A nondestructive sampling method was utilized to evaluate the above-ground carbon stock of a tree plantation forest by laying 10 plots of size 25m*25m. All trees within the sample plot were recorded and DBH and height were measured by a caliper and a clinometrer, respectively. To determine the above-ground biomass of trees, the formula IPCC = 0.0673(ρHD²)^0.976 was applied. To obtain the below-ground biomass, the above-ground biomass was multiplied by 20 percent. To convert biomass into carbon quantity, biomass was multiplied by 47 percent. To see the relationship between variables, SPSS version 20 was used and one-way ANOVA and t test were used. In the plantation forest in this study, an area of 110 tree/ha was found, which indicated that the trees were sparsely populated or its density was very low. The total above-ground biomass was 902.377 tons and the below-ground biomass was 180.46 tons. There was no significant relationship between quadrat and number of trees, as r² is 0.262 and the Durbin–Watson coefficient is 2.825. The results of ANOVA showed p values of 0.130^b, which is also not significant. Diameter at breast height (DBH) and height have very strong relationship because ANOVA indicated p=.000^b. These three factors had a very strong correlation, according to sample tree correlation. R-Squared (R²) =0.994 indicated that the above-ground biomass, height and DBH had a strong positive and linear relationship. The total carbon density was 508.8972 tons. Cupressus lusitanica could accumulate a larger amount of biomass than others at a proportion of 36.78 percent; followed by Eucalyptus camaldulensis, which covered 32.72 percent; while Grevillea robusta had 30.5 percent of the total accumulation. There was a significant difference between the biomass accumulations of the three investigated plant species because the t value for above-ground biomass was 0.006 and that for below-ground biomass was 0.009.