A Test of the Accuracy of Two Individual Tree Growth Functions for Picea abies

1989

2 Abb., 7 Tab., 13 Lit. Ang.

Unselbständiges Werk

12244

200022776

The accuracy of two distant-independent diameter growth function for individual trees of Picea abies L. (Karst.) are tested on plots older than 55 years b.h., and with relatively few trees per hectare. Both funtions (I1 and I2) have site index, stand basal area, and individual tree basal area as explanatory variables; in addition age at breast height is used in Function I1. Relative to mean measured increment. Functions I1 and I2 underestimate the growth of the test plots by 4.4% and 10.9% respectively; Function I1 shows a root mean squared deviation of 29.2% for single plot predictions, and 5.4% for mean of all plots. Function I1 predicts the growth as well as some stand functions frequently in use in Norway. Functin I2 is unacceptable because age is not independent variable.