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An Evaluation of Crown Structure and Site Index to Determine Crown Closure in Eucalyptus urophylla × E. grandis Stands in Guangxi,China

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Agricultural Science & Technology 2014年第6期15卷 1005-1011页

作者：陶玉华 Roger WILLIAMS Carol BROWN 曹书阁 Rachael CRANE Raymond DUVAL Dani FLOWERS jonathan franko Rachel HEFFLINGER jonathan JOO Anne MAURO Crista RIEDY Margaret SMYTH Shawn STONE 谭丽凤广西生态工程职业技术学院广西柳州545004 美国俄亥俄州立大学环境和自然资源学院美国哥伦布43210

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.

关键词： Site index Crown structure Forest canopy Relative spacing Crownclosure

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