Coppice growth traits in sand dune willow (Salix cordata) and comparisons with two common North American shrub willows used for biomass production

Abstract

Among eight native North American willow species examined for coppice growth performance, the sand dune willow, Salix cordata Michx. (COR) has proved to be one of the most productive and useful for woody biomass production. In a common garden study, clones from the eastern and southwestern regions of Ontario, Canada, outperformed those from northern populations. Geographic region, populations within regions, and clones within populations all accounted for large portions of total variation in coppice growth traits that were compared with two other willows commonly used for biomass production, S. discolor Muhl. and S. eriocephala Muhl. Each species varied significantly in coppice structure and growth. The number of coppice stems per plant (coppice stem number) showed strong positive relationships to stem dry mass in 1- and 3-year-old coppices. Female COR plants were often slightly larger than male plants in this dioecious species, but these differences were not statistically significant, and provided no evidence of a reproductive cost expressed as a differential reduction in subsequent vegetative growth in female vs. male plants. This indicated that a zero sum model in which reproductive and vegetative structures compete for assimilates was not supported by our results. In all three species, clonal selection for growth and commercial biomass production, coppice stem number (not plant sex, longest stem length or corresponding basal stem diameter) was the best criteria for selecting superior willow clones.