Abstract:

Enhancement of carbon storage through the establishment of man-made forests has been considered as a mitigation option to reduce increasing atmospheric CO₂ levels. Therefore the present study was carried out to estimate the biomass and carbon storages of the above ground parts of Eucalyptus grandis growing as plantations in Sri Lanka. In addition, it was expected identify the variation of biomass and carbon storage in the above ground parts of the selected species with stem volume.

E. grandis plantations were selected using FORDATA database of the Department of Forest Conservation of Sri Lanka. Those plantations were selected from Badulla and Nuwara Eliya Forest Divisions where the selected species is growing in large scale. Using the random sampling, tree diameter, total height, lower and upper crown height were measured. Crown measurements were obtained using a digital photographic analysis method. Number of branches in each tree was counted. Stem volume was estimated using the breast height diameter and tree height using a previously developed individual stem volume prediction modes for the same species. Stem and branch biomass values were estimated using extracted core samples and the crown biomass was separately estimated. For this reason, crown volume was estimated using equations of conoid, paraboloid or hemisphere after determining the crown shape with the digital photographic analysis. Stem and leaf carbon were determined using Walkley-Black method and finally the biomass values were converted separately to the carbon values for different above ground parts of the tree.

Non-liner regression analysis was employed for the construction of models which had age as the explanatory variable. Both exponential and logistic curves were tested for this purpose. Linear regression was used in order to build the models to predict the above ground and stem biomass and carbon using volume. For both linear and non-linear types, the model quality was tested using R² and fitted line plots.

According to the results, above ground biomass and carbon values at the 7^th year were 138.8 kg and 82.9 kg respectively. Annual biomass increment for E. grandis was 33.1 kg. Above ground biomass and carbon values at the 40^th year were 1,323.5 kg and 822.1 kg respectively showing annual carbon storage of 22.4 kg. 65.9% of the above ground stem biomass was carbon.

Exponential models were proven to be better than the logistic models to predict the diameter, height, stem volume, above ground biomass, stem biomass, branch biomass, crown biomass, above ground carbon, stem carbon, branch carbon and crown carbon with the age. The R² values and the fitted line plots indicated the strength of the selected models. Linear models built to predict the above ground biomass, stem biomass, above ground carbon and stem carbon using stem volume also showed the high predictability of the models. R² values were above 97.9% for all linear models. Therefore the models built in the present study can be used to estimate the stem and crown growth, above ground biomass and above ground carbon for E. grandis in effective manner.