Dynamic Simulation For Different Planting Density Of Hybrid Larch In Young Growth

Hybrid Larch, being an interspecific hybrids of other Larch, is one of local parent species and has become a fast growing and high yield species with high recommendation in Heilongjiang province due to the hybrid advantages of growth, resistance and wood quality. It is urgent and necessary to solve the technological question that how to reasonably manage Hybrid Larch plantation. This dissertation explored growth pattern and implemented growth dynamic simulation of Hybrid Larch planation with different planting densities, which provided theoretical basis for exploring optimal cultivations and management modes.Data were collected from 48 sample plots with four planting densities (2500 trees/hm2, 3300 trees/hm2,4400 trees/hm2 and 6600 trees/hm2) founded in 2004 during 12 years in 20 hm2 Hybrid Larch density experiment forest, which was established in 1998 in Jiangshanjiao forest farm of Heilongjiang Academy of Forestry. Based on the datasets, this study explained the fast growth characteristics and compared individual tree growth and stand growth of Hybrid Larch under different planting densities from light and physiological characteristics perspectives. Individual tree growth model, diameter distribution model, whole-stand growth model, and compatible individual tree and stand biomass models were developed using dummy variables; carbon stock density of different components (i.e., trunk, branch, foliage and root) were estimated and growth of Hybrid Larch plantation was dynamically simulated.The main innovations of this dissertation included:a systematical studying of dynamic growth simulation of Hybrid Larch with different planting densities for the first time; a reasonable explanation of effects of planting density on prediction accuracy of growth models using dummy variables, and a appropriate dynamical simulation of stand growth; establishment of compatible individual tree and stand biomass models.The main conclusions were drawn as follows:(1) The diameter at the breast height (DBH), tree height and volume growth of 14a Hybrid Larch has reached the growth level of Larix olgensis with 18-20a under the same planting density and forest condition. The current annual increment of basal area and volume of Hybrid Larch were higher than that of Larix olgensis by 30% and 40%, respectively, and the total amount of 14a Hybrid Larch has exceeded 50% and 60% compared to the latter. Comparing photosynthetic characteristic value of different canopy layers of Hybrid Larch and Larix olgensis, the photosynthetic capacity of Hybrid Larch was stronger than that of Larix olgensis under both strong and weak light conditions, which explained the fast-growth characteristics of Hybrid Larch from physiological ecological point of view.(2) The growth rate of basal area and volume for the stands with high densities (i.e.,6600 trees/hm2 and 4400 trees/hm2) dramatically decreased after 14a, which indicated that intermediate thinning should be implemented before 14a. The average DBH of stands decreased with the increase of planting density. There was no significant difference of tree height growth among plots with different planting densities.(3) Two-level nested nonlinear mixed effect models of DBH and tree height growth were established in the study. Stand planting density and tree size class had great effects on DBH growth, however, stand planting density had little effect on the tree height growth.(4) Based on the dynamic data of individual tree DBH growth data during 11 periods, individual tree growth model and mortality model with 1a interval were established using dummy variable for Hybrid Larch. The model fitting were improved and prediction error were reduced resulted from planting density by applying dummy variable according to goodness-of-fit tests and model validation.(5) AUC of Logit, Gompit and Probit mortality model were all greater than 95%; the overall accuracies of three models all reached about 96%; the accuracies of individual survival were greater than 96%; and the accuracies of mortality were all over 74%.(6) Generally, skewness of diameter distribution decreased first and then increased. The higher stand planting density was, the earlier changing time from negative to positive skewness was. The skewness changed from negative to positive for stands with 6600 trees/hm2,4400 trees/hm2 and 3300 trees/hm2 in 14a,16a and 17a, respectively, which indicated that thinning should be implemented before corresponding stand age when competition became intensive among trees. Kurtosis generally increased first and then decreased, and was always negative for stands with 6600 trees/hm2, which indicated that the number of suppress trees increased with the increase of differentiation degree of tree diameter.(7) DBH distribution was fitted using Weibull distribution, Beta distribution, SB distribution and normal distribution which had the highest acceptance rate of 78.99%. As a constraint of normal distribution parameters of DBH, PPM of predicting normal distribution parameters using dummy variable and 2a interval was developed, which obtained good model fitting and validation results.(8) Equation set of stand basal area growth model and volume growth model with dummy variable was established by introducing the concept of measurement error. Two-stage least squares (2SLS) or three-stage least squares (3SLS) were applied to estimate model parameters and solved measurement error problem that was not solved by traditional least squares method. And the stand basal area growth and volume growth were dynamically simulated for Hybrid Larch under different planting densities.(9) The compatible individual tree biomass model and stand biomass model with dummy variable were developed. Weighted function was applied to eliminate unequal variance of biomass dataset. Model with dummy variable had improved results of model fitting and validation. And the stand biomass was dynamically simulated for Hybrid Larch under different planting densities. Carbon content rate of every component of Hybrid Larch were measured, and it has filled the gap of carbon content rate of Hybrid Larch.