Populustrichocarpa × Populusdeltoides hybrids for short rotation culture: variation patterns and 4-year field performance

Abstract

Studies were conducted on the comparative growth and morphology of Populustrichocarpa (T), P. deltoides (D), F1 hybrids (T×D), F2 hybrids (TD × TD), and B1 hybrids (T × TD, TD × T) at one nursery and two plantation sites in western Washington and Oregon. First coppice resprouts in the nursery showed intermediacy of the F1 and F2 between parentals in four of five morphological leaf traits measured, and intermediacy of B1 values between F1 and T in three. Amounts of variation generally conformed to the model of F2 > B1 > F1. The percent significant trait correlations were 11.6 for the F1, 8.7 for the B1, and zero for the F2. No simply inherited traits were identified. Growth in the first and successive coppices in the nursery was significantly greater in the F1 than in the B1 and F2 generations. The same trend was observed in two field tests at Pack Forest, Washington and Westport, Oregon in which 691 and 381 clones from 60 and 42 families, respectively, gave a rank order in 4-year volume growth of F1 > B1 > T > F2 > D. Several F1 families and clones showed high rank consistency between years and locations. The results confirm earlier studies and are discussed in relation to the mechanisms that underlie T × D hybrid superiority.