Modelling the edge effect in even-aged Monterey pine (Pinus radiata D. Don) stands

Six edge effect models are presented. Modelling results for the edge effect on the DBH, total height, crown height, and basal area in even-aged stands of Monterey pine (Pinus radiata D. Don) are provided. Free edges and edges under external competition pressure were analysed. Model fitting was carried out in two phases. In the first phase, independent fittings for each border type by sampled cardinal point in each stand were carried out to detect differences in edge effect intensity and depth according to edge aspect. In the second fitting phase, the best models selected by edge aspect in the first phase were restricted to estimate the same value for each variable in the stand interior, independently of the border where it was analysed.

The edge effect intensity and depth varied depending on the analysed variable and edge type. Modelling of the edge effect on DBH and total height on free edges of old stands requires a model with independent parameters for each border aspect; the models can be restricted to estimate the average value of each variable in stand interior. A model with independent parameters for each border aspect should be also used for modelling the effect on total height, crown height and basal area for the edges of young stands under external competition pressure. The modelling of basal area and crown height on free edges of old stands, DBH on edges of young stands under external competition pressure, and all variables mentioned on free edges of young stands can be carried out through an average fitting. DBH and basal area are directly affected by stand density; thus, modelling of edge effect on these and others variables which are affected by stand density can improve with the inclusion of a competition index or a point density index.     

核桃树体N、P、K营养元素诊断中采叶时间的确定*

树体营养指标的确定是通过叶分析来实现的。对此,有关学者认为一个至关重要的问题是采叶时间。叶分析的结果能否用于树体营养诊断,在很大程度上是由取样时间、部位所决定的。因为叶片中营养元素含量在年周期中变化很大。关于采叶的最佳时间众说不一,美国有人提出在盛花后6～8周采样,还有人提出在7～8月初。在我国一般在年生长稳定时期即7、8月采叶来确定树体营养元素的含量,一致认为要采生理成熟的叶子。对经济林木来说,它的产量和质量在很大程度上决定于树体营养的累积。为了使树体的营养水平数量化、指标化,更具有科学性,以便能指导实践,所以必须解决采叶的时间问题。     

马尾松优良菌根真菌(S.l)液培条件的研究

作者经过对褐环乳牛肝菌［Ｓｕｉｌｕｓｌｕｔｅｕｓ（Ｌ．ｅｘＦｒ．）Ｇｒａｙ］的一系列研究,业已证明它是我国亚热带地区特有树种马尾松（ＰｉｎｕｓｍａｓｏｎｉａｎａＬａｍｂ．）共生的优良菌根真菌。它具有生长快速、繁殖容易、拮抗性强、适生范围广、制剂简便、...