Genetic parameters for spiral-grain angle in two 19-year-old clonal Norway spruce trials Björn Hannrup, Michael Grabner, Bo Karlsson, Ulrich Müller, Sabine Rosner, Lars Wilhelmsson and Rupert Wimmer Ann. For. Sci., 59 5-6 (2002) 551-556 DOI: 10.1051/forest:2002040