Canopy Growth and Density of Wyoming Big Sagebrush Sown with Cool-Season Perennial Grasses

Abstract

Post-mining revegetation efforts often require grass seeding and mulch applications to stabilize the soils at the same time as shrub seeding, creating intraspecific competition between seeded shrubs and grasses that is not well understood. Artemisia tridentata Nutt. ssp. wyomingensis (Beetle and Young) (Wyoming big sagebrush) is the dominant premining shrub on many Wyoming mines. The Wyoming Department of Environmental Quality, Land Quality Division requires reestablishment of 1 shrub m−2on 20% of post-mined lands in Wyoming. Reclamationists seldom document the impacts of grass competition on shrub canopy size after reclamation plantings become established even though shrub canopy development is important to vegetative structural diversity. In 1999, we initiated a study at the Belle Ayr Coal Mine near Gillette, Wyoming, to evaluate the influence of grass competition on establishment and growth of Wyoming big sagebrush. Combinations of three sagebrush seeding rates (1, 2, and 4 kg pls ha−1) and seven cool-season perennial grass mixture seeding rates (0, 2, 4, 6, 8, 10, and 14 kg pls ha−1) were seeded during winter 1998–1999. Shrub density and grass cover were assessed from 1999 to 2004. We monitored sagebrush canopy size in 2001, 2002, and 2004. All sagebrush seeding rates provided shrub densities ≥1 shrub m−2 after six growing seasons. Grass production ≥75 g m−2 was achieved by seeding grasses at 6 to 8 kg pls ha−1. Canopy growth of individual sagebrush plants was least in the heaviest grass seeding rate. Reduced grass seeding rates can aid in achieving Wyoming big sagebrush density standards and enhance shrub canopy growth.