Research Associate Denver Botanic Gardens Denver, Colorado, United States
Background/Question/Methods
Land management practices, including control of non-native invasive species with herbicide, might alter propagule availability and thus community assembly following fire. We sampled plant communities after the 2020 Calwood Fire in Boulder County, CO, to explore how pre-fire herbicide treatments including Rejuvra® shaped plant community response to relatively low- severity grassland fire. Given Rejuvra®’s pre-emergence control of short-lived grasses and forbs, we assessed post-fire response of target (Bromus tectorum,Bromus japonicus, and short-lived non-native forbs) and non-target (short-lived native grasses and forbs) species in sprayed and unsprayed areas that were burned or not (i.e., using a factorial design). We also assessed long-lived species that have been shown to benefit from the use of Rejuvra® in other systems.
Results/Conclusions
Bromus tectorum and Bromus japonicus were successfully controlled in burned (96% lower cover of both species where sprayed) and unburned (93% lower cover of B. tectorum; 83% lower cover of B. japonicus) areas. Non-native short-lived forbs were also controlled both in the presence and absence of fire (burned areas: richness, 55% lower in sprayed areas; cover, 63% lower in sprayed areas; unburned areas: richness, 43% lower; cover, 58% lower). The two native annual grasses present at our study site (Vulpia octoflora and Hordeum pusillum) were too uncommon to statistically assess. For short-lived native forbs, richness was 75% lower in burned areas that had been sprayed than those that had not. This reduction did not occur in unburned areas, providing evidence for a non-target effect that emerges in the presence of fire. This potential non-target effect was not observed for percent cover. Further, long-lived native forbs and grasses had higher cover in sprayed areas, whether burned (forbs, 19% higher; grasses, 40% higher) or unburned (forbs, 40.5% higher; grasses, 39% higher), corroborating previous findings. Taken together, our results show that Rejuvra® is a promising tool for land managers, but more work in needed to understand its effects in fire-prone natural areas.
