Sagebrush steppe recovery after fire varies by development phase of Juniperus occidentalis woodland

Woodland ecosystems of the world have been changed by land use demands, altered fire regimes, invasive species and climate change. Reduced fire frequency is recognised as a main causative agent for Pinus–Juniperus L. (piñon–juniper) expansion in North American woodlands. Piñon–juniper control measures, including prescribed fire, are increasingly employed to restore sagebrush steppe communities. We compared vegetation recovery following prescribed fire on Phase 2 (mid-succession) and Phase 3 (late-succession) Juniperus occidentalisHook. (western juniper) woodlands in Oregon. The herbaceous layer on Phase 2 sites was comprised of native perennial and annual vegetation before and after fire. On Phase 3 sites the herbaceous layer shifted from native species to dominance by invasive Bromus tectorum L. (cheatgrass). After fire, shrubs on Phase 2 sites were comprised of sprouting species and Ceanothus velutinus Dougl. (snowbrush). On Phase 3 woodland sites the shrub layer was dominated by C. velutinus. The results suggest that Phase 2 sites have a greater likelihood of recovery to native vegetation after fire and indicate that sites transitioning fromPhase 2 to Phase 3 woodlands cross a recovery threshold where there is a greater potential for invasive weeds, rather than native vegetation, to dominate after fire. Additional keywords: Artemisia tridentata, Bromus tectorum, Great Basin, mountain big sagebrush, state-andtransition, threshold. Received 4 December 2012, accepted 19 June 2013, published online 10 September 2013