First-year establishment, biomass and seed production of early vs. late seral natives in two medusahead (Taeniatherum caputmedusae) invaded soils

Authors: USELMAN, SHAUNA - University Of Nevada; Snyder, Keirith; LEGER, ELIZABETH - University Of Nevada; Duke, Sara

Submitted to: Invasive Plant Science and Management
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/8/2014
Publication Date: 4/1/2014
Citation: Uselman, S.M., Snyder, K.A., Leger, E.A., Duke, S.E. 2014. First-year establishment, biomass and seed production of early vs. late seral natives in two medusahead (Taeniatherum caputmedusae) invaded soils. Invasive Plant Science and Management. 7:291-302.

Interpretive Summary: Medusahead is a noxious, exotic annual grass that that has invaded into the Intermountain West of the U.S., reducing native species biodiversity and increasing fire frequency. Most re-seeding efforts to restore or rehabilitate degraded rangelands have been expensive and had low success rates. We compared the performance of an early seral seed mix (annual forbs, early seral grasses and shrubs) to that of late seral seed mix representative of species commonly used in restoration, when seeded with and without medusahead in two soils of contrasting texture (sandy loam and clay loam). The early seral native annual forb, bristly fiddleneck, was an effective competitor with medusahead in both soil types, significantly reducing biomass and seed production by 16% to 17%, respectively. Given that this effect was relatively small, further research to examine whether the use of increased seeding density of bristly fiddleneck and/or whether greater diversity of species in the seeding mix would enhance exotic suppression is warranted. Native perennial grasses, particularly early seral grasses, established in higher numbers than native forbs and shrubs, demonstrated their importance in restoration seedings. Although they did not appear to have a suppressive effect on medusahead during their first growing season, perennial grasses have been found to be effective competitors with exotic annual grasses once mature. Our findings suggest that efforts to find additional novel candidate species for seed mixtures may be best focused on early successional species, similar to bristly fiddleneck, to improve restoration/rehabilitation outcomes in disturbed rangeland ecosystems.

Technical Abstract: Re-seeding efforts to restore or rehabilitate Great Basin rangelands invaded by exotic annual grasses are expensive and have generally achieved limited success. There is a need to identify new strategies to improve restoration outcomes. We tested the performance of an early seral mix (annual forbs, early seral grasses and shrubs) with that of a late seral mix representative of species commonly used in restoration when growing with medusahead in soils of contrasting texture (sandy loam and clay loam). Natives were also seeded without the exotic. We measured establishment, aboveground biomass production, and seed production of both natives and exotics through the first growing season after seeding. We found that the early seral seed mix significantly reduced aboveground biomass and seed production of medusahead by 16% and 17% respectively, likely due to competition with the early seral native forb, bristly fiddleneck. Exotic performance was reduced in both soil types, suggesting utility of bristly fiddleneck in restoration is not limited to only one soil type. In contrast, the late seral seed mix did not suppress establishment, aboveground biomass or seed production of the exotic. Although the native perennial grasses, particularly early seral species, were able to establish with medusahead, these native grasses did not appear to have a suppressive effect on the exotic during the first growing season. Medusahead was able to establish and produce seeds on both soil types, demonstrating an ability to expand its current range in the Intermountain West, though aboveground biomass and seed production was higher in the clay loam. Our results suggest that certain species may play a key role in restoration, and that targeting early seral species in particular to find additional native species with the ability to suppress exotic annual grasses is an important next step in improving restoration outcomes in desert ecosystems.