Soil Carbon Sequestration Differentials among Key Forest Plantation Species in Kenya: Promising Opportunities for Sustainable Development Mechanism

摘要

Soil organic carbon (SOC) contributes to the productivity of forests and enhances carbon sink in forest ecosystem. However, the available data on forest based carbon projects among African countries that have ratified Kyoto Protocol and are party to United Nations Framework Convention on Climate Change (UNFCCC) shows little emphasis on SOC, deadwood and litter. Kenya, for example, has piloted five afforestation and reforestation Clean Development Mechanism (AR-CDM) activities in government forests of which none addresses SOC, and yet studies elsewhere have shown that forest soils consist about 73 % of global carbon storage. This study therefore, sought to determine soil carbon sequestration differentials among selected key forest plantations in Kenya and their future implications on sustainable development mechanism. Soils were sampled at 0-20, 20-50 and 50-80 cm depth from Pinus patula, Cupressus lusitanica, Juniperus procera and Eucalyptus saligna/grandis plantations in Central Kenya for analysis of carbon, soil pH, nitrogen, phosphorous and potassium. The litterfall collected from each of these forest plantations were analysed for nitrogen and carbon. The Pinus patula plantations had significantly (p<0.01) higher amount of soil carbon (132.2 ± 12.55 MgC ha~(-1)) as compared with Cupressus lusitanica (114.4 ± 12.55 MgC ha~(-1)) and Eucalyptus saligna (85.0 ± 12.55 MgC ha~(-1)) plantations. Specifically, Pinus patula plantation had sequestered almost twice of soil carbon as compared to above and below-ground carbon pools whereas that of Cupressus lusitanica and Eucalyptus saligna /grandis were about 1.2 and 1.3 times higher, respectively. The levels of acidity varied among species, between and within sites from very strongly acidic to very slightly acidic. The amount of soil nitrogen, phosphorous and potassium between sites, tree species and soil depths differed significantly. This study therefore reveals soil carbon potentials in forest plantations that need to be considered in the development and implementation of afforestation and reforestation activities under Clean/Sustainable Development Mechanism (SDM). Equally, differences on soil carbon sequestered among species need to be taken into account when evaluating carbon stocks under certified and voluntary carbon offset markets in order to promote trees with high potential of carbon sequestration for sustainable development. This is important because, introduction of Reducing Emissions from Deforestation and forest Degradation (REDD+) and forest based Clean Development Mechanisms (CDM) have provided impetus to African governments in implementing afforestation and reforestation (AR) programmes to enhance carbon stock and improve resilience of biophysical and social systems against impacts of climate of change.