PS 12-107 - Legacies of shrub removal shape initial stages of post-fire steppe recovery

Monday, August 15, 2022

5:00 PM – 6:30 PM EDT

Located in: ESA Exhibit Hall

Presenting Author(s)

Joshua B. Grinath

Assistant Professor
Idaho State University, United States

Coauthor(s)

PK

Patricia Kerner

Idaho State University, United States
KL

Kathleen A. Lohse

Idaho State University
Pocatello, ID, United States
KT

Kathryn Turner

Idaho State University, United States
BF

Bruce Finney

Idaho State University, United States
KR

Keith Reinhardt

Idaho State University, United States

Background/Question/Methods

Vast areas of the western US have burned in recent years, and the need to anticipate how ecosystems will recover is growing along with the threat of wildfire. Of particular need is an understanding of how ecological memories of past disturbances shape post-fire trajectories of ecosystem recovery via lasting impacts on the abiotic and biotic environment. However, many legacy effects occur over long time scales that are difficult to study, especially in combination with wildfire. For example, dominant shrub removal is a common rangeland management practice that increases soil water availability and encourages exotic plant invasion, effects that last years as shrubs slowly recover. Such legacy effects may persist following wildfire, favoring invasive species and compromising revegetation efforts, but these effects are unclear. In this study, we build on over two decades of research on shrub removal to evaluate legacy effects on a sagebrush steppe ecosystem following wildfire. From 1997-2010, researchers at Idaho State University conducted a shrub removal experiment that had lasting effects on soils and plants. The experimental site (Pocatello, Idaho) burned during summer 2020, and we used this opportunity to evaluate whether legacies of shrub removal impact post-burn soil properties and plant assemblages.

Results/Conclusions

We found clear evidence for shrub removal effects on the post-burn ecosystem, even though ten years had passed since shrub removal was last maintained. In spring following the fire, there were significantly lower ammonium and higher nitrate levels in soils from shrub removal plots compared to control plots. During the ensuing summer, we found that soil nitrate levels were lower and soil electrical conductivity tended to be higher in shrub removal plots. Also, total plant cover was much greater in shrub removal plots. This response was largely driven by invasive plant species, especially cheatgrass (Bromus tectorum) which in the shrub removal plots accounted for 55.1% of all pin counts used to measure plant cover, while cheatgrass represented only 2.3% of pin counts in the control plots. Germination of soil cores collected two months post-fire revealed that shrub removal plots had seedbanks with greater total seed abundances than control plots and that were largely composed of invasive species. Altogether, these results indicate that shrub removal has lasting effects on soil properties and seedbanks that favor invasive plants in post-burn environments. These and other ecological memories must be considered in post-fire ecosystem management to understand trajectories of community reassembly.