科研之友
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摘要
Our investigation aims (1) to derive a dynamic model for mean volume and biomass growth projection over time, considering the competition-induced tree mortality (dynamic size-density model), (2) to design a compatible two-component modelling system composed of the dynamic size-density model and an appropriate density decrease function, and (3) to examine the applicability of this composite natural thinning model to describe the growth dynamics of even-aged coniferous and broadleaved stands. The stand growth projection system was formulated to include three dynamic equations: a density decrease model expressing the reduction in tree number with dominant height growth, and two dynamic size-density models, for mean stem volume and tree biomass respectively. Two size-density formulations (M1 and M2) were derived, each including one local (site- or stand-specific) and three global (common to all stands of the species) parameters. Model Ml suggests a polymorphic set of size-density curves, while model M2 describes size-density curves with variable asymptotes. The goodness-of-fit statistics showed that for radiata pine (Pinus radiata D. Don) and Scots pine (Pinus sylvestris L.) datasets the three-model system based on M1 performed better than the one based on M2. The growth trajectories of downy birch (Betula pubescens Ehrh.) and English oak (Quercus robur L.) stands were described only by model M2. The systems of projection equations explained more than 95% of the variation in most cases. The two-component modelling system is implicitly defined by the stand density and mean tree size (biomass and/or volume) values for a given dominant stand height and set of global model parameters; it does not require any additional stand variables, constants of contested universality or standard-base variable values. It uses stand dominant height as a proxy for time, and inclusion of this growth stage indicator enables the bidirectional dependence between stand density and tree size to be reflected. The composite natural thinning model estimates sets of polymorphic curves with multiple asymptotes. Together with the stand-specific rate of density decrease, this also yields the stand-specific rate of size increase over time and the reduction in tree number, thus enabling prediction of contrasting individual growth patterns of stands of similar initial densities. It accounts for the isometric relationship between plant volume and biomass and can be considered for incorporation as a principal component of a dynamic Stand Density Management Diagram.
- 出版日期2017-2-1
