Analysis of the sensitivity of absorbed light and incident light profile to various canopy architecture and stand conditions
Analysis of the sensitivity of absorbed light and incident light profile to various canopy architecture and stand conditions
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DOI：
10.1093/treephys/tpq098
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发表时间：
2011-01-01
期刊：
影响因子：
4
通讯作者：
Oren, Ram
中科院分区：
文献类型：
--
作者：
Kim, Hyun-Seok;Palmroth, Sari;Oren, Ram
我们分析了简化假设的辐射传输模型的冠层表示的效果，比较模拟的漫射非拦截和光合光子通量密度与测量在不同层次的复杂松阔叶冠层叶面积指数的季节变化大。最详细的模型包括树木的丛生（即，林分密度）和叶角分布和枝丛的垂直规格。一个不太详细的模型取代了垂直指定的变量与他们的平均值。最简约的模型既不拍摄丛生，也不占林分密度。垂直规格的拍摄丛生和叶角分布只有轻微改善垂直和季节开放度和光估计使用的平均值。进一步简化对总吸收光的影响不大，但对开放度和冠层吸收光的垂直分布的估计更具风险，这将影响光合作用的估计，由于光合光响应的非线性。包括木质表面在冬季，当叶面积低，是必要的复制正确的测量。敏感性分析表明，忽略（i）芽丛生可能会导致大量高估的总吸收光的误差增加，减少叶面积和（ii）在稀疏的林分密度可能会导致大量高估的总吸收光，效果在很大程度上是独立的叶面积。此外，（iii）改变叶角分布的效果增加，减少叶面积，并更大，更持久的沿着叶面积范围增加丛生。总的来说，考虑树木聚集对吸收光的影响在由树叶不是非常聚集的物种组成的林分中是最重要的（例如，阔叶的）。然而，即使在芽高度丛生的森林中（即，针叶林），在林分中吸收光分布的准确估计需要在模型中纳入林分密度。
We analyzed the effect of simplifying assumptions in canopy representation of radiation transfer models, comparing modeled diffuse non-interceptance and photosynthetic photon flux density with measurements at different layers of complex pine-broadleaved canopy with large seasonal variation of leaf area index. The most detailed model included clumping of trees (i.e., stand density) and a vertical specification of leaf angle distribution and shoot clumping. A less detailed model replaced the vertically specified variables with their means. The most parsimonious model accounted for neither shoot clumping nor stand density. The vertical specification of shoot clumping and leaf angle distribution only slightly improved vertical and seasonal openness and light estimates over using mean values. Further simplification had little effect on total absorbed light but was more risky for estimates of the vertical distributions of openness and light absorbed by the canopy, which will affect photosynthesis estimates due to the non-linearity of photosynthetic light response. Including woody surfaces in winter, when leaf area was low, was essential for reproducing the measurements correctly. A sensitivity analysis showed that ignoring (i) shoot clumping could result in a substantial overestimation of total absorbed light with errors increasing with decreasing leaf area and (ii) stand density in sparse stands could lead to substantial overestimation of total absorbed light, and the effect is largely independent of leaf area. Also, (iii) the effect of changing leaf angle distribution increased with decreasing leaf area, and was larger and more persistent along the leaf area range with increasing shoot clumping. Overall, accounting for the effect of tree clumping on absorbed light is most important in stands composed of species where leaves are not very clumped (e.g., broadleaved). However, even in forests with highly clumped shoots (i.e., coniferous), an accurate estimation of absorbed light distribution in stands requires incorporation of stand density in the model.