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Title: Arid oil-field restoration: native perennial grasses suppress weeds and erosion, but also suppress native shrubs

Author
item Porensky, Lauren
item LEGER, ELIZABETH - University Of Nevada
item DAVISON, JAY - University Of Nevada
item MILLER, W - University Of Nevada
item GOERGEN, ERIN - University Of St Petersburg
item Espeland, Erin
item MOORE, ERIN - University Of Nevada

Submitted to: Agriculture, Ecosystems and Environment
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 11/21/2013
Publication Date: 2/1/2014
Publication URL: http://handle.nal.usda.gov/10113/58316
Citation: Porensky, L.M., Leger, E.A., Davison, J., Miller, W.W., Goergen, E.M., Espeland, E.K., Moore, E.C. 2014. Arid oil-field restoration: native perennial grasses suppress weeds and erosion, but also suppress native shrubs. Agriculture, Ecosystems and Environment. 184:135-144.

Interpretive Summary: Shrubs provide soil stabilization, herbaceous plant facilitation, carbon storage, and wildlife habitat in arid lands. Invasive species and water stress prevent shrub establishment. Does applying short-term irrigation and seeding native perennial grasses enhance native shrub establishment by reducing erosion and weed abundance? Using a field experimental approach, after two years irrigation had increased the density and biomass of seeded grasses by more than ten-fold. The combination of irrigation and grass seeding was associated with significantly lower wind erosion, weed density and weed biomass. Three years after irrigation ended, seeded grasses remained significantly more abundant in irrigated than nonirrigated plots. Previously irrigated plots also had significantly less bare ground, annual plant cover, and weed biomass than non-irrigated plots. Although seeded grasses reduced erosion and invasion, they failed to enhance native shrub establishment. Shrub cover and density were highest in plots that had been historically irrigated, but lacked perennial grasses. Our results indicate that short-term irrigation has persistent restoration benefits, and that a tradeoff exists between the benefits and costs of seeding perennial grasses into degraded arid shrubland sites.

Technical Abstract: 1. Long-lived, drought-tolerant shrubs are dominant components of many arid ecosystems, and shrubs provide multiple ecosystem services (e.g., soil stabilization, herbaceous plant facilitation, carbon storage and wildlife habitat). On denuded sites, shrub restoration is hindered by abiotic (erosion and water stress) and biotic (invasive species) challenges. Shrubs are unlikely to establish unless steps are taken to mitigate these restoration barriers. 2. We hypothesized that applying short-term irrigation and seeding native perennial grasses would facilitate native shrub establishment by reducing erosion and weed abundance. Using a blocked split-plot design, we evaluated the separate and combined impacts of short-term irrigation and perennial grass seeding on five-year restoration outcomes (including direct measurements of wind erosion) at two former agricultural fields in the Great Basin. 3. After two years, irrigation had increased the density and biomass of seeded grasses by more than ten-fold. The combination of irrigation and seeded grasses was associated with significantly lower wind erosion, weed density and weed biomass. 4. Three years after irrigation ended, seeded grasses remained significantly more abundant in irrigated than nonirrigated plots. Previously irrigated plots also had significantly less bare ground, annual plant cover, and weed biomass than non-irrigated plots. Large plant canopy gaps were fewer in irrigated and seeded plots. 5. Although seeded grasses reduced erosion and invasion, they failed to facilitate native shrub establishment. Shrub cover and density were highest in plots that had been drill-seeded and irrigated, but lacked perennial grasses. 6. Synthesis and applications: Our results indicate that short-term irrigation has persistent restoration benefits, and that a tradeoff exists between the benefits and costs of seeding perennial grasses into degraded arid shrubland sites.