Site Index Model for a Sugi Plantation (Cryptomeria japonica) in Zenlen Area, Taiwan

立地潛在生產力（potential site productivity）之推估是在森林生長預測中之要務之一。地位指數之建立則是目前使用最廣來數量化立地潛在生產力之方法。本研究使用單形態地位指數曲線（anamorphic site index curve）和多形態地位指數曲線（polymorphic site index curve）兩種方式，以樹幹解析資料，使用不同之模式進行人倫地區柳杉人工林地位指數曲線之建立，並進行配置模式間推估值正確性和精確性之比較。研究顯示在同時考慮正確性和精確性而言（mean square error, MSE），所有模式中以Payandeh and Wang（1994）進行地位指數推估之成效最高，整體之平均相對偏差率為-0.36。基準齡無關（base-age invariant）之地位指數模式雖然具有模式配置不受到不同基準齡影響之優點，但其推估能力較基準齡相依之地位指數模為差，尤其是對林齡小於10年生之林分，其差異現象更為明顯。同時，地位指數之推估正確性會隨著推估地位指數時所有採用之預測林齡（predictor age）呈現相當大之變化。一般而言，推估地位指數時使用之預測林齡越接近基準年，其推估則會呈現更為精確之趨勢。

關鍵字

單形態地位指數曲線；多形態地位指數曲線；基準年

並列摘要

Assessing potential site productivity is important for forest planning and predicting forest growth and yield. The most common measure of site productivity is the site index (SI), defined as the average height of dominant and co-dominant trees (top height) at a specified (index) age. Two types of SI curves were investigated in this study to build up a SI curve for a Sugi plantation in Zenlen area, Taiwan. Several models were used to compare the performance among models. Pairs of height-age observations were obtained through a stem analysis. Based on the mean square error criterion, the base-age-specific SI model proposed by Payandeh and Wang (1994) was ranked the best one with an average bias in percentage of -0.36. Despite the advantage of being invariant with the base age used, this study showed a large loss of accuracy and precision caused by base-age-invariant models, especially for those trees younger than 10 yr. Moreover, the accuracy of the SI models varied considerably depending on the choice of predictor age for estimating the SI value at the base age. This study showed a tendency that the closer the predictor age was the base age, the higher the accuracy was that was obtained.

並列關鍵字

anamorphic site index curve ； polymorphic site index curve ； base age

國際替代計量

Site Index Model for a Sugi Plantation (Cryptomeria japonica) in Zenlen Area, Taiwan

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