OpenUCT :: Browsing by Author "Hoffman, Timm"

Browsing by Author "Hoffman, Timm"

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Open Access
A pluralistic, socio-ecological approach to understand the long-term impact of mountain conservation: a counterfactual and place-based assessment of social, ecological and hydrological change in the Groot Winterhoek Mountains of the Cape Floristic Region
(2018) Holden, Petra Brigitte; Hoffman, Timm; Eckardt, Frank; New, Mark; Smit, Julian; Visser, Martine; Ziervogel, Gina
The problem: For protected areas to remain relevant, we need to understand their impact on a wide set of conservation objectives and environmental outcomes. We also need to evaluate how this influence relates to the socio-ecological environment within which they occur. This is a complex endeavour requiring a pluralistic approach, which draws on a wide range of interdisciplinary fields. Research question: This thesis addresses the following question: What effects do mountain protected areas have on ecosystem services over time and how does this influence relate to broader socio-economic and ecological drivers of landscape change? Aim and objectives: I use a pluralistic, socio-ecological framing to assess the impact of ~40 years of mountain protection, drawing on comparisons of ~30 and ~40 years before and after protection respectively, with an adjacent area of similar terrain informing scenarios of counterfactual conditions. I also investigate what types of values (economic and intrinsic) are important when determining the impact of mountain protected areas. Thesis approach and methods: I operationalise the concepts of socio-ecological systems, ecosystem services, land use transitions and counterfactuals to investigate socio-ecological change and how it relates to protected area impact in the Groot Winterhoek, a mountain catchment in the south-western Cape of South Africa. This mountain catchment is important for regional water supplies for agricultural and domestic uses and falls in the Cape Floristic Region, a global biodiversity hotspot. It is comprised of privately owned mountain wildlands and a wilderness-protected area, known as the Groot Winterhoek Wilderness Area, established in 1978 (gazetted in 1985) which forms part of the Cape Floristic Region World Heritage Site. I combine methods from social science, ecology, environmental geography, geomatics and hydrology to understand the history of land use and cover (land use/cover) and associated ecosystem service trade-offs, how they are perceived by landowners as well as their wider impact on the region. Specifically, I assess the impact of protection on land use/cover, vegetation, fire and water flows over the last ~50 years, by comparing and contextualising results of change within the protected area to alternative scenarios of “no protection” (the counterfactual conditions). Vegetation and land use/cover change inside the protected area were determined respectively using 72 repeat terrestrial photographs and vegetation surveys, and an analysis of orthorectified aerial imagery. Methods used to construct the counterfactual scenarios of mechanisms (e.g. changes in land use/cover) that would likely drive vegetation changes inside the protected area included: i) 60 repeat surveys and in-depth interviews with landowners adjacent or proximal to the protected area owning unprotected land of similar terrain to the protected area; and ii) land use/cover change analysis of orthorectified aerial imagery of adjacent unprotected land of similar terrain before and after protected area establishment. 4 This latter information was used to understand the role of the protected area in driving vegetation changes inside the protected area. Social, biophysical and remote sensing results were directly used to parameterise land use/cover components of a hydrological model to determine the influence of protection on water flows. Specifically, water flows were simulated for the current state of the environment inside the protected area as well as for several counterfactual scenarios i.e. the alternative land use/cover scenarios of “no protection”. These counterfactual scenarios included land use/cover at two-time steps of ~30 and ~8 years before protection and one-time step ~40 years after protection both inside and outside the protected area. Results: Long-term change in ecosystem service use outside the protected area on privately owned land of similar terrain to inside the protected area (Section 3): Over the last ~50 years, outside the protected area, there was a shift from livestock-based, subsistence agriculture and small-scale farming to a diversified set of ecosystem service uses. The combined area of grazing and wildflower harvesting declined by 39%, while the number of landowners using the mountains for personal nature-based recreation and ecotourism increased by 61% and 23% respectively. Agriculture intensified in suitable areas of mountain land with the number of landowners cultivating land increasing by 20%. Exogenous socioeconomic drivers associated with globalisation and economic growth were important causal mechanisms of land use change. Landowners valued mountain protection for intrinsic and non-use reasons (73-80% of landowners), including existence, bequest and option values, as well as for the indirect use of water supply (72% of landowners) in comparison with direct use reasons such as spiritual/cultural experiences and nature-based recreation inside the protected area (18 and 50% of landowners respectively). Personal, nature-based recreation outside the wilderness-protected area was associated with valuing the protection of mountain land for intrinsic and non-use reasons. Long-term vegetation change inside the protected area and plausible mechanisms driving vegetation change (Section 4): Inside the mountain protected area, fynbos vegetation cover increased on average between 11 and 30% and there were significant declines in bare ground and rock cover. In 5 accumulation and fire intensities. However, these latter changes in land use/cover also occurred outside the protected area (see results summarised for Section 3 above and Section 4 below) and therefore cannot be attributed to protected area establishment. Land use/cover and the influence on water flows inside the protected area compared to counterfactual scenarios of no protection (Section 5): Declines in grazing and changes to the fire regimes occurred regardless of the protected area boundaries. In the past, there was a high frequency of small, low intensity fires across the landscape, both inside and outside the protected area. More recently, fires have been actively suppressed and this resultsin the build-up of biomass and the development of extensive, high intensity fires which, under suitable conditions, burn large expanses of the mountain catchment. Hydrological modelling showed that a high intensity burning regime negatively affected streamflow regardless of protected area boundaries. Streamflow increased by more than 80% under high flow conditions and decreased by more than 40% under low flow conditions relative to an unburnt ‘natural’ scenario. Over the last 50 years there has also been a substantial increase in dams, buildings and roads and minor increases in cultivation outside the protected area. This has been avoided inside the protected area where these land use/cover classes declined. If the increase in these land use/cover types observed outside the protected area occurred inside the protected area this would have resulted in reductions in daily streamflow leaving the protected portion of the catchment. For example, outside the protected area reductions of 8% to 25% of streamflow were observed during mid and low flow conditions respectively, particularly during dry years, in comparison to a ‘natural’ scenario. In contrast, inside the protected area streamflow recovered from past conditions to more closely resemble the natural flow conditions of the catchment. Therefore, had the protected area not been established there would have been losses in streamflow from the catchment as well as an increase in the degree of fragmentation within this mountain area. However, with increased water storage and fragmentation outside the protected area has also come increased socio-economic opportunities such as employment and local opportunities for ecotourism and sustainable agriculture e.g. indigenous cut flows. This highlights the importance of maintaining various forms of land management systems (multifunctional landscapes) within mountain ecosystems but also the need to understand the sustainability of different land management system types. Determining appropriate land management systems for mountain areas should be based on a full understanding of the impacts on ecosystem service benefits and costs at local and regional levels between social groups both spatially and temporally. Broader significance: This thesis contributes to the conservation literature on two main fronts. Firstly, it contributes conceptually and theoretically to understanding the dynamics of ecosystem services in relation to mountain protection. Secondly, it contributes methodologically by using an inclusive, trans- and interdisciplinary research approach for evidence-based conservation at a place-based and landscape level. The study provides a case 6 study example of the positive impact that mountain protection has on water-related ecosystem services, notably by maintaining streamflow throughout high to low flow periods and during dry years. It also provides clear evidence that ecosystem service trade-offs do not remain constant over time and shows that intrinsic and non-use values are required when describing the importance of mountain protected areas. In terms of understanding the impact that protected areas have in mountain regions, the research shows that complex processes are at play that extend beyond the boundaries of a specific protected area in both time and space. Interactions between global and local drivers were found to be prominent causal mechanisms of socio-ecological change and ultimately determined the influence of mountain-protection on land use/cover, fire, vegetation and water-related ecosystem services. The thesis emphasises that counterfactual framings are necessary to understand and attribute the impacts of protected areas on environmental outcomes, however pluralism and socio-ecological approaches are critical to determine plausible counterfactual conditions. This thesis focused only on landowners adjacent and proximal to the protected area owning the majority of mountain catchment land of similar terrain. It is likely that multiple socioeconomic trade-offs have occurred between different social groups and generations at both local and regional levels. Understanding how the disadvantages and benefits of the impacts of protected areas are apportioned across the landscape and temporally is an aspect that requires future research. Central to this would be to fully consider how human well-being is influenced both upstream and downstream, including at regional levels, and between social groups and across generations. Considering the impact of protected areas on the full range of ecosystem services and linking this to societal preferences and perceptions should be incorporated into the overall goal of developing an evidence base for conservation. This is because it is both scientific evidence and societal change that can determine protected area persistence and thus long-term protected area impact.
Open Access
Aliens in the nursery : assessing the awareness and attitudes of Cape Town nursery managers in regard to invasive species regulations
(2015) Cronin, Kate; Hoffman, Timm; Kaplan, Haylee
The horticultural industry is recognised as one of the major pathways for the introduction and spread of invasive alien plants (IAPs). In recognition of this, the South African government has recently enacted a new set of Alien and Invasive Species regulations, under the National Environmental Management Biodiversity Act (NEMBA), that are intended, in part, to improve controls on the horticultural industry's role in the spread of IAPs. In order to assess, and possibly enhance, the likely effectiveness of NEMBA, it is critical to build an understanding of stakeholders' awareness and attitudes towards the control of IAPs and associated regulatory policies. A two-pronged approach â€“ involving nursery manager interviews (n=30) and plant stock audit assessments (n=41) - was used to gauge the awareness, compliance and attitudes of Cape Town nursery managers towards the NEMBA regulations. Results showed that less than ten percent of the city's audited nurseries were compliant with the NEMBA regulations, and that over fifty percent were stocking IAPs that have been regulated for at least thirteen years under a previous set of regulations (the Conservation of Agricultural Resources Act, CARA). This is despite high levels of awareness about the CARA regulations reported in the interviews, reported enthusiasm for compliance, apparent concern for the environment, evidence that managers understand the problems that IAPs cause, extensive reported support for the control of IAPs, and a reportedly strong sense of duty to protect the environment. The vast majority (73.5%) of IAP species found in nurseries were NEMBA category 1b invaders such as Nerium oleander, Lantana montevidensis and Canna indica. These are species that are widespread and well-established invaders that require control. This study suggests that a range of factors are likely to negatively influence compliance including a perceived lack of enforcement, weak communication from government, issues related to the clarity of the regulations, the lack of inclusion of the industry in the regulatory process, and a lack of awareness, with at least half of the managers reporting that they had not heard about the enactment of NEMBA. Any attempt to improve the impact of the new regulations will need to adequately address each of these factors. The results of the study suggest that enhancing the impact of NEMBA will require improving aspects of the legislation itself, and supplementing the current top-down approach to regulation with an inclusive partner-centred approach.
Open Access
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.
Open Access
Analysis of long-term changes in populations of the Clanwiliam Cedar (Widdringtonia cedarbergensis) using repeat photography
(2013) White, Joseph Douglas Mandla; Hoffman, Timm; Jack , Sam; February, Edmund C
Repeat photography photosets were used to analyse 20th century changes in populations of Widdringtonia cedarbergensis from four sites in the Cederberg Mountains, South Africa. Systematic evaluation of 115 photosets was combined with field observation and environmental data to determine the age class and degree of foliage cover, as well as fire frequency, rockiness of habitat, altitude, aspect of slope, annual mean temperature and annual precipitation for each tree viewed in photosets. Mortality and recruitment events were documented in each of the photosets. A total of 1315 trees were recorded in historical photographs (1931- 1982), with 968 of these shown to have died in the repeat photographs (2007-2013), indicating 74% mortality. With only 45 (3.4%) recruits being recorded, the total current living population of W. cedarbergensis in the repeat photographs was 392. There was no significant difference found in mortality or recruitment across the sampled sites. From the historical to repeat photosets there was an 8% increase in the proportion of mature adults and a 13% increase in the proportion of W. cedarbergensis individuals with sparse foliage cover. A generalized linear model was used to determine the effects of environmental factors on W. cedarbergensis mortality in natural populations.
Open Access
An assessment of ecological impacts of community-based restoration on communal grasslands in the Drakensberg foothills
(2011) Marx, Dane Lee; Hoffman, Timm
Okhombe is a ward in the Northern Drakensberg where community based restoration of degraded lands has been conducted for over a decade. In this important water supply region, payment for ecosystem services has been suggested as a means through which to conserve biodiversity, improve veld condition, provide income to local communities, and ensure water security. However, before such alternative market mechanisms can be considered, the effects of community based restoration must be properly quantified. The primary aim of this study was to determine some of the ecological impacts of community based restoration in these communal grasslands.
Open Access
An assessment of the distribution and conservation status of endemic and near endemic plant species in Maputaland
(2016) Matimele, Hermenegildo Alfredo; Raimondo, Domitilla; Hoffman, Timm; Timberlake, Jonathan; Lötter, Mervyn; Burrows, John
The Maputaland Centre of Endemism (MCE), an area stretching from northern-east KwaZulu-Natal in South Africa to the Limpopo River in southern Mozambique, holds more than 2,500 native plant species. Of those, over 203 are endemic or near endemic to this area. However, the current high human population density in MCE, coupled with high population growth, has increased the pressure on the natural resources of the region and threatens the natural vegetation and plant diversity. Therefore, there is a pressing need to fully understand the threats faced by the Maputaland endemic and near endemic plants and to carry out appropriate conservation actions. In this context, the main aim of the study was to document the distribution of the MCE endemic plant species, with particular emphasis on southern Mozambique. The study also aimed to document the threats to these species and to assess their global conservation status using the International Union for Conservation of Nature (IUCN) Red List Categories and Criteria. This was done by gathering historical species distribution data from herbarium specimens and by assessing their current distribution in the field. In addition, a land cover data set was used to evaluate the level of habitat transformation over time. As a result, 13 endemics were assessed, 11 of these species for the first time. Of the 13 species assessed, two were assessed as Least Concern, five as Vulnerable, four Endangered, one Critically Endangered, and one possibly Extinct. MaxEnt models were used to model the potential distribution of the species assessed and to identify hotspots and priority areas for conservation. The priority areas represent sites of greatest overlap, where 50% of all modelled species overlap in their suitable potential distributions. With this approach, priority areas were identified that can be used in conservation planning, protected area expansion, or other conservation projects. This analysis showed that the highest number of the study species (>7) is concentrated within the Licuati Forest, located south of Maputo in Matutuine District, southern Mozambique. The main threat to this area is charcoal extraction and although none of the endemic species are targeted for charcoal production, the impact of the associated habitat destruction on the endemic species is expected to cause severe declines. It is recommended that studies on the dynamics of the Licuati Thicket vegetation are needed, particularly in terms of the impact of charcoal extraction on the endemics.
Open Access
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?
Open Access
Changes in abundance and distribution of Protea caffra in the central and northern Drakensberg as a consequence of climate and land use change
(2014) Poultney, Daniel Mika-Nsimbi; Hoffman, Timm; February, Edmund C; Rebelo, Anthony G; Puttick, James; Jack,Sam
The study investigated changes in populations of Protea caffra at five sites in the central and northern regions of the uKhlahlamba Drakensberg Park, a UNESCO world heritage site. Based on an archaeological study in 1994 that used charcoal remains to compare the size of Protea species populations in the Drakensberg to a much earlier era (between 1260 to 1880 BP), it was hypothesized that there would be a further decline in the number of individuals. A total of 76 historical photographs (dated from 1950-1995) were re-photographed in 2014 and the number of individual P. caffra plants in the two sets of photographs counted to assess the extent and rate of population change. The landform units were demarcated on each photograph according to their catenal position, aspect, elevation and the extent of rocky cover. Geological parameters for each landform unit were obtained from GoogleEarth, climatic data from the South African Atlas of Climatology and Agrohydrology and fire data from MODIS. In 76% of the landform units there was an increase in the number of individuals over time, in 17% a decrease and in 7% there was no change over time. Several hypotheses were generated from a conceptual model based on ecological insight into the study area to explain change in the abundance and distribution of P. caffra. Using an Akaike test, the input models were ranked according to how representative the explanatory variables were of the observed change. The model with aspect and elevation as explanatory variables was ranked the best predictor of change. A greater proportion of increase in the size of the population was found on lower slopes. With increasing atmospheric CO2, P. caffra on the warmer lower slopes are likely to have increased photosynthetic rates and increased productivity. A greater proportion of landform units showing a decrease in P. caffra was shown at higher elevations. The reason could be higher fire intensity at higher elevations. The variation in change influenced by fire suggests it is an important regulator of P. caffra numbers. The fact that there is no relationship between fire frequency and landform units showing an increase in P. caffra implies that the majority increase in the species is more likely to be driven by climatic changes, i.e. increases in atmospheric CO2 rather than a change in the fire regime. Increasing atmospheric CO2 levels lead to enhanced growth rates, postburn recovery and resprouting of tree species in grasslands and savannas, which could account for the majority increase in P. caffra populations in the grassland of the Drakensberg. This has important conservation management implications for the reserve, in that the current fire regimes do not appear to be having a negative impact on the abundance in P. caffra. Further, fire will continue to be an important management tool in maintaining the vegetation structure and grasstree codominance in the reserve.
Open Access
Changes in distribution of indigenous forest in Table Mountain National Park from 1880-2012
(2013) Poulsen, Zoe Chapman; Hoffman, Timm
South Africa's indigenous forest only covers 0.56% of the country's total land area. Its highly fragmented distribution and historically extensive exploitation has led it to be perceived as one of the South Africa's most vulnerable vegetation types. Despite this, forest remains one of South Africa's most under-researched ecosystems and the country has few dedicated forest ecologists. This research examines changes in distribution of Western Cape Afrotemperate Forest and Western Cape Milkwood Forest in Table Mountain National Park. Forest – Fynbos spatial ecotonal change and forest patch count was mapped from 1944 to 2008 using aerial photographs in ArcGIS 10. A full survey of species composition was undertaken and this dataset was used to produce an objective classification of the Cape Peninsula forests. Ground-based repeat photography was used to determine land cover change from 1880 to present with finer scale resolution. An analysis using transition matrices projects future land cover changes to 2050. A total of 174 forest patches were identified in Table Mountain National Park. Total indigenous forest cover has increased by 65.3% from 1944 to 2008. This increase was predominantly visible within the Peninsula's Western Cape Afrotemperate Forest and the highest expansion rates were recorded in Orange Kloof and Blinkwater Ravine on Table Mountain. Only 13 of the forest patches surveyed decreased in cover after 1944. Most of these patches were areas of Western Cape Milkwood Forest located in proximity to expanding coastal development. This trend was also reflected in the repeat photography dataset. There has also been an increase in vegetation biomass recorded at all sites. Further research is required to determine whether these changes have caused a decrease in fynbos species diversity. Non-parametric statistical analysis showed no correlation of forest change with variation in aspect, temperature, precipitation, geology, soils or fire frequency post 1975. These findings indicate that forest patches are influenced by localised ecological factors and suggests a dominant role for other drivers. Historical evidence indicates the key driver of forest expansion is vegetation recovery from past high fire frequency alongside the influence of current fire suppression policies. Increases in CO2 may also be a contributory factor although localised variation in extent of forest expansion suggests that this is not the strongest driver of change. These results hold significance for the future ecological management of Table Mountain National Park in the face of changing climate.
Open Access
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
Open Access
Elephant impacts on woody vegetation around artificial waterholes in Zambezi National Park, Zimbabwe
(2020) Wilson, Luke; Hoffman, Timm; Cumming, David
Elephant are renowned for their ability to substantially alter vegetation. However, as they need to drink regularly, surface water exerts a strong influence over the distribution and magnitude of elephant impacts on vegetation. This study was conducted in Zambezi National Park, a 560 km2 unfenced protected area in northwest Zimbabwe. It aimed to investigate the impacts of elephant on woody vegetation, particularly in relation to artificial waterholes. Sampling plots were located at different distances from four pumped waterholes in teak (Baikiaea) and Terminalia woodlands, the two main woody vegetation types recognised in the study area. Plots were set at 200, 500, 1000, 2000 and 4000 m from waterholes in the teak woodland. Due to the close proximity of waterholes, a lower maximum distance of 2500 or 3000 m from waterholes had to be used in the Terminalia woodland, but sampling intervals from 200-2000 m were otherwise the same. Assessment of elephant browsing and a series of measurements were performed on trees and shrubs within these plots, with plants assigned to one of three height classes (0.2 - < 1 m; 1 - <3 m and ≥3 m). Elephant dung counts were also conducted in these plots, to provide a measure of elephant occupancy. A clear decline in elephant browsing with distance from waterholes was evident in both the teak and Terminalia woodlands. However, elephant browsing was consistently higher in the latter woodland type. Averaged across all plant height classes, elephant had removed 30-45% of plant canopies in most Terminalia woodland plots. More moderate canopy removal of 10- 30% was found in most teak woodland plots. Plants ≥3 m were particularly highly browsed in the Terminalia woodland, with over 50% of their canopy volume removed in most plots. Elephant browsing impacts were also considered at the species level, which revealed clear differences in browsing levels among species. Some uncommon and highly browsed species were flagged as being potentially vulnerable to disappearance from the area, even in the teak woodland where overall elephant browsing was lower. The effects of elephant browsing on vegetation structure at different distances from artificial waterholes were also investigated. Little change was apparent in the teak woodland, where the only noted impact was a reduction in the density and canopy volume of plants 1 - <3 m tall, limited to within 1 km of waterholes. More pronounced structural impacts were evident in the Terminalia woodland. Substantial declines in the basal area and canopy volume of trees (i.e. plants ≥3 m) occurred closer to waterholes, with widespread conversion of woodland to shrubland evident. Reductions in both tree and shrub canopy volumes closer to waterholes also suggested a reduction in browse availability in the Terminalia woodland. Finally, elephant dung declined with distance to waterholes, confirming that elephant were found in higher densities closer to waterholes. However, dung counts did not reveal different levels of elephant occupancy between the two vegetation types, despite higher browsing in the Terminalia woodland. This finding suggests elephant might be using the teak woodland for purposes other than just browsing, such as for shade. The study thus provided evidence that waterholes have had a significant impact on vegetation in the area, particularly on the favoured Terminalia woodland. Acknowledging the tourism value of retaining waterholes in the area, it is suggested that distances between waterholes should be increased, through only continuing pumping at waterholes with viewing platforms. This could result in a more heterogeneous elephant browsing regime across the highly impacted Terminalia woodland in particular, and lessen further homogenisation of this vegetation type towards a shrubland.
Open Access
Environmental change in Riemvasmaak, Northern Cape, South Africa twenty years after resettlement
(2016) Fleury, Gabriela; Hoffman, Timm; Todd, Simon W
The 75,000 ha area of Riemvasmaak, located north of the Orange River within the Northern Cape Province, is an important case study with regard to land restitution and livestock impacts upon arid rangelands hypothesized to be at disequilibrium. As part of a 'black spot' removal program during apartheid, about 1,500 people from Riemvasmaak were forcibly moved off their land in 1974. With many returning to the area in January 1995, Riemvasmaak represented the first successful land restitution case in post-apartheid South Africa. This study follows up on a long-term environmental monitoring project set up in 1995 and revisited in 2005 and early 2015 to determine the impact of the returnees on the vegetation and ecology of the region. It builds upon the repeat photography methodology utilized by Hoffman et al. (1995) and Hoffman and Todd (2010) in order to provide a robust and accessible measure of change in the herbaceous and woody components of the vegetation. The percentage cover of herbaceous and woody vegetation was visually estimated in repeat photographs from 27 photo stations for the years 1995, 2005, and 2015. The results of a linear mixed-effects model suggest that herbaceous vegetation decreased significantly from 1995 to 2005 (p< 0.001) and increased significantly from 2005 to 2015 (p< 0.001) while woody cover did not change significantly from 1995-2015. There was no difference in these trends between the three landform units assessed (rivers, sandy pediments and rocky slopes). Linear regressions utilizing size class and density of individuals for Acacia erioloba (Vachellia erioloba) indicated that there had been little recruitment over the period 1995-2015 in comparison to the period prior to the initial survey in 1995. Fifteen face-to-face interviews with livestock owners, herders, and the local Agricultural Collective in 2015 outlined the socioeconomic and cultural changes that had occurred in Riemvasmaak since 1995. One such change, a directive issued by the Riemvasmaak Municipality in 2009, that ownership of livestock would no longer be allowed within Municipality boundaries, resulted in the removal of livestock from Riemvasmaak in the years directly before 2015 and corresponded temporally with the rise in herbaceous cover seen in 2015.
Open Access
An ethnobotanical, phytochemical and metabolomics investigstion of plants from the Paulshoek Communal Area, Namaqualand
(2014) Wheat, Nicola M; Gammon, David W; Hoffman, Timm; Chibale, Kelly
The aim of this thesis is to investigate medicinal plants from different perspectives in an attempt to arrive at a new, integrated and streamlined method for the discovery of bioactive secondary metabolites of plant origin. This will be done through a focused study of the traditionally used medicinal plants of the Paulshoek region of Namaqualand and a demographic study of the people who use them. Trends in traditional medicinal plant choice will be investigated and methods of traditional knowledge acquisition and transfer will be examined. Additional assessment of bioactivity and trends in bioactivity will be conducted and a variety of physico-chemical and computational techniques will be used to determine the major metabolites present in selected plant species. These different approaches to medicinal plants will be brought together in a single holistic method put forward as a possible way of conducting future studies into discovering active metabolites for potential drug development.
Open Access
Extinctions: Past and Present Week 5 - Landscape changes
(2017-03-17) Chinsamy-Turan, Anusuya; Hoffman, Timm
In this video, Professor Anusuya Chinsamy-Turan interviews Professor Timm Hoffman, a plant biologist, on the slopes of Table Mountain where he shows a visual example of landscape change due to human activity. He describes the a citizen science project he runs (RePhoto) which collects old photographs to track changing landscapes.
Open Access
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.
Open Access
The impact of grazing along an environmental gradient in the Kamiesberg, South Africa
(2008) Anderson, Philippa Mary Levick; Hoffman, Timm
The Kamiesberg Mountain range, which is situated within the arid Succulent Karoo biome, South Africa, is internationally-recognised for its high conservation value and forms the study site for this project. The Kamiesberg is straddled by the Leliefontein communal area, which has been stocked for many years at twice the rate of the adjacent private rangelands. This presents an opportunity to test whether and how high stock numbers impact on vegetation. In the literature the drivers of rangeland ecology are discussed predominantly in the context of the equilibrium versus non-equilibrium debate, where density-dependent or climatic factors influence the vegetation respectively. Recent dissatisfaction with these paradigms has lead to the exploration of models better placed to incorporate the complex dynamics of rangelands.
Open Access
The influence of rainfall seasonality and climate change on the demography of Aloe Dichotoma, a long-lived succulent tree from semi-arid southern Africa
(2014) Gallaher,Kirsten Sarah Leilani; Hoffman, Timm; Rebelo, Anthony G; Jack,Sam
In the arid and semi-arid western parts of southern Africa, Aloe dichotoma Masson, a long-lived succulent tree species, is thought to be responding to anthropogenic climate change. However, differences in response across its distribution are likely to be related to rainfall seasonality. This study investigated change in ten Aloe dichotoma populations within winter and summer rainfall zones in South Africa and southern Namibia. Using repeat photography over a timespan of approximately 30 years, demographic patterns, population dynamics (including mortality, recruitment and overall population change) and growth were assessed and modelled with climatic variables. Long-term patterns of recruitment and longevity were also investigated by using individual plant growth data to reconstruct recruitment histories for each population. Finally, the influences of climatic conditions on recruitment were evaluated by superimposing historical rainfall and temperature data. Differences in response between rainfall zones are clearly evident throughout. Generalised linear models revealed lower mortality, higher recruitment and positive population change at winter rainfall sites, while summer rainfall sites showed negative population change. Growth data revealed more rapid growth in height of juveniles than adults, and slower growth in height in the winter rainfall zone, most likely related to differences in tree architecture. It is evident that biotic and anthropogenic factors such as herbivory, nurse plants and theft are likely to moderate observable patterns as opposed to driving them. Recruitment modelling suggested that A. dichotoma attains a maximum age of 300 to 350 years, and revealed recent recruitment peaks in the winter rainfall zone and peaks around the turn of the 19th century in the summer rainfall zone. Changes in temperature and rainfall are likely to be the main drivers. Rising temperatures within the last century may have driven increased recruitment and low mortality in the cold-limited winter rainfall zone, while decreasing rainfall within the summer rainfall zone, combined with increasing temperatures, may explain this region's low recruitment and high mortality. The advancement of knowledge of broad spatial and temporal patterns in A. dichotoma and the likely causes, coupled with fine-scale future studies, will enable more detailed prediction of the species' response to future global change.
Restricted
Landscape change and ecological processes in relation to land-use in Namaqualand, South Africa, 1939 to 2005
(2009) Hongslo, Eirin; Rohde, Rick; Hoffman, Timm
This paper examines the consequences of land use on vegetation over a sixty-six year period, within various agrarian landscapes across the winterhummer rainfall ecotone in northern Namaqualand. We employ repeat ground and aerial photography and interviews with land users to elucidate the causal factors that explain environmental change and stability. Ecological literature on landscape change in Namaqualand has suggested that communal land-use is detrimental to vegetation cover and species richness. Our study shows that there have been very few changes in vegetation cover and species richness in cultivated and grazed communal areas during the last 65 years, but that there has been a regeneration process in the private and protected areas. We demonstrate that these different vegetation responses reflect different land management histories. This evidence suggests that the potential for increased vegetation cover and species richness in response to land-use change is higher than was previously assumed and provides a new perspective on the latent capacity of communal landscapes to regenerate from changes caused by cultivation and grazing pressure. The environmental history presented in this paper spans a temporal and spatial scale that elucidates the complex relationship between land-use, climate, soils and vegetation change.
Open Access
Life history traits of South African Encephalartos spp. (Zamiaceae) and their implications for understanding population structure, responses to threats and effective conservation action
(2016) Konings, Kim Martina; Donaldson, John Sydney; Hoffman, Timm
Understanding life history traits and how they influence population-level processes under different conditions have been important areas of study in evolution and ecology. One application in ecology has been to determine whether there are general responses that apply to species with similar life history traits, which could provide a predictive understanding of species with shared traits rather than having to adopt a speciesspecific approach to management. In this study, an analysis of life history traits was applied to cycads, the oldest living seeds plants which are at risk of extinction due to vulnerability to illegal wild harvesting and habitat loss. The study focused on South African cycad species within the genus Encephalartos, as well as two species from Swaziland. The first objective was to identify groups of species with similar life histories and to assess whether these groups are aligned with phylogenetic relationships or an association with particular environments. The second objective was to determine whether species with shared suites of life history traits exhibited a similar population stage structure. Hierarchical cluster analysis and Principal Component Analysis (PCA) were used to identify groups based on key life history traits, namely, cone number and coning interval, number of seeds produced, number of stems, stem height and plant habit. Four life history groups emerged, these were: Group 1 with single-stemmed, subterranean species such as E. villosus; Group 2 generally characterised by medium-height species with many stems such as E. lehmannii; Group 3 with the tallest species which generally produce the most cones at the most frequent interval such as E. natalensis; and Group 4 with dwarf-arborescent, multi-stemmed species such as E. horridus. The groups were not found to correspond with the most recent phylogeny for Encephalartos and thus phylogenetic constraints were excluded. An analysis of environmental variables for 193 populations of species in all groups, including maximum and minimum temperatures, mean annual precipitation, moisture index, rainfall co-efficient of variation and fire return frequency, showed that the means per group were not significantly different from each other for most of the variables. However, it was evident that the variable ranges showed clear trends with biological significance. These tended towards more stable, less variable environments with more predictable rainfall for Group 1 species, and less stable, more variable environments with less predictable rainfall for species within Group 4. Groups 2 and 3 showed a large range and overlap in environmental associations with no consistent patterns. Population structure is valuable for determining whether recruitment in a population is adequate for species survival. Static life tables and Chi-Squared analyses were used to test differences in the population structure and survivorship patterns of species between and within the life history groups. If particular demographic patterns were shown to be emergent properties of certain suites of life history traits, autecological studies may be avoided for predictive-ecological conservation frameworks. The results showed that species in Group 1 had populations with a high proportion of juveniles and fewer reproductive adults, indicating high recruitment as well as high juvenile mortality. In contrast, species in Group 4 had populations with a high proportion of adults and fewer juveniles indicating low recruitment and high juvenile mortality with primary investment into adult plant persistence through vegetative suckering. Group 2 consisted mostly of rare species with very small populations and high proportions of adult plants showing evidence of episodic recruitment events. Species in Group 3 showed a similar trend towards intermittent recruitment with adult persistence, however, no explicit population structure emerged. This led to the conclusion that Groups 1 and 4 are relatively consistent and predictable, however, Groups 2 and 3 would better benefit from an autecological approach to management. This study was helpful to assemble life history data for South African Encephalartos, as well as environmental parameters for each species. Ultimately, it has shown that primary investment into seeds versus persistence, or a combination thereof, can influence population structure.
Open Access
Living in a changing world: an integrated approach to documenting and understanding medium to long-term vegetation changes in three contrasting land use systems in a mesic savanna, Nothern Zululand, South Africa
(2007) Wigley, Benjamin J; Bond, William J; Hoffman, Timm
There is an increasing amount of evidence suggesting that the balance between trees and grasses in savannas and grasslands has been disrupted in the recent past. Numerous studies from around the world have reported an increasing woody component at the expense of the grass layer. The causes most frequently cited for this shift are linked to changing land use practices. This study was therefore set up to investigate the effects of three contrasting land use systems on long-term vegetation dynamics in a mesic savanna. I aimed to determine if land m;e practices alone could account for the changes in vegetation cover evident at the study sites between 1937 and 2004. An alternative explanation for the changes could be linked to a global driver such as changing climate or increasing atmospheric CO2 concentrations. The rate and extent of vegetation changes were measured and recorded in areas that have remained under communal, commercial and conservation tenure for approximately the past century. Changes in vegetation were determined for a 25 km2 area in each area using repeat panchromatic aerial photography from 193 7, 1960 and 2004. Images were mosaicked and georeferenced then overlaid and manually classified. A comparison between manual classifications and machine-generated classifications using eCognition software was also undertaken. Past land use practices for the three study areas were reconstructed using a combination of archive materials and oral histories. The managers, land users or landowners from areas under communal, commercial and conservation tenure were extensively interviewed to determine their perceptions of the changes, consequences of the changes and reactions to the changes in vegetation. The results showed that significant increases in woody cover occurred during the 67-year period at all three sites. The communal study site showed the least increase in tree cover. However, the overall increase in tree cover at the communal site, from 6.2 to 25.7 % (fourfold increase), is still a highly significant change. The greatest increase in tree cover was evident at the commercial study site where tree cover increased seventeen fold. Total tree cover increased from 2.7 to 50.8 % during the 67-year period. The increase in tree cover at the conservation study site was also highly significant. Tree cover increased by ~360 %, from 14.7 % in 1937 to58.5 % in 2004. These vegetation changes correspond to major losses of grassy habitats in each area. The biodiversity losses associated with these changes are largely unknown but are likely to be substantial. Past land use practices and histories in each area were also shown to be significantly different with major differences in human densities, stocking rates, herbivore feeding types and burning practices. Long-term rainfall records did not show any significant changes in the quantity or seasonality of rainfall. The results suggest that past land use practices did have some impact on the type of and extent of bush encroachment. The study found that although the land users were aware of and concerned about the changes in woody cover in each area, they were not doing much to combat these changes. The perceived importance of the different causes of woody increase was also found to be substantially different amongst the different land users. The findings suggest that land use practices alone cannot explain the widespread occurrence of bush encroachment in the area. This could suggest that a global driver is contributing to the increasing tree component.