Environmental characteristics linked to successful introductions of a rare wetland grass (Pleuropogon oregonus)

Authors: Copeland, Stella; Hamerlynck, Erik; PALMER, BRANDON - Oregon Desert Land Trust; STERNICK, SARA - Suny College; WILLIAMS, COLLIN - Burns Paiute Tribe; HAGLE, CALLA - Bureau Of Land Management; CROUCH, CARTER - International Crane Foundation

Submitted to: Natural Areas Journal
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 7/15/2025
Publication Date: 11/7/2025
Citation: Copeland, S.M., Hamerlynck, E.P., Palmer, B.J., Sternick, S.I., Williams, C.W., Hagle, C.R., Crouch, C.G. 2025. Environmental characteristics linked to successful introductions of a rare wetland grass (Pleuropogon oregonus). Natural Areas Journal. 45(4):269-278. https://bioone.org/journals/Natural-Areas-Journal.
DOI: https://doi.org/10.3375/2162-4399-45.4.5

Interpretive Summary: Oregon semaphoregrass is found in only a handful of montane meadows in eastern Oregon. Efforts to increase population size and number via introductions for this species are seldom successful. We conducted a study to identify environmental factors linked to introduction success with a series of years, and dozens of plantings, in Logan Valley on Burns Paiute Tribal lands. We found that sites with high light competition, mostly from dense sedges and grasses or high soil moisture throughout the growing season should be avoided by managers in outplanting efforts due to low success in these conditions. These outcomes provides managers site selection criteria for increasing the success of the intensive propagation and planting efforts necessary for conservation of this extremely rare species.

Technical Abstract: Rare plant conservation often includes introductions via outplantings or seedings, yet these efforts are often unsuccessful. Observational studies including experimental plantings could assist with identifying the environmental characteristics associated with success. This study leveraged an existing introduction program to assess the environmental characteristics associated with outplanting success (survival, growth, and reproduction) for a rare grass species, Pleuropogon oregonus (Oregon semaphoregrass), in a large wetland site in eastern Oregon. The study included 4 years of transplants following standardized propagation and outplanting methods and evaluated associations between success and environmental variables suggested by previous observations including soil moisture metrics (VWC minimums, dry down patterns), light competition (leaf area index), and surface cover. We also tested for co-occurring species as potential indicators of successful planting locations. We found that higher soil moisture and light competition was associated with lower survival and abundance of first year plantings. Bare ground cover was positively associated with first year abundance. However, yearly growth rate was not associated with any of the environmental variables. Co-occurring species indicators of first year failure (no survival) notably included a common introduced grass found in natural populations, meadow foxtail (Alopecurus pratensis). Our results suggest that outplanting efforts for this species should avoid areas with high soil moisture throughout the growing season and high light competition for increased initial success. Further research is needed to identify environmental characteristics favoring long-term introduction success, as indicated by population growth, as these were not clearly linked to the same factors associated with survival.