Submitted to: Western Society of Weed Science
Publication Type: Abstract Only
Publication Acceptance Date: November 9, 2011
Publication Date: March 15, 2012
Citation: Clements, C.D., Young, J.A., Harmon, D.N. 2012. Phenology of exotic invasive weeds associated with downy brome [abstract]. Western Society of Weed Science. 64:10. Technical Abstract: The exotic and highly invasive annual grass downy brome (Bromus tectorum) has invaded millions of hectares of rangelands throughout the Intermountain West. Downy brome increases the chance, rate, season and spread of wildfires, resulting in the destruction of native plant communities and the wildlife that depend on these communities. The increased frequency of wildfires has led to the conversion of formerly big sagebrush (Artemisia tridentata)/bunchgrass communities to annual grass dominance by downy brome. Downy brome is the aspect dominant of vast areas of rangelands, often referred to as downy brome mono-cultures. Upon further inspection, these so-called mono-cultures actually host a number of exotic species that are components of these downy brome dominated rangelands. We investigated the phenology of 11 exotic invasive annual species associated with downy brome communities to obtain knowledge on how this array of weeds contributes to the truncation of succession. The array of exotic weed species that we investigated segregated into 1) bare-ground stage, 2) mustard stage, 3) downy brome dominance, 4) extreme ephemeral, 5) downy brome cohorts, and 6) annual species that replace downy brome. The bar-ground successional species [i.e. halogeton (Halogeton glomeratus)] all mature in late summer and early fall, much later than downy brome. The increasingly diverse mustard species stage matures in late spring and early summer, generally later than downy brome. The extremely ephemeral bur buttercup (Ranunculus testiculatus) germinates with downy brome in the winter, but matures before any species in the continuum. Several species repeatedly occur in downy brome dominated seral communities and have similar and contrasting life forms to downy brome [i.e. filaree (Erodium cicutarium)]. Annual species that can replace downy brome on specific sites such as medusahead (Taeniatherum caput-medusa) and yellow starthistle (Centaurea solstitialis) are strikingly different in phenology. Yellow starthistle is much later in maturity, while medusahead mimics downy brome, but is slightly later to mature.