Abstract:

Based on the mensuration data of diameter at breast height (dbh)from about 40 thousand survival trees in 2013 Qinghai forest inventory of the 8^th National Forest Inventory in China,the differences in external expression and similarities in inner essence between individual tree dbh growth,ratio,and rate models were analyzed,and growth rate models for 4 tree species were developed.It is showed that:1)individual tree dbh growth,ratio,and rate models are only different mathematical expressions reflecting tree growth information,even though the statistical indices of developed models exhibit great differences,when they are used to estimate dbh growth or dbh at the end of interval period,the differences are very few.2)When the sample trees are too many and distributed unevenly by diameter class,it is suggested to merge the data of trees with same diameter,and use the average values for modeling.However,the calculation of statistical indices of fitted models should be based on the data of all sample trees,not the merged data for modeling,otherwise the goodness-of-fit of models will be over-rated.3)The determination coefficients (R²)are more than 0.93,and mean prediction errors (MPE)are less than 0.3%,when dbh growth rate models for 4 tree species in Qinghai are used to estimate diameters at the end of interval period.The developed dbh growth rate models will provide quantitative basis for determining whether the dbh growth of trees is too large in field survey of Qinhai forest inventory of the 9^th National Forest Inventory.

Key words: diameter growth, growth rate, continuous forest inventory, survival tree, Qinghai