Preserving prairies: understanding temporal and spatial patterns of invasive annual bromes in the Northern Great Plains

Abstract

Abstract. Two Eurasian invasive annual brome grasses, cheatgrass (Bromus tectorum) and Japanese brome (Bromus japonicus), are well known for their impact in steppe ecosystems of the western United States where these grasses have altered fire regimes, reduced native plant diversity and abundance, and degraded wildlife habitat. Annual bromes are also abundant in the grasslands of the Northern Great Plains (NGP), but their impact and ecology are not as well studied. It is unclear whether the lessons learned from the steppe will translate to the mixed-grass prairie where native plant species are adapted to frequent fires and grazing. Developing a successful annual brome management strategy for National Park Service units and other NGP grasslands requires better understanding of (1) the impact of annual bromes on grassland condition; (2) the dynamics of these species through space and time; and (3) the relative importance of environmental factors within and outside managers' control for these spatiotemporal dynamics. Here, we use vegetation monitoring data collected from 1998 to 2015 in 295 sites to relate spatiotemporal variability of annual brome grasses to grassland composition, weather, physical environmental characteristics, and ecological processes (grazing and fire). Concern about the impact of these species in NGP grasslands is warranted, as we found a decline in native species richness with increasing annual brome cover. Annual brome cover generally increased over the time of monitoring but also displayed a 3-to 5-yr cycle of reduction and resurgence. Relative cover of annual bromes in the monitored areas was best predicted by park unit, weather, extant plant community, slope grade, soil composition, and fire history. We found no evidence that grazing reduced annual brome cover, but this may be due to the relatively low grazing pressure in our study. By understanding the consequences and patterns of annual brome invasion, we will be better able to preserve and restore these grassland landscapes for future generations.

Experimentally derived nitrogen critical loads for northern Great Plains vegetation

“…In the absence of Amorpha , the nonnative component of plant cover doubled to tripled at N addition levels within the range of current deposition, and this increase featured invasive annual Bromus grass species known to be problematic, and in some places increasing in prominence, in NGP grasslands (Ashton et al. ).…”

“…Nonnative species abundance increased in only one site (Hilltop), but this increase was one of the most striking and consistent responses to N addition in our study, serving as a basis for one critical load estimate for this site. In the absence of Amorpha, the nonnative component of plant cover doubled to tripled at N addition levels within the range of current deposition, and this increase featured invasive annual Bromus grass species known to be problematic, and in some places increasing in prominence, in NGP grasslands (Ashton et al 2016).…”

Using phenological niche separation to improve management in a Northern Glaciated Plains grassland

“…Many patches of grassland that remain are severely invaded (Wilsey et al ), with cool‐season perennial grasses Bromus inermis and Poa pratensis being dominant invaders (Cully et al ; DeKeyser et al ). In fact, more than 80% of the annual production in some grasslands come from B. inermis and P. pratensis (DeKeyser et al ; Ashton et al ). Restoration and management to control invasive cool‐season grasses in these grasslands are often met with limited success (reviewed in Ellis‐Felege et al ) and cool‐season invasive grasses often persist after intensive initial restoration efforts (Larson et al ).…”

Ecological monitoring and evidence‐based decision‐making in America's National Parks: highlights of the Special Feature

“…Instead of a search for generality, the place-based approach steeps itself directly in the messy, idiosyncratic details of real ecosystems. Ashton et al (2016) replicated vegetation surveys among prairie parks and found previously undescribed cyclical variation in invasive brome grass dynamics that will greatly benefit park weed management. For example, Brown et al (2016) applied a common protocol to coral reefs in four parks that revealed among-park variation in stressors and subsequent management recommendations.…”