Shrub Microsite Influences Post-Fire Perennial Grass Establishment

Authors: Boyd, Chad; Davies, Kirk

Submitted to: Eastern Oregon Agricultural Research Center
Publication Type: Experiment Station
Publication Acceptance Date: 3/1/2009
Publication Date: 6/1/2009
Citation: Boyd, C.S., Davies, K.W. 2009. Shrub microsite influences post-fire perennial grass establishment. p. 74-79. In: Range Field Day 2009: Progress Report. Oregon State University Special Report 1092. Eastern Oregon Agricultural Research Center.

Interpretive Summary: Woody plants can cause localized increases in resources (i.e. resource islands) that persist after fire and create a heterogeneous environment for restoration. We tested the hypothesis that burned subcanopies (formerly under shrubs, Artemisia tridentata ssp. wyomingensis Welsh) would have increased seeding establishment (density) and performance (height) of post-fire seeded perennial bunchgrasses compared to burned interspaces. Results indicated that one year post-seeding subcanopy microsites had dramatically higher seedling density and taller seedlings than interspace microsites and that seedling density was almost eight times higher for non-native as compared to native seedlings. Our data underscore the importance of shrub conservation for providing microsites with elevated chances of restoration success, particularly in low elevation sagebrush communities where establishing perennial grasses can help reduce susceptibility to invasion by exotic annual grasses

Technical 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. 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 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. 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 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. Others have found that subcanopies have increased soil organic matter, nitrogen and carbon (i.e. resource islands) and elevated post-fire soil temperature.