首页 > , Vol. , Issue () : -
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.