紅檜人工林疏伐後不同期間之疏伐效益分析

Analysis of thinning effects on different periods after thinning for a Taiwan red cypress (Chamaecyparis formosensis Matsum.) plantation

本研究之目的在於探討紅檜人工林採不同強度疏伐處理於疏伐後不同時期之效益，研究區域為臺灣中部大雪山地區之紅檜人工純林，該林分於29年生時實施強度及中度之疏伐作業，並保留未疏伐之對照區，同時設置永久樣區進行疏伐後之監測。本研究採用永久樣區自疏伐後當年至疏伐後4年（疏伐後初期）及疏伐後4年至疏伐後8年（疏伐後晚期）之二期資料進行疏伐效益分析，結果顯示，疏伐後晚期之定期年生長率較初期降低了約30％，然而，無論疏伐後初期或晚期，疏伐林分之定期年生長率均較未疏伐林分提升了約40％，顯示隨著林齡增加，林分的生長已漸減緩，但即使已過8年之久，疏伐促進生長之效益仍持續發生中。本研究所得之結果可提供評估紅檜人工林不同面向之疏伐效益。

The purpose of this study was to compare thinning effects between different periods after thinning for a Taiwan red cypress (Chamaecyparis formosensis) plantation with different thinning intensities. This plantation was a pure stand located in the Dasyueshan area of central Taiwan. The plantation was thinned at 29-year-old with three treatments, heavy, moderate and no thinning. Permanent plots were set up for monitoring stand developments after thinnng. Thinning effects were evaluated at two periods, 0 to 4 years after thinning (early period, EP) and 4 to 8 years after thinning (late period, LP). The results showed that the periodic annual relative growth rate (PARGR) of stands in the LP reduced 30% compared with the EP, whereas the PARGR of thinned stands increased 40% compared with the control stand for both periods,suggesting that the growth of stand decreased as of stand age increased while the thinning effects was still obvious 8 years after thinning. The results of this study could provide concise information for assessing thinning effects in various aspects for Taiwan red cypress plantations.