Plants have gone from flowering one year to sterile the next and back to flowering. The number of stems an individual plant has can vary with moisture conditions and in response to dormancy and vigorous growth. These shifts indicate increased vegetative growth after dormancy and decreased vigor after an exceptionally vigorous growth year. Six year stem counts for some plants indicate there may be a decline in stems with age, but more monitoring is needed to determine this. Many formerly vigorous plants were missing in the drought year of 1991 and some of these are surely dormant rather than dead.
Moisture restricts mature plant vigor and can cause mortality, especially of young plants.
Spring burns and adequate moisture are needed for seedling establishment. Frost heave can kill plants, especially young ones, and is increased in severity by fall burning. Severe rabbit grazing in conjunction with drought can kill plants and reduces seed production.