Elymus elymoides and Pseudoroegneria spicata are common native bunchgrasses in sagebrush steppe ecosystems of the western U.S.A. Fire is a natural disturbance within these ecosystems and these grasses recover from fire through surviving buds that sprout from the remaining unburned plant crown. Tillers produced after fires may be viewed as the initial population of tillers representing a given bunchgrass. It is thought that tillers produce buds for the next generation of tillers at their leaf axils at the base of the leaf sheath and that plant growth will be sustained if tillers are replaced at a rate of one daughter per mother tiller. However, there have been no detailed examinations of tiller dynamics following fire for E. elymoides and P. spicata. We examined tiller survival and replacement rates for these two species by observing the presence 5 tillers on each of 14 plants per species during the second growing season after fires at two sites in eastern Oregon. We tracked daughter tiller production per mother tiller during this same time. We asked if these tillers replaced themselves between fall 2015 and fall 2016 and if these species responded similarly to fire.
Results/Conclusions
Preliminary results indicate that nearly all tillers marked in fall 2015 died by fall 2016, but unexpectedly, both species had at least one mother tiller that survived the summer drought and remained green into fall 2016. For both species, daughter tillers produced during winter and spring 2016 had a higher one-year survival (15%) than did initial fall mother tillers (1.4%). Between fall 2015 and 2016, replacement of mother tillers was similar for E. elymoides (16 and 30%) and P. spicata (24 and 30%) at the two sites. The original five mother tillers per plant produced a median of two daughter tillers ranging between zero and six daughters. Two years after a fire, both E. elymoides and P. spicata did not appear to be replacing mother tillers at a rate that would sustain the tiller population. Two growing seasons of post-fire recovery may be insufficient for tiller populations to sustain and increase. Alternatively, these plants may be initiating additional non-axillary buds (root crown buds) to compensate for low tiller replacement and to sustain the tiller population and ultimate plant survival.