Study On Control Technology For Thinning Of Eucalyptus Urophylla × E.grandis Plantation

As the most productive plantation ecosystem of the world,Eucalyptus urophylla× E.grandis plantation plays an important role in social and economic development and ecological environment protection.However,due to long-term predatory management,Eucalyptus urophylla × E.grandis plantation have experienced a series of ecological problems such as productivity decreased,soil fertility declined,serious pests and diseases,and appeared large-scale low-efficiency forests,while the short-rotation Eucalyptus urophylla × E.grandis plantation are particularly obvious.A typical plot survey of Eucalyptus pure forests from 1 to 5 years old in the Peninsula was carried out.The diameter structure and spatial structure of Eucalyptus urophylla × E.grandis plantation were analyzed.The model of tending and thinning forest stand was established,and the control measures of stand structure were proposed to provide a practical basis for improving Eucalyptus urophylla × E.grandis plantation quality accurately.The main conclusions are as follows:1.Regarding the fitting effect of each empirical distribution function on the diameter distribution of Eucalyptus plantation,the Normal distribution fitted the diameter distribution best,and the Weibull and Logistic distributions were second.The theoretical tree numbers of diameter structure on Normal distribution had guiding significance for forest management.In terms of the fitting kurtosis and skewness,the diameter distribution of the 1-year-old stands was relatively concentrated,and the diameter distributions of the 2,3,and 5-year-old stands were relatively scattered.The DBH of the most of the 1,3,and 5-year-old stands were below the average,while the 2 and 4-year-old stands were above the average.2.In terms of spatial structure of each stand ages,the difference of timber size between1-5 years old Eucalyptus plantation was not obvious,but the timber size of 1-year-old forest stands was different obviously.The angle index indicated that 1-5-year-old forest stands were evenly distributed,and most of the single-timber positions in each stand ages were evenly or randomly distributed.In terms of forestry survival competition pressure,the1-5-year-old forest stands generally had less competitive pressure.The 1-year-old stand had the smallest,because it has not been closed and the growth of the forest was less covered by the upper and the side of the adjacent trees canopy.In the 2-5-year-old forest stands,the growth of trees were affected by neighboring trees,resulting in increased competition pressure.The change of open degree was similar to the competition pressure of forest stands.The growth space of trees in 1-year-old forest stands was sufficient,The open degree of gradually decreased with the growth of forest trees and reached a minimum at 3-year-old.3.After Establishing the evaluation index,multi-objective planning for each spatial structure parameter by multiplication and division method,determining the calculation formula of the evaluation index,quantitatively describing the spatial structure stability of the stand by the evaluation index,the results are that the spatial structure stability of the1-year-old forest was the worst and 3-year-old was best.4.With the goal of maximizing the evaluation index of forest stands after thinning,the Monte Carlo method and the woodland griding method were used to establish the random thinning model and the grid thinning model.The two models were compiled into computer programs using C language,and the 3-5-year-old Eucalyptus urophylla × E.grandis plantation were used as examples.Both thinning models were found to be suitable for3-5-year-old Eucalyptus urophylla × E.grandis plantation.Choosing the appropriate thinning intensity,the structural parameters of the felled forest stands were optimized,and the overall spatial structure stability of stands was enhanced.The thinning scheme output by was more suitable for the Eucalyptus plantation.Using the optimal thinning output scheme by the grid thinning model was superior to the randomized thinning model in determining the difficulty of feller trees and optimizing the spatial structure of the forest stands.