Purves Drew W, Lichstein Jeremy W, Strigul Nikolay, Pacala Stephen W
Computational Ecology and Environmental Science Group, Microsoft Research, Cambridge CB3 0FP, United Kingdom.
Proc Natl Acad Sci U S A. 2008 Nov 4;105(44):17018-22. doi: 10.1073/pnas.0807754105. Epub 2008 Oct 29.
The perfect-plasticity approximation (PPA) is an analytically tractable model of forest dynamics, defined in terms of parameters for individual trees, including allometry, growth, and mortality. We estimated these parameters for the eight most common species on each of four soil types in the US Lake states (Michigan, Wisconsin, and Minnesota) by using short-term (</=15-year) inventory data from individual trees. We implemented 100-year PPA simulations given these parameters and compared these predictions to chronosequences of stand development. Predictions for the timing and magnitude of basal area dynamics and ecological succession on each soil were accurate, and predictions for the diameter distribution of 100-year-old stands were correct in form and slope. For a given species, the PPA provides analytical metrics for early-successional performance (H(20), height of a 20-year-old open-grown tree) and late-successional performance (Z*, equilibrium canopy height in monoculture). These metrics predicted which species were early or late successional on each soil type. Decomposing Z* showed that (i) succession is driven both by superior understory performance and superior canopy performance of late-successional species, and (ii) performance differences primarily reflect differences in mortality rather than growth. The predicted late-successional dominants matched chronosequences on xeromesic (Quercus rubra) and mesic (codominance by Acer rubrum and Acer saccharum) soil. On hydromesic and hydric soils, the literature reports that the current dominant species in old stands (Thuja occidentalis) is now failing to regenerate. Consistent with this, the PPA predicted that, on these soils, stands are now succeeding to dominance by other late-successional species (e.g., Fraxinus nigra, A. rubrum).
完美可塑性近似模型（PPA）是一种在分析上易于处理的森林动态模型，它依据单株树木的参数来定义，包括异速生长、生长和死亡率。我们利用单株树木的短期（≤15年）清查数据，估算了美国湖泊地区（密歇根州、威斯康星州和明尼苏达州）四种土壤类型中每种类型上最常见的八个物种的这些参数。基于这些参数，我们进行了100年的PPA模拟，并将这些预测结果与林分发育的年代序列进行了比较。对每种土壤上断面积动态和生态演替的时间及幅度的预测是准确的，对100年林分直径分布的预测在形式和斜率上也是正确的。对于给定的物种，PPA提供了早期演替表现（H(20)，20年生孤立木的高度）和晚期演替表现（Z*，单作中的平衡林冠高度）的分析指标。这些指标预测了每种土壤类型上哪些物种是早期或晚期演替物种。对Z*进行分解表明：（i）演替既由晚期演替物种在林下和林冠层的优势表现驱动，（ii）表现差异主要反映死亡率的差异而非生长差异。预测的晚期演替优势种与旱中生境（红栎）和中生境（红花槭和糖槭共优势）土壤上的年代序列相匹配。在湿中生境和湿地土壤上，文献报道老龄林分中的当前优势种（美国金钟柏）现在无法更新。与此一致的是，PPA预测在这些土壤上，林分现在正被其他晚期演替物种（如黑梣、红花槭）取代并占据优势。
