Biological Sciences

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Seeing the wood for the trees : an evaluation of the Buffelsdraai Landfill Community Reforestation Project.
(2016) Roy, Kathryn Elizabeth.; Kirkman, Kevin Peter.; Adie, Hylton Ralph.; Douwes, Errol.; Roberts, Debra Cynthia.
Cities, and African cities in particular, will need a suite of relevant tools and approaches to deal with the varied climate change-related threats that these cities will likely endure in the future. African cities will be most affected due to the challenges of underdevelopment and resource shortages and, therefore, must address the climate change challenge in a way that ensures meaningful developmental co-benefits and overall cost-effectiveness. Local level actions, such as ecosystem-based adaptation (EBA), and community-based adaptation (CBA), are both effective forms of adaptation for African cities. The City of Durban (eThekwini Municipality, South Africa), has embarked on a novel approach that combines both these tools, the community ecosystem-based adaptation (CEBA) concept, of which the Buffelsdraai Landfill Community Reforestation Project (BLCRP) is a powerful example. The BLCRP is restoring indigenous forest in the buffer zone surrounding the Buffelsdraai Regional Landfill Site. The project aims to sequester a proportion of CO2 emissions generated locally during the 2010 FIFA World Cup™, whilst also uplifting local impoverished communities and building functional ecological infrastructure. The need to build the resilience of the city to climate change, in the face of increased uncertainty and risk, is considered urgent by planners. Building functional ecological infrastructure, which includes indigenous forest ecosystems, can help bolster this resilience. Early detection in restoration projects, such as the BLCRP, can allow problems to be identified and rectified through adaptive management in the early stages of restoration. This approach will affect the success and cost effectiveness of the restoration project. The BLCRP is currently in the establishment phase, a time when enrichment planting is best evaluated. This study examines the extent to which the composition, measures of diversity, and functional traits of planted species at restoration sites, are comparable with a local forest reference site. After three to five years, restored sites show low similarity with the reference forest due to different species composition and low species diversity and richness. Functional richness is significantly lower in two of the Buffelsdraai sites. Additionally, few bird-dispersed species were planted at Buffelsdraai and the restoration sites are infested with invasive alien plants compared with the reference ecosystem site. Furthermore, planted tree densities at the restoration site were considerably lower than figures recommended for restoration projects. Given these findings, the BLCRP is unlikely to meet long-term goals. To address these project shortfalls, I propose a higher planting density and a rigorous process to select tree species for planting. This includes implementing the framework species method at Buffelsdraai, which has proven successful in various countries. The framework species method encompasses the planting of mixtures of early and late successional species to capture the site, establish a multi-layered canopy, modify the microclimate and diminish weed growth in the years immediately after plantings. Species planted will also attract animals that will further disperse seeds into the planted area. A desktop assessment of forty-eight tree species helped determine which species would be suitable for field-testing and for eventual planting as framework species at Buffelsdraai. These included tree species common to the vegetation type found at the reference ecosystem site. A total of 18 species were considered unacceptable and removed, leaving 30 species as candidates for future testing. Best performing species were Celtis africana, Ekebergia capensis, Ficus natalensis, Bridelia micrantha and Croton sylvaticus due to their ability to attract wildlife, grow fast and tall and remain resilient to climate change. Worst performing species were Eugenia natalitia, Dalbergia obovata, Millettia grandis, Allophylus natalensis and Baphia racemosa, all of which were rejected from further testing. Future steps, such as nursery- and field-testing of candidate species, are recommended. The framework species method can be integrated with the current restoration method at Buffelsdraai. These recommendations will enhance biodiversity, increase canopy closure and reduce site management costs. Critically, appropriate and continuous monitoring is required to initiate appropriate management responses.
Vegetation and ant dynamics in the southern Karoo.
(1997) Adie, Hylton Ralph.; Yeaton, Richard I.; Van Staden, Johannes.
The aim of this thesis was to describe the structure and dynamics of ant and plant communities in the southern Karoo and to assess mechanisms of species coexistence in ant and plant communities. The role of species interactions in structuring natural communities was emphasised. Diversity indices were used to determine the importance of habitat in maintaining ant species diversity. Ant species diversity was not predicted by measurements of plant species diversity or vegetation structural diversity. Ant species richness was correlated with vegetation structural diversity but not with plant species diversity. Ant species appeared to respond to aspects of vegetation height. Although vegetation complexity influences ant species richness, competitive effects, particularly of dominant ant species, appear to suppress sub-ordinate ant species influencing measures of richness and diversity. Aggressive dominant ant species determine the distribution and abundance of sub-ordinate ant species. Interference competition for space was prevalent between dominant ant species and competitive success was a function of vegetation. It was not clear whether ants respond directly to physical conditions created by vegetation which then influences foraging activity or, alternatively, whether ants respond to productivity gradients which are affected by vegetation. Understanding vegetation dynamics is critical to interpreting patterns of ant species distribution and abundance. A patchy habitat disrupts the competitive dominance of aggressive dominant species, removing the potential towards habitat monopolisation, and therefore maintaining ant species diversity. In the Portulacaria afra rangeland, Pheidole sp. 2 was superior in well-shaded microhabitats but Messor capensis nested successfully under woody shrubs and several ant species (Tetramorium peringueyi, T. quadrispinosum, Monomorium alamarum, Ocymyrmex barbiger) persisted on bare nutrient-rich patches. Rangeland dominated by grass would favour Pheidole sp. 2 at the expense of other ant species which would be unable to establish successfully. There is no evidence supporting the notion that ant communities are at equilibrium. Rather, dominance hierarchies lead to the replacement of species over vegetation gradients with the tendency towards the aggressive acquisition and monopolisation of space. The coexistence of dominant ant species at study sites in the southern Karoo was a combination of territorial strategy and colonisation ability. In the P. afra rangeland most ant species escaped the severe competitive effect of Pheidole sp. 2 by persisting as fugitives on bare areas of local disturbance where Pheidole sp. 2 was less successful. At Tierberg, competitively inferior ant species with a decentralised territorial system coexisted with competitively superior ant species in an unstable equilibrium by pre-empting newly available space through the lateral expansion of territories. Competitively superior species, however, replace the inferior competitor (yet, superior coloniser) in time. Plant succession in the Portulacaria afra rangeland follows a deterministic pattern of cyclical replacement. No single mechanism adequately explains the coexistence of all plant species in this community. Nurse-plant effects were important for the establishment of P. afra and later-successional trees below woody shrubs and P. afra respectively. Soil moisture and nutrient levels below nurse plants were favourable for the successful establishment of seedlings but nurse plants also disrupt the inhibitory effect of grass on seedlings and young plants. Linked to the facilitative process is the directed dispersal of seeds by biotic vectors. Seed dispersal by ants and birds moves propagules away from the harsh competitive environment of established adult plants (particularly grass) to safe establishment sites below nurse plants. Complementary root systems of seedlings and nurse plants may facilitate the establishment of young plants but ultimately competition will reduce nurse plant vigour leading inevitably to the death of the nurse plant. At least two plant species (Lycium cinereum and Psilocaulon absimile) persist in the P. afra rangeland as fugitives on areas of local disturbance. The relatively cool and moist environment below P. afra clumps supports a variety of detritivorous taxa that enrich the soil. Once the P. afra clump collapses and dies, bare nutrient rich patches that favour the establishment of L. cinereum and P. absimile, ahead of the competitively superior grass component, remain. However, the replacement of the fugitive plant species by grass is inevitable as the soil nutrient levels decline. The competitive superiority of grass controls the dynamics of the P. afra rangeland system. Disruption of the inhibitory effect of grasses by elevated nutrient levels (e.g. detritivore activity, ant nests) permits plant species to establish that would otherwise be unable to in the absence of disturbance. Degradation of the grass component by overgrazing at the P. afra rangeland site has the same effect as disturbance by soil-nutrient enrichment and results in an increase in plant species diversity. All stages of the cyclical process would be relatively uncommon in a grass dominated system because of the inability of plants to establish successfully in grass. Strong feedback links exist between the ant and plant communities studied. Habitat patchiness maintains ant species diversity by disrupting dominance hierarchies. Ants maintain plant species diversity by moving seeds out of competitively harsh microhabitats into safe sites (often below nurse plants) for establishment. Soil nutrient enrichment (ant nests and various detritivore taxa) create disturbances which also facilitates plant establishment. Overgrazing by domestic stock causes the replacement of palatable by unpalatable plant species. Unpalatable plant species, released of suppressive effects, develop into a monospecific stand that inhibits the further establishment of seedlings. Loss of habitat patchiness results in habitat monopolisation by one (or two) dominant ant species. Habitat degradation therefore severs the complex feedback links between the plant community and the important invertebrate component (dispersal agents and detritivores) which disrupts the dynamic processes driving the system.

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Browsing Biological Sciences by Author "Adie, Hylton Ralph."