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Do post-fire fuel treatments and annual grasses interact to affect fire regimes in the Great Basin? - Final Report to the Joint Fire Science Program

Author(s): Beth A. Newingham, Eva K. Strand
Year Published: 2018

Shifting climates and annual grass invasions have contributed to the increased number and size of fires in the western United States costing millions of dollars in fire suppression and post-fire rehabilitation. Post-fire rehabilitation implements fuel treatments, such as aerial and drill seeding, to control annual grass invasion and alter fuels and subsequent fire behavior and effects. However, the effectiveness of these fuel treatments at a landscape scale is virtually unknown for Great Basin rangelands. Additionally, little is known about how grazing practices after rehabilitation affect perennial grass establishment and survival. Post-fire rehabilitation treatments, post-fire grazing, as well as burn severity, will likely affect plant responses to these disturbances. This project investigated 1) the impact of post-fire fuel treatments (seeding) on post-fire community trajectories, fuels composition, and fire return intervals, 2) the effects of livestock grazing on seedling and community recovery, and 3) how burn severity relates to post-fire recovery in the Great Basin. To assess the effects of aerial and drill seeding on plant community trajectories, fuel composition, and fire regimes, we collected geospatial datasets spanning 209,000 ha of sagebrush steppe on BLM land in southern Idaho. In the field, we sampled fuel and plant community composition by sampling 68 sites in 2014 and 2015 across areas that had burned 1-6 times and had no, aerial, drill, or aerial + drill seeding. We found that 1) fire and rehabilitation shaped plant communities, 2) drill seeding after multiple fires in dry, low elevation sites prevented conversion to cheatgrass-dominated systems, 3) drill seeded sites had fewer fires and increased in fire frequency more slowly than aerial seeded sites, 4) the on-the-ground conditions that led to the decision to aerially seeding after a fire led to more frequent and numerous fires. To examine the effects of post-fire grazing on seedling establishment, we varied surrounding plant communities around target bunchgrasses by removing either neighboring adult or seedling grasses. Grazing was simulated by clipping plants either in the dormant or growing season one or two years after fire. Timing of senescence, plant growth and survival were measured for three years after wildfire. We found that 1) seedling removal delayed senescence and decreased seedling cover and density, 2) spring defoliation led to negative effects for both within-and across-season metrics, 3) delaying defoliation from year one to two decreased negative effects on seedling growth, and 4) seedling survival did not vary by either neighbor removal or defoliation. We also used the Monitoring Trends in Burn Severity (MTBS) database to 1) quantify area burned in the Great Basin and identify regional hotspots, 2) characterized burn severity classes across vegetation types, and 3) examine cover types in relation to burn severity one year after fire. We found that 1) over 8 million hectares has burned with some areas burning seven times from 1984-2016, 2) burn severity values varied across vegetation type, and 3) annuals and char increased with burn severity while soil decreased with increasing burn severity. Our results provide managers with knowledge of 1) the effects of post-fire fuel treatments on plant community trajectories and subsequent fire regimes across climate and environmental gradients, and 2) the effects of grazing on perennial bunchgrass establishment after post-fire seeding, and 3) the use of burn severity indices in rangelands. Results will provide insight into the most effective use of limited fiscal and labor resources and contribute to maintaining sustainable rangelands that are resilient to fires and resistant to annual grass invasion.

Citation: Newingham, Beth A.; Strand, Eva K. 2018. Do post-fire fuel treatments and annual grasses interact to affect fire regimes in the Great Basin? - Final Report to the Joint Fire Science Program. JFSP Project No. 14-1-01-7. Reno, NV: USDA Agricultural Research Service. 33 p.
Topic(s): Fire Effects, Fuels, Recovery after fire, Restoration
Ecosystem(s): None
Document Type: Technical Report or White Paper
NRFSN number: 18252
FRAMES RCS number: 56677
Record updated: Nov 5, 2018