Statistical description of the architecture of a fast growing willow coppice

Abstract

The investigation of the PAR variability in a willow forest requires a detailed description of architecture at the leaf, branch, stem and canopy levels. Due to the great variability of the object under study, parameters of the architecture should be considered as stochastic quantities and expressed by their probability density functions (PDF). Establishment of correlations between different architectural parameters enables a reduction in the great number of phytometrical measurements. A statistical phytometrical methodology, describing plantation architecture during the first three growing years, has been elaborated and applied for a willow ( Salix viminalis) coppice. The whole canopy was divided into three layers. The upper foliage layer consists of foliage cylinders (current year shoots and branches with leaves) with given geometrical characteristics. The lower foliage layer consists of previous year stems and branches as well as current year shoots and can be modelled as horizontally homogeneous turbid plate medium. The lower leafless layer consists of nearly vertical stems only. The dynamics and development of these layers was analyzed during the years 1994–1996. The vertical distribution of leaf area density for the whole canopy is not uniform; but can be approximated by a normal distribution. At the relative coppice height 0.6–0.7 leaf area density reaches its maximum value of 23 m 2 leaf area per m 3 canopy volume. In the years 1994, 1995 and 1996 at the end of July the leaf area index reached maximum values 1.2, 2.6 and 4.2, respectively. The leaf inclination angle distribution is not uniform, the maximum being located between 20 and 40 degrees.