Estimation of carbon stocks in the forest plantations of Sri Lanka

Forest plantations have the ability to sequester carbon in their biomass and reduce the rate of increase of atmospheric carbon dioxide. Therefore, plantation forestry forms an important option for mitigating global warming and consequent climate change. The objective of the present study was to estimate the biomass and carbon stocks of the existing forest plantations in Sri Lanka. Height and diameter measurements of the trees at breast height from 22 monocultures and 51 mixed-cultures, established and maintained by the Forest Department, were obtained from the FORDATA data base and used to calculate the existing carbon stocks using allometric relationships. The total estimated monoculture C stock in 2008 amounted to 4.23 million metric tons in an area of 57618.8 ha. Around 89% of this total C stock in monocultures is contributed by five tree species, namely, Pinus caribaea (44%), Tectona grandis (21%), Eucalyptus grandis (11%), Eucalyptus camaldulensis (7%) and Swietenia macrophylla (6%), occupying 92% of the area. Total C stock in mixed cultures in 2008 amounted to 0.681 million tons in 5949.6 ha. Five mixed cultures, i.e. Eucalyptus robusta and E. grandis (17%), Pinus mixed (13%), E. grandis and E. microcotys (12.5%), Eucalyptus mixed (7%) and Acacia mangium and A. auriculiformis (5%), contributed to 55% of this C stock. Monocultures, which showed the highest per ha C stocks were Pinus caribaea in Badulla (205 t ha(-1)) and Nuwara Eliya (164 t ha(-1)) and Eucalyptus grandis in Ratnapura (197 t ha(-1)) and Nuwara Eliya (168 t ha(-1)). Mixed plantations of Acacia decurrens and different species of Eucalyptus grown in Nuwara Eliya showed the highest combined per ha C stocks ranging from 226 279 t ha(-1). The maximum per ha C stock in some of the Sri Lankan forest plantations in different climatic zones were either on par or above the benchmark average C stock values specified by the IPCC for the respective climatic zones. Age distribution of the monoculture C stocks showed that the highest percentage (i.e. 39%) was in the 21-30 year plantations, followed by the 31-40 year plantations (32%).