Implications of vertical distribution and within‐stand variation in moisture content for biomass estimation of some willow and hybrid poplar clones

Abstract

The vertical variation of moisture content (MC) in shoots from two clones of Salix dasyclados (1–3 and 10 years old), one clone of Salix viminalis (1–4 years old) and one clone of Populus × interamericana (4 years old) were analysed during the harvest season. Compared with the whole‐shoot MC, the basal part of stems of S. dasyclados were high in MC and MC generally decreased with height, whereas S. viminalis showed the opposite pattern. None of the compared within‐stem sampling procedures performed better than 1.5 percentage units of MC‐bias, which for a MC of 50% would lead to a whole‐shoot dry weight estimate error of 3%. In Salix, whole‐shoot MC decreased with stem diameter and shoot age. Shoot age did not affect the vertical MC profile in a consistent manner. During the harvest season (November to March) a four‐year‐old S. viminalis increased its MC by about 1.5 percentage units. Owing to the skewed shoot diameter distribution of this stand and the diameter dependency of MC, the above‐ground biomass MC was about one percentage unit lower than the average shoot MC. Consequently, it is important to use the correct calculation method depending on the purpose of the MC determination.