Taper Modeling on Taiwania Plantation Trees in the Liukuei Area

六龜地區台灣杉人工林林木尖削度模式之建立

汪大雄(Dar-Hsiung Wang) ； 謝漢欽(Han-Ching Hsieh) ； 湯適謙(Shyh-Chian Tang)

《台灣林業科學》 22卷3期 (2007/09) Pp. 339-353

https://doi.org/10.7075/TJFS.200709.0339

摘要

林木尖削度(taper)是指樹幹不同部位直徑之尖削程度，不同形狀之樹幹其尖削程度不一。尖削度模式又稱為樹幹剖面模式(stem profile)，是描述樹幹連皮或去皮直徑隨著某特定高度之變化情形。尖削度之重要性是在可以計算一株樹在不同利用標準下之木材利用材積。因此，對木材工業而言，良好之尖削度模式可以在不同標準規格下提供準確有效之木材利用率。一般言之，尖削度模式種類甚多其配置之方式亦不同。本研究使用五種不同類別之模式探討六龜地區台灣杉人工林林木尖削度模式之建立，並就各模式之推估能力進行比較。研究結果顯示就總體之推估能力(含偏差與精密度)言之除三角模式外，各模式之間之差異不大，但描述各不同段位之能力則有明顯之差別。以從根株至10%樹高高度之部位觀之，幾何形狀一般式和單一低階多項式之預測能力顯然較變動形數模式和分段式多項式為差。變動形數模式和三段式多項式，雖然其數學模式較為複雜，然不但其總體之偏差百分比小於4%，其幹材較低部位之偏差亦為最低，因比，變動形數模式和三段式多項式是為比較理想之尖削度模式。

關鍵字

樹幹剖面模式 ； 變動形數模式 ； 分段式多項式

並列摘要

Taper is used to measure the rate of decrease in the stem diameter of a tree from the bottom upwardly. Taper equations express the expected stem diameter with or without bark, as a function of the height above ground level, total tree height, and the diameter at breast height. Five tapering modeling approaches were used to estimate the stem diameter at a given height above the stump in Taiwania plantations, and their levels of accuracy and precision were compared. The results indicated that based on 3 criteria simultaneously considered, the trigonometric taper modeling approach was the worst for describing the taper of the entire tree bole, followed by the sigmoid form approach. Three-segmented polynomials, the variable-form stem profile and the polynomial form with higher-order approaches were preferred to describe the taper of the entire stem. The mean relative biases in percentage for these models on the validation trees were all ＜4%. Along the bole, the root swell (the segment from 0.3 to 1.3m in height) was the most difficult part to predict by taper modeling. However, the precision and accuracy of the prediction of tree root swell can be significantly improved using the 3-segmented polynomials or variable-form taper models.

並列關鍵字

stem profile ； variable form model ； segmented polynomials model