Seed production, seed rain, and the seedbank of fringed sagebrush

Abstract

Increases in fringed sagebrush (Artemisia frigida Willd.) following disturbance on Northern Mixed Prairie are due to enhanced growth of established plants and seedling recruitment. The roles of seed production and the soil seedbank in population dynamics of fringed sagebrush following disturbance are, however, unknown. Furthermore, seed rain has not been documented for this species. The objectives of this study were to determine: 1) the effect of disturbances in the sward on seed production; 2) relationships between the soil seedbank and current seed production; and 3) seed rain over time for fringed sagebrush. Disturbances of clipping, litter removal, tillage, and a combination of clipping and litter removal were imposed on a sandy range site in central Saskatchewan. Following disturbance seed production plant-1 either increased or was unchanged compared to the undisturbed control. Greater seed production resulted from increased production of seeds head-1, heads inflorescence-1 and inflorescences plant-1. The timing of seed rain varied considerably among individual plants. Five temporal patterns of seed rain were identified for individual fringed sagebrush plants: 1) 5.2% of the plants began and completed dispersing seeds within 6 to 8 weeks of flowering; 2) 20.8% began dispersing within 6 to 8 weeks of flowering and completed dispersal before snow was received in autumn; 3) 37.7% began dispersing seeds within 6 to 8 weeks of flowering and continued over the winter; 4) 29.9% delayed dispersal of seeds more than 8 weeks after flowering and continued over the winter; and 5) 6.5% began and completed seed dispersal during the winter. The number of fringed sagebrush seeds in the soil was correlated with seed production only when many seeds were produced (r=0.76), indicating that annual seed production is of limited importance for maintaining a seedbank. A persistent seedbank is important in maintaining fringed sagebrush populations when seed production is limited. Diverse rates and times of seed rain along with a persistent seedbank may enable fringed sagebrush to occupy safe sites that develop in time.