柳杉人工林疏伐後7年之林分生長、林分結構及森林健康探討

Assessment of stand development, stand structure and forest health of a Japanese cedar (Cryptomeria japonica D. Don) plantation 7 years after thinning

本研究旨在探討疏伐對於柳杉人工林不同層面之影響，包括林分生長、林分結構及森林健康等層面。林分疏伐試驗主要包括：下層疏伐35％（BT-35％）、下層疏伐45％（BT-45％）、上層疏伐35％（AT-35％）及對照組（UT）等四種不同處理，並於疏伐7年後評估其對不同層面之影響。在分析方法上，本研究採用變異數分析探討林分生長、Weibull機率密度函數模擬林分直徑分佈、森林健康指標評估森林健康，所得結果顯示林分於疏伐7年後，對生長性態值之影響較不明顯。由Weibull機率密度函數模擬不同疏伐處理於林分之結果可知，UT在疏伐後7年的直徑變異性較大。在森林健康評估方面，不同處理對於各直徑級之林木其健康等級所佔之比例，隨直徑級增加而增加，且不論何種處理（包括UT）皆有此趨勢。就整體林分而言，不同處理間健康分數具有差異性（F=12.99, P<0.01），在統計差異上，經疏伐處理者之分數皆顯著高於UT （28.08±9.10），三種疏伐處理之分數，以BT-45％ （32.61±6.46）顯著高於BT-35％（30.75±7.01），唯AT-35％（31.31±6.86）與其它二種疏伐處理之間並無顯著差異。由林分不同處理健康的表現可歸納得知，疏伐在健康的表現具有明顯的促進效果。整體而言，本研究所得結果，將可提供疏伐對不同面向具體的參考資訊，作為柳杉人工林經營管理之參考。 The purpose of this study was to assess the stand growth, stand structure and forest health for a Japanese cedar (Cryptomeria japonica D. Don) plantation 7 years after thinning. Four treatment levels were conducted at this trial, including low-thinning 35% (BT-35%), low-thinning 45% (BT-45%), crown-thinning 35% (AT-35%) and un-thinning (UT). We used analysis of variance (ANOVA), the Weibull function and forest health indicators to access stand growth, stand structure and forest health for the 4 treatments, respectively. Our results showed that stand growth performance was not significant among treatments. On the other hand, simulation of the stand diameter distributions for each treatment 7 years after thinning by Weibull function showed that the UT treatment had larger variance compared to the other 3 treatments. Moreover, the performance of forest health was significantly different among treatments. We grouped the trees into 5 classes based on their diameter at breast height and compare the performance of health conditions among classes. The results showed a trend of increasing health scores with increasing DBH regardless of treatments. The ANOVA results showed a significant treatment effect (F=12.99, P<0.01). According to the Games-Howell test, the UT had the lowest score (28.08±9.10) and was significantly different from other treatments, indicating that stands with thinning obtained higher scores than the un-thinning treatment. Overall, BT-45% had the highest health score (32.61±6.46), followed by AT-35% (31.31±6.86) and BT-35% (30.75±7.01). BT-45% and BT-35% had significant differences whereas AT-35% was not significant different with the other two treatments. The results of this study provide basic information of stand development after thinning for the management of Japanese cedar plantations.

The purpose of this study was to assess the stand growth, stand structure and forest health for a Japanese cedar (Cryptomeria japonica D. Don) plantation 7 years after thinning. Four treatment levels were conducted at this trial, including low-thinning 35% (BT-35%), low-thinning 45% (BT-45%), crown-thinning 35% (AT-35%) and un-thinning (UT). We used analysis of variance (ANOVA), the Weibull function and forest health indicators to access stand growth, stand structure and forest health for the 4 treatments, respectively. Our results showed that stand growth performance was not significant among treatments. On the other hand, simulation of the stand diameter distributions for each treatment 7 years after thinning by Weibull function showed that the UT treatment had larger variance compared to the other 3 treatments. Moreover, the performance of forest health was significantly different among treatments. We grouped the trees into 5 classes based on their diameter at breast height and compare the performance of health conditions among classes. The results showed a trend of increasing health scores with increasing DBH regardless of treatments. The ANOVA results showed a significant treatment effect (F=12.99, P<0.01). According to the Games-Howell test, the UT had the lowest score (28.08±9.10) and was significantly different from other treatments, indicating that stands with thinning obtained higher scores than the un-thinning treatment. Overall, BT-45% had the highest health score (32.61±6.46), followed by AT-35% (31.31±6.86) and BT-35% (30.75±7.01). BT-45% and BT-35% had significant differences whereas AT-35% was not significant different with the other two treatments. The results of this study provide basic information of stand development after thinning for the management of Japanese cedar plantations.