Spatial-temporal dynamics of savanna ecosystems (tree-grass interactions, grass quality/quantity, biodiversity) as a life support system to wildlife and livestock production in and around Kruger National Park
Lead Author: Abel Ramoelo (CSIR)
Contributors: Moses A. Cho (CSIR), Renaud Mathieu (CSIR), Antonello Provenzale (CNR)
The Kruger National Park (KNP) and surrounding areas are located in a semi-arid Lowveld of South Africa and support high wildlife diversity in the park and livestock production in adjacent communal lands. Ecotourism represents the main income generating activity in the park and contribute substantially to the South African economy. Livestock production is the mainstay of the rural economy in the communal lands – including food and energy security. KNP is representative of South African savanna ecosystem and is a unique laboratory for research on savanna dynamics and ecosystem services. Savanna ecosystems are open canopy forests (about 50% or less tree cover) made of heterogeneous layers of grass and woody plants. As the largest biome in sub-Saharan Africa (approximately half of the land surface), these ecosystem hosts a large proportion of the African population – human densities are proportionally higher than in denser forests e.g. Congo basin, generally the poorest communities who rely extensively on ecosystem services, e.g. fuel wood, timber, grazing resources and edible fruits. The woody component or tree cover plays a key role in ecosystem functioning, impacting on the fire danger, rates of transpiration and biomass production, nutrient cycling, soil erosion, and water distribution, and more widely on food and energy security. Bush encroachment impacts negatively on available grass resource for herbivores including wildlife and livestock. On the other hand, about 90% of rural community relies on fuelwood as their main source of energy and livestock production as their mainstay for livelihood.
Grazing and browsing resources supporting wild fauna and livestock production are the main provisioning ecosystem services and ecotourism is the main cultural ecosystem service provided by the KNP and adjacent communal areas. These provisioning services are crucial to sustaining ecotourism and rural livelihoods in the region. However, grazing and browsing resources are threatened by phenomena such as bush encroachment, overgrazing, elephant impacts and poaching of large mammals. The KNP has witnessed high levels of rhino poaching in recent years. Bush encroachment is affecting the availability and quality of forage for wildlife and livestock. Bush encroachment is a national problem which affects 10M ha in South Africa (O’Connor 2014). Overgrazing in the communal lands has resulted into highly levels of depletion of grazing resources in terms of quantity (as measured by biomass) and quality (leaf nitrogen concentrations). The latter factors influence the occurrence and population dynamics of animals at a particular point in time. At the same time mega herbivores such as elephants do have an impact on a reduction of large trees which are important for the preservation of some species (e.g. bird species). Therefore, an understanding of the tree-grass interaction (Scholes & Archer 1997) in a spatially explicit manner will enhance our understanding of the functioning of savanna in providing the vital provisioning services to both wildlife and humans.
The underlying factors influencing the savanna landscape and the vegetation productivity are edaphic (soil and topography), climatic (precipitation and temperature) and anthropogenic (e.g. fire, grazing, fuelwood collection) and biotic factors e.g. elephant activities (Venter 2003). The savanna ecosystem is regarded as one of the heterogeneous ecosystems – patchiness of grass nutrients, tree species driven by geological types and climatic variables. For example, dominant geological types include basalt (highly fertile soils), gabbro (moderately fertile soils) and granite (infertile soils) influences the distribution of vegetation types, the nutrient quality and quantity of the foraging and browsing resources. The quality and quantity of grazing and browsing resources are therefore key indicators to monitor in the savanna system to ensure their sustainability.
The overarching ecosystem service in the KNP is ecotourism which is mainly linked to vegetation productivity (ecosystem) and animal presence (especially the Big Five). Kruger National park is famous for Ecotourism and generates high economic returns in the South Africa, and it is surrounded by poor rural communities which present interesting dynamics of conservation activities. The main objective is to investigate the dynamics of the savanna ecosystems and their impact on key ecosystem services in KNP. The proposed approach relies on various remote sensing technologies depending on the type of vegetation. Herbaceous biomass (available grazing resources) and quality (leaf nitrogen) for grazing animals will be assessed using high spatial resolution images such as Sentinel – 2 and WorldView-3, with strategically placed red-edge band for assessing vegetation health. For the tree layer, woody biomass and tree cover will be assessed using a combination of state of art Synthetic Aperture Radar (SAR) and LiDAR technology. The estimated vegetation parameters will be further used for modelling ecosystem dynamics and carbon and water fluxes through the soil-vegetation-atmosphere system in different geological frameworks, as well as to assess, through modelling, the response of savanna ecosystems to changes in climate and/or in the fire and grazing regimes. Statistical models relating fire occurrence to climatic conditions will also be considered.
References
O’Connor T.G. et al. 2015. Bush encroachment in southern Africa: changes and causes, African Journal of Range and Pasture Science
Scholes R.J., Archer S.R. Tree-grass interactions in savannas, Annu. Rev. Ecol. Syst., 28, 517–544 (1997).
Venter F.J., Scholes R.J., Eckhardt, H. C. 2003. The abiotic template and its associated vegetation pattern. The Kruger experience: Ecology and management of savanna heterogeneity, 83, 129.