Research Note 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 and create a heterogeneous environment for restoration. Others have found that subcanopies have increased soil organic matter, nitrogen, and carbon and elevated post-fire soil temperature. 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 used a randomized complete block design with five study sites located in southeast Oregon. The area was burned in a wildfire (2007) and reseeded 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 2008 in burned subcanopy and interspace microsites. Non-native perennial grasses had greater densities than native species (P, 0.001) and were six times more abundant in burned subcanopies compared to burned interspaces (P, 0.001). Density of natives in burned subcanopies was 24-fold higher than burned interspaces (P5 0.043). Seedlings were taller in burned subcanopies compared to burned interspaces (P5 0.001). Subcanopy microsites had more reproductive seedlings than interspace microsites (P, 0.001). Our results suggest that under the fire conditions examined in this study, pre-burn shrub cover may be important to post-fire restoration of perennial grasses. Determining the mechanisms responsible for increased seeding success in subcanopy microsites may suggest tactics that could be used to improve existing restoration technologies.