Tiller recruitment of perennial grasses in mixed-grass prairie primarily occurs from belowground buds. Environmental conditions, such as temperature, soil moisture and grazing can affect bud outgrowth of both invasive and native perennial grasses. Differential bud outgrowth responses of native and invasive species to climate change and grazing could alter competitive interactions that have implications for future land management. The aims of this work were to (i) compare how spring temperature altered bud outgrowth of native Pascopyrum smithii (Rydb.) Á. Löve (western wheatgrass) and introduced Bromus inermis Leyss.(smooth brome), (ii) compare how watering frequency altered bud outgrowth of these two species and (iii) evaluate how clipping interacts with spring temperature or watering frequency to affect P. smithii bud outgrowth.

Individual plants of B. inermis and P. smithii were harvested from North American mixed-grass prairie. Bud outgrowth from tillers of both species were evaluated under three spring temperature regimes (Average: 12, 18 and 24°C) and two watering frequencies (frequent and intermittent) in a growth chamber experiment. The response of P. smithii bud outgrowth to clipping was also examined.

Bromus inermis had more buds per tiller and initiated a greater proportion of these buds than P. smithii under all temperature and moisture conditions. Pascopyrum smithii bud development was reduced at 24°C. Intermittent watering did not significantly impact bud outgrowth of either species. Clipping increased P. smithii bud mortality and reduced its bud development for the 2-week period of the study. The robust vegetative reproductive capacity of B. inermis under a range of environmental conditions is a key mechanism enabling the expansion of B. inermis into P. smithii-dominated mixed-grass prairie in North America. Mixed-grass prairie dominated by P. smithii experiencing repeated defoliation may require longer recovery times and be more susceptible to B. inermis invasion due to the negative impact of grazing on P. smithii bud outgrowth. Successful tiller recruitment and establishment of native perennial grasses via the bud bank will be necessary for mixed-grass prairie to be resilient to climate change, plant invasions and grazing.