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引用本文:

DOI:

10.11834/jrs.20219400

收稿日期:

2019-10-30

修改日期:

2020-08-02

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半椭球形树冠对冠层间隙率与聚集度指数的影响研究
王少腾1, 耿君1, 涂丽丽2, 尹高飞3
1.合肥工业大学土木与水利工程学院;2.安徽农业大学资源与环境学院;3.西南交通大学地球科学与环境工程学院
摘要:

森林冠层结构特征直接影响着森林截获太阳辐射的程度,进而影响到林冠与外界环境的能量交换。树冠形状是森林冠层结构的重要组成部分,定量分析树冠形状的影响对森林冠层结构参数的计算有重要意义。之前的研究将树冠假设为圆锥形、圆柱形、圆锥+圆柱形等形状计算了冠层间隙率与聚集度指数。然而,树冠生长受外部环境以及内部顶端优势等因素的影响,相较于上述理想化的树冠形状,半椭球形更符合树冠自然生长规律。事实上,半椭球形是一种十分常见的树冠形状。本文推导出半椭球形树冠的冠层间隙率与聚集度指数计算公式,并进一步扩展到双半椭球形树冠。同时将以上两种形状的树冠与理想的圆锥形、圆柱形、圆锥+圆柱形树冠的冠层间隙率和聚集度指数的进行对比分析。结果表明:(1)半椭球形树冠与其它形状树冠的冠层间隙率有较大差异,且随着观测天顶角增加,其冠层间隙率的相对误差也逐渐增大。当观测天顶角70°时,圆锥形树冠与半椭球形树冠的冠层间隙率相对误差已接近100%;(2)半椭球形树冠与其它形状树冠的聚集度指数误差不容忽视,当观测天顶角为10°时,圆柱形树冠与半椭球形树冠相对误差最大达到20%;(3) 在半球空间聚集度指数期望值的计算中,半椭球形树冠值比圆锥形树冠值高约16%,半椭球形与双半椭球形树冠的值较为接近,混用树冠形状对结果影响不大。

Influences of semi-ellipsoid crown on gap fraction and clumping index
Abstract:

The structural characteristics of forest canopy directly affect the radiation interception of forest, which in turn affect the energy exchange between the canopy and the external environment. The crown shape is an important part of the forest canopy structure. Quantitative analysis of the influence of crown shape is of great significance for the calculation of canopy structure parameters. Researchers have calculated the gap fraction and the clumping index by simulating the crown shape as basic geometry such as cone, cylinder, cone + cylinder. However, the growth of the crown is influenced by factors such as the external environment and the internal apical dominance. Compared with the above crown shapes, the semi-ellipsoid is more in line with the natural growth of the crown. In fact, the semi-ellipsoid is a very common crown shape. The semi-ellipsoid is significantly different from other crown shapes, and has an important influence on the calculation of canopy structure parameters such as gap fraction of canopies and clumping index.In this paper, the formula for calculating the gap fraction and clumping index of semi-ellipsoid canopy is derived based on the Poisson distribution of the canopy, and further extended to the double semi-ellipsoid crown. Meanwhile, we analyzed the difference of gap fraction and clumping index between semi-ellipsoid crown and crowns of other shapes such as cone, cylinder, cone + cylinder.The results show that: (1) the gap fraction of canopies between semi-ellipsoid crown and crowns of other shapes is quite different. With the increment of observation zenith angle, the relative error of gap fraction increases. When the observation zenith angle is 70°, the relative error of gap fraction between the cone crown and the semi-ellipsoid crown is close to 100%. (2) the error of the clumping index between semi-ellipsoid crown and crowns of other shapes can’t be ignored. When the observation zenith angle is 10°, the relative error of clumping index between the cylinder crown and the semi-ellipsoid crown is up to 20%. (3) When calculating the value of expectation of clumping index in hemisphere space, the value of semi-ellipsoid crown is about 16% higher than the value of cone crown, and the value of semi-ellipsoid crown and double semi-ellipsoid crown are close to each other, so the mixed crown shape has little effect on the results.

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