| Popis: |
22年生林分を対象として, 下層, 上層, 中層および機械的の4種類の間伐法にそって間伐案を立て, 間伐による林冠構造と立木の受光状態の変化を比較検討した。(1)間伐率を樹冠の全器官表面積あるいは幹材積によって表わした場合, 林分の樹冠体積V_, 林冠孔隙体積V_および樹冠競合体積V_などの林冠構造諸量の間伐による変化は, 次のようになる。同一間伐率におけるV_の減少, V_の増大およびV_の減少は, 下層間伐で大きく, 上層間伐で小さい。中層間伐と機械的間伐では, 両者の中間的な変化を示す。一方, 間伐率を立木本数によって表わした場合, 同一間伐率における林冠構造諸量の変化は, 反対に, 下層間伐で小さく, 上層間伐で大きい。(2)間伐による平均葉面相対照度R_の上昇も, 間伐法で異なる。間伐率を樹冠の全器官表面積, 幹材積, 立木本数のいずれによって表わしても, 同一間伐率におけるR_の上昇は, 下層間伐で小さく, 上層間伐で大きい。中層間伐や機械的間伐では, 両者の中間的な変化を示す。 The effects of thinning on the canopy structure and on the light environment within the canopy are estimated by simulating four different types (lower-story, upper-story, middle-story, and mechanical) of thinnings in a 22-year-old stand. Simulations of lower-and upper-story thinnings which remove the same surface area of crown-components or the same stem volumes, indicate that lower-story thinnings reduce the total volume of crowns (V_) more than upper-story thinnings. As a result, the canopygap volume (V_) is increased more, and the crown-competition volume (V_) is decreased more through lower-story thinnings. The effects of middle-story and mechanical thinnings upon V_, V_, and V_ are similar and are intermediate between lower- and upper-story thinnings. Comparison of lower and upper-story thinnings which remove the same number of trees, indicates that V_ and V_ are reduced more and the V_ is increased more through upper-story thinnings. The increase of the mean relative light intensity on the leaf surface (R_) due to thinning varies with the thinning type. When the surface area of the crown-components, or the stem volume, or the number of trees removed by thinning is the same, the increase of R_ is larger for upper-story thinnings and smaller for lower-story thinnings. |
