Eucalyptus forests are grown in many parts of the world for their commercial value and use in construction projects. Density management becomes im- portant as a means to attain the management goals in these forests. Changes in canopy and tree crown structure were quantified for Eucalyptus urophylla x E. grandis forests at different ages to determine when canopy closure occurs and the onset of competition begins. Site index was developed for these forests to determine whether site quality affects the canopy structure. Site index had little effect in the forests sampled, with the forest canopy on the better sites becoming slightly more elongated. Based upon crown projection ratio and crown diameter： dbh （diameter at breast height） ratio, it appears that crown closure occurs by age 4 years in these forests. The age at which this occurs was also checked and verified with the evaluation of relative spacing, RS （the ratio of the mean distance between trees to the average dominant height of the stand）. The RS value displayed a rapid decline until age 4 years, and then became relatively flat through age 21 years. The rapid height growth during the first 3 years with no change in density accounted for this rapid decrease. By age 4 years, reductions in the number of trees due to mortality began to have more of an influence on this value, resulting in a more gradual de- cline. The implications for management are discussed.
以2001—2016年刊载于Web of Science数据库的404篇与网络欺凌相关的SSCI文献为研究对象,运用CiteSpace软件进行知识图谱分析,揭示了21世纪以来国外网络欺凌研究的热点内容。使用CiteSpace软件的关键文献定位功能,选择10篇有关网络欺凌实践对策的关键文献进行深入分析,探讨应对网络欺凌的有效对策。希望能为我国的网络欺凌研究及解决网络欺凌问题提供研究依据。
