Does fall prescribed burning Artemisia tridentata steppe promote invasion or resistance to invasion after a recovery period?

Abstract

Artemisia tridentata ssp. wyomingensis (Beetle & A. Young) S.L. Welsh-bunchgrass communities were used to analyze the influence of disturbances on invasibility after a recovery period. These communities evolved with periodic fires shifting dominance from shrubs to herbaceous species. However, fire can facilitate Bromus tectorum L. invasion of these plant communities. We evaluated the invasibility of A. tridentata ssp. wyomingensis-bunchgrass communities 4 years after prescribed fall burning at six sites by comparing burned to unburned (control) communities. These communities did not have B. tectorum present prior to introduction. B. tectorum was introduced at 1, 10, 100, 1000, and 10,000seedsm−2 in burned and unburned communities. B. tectorum individuals established only when introduced at 10,000seedsm−2. In the areas seeded at 10,000seedsm−2, B. tectorum density and cover were more than three-fold higher in the control than burned treatments (P=0.04 and 0.08, respectively). Total herbaceous vegetation cover, density, and production increased with burning (P<0.01, 0.02, and <0.01, respectively). Bare ground and inorganic nitrogen were higher in the control than the burned treatment (P=0.02 and <0.01, respectively). Prescribed fall burning of late seral A. tridentata ssp. wyomingensis-bunchgrass communities stimulated the herbaceous component and increased the resistance of the communities to B. tectorum invasion 4 years post-burn. However, we do not suggest the use of prescribed burning in communities where invasive annual grasses are present or in close proximity. We acknowledge that our results would probably have been drastically different if B. tectorum or other invasive annual grasses had been a component of the plant communities prior to prescribed burning or became a component immediately after burning.