Site Index Curve for Taiwania Plantations in the Liukuei Area

六龜地區台灣杉人工林地位指數模式之建立

汪大雄(Dar-Hsiung Wang) ； 湯適謙(Shyh-Chian Tang) ； 謝漢欽(Han-Ching Hsieh) ； 鍾智昕(Chih-Hsin Chung)

《台灣林業科學》 23卷4期 (2008/12) Pp. 335-349

https://doi.org/10.7075/TJFS.200812.0335

摘要

立地品等(site quality)之有效數量化是森林經營中至為重要之要務之一。由於林分之優勢樹高生長是為林齡和地位之函數，因此要計算林分優勢樹高之前必須先對立地之品等進行評量。本研究使用單形地位指數曲線(anamorphic site index curve)和多形地位指數曲線(polymorphic site index curve)兩種方式，以樹幹解析資料，使用不同之模式進行六龜地區台灣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和Wang發表(1994)並經本研究調整後之模式，就所有觀測到各林齡之台灣杉人工林言之，其進行地位指數推估之成效最高，驗證資料顯示其相對偏差小於3%。基準年無關(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年影響之優點，但本研究發現和基準年相依(base-age-specific)之地位指數模式相比，前者之推估能力較後者為差，尤其是對林齡小於11年生之林分，其差異現象更為明顯。此外，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起初林齡(predictor age)呈現相當大之變化。一般而言，研究結果顯示在推估地位指數時使用之起初林齡越接近基準年，則其推估會呈現更為精確之趨勢。

關鍵字

基準年特定地位指數模式 ； 基準年無關地位指數模式 ； 多形高生長曲線

並列摘要

An effective characterization of site quality is very important in forest management. Dominant height growth is calculated as a function of tree age and site, and, therefore, the evaluation of site quality is a prerequisite to computing the stand dominant height growth. Both anamorphic curves and polymorphic curves approaches were used to develop the site index model for Taiwania plantations in the Liukuei area, and their accuracy and precision were compared. Pairs of heightage observations were obtained through a stem analysis. The results indicated that based on simultaneously considering the accuracy and precision, i.e., the mean square error (MSE), the base-agespecific site index model developed by Payandeh and Wang (1994) and modified by this study was the best at estimating the site index value for all tree ages observed. In relative terms, the mean bias was ＜3% for the chosen model in the validation dataset. While there is an advantage that the estimate and application of the base-age-invariant site index model was not affected by the baseage used, this study showed a great large loss of accuracy and precision caused by base-age-invariant models, especially for those trees younger than 11 yr. Moreover, the accuracy of the site index model varied considerably depending on the choice predictor age in estimating the site index value at the base age. This study showed the tendency that for a predictor age, the closer to the base age it was, the higher the accuracy that was obtained.

並列關鍵字

base-age-specific site index model ； base-age-invariant site index model ； polymorphic height growth