title: A reassessment of carbon content in tropical trees.
abstract: Accurate knowledge of carbon (C) content in live wood is essential for quantifying tropical forest C stocks, yet generic assumptions (such as biomass consisting of 50% carbon on a weight/weight basis) remain widely used despite being supported by little chemical analysis. Empirical data from stem cores of 59 Panamanian rainforest tree species demonstrate that wood C content is highly variable among co-occurring species, with an average (47.4±2.51% S.D.) significantly lower than widely assumed values. Prior published values have neglected to account for volatile C content of tropical woods. By comparing freeze- and oven-dried wood samples, we show that volatile C is non-negligible, and excluding the volatile fraction underestimates wood C content by 2.48±1.28% (S.D.) on average. Wood C content varied substantially among species (from 41.9-51.6%), but was neither strongly phylogenetically conserved, nor correlated to ecological (i.e. wood density, maximum tree height) or demographic traits (i.e. relative growth rate, mortality rate). Overall, assuming generic C fractions in tropical wood overestimates forest C stocks by ∼3.3-5.3%, a non-trivial margin of error leading to overestimates of 4.1-6.8 Mg C ha(-1) in a 50-ha forest dynamics plot on Barro Colorado Island, Panama. In addition to addressing other sources of error in tropical forest C accounting, such as uncertainties in allometric models and belowground biomass, compilation and use of species-specific C fractions for tropical tree species would substantially improve both local and global estimates of terrestrial C stocks and fluxes.
authors.affiliation: Faculty of Forestry, University of Toronto, Earth Sciences Building, Toronto, Ontario, Canada. adam.martin@utoronto.ca
authors.forename: Adam R
authors.initials: AR
authors.lastname: Martin
authors.forename: Sean C
authors.initials: SC
authors.lastname: Thomas
mesh_terms: D000465:Algorithms; D000704:Analysis of Variance; D018533:Biomass; D002244:Carbon / Q000032:analysis* / Q000378:metabolism; D017753:Ecosystem; D016014:Linear Models; D010176:Panama; D013045:Species Specificity; D014197:Trees / Q000145:classification / Q000254:growth & development / Q000378:metabolism*; D014329:Tropical Climate; D014934:Wood / Q000254:growth & development / Q000378:metabolism*
chemical_list: D002244:Carbon