Temperate forests absorb between 10 and 20 tons of carbon dioxide per hectare each year through photosynthetic conversion into starch, cellulose, lignin, and wooden biomass. A 40-year study of African, Asian, and South American tropical forests by the University of Leeds, shows tropical forests absorb about 18% of all carbon dioxide added by fossil fuels. Truly mature tropical forests, by definition, grow rapidly as each tree produces at least 10 new trees each year. Based on studies of the FAO and UNEP it has been estimated that Asian forests absorb about 5 tonnes of carbon dioxide per hectare each year. The global cooling effect of carbon sequestration by forests is partially counterbalanced in that reforestation can decrease the reflection of sunlight (albedo). Mid-to-high latitude forests have a much lower albedo during snow seasons than flat ground, thus contributing to warming.
Furthermore, forest carbon moves between the atmosphere (as carbon dioxide) and the tree (as carbon) in a continuous cycle, known as the forest carbon cycle and carbon can be released at any time through deforestation or forest fires.
Historically the international focus on carbon sinks has been on afforestation and avoiding deforestation (REDD+). However, there is a need to restore and sustainably manage grasslands and savanna ecosystems because grasslands are key carbon sinks. Interestingly, carbon accumulation in grassland ecosystems occurs mainly below ground where soil organic matter is located. In South Africa, over 60% of the national terrestrial carbon stock is located in grassland and savanna ecosystems – and within these two ecosystems, over 90% of the total carbon pool is located mainly belowground mainly in the form of soil organic carbon (Department of Environmental Affairs, 2015).
Besides carbon sequestration, grasslands are important because they contribute to both mitigation of and adaptation to climate change e.g. prevention of floods etc, improvement of land and ecosystem health and resilience, biological diversity and water cycles while serving as a basis of agricultural productivity and economic growth (Food and Agriculture Organisation of the United Nations, 2010).
Oceans and coastal wetland systems
‘The ocean is the largest carbon sink on Earth.’ (Laffoley & Grimsditch, 2009) and oceans absorb more than a quarter of the carbon dioxide that humans put into the air. Besides their ability to sequestrate carbon, oceans are key ecosystems because of the significant goods and services they provide such as food security.
Coastal wetland ecosystems, which are made up of salt marshes, mangroves, kelp forests and seagrass beds, are particularly important as carbon sinks because their plants tend to grow faster than terrestrial plants, allowing them to capture large amounts of CO2 and because their soils are largely anaerobic (without oxygen) so carbon that gets incorporated into the soils decomposes very slowly and can persist for hundreds or even thousands of years (carbon storage).
For African countries with long coastlines and extensive coastal vegetation, coastal ecosystems are of high importance to the wellbeing of Africans because of the significant goods and services they provide as well as carbon management potential. Therefore, African countries need to reduce the sediment run-off from land; replant mangrove forests that have been displaced due to urban development and aquaculture; and stop over-fishing in their waters.