Temporal Patterns of Seedling Emergence and Early Survival of Great Basin Perennial Plant Species

We seeded Agropyron cristatum and 16 native Great Basin perennial species on Bromus tectorum–dominated sites to compare temporal patterns of seedling emergence and early survival among species. To indicate variability between sites and between years, plots were planted on 2 sites in western Utah in autumn 1994, and plantings were repeated near 1 site in autumn 1995. Two sites included burned and unburned seedbed treatments. We monitored seedling emergence and survival from early winter until July of the 1st year. Four seasonal patterns of emergence were evident, indicating considerable potential for different seasonal patterns of precipitation to favor recruitment of different species. Emergence of all shrubs, except Ephedra nevadensis, began in February and essentially ended by April. Seedlings of Ephedra nevadensis and of the grasses Agropyron and Pseudoroegneria spicata emerged over an extended period from February through June. Most other grasses and the 2 forbs began emerging in April and continued into June. Pleuraphis jamesii emergence did not begin until May. Although many seedlings of the 3 chenopod shrubs emerged, none survived, suggesting their episodic recruitment is more a function of survival than of emergence. Survival of 2 Chrysothamnus species was also low. Pseudoroegneria and Agropyron had the highest numbers of seedlings surviving on the moister site, followed by Elymus elymoides and Stipa comata. Survival of Agropyron, but not the native Elymus, was more depressed on the drier of the 2 sites planted in 1994. Stipa, Oryzopsis hymenoides, Pleuraphis, and Ephedra survived as well on the drier site as on the moister site, or better. On the 1995 planting site Bromus was greatly reduced by the burn treatment, and, in contrast to the effect of burn treatments on the 1994 site, survival of all species except Oryzopsis and Ephedra was higher on burned than on unburned treatments. Overall, Stipa, Oryzopsis, and Pleuraphis had low emergence but consistently high survival