Project topics and materials
Get Complete Project Material File(s) Now! »
Overview of grassland ecosystem in tropical Africa
Grasslands represent about 26% and 70% of world land and agricultural areas, respectively. Grasslands also contain about 20% of the world’s soil C and N stocks (Lal 2004; FAO 2009). The grassland and Karoo biomes cover more than 50% of the land surface in South Africa (Smet & Ward 2006). These ecosystems are important for maintaining biological diversity, supporting livestock productivity, and providing key resources for native and domestic ungulate grazers in arid lands of the country (Williams 1996; Steinfeld et al. 2006). Milk, beef, wool, mohair and other valuable products are usually associated with grasslands, and are a way of life for more than 800 million grassland-dependent rural communities (Steinfeld et al. 2006; Briske et al. 2008; FAO 2010). Parts of South Africa are located in a subtropical region, with temperatures modified by altitude. The interior, where the bulk of grasslands are found, is semi-arid to arid, with rainfall decreasing westwards. Apart from soil formation differences, the interface between grasslands and other biomes in South Africa contributes substantially to their floristic and faunal diversity and to the important role they play in the agricultural economy (Hoffman & Ashwell 2001).
Food security
Significant portions of world milk (27%) and beef (23%) production occur on grasslands managed solely for these products (Conant et al. 2001). Occupying about 87% of the land surface, the grazing industry has been an important contributor to the overall economic growth of South Africa. Many livestock products (beef, mutton, fleece and hides) are derived directly from grasslands (Schulze et al. 1997; Du Preez et al. 2011a), contributing substantially to the livelihoods of farmers, ranchers and commercial farm owners (Tainton & Hardy 1999; Kotzé et al. 2013).
Land-based livelihood strategies such as livestock farming, crop production, and harvesting of wild natural resources play important roles in rural society in the communal areas of South Africa (Du Preez et al. 2011a). When reliable growing days drop below the number that are necessary for maize production in eastern and southern Africa, grassland ecosystems become more and more important sources of feed for livestock (Thornton & Jones 2009). But the challenge is that 65% of grasslands of South Africa are affected by desertification (UNEP 1997; Hoffman & Ashwell 2001), and are vulnerable to climate change (FAO 2010). In countries such as South Africa, with such a high level of aridity and environmental fragility, the consequences of desertification threaten the livelihoods of pastoral and agro-pastoral communities (Hoffman & Ashwell 2001; FAO 2006; Steinfeld et al. 2006), who have based their lives on grasslands. The implication is that revitalizing grasslands is vital to improve the livelihoods of the poorest communities of the continent.
Biodiversity
Diversity comprises a broad spectrum of biotic scales and can generally be described as the number of entities, the evenness of their distribution, the differences in functional traits, and their interactions (Diaz et al. 2006). Besides the numbers of species, the numbers of functional groups are important in biodiversity. Species diversity, the number and composition of plant species present at a site, is the most frequently considered aspect of biodiversity. Increased species composition has been shown to increase primary productivity, improve plant allocation patterns (Diaz et al. 2006; Hatier et al. 2014), and reduce invasibility by unsown species that change herbage composition (Kirwan et al. 2007). For most plant species, biodiversity declines with increasing aridity (Wang et al. 2014b).
Diverse plant species in grasslands support a long-term stable ecosystem because they exhibit complementary functionality. Species diversity has two basic components: richness or number of species in a given area, and evenness or how relative abundance or biomass is distributed among species. Increased species richness reduces the vulnerability of grassland ecosystems to drough FAO 2007; Wang et al. 2014b), increases the carbon source strength (Diaz et al. 2006), and may increase N fixation and protect against nitrogen leaching (Oenema et al. 2005). South Africa’s grasslands are rich in species diversity, comprising an estimated 3788 plant species (Gibbs Russell 1987). However, losses of biodiversity have been reported due to shifts in species composition in response to heavy grazing (Moussa et al. 2007; Khumalo et al. 2012). Changes in growing season rainfall have been reported to be associated with declining richness in grass species (Wilkes 2008). This perturbation in the long-term droughts most notably affected the dominant species, which play a significant role in maintaining community structure, and are replaced with less palatable species and ruderals (Schuman et al. 1999; Du Toit et al. 2008; Evans et al. 2011). The implication is that any influences that affect the dominant species have large effects on the biodiversity of grassland ecosystems (Olff & Ritchie 1998; Evans et al. 2011; Khumalo et al. 2012).
Sources and sinks of greenhouse gases
Grasslands face a wide range of challenges from climate change, including the effects of elevated atmospheric carbon dioxide, higher temperatures, changes in the precipitation regime, and increasing concentrations of ground-level ozone (FAO 2007, 2010; IPCC 2007). In spite of notable impacts of climate change on grasslands (Schulze 1997), properly managed soils can store relatively stable and significant proportion of C. The global C stock in grasslands is estimated at 343 Gt C, which is about 50% more than the amount stored in forests globally (Lal 2004). Food and Agricuture Organization of the United Nations, FAO (2010) estimated that the SOC sequestration potential of the world’s grasslands is 0.01-0.3 Giga tone (Gt) C yr−1. This amount is 3 times more than the size of atmosphere (770 Pg) and 3.8 times more than the size of biotic pools (610 Pg) (Lal 2000, 2002). Permanent pastures could offset up to 4% of global greenhouse gas (GHG) emissions through carbon sequestration (Soussana et al. 2004), whereas under poor management they become GHG sources (Wilson et al. 2012).
CHAPTER 1 Literature review
1.1. Overview of grassland ecosystem in tropical Africa
1.2. Significances of grasslands in tropical Africa .
1.2.1. Food security
1.2.2. Biodiversity
1.2.3. Sources and sinks of greenhouse gases
1.3. Drivers of grassland ecosystem
1.4. Conclusion and hypothesis formulation
1.5. Specific objectives
CHAPTER 2 Influences of land-use types on soil organic carbon, total nitrogen and related soil properties in semi-arid area, Pretoria
2.1. Abstract
2.2. Introduction
2.3. Materials and methods
2.4. Results
2.5. Discussion .
2.6. Conclusion
CHAPTER 3 Long-term impacts of stocking rate on soil carbon sequestration and selected soil properties in the Middleburg, Eastern Cape, South Africa
3.1. Abstract
3.2. Introduction
3.3. Materials and methods
3.4. Results
3.5. Discussion
3.6. Conclusion
CHAPTER 4 Long-term impacts of season of grazing on soil carbon sequestration and selected soil properties in the Middleburg, arid Eastern Cape, South Africa
4.1. Abstract
4.2. Introduction
4.3. Materials and methods
4.4. Results
4.5. Discussion
4.6 Conclusion.
CHAPTER 5 Soil water content, herbage yield and rain-use efficiency of semi-arid native pasture subjected to different levels of precipitation and defoliation interval
5.1. Abstract
5.2. Introduction
5.3. Materials and methods
5.4. Results
5.5. Discussion
5.6. Conclusion
CHAPTER 6 Yield and nutritive quality of dominant forage species subjected to different levels of precipitation in subtropical native pasture, Pretoria
CHAPTER 7 Conclusion, recommendation and critical evaluation
References
GET THE COMPLETE PROJECT
Quantitative and qualitative herbage yield, and carbon sequestration in subtropical grasslands subjected to different precipitation, grazing management and land use type
