六龜地區紅檜人工林疏伐效果之研究

Effects of Thinning on Taiwan Red Cypress (Chamaecyparis formosensis Matsum) Plantation in Lu-Kuei Area

羅卓振南(Chen-Nan Lo-Cho) ； 鍾旭和(Hsu-Ho Chung) ； 羅新興(Hsin-Hsing Lo) ； 周朝富(Chau-Fu Chou)

《林業試驗所研究報告季刊》 2卷3期 (1987/09) Pp. 187-198

https://doi.org/10.7075/BTFRI.198709.0187

摘要

紅檜人工林乃以生產大徑木生產為經營之導向，因此，其生長過程中，由於樹冠鬱閉林木生長時，木經營之收益即應實施疏伐撫育作業，以調節有效之生長空間，促進主伐木質與號之生長而影響增進林本經營之收益。
本研究乃對六龜地區之22年生紅檜人工林遣行疏伐試驗，以瞭解不同疏伐度對林木生長及林分結構狀態之效應。不同疏伐度係以每公頃胸高斷面積保留量為基準，計分為四種：(A)弱度疏伐：保留量為34m^2/ha；(B)中度疏伐：保留量為29m^2/ha；(C)肱度疏伐：保留量為24m^2/ha；(O)對照區。疏伐木之選定，依照下層疏伐法之原則實施。試驗林分於林齡達22年生時施行疏伐，7年後實施結果調查。其結果顯示中度疏伐之效應最能增進林分質與量之生長。

關鍵字

紅檜 ； 疏伐 ； 定期生長量 ； 生長率

並列摘要

The present study was carried out in a 22-years old red cypress (Chamaecyparis formosensis Matsum) plantations located in Lu-Kuei Area. Four thinning treatments, based on the absolute basal area (BA) left after thinning, were applied in the present study; namely (A) light thinning with 34m^2/ha BA retained, (B) intermediate thinning with 29m^2/ha of BA retained, (C) heavy thinning with 24m^2/ha of BA retained, and (O) control. Seven years after treatments results of thinning effects can be summarized as follow:
1. As a results-of thinning treatments' there was a decrease, in terms of dbh distribution, in the coefficient of variation and an increase in the uniformity of the thinned plantations. Thinning would also increase the ratio of large diameter trees and, thus, improve both the quantitative and qualitative growth of the plantations which, in turn, would result in the economic of productions. These thinning effects are particularly evident in the heavily and the intermediately (i.e. treatments (B) and (C)) thinned plantations;
2. The periodic increments, as expressed in average dbh, over the 7 years after thinning increased significantly. The increments were the highest in the heavily thinned plantation followed by the intermediately and the lightly thinned ones. The increments were the lowest in the control or the unthinned plantation;
3. In terms of average height, the periodic increments over the 7 years after thinning were the highest in the intermediately and the heavily thinned plantations followed by the lightly thinned one. The average height increments in the unthinned control plantation, again, was the lowest;
4. As a result of long canopy closure, the mortality in the control or the unthinned plantation (i.e. treatment (O)) was about 157 trees per ha over the 7 years of experimental period which accounts for a loss of 6.73m^3/ha of wood. Death of trees due to canopy closure did not occur in thinned plantations.
5. The periodic inorements during the 7 years after thinning were 65.2 m^3/ha. 59.6m^3/ha, 51.9m^3/ha and 40.0 m^3/ha, respectively, for the heavily thinned (i. e treatment (B). the intermediately thinned (treatment (C)), the lightly thinned (treatment (A)) and the unthinned plantations; these results indicated that treatment (B)) would result in the highest increment followed by treatment (C) and, then, treatment (A), unthinned plantation has the lowest volume increment;
6. On the per hactre basis the plantation volume growth percentage during the 7 years after thinning were 5.5%, 5.1%, 3.6% and 2.7%, respectively, for treatments (C), (B), (A) and (O) indicating the volume growth rates in the heavily and the intermediately thinned plantations were far better than the lightly and/or the unthinned plantations; and
7. In summary, results of the present study showed that for 22-years old red cypress plantations of Lu-Kuei Ares the intermediate thinning which retained 29m^2 BA or about 1,080 trees per heetre would result in the best qualitative and quantitative growth.

並列關鍵字

Taiwan Red Cypress ； Thinning ； Periodic increment ； growth percentage