier, as indicated by the dominance of C4 plants in the stable isotope record. Similar patterns of change in the pollen record, with a further increase in grasses and pioneer taxa, were recorded around AD 1900. Charcoal influx also started to increase drastically at this time, suggesting fire and forest clearance associated with a shift to agriculture. These large shifts in human land-use (probably a combination of both pastoralism and agriculture) coincided with the decline of floral diversity of the landscape, as indicated by pollen rarefaction. However, the diversity of the floral community gradually recovered, because of the persistent heterogeneity of the landscape. The core from the southern site (Lake Tsizavatsy) had a basal date of approximately 700 years BP but presented a hiatus of about 500 years from AD 1420-1910. The preceding period of AD 1300-1420 was marked by a decrease in the abundance of trees during the wettest period in the region, which was most likely because of human activities (foraging and pastoralism), as inferred by the increase in charcoal influx and pioneer taxa. During the second period, from AD 1910- 2010, there was an increase in xerophytic taxa, which suggests a long dry climate, recorded prior to this period. In addition, from AD 1950, trees decreased while pioneer taxa increased, despite the stable influx of charcoal recorded during this period. This possibly indicates the effect of human activities that did not involve the use of fire, probably conducted by ethnicities other than the forager communities, which are still present in the area today. This thesis contributes significantly to the understanding of palaeoclimate, palaeoecology and the history of human subsistence in a biodiverse region of Madagascar, where no other record is currently available. Results from stable isotope analysis from baobabs showed a drying trend over the past 700 years, which has interacted with land-use to affect vegetation structure and composition over time. The pollen and charcoal results suggest the northern site, where vegetation was a mosaic of dry forest and riparian forest, experienced an impact of human activities through a shift to agriculture especially in the last 100 years. The savanna woodland of the southern site, however, was less affected by humans, probably as occupants were subsistence foragers, but the vegetation had a higher response to aridity. The results show that two distinctive human subsistence (pastoralism and foraging) were present simultaneously in the region until modern times. The northern site has evolved possibly from foraging into extensive agriculture, probably related to the fertility of the alluvial soil in the area, while the southern community remained dominated by foragers, while adopting today a seasonal practice of agriculture. From a conservation perspective, strategies of conservation for each ecosystem investigated here are proposed. In the northern site, monitoring and reducing fire-use within the dry forest ecosystem would allow tree recovery. In addition, restoring and establishing protected areas within the riparian forest would allow these ecosystems to act as refugia for regional biodiversity. Such measures will likely reduce the pressure on these ecosystems, where agriculture is a threat due to the availability of both water and fertile soil in their surroundings. Alternative livelihoods are required for the northern populace, for example through the exploitation of invasive aquatic plants such as Typha, which can be used in making of handcrafted artefacts, to reduce pressure on forest ecosystems through agricultural practices. For the southern site, maintaining the resilience of the savanna woodland through reforestation of functional species is also important to allow sustainability of services provided by these ecosystems. These strategies are applicable locally for Madagascar and for worldwide tropical dry forests, one of the globally most threatened vegetation types due to anthropogenic pressure and climate change.
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    Long-term ecosystem dynamics of contrasting grasslands in South Africa
    (2022) Dabengwa, Abraham Nqabutho; Gillson, Lindsey; Bond, William John
    Rainfall, fire, and grazing all control changes in vegetation and soil in grassland and savanna ecosystems. In these ecosystems, wetlands are key resource areas because they keep moisture and collect nutrients that support grass production. The grass production supports high grazer densities in landscapes, especially during dry climatic periods.
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    Long-term vegetation change in the Cape of Good Hope section of Table Mountain National Park, in response to climate, fire and land use
    (2013) Powell, Robyn Faye; Hoffmann, Timm; Gillson, Lindsey
    Climate change, fire and land use are known threats to biodiversity and are predicted to have a major impact on the Cape Floristic Region of South Africa over the next fifty years. This study investigated long-term (1966-2012) changes in the vegetation of the Cape of Good Hope Section of Table Mountain National Park in response to 20th century changes in climate, fire and land use. Climate variables and fire history were assessed over the last 100 years using linear regression, segmented regression and GIS analyses. Seventy eight repeat photographs were taken at stratified points set out across the reserve and changes in total vegetation cover and the cover of major growth forms (broad leaved shrubs, proteoids, ericoids and restioids) within three main vegetation types (Dune Asteraceous Fynbos, Restioid Fynbos and Proteoid Fynbos) were assessed. Transition matrices were used to investigate the extent of vegetation change likely over the next fifty years. In a separate study changes in the number of individuals as well as the cover of several Proteaceae species (Mimetes fimbriifolius, Leucospermum conocarpodendron and Leucadendron spp.) were also investigated using the repeat photographs.
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    The macro-charcoal signature in Bwabwata National park, north-east, Namibia: Calibrating surface macro-charcoal with environmental variables
    (2014) Setzer, Christian Karlheinz; Gillson, Lindsey; Humphrey, Glynis
    Fire is a major driver of vegetation patterns in the savanna biome of southern Africa and is hypothesized to allow for the tree-grass co-existence. However, to better understand the drivers of the savanna vegetation structure, more research is required. Furthermore, fire management can benefit greatly from the knowledge of fire history and vegetation change. Palaeo-ecological studies endeavour to fill this knowledge gap by investigating past ecological changes throught the use of paleao-proxies. Charcoal - burned pieces of vegetation - is a proxy for fire and vegetation history. However, little is known about the relationship between charcoal found in sediment and environmental features in the savanna biome. This study aims to fill the knowledge gap by investigating the links between macro-charcoal ( > 150 ìm) from surface samples and fire history and physical characteristics of the landscape, vegetation composition and settlement density. Sediment surface samples (top 2cm) were taken from six sample sites in Bwabwata National Park (BNP), Namibia and analysed for macro-charcoal pieces using the swirling method. Here we show that there is a strong relationship between charcoal abundance and burned area, as well as charcoal abundance and grassy vegetation density. Thus broad inference can be made about the past vegetation composition and burned area by looking at long-term charcoal data. This information is useful for fire management, as past burn history can act as a reference point for current burn policy. This calibration work will inform long-term palaeo-data from sediment cores.
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    Modelling the complex dynamics of vegetation livestock and rainfall in a semiarid rangeland in South Africa
    (2010) Richardson, F D; Hoffman, Michael Timm; Gillson, Lindsey
    Predicting the effect of different management strategies on range condition is a challenge for farmers in highly variable environments. A model that explains how the relations between rainfall, livestock and vegetation composition vary over time and interact is needed. Rangeland ecosystems have a hierarchical structure that can be described in terms of vegetation composition, stocking rate and rainfall at the ecosystem level, and the performance of individual animals and plants at the lower level. In this paper, we present mathematical models that incorporate ideas from complex systems theory to integrate several strands of rangeland theory in a hierarchical framework. Compared with observed data from South Africa, the model successfully predicted the relationship between rainfall, vegetation composition and animal numbers over 30 years. Extending model runs over 100 years suggested that initial starting conditions can have a major effect on rangeland dynamics (divergence), and that hysteresis is more likely during a series of low rainfall years. Our model suggests that applying an upper threshold to animal numbers may help to conserve the biodiversity and resilience of grazing systems, whilst maintaining farmers’ ability to respond to changing environmental conditions, a management option here termed controlled disequilibrium.
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    Muddy memories : environmental change at Hluhluwe Imfolozi Game Reserve, KwaZulu-Natal, South Africa - evidence from diatoms
    (2010) Fordyce, Nicholas; Gillson, Lindsey; Kirsten-Sardinha, Kelly
    Diatoms are microscopic algae found in almost all aquatic environments. They are habitat specific and have silica frustules which preserve well in sediments. They have been used extensively to provide a multitude of palaeoecological data relating to pH, nutrient loads and water levels. Here, the diatoms in a lake sediment core from Hluhluwe-Imfolozi, South Africa, are analysed to show fluctuations in littoral to benthic taxa, and brackish to freshwater taxa as indicators of lake level changes over time. Changes in lake level act as a proxy for warm/dry or cold/wet periods over time. During the last 240 years lake levels have remained consistently low but nevertheless indicate four alternating periods of cold/wet and warm/dry climate. From c. A.D. 1770 (the last few decades of the Little Ice Age) to the c. A.D. 1840 the climate was cool and wet, but nonetheless gradually warmed up and became drier. From c. A.D. 1840 through to c. A.D. 1920 a there was a gradual increase in temperature and corresponding decrease in rainfall. Then, from c. A.D. 1920 till c. A.D. 1980 there was another colder, wetter period. Finally, very recently, from around c. A.D. 1980 till the present day, Hluhluwe-Imfolozi has experienced warmer, drier conditions once. Pollution-tolerant diatoms increase during the last 100 years and indicate eutrophication of the lake, a consequence of anthropogenic activity in the region. The diatom sequence from Phindiswene provides a high resolution climatic proxy for the critical period covering the latter stages of the Little Ice Age (LIA), post LIA warming, and recent increasing anthropogenic impacts.
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    Palaeoecology and vegetation dynamics in the Cederberg wilderness area
    (2010) Ballantyne, Fiona; Gillson, Lindsey; February, Edmund C
    The Cederberg Wilderness Area, in the Cape Floristic Region, South Africa, contains over 2000 plant species, 280 of which are endemic. The area has been subject to various forms of land use for millennia ranging from hunter-gatherers, herders, and farmers to visitors today. This study used palaeoecological techniques to investigate the impacts of past land use, specifically the transition from hunter-gathering to farming and herding in order to provide a baseline for current wilderness management. A sediment core was extracted from a wetland adjacent to the De Rif farmstead, analysed for fossil pollen and charcoal and dated using AMS radiocarbon dating. Historical records were used to link changes with land use history. A vegetation survey of the site focussed on the grass component of the vegetation. The largest impacts on vegetation during the last 2300 years are due to grazing and agriculture during the 1800s to 1940. Fire-sensitive taxa have not declined, apart from possibly Ericaceae, suggesting that changes in fire have not exceeded a threshold that affects the community at a family level. Changes in the fire regime, combined with disturbance by ploughing and grazing have increased the abundance of Poaceae and Cyperaceae, resulting in a decrease in Restionaceae. Ploughing affected the height structure and species composition of the site, and allowed the invasion and persistence of exotic grasses which now make up 43% of total grass cover on the previously ploughed area. Few indigenous fynbos grasses were found suggesting that the grass community is depauperate due to disturbance. The higher grass abundance preceded the largest fire recorded in the charcoal record suggesting a grass fire cycle has started at De Rif. Ploughing, grazing and invasive grasses, rather than changes in fire regime or resource extraction, are the main causes of vegetation change at De Rif and still affect the site today. Wilderness management will need to mitigate the impacts of livestock and agriculture on De Rif and monitor the recovery of this and other previously farmed areas to ensure that they do not become as a source of invasive species in the future under novel disturbances such as anthropogenic climate change.
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    Phytolith Analysis as a Palaeoecological Tool for Reconstructing Mid-to Late-Pleistocene Environments in the Olorgesailie Basin, Kenya
    (2012) Kinyanjui, Rahab; Meadows, Michael; Gillson, Lindsey
    Olorgesailie Basin is an important prehistoric locus and holds a prominent place in African Quaternary research. It is located in the southern Kenya rift system (1˚ 35´S and 36˚ 27´E) and has preserved numerous archaeological findings of the Acheulean, Sangoan and Middle Stone Age occupations and most importantly, hominin cranium associated with the Acheulean hand axes. Evidence of past vegetation has hitherto been scarce, because the arid / semi-arid conditions are not conducive for preservation of organic plant microfossils. Phytolith analysis is used to reconstruct the vegetation history and understand hominin habitat preference during mid-late Pleistocene (~746-64 ka). A localised modern phytolith analogue is used to interpret the fossil assemblage. Descriptive analysis identified fifty nine phytolith morphotypes which were categorised into three major groups; grass short-cell phytolith, epidermal silicified appendages and sedge phytoliths. The identification and classification was based on the International Code for Phytolith Nomenclature and other existing literature. In order to determine the significance of the identified morphotypes in interpreting fossil data, two multivariate statistical analyses were performed on the database; Correspondence analysis distinguished vegetation components according to a moisture gradient while Cluster analysis identified unique morphotypes that were taxonomically affiliated to their parent plant species. However, the analyses were not able to distinguish plants along the altitudinal gradient. Fossil phytoliths derived from sixty palaeosol samples extracted from eight geological sections in three localities of the Olorgesailie Basin, were identified and tallied to determine vegetation cover and how this changed both spatially and temporarily during the mid-late Pleistocene period. Fossil phytolith frequencies were plotted on TILIA diagrams against the available 40Ar/39Ar dates. Correspondence analysis identified three vegetation components; grasslands, woody & herbaceous and aquatic and identified moisture availability as the major underlying factor influencing the morphotype clusters on the ordination space. An additional cluster analysis of forty morphotypes derived from grasses confirmed the known taxonomic affiliation of major grass short-cell phytoliths to four grass subfamilies (saddle ovate- C3 Arundinoideae, bilobate concave- and convex- outer margin short shaft and quadralobate-C4 Panicoideae, saddles-C4 Chloridoideae and bilobates convex outer margin long shaft-C4 Aristidoideae). From the non-grass category, achene and papillae phytolith morphotypes were identified as belonging to the Cyperaceae.
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    Reconstructing the long-term history of water quality and availability using fossil diatoms at an agricultural site in the Cape lowlands
    (2019) Hoffenberg, Amy; Gillson, Lindsey; Forbes, Cherié; Delaney, Kelly
    The Berg River is a pivotal source of fresh water for domestic, industrial and agricultural use as well as for in stream ecology, therefore knowledge of what impacts this rivers water quality and assessing whether ecological resilience has been surpassed are of the utmost importance. Since diatom assemblages are inextricably linked to the chemical, physical and biological characteristics of their environment, they were chosen for this study to investigate long-term changes in water quality and availability and suggest potential drivers of such changes at an agricultural site (Rhenostervlei Farm) adjacent the Berg River in the Cape lowlands through fossil diatom analysis of a sediment core (RV3). Diatoms were extracted along the length of the RV3 core, chemically and physically treated to remove unwanted material and then were mounted on a slide to be counted. Twenty abundant diatoms were chosen as environmental indicators for the analysis. Their abundances were plotted against depth and age and changes in water quality and availability were inferred based on their autecological characteristics. The most prominent shift in the indicator diatoms at Rhenostervlei Farm as shown by the stratigraphic diagrams, CONISS analysis and the PCA occurred at the onset of the 20th century CE and was characterised by a shift from a saline, dry and nutrient-poor environment (ca. 1790-1890 CE) to a more turbid, nutrient-rich environment with increased freshwater influence that was prone to periodic flooding (ca. 1890-2011 CE). Through the chronological analysis and the interpretation of the historical record (climate and land-use) as well as other environmental proxies (sediment accumulation rate and macro-charcoal), the causes of the detected change in water availability and quality at the floodplain site were likely related to land-use change in the form of agricultural intensification at Rhenostervlei Farm and potentially in the Berg River catchment as a whole. This could have involved burning, clearance of natural vegetation, soil disturbance and fertilizer use - all of which contributed to increased surface runoff, erosion and nutrient and sediment loading into the site. Furthermore, water extraction and diversion in the 1950s could explain the decreased flooding signal (i.e. lower abundance of Aulacoseira granulata). Although no evidence of a catastrophic regime shift was identified, if land-use practices continue to intensify (e.g. increased fertilizer use) and future climate change interacts and influences the agricultural alterations to hydrological systems, we may expect increased vulnerability to global change and unexpected ecological outcomes such as regime shifts. In order to improve the interpretation of fossil diatom records in terms of changing water quality and availability, a study with multiple proxies should be undertaken to help infer environmental conditions in a complex environment that has many potential drivers, such as the Berg River.
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    Reconstruction of late Holocene vegetation and climate of Hluhluwe Mfolozi area using phytoliths
    (2010) Gallaher, Kirsten S L; Gillson, Lindsey
    This study presents a phytolith record from a late Holocene sedimentary core from the Hluhluwe-iMfolozi area in northeastern KwaZulu-Natal. Radiocarbon dating showed the oldest sediments to be from 23 80 ± 40 BP. Phytoliths are present throughout the record. There was a high degree of unclassifiable phytoliths (>79% per sub-sample), but preliminary trends identified include a dominance of C₄ grasses throughout (Chloridoideae and Panicoideae; adapted to higher temperatures and greater insolation), and slightly more C₃ grasses (Pooideae; adapted to cooler temperatures and/or winter rainfall) towards the base. The tree cover density index (D/P) does not reflect increased bush encroachment at this site, but appears to show a closed forest at 36cm depth and relatively densely-wooded savannas throughout, while the humidity-aridity index (lph) and water stress index (Fs) suggest a move towards a xerophytic short grass savanna, and increased water stress at the top of the sequence, which could reflect the climate becoming hotter and drier due to global warming. Future studies should be done to identify phytoliths specific to the vegetation of the study site and to calibrate the indices used to confirm their utility for this area.
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    The role of humans, climate and vegetation in the complex fire regimes of north-east Namibia
    (2018) Humphrey, Glynis; Gillson, Lindsey
    This thesis explores how interactions and feedbacks between environmental and socio-historical factors influenced fire management dynamics in north-east Namibia. Fires are mostly human ignited, but precipitation patterns influence when and where fires can occur, and there are feedbacks between fire, climate and vegetation cover. Yet, knowledge of historical and contemporary use of fire by societies is fragmented in southern Africa, and is therefore disputed. As a result, the complex interaction between climate, vegetation and human factors that influence fire dynamics remains poorly understood. This thesis explores how the political history, livelihoods, land-use practices, policy changes, vegetation and climatic variation are relevant to present-day fire regimes and management. The study is located in Bwabwata National Park (BNP), north-eastern Namibia, which is managed for both conservation objectives and people’s livelihoods. The park is inhabited by the Khwe (San), former hunter-gatherers, who have been using fire for millennia, and the Bantu-speaking Mbukushu people, who are agriculturalists and pastoralists. The area has been subject to colonial regimes, war, inter-ethnic conflict, social-political resettlement, conservation and associated changing fire management approaches since the 19th century. The vegetation includes omiramba grasslands, savanna-woodlands, Burkea shrublands and riparian types. For this study, qualitative semi-structured interviews with Namibian stakeholders, in combination with multi-year (2000 – 2015) remote sensing products, were used to understand the past and present fire regime characteristics. Interviews with community stakeholders revealed that the Khwe and Mbukushu communities use fire for a diverse range of livelihood activities. Specifically, early season burning is used to assist in hunting, tracking and gathering of veld foods, and for improving forage for livestock. The traditional practice of early season burning is not only culturally and ecologically significant, but has positive consequences for Bwabwata National Park’s conservation objectives, and fire policies, in terms of suppressing late season fires. However, explicit marginalisation of the Khwe since the C19th due to colonial regimes and cross-border wars has disrupted traditional fire management. Interviews with government and conservation stakeholders revealed recognition of the benefits of early season burning for biodiversity. Furthermore, despite the complex social-ecological history of the area, recent policy changes reveal an emerging willingness to incorporate traditional fire management into fire management policy. Moderate Resolution Imaging Spectrometer (MODIS) data was used to analyse the fire regime (burned area, fire frequency, fire number and size, intensity, and seasonality), together with climate (El Niño Southern-Oscillation [ENSO] events; local rainfall patterns) and vegetation data in multiple use (inhabited) and core conservation areas, over a time period that covered a shift in policy from fire suppression (2000-2005) to early season burning (2006-2015). Results from the analysis of the MODIS data revealed that a high frequency of early season burning in the inhabited areas of the park reduced the late season fires and dampened the local rainfall and burned area relationship. Nonetheless, grass growth (i.e. available biomass) during ENSO wet season events (La Niña) resulted in greater area burned and fire sizes in above average rainfall years in the early dry season in the community inhabited areas. In contrast, higher fire intensity and larger fire sizes were evident in the conservation core areas where people were not actively burning. Fire frequencies and burned areas were highest in the omiramba grasslands and savanna-woodlands, in the early dry season under the early burning policy in the east of the park, which reduced fire intensities in these vegetation types. In contrast, burning in the Burkea shrublands was frequent in the late dry season, at higher intensities in the Western conservation area under both policy phases. This study indicates that burned area depends on rainfall, ignitions and fire sizes in inhabited landscapes, where people practice early burning, which has consequences for decreasing the intensity and therefore spread and impact of fires on vegetation. This study highlights the complex interactions between people, rainfall seasonality and fuel availability, as well as the need to incorporate historical factors. The study uses a pyrogeographic framework to integrate the social-cultural, climatic-biological, and topographic-environmental factors with fire. The synthesis reveals that the park communities are currently socially and ecologically vulnerable to global environmental change, given their dependence on fire for ecosystem services. However, the study also highlights how traditional fire management, and specifically early season burning, improves food security and contributes to livelihood subsistence and biodiversity conservation in the park. BNP is characterised by complex historical and present-day social-ecological fire dynamics. The study highlights the importance of understanding the historical and political context of fire for determining and managing current spatial-temporal fire patterns. Respect for diverse fire knowledge and culture, communication and shared governance are central to improving community livelihoods and fire management strategies in BNP. Specifically, the shared interest in early season burning provides a point of confluence between diverse stakeholders in BNP and a basis for fire management policies that benefit biodiversity as well as livelihoods.
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    Using applied palaeoecology and participatory system dynamics modelling to investigate changes in ecosystem services in response to climate and social-ecological drivers within the middle berg river catchment, South Africa
    (2022) Dirk, Cherié Janine; Gillson, Lindsey; Hoffman Michael
    Conservation and agricultural landscapes are social-ecological systems that co-produce ecosystem services, which change over time in response to environmental, biotic and social drivers. Failure to consider this variability, and the feedbacks that cause system instability, can have consequences for sustainable ecosystem services provision. A transdisciplinary approach is needed to understand the interacting processes that drive the dynamics of ecosystem service provision. This study applies a conceptual meta-framework: past-present-future lens of environmental change to interpret changes in land cover and ecosystem services, with the aim of informing sustainable land-use management within the Cape Floristic Region, a globally recognised biodiversity hotspot. The project methodology followed a four-part structure: (1) Changes in land cover, fire, herbivory, and hydrological indicators were reconstructed using palaeoecological proxies (fossil pollen, charcoal, coprophilous spores, geochemistry, and diatoms) from two sites and associated sedimentary cores. (2) Palaeoecological data were interpreted in terms of supporting/provisioning (plant biodiversity) and regulating (water quality and soil erosion regulation) services, and (3) the drivers of these changes (climate, fire and herbivory) were analysed. (4) A pilot study used participatory system dynamics modelling to articulate dynamic feedbacks and explore future scenarios. Palaeoecological and modelling results explored resilience and thresholds in ecosystem services, defined the historical range of variability and was used to generate management recommendations. Results showed that (1) high temporal resolution, multi-proxy data suggested variability in ecosystem services. (2) Ecosystem change was driven mainly by climate in the early palaeo-records with increasing anthropogenic influence from the mid-20th C, and (3) although some plant biodiversity and landscape heterogeneity was lost, the main vegetation elements remain, suggesting no environmental thresholds have yet been crossed. (4) Even so, model simulation results show that it may be difficult to return to past ecological states. Adaptive grazing-fire management is recommended to maintain and restore ecosystem function, thereby decreasing the likelihood of future regime shifts to a degraded alternative stable state. This innovative interdisciplinary approach provides a contextual understanding of processes that influence dynamic social-ecological systems and translates long-term data into a form that can be used by policymakers and land-use managers to inform sustainable management of ecosystem services.
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    Using Sporormiella to track herbivore biomass within the Hluhluwe-Imfolozi game reserve
    (2007) Thomas, Alicia Jessica; Gillson, Lindsey; Bond, William J
    Historical fossilised spores of Sporomiella, a coprophilous fungus that only grows on the dung of herbivores. has been used to infer unknown herbivore abundances or biomass and identity periods of mega-herbivore extinction in the palaeo-record. ln Africa. however. mega-herbivores are still extant and there is therefore a unique opportunity to calibrate Sporomiella abundance against known herbivore biomass. This study was carried out within the Hluhluwe-lmfolozi Game Reserve, KwaZulu-Natal South Africa (28°00'-28°26'S. 31°43'-32°00'E. Fig 2(a) and (6)). We evaluated the relationship between Sporomiella concentration and herbivore abundance. as indicated by total dung abundances. We investigated three aspects of this relationship: [1] the relationship between Sporomiella abundance and total herbivore dung abundance. [2] the relationship between Sporomiella and individual herbivore species, where we also divided all the herbivores into Mega-herbivores and Meso-herbivores to determine their relationship with Sporomiella densities. [3] finally, we tested the differences between the regions of the reserve by comparing the different areas of the park, as each system has its own unique drivers (Hluhluwe (fire driven), Imfolozi (herbivore driven) and the corridor (fire and herbivore driven)), with the concentration of Sporomiella. We found no significant relationships between Sporomiella concentration and total herbivore dung abundances, which suggests that the fungus may be selectively growing on certain herbivore species rather than on all herbivore dung and / or the amount of dung for each species is not accurately reflected by dung counts [because amount of dung per species isn't accurately reflected by dung counts?]. This isn't reflected in clung counts. When the sites that had zero Sporomiella were excluded from the analysis. Sporomiella concentration was significantly related to elephant and white rhino dung abundance, which could be related to site specific condition. Mega-herbivores and meso-herbivores dung abundance showed no significant relationship with Sporomiella concentrations. implying that neither group is the main contributors to Sporomiella concentration. There was also no significant difference in Sporomiella-concentration between the different areas of the park, providing no evidence that spores are differentially distributed throughout the park. Sporomiella concentrations showed no significant difference between the different types of vegetation and grasses within the park. This suggests that the spores are not specific to certain vegetation or grass types.