Directing plant establishment after road construction through soil resource manipulation in Rocky Mountain National Park

Background/Question/Methods

Disturbance along roadsides leads to changes in resource availability, which alters native and exotic plant germination and establishment. In Rocky Mountain National Park (RMNP), 23 acres of roadsides were hydro-seeded with native grasses and forbs after road realignment and widening. We monitored post-construction plant densities one year after hydro-seeding at seven sites. We found initial establishment of native seeded and volunteer and exotic species. Exotics included Bromus inermis, Bromus tectorum, and Cirsium arvense, which are considered invasive species in RMNP. We propose that changes in water and nitrogen availability, which can be manipulated through application of soil amendments, effect native perennial and invasive species establishment differentially. We will test whether native perennial species can be favored over weedy species through application of amendments that (1) supply N and increased water holding capacity through organic matter decomposition(yard waste compost),(2) extend water and N availability(super-absorbent polymers), (3) reduce readily available N, water loss, and soil temperature fluctuations (wood mulch). Our field study will measure plant establishment, soil N and water availability, soil temperature, and precipitation. We will analyze changes in water-holding capacity and water-release rates of amended soils.

Results/Conclusions

Along Bear Lake Road, grass species accounted for 90% of established species, with the majority of these represented by Elymus elymoides and Elymus canadensis.  Invasive species of concern, Bromus inermis, Bromus tectorum and Cirsium arvense accounted for 43%, 6%, and 3% of observed exotic species respectively. On average, twenty-eight seeded, four native volunteer, and one exotic species were observed per m² in the first year of establishment. We expect that increasing water holding capacity and nitrogen availability with compost will favor establishment of native perennial and weedy species.  SAP application will increase differential establishment of natives, particularly in sites with Bromus tectorum.  We anticipate mulch application will reduce  initial establishment of all species and particularly invasive species that respond to readily available nitrogen.  The results from our study can improve future management of roadside soils and inform best management practices in restoration.