Abstract:
Tree volume is one of the most important and difficult variable in an ecosystem. It has to be predicted using a reliable method since all the management decisions are taken on the volume production of the
tree. Annona glabra is a widely spread invasive species which can significantly impact native communities and ecosystems in Sri Lanka by widely reducing biodiversity. The objectives of the study were to (a) construct a volume predication model, [b) determination of the root and shoot ratio, [c) measure
biomass of A. glabra, and root: (d) determine shoot variation with DBH, tree height and tree volume of A.
glabra for making suitable management decisions. Random sampling was used in 0.01ha sample plots on Thalangama tank to collect the data of 60 individual trees stratified by age into two age classes of 7 years 2009-2016) and 12 years [2004-2016).All the reliable tree measurements of each tree were measured
by using standard methods. Using these measurements, log volume was estimated by Newton,s formula
and the volume of final section was calculated by assuming as a cone. The tree volume was then calculated by adding all the section volumes together. Total biomass was estimated using fresh weight and dry weight of destructive tree samples. Estimated mean total tree biomass for 7 years and 12 years old.A. glabra were 698kg per tree (0.42) and 7.5gkg per tree (0.40) respectively. Estimated root: shoot ratio ' for 7 years and 12 years,A. glabra in Thalangama tank area were 1.:2.6 and 1: 2.4 respectively. Model for
tree age prediction was built as a function of tree height while tree volume prediction model was built as a
function of tree height and basal area using SPSS. The best models were selected based on R2 value and distribution of the standardized residual. Accordingly, selected models for tree age and tree volume with the R2 values were 94o/o and 92o/o respectively. Finally, it is recommended that the volume prediction model of.A. glabra able to use as management decision tool in Sri Lankan wetlands
