本研究旨在探討不同栽植密度的臺灣杉人工林林分，於15年生時進行下層疏伐，探 討處理後5年、11年、18年、23年、29年之生長差異，結果顯示：林分存活株數在不同林分密 度對各時期的蓄積量有決定性的影響，從而影響林分不同時期的林分生產力，經下層疏伐處 理後，林分密度為每公頃1300株者有最高的存活率。在生長初期的樹高生長與林分密度無相 關性，隨著林齡增加，疏伐的處理、林木間競爭的結果與生育地環境綜合因子影響之下使得 林分密度低者樹高生長較高於林分密度高者；而胸徑生長與林分密度成反比，於下層疏伐區 中44年生時四種林分密度之臺灣杉人工林胸徑生長無顯著性差異。林分密度為1300株未疏伐 者在歷年的調查中有較佳的單木材積生長以及蓄積量，密度為5200株者於15年生時進行下層 疏伐在未來能有效的提升單木材積生長。未來若欲進行臺灣杉造林，以栽植密度每公頃1300 株者為佳，建議輔以修枝作業，在未來俾能生產優質無節大徑木。

This research aimed to low thinning effects of different stand densities of Taiwania plantation on the growth variation were investigated after 15-year plantation which study on the grown variation at 5, 11, 18, 23, 29 year. Result showed that was decisive influence in survival ratio of different forest stand density on the amount of each period of volume stock, thus affecting the productivity of stands at different times, after treatment by the lower thinned, 1300 trees per hectare of stand has the highest survival ratio. In the early growth stage of tree height, there were no significant differences between different stand densities. With the increase of stand age, thinning treatment, the result of competition between trees and the habitat influence of environmental factors revealed that the height growth of low-density stands was higher than that of high-density stand. However, The DBH decreased with increasing stand density. No significant differences of DBH were found between different stand densities through low thinning after 44-year plantation. Hereis individual volume and volume stock growth better in 1300 trees per hectare of stand among per period, and worked low thinning be able to increase individual volume effectively in 5200 trees per hectare after 15 years. In the future, if we will planting Taiwania fir plantation, density of 1300 trees per hectare is better. And Suggested with pruning that being production quality and large log.