Evaluating Site Quality For Uneven-aged Forests Based On National Forest Inventory Of Mongolia

Evaluation of site quality is essential for stand development and forest management decision in uneven-aged natural boreal forest.Height-diameter relationship models have been extensively used in Mongolia’s forest inventory to avoid the time-consuming task of measuring heights of all individual trees.In this study,site quality evaluated different forest types in boreal forest based on Multi-purpose NFI(National Forest Inventory)data.The study involved various stand structures of uneven-aged boreal forest in Mongolia.One-time observation data were obtained from 3 904 permanent cluster sampling plots including three circle sub-plots.The trees were grouped and sampled within three different radii according to DBH(dimeter at breast height).Totally,ten height-diameter relationship base models are presented for five conifer and two broadleaf trees.New height-diameter relationship models were evaluated along with stand variables relying on statistical analysis.Indirect methods,including site form and site index,predicted based on height-diameter relationship models.Site form model was constructed based on Chapman-Richards model for different forest types and different regions.The reference diameter of site form was 20 cm for each species.Based on tree ring data from 69 permanent plots,site productivity were evaluated by calculating basal area increment,mean annual increment and biomass production.Meanwhile,current volume was estimated for all permanent sample plots.The height-diameter models with best performances included dominant height,mean quadratic diameter and Shannon index as independent variables.The height-diameter relationship models for seven trees in this study were more accurate than models developed in the past.The site form classes varied from 14 m to 20 m and the patterns were indicating species-specific differences in uneven-aged forest.Site index of Siberian larch stand varied from 20 m to 26 m.Comparison of site productivity demonstrated that mixed forests are more productive than pure stand.Meanwhile,the basal area increment of pure stand were lower than that of mixed stand,contrast mean annual increment of mixed stand lower than pure stand.And site productivity was highest in loamy sand and lowest in clay loamy soil.Otherwise,pure Siberian larch forest was more productive than mixed forest.The direct and indirect methods showed strong correlations with site productivity and site quality measures...