Crown Structure And Growth Model For Larix Olgensis Plantation

Forest plantation is an important approach for forest sustainable management, how to improve the forest yield and timber quality is one of major tasks in the current forest management. Tree crown is an essential place for the photosynthesis, its structure determines the production and ecological benefit. Knowing the crown structure and development would help to evaluate and forecast the stem growth, wood quality attributes. The thesis based on the data of field inventory, branches attributes, biomass, leaf area, stem rings analysis for the Larix olgensis plantation from different stand ages at Dongzhelenghe forest farm in Heilingjiang province. The methods of forest management, quantitative analysis, mathematical models were used in analyzing and simulating the crown structure and stem development. The canopy structure and quantitative model were analysed and developed for the branches attributes, crown shape and sizes, biomass and leaf area from branches, canopy layer and overall crown in this paper. We tried to discuss the relationship between the crown structure and tree growth, providing the basement for nurturing the crown structure which is benefit for using solar energy to improve timber production and wood quality. The main conclusions are summarized as follows:(1)The analysis of the canopy structure for branches attributes (branches number, diameter, length and angle) from different growth stages show that branches density significantly related to the distance into canopy (DINC), the ratio of tree height to diameter at breast height (H/D). The average branches diameter increased with DINC from tree top to down, while the maximum branches diameter per canopy increased with the DINC like a single peak shape, showing the largest diameter at the65to75%of relative distance into canopy layer to crown length (RDINC). The vertical structure of branches length showed parabolic shape with a maximum value in the60to95%of RDINC. The branches angle showed no statistically significant differences between different ages, increasing with canopy depth. The developed quantitative models of branches number, diameter, length and angle with a high coefficient of determination.(2) Based on the main-axis cutting method and crown architecture method calculated the crown radius, volume and surface area. The allometric equation was good for modeling crown shape, crown volume and crown surface area. The height of the largest crown width (HLCR) was significantly related to DBH and crown width. The power equation was optimal for modeling the profile of crown radius increased with DINC above the HLCR, with a94.1%of forecast accuracy. The allometric equation with the combination variables of DBH,crown width and crown length was the optimum equation for estimating crown volume and crown surface area. (3) The precision of fitting model was affected by the selected variables and its combination for tree crown ratio, height of crown base (HCB) and crown width models. Stand basal area (BA).crown competition factor index (CCF) and tree size (DBH, HT) were significantly related the crown ratio and HCB. The Exponential equation was better than Logistic model for the optimal crown ratio model, the HCB model fitting better than the crown ratio model, with a0.725of determination coefficient. The crown competition factor larger than objective tree (CCFL) was the best predictive variable for crown width model, with an explaining56.6%of variation.(4) The dry weight of branches linearly correlated with fresh weight, and the branches level-biomass fitted well with allometric relationship from different ages. The exponent value (b) of branches wood biomass allometric equation was close to the theoretical values (8/3). The canopy biomass of foliage and branches increased with the top5m regardless of stand ages. The best fitting models for the vertical cumulative distribution of branches biomass (BW) and leaves biomass (LW) with were the modified weibull model F{BW)=1.305x(1-exp(2.742×RDINC2.544)) and F{LW)=1.030×(1-exp(3.337x RDINC2.424)). DBH is the best predictor for estimating crown biomass, adding the stand age or HCB to some extent improving the fitting accuracy of crown biomass model.(5) The specific leaf area (SLA) was significantly affected by stand age and crown layer, respectively. SLA increasing from the top canopy layer to the bottom, the SLA of upper, middle and lower crown was101.08,117.37and129.91cm2/g separately. The SLA of young, middle-aged, sub-mature and mature Larix olgensis plantation was145.34,111.55,92.60and128.03cm2/g separately. with an average value116.39cm2/g of different stand ages. Branches-level leaf area model fitting well with allometric equation using branches diameter as prediction variable, a segmented branches leaf area allometric model was developed in order to improve the model precision. The crown leaf area fitted well with a modified power function using DBH and H/D as independent variables:LA=0.3024×DBH1.944-0.1965×HD.The dynamic of the leaf area index of larch plantation with aging show that increasesd in middle-aged forest, maintained stability in sub-mature forest and tended to decrease in mature forest.(6) The radial growth process of annual ring width shows that increased in the earliest age, attaining a maximum ring width from the third to the sixth year, decreased to about20years, and then remained a relative steady value after20years. The young crown is freedom crown in the first five years, affecting stem ring growth with the same pattern. The average annual ring width and area were not significant difference in the first three and five years. The average annual width and area of the last three or five years were not significant difference under crown base from middle age and sub-mature stands, but there are significant differences in ring area increment during the three or five years under crown base in mature forest, decreasing along stem height from the tree base to top. The annual ring growth within crown showed the same pattern. The initial heartwood formation of Larix olgensis estimate at the fifth years, the average heartwood formation rates were0.65ring/year and0.96ring/year under30years and older than30years, respectively. The best fitting heartwood ring number with cambial age was quadratic curve equation. The heartwood and sapwood volume allometric equations as a function of DBH and HT were fitted well (HWV=4.0*10-6DBH2.149250HT1.296038,R2=0.989, and SWV=1.02*10-4DBH0.750383HT673065, R2=0.943). The bark thickness as a function of relative stem height was fitted well with the logarithmic equation. The trend of bark factor along the stem height turned increase and then decrease to tree top. The optimal model of the diameter inside-bark at breast height, tree height and volume without bark was Richard model for Larix olgensis plantation.