Individual Tree Growth Models And Competitors Harvesting Simulation For Target Tree-oriented Management

Target-tree management is an essential technique for close-to-nature forest management, and quantitative modeling target tree growth under harvesting scenarios is an important topic. However, there is a knowledge gap on modeling the selection of target-trees and competitor trees, and their growth. Individual tree growth and yield model is an important tool for target-tree management. Based on 20 long-term permanent sample plots of larix-spruce-fir forests remeasured in nearly 30 years in Wangqing forestry bureau, Jilin Province, this paper established the distance-dependent individual tree growth models by tree species of larch, spruce, fir, Korean pine, hardwood, soft broad-leaved tree species including individual tree diameter growth model, height-diameter model, crown length model, crown width model, mortality model and target tree selection model. We developed programe and simulated target tree growth under scenarios with different target tree density and number of competitor trees. The main results are as follows:1. The area of weighted Voronoi diagram(WVA) was used as single tree competition index for individual tree growth models, and programe on computing WVA was developed. There was strong correlationship between diameter weighted WVA and diameter growth(r=0.38), which was higher than existedtraditional competition indices(r=0.19-0.29).2. We developed distance-dependent individual tree growth mixed-effect models with plot as random effect including individual tree diameter growth model, height-diameter model, crown length model, crown width model, mortality model and target tree selection model. The coefficients of determination for diameter growth models varied form 0.98-0.99, mean relative error from 0.79% to 5.55%, and RMSE from 0.73 to 0.87 m. The main factors affecting tree diameter growth were initial DBH and WVA. The coefficients of determination for heightdiameter models varied form 0.59-0.76, mean relative error from 13.38% to 22.20%, and RMSE from 2.62 to 3.65 m. The coefficients of determination for crown length models varied form 0.47-0.51, mean relative error from 33.56% to 34.10%, and RMSE from 2.74 to 3.10 m. The coefficients of determination for crown width models varied form 0.35-0.39, mean relative error from 28.54% to 34.84%, and RMSE from 0.54 to 0.64 m. The main factors affecting trees crown length included initial DBH and WVA. Initial DBH, BAL and WVA had significant effects on tree crown width.The area under curve(AUC) for tree mortality models were from 0.80 to 0.84 and target tree selection model from 0.90 to 0.92.3. Programe for realizing target tree selection and growth simulation was developed. Based on the target tree selection model and individual tree growth model mentioned above, we modeled growth change of target trees under two target tree density and three tree competitor tree scenarios of larix-spruce-fir forests with 30 years. We found cutting competitor trees improved target tree growth. Compared with control(no competitor tree cutting scenario), diameter growth of larch tareget trees increased by 78%-136% for two-competitior-tree cutting scenario, by 42%-63% for one-competitior-tree cutting scenario; diameter growth of broadleaved tareget trees increased by 50%-77% for two-competitior-tree cutting scenario, by 10% for one-competitior-tree cutting scenario; other conifer trees were not sensitive to competitior-tree cutting. For current stand with density of 760 trees/hm2 and average diameter of 21.1cm, the optimal scheme for target tree management is the density of 100 plants per tree and two-competitior-tree cutting.