Influence of Weather on Low Larkspur (Delphinium nuttallianum) Density

Delphinium nuttallianum (low larkspur) causes serious cattle losses on mountain rangelands in western North America. Risk of cattle deaths is related to density of low larkspurs. Our hypothesis was that warmer winter/spring conditions, coupled with below average precipitation, would result in reduced low larkspur density (plants/m2). We measured larkspur density using 4 transects at 4 sites: Collbran and Yampa, Colorado; Huntington, Utah; and Calf Creek (Teton Mountains), Wyoming over a 7-9 year period. Weather data was collected at nearby weather stations. Larkspur density was often related to previous winter and spring precipitation, with increased precipitation resulting in higher plant densities. Higher ambient temperatures during winter and spring were related to lower plant densities. Further, there was a relationship between weather during the previous growing season (May to July) and larkspur density the next year, with warmer temperatures and/or low precipitation related to reduce densities at 3 of 4 sites.