Browsing by Author "February, Edmund"

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    An environmental history of the Cederberg : changing climate, land use and vegetation patterns
    (2009) Bonora, Daniela Vincenza; Hoffman, Timm; Rohde, Rick; February, Edmund
    This thesis documents how climate and land use practices have changed in the Cederberg over the last century and how these changes have affected vegetation patterns. Along with a description of the major geological, climatic and vegetation gradients in the study area, changes in rainfall, temperature, A-pan evaporation and fire regimes over the 20th century are analysed from official records. While rainfall has not changed significantly from 1900-2007, the last 30 years have been drier than the mean value. The temperature records show an increase of 1°C since the I 960s; however, A-pan evaporation values have declined significantly over the last 30 years. The fire records suggest an increase in area burnt and in frequency since the mid 1940s. Changes in land use and its impacts on Cederberg landscapes are then assessed through a combination of archival sources, repeat photography and oral history. A zonal theme was adopted to analyse the environment of the Cederberg, and land use and landscape changes of the lowlands, midlands and uplands are examined independently. Results show that the Cederberg lowlands have experienced the largest degree of transformation over the course of the 20th century, primarily as a result of the intensification of agriculture, specifically fruit, vine and potato cultivation. Large areas of the midlands have also been transformed, although to a lesser extent than the lowlands. The midlands have experienced a complex history with changes differing between the northern and southern parts of the Cederberg. Evidence from 17 repeat photograph pairs suggests that the natural vegetation of the northern midlands has witnessed a recovery, with a contraction of traditional forms of farming and an increase in tourism and wine making. The southern midlands, on the other hand, have seen an expansion in agricultural production similar to the trends recorded in the lowlands. In contrast to the lowlands and midlands, human-induced transformation of the Cederberg uplands has been minimal. In this region, the impacts of a changing climate and fire regime are most clearly observed, and best explain the declining populations of the endemic Clanwilliam cedar tree (Widdringfonia cedarbergensis). Evidence from 15 repeat photographs shows that there has been a rapid decline (average of 2.5% per annum) over the last 70 years, and if current rates of decline continue, the species will be extinct in the region within 300 years. An increase in fire frequency is the best explanation for the demise of the cedar, although changes in rainfall, temperature and the impacts of disease deserve further investigation. The results of this thesis are relevant for land owners, agriculturalists, conservationists and the tourism industry, and by using repeat photograph pairs, it provides a richly illustrated account of changes in the region over the last 100 years.
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    Global change drivers and their impact on herbaceous, ant, and grasshopper assemblages in an African semi-arid savanna
    (University of Cape Town, 2020) Trisos, Matthew Owen; February, Edmund; Parr, Kate; Picker, Michael David
    Assessments of the anthropogenic threats to savanna ecosystems are primarily focussed on land use change, bush encroachment, and biological invasions. There is, however, very little understanding as to the threats from atmospheric pollution. South Africa is the major emitter of CO2 on the African content while the Mpumalanga region bordering the Kruger National Park (KNP) is among the leading regions for nitrous oxide pollution in the world. It is not only increasing atmospheric pollution, but rainfall intensity is also predicted to increase for southern Africa. As savannas are nutrient limited, an increase in nitrogen deposition will have major consequences for vegetation structure and this can only be exacerbated by increased rainfall amounts. Current research suggests that these predicted increases in water and nutrients will result in increasing grass biomass and decreasing herbaceous species richness. The effects of global change drivers on savanna vegetation are also likely to propagate through to multiple trophic levels, with changes in vegetation structure cascading down to invertebrate assemblages. As invertebrates are ubiquitous, form the bulk of metazoan species diversity and biomass on earth, and play a pivotal role in many ecosystems, I discuss in the introductory chapter of this thesis why the influence of global change on these assemblages should not be ignored. In my first data chapter, Chapter 2, I examine the effect that increases in available nutrients and water may have on vegetation structure, and how this may cascade down to grasshopper and ant assemblages. I do this using a fully factorial experiment in KNP with nutrient and water additions where I assessed both herbaceous (forb and grass) and insect (ant and grasshopper) assemblages five years after resource additions began. My results show that there was a substantial increase in grass biomass while plant and insect species richness declined with water addition alone and that a combination of nutrients and water resulted in the greatest increases in grass biomass and concomitant decreases in plant and insect species richness. The effects of nutrient and water additions on the insect community assembly was primarily driven by a decrease in grasshopper species and ant abundance respectively. An analysis of ant functional traits showed that the rare ant species mediated the impact of the resource additions on the ant assemblage. Fire is inherent to savanna systems with profound effects on vegetation structure. There has, however, been relatively little research on the effects of fire on savanna invertebrate fauna. In Chapter 3 I look at the effect that fire may have on the vegetation and insect community assembly at my study site between five and eight months after the site had been burned. These results show an increase in grass biomass and decrease in plant and insect species richness with a combination of nutrients and water. My results also show that grasshopper biomass, abundance, and species richness decreased as herbaceous biomass decreased. While ant species richness decreased, ant abundance increased post-fire, primarily related to an increase in patches of bare ground. With global change, drought frequency is also expected to increase. The insect and grass assemblages, both on and off Macrotermes mounds, at two sites in the southern section of KNP had been sampled in a separate study in 2012. In Chapter 4 I describe a study where I resampled these mounds during the peak of the most severe drought in 30 years. The two sites differed in drought severity, one where the drought severity was very high and the other where severity was much lower. The objective was to determine the effects that drought may have on the grass and associated insect assemblages both on and off termite mounds. My results show that at the high severity site grass cover and biomass and grasshopper abundance decreased both on and off mounds. The overall reduction in habitat structure resulted in an increase in both ant abundance and species richness but the mound and matrix ant assemblages diverged during drought. Where the drought was less severe there was an increase in large mammal herbivores as animals moved out of the more affected areas. This increase in mammal herbivory was more evident on rather than off mounds resulting in grass biomass being lower on rather than off mounds. The cascading effect saw grasshopper abundance decrease on and increase off mounds. The mound and matrix ant assemblages did not respond to the comparatively smaller change in habitat structure. Finally, in the synthesis chapter I discuss my results in the broader context of how global change drivers such as increased nitrogen deposition may cascade down from plant to insect community assembly. At present there is very little understanding of the amounts of nitrogen being deposited in KNP or the effect that this may have. The results of my study would suggest that this increase in nitrogen deposition will have major consequences for vegetation structure and that this will cascade down to the insect assemblage. In mitigating for this, it is therefore essential that management in KNP adapt a monitoring protocol for nitrogen deposition, especially when considering that where N deposition is really high fire may not volatilise everything to allow the system to reset itself back to its original state. It is not only nitrogen deposition, but drought frequency is also likely to increase. In mitigation for this there should also be monitoring programmes to consider the effects of drought as animals may move from areas of high drought severity to areas where severity is lower. Such movement will increase grazing pressure on both low and high nutrient environments with cascading effects on vegetation structure and insect assemblages.
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    Investigating the habitat selection and dietary preferences of a largely sedentary population of blue wildebeest in the Kgalagadi Transfrontier Park – impacts of permanent surface water provision in a semi-arid environment
    (2018) Weeber, Joshua; February, Edmund; Hempson, Gareth
    The continued provision of waterholes since the early 1930s has facilitated the formation of a largely sedentary population of blue wildebeest (Connochaetes taurinus) in the Kgalagadi Transfrontier Park. However, other environmental variables may influence the distribution of this resident herd within the riverbeds of the Park. I explore the effects of water quality, forage abundance, tree density and river width on wildebeest habitat selection. I do this through a combination of an analysis of two years of wildebeest census data, published water quality data and a series of transects across the Auob and Nossob rivers for dung and grass sampling in the Park. My results show that water quality is a key predictor of wildebeest distribution, with animals strongly selecting for areas with access to fresh water over areas with saline or no water. Shade also emerged as a strong predictor of wildebeest distribution, demonstrating the importance of thermoregulatory behavioural adaptations in this arid savannah system. Wildebeest avoided areas of the riverbed that were densely vegetated, instead showing a preference for wider, open areas. This preference is likely a combination of two factors; enhanced predator detectability in open regions of the riverbed and the larger area of short grass communities present in this habitat. In this arid environment the distribution of available graze has long been considered an important variable in determining the distribution of wildebeest. I further examine my results showing that forage availability and quality plays a key role in wildebeest habitat selection through a stable carbon and nitrogen isotope analysis of wildebeest dung and the leaves of common shrubs and grasses to explore the spatial and temporal variation in wildebeest diet. These results show that wildebeest in my study site consumed a higher proportion of C3 plants than previously recorded in other areas of their range. This C3 intake increases in the dry season and in marginal, low use areas of the Park, suggesting that C3 plants are an important alternative food source to wildebeest during drought periods. This increase in C3 plants allow the animals to maintain their crude protein requirements throughout the dry season, despite a pronounced drop in the quality of available graze during this period. These results suggest that wildebeest were not food limited during the study period, although the distribution of these animals appears to largely reflect bottom up (resource based) mechanisms. A portion of the resident herd displayed some level of local movement, dispersing out of the riverbeds during the wet season before concentrating again near good quality waterholes in the dry season. This movement is likely driven by increased wet season forage outside the riverbed habitat and facilitated by ephemeral pools of water that form in pans in the rainy season. Grass species counts and grazing evidence were used to investigate the grazing habits of all herbivores in the riverbeds of the KTP. My results suggest that herbivores are more restricted in their grazing choices during the dry season. While there was no conclusive evidence to suggest that this was a direct result of grass quality, it is likely that the pronounced decrease in grass quality during the drier months does play a role in herbivore grazing habits.