Abstract
Current models for oak species could not accurately estimate biomass in northeastern China, since they are usually restricted to Mongolian oak (Quercus mongolica Fisch. ex Ledeb.) on local sites, and specifically, no biomass models are available for Liaodong oak (Quercuswutaishanica Mayr). The goal of this study was, therefore, to develop generic biomass models for both oak species on a large scale and evaluate the biomass allocation patterns within tree components. A total of 159 sample trees consisting of 120 Mongolian oak and 39 Liaodong oak were harvested and measured for wood (inside bark), bark, branch and foliage biomass. To account for the belowground biomass, 53 root systems were excavated following the aboveground harvest. The share of biomass allocated to different components was assessed by calculating the ratios. An aboveground additive system of biomass models and belowground equations were fitted based on predictors considering diameter (D), tree height (H), crown width (CW) and crown length (CL). Model parameters were estimated by jointly fitting the total and the components’ equations using the weighted nonlinear seemingly unrelated regression method. A leave-one-out cross-validation procedure was used to evaluate the predictive ability. The results revealed that stem biomass accounts for about two-thirds of the aboveground biomass. The ratio of wood biomass holds constant and that of branches increases with increasing D, H, CW and CL, while a reverse trend was found for bark and foliage. The root-to-shoot ratio nonlinearly decreased with D, ranging from 1.06 to 0.11. Tree diameter proved to be a good predictor, especially for root biomass. Tree height is more prominent than crown size for improving stem biomass models, yet it puts negative effects on crown biomass models with non-significant coefficients. Crown width could help improve the fitting results of the branch and foliage biomass models. We conclude that the selected generic biomass models for Mongolian oak and Liaodong oak will vigorously promote the accuracy of biomass estimation.
Highlights
IntroductionEx Ledeb.) and Liaodong oak (Quercus wutaishanica Mayr) are very similar in both morphological characteristics and geographical distribution
Developing individual-based biomass models and estimating forest biomass has long become a prerequisite for studying productivity and in more recent times for assessing carbon accounting and its potential in mitigating climate change [33,34]
The two additive systems of aboveground biomass equations (Table 4) and the D-based root biomass equation obtained in the present study for two natural oak species (Mongolian oak and Liaodong oak) provide an operational approach for gaining precise biomass estimation in northeastern China
Summary
Ex Ledeb.) and Liaodong oak (Quercus wutaishanica Mayr) are very similar in both morphological characteristics and geographical distribution. Both species are valuable and occupy the secondary broadleaved deciduous forest regions widely distributed in northeastern China [1]. The use of destructive sampling is enormously time-consuming, expensive and restricted to small trees or small sample sizes; it is not recommended in nature reserves and on endangered tree species [5] To overcome these limitations, the indirect estimation of biomass based on allometric equations is an alternative and rapid method without destruction if accuracy is not compromised [6,7]. Almost no biomass models exist for Liaodong oak, and especially no generic biomass equations have been reviewed for the two species
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