Researcher: Abraham Nqabutho Dabengwa
Region: KwaZulu-Natal, South Africa
The KwaZulu-Natal (KZN) Province of South Africa is biome rich. These biomes are defined using climate and major plant growth forms (i.e., trees, grasses and forbs). Grasslands are dominated by grasses; the savannah comprises variable tree cover in a continuous grass layer; the Indian ocean costal belt (IOCB) is a mix forest and grassland patches; forests are a continuous and stratified layer of trees and azonal is a mix of growth forms at biome boundaries and along drainage lines.
This diverse vegetation assemblage can be partly explained by climatic and anthropogenic factors like rainfall abundance and seasonality, temperature ranges, soil texture, soil nutrient availability, soil moisture, topography and competition, fire and disturbance by humans. Climate is the most commonly used determinant of biome distribution because of the effect it has on specific plants and communities, which has led to the use of vegetation as a proxy for climate.
However, climate is dynamic and it is therefore unlikely that vegetation can achieve equilibrium with its environment because temperature and rainfall have changed on geological, millennial, centennial and anthropogenic timescales. Further, Nguni and European settlers have subjected the KZN landscape to successive and intense waves of disturbance. More recently, industrialisation has increased the scale of disturbance and therefore a pre-settlement vegetation benchmark and an understanding of post-settlement vegetation dynamics may offer insights into managing biomes in human affected ecosystems.
These anthroprogenic factors are also interactive with natural disturbance regimes (e.g., fire and herbivory) by synergistic effects on modification of plant populations or in opposition by cancelling each other’s effect on vegetation dynamics. In addition, many of the processes mentioned are beyond the reach of conventional ecological approaches that work on annual to decadal time-scales.
One approach to understanding how these complex factors have affected vegetation over time is to study vegetation-climate, herbivory and fire through palaeo-ecological methods.
The aim of the study is to assess how grassland, savannah, forest and thicket dynamics at ecotones in KwaZulu-Natal are related to climate, competition, herbivory, and nutrient biogeochemistry at millennial-decadal timescales. This knowledge may be used by scientists, conservation and development practitioners, to develop biome-specific baselines and targets for ecosystem management in a changing world. Although climate cannot be manipulated at the local scale, herbivory and fire are potential management tools that can be used to conserve favoured species assemblages and to preserve ecological processes and ecosystem services.
- Explore how the drivers of vegetation dynamics (i.e., climate, herbivory, fire and nitrogen availability and human land use) interact and determine the feedback mechanisms between them that may be responsible for shifts in vegetation assemblage(s).
- Explore whether drivers or switches are homogeneous (regional) or heterogeneous (localised) by comparing pollen diagrams in study areas.
- To examine the implications of the above for South Africa’s current conservation, ecosystem management, restoration, climate change, and agricultural policy
This work involves the use of plant fossils and remains of peatland sediments to try draw conclusions of past environments (vegetation and climate) over long time periods. Skills to be developed include palynological and pollen analysis, radiometric dating, ecological succession and plant-environment relationships arising from these in order to better understand how to conserve our current biodiversity.
A review and synthesis of the palaeoecological, archaeological and historical literature will be used as a method of establishing pre-colonial and early benchmarks of vegetation composition and structure. Adding a deeper time perspective to these data, we will analyse fossil pollen and charcoal from sedimentary sequences to reconstruct vegetation dynamics over timescales of centuries to millennia. AMS radiocarbon dating and Pb210 dating will be used to establish a chronology for these vegetation changes.
Where possible, we will sample sediments from close to present day ecotones, because the boundaries between biomes are where species are at their biological and/or environmental limits; thus biomes are especially useful in the study of vegetation change, particularly in terms of identifying critical thresholds, or points where one biome collapses and reorganises into a different vegetation assemblage.
Extraction and preparation of pollen samples will be by standard methods and/or via the testing of a gravimetric separation method still to be tested. Pollen identification will utilise the pollen reference collection at the Plant Conservation Unit, Cape Town, as well as keys and reference plates.
The proposed study is expected to contribute towards improving our understanding of plant succession at selected biome boundaries, essential elements in plant and restoration ecology. The identification of plant community states and transitions (vegetation dynamics), and environmental drivers forms the basis for landscape history that can be applied as a template for similar bioregions.
Most importantly, improving our understanding of mechanisms causing shifts in dominance between tree-dominated and herbaceous/grass-dominated systems will fill the void that currently exists in literature in Southern Africa. This understanding will equip ecosystem and landscape managers in the potential identification of plant community thresholds, plant community resilience, both essential tools when designing intervention strategies in restoration ecology and in the management of disturbed and/or sensitive communities. The net benefit of functional ecosystems is the provision of essential services like energy, food, clean water, pasture which fit into the nation’s programmes of poverty reduction and rural development.