Shrub Microsite Influences Post-fire Perennial Grass Establishment

Woody plants can cause localized increases in resources (i.e., resource islands) that can persist after fire. We tested the hypothesis that burned sagebrush subcanopies would have increased seedling establishment and performance of post-fire seeded perennial bunchgrasses compared to burned interspaces. We utilized five study sites in southeastern Oregon. The area was burned in a wildfire (2007) and re-seeded in the same year with a seed mix that included non-native and native perennial bunchgrasses. Seedling density, height, and reproductive status were measured in October of 2008 in burned subcanopy and interspace microsites. Seeded nonnative perennial grasses had greater densities than seeded native species and were six times more abundant in burned subcanopies compared to burned interspaces. Density of natives in burned subcanopies was 24times higher than burned interspaces. Seedlings were taller in burned subcanopies compared to burned interspaces and subcanopy microsites had more reproductive seedlings than interspace microsites. Our results suggest pre-burn shrub cover may be important to post-fire restoration of perennial grasses. Others have found that subcanopies have increased soil organic matter, nitrogen, and carbon (i.e., resource islands) and elevated post-fire soil temperature. Determining the mechanisms responsible for increased seeding success in subcanopy microsites may suggest tactics that could be used to improve existing restoration technologies.