Phenological Variation in Bluebunch Wheatgrass (Pseudoroegneria spicata): Implications for Seed Sourcing, Harvest, and Restoration

Abstract

To reduce maladaptation in cultivated seed lots, seed transfer zones (STZs) have been developed for grasslands and other habitats using morphological traits and phenological measurements that only capture the first day of events such as flowering and seed ripening. Phenology is closely linked to plant fitness and may affect genetic loss during harvests of seed raised for ecological restoration. Here, we measured the detailed phenologies of 27 populations from six STZs of bluebunch wheatgrass (Pseudoroegneria spicata) (Pursh) Á. Löve (Poaceae) raised in a common garden to test whether existing STZs created using a combination of plant morphology and “first-day” phenological measurements adequately capture population-level variation in season-long, detailed phenologies. We also used detailed phenologies to test whether genetic losses may occur during single-pass harvests of commercial seed. Mixed and random effect models revealed differences in detailed reproductive phenology among populations within two of six STZs. The number of individual plants within an STZ not producing harvestable seed during peak harvest levels indicated that 10–27% of individuals from a seed lot could be excluded from a single-pass harvest. Although our findings generally support current STZ delineations for P. spicata, they point to the possible precautionary importance of sourcing from multiple populations and harvesting with multiple passes when resources permit.