Secondary succession that occurs on abandoned farmlands is an important source of biomass carbon stocks. Both direct and indirect tree biomass estimation methods are applied on forest lands. Using empirical data from 148 uprooted trees, we developed a seemingly unrelated mixed-effects models system for the young silver birch that grows on post agricultural lands in central Poland. Tree height, biomass of stem, branches, foliage, and roots are used as dependent variables; the diameter at breast height is used as the independent variable. During model elaboration we used restricted cubic spline: 5 knots at the quantiles (0.05, 0.275, 0.5, 0.725, and 0.95) of diameter at breast height provided sufficiently flexible curves for all biomass components. In this study, we demonstrate the use of the model system through cross-model calibration of the biomass component model using tree height measured from 0, 2, 3, and 4 available extreme trees feature in the plot in question. A different number of extreme trees were measured for final model system and our results indicated that for all analyzed components, random-effect predictions are characterized by higher accuracy than fixed-effects predictions.

中文翻译：

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后农业用地上年轻的白桦林看似无关的混合效应生物量模型

在废弃农田上发生的次生演替是生物量碳储量的重要来源。直接和间接树木生物量估算方法都适用于林地。利用来自148根连根拔起的树木的经验数据，我们为生长在波兰中部后农田上的年轻白桦树建立了看似无关的混合效应模型系统。树高，茎，枝，叶和根的生物量用作因变量。乳房高度的直径用作自变量。在模型制作过程中，我们使用了受限的三次样条：在胸高处的分位数（0.05、0.275、0.5、0.725和0.95）处的5节速度为所有生物质成分提供了足够灵活的曲线。在这个研究中，我们通过对生物量组分模型进行交叉模型校准来证明该模型系统的使用，该模型使用从所涉及地块中的0、2、3和4个可用的极端树特征测得的树高。对于最终模型系统，测量了不同数量的极端树，我们的结果表明，对于所有分析的组件，随机效应预测的特征是比固定效应预测的准确性更高。