Seeding Causes Long-Term Increases in Grass Forage Production in Invaded Rangelands

Seeding is sometimes used in attempts to increase grass forage production in invaded rangelands, but insufficient long-term data prevent determining if seeded grasses are likely to become and remain productive enough to justify this expensive practice. We quantified long-term seeding outcomes in a widespread Rocky Mountain foothill habitat invaded by leafy spurge (Euphorbia esula L.) and several exotic grasses. Fourteen yr after seeding, the most productive grass (bluebunch wheatgrass [Pseudoroegneria spicata (Pursh) A. Love]) produced 900 (100, 12 000) kg ha−1 [mean (95% CI)], which was about 70% of total plant community biomass. This result was not greatly altered by grazing according to an unreplicated, grazed experiment adjacent to our replicated ungrazed experiment. Regardless of treatment, E. esula gradually became less productive and seeded and unseeded plots produced similar E. esula biomass 14 yr after seeding. P. spicata reduced exotic grasses about 85%. Our results resemble those of another foothills study of another invasive forb (Centaurea stoebe L. ssp. micranthos [Gugler] Hayek) and a Great Plains study of E. esula, so foothills seeding outcomes seem somewhat insensitive to invader composition, and seeding can increase forage across much of E. esula’s range. While there is always some risk seeded grasses will fail to establish, our study combined with past studies identifies invaded habitats where seeded grasses have a good possibility of forming persistent, productive stands.