Earlier fall precipitation and low severity fire impacts on cheatgrass and sagebrush establishment

Abstract

In arid and semiarid ecosystems, invasion by exotic grasses may be driving state changes in vegetation defined by losses of native shrub communities. Changes in wildfire regimes and fall precipitation timing related to climate change may promote fluctuations in resource availability that reinforces invasion and state changes in vegetation. The objective of this study was to investigate how earlier fall precipitation timing and fire affected the germination, establishment, and growth of the dominant native shrub Wyoming big sagebrush (Artemisia tridentata subsp. wyomingensis), and one of the most problematic invaders, cheatgrass (Bromus tectorum L.) in the Great Basin. We extracted soil cores from Rush Valley, Utah (UT), USA, on the eastern side of the Great Basin ecoregion and placed them in a common garden in Provo, UT, and planted seeds of sagebrush and cheatgrass in individual cores. We measured the response of sagebrush and cheatgrass to experimental fire and two fall precipitation timing pulses in a full factorial design. Water was added for two weeks in early September (early fall treatment) and mid-October (late fall treatment). We measured seedling emergence, plant height, biomass, density, seed production, and survival. Early fall precipitation did not significantly affect the amount of cheatgrass or sagebrush seedling emergence. Early fall precipitation significantly increased cheatgrass density, height, biomass, and seed production, and sagebrush height and biomass, but not density. Surprisingly, cheatgrass did not respond positively to fire. In contrast, fire increased sagebrush density (twofold) and survival. These findings indicate that fire can have positive impacts on sagebrush establishment. The data suggest that projected increases in fall moisture in the Great Basin due to climate change are likely to have positive impacts on both cheatgrass and sagebrush. However, additional studies are needed to identify how fall precipitation timing and fire might impact competitive interactions between sagebrush and cheatgrass and the bearing on invasion success at influencing state changes in the Great Basin.

Postfire restoration seeding success increases with early fall seeding and simulated precipitation in the Great Basin Desert of North America

“…We did not find support for our second hypothesis that the altered seedbed environment related to the burn treatment would have a widespread positive effect on plant growth. While our burned seedbed treatment did affect emergence for some species, effects tended to be muted or negative and did not appear to be as dramatic as the impacts of more severe fires created by perennial woody vegetation (Booth et al 2003; Germino et al 2018; Bishop et al 2020). There was mixed support for our third hypothesis, where the effects of seeding/precipitation timing and burning differed among species and functional groups.…”

“…This study was a 2 × 2 full‐factorial block design replicated four times with burning and seeding/precipitation timing treatments randomly positioned within each block. The study included four treatment combinations: burned–early fall seeding and precipitation; burned–mid‐fall seeding and precipitation; unburned–early fall seeding and precipitation; and unburned–mid‐fall seeding and precipitation (Bishop et al 2020).…”

“…Research suggests that earlier fall precipitation and more rain than snow tend to increase plant species invasion potential (e.g. Prevéy & Seastedt 2015; Horn et al 2017; Pilliod et al 2017; Gill et al 2018; Bishop et al 2020). Variability in climate increases the need to understand how seeding timing responds to projected increases in early fall precipitation and warmer temperatures.…”

“…In contrast, shrub species, such as sagebrush, are broadly characterized by slow germination rates linked to light requirements and cold stratification followed by relatively slow growth rates (Bonner & Karrfalt 2008). Research also shows that invasive annual grasses can take advantage of earlier fall precipitation timing in ways that reinforce invasion success (Horn et al 2015; Horn et al 2017; Bishop et al 2020). This highlights the need to better define optimal planting windows for stabilization and restoration seed mixes in response to changing climates.…”

“…Matching fall seeding dates to earlier precipitation timing has the potential to improve restoration outcomes (e.g. Boyd & James 2013; Boyd & Lemos 2015; Bishop et al 2020; Harvey et al 2020). Unfortunately, there is limited understanding of how plant species used in restoration efforts respond to changing climate conditions and how modifying the timing of seeding may influence establishment success.…”