Wildland fire plays a key role in shaping natural communities on semi-arid landscapes around the world. The composition and structure of plant communities are often tied to specific patterns of fire frequency and size. Knowledge of fire characteristics compatible with sagebrush-dominated communities of the Intermountain West is critical for maintaining habitat critical for sagebrush-dependent wildlife, such as greater sage-grouse.
Big sagebrush plants (Artemisia tridentata ssp. vaseyana) are easily killed by fire, thus post-fire recovery must be from seeds that either survive fire or are spread from unburned areas, and recovery rate is dependent upon how fast new sagebrush plants are able to establish after fire. A research team, including Rocky Mountain Research Station scientist Stanley Kitchen, investigated natural recovery of mountain big sagebrush for 36 fires in the Great Basin and Colorado Plateau ecoregions.
Time since fire varied from 1 to 36 years. Sagebrush recovery rate in burned areas was highly variable relative to paired unburned areas, with full recovery estimated to take from 25 to 75-plus years. Recovery rate was most influenced by the amount of winter and spring precipitation the year after fire, suggesting the importance of sufficient soil moisture for seedling growth and establishment during the first growing season. Results also suggest that the opportunity for initial post-fire regeneration of mountain big sagebrush is fleeting due to a short-lived soil seed bank, and if missed, the time needed for big sagebrush recovery may be extended by several decades. Thus, conditions that result in short fire-free intervals or more frequent drought are likely to be less compatible with big sagebrush dominance, increasing risk for wildlife species dependent on this habitat type including the greater sage-grouse.
Knowledge of past fire regimes associated with mountain big sagebrush-dominated landscapes is inadequate for accurate assessment of current departures from historical conditions and scientifically-based fire planning by land managers. Widely utilized estimates of fire frequency are based upon a few problematic studies using fire-scarred proxy trees located at the forest/shrubland ecotone. These studies, all conducted in the northern half of the species distribution, generally fail to adequately address questions of fire behavior across the fuels threshold at the forest/shrubland ecotone.
Alternatively, fire frequencies compatible with big sagebrush have been suggested based upon post-fire succession rates. Specifically, minimum and maximum fire free intervals are estimated based upon the time required for big sagebrush recovery or tree invasion and dominance, respectively.
Published studies of mountain big sagebrush post-fire recovery are also limited primarily to higher latitudes, and as a rule are not linked to tree invasion studies. Big sagebrush does not sprout after fire and recovery is dependent upon the availability of seed and post-burn survival of seedlings. Factors that affect seed production, seed bank retention, and post-fire seed survival are not adequately understood.