The estimation of basket willow (Salix viminalis) yield - New approach. Part I: Background and statistical description

The paper presents an innovative method of probabilistic description of biometric features of basket willow (Salix viminalis). It concerns the descriptive statistics regarding the characteristics of that plant with which it is possible to relate the diameter and length of the shoots of basket willow with its mass, introducing the concept of shoot volume index. For this purpose the results of biometric measurements, consisting in cutting randomly selected shoots in the period of vegetation and measuring their length, diameter in the middle of the length and their mass, were used. The measurements were conducted in 2011-2013, a period covering the second, third, and fourth years of extensive cultivation of basket willow. Those years were evidently distinctive as regards the weather (thermal and water) conditions. Two features of basket willow shoots were suggested for analysis: their volume index and their mass. They are statistically correctly described by a mixture of two gamma distributions, independent of plantation age and of the moment when the measurement was conducted in the period of vegetation. The number of shoots in a bush was described by shifted Pascal distribution. In each year of cultivation, this distribution statistically correctly described their number.