An examination of the genetic control of Douglas-fir vascular tissue phytochemicals: Implications for black bear foraging

Silvicultural practices can influence black bear ( Ursus americanus) foraging preferences for Douglas-fir ( Pseudotsuga menziesii) cambial-zone vascular tissues, but little is known about the role of genetics. To study the impact of genetic selection, vascular tissue samples were collected from Douglas-fir trees in six half-sib families from five different sites in north central Oregon. Four replications of three-tree non-contiguous plots were sampled at each site to examine inter- and intra-site variation. Tree growth was measured as tree diameter at breast height and the absolute concentrations of 26 different terpenoids were determined by gas chromatography/flame ionization detection from ethyl acetate extracts. The simple carbohydrates fructose, glucose, and sucrose, and the phenolic glycoside coniferin were quantified using anion-exchange chromatography with pulsed amperometric detection. Cluster analysis was used to reduce the number of variables used in analyses of variance. Results for the families studied here indicate that tree growth and some terpenoids were under some level of genetic control. Furthermore, allocation of constitutive terpenoids in vascular tissues was not at the expense of tree growth. The sugars present in vascular tissue were affected by environment (site) and genetics (family) and their interaction.