六龜地區臺灣杉人工林疏伐修枝效果之研究

Effects of Thinning and Pruning on Taiwania (Taiwania cryptomerioides Hayata) Plantation in Lu-Kuei Area

羅卓振南(Chen-Nan Locho) ； 鍾旭和(Hsu-Ho Chung) ； 邱志明(Chih-Ming Chiu)

《林業試驗所研究報告季刊》 7卷4期 (1992/12) Pp. 291-304

https://doi.org/10.7075/BTFRI.199212.0291

摘要

臺灣杉樹形高大，材性優良，因此，其人工林之經營應以生產長伐期高品質之大徑材為目標，而期中撫育之施行，則應以培植幹材為導向。本研究係以林業試驗所六龜試驗林第3林班，以原實施第一次修枝試驗之臺灣杉人工林，繼續施行第一次疏伐及觀測修枝後節之癒合。疏伐木之選定，係以自由疏伐法的原則進行。而其疏伐度則依每公頃胸高斷面積保留量為準，計分為四種：(A)弱度疏伐：保留42m^2/ha；(B)中度疏伐：保留35m^2/ha；(C)強度疏伐：保留30m^2/ha；(D)對照區。疏伐後保留木再以第一次修枝試驗最佳成果為依據，均施以4.5公尺高之修枝處理，以資觀測節癒合情形。試驗結果分析如下：
1.強度疏伐和中度疏伐處理，均可明顯增進臺灣杉林木胸徑和樹高的生長，並提高林分胸高斷面積和材積之生長量。
2.強度疏伐對斷面積和材積之生長潛能具最大助力，至第5年時其生長曲線仍呈顯著上升之趨勢，而其他處理已呈平緩現象。因此，就疏伐撫育目標而言，強度疏伐應為最佳之疏伐度。
3.本試驗林分樹幹分叉者約佔總林木株數之35%，採用強度及中度之自由疏伐法，可伐除此類幹形不良之林木，而有助於改善林分結構，以及增進林木品質生長之效果。
4.臺灣杉林木之側枝衆多，平均每公尺樹幹所著生之枝條約為21枝。枝條節徑之大小界於0.2~3.4cm間，由癒合節之觀測結果顯示修枝傷口在4年內均已先後癒合，此後幹材之年輸生長顯現圓滿無節狀態，由此可見修枝確能提高林木之品質生長。
5.優勢木（包括次優勢木）之枝條節徑較中庸木粗大，但其傷口癒合時間卻較中庸木者為快，故疏伐時應儘量留存優勢木及次優勢木。
6.未作修技之對照區林木，冠層下方之側枝約於11年生時即逐漸乾枯，但至19年生時其枯枝仍殘留於幹上而無法自助脫落，致成死節，此點顯示臺灣杉人工林實施人工修枝確實必要。

關鍵字

臺灣杉 ； 疏伐 ； 修枝 ； 定期平均生長 ； 連年生長 ； 傷口癒合

並列摘要

The present study was carried ant in a l4-year-old Taiwania (Taiwania cryptomerioides Hayata) plantation located in Lu-Koei area of southern Taiwan. The plantation was experimentally prunned once at age of nine. In the present study it was, then, subjected to thinning and second time pruning experiments at age of fourteen. Four thinning regimes, based on the absolute basal area (BA) per hactare left after thinning, were applied; namely (A) light thinning with 42m^2/ha of BA retained; (B) intermediate thinning with 35m^2/ha of BA retained; (C) heavy thinning with 30m^2/ha of BA retained; and (D) control. All trees retained after thinning were penned up to 4.5m tree height and the occlusion tendencies of branches after pruning were observed. Observations were made daring the five consecutive years after thinning and pruning treatments; and the result can be summarized as follows:
1. Heavy and intermediate thinning significantly increased the D. B. H. and height growth of individual trees at welt at the BA and volume growth of the plantations.
2. Heavy thinning significantly promoted the growth potential of both BA and volume of the plantation; end even at the fifth year after thinning, the growth curves of the plantation-still showed strong tendency of raising, whereat the growth carves of the plantations treated with other thinning regimes were already leveled off. In term of thinning intensity, heavy thinning, therefore, was the best for plantation growth.
3. The plantation selected for the present study contained 35% deformed and over topped trees. Removal of these deformed trees by heavy and intermediate thinnings can improve the structure of the plantation and, thus, improve its qualitative production.
4. Taiwania is highly branching; nod there were 21 branches on every one mater of stem. The branches of 0.2-3.4cm in diameter occluded within 4 years after penning; pruning, hence, improve the quality of timber produced from plantations.
5. Although the branches of dominant and co-dominant trees were, in terms of diameter, larger than that of intermediate ones, the occlusion time, after pruning, of the former, however, is shorter than the later. Hence, in the selection of trees during the thinning operation, the dominant and co- dominant trees, wherever and whenever possible, should be retained.
6. The branches of trees located on the lower layers of unpruned trees died back when the trees were 11-year-old. They, however, did net drop off even when trees reached 19-year-old. Dead knotes were, therefore, formed in the stems of these unpruned trees. Pruning, hence, is necessary in managing Taiwania plantations.

並列關鍵字

Taiwania cryptomerioides Hayata ； Thinning ； Pruning ； Periodic annual increment ； Current annual increment ； Occlusion