Initial Divergent Postfire Recovery Converges Over the Long-term: A Case Study in Juniper-Encroached Sagebrush Steppe

Reduced fire frequency is recognized as a main cause of piñon–juniper (Pinus–Juniperus L.) expansion in western North American sagebrush steppe and grasslands. Piñon–juniper woodland control using prescribed fire and mechanical treatments have increased the past three decades with the goal of restoring sagebrush steppe plant communities. Factors shaping the response of sagebrush steppe communities following woodland treatment include shrub and herbaceous composition, level of tree dominance, and site characteristics. We compared vegetation recovery spanning 20 yr following prescribed fire on mid-succession and late-succession western juniper (Juniperus occidentalis Hook.) woodlands on Steens Mountain, Oregon. Our objective was to evaluate vegetation dynamics between early (first decade) and later successional (second decade) time periods after fire. The first decade after fire vegetation on burned mid-succession sites were codominated by native herbaceous perennials and sprouting shrub species and on late-succession sites vegetation was codominated by nonnative cheatgrass (Bromus tectorum L.) and snowbrush (Ceanothus velutinus Dougl.). During the second decade after fire, vegetation composition converged and both mid-succession and late-succession sites were codominated by herbaceous perennials, mountain big sagebrush (Artemisia tridentata spp. vaseyana [Rydb.] Beetle), round-leaf snowberry (Symphoricarpos rotundifolius A. Gray) and snowbrush. Herbaceous and shrub vegetation composition of both burned woodland phases proved to be highly resilient to fire, the difference was that native shrub-herbaceous recovery on late-succession sites required about twice as much time as mid-succession sites. The resilience of both mid-succession and late-succession woodland sites was likely a product of ecological site characteristics (e.g., elevation and precipitation zone) that affords a competitive advantage for native perennial species over invasive annuals.