Tree species play a very important role in storing and sequestration of carbon by preventing the accumulation of carbon dioxide in the atmosphere as greenhouse gases. Carbon stock assessment is a useful tool in estimation of the importance of an area in terms of its carbon storage capacity. Trees with at least 5cm-diameter at breast height were recorded from 27 plots with a total area of 10800 square meter. A total of 139 species with 2239 individuals were identified with a total of 306.48 t [ha.sup.-1] carbon content based on the live trees' aboveground and belowground biomass. Regression analysis showed that there was no significant relationship between tree carbon stock and basic parameters namely, species richness, species abundance, and elevation. Ecologically important species, particularly the Philippine endemics and threatened, yielded a total of 172.65 t [ha.sup.-1]. Among the species found within the area, Xanthostemon philippinensis Merr. (Myrtaceae) had the highest carbon stored of 68.60 tons. The study revealed that the ultramafic forest in Sitio Dicasalarin, Baler, Aurora, Philippines is a critically important area with tremendous carbon storage capacity mainly contributed by the endemic and threatened species as found. Keywords: carbon stock; species richness; ultramafic forest; Philippine endemics; biomass