Immediate Effects of Thinning with a Small Patch Clearcut on Understory Light Environments in a Cryptomeria japonica Plantation in Central Taiwan

小區塊皆伐式疏伐對台灣中部柳杉人工林林下光照環境的立即影響

江智民(Jyh-Min Chiang) ； 林國銓(Kuo-Chuan Lin) ； 黃正良(Jeen-Liang Hwong) ； 王雪卿(Hsueh-Ching Wang) ； 林登秋(Teng-Chiu Lin)

《台灣林業科學》 27卷4期 (2012/12) Pp. 319-331

https://doi.org/10.7075/TJFS.201212.0319

摘要

疏伐是重要的森林經營手段然而其對熱帶及亞熱帶生態系微棲地環境影響的研究相當少。本研究利用半球面影像檢驗25%疏伐（100個小樣區伐除25個）及50%疏伐（1/2小樣區伐除）對台灣最常見的柳杉（Cryptomeria japonica）人工林林下光環境的影響。疏伐對林下光環境變異的影響更甚對林下光量的影響。林下光照量在25及50%疏伐後分別增逾40與120%，而變異數則增加了2.4到9.9倍。在25%疏伐後逾40%的林下光照增加遠超過1996年強烈颱風賀伯在東北部的森林所造成的25%增加量，而且在賀伯颱風侵襲後林下光環境的變異減少而非增加。颱風是台灣最常見的自然擾動，本研究結果顯示超過25%的疏伐將使林下光照量及其變動範圍提升到在颱風擾動下不易出現的程度。此外研究中所使用的0.01 ha區塊式疏伐使得林下微棲地的光照在疏伐前後相關性偏低，反之颱風擾動的影響較疏伐分散而全面，故林下微棲地的光照在擾動前後有顯著而高度的正相關。疏伐後森林的演替軌跡是否與颱風擾動後的回復有明顯差異需有長期監測才能完整評估。

關鍵字

半球面影像技術 ； 孔隙 ； 光環境 ； 疏伐

並列摘要

Thinning is an important forest management practice; however, its effects on the microenvironment have rarely been investigated in tropical and subtropical ecosystems. We examined the effect of 25% (25 of 100 10 x 10 m subplots were clearcut) and 50% (1/2 of the subplots were cut) thinning on understory light environments characterized using hemispherical photography at a Cryptomeria japonica plantation, Taiwan's most common plantation species. Thinning had a greater effect on the variability than on the availability of understory light, with the former increasing 40 and 120% under 25 and 50% thinning intensities, respectively, and the variance increasing 2.4~9.9-fold. The ＞ 40% increase in understory light availability following 25% thinning was much greater than the 25% increase in light at a forest in northeastern Taiwan following the 1996 category-3 typhoon Herb, which decreased variability of understory light. Typhoons are the most important natural disturbance in Taiwan. Thus, mechanical thinning at intensities ＞ 25% increases light availability and variability to levels that rarely exist following typhoon disturbance. In addition, mechanical thinning of 0.01-ha patches as applied in this study led to an understory light environment that was decoupled from the pre-thinning condition. In contrast, typhoon disturbances are typically more evenly spread, resulting in positively correlated pre- and post-typhoon light environments. Long-term monitoring is required to understand differences in successional trajectories following mechanical thinning and typhoon disturbance.

並列關鍵字

hemispherical photography ； gap ； light environment ； thinning