& Key message This synthesis of the literature on incorporation of genetic gain into growth and yield models reveals a fundamental challenge associated with the rapid progress in genetics and breeding and limited empirical data on improved stands. Model improvements depend on a better understanding of both the biological basis for gain and of interactions between genetic and non-genetic factors on gain. & Context Continued development of new genetic varieties of trees requires accurate stand growth and yield models to predict growth trajectories and genetic gain of the new varieties using early-age growth data. & Aims To identify how the effects of genetic variety on growth and yield models could be analyzed and genetic information could be incorporated into these models for accurate growth simulation and improved yield prediction of genetically improved stands. & Results Genetic variety may affect one or several of the asymptotic parameters, shape parameters, and rate parameters of growth and yield models, which can be assessed by testing the parameter differences of the models. After determination of the influence of genetic varieties on model parameters and considering the existing general stand growth equation, the genetic gain can be incorporated into growth and yield models by calculation of genetic gain multipliers, adjustment of the site index, and calibration of the new model parameters. & Conclusion Accurate and effective growth and yield models for genetically improved stands require a better understanding of the effects of genetics, environment, and silviculture measures on tree and stand growth.
How trees allocate their biomass among different components has important implications for their survival and growth and ecosystem carbon cycling. Data on the distribution pattern and dynamics of tree biomass are essential for fully exploiting forest carbon sequestration potential and achieving the goal of carbon neutralization. However, there has not been enough research to-date on tree biomass spatial allocation and temporal dynamics in different site qualities at specific tree species scales. This study aimed to evaluate the biomass allocation patterns within tree components of Chinese fir and to examine how they are affected by tree age and site quality. A total of 87 trees were destructively sampled and measured for stem, branch, leaf, bark and root biomass. The biomass proportion difference of tree components in different age stages (8-40 years) was analysed, and the influence process of tree age and site quality on biomass allocation was examined. Our results indicate that the biomass allocation varied with tree age and was also affected by site quality. Stem biomass accounted for the largest proportion of total tree biomass, followed by leaf, root, branch and bark biomass in young forests, and it was followed by root, bark, branch and leaf biomass in other age groups. The biomass proportion of each component all nonlinearly changed with tree age. The proportion of stem biomass increased with increasing tree age, and the biomass proportion of branches and leaves decreased with increasing tree age. The proportion of root biomass first increased and then decreased with tree age, while the bark biomass proportion first decreased and then increased with increasing tree age. Site quality had a positive effect on the biomass proportion of stems but a negative effect on the biomass proportion of branches and bark. The interaction of tree age and site quality also had a significant effect on the proportion of stem biomass as well as root biomass. Therefore, to obtain accurate estimates of Chinese fir forest biomass and carbon stocks, age-specific changes and the influence of site conditions on it need to be considered.
Studying tree biomass dynamics and allocation is crucial to understanding the forest carbon cycle and the adaptation of trees to the environment. However, traditional biomass surveys are time-consuming and labor-intensive, so few studies have specifically examined biomass formation in terms of the increase in individual tree biomass, and the role that tree age and site conditions play in this process, especially tree roots, is unclear. We studied the tree ring characteristics of 87 sample trees (8–40 years old) from 29 Chinese fir plantations with different site conditions and measured the biomass of their stems, crowns, and roots. The biomass increment at various age stages during tree growth was determined via using tree ring analysis, and a generalized additive mixed model (GAMM) was used to analyze biomass formation and allocation, as well as the specific impact of site conditions on them. The results showed that the biomass increment of Chinese fir trees first increased and then decreased with age, and improving site conditions delayed the carbon maturation of the trees. The proportion of stem biomass increased with age, while the proportion of crown biomass decreased and the proportion of root biomass increased and then decreased. The effect of the site conditions on the tree biomass allocation showed a nonlinear trend. Tree ring analysis provides a feasible and effective method for assessing tree growth and biomass dynamics. Forest managers can use the findings of this study to scientifically optimize the management of increasing forest carbon sequestration.
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