Submitted to: Western Society of Weed Science
Publication Type: Abstract Only
Publication Acceptance Date: 11/9/2011
Publication Date: 3/15/2012
Citation: Harmon, D.N., Clements, C.D., Young, J.A. 2012. Downy brome seed ecology: From flower to emergence [abstact]. Western Society of Weed Science. 64:42.
Technical Abstract: Downy brome (Bromus tectorum) seed is very common in seed banks throughout Great Basin rangelands. Previously, using a soil bioassay method, we tested 100 separate sites within the Great Basin (1000 samples) to measure downy brome seed bank densities. The locations differed greatly by precipitation, disturbance history, plant community, and soil type. Out of the 1000 samples, very few did not contain downy brome seed. Based on our observations of vegetative plasticity, we hypothesized that characteristics of downy brome reproduction would also differ by population. We monitored flowering, seed maturation, seed dormancy, emergence, and seed banks of five downy brome population categories. A total of 15 locations, three replicates of population categories, were monitored and sampled. All locations were within 60km of each other. Our results found that flowering occurred as early as April with viable seed being produced the first few days of May. Seed production existed through July based on the observance of green seed. Only the high elevation population differed greater than the annual intra population flower timing difference. Primary seed dormancy differed by population. Salt desert populations exhibited greater dormancy than higher elevation or Wyoming big sagebrush (Artemisia tridentata) invaded populations. Emergence timing differed by year more than population, except for the high elevation population which, similar to flowering, exhibited delayed emergence. The only seed characteristic that differed among population habitat types regardless of the annual weather conditions was primary seed dormancy. Seed dormancy could be an adaptive response to avoid summer germination, which was observed at the salt desert locations. Seed banks differed by population and were not ultimately determined by primary seed dormancy patterns. Secondary induced seed dormancy principally affects seed banks. Downy brome reproductive phenology is largely determined by the unpredictable annual weather making seed dormancy predictability a useful tool for management.