Chemical properties of black cottonwood and balsam poplar

Abstract

Taxonomically, black cottonwood and balsam poplar are varieties of the same species. However, black cottonwood is excluded from the "northern aspen" species group embraced by the National Lumber Grading Agency grading rules for dimension lumber and from the use as core material in softwood plywood. This study examines the chemical properties of these two species varieties to assess whether continuing differentiation in their utilization is justified. Black cottonwood was sampled at three sites in British Columbia (Fraser Valley, Squamish Valley, Kingcome Inlet) and balsam poplar was sampled at three sites in Alberta (Lodgepole, Slave Lake, Lac La Biche). Representative subsamples of wood and bark meal were prepared from each original sample. Black cottonwood and balsam poplar did not differ significantly in lignin content. Within each species, the heartwood had higher lignin contents than the sapwood. The mean extractive content of the female trees is higher than that of the male trees, but this was statistically significant for only the benzene–alcohol extractive content of the black cottonwood sapwood. The pH and acidity did not differ significantly between species. However, there was a large difference between heart-wood and sapwood pH values in both species; sufficient to provide a basis for their differentiation. Acidity values were higher for both sapwoods than for heartwoods. The chemical component contents of black cottonwood and balsam poplar bark were the same, except for the benzene–alcohol extractive content, which was twice as great in balsam poplar. However, the same chemical components were found in each extractive mixture. Results do not provide any basis for separate commercial utilization of these two varieties of the same species.