Germination timing and rate of locally collected western wheatgrass and smooth brome grass: the role of collection site and light sensitivity along a riparian corridor

Abstract

Native perennial grasses in riparian areas are threatened by the invasion of weedy competitors, such as smooth brome grass (Bromus inermis Leyss. [Poaceae]). Smooth brome actively invades disturbed riparian zones through high seed production and fast seedling establishment. Restoring native perennial grasses to these regions is challenging because continual disturbances along riparian corridors open niches for further plant invasions. Identifying growth traits of common native perennial grasses, such as western wheatgrass (Pascopyrum smithii (Rydb.) Á. Löve [Poaceae]), as well as for smooth brome, should provide managers with necessary information about smooth brome invasion and native plant restoration. In this study, we sought to identify how the germination timing and rates of smooth brome and western wheatgrass were affected by seed site location and light availability. Regardless of site or light dynamics, we found that smooth brome grass germinated 2 d earlier and at a 5× higher rate than western wheatgrass. Sites that were frequently disturbed by human activity also had higher seedling germination rates than sites with little disturbance for both smooth brome and western wheatgrass. In addition, when light was restricted for the first few growing days, seedling germination of both species was higher than in diurnal light environments. These findings suggest the use of 2 management tools for enhancing western wheatgrass populations in smooth brome–invaded riparian zones: high seeding rates to improve western wheatgrass competitiveness and deep planting methods such as drill-seeding to improve germination rates and percentage.