Performance of Weibull function as a diameter distribution model for Pinus thunbergii stands in the eastern coast of South Korea

This study was carried out to determine the performance of percentile-based Weibull diameter distribution model for Pinus thunbergii stands thriving along the eastern coast of South Korea.The parameter recovery technique was used to estimate the three parameters of the Weibull model.The analysis demonstrated satisfactory results based on the following test statistics for the principal percentile models:fit index(FI) range from 0.501(minimum diameter) to 0.932(50th diameter percentiles) and root mean square error(RMSE) range from 0.112(quadratic mean diameter) to 3.572(minimum diameter).The developed model was further evaluated by determining the mean bias(ē) in trees per ha(TPH) for each diameter class,and the results showed highest over-prediction in the 20 cm,andunder-prediction in the 16 cm and 24 cm diameter classes.The goodness of fit tested by KolmogorovSmirnov(KS) test showed no significant differences(p>0.05) between the observed and predicted diameter distributions for almost all plots.Using site index and aboveground biomass(AGB) models developed for P.thunbergii in South Korea,a model to predict the AGB per ha for each diameter class and subsequently the total AGB of the stand was created.An application guide was also created,which will serve as a decision-support tool for forest managers in quantifying the future total AGB in P.thunbergii stands located in the eastern coast of South Korea and,subsequently,the quantification of potential carbon stocks aside from being a vital input in designing efficient management and protection strategies for these stands.

Comparative Analysis of Four Stem Taper Models for Quercus glauca in Mount Halla,Jeju Island,South Korea

This study was conducted to fit the diameter-height data of Quercus glauca in Jeju Island, South Korea to the four commonly used stem taper equations and to evaluate the performance of the four stem taper models using four statistical criteria: Fit index(FI), root mean square error(RMSE), bias( E), and absolute mean difference(AMD). Results showed that the Kozak02 stem taper equation provided the best FI(0.9847), RMSE(1.5745), E(-0.0030 cm) and AMD(1.0990 cm) while Max and Burkhart model had the poorest performance among the four stem taper models based on the four evaluation statistics(FI : 0.9793, RMSE : 1.8272, E : 0.3040 cm and AMD : 1.3060 cm). These stem taper equations can serve as a useful tool for forest managers in estimating the diameter outside bark at any given height, merchantable stem volumes and total stem volumes of the standing trees of Quercus glauca in the Gotjawal forests located in Mount Halla, Jeju Island, South Korea.