A Bark Thickness Model for White Spruce in Alaska Northern Forests

Table 2

Parameters of the six area models and the statewide model to estimate the bark thickness of white spruce in Alaska northern forests.

Model	Estimated right hand side of equations	𝑅^2	n	RMSE
Copper River Valley	0.412* + 0.037 × dbh*	0.77	100	0.030
Delta area	0.115* + 0.043 × dbh*	0.69	100	0.086
Fairbanks area	0.239* + 0.034 × dbh*	0.74	100	0.054
Kenai Peninsula	0.313* + 0.038 × dbh*	0.76	100	0.028
Mat-Su Valley	0.314* + 0.028 × dbh*	0.59	100	0.042
Tok area	0.247* + 0.034 × dbh*	0.54	100	0.070
Alaska	0.303* + 0.035 × dbh*	0.63	600	0.064

Note: Response variable is the thickness of bark (cm), dbh stands for the diameter-at-breast height (cm). ^∗representsthat the coefficient is significant at 0.01 level. 𝑅², coefficient of determination; 𝑛, number of sampled trees; RMSE, root mean square error.