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.