Is pile seeding wyoming big sagebrush (artemisia tridentata subsp. wyomingensis) an effective alternative to broadcast seeding?

Abstract

Sagebrush plays an important role in the ecological functions of sagebrush steppe plant communities and is a necessary component of habitat for a variety of wildlife including greater sage-grouse (Centrocercus urophasianus). At lower elevations, increased fire frequency associated with exotic annual grass invasion has heightened the need for effective sagebrush restoration strategies, but existing techniques have been largely ineffective. Our objective was to evaluate "pile seeding" (placing mature seed heads on the ground) of Wyoming big sagebrush (Artemisia tridentata subsp. wyomingensis) as an alternative to broadcast seeding. We used a randomized block design (n=5) replicated in 2 yr at two contrasting ecological sites in southeastern Oregon. Treatments applied to 100×1.5 m plots included 1) pile seeding (four mature seed heads·pile- 1×10 piles·plot -1), 2) broadcast seeding (0.5 kg pure live seed [PLS]·ha -1), and 3) natural recovery (i.e., nonseeded). Planting occurred in fall 2008 and 2009, and plots were monitored for seedling establishment for three or two growing seasons postplanting. Seedling density was estimated at the plot scale within a 50-cm radius of each seed head pile ("island scale"). In the year following planting, sagebrush seedling density at the plot scale was up to 60-fold higher (P≤0.05) in pile-seeded plots compared to natural recovery and broadcast plots. Seedling mortality was high (up to 98% reduction in density) for pile-seeded plots between the first and second growing seasons postplanting and differences between broadcast and pile-seeded plots dissipated by 2-3 yr postplanting. Although pile-seeding had higher initial density than broadcast seeding, neither technique had sufficient multiyear survival to suggest restoration efficacy at the plot scale. Seedling density at the island scale suggests that pile-seeding may be useful for establishing sagebrush islands, depending on year conditions. Research is needed to determine strategies capable of increasing long-term sagebrush seedling survival.