觀霧地區柳杉人工林不同強度疏伐後微環境及植群之比較

Comparisons of Microenvironment and Vegetation Changes after Different Thinning Intensities in a Sugi (Cryptomeria japonica) Plantation at Guanwu, Northern Taiwan

翁世豪(Shih-Hao Weng)

指導教授 ： 郭幸榮

國立臺灣大學/生物資源暨農學院/森林學研究所/碩士(2004年)

https://doi.org/10.6342/NTU.2004.01306

摘要

本試驗於觀霧30年生柳杉人工林進行單株下層疏伐，區分為強度疏伐（每公頃保留500株）、中度疏伐（每公頃保留680株）、弱度疏伐（每公頃保留960株）及對照組（未疏伐，每公頃原有1540株）4種不同疏伐強度處理，探討各處理在短期內微環境之變化、林下地被植物之變動及柳杉留存木之生長反應。

疏伐作業於2001年10月至12月實施，微環境監測自2002年2月起至2004年1月止，以評估疏伐後短期之效應。透光率至少每月測定一次，冠層鬱閉度每季測定一次，覆賓蚳C年測量一次，氣溫、相對濕度、土壤溫度及土壤水勢每2小時記錄一筆，採連續監測。留存木量取疏伐前及疏伐2年後之胸徑，以計算生長量。林下植生調查以木本小苗為主，於疏伐後（2001年12月）及2003年8月進行調查。

自2001年10月疏伐後，經2年期間的監測結果：疏伐後會改變林分結構，留存木的胸徑及株數分布會呈左傾(left skew)，林分之平均胸徑及株距較疏伐前高。疏伐強度愈強則冠層鬱閉度及覆賓袪V低，在時間序列上之變動幅度越大，透光率隨疏伐強度增強而升高，變動幅度愈大且不穩定，即對照區為最弱之透光率，且呈現持續的穩定現象。疏伐度越高，回復穩定越慢。疏伐強度越高，林下可獲得較高之R/FR值。強度疏伐土壤溫度及氣溫在生長季較其他處理略高1.6℃~2℃及1.2~1.5℃，其他季節相差小於1℃。土壤水勢隨疏伐度增加而提高，尤以乾旱季節較為明顯。隨疏伐強度愈強則空氣之相對溼度愈低。

林下地被植生之木本小苗數量及種類以強度疏伐區最多。在強度疏伐及弱度疏伐區出現大量山胡椒及柳杉小苗，致二者的植生優勢度指數較高，歧異度指數則較低。疏伐後洩K落葉堆積量及草本覆遠|影響小苗的出現，疏伐後洩K落葉堆積量及草本覆遘

關鍵字

冠層鬱閉度 ； 林分結構 ； 透光率 ； 優勢度指數 ； 冠層覆蓋度 ； 下層疏伐 ； 歧異度指數 ； 微環境

並列摘要

This study was carried out in a 30-years-old Cryptomeria (Cryptomeria japonica) plantation at Guanwu, Northern Taiwan. We thinned the plantation from below with four treatments which were heavy (existing 500 stems/ha retained), moderate (680 stems/ha), light (960 stems/ha) and control (unthinned, 1540 stems/ha).The objective was to investigate the short-term microenvironment changes, understory woody vegetation dynamics and growth of retained trees in different thinning treatments.

The thinning was operated from October to December, 2001. The microenvironmental conditions was monitored from February, 2002 to January, 2004 for assessing the short-term effects after thinning. The PPFD transmittance was measured at least once a month. The canopy closure was measured every season. The canopy cover was measured once a year. The air temperature, relative humidity, soil temperature and water potential were continuously recorded with two hour interval. The DBH of the retained trees were measured just before thinning and two years after thinning to estimate the growth response. The understory woody vegetation was recorded in December,2001 and August,2004.

After two-year monitoring, the result showed that the stand structure changed, that is to say, the distribution was left skew and the mean DBH, and the mean distance between trees were higher than those before thinning. The thinning not only decreased the canopy closure and the canopy cover but also increased the variation in time series. With the increasing thinning intensity, the unstable variation was increased. That means of PPFD transmittance was the lowest in the control and approached to stable. The higher the thinning intensity was, the more time it would take to recover to stable status and the higher R/FR ratio was. In heavy thinning treatment, the soil and air temperature were 1.6℃~2℃ and 1.2~1.5℃ higher than other treatments during growing seasons, and the difference was less than 1℃ during other seasons. The soil water potential was increased with thinning intensity. It was more apparently in the drought season. With the increasing thinning intensity, the relative humidity was lower and the variation would be increased.

The species and numbers of understory woody vegetation were the most in heavy thinning treatment. The Litsea cubeba and Cryptomeria japonica seedlings appeared a lot in heavy and light treatments, respectively, so that the dominant indices of these two treatments were higher, the diversity i indices were lower. The litter accumulation and herb cover would impede the emergence of woody seedlings. The more the litter and herb covers were, the less the seedlings was.

DBH growth of retained trees increased among all treatments, but the difference was not significant among thinning densities. It is suggested that thinning had no obvious effect on single tree growth of the first 2 years after thinning. However, basal area per hectare increased significantly.

並列關鍵字

dominance index ； diversity index ； canopy closure ； canopy cover ； stand structure ； thinning from below ； light transmittance ； microenvironment

參考文獻

王明光、鄒裕民、莊璟芳 2001 疏伐對枯枝落葉分解及土壤理化性質的效應。人