摘要
世界上很多地区基于桉树的商业价值开展了桉树人工林的经营。密度管理在桉树人工林经营管理中往往成为很重要的手段。该研究以不同林龄的桉树人工林为研究对象,在森林郁闭和树木生长竞争期,量化其森林郁闭度和冠层结构。通过对桉树人工林的调查,研究了其林地指数对其林冠郁闭度的影响。结果表明:立地指数对郁闭度影响不大,在好的立地条件下森林郁闭度有轻微的影响。基于树冠投影面积比和树冠直径和胸径的比值研究表明:桉树林在4年生时开始郁闭。对不同林龄的相对间距RS值的研究表明:相对间距值在第4年时表现出快速降低,到21年的时候逐渐变得相对平缓。桉树林在前3年表现出快速的高生长,由于速生,其在密度上没有多大变化。4年生桉树林由于死亡率导致树木个体数量的减少,影响了RS值,导致其逐渐下降。
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.
基金
Supported by Undergraduate Research Abroad Program,Ohio State University,USA(11731-011000)~~
