Biomass in context
An overview of the factors affecting Biomass availability in South Africa
Authors: Hayden Wilson
The availability and type of feedstock that is available for BioEnergy production in South Africa is determined by a number of factors, such as: climate, soil, land use practice and population density (Hugo, 2015). Volume of available feedstock varies temporally, with certain feedstocks following a cycle that is determined by seasonality while the availability of other feedstocks such as agricultural and forestry residues vary according to the management objectives of the activities that produce the feedstock. This document provides an overview of the factors that determine the availability of the BioEnergy feedstocks in South Africa that were assessed as part of the BioEnergy Atlas Project.
Biomass production in South Africa largely follows a climatic gradient primarily driven by rainfall, with the highest biomass production occurring within the eastern regions of the country or in close proximity to the coastline.
Within the content of the BioEnergy Atlas, productivity is described as the rate at which biomass is produced. There are two basic types of productivity: gross and net.
Gross primary productivity, or GPP, is a measure of the total amount of carbon captured by plants as a result of photosynthesis (Amthor and Baldocchi, 2001)
Net primary productivity, or NPP, is the difference between gross primary productivity and amount of carbon released back into the atmosphere as a result of Cellular respiration. NPP can this be used as a rate at which energy is stored as biomass by plants or other primary producers and made available to the consumers in the ecosystem (Schultze, 2007).
Net Primary Productivity (Schultze, 2007) is viewed as a raw potential or baseline for biomass production, and this is extensively modified by land use. Hence, the local soil types, current land cover, extent of degradation, and improved yields due to intensive agriculture all play a role in modifying the baseline NPP.
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South Africa is located on the southern tip of Africa (between latitudes 22° and 35°S, and longitudes 16° and 33°E) and is bordered by the Atlantic Ocean on the west and Indian Ocean on the south and east. It encompasses a coastline of 2 798 km and has a surface area of 1 219 602 km2, making South Africa the 25th largest country in the world.
South Africa generally experiences temperate conditions throughout the year, due to its subtropical location, but the moderating effect of the Atlantic and Indian Oceans, and its varied topography result in a great variety of climatic zones, ranging from the dry north-western to the wet eastern regions of the country. Most of South Africa is semi-arid and water stressed, with an average rainfall of about 450 mm, which is approximately 60% of the world average (Schulze 2008). Its precipitation is highly variable with an uneven spatial distribution and seasonality of rainfall. The eastern and southern parts of the country receive significantly more rain than the northern and western regions. While most of the country is generally a summer-rainfall region, the extreme southwest has a Mediterranean climate characterized by marked aridity during summer months. The rainfall in this region occurs predominantly during the winter period (Tyson and Preston-Whyte 2000).
The coldest days occur in June to August (winter), with the southern and western parts of the country experiencing the lowest temperatures. The warmest areas are the coastal areas of KwaZulu-Natal, the Lowveld of KwaZulu-Natal and Mpumalanga, the Limpopo valley and the interior of the Northern Cape. The warm Agulhas current on the Indain ocean side causes the eastern coastal areas to have a warm and humid climate, whilst the cold Benguela current along the Atlantic west coast contributes to the arid climate and lower temperatures of this region (Tyson and Preston-Whyte 2000). A detailed overview of the climate of South Africa an be found in (Walker 1990, Tyson and Preston-Whyte 2000, etc.,). Due to the variations in precipitation, primary productivity varies considerably both spatially and temporally
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Land use and Landcover changes dramatically modify the basal Net Primary Productivity. Practices such as intensive agriculture can dramatically increase the volume of biomass being produced in an unproductive area, whereas changes from one land cover type to another, such as forestry to crop agriculture would have the opposite effect. Human activity is one of the biggest drivers of variability in biomass availability and volume. Processes such as urbanisation reduce the areas for biomass production, but at the same time, activities such as the transportation and production of fuel and food for growing urban populations, as well as the resultant waste streams, may make significant point or distributed contributions to the availability of Biomass.
South Africa, being a relatively dry country, is constrained in terms of land availability for biomass production. Competing interests for land use in the relatively more productive areas of the country include:
Current agricultural land and food security: This is probably the most contentious aspect. There are three additional sub-considerations here:
Commercial forestry: High productivity areas of South Africa have a sizeable allocation to commercial forestry, and while the waste products are of some use as bioenergy sources, we are assuming here that the existing plantation area will not be repurposed but that forestry residue is available for beneficiation.
Urban and mining areas: These are by definition not available for biomass production, but rehabilitated mining land could support biomass feedstock streams, such as future urban growth, which would contribute somewhat to the availability of domestic or industrial waste.
Protected and sensitive areas: We need to consider the following:
Non-usable land These are areas that may or may not be suitable for biomass generation, but are excluded on the basis of accessibility, slope, soil conditions, or other factors that will make sustainable biomass generation difficult.
|#||Constraining Step||Welfle et al (2014)|
Approach adopted in BEA 2.0
|“Theoretical: … represent the biomass resource potentially grown/harvested/collected limited only by physical and biological barriers.”||The upper limit for sustainable production is the Net Primary Productivity (NPP).|
|“Technical: …reflect biomass resource extent taking into consideration technical constraints such as land area, ecological impacts, and agro-technological constraints.||A yield potential is calculated from published data for major crops and bioenergy sources.|
Current and future land use exclusions
|Not directly considered in BEA 1.0|
Land that is currently used for urban areas, and mining are excluded. Yields from agricultural and forestry land are calculated on a per crop basis.
|Included in ‘Technical’ above||Land availability is constrained by formal and prospective protected areas, sensitive biodiversity areas, and important ecosystem service areas.|
|Not directly considered in BEA 1.0||Land availability is further constrained by inaccessible slopes, high water tables, etc.|
Feasibility and cost
|“Market Economic: … demonstrate biomass resource that reflects economic considerations, fundamentally driven by supply/ demand curves.”||This evaluation is done on the basis that demand will always outstrip supply for bioenergy sources in South Africa; hence, the economic feasibility is determined by location-sensitivity, process pathways, and the price of alternatives.|
|“Implementation/ Realistic Potentials: … represent biomass resource availability without inducing detrimental environmental, social, or economic impacts”.||Outcomes of feasible options are further qualified in respect of greenhouse gas emissions, job creation, social justice, and environmental impacts.|
The charts above indicates the volumes, availability, current utilisation and physical characteristics of the various biomass feedstocks that have been assessed in the BioEnergy Atlas. The various feedstock streams are presented according to their total volume, the amount that is already being utilised and is thus unavailable, the proportion that is available for BioEnergy production at present and the proportion that could potentially be made available through changes in process or through interventions such as using purposefully grown crops. Additionally, the energy density, water content and energy equivalent are presented. The following sections describe…..
Forestry accounts for 1, 37 million hectares of land (1.1%) of the available land in South Africa (ICFR, 2020). Of that, the majority of the land (820 530 ha) belongs to corporates, with the remaining land being broken into the other categories as showcased below:
The forestry industry represents a significant producer of biomass in the form of wood for the timber, paper and pulp industries. A breakdown of the volumes of biomass produced in 2018 is as follows:
Forestry residue also represents a significant source of Biomass, however, the volume of residue that is available is largely determined by the land management decisions for the maintenance of soil quality.
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Increases in woody plant density have been observed in non-forest regions of Southern Africa since the late 19th century (O’ Connor et al., 2014). While increased precipitation and CO2 levels within the atmosphere do convey a competitive advantage to C3 woody species, the drivers for an increase in woody plant density are closely linked to land management practices, where processes such as herbivory and fire frequency account for 78% of the differences in spatial coverage of bush encroached areas (Venter et al., 2018). It has been observed that woody plant encroachment has been most rapid within small protected areas and significantly slower within communal rangeland areas and large protected areas where macro-herbivores are present.
Grazing pressure on grasslands has been shown to affect the rate of woody plant encroachment, where the greatest increases in woody cover occurred during the 1970’s when there was significant pressure on grasslands following the drought of the 1960’s and the volume of cattle being maintained on grassland ecosystems. Within areas where fire and herbivory are excluded, It has been observed that there is a linear relationship between woody plant growth and mean annual rainfall (O’Connor et al., 2014).
The clearing of Bush encroachment from areas, has the potential to provide a significant source of biomass for beneficiation industries; while also meeting land owners management objectives in the form of bush clearing.
Invasive Alien Plant Species (IAPS) are plant species that have been introduced to South Africa from other regions. These plants are able to out compete indigenous species due to having very few natural predators as well as having physical traits that allow them to better access resources than indigenous species (Rodríguez-Labajos et al., 2009).
In addition to representing a significant threat to biodiversity and ecosystem function, IAPS also affect South Africa’s water security. Of the estimated 9000 plants introduced to this country, 198 are currently classified as being invasive. It is estimated that these plants cover about 10% of the country and the problem is growing at an exponential rate. Programs such as the Working for Water Program (administered by the Department of Environment, Forestries and Fisheries Natural Resource Managment Unit) have been set up to assist with the eradication of alien invasive plant species and they are responsible for clearing more than one million hectares of invasive alien plants while also providing jobs and training to approximately 20 000 people from among the most marginalized sectors of society per annum (https://www.environment.gov.za/projectsprogrammes/wfw).
A number of IAPS are suitable candidates to serve as BioEnergy Feedstocks (Pinus, eucalyptus, prosopis to name a few). A summary of the available biomass that can be sourced from invasive alien plant species is presented below:
Organic waste production in South Africa represents another potential source of biomass. Liquid biomass in the form of sewerage has the potential for the production of BioGas, while solid organic waste can be used to produce a variety of BioEnergy products.
Organic waste falls into two categories, serviced waste which is collected from municipalities and processed within waste disposal sites and unserviced waste – which is typically burnt or disposed of informally.
The volumes of each waste category are presented below:
Agriculture is the cultivation of soil for growing crops. The total land used for commercial agriculture was 46,4 million hectares in 2017 (which represents 37,9% of the total land area of South Africa (122,5 million hectares), of which arable land comprised (7,6 million hectares) (Statssa 2017 Agriculture Census)