Restoration and evolution in the Great Basin: non-target herbicide effects and potential for adaptive responses to fire
Loading...
Authors
Shriver, Laura Cecilia
Issue Date
2022
Type
Thesis
Language
Keywords
Ecology , Evolution , Great Basin , Invasive plants , Native plants , Restoration
Alternative Title
Abstract
Cheatgrass (Bromus tectorum) has dramatically transformed the Great Basin and increased the incidence of fire to the detriment of native plants. In Chapter 1, we assessed the potential for rapid evolution in Great Basin native plants in response to fire and associated changes. Through a resurrection study, we examined how populations with or without a recent wildfire have changed over time by comparing past collections (collected 3-11 years ago through the Bureau of Land Management’s Seeds of Success program) and contemporary re-collections from the same populations. We grew seeds in a common greenhouse environment and assessed how burn status and collection time influenced plant responses. We found evidence consistent with rapid evolution for at least one trait in every species, and temporal changes were concentrated in early seed and seedling traits. We saw potential evidence of rapid evolutionary response to fire in Elymus elymoides with temporal changes in burned populations towards potentially adaptive traits, including higher seed weight, higher emergence, and earlier emergence relative to the past collections. Our results support the effort of seed banking programs, as genotypes may shift over time within a population. In Chapter 2, we assessed the effects of the herbicides imazapic and indaziflam on target and non-target plants in 1) a natural, invaded field setting, 2) an agricultural field used to grow native annual forbs, and 3) on seeds of the perennial grass E. elymoides at various planting depths. In the natural field experiment, the density of non-native plants declined or remained low in all herbicide treated plots, while increasing dramatically in control plots. The combination and imazapic treatments also benefited native plants, the majority of which were perennial. All herbicides harmed at least some native annual forbs in the agricultural field experiment, although there were offsets at lower application rates, and some species were less susceptible than others. Herbicides reduced E. elymoides emergence, but planting seeds at 2-3 cm instead of the recommended 1 cm helped offset these negative effects, particularly for imazapic. We suggest that land managers make efforts to survey and protect native annual plants before applying herbicides, and that the combination of these two herbicides with potentially lower application rates may help balance weed control with promoting native diversity in sagebrush systems.