基于营林数据林分郁闭度测算模型与检验

The method of using canopy projection model to calculate the degree of pure forest canopy of artificial age

依据人工同龄纯林树冠垂直投影模型,提出一种精度高、操作简便的郁闭度测算方法。根据树冠面积和林木株行距的关系,把树冠垂直投影模拟为椭圆,应用营林数据中林分平均冠幅、株行距和保存率,用微积分的方法,求出树冠投影面积与总面积比,推算林分郁闭度,提出基于林分数据的林分郁闭度测算模型。采用数码相机获取林冠数字图像,通过Hemiview冠层分析系统计算林分郁闭度,对比模型计算值验证模型相对误差。采用树冠投影法测算了27块样地的郁闭度值,并以Hemiview冠层分析系统配合鱼眼镜头测得的各样地郁闭度为基准值,运用SPSS 22.0进行检验分析,两种方法测得的郁闭度无显著性差异,相对误差小于6%。分析样地之间间隙率的差异特征,不同林龄或不同样地间,林木的平均株间冠幅和平均行间冠幅差异性极显著。Hemiview冠层分析系统计算不同林龄或不同样地间,树冠间隙率差异性极显著。在桉树人工林同龄纯林中,基于营林数据的树冠投影法林分郁闭度测算模型能满足林分郁闭度精确调查的需要,可应用于生产中,在发展林下经济、林下种植时测算人工林同龄纯林的林下光照条件。

Based on the vertical projection model of artificial age-matched pure forest canopy,a high precision and easy to operate estimation method of crown density was proposed.According to the relationship between the canopy area and the tree line spacing,the vertical projection of the canopy was simulated as an ellipse.The ratio of the canopy projection area to the total area was calculated by the method of calculus using the average canopy width,the spacing between tree lines and the preservation rate in the forest data,and the forest canopy closure was calculated.The forest canopy closure calculation model based on the forest data was proposed.A digital camera was used to obtain the digital canopy image,and the Hemiview canopy analysis system was used to calculate the crown density of the forest,and the relative errors of the model were verified by comparing the calculated values of the model.Canopy projection method was used to measure the crown density of 27 samples,and the total closure value was measured by the analysis system of the Hemiview canopy analysis system and the fisheye lens.SPSS 22.0 was used for testing and analysis,and there was no significant difference between the two methods.The relative error was less than 6%.By analyzing the difference characteristics of gap rate among sample plots,the average canopy width between plants and between rows of trees at different ages or in different plots are very significant.Hemiview canopy analysis system calculated that the canopy gap rate varied significantly at different ages or in different plots.In eucalyptus plantation of the same age in pure forest,the canopy projection model based on the data can meet the need of accurate investigation of stand closure.It can be used in production to measure the understory light condition of pure forest of the same age in plantation when developing understory economy and planting.