3College of Natural Sciences, Department of
Plant Biology and Biodiversity Management Addis Ababa University, P. O.
Box 3434, Addis Ababa, Ethiopia, e-mail: kooket@gmail.com
Abstract
This study was conducted in Gerba Dima Forest, South Western Ethiopia to
formulate allometric equations for Pouteria adolfi-friederici .
Prior to collecting data for tree allometry, the study forest was
stratified into 3 forest strata based on altitudinal variation. By
employing semi-destructive technique, 30 individuals were systematically
selected and sampled for measuring biomass along the three forest
strata. Based on the data collected, several equations were developed.
Before establishing the allometric equation, scatter plots were used to
see whether the relationship between independent and dependent variables
was linear. Furthermore, several allometric relationships between
independent and dependent variables were tested. The best-fit model
developed was validated by testing the regression assumptions. AGB was
regressed against the various forms of predictors (i.e., DBH, H and WD)
and three allometric models showed significant performance (p
< 0.05) on their F-test. Among the three allometric equations
which showed significant performance, the selection of the best-fit
model was conducted based on their P-value, adjusted
r2, AIC, RMSE. The two models are nested to the third
model and hence the complete model, lnAGB=1.806+1.419×lnDBH+0.628×lnWD,
is selected as the best-fit model against the other two nested models
since the p-values of coefficients of the complete model are significant
(p < 0.05).
Key words/Phrases: Allometric equation, Model fitting, Model validation,
Regression