Carbon sequestration potential of replanted Rhizophora mucronata in Puttlam Lagoon, Kalpitiya, Sri Lanka

U.Y.I.L. Dharmasoma1, D.M.S.H.K. Ranasinghe1 and S. Wahala2
Department of Forestry and Environmental Science, University of Sri Jayewardenepura, Sri Lanka
Department of Tourism Management, Sabaragamuwa University, Sri Lanka

The potential of trees to act as carbon sinks is very important as global warming, which occurs due to increasing levels of carbon dioxide is risen over decades. Mangroves as any other tree are capable of removing carbon from atmosphere through the carbon stored in their biomass. The present study was carried in the mangrove replanted sites with 6 months, 5 and 10 years old Rhizophora mucronata in the Kalpitiya Peninsula in the Puttlam Lagoon in North West of Sri Lanka. Objectives of the present study were to assess the carbon sequestration potential of replanted R. mucronata at different ages in Puttlam Lagoon and to estimate biomass partitioning in R.mucronata in selected sites.

Transects were demarcated in each sampling site traversing from the Lagoon to inland to cover the entire width of the plantation. The width of transects were 5m and they were laid at 15m intervals within the plantation. Each transact was divided in to 5m x 5m sample plots at 5m intervals. A representative tree was selected from each diameter class in each study site for destructive sampling. The above ground parts of uprooted trees were separated in to plant components.

The belowground roots in 1m×1m area around each uprooted tree were collected by digging soil up to 30 cm depth. Fresh weight of each component was measured in the field and representative sub samples were taken to the laboratory, oven dried to constant weight at 1050C in order to calculate wet-dry weight ratio.

According to the results, average total carbon content that could be lodged in 6 months, 5 and 10 years old R. mucronata stands having survival rates of 60.67%, 83.46%, 77.33% are 0.08 t C ha-1, 1.39 t C ha-1 and 66.30 t C ha-1, respectively. Average total CO2 that could be stored as carbon without being emitted to the atmosphere in 6 months, 5 and 10 years old R. mucronata are 0.28 t C ha-1, 5.13 t C ha-1 and 243.33 t C ha-1, respectively. Carbon sequestration rate of 6 months, 5 and 10 years old R. mucronata are 0.1564 t C ha-1 yr-1, 0.3134 t C ha-1 yr-1.and 6.6302 t C ha-1 yr-1, respectively. The percentage of biomass in propagule, stem, leaves and roots of 6 months old R.mucronata are 72.95%, 9.41%, 9.64% and 8.00%, respectively. In 5 years old replanted R.mucronata the proportion of biomass in stem, leaves, branches, stilt roots and roots are 23.75%, 17.36%, 9.31%, 38.76% and 10.91%, respectively. The percentage carbon partitioning in trees are similar to percentage biomass partitioning. Root: shoot ratio of 6 months, 5 and 10 years old R.mucronata is varied with the age and the values are 1:11.5, 1:8 and 1:4.7, respectively.

Assessment on timber and carbon in rubber plantations with special reference to the wet zone of Sri Lanka

E S Munasinghe, V H L Rodrigo P K W Karunathilaka and U A D P Gunawardena
Rubber Research Institute of Sri Lanka.
Department of Forestry and Environmental Science, University of Sri Jayewardenepura, Sri Lanka

Rubber (Hevea brasilensis) has traditionally been cultivated for the latex extraction; however, its importance in other uses, particularly producing quality timber and sequestering atmospheric carbon as a permanent sink, is also often highlighted. The amount of timber produced and carbon sequestered in rubber trees has been assessed in isolations. Those values would differ under different growth conditions and to date, no simple protocol is available to quantify the amount of timber and carbon in rubber plantations. Therefore, the study reported here was aimed to develop simple growth models to assess the timber production and carbon fixing capability of rubber plantations in Sri Lanka.

Initially, a growth function was developed to assess the girth development with respect to age and thereafter another three functions to quantify the amount of timber, biomass and carbon in the rubber tree based on girth diameter. Also, wood density variation with age of the tree was modeled to determine the biomass in timber under different age categories. The assessment on the available carbon was based on the carbon content in unit biomass and the total amount of biomass in the tree. Growth data required for the girth development function were gathered from secondary sources and girth measurements made on existing rubber clearings. Destructive sampling was conducted to assess the timber, biomass and wood density.
Based on above models, an average rubber tree at 30 years achieves a girth of 88.64 cm and produces 0.656 m3 of timber and 594.46 kg of biomass. The amount of atmospheric carbon fixed in timber at this age was estimated as 193.7 kg per tree and 45.86 MT per hectare. However, total amount of organic carbon fixed in above ground components was 220.8 kg per tree and 52.27 MT per hectare. The models of this study were developed under general conditions in the wet zone, hence should be validated for drier regions of the country before any wide scale adoption.