Assumptions Made in Protocols for Shoot Biomass Estimation of Short-Rotation Willow Clones Underlie Differences in Resul
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Assumptions Made in Protocols for Shoot Biomass Estimation of Short-Rotation Willow Clones Underlie Differences in Results Between Destructive and Non-destructive Methods Theo Verwijst & Johannes Albertsson
# Springer Science+Business Media New York 2015
Abstract Yield estimates from single stands in short-rotation willow (Salix spp.) have been reported to differ substantially, depending on the estimation methods used. The magnitude of differences in estimates resulting from different methods may vary among clones on the same site. This indicates that some assumptions, implicitly made by using a certain method, cannot be generalised for all clones. To assess why estimates of different methods may differ and why the magnitude of the differences may be clone-specific for a given site, a number of assumptions underlying destructive and non-destructive protocols for the estimation of aboveground willow biomass were tested. Apart from general problems in satisfying the demands of representative sampling and meeting the assumptions that underlie the proper use of statistical models, it was found that basic assumptions with regard to the physical structure and phenology of willow may lead to the observed differences. For a given clone, the moisture content of willow shoots may vary over time and may be dependent on shoot size. For a given shoot, the moisture content of basal, apical and central stem parts may differ, with the magnitude of differences being dependent on the clone. Stem taper and curvature may be clone-specific and can also underlie differences in biomass estimates obtained by different methods. To improve estimates of aboveground biomass in short-rotation willow, it is important to state explicitly the assumptions underlying the methods used and, wherever possible, to test the assumptions and evaluate the effects of their violation on the resulting estimates. T. Verwijst (*) Department of Crop Production Ecology, Swedish University of Agricultural Sciences, P.O. Box 7043, 75007 Uppsala, Sweden e-mail: [email protected] J. Albertsson Department of Plant Breeding, Swedish University of Agricultural Sciences, P.O. Box 101, 23053 Alnarp, Sweden
Keywords Clone . Moisture content . Salix . Sampling . Stub height
Introduction Biomass from short-rotation willow (Salix spp.) is used as a feedstock for renewable energy in countries such as Sweden, Denmark, the UK and the USA. This perennial crop has an expected productive life span of about 20 years and is commonly harvested in winter every 3–4 years. Since the start of development and commercialization of willow coppice as an agricultural crop, attempts have been made to develop, refine and compare different willow biomass estimation methods [1–3]. Among other things, these methods have allowed researchers to follow their trials season after season and allowed farmers and extension workers to estimate biomass production as a basis for deciding when to harvest. Due to the long period between planting and harvest and between harvests and as a result of the lar
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