Crown architecture in relation to productivity of Populus clones in the Pacific Northwest, U.S.A R. Ceulemans, T.M. Hinckley, P.E. Heilman, J.G. Isebrands and R.F. Stettler Ann. For. Sci., 46 Supplement (1989) 199s-201s DOI: 10.1051/forest:19890546