應用鑽孔抵抗法推估六龜地區台灣杉不同疏伐處理之碳貯存量

本研究應用非破壞性之鑽孔抵抗法的年輪特徵值之密度值及永久樣區生長資料以推算不同疏伐處理對幼齡時期台灣杉的生物量及碳貯存量影響。在相同樹齡中，單株樹木疏伐處理的碳貯存量較未疏伐處理為高，其原因為單株材積（胸徑及樹高）隨疏伐處理增加而增加。而林木生物量及碳貯存量隨著樹齡增加而增加。不同疏伐處理，12年後單位面積林木總生物量及碳貯存量，其大小依序為未疏伐、中度疏伐、強度疏伐，但若以單位面積淨生產量而言，大小順序則為中度疏伐、未疏伐及強度疏伐，且在疏伐後6 年，中度疏伐區生產力（生物量及碳貯存量）即超越未疏伐區。疏伐後12 年，23年生時，強度疏伐區之林木株數枯死率為3.8%，中度為4.1%，未疏伐區為11.1%，而各處理區留存木平均每年之生產力差異不顯著，顯示林木又再度鬱閉，產生競爭，需再進行第二次疏伐處理。又林木疏伐後搬出利用，則可轉為木質材料應用及以碳素儲存形式存在木材產品中；未疏伐之林分，林木因競爭而枯死，將碳素釋放至大氣中，若將此加以考量，則中度疏伐區單位面積之林木總生產力之生物量及碳貯存量超越未疏伐區，且強度疏伐區和未疏伐區之差距更小，此更顯示人工林適當經營之重要。This study utilized the density values of annual ring characteristic indices derived from the non-destructive drilling resistance method, combined with growth data from permanent sample plots, to evaluate the impacts of varying thinning treatments on the biomass and carbon storage of young-aged Taiwania cryptomerioides. For trees of the same chronological age, the carbon storage of individual trees subjected to thinning treatments was higher than that of unthinned individuals. This was attributed to the increase in individual tree volume (diameter at breast height (DBH) and tree height) with increasing thinning intensity. Additionally, forest stand biomass and carbon storage both increase with stand age. For different thinning treatments, the total stand biomass and carbon storage per unit area 12 years post-treatment followed the order: unthinned > moderate thinning > intensive thinning. In contrast, when measured by net primary productivity (NPP) per unit area, the ranking was moderate thinning > unthinned > intensive thinning. Notably, 6 years after thinning, the productivity (biomass and carbon storage) of the moderate thinning plots exceeded that of the unthinned plots. Twelve years after thinning (when the stands reached 23 years of age), the tree mortality rate of the intensive thinning plots was 3.8%, that of the moderate thinning plots was 4.1%, and that of the unthinned plots was 11.1%. No significant difference was observed in the average annual productivity of retained trees across all treatment groups, indicating that the forest canopy had reclosed, triggering intraspecific competition, and a second thinning treatment was necessary. Furthermore, when felled trees from thinning operations are removed and utilized, they can be processed into wood-based materials, with carbon stored permanently in the resulting wood products. For unthinned forest stands, trees die due to intraspecific competition, releasing carbon dioxide into the atmosphere. When this carbon release factor is accounted for, the biomass and carbon storage associated with total net primary productivity per unit area in moderate thinning plots exceed those of unthinned plots, and the gap between intensive thinning plots and unthinned plots is even smaller. This further underscores the importance of proper management of plantation forests.