疏伐對臺灣杉人工林直徑生長之研究

EFFECT OF THINNING ON THE DIAMETER INCREMENT GROWTH OF TAIWAN CEDAR

彭炳勳(Ping-Hsun Peng) ； 潘孝隆(Hsiao-Lung Pan) ； 唐盛林(Sheng-Lin Tang) ； 邱志明(Chih-Ming Chiu) ； 蔣華蕾(Hua-Lei Chiang) ； 陳建璋(Jan-Chang Chen)

《中華林學季刊》 52卷4期 (2019/12) Pp. 205-221

摘要

本研究以林業試驗所六龜研究中心臺灣杉人工林14年生時進行之下層疏伐試驗區為研究對象，為了解疏伐後造林木的生長隨時間推移的變化，探討1.林分胸徑定期平均生長量的變化，以及2.不同直徑階生長量於疏伐強度間的比較。疏伐採逢機完全區集設計，分為強、中、弱度疏伐與對照組，並於伐後第2、5、7、13、17年進行5次調查。結果顯示，在林分胸徑定期平均生長量上，經疏伐處理之留存木於5次調查時，其與對照組均具極顯著差異（P值＜0.01），各疏伐強度以疏伐後2-5年差異較大，之後隨伐後年期增加而漸不明顯；以5 cm直徑階之徑級分布為比較基礎，發現疏伐強度越高，其促進生長的效果越好，維持生長的時間越長，各直徑階定期平均生長量相對百分率於伐後5-7年達高峰；各疏伐度間，胸徑20 cm以下的留存木因林分密度的下降程度不同，故恢復樹冠鬱閉所需時間不同，其生長量差異大，因此於伐後第7年生長開始衰退時，各疏伐度間的生長下降程度不一，而胸徑20-30 cm的留存木對於強度、中度疏伐生長促進表現相似，疏伐後5年內平均生長量較對照組高2.4倍，伐後第17年時則緩降至1.8倍，顯示疏伐強度對於優勢木胸徑生長促進效果有一定上限；弱度疏伐於伐後第5年到達高峰後穩定維持1.4倍的生長，對該直徑階差異隨時間而趨於不顯著。

關鍵字

臺灣杉人工林 ； 疏伐 ； 定期生長量 ； Weibull分布

並列摘要

This study aims to explorer the post-thinning mean annual DBH increment and the comparison of increment in DBH classes among thinning treatments of Taiwan cedar (Taiwania cryptomerioides Hayata) after thinning at the stand age of 14 in Liougui Research Center, located in southern Taiwan, of Taiwan Forestry Research Institute. The thinning followed a randomized complete block design with 4 replicas for each heavy-, moderate-, light-thinned, and unthinned treatment, and were revisited after the 2nd, 5^(th), 7^(th), 13^(th), and 17^(th) years. The results showed that the mean annual increments of all thinned classes are significantly greater than the un-thinned in five inventory, and the mean annual DBH increment of all thinned stands reaches peaks after 2-5 years of thinning and later declined gradually. Comparison of the DBH class distributions (5cm width) of five inventory indicated that the more intense the thinning, the more the increment and the longer the thinning effect sustained. The mean annual increment of all DBH class peaks at 5-7 years after thinning. The increments of small remaining trees (DBH less than 20 cm) vary among treatments resulted from the different thinning intensity and the time required for crown closure, but they reach the maximum at 7 years after thinning. In contrast, the large remaining trees (DBH between 20 -30 cm) of heavy- and moderate-thinned stands showed a similar amount of increment, which implies heavy thinning has bounded effect for enhancing diameter growth, and they reached the maximum increment of 2.4 times of the unthinned stands after 5 years of thinning and decent to 1.8 times after 17 years of thinning. The large remaining trees of the light-thinned stands remain 1.4 times growth of the unthinned stands and reached the maximum after 5 years of thinning and its effect on the increment of the DBH class diminishes with time.

並列關鍵字

Taiwania plantation ； Thinning ； Mean annual increment ； Weibull distribution