Carbon Sequestration Dynamics and its Implication on Climate Variability in the South West Mau Forest, Kenya

Abstract

Forests are important for regulation of the global carbon balance and climate stabilization. Increase in forest biomass enhances atmospheric carbon sequestration decreasing climate variability, while decrease in forest biomass contributes to carbon dioxide emissions increasing climate variability. World over, forest biomass has been declining due to forest loss and degradation. The South West Mau has experienced significant forest loss since 1964. The decline is posited to have significant impacts on carbon sequestration, carbon storage, carbon dioxide emissions, status of atmospheric carbon dioxide, and consequently localized climatic conditions. This study assessed interannual trend and variability as well as change point detection in carbon sequestration, average annual air temperature and annual total surface precipitation in South West Mau Forest, Kenya between 1985 and 2015. Covariance analysis was performed between carbon sequestration dynamics and the climate variables to establish their relationship. Above ground biomass carbon sequestration was quantified based on the Carnegie-Ames-Stanford Approach (CASA) and carbon fraction for tropical climate domain. Carbon sequestration dynamics were characterized by increase-decrease cycles of approximately 3 years and low interannual variability (CV= 9.13). It emerged that South West Mau Forest was a net carbon emitter with a carbon sequestration balance of -588.3996 Kg/ha between 1985 and 2015. Annual average air temperature over the South West Mau forest pointed towards climate warming of 0.01880C per year (Kendall’s tau = 0.3677, p value = 0.0033) but with low interannual variability (CV= 0.11%). A shift in the annual average air temperature of 0.3680C at p= 0.0051 was detected between 1985-1998 and 1999- 2015. There was a weak positive anomaly in the annual average air temperature with a slope of 0.0192 and R2 = 0.3074. There was an increasing trend in the annual total surface precipitation (Kendall’s tau = 0.4968, Sen’s slope = 71.455, and p = 0.0001) with moderate interannual variability (CV=27.9%). A shift in the total surface precipitation with increase of 1611mm was detected between 1985- 2003 and 2004 -2015. There was moderately strong positive anomaly in the total surface precipitation with a slope of 79.791 and R2 = 0.5. A weak negative covariance between above ground carbon sequestration and annual average air temperature (r = -0.1563, R2= 0.0244) and a weak positive covariance between above ground carbon sequestration and annual total surface precipitation (r = 0.3408, R2= 0.1162) were established. This indicated that variability in carbon sequestration were inversely related to variability in annual average air temperature and directly related to variability in annual total surface precipitation. The study concluded that the above ground biomass pool in South West forest was a net carbon emitter. The region experienced climate warming and increased total surface precipitation. Overall, the results of this study demonstrate that variability in above ground carbon sequestration explained only 2.4% inter annual variability in average air temperature and 11.62% interannual variability in total surface precipitation.