Reproductive and growth traits related to life histories of two rangeland grasses of western North America

Elymus elymoides (squirreltail) and E. wawawaiensis (bluebunch or Snake River wheatgrass) are two native grasses used for revegetation in sagebrush steppe regions of the western USA.  Elymus elymoides is thought to be a more ruderal species.  We examined reproductive and growth traits of these two species related to ruderal versus competitive or stress-tolerant life histories.  We tested effects of initial size of the target plant at the start of the experiment, and competition from neighbor grasses on Relative Growth Rate (RGR; final weight / initial weight) and Reproductive Effort (RE; reproductive weight / vegetative weight) of these two species.  In semiarid central Utah, we established one m² plots with ranges of densities of mature E. elymoides and E. wawawaiensis using plots from a previous experiment.  We also seeded a range of densities of the introduced annual, Bromus tectorum on these plots.  In March 2004, we measured ramet number and height of E. elymoides and E. wawawaiensis neighbors and target plants, from which we calculated initial biomass per plant, and we counted B. tectorum seedlings per plot.  We clipped end-of-season biomass of target plants in July 2004, clipping reproductive and vegetative biomass separately.  Elymus elymoides had higher RE than E. wawawaiensis (means of 0.41 versus 0.07), and RE of E. elymoides increased quickly with increasing initial plant size, suggesting a ruderal species, while RE of E. wawawaiensis increased only slightly (marginally significant) and gradually with increasing initial size.  RE of E. elymoides decreased with increasing competition, but competition did not significantly affect RE of E. wawawaiensis.  For both species, RGR decreased with increasing initial size, and with competition.