资源环境科技发展态势分析平台

The world's forests sequester and store vast amounts of atmospheric carbon, playing a crucial role in climate change mitigation. Internal stem decay in living trees results in the release of stored carbon back into the atmosphere, constituting an important, but poorly understood, countervailing force to carbon sequestration. The contribution of internal decay to estimates of forest carbon stocks, though likely significant, has yet to be quantified, given that an accurate method for the non-destructive quantification of internal decay has been lacking. To that end, we present here a novel and potentially transformative methodology, using sonic and electrical resistance tomography, for non-destructively quantifying the mass of stored carbon lost to internal decay in the boles of living trees. The methodology was developed using 72 northern hardwood trees (Fagus grandifolia, Acer saccharum and Betula alleghaniensis) from a late-successional forest in northwestern Connecticut, USA. Using 105 stem disks corresponding to tomographic scans and excised from 39 of the study's trees, we demonstrate the accuracy with which tomography predicts the incidence and severity of internal decay and distinguishes active decay from cavities. Carbon mass fractions and densities, measured and calculated from 508 stem disk wood samples corresponding to density categories, as predicted by sonic tomography, were used with stem disk volumes to generate indirect estimates of stem disk carbon mass accounting for decay, C-SD, or assuming no decay, C-ND; these indirect estimates were compared with direct estimates calculated using stem disk mass, C-mass) and carbon mass fraction data. A comparison of three linear regression models with C-mass as the response variable and C-SD or C-ND as the predictor variable (C-mass similar to C-SD, R-2 = 0.9733, Model1; C-mass similar to C-ND, R-2 = 0.8918) demonstrates the accuracy with which C-SD predicts C-mass. Forcing the C-mass similar to C-SD regression through the origin resulted in improved metrics (R-2 = 0.9930, Model 2) for which a null hypothesis that y = x (Model 3) could not be rejected (p < 0.00001). For each of the study's 72 trees, two estimates of lower bole carbon mass-C-bole accounting for decay, and Cbole-ND, assuming no decay-were obtained using all three models, with the difference between C-bole and Cbole-ND used to estimate the proportion of the lower bole's carbon lost to decay, %C-dec. Overall, tomography identified decay in 47 of the 72 trees, with %C-dec values ranging from 0.13% to 36.7%. No decay was detected by tomography in the remaining 25 trees. The combined uncertainty due to both measurement error and model prediction error was +/- 2.1% for all three models. These results demonstrate the efficacy of the proposed methodology in non-destructively quantifying the carbon loss associated with internal decay in the boles of living trees, and its applicability to studies aimed at measuring internal decay rates, and more accurately quantifying forest carbon stocks.