Post-fire spatial recruitment patterns of Wyoming big sagebrush (Artemisia tridentata ssp wyomingensis)

The increasing rate at which sagebrush steppe ecosystems are being lost to fragmentation and exotic species invasion has prompted land managers to consider active restoration as a means of improving big sagebrush reestablishment subsequent to fire, thus providing habitat structure to obligate species.  Because a better understanding of natural recruitment patterns may be useful for developing better restoration strategies, we characterized seedling occurrence patterns across several large burns.  We analyzed seedling position and abundance data with reference to i) the negative exponential decay model of rapidly decreasing abundance from the upwind, unburned edge, ii) abundance patterns associated with remnant, unburned islands, and iii) distribution patterns unrelated to the proximity of potential seed sources.  Our results indicate that spatial patterns of natural sagebrush recruitment are generally unrelated to proximity of a potential seed source, suggesting that occasional events in the tail of the seed dispersal curve are disproportionately important in influencing patterns of seedling abundance.  Furthermore, seedlings tended to occur in clumped distributions at small spatial scales.  These combined results support a “nucleation” pattern of sagebrush reestablishment, in which a small amount of seed reaching microsites appropriate for germination and establishment are far more important in influencing recovery than a large amount of seed dispersed adjacent to an unburned edge or island.  Future efforts at accelerating big sagebrush reestablishment can likely be improved by ensuring the successful establishment of fewer individuals across the burned landscape, rather than planting large islands or mass seeding for individuals unlikely to survive germination and establishment.