Effects Of Planting Density On Eucalyptus Urophylla×E. Grandis Plantation With Theoretic Growth Equations

Stand growth processes on average height, average diameter at breast height (DBH) and average stand volume of Eucalyptus urophylla×E.grandis plantation with 6 spacing treatments aged at14-year-old were represented with 6 theoretic growth equations (Korf, Logistic, Richards, Schumacher and Weibull). Levenberg-Marquardt iteration method was used to estimate the parameters of equations and achieved a good precision. Stand cumulative diameter distribution equations at the 62nd month, 110th month and 161st month were represented with three theoretic growth equations (Logistic, Richards and Weibull). Several suggestions on the plantation management were proposed. Conclusions are followed:1. There were differences in average height of stand trees and DBH among 6 treatments at the same age. With the stand growth, the differences among each treatment became more significant. The differences of stand volume among each treatment only presented before 8 years old. And then, there were not significant differences of stand volume among 6 spacing treatments.2. Levenberg-Marquardt iteration method could be adopted to estimate the parameters of the theoretic growth equations precisely and each theoretic growth equation fit the growth process of stands with high precision and correlation. The coefficient of determination of each equation was more than 0.95. In total, Korf equation and Richards equation were much better than the other theoretic growth equations. To fit the average height and DBH growth process of dense stands, the precisions of each equation were much higher than sparser ones. The similarity trends did not present when modeled the stand volume of the same object. The mean residual of each equation aged from 50 to 100 month was smaller than younger and elder ones.3. The theoretic maximums of height and DBH of sparse stands estimated with the theoretic equations were higher than denser ones. But, there were not significant differences of the theoretic maximum of stand volume estimated with the theoretic equations among 6 spacing treatments. With the planting density increase, the intrinsic rate of increase of height growth equations became bigger, the intrinsic rate of increase of DBH growth equations become smaller, and significant differences of intrinsic rate of increase of stand volume growth equations were not presented. The rates of increment of tree height of denser stands were much higher, but lasting time was short.4. To represent the stand cumulative diameter distribution, the modeling precision of Weibull equation was the highest, Richards equation and Logistic equation were lower, respectively. The precisions of cumulative diameter distribution equations of denser stands were higher than the sparser ones. The DBH classes of stands with 883 trees/ha and 667 trees/ha transferred holistically, the others were not.5. Age of quantitative maturity of every treatment stands were estimated. It showed that the ages of quantitative maturity were delayed with the planting density increase. The age of quantitative maturity of the densest stand with 2222 trees/ha was 6 years and the sparest stands (667 trees/ha) would be 10 years.6. Stands with 2222 trees/ha, 1667trees/ha and 1250 trees/ha are reasonable for production of pulp and veneer. Stands with 883 trees/ha and 667 trees/ha might be for sawtimber production. It is much more economy to establish plantation with initial density of more than 1667 trees/ha, and thinning should be made.