Land use change and carbon stock dynamics in Sub-Saharan Africa - Case study of Western Africa – Ghana
Author(s)
Grieco, Elisa
Date Issued
March 10, 2011
Type
Doctoral Thesis
Abstract
Climate change is perhaps the greatest environmental challenge emerged in the twenty-first century. It can be considered a source of the major global threats, such as hunger, poverty, armed conflict, displacement, air pollution, soil degradation, desertification and deforestation. These global issues are intricately intertwined and all contribute to climate change, necessitating a comprehensive approach to a solution (Stone and Chacón León, 2010).
The role of the African continent in the global carbon cycle, and therefore in climate change, is increasingly recognized (Houghton and Hackler, 2006; Williams et al., 2007). Of all the region in the world, Africa has contributed less than any other region to the greenhouse gas emissions, which are widely held responsible for global warming and consequently for climate change. But the continent is also the most vulnerable to the consequences and sub-Saharan Africa (SSA) is the least well equipped to face the issues related to climate change (Justice et al., 2005). In Sub-Saharan Africa the role of land use change in controlling CO2 emissions and annual C budgets at regional and global scale may be more critical than in any other regions (Houghton and Hackler, 2006). According to the IPCC in its Fourth Assessment Report, reducing and/or preventing deforestation is the mitigation option with the largest and most immediate carbon stock impact in the short term (UNFCCC, 2010). International community decided to face climate change problems related to deforestation, through specific policies to Reducing Emissions from Deforestation and forest Degradation and the role of conservation, sustainable management of forests and enhancement of forest carbon stocks (referred as REDD+). Deforestation and other land-cover changes typically release carbon from the terrestrial biosphere to the atmosphere as CO2 (carbon dioxide), while recovering vegetation in abandoned agricultural or logged land removes CO2 from the atmosphere and sequesters it in vegetation biomass and soil carbon. Emissions from land-use and land-cover change are perhaps the most uncertain component of the global carbon cycle, with enormous implications for balancing the present-day carbon budget and predicting the future evolution of climate change (Ramankutty et al., 2007). A common paradigm about the reduction of emissions from deforestations estimated for the purpose of promoting it as a mitigation option in the context of the United Nations Framework Convention on Climate Change (UNFCCC) is the high uncertainties in input data - i.e., area change and C stock change/area - that may seriously undermine the credibility of the estimates and therefore of reduced deforestation as a mitigation option. It is likely that the most typical and important example of incomplete estimates will arise from the lack of reliable data for a carbon pool (Grassi et al., 2008). Uncertain rates of tropical deforestation, account for more than half of the range in estimates of the global carbon flux. Three other factors account for much of the rest of the uncertainty: (1) the initial stocks of carbon in ecosystems affected by land-use change, (2) per hectare changes in carbon stocks in response to different types of land-use change, and (3) legacy effects; that is, the time it takes for carbon stocks to equilibrate following a change in land use (Houghton and Goodale, 2004). Considering the source of uncertainty and the lack of field data for sub-Saharan Africa, it has been decided to place the study in the Ghana (Jomoro district, Western Region) where for more than 20 million Ghanaians, particularly people living in the rural areas, the forest is the only source of wood that is used locally as fuel wood, and for construction and furniture (Blay et al., 2007) and where deforestation annual rate reaches 2.19% for the period 2005-2010 (FAO, 2010). The study will analyze the above mentioned gaps related to deforestation and land use change, by assessing: 1) initial carbon stocks (tropical rain forest), 2) per hectare changes in carbon stocks as consequence of deforestation followed by six different main land uses [tree plantations (rubber, coconut, cocoa, oil palm, mixed) and secondary forest], 3) dynamics of soil carbon stocks through the time considering chronosequences. Moreover some specific carbon pool issue has been taken into consideration. When accounting changes in carbon stocks in the UNFCCC framework, it is required to consider 5 carbon pools that are: aboveground biomass,
belowground biomass, litter, dead wood and soil. Within REDD+ mechanism there are not official methodologies but some guidelines developed for the voluntary standards (e.g. BioCarbon Fund- Methodology for Estimating Reduction of GHG Emission from Mosaic Deforestation, Voluntary Carbon Standard (VCS) - Tool for AFOLU Methodological Issues, etc.) and it is clear that only aboveground pool has to be always considered, belowground biomass is recommended and the others are facultative. Evidence from official reports (e.g., UNFCCC 2005a, UNFCCC 2005b, FAO 2006) suggests that only a very small fraction of developing countries currently reports data on soil carbon, even though emissions from soils following deforestation are likely to be significant in many cases (Grassi et al., 2008). Despite the common understanding about the effects of deforestation on different compartment in terms of carbon variation - an increase or disappearance of biomass relatively visible, variations in soil carbon much less perceptible, even after a radical change in land use (Calmel et al., 2010) - this study brings in the spotlight the soil reaction to radical land use change in the long run demonstrating that it is not so trifle as commonly believed. Importance of considering soil carbon stock for accounting the land use change dynamics is not properly recognize in the international deforestation policies and its influence and role in mitigating climate change is nowadays neglected but it is really not negligible.
Additional information
Dottorato di ricerca in Ecologia forestale
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