Shrub Microsite Influences Post-Fire Perennial Grass Establishment

Abstract

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 (P=0.043). Seedlings were taller in burned subcanopies compared to burned interspaces (P = 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.