Fire is an integral part of the ecological process of many plant communities in the Bighorn Basin. Several vegetation types in the basin have developed under a regime of intermittent fire and have adapted to the effects of fire in some way. Fire behavior within each vegetation type varies with many factors, including topography and site productivity. Highly productive sites, such as north slopes, generally have more biomass and, therefore, can carry fires better than less productive sites.
The BLM fire management program focuses on two categories of wildland fire - wildfires (previously referred to as unplanned ignitions) and prescribed fires (previously referred to as planned ignitions). Within the Planning Area, the BLM manages wildfires and prescribed fires in accordance with the Northern Zone Fire Management Plan (FMP) (BLM 2004a). The Northern Zone FMP was prepared in response to the Federal Wildland Fire Management Policy of 2001, which directs BLM field offices to have an FMP for all areas with burnable vegetation, a program review in 1995, and the threats posed by current fuel loading in the Intermountain West. According to the Federal Wildland Fire Management Policy of 2001, an FMP must provide for firefighter and public safety; include fire management strategies, tactics and alternatives; address values to be protected and public health issues; and be consistent with resource management objectives, activities of the area, and environmental laws and regulations.
The BLM Wyoming Northern Zone is in the Big Horn Basin Fire Planning Unit. The Big Horn Basin Fire Planning Unit consists of the Bighorn National Forest, Shoshone National Forest, Wind River Indian Reservation, and the Bighorn Canyon National Recreation Area (BLM 2004a). The BLM has interagency cooperative agreements with the agencies responsible for managing these areas. The Cody Interagency Dispatch Center coordinates fire suppression operations (BLM 2004a).
In accordance with Guidance for Implementation of Federal Wildland Fire Management Policy (USFS et al. 2009), the BLM will continue interagency and local cooperation to set priorities for fire management planning, preparedness, prevention, suppression, use of wildland fire, restoration and rehabilitation, monitoring, research, and education. Interagency cooperation ensures accountability by instituting meaningful performance measures and monitoring results.
Table 3-18 lists the annual average number of acres of wildfires, prescribed fires, and mechanical and chemical treatments in the Planning Area. The acreage burned has been calculated as an annual average since 1981 for both prescribed fires and wildfires. The BLM also modifies fuels with mechanical and chemical treatments in the Planning Area. The BLM did not use mechanical and chemical treatments to reduce fuel loads in the Planning Area until 2002, when the National Fire Plan began making funds available for these kinds of projects.
Table 3.18. Wildfires, Prescribed Fires, and Mechanical and Chemical Treatments in the Planning Area
| Wildfire | Prescribed Fire | Mechanical Treatment | Chemical Treatment | |
| Average Acres Per Year | 5,881 | 3,294 | 1,408 | 250 |
| Source: BLM 2009k | ||||
Title 1 of the Healthy Forest Restoration Act of 2003, requires identification and mapping of the fire regimes and fire regime condition classes on BLM-administered lands at risk for wildfires and insect or disease epidemics. Fire policy requires current and desired resource conditions related to fire management be described on scales consisting of three condition classes of ecosystem health and five fire regimes. The Fire Regime Condition Classification System (FRCC) classifies existing ecosystem conditions to determine priority areas for treatment (Table 3–19). The FRCC measures the vegetation’s degree of departure from reference conditions, or how different the current vegetation condition is from a particular reference condition. This could result in changes to key ecosystem components such as vegetation characteristics; fuel composition; fire frequency, severity and pattern; and other associated disturbances (e.g., insect- or disease-related mortality). FRCC involves two pieces of information - (1) the historic fire regime and (2) the condition class. Fire regime is the inferred historic fire return interval and severity on a given landscape; condition class is the departure of the given area from the historic fire interval. Fire regimes in the Planning Area, by vegetation type, appear in the Northern Zone FMP (BLM 2004a).
Table 3.19. Fire Regime Condition Classification System
| Group | Frequency | Severity | Severity Description |
|---|---|---|---|
| I | 0 to 35 years | Low/mixed | Generally low-severity fires replacing less than 75% of the dominant overstory vegetation; can include mixed-severity fires that replace up to 75% of the overstory. |
| II | 0 to 35 years | Replacement | High-severity fires replacing greater than 75% of the dominant overstory vegetation. |
| III | 35 to 100 years | Mixed/low | Mixed-severity with less than 75% of the overstory vegetation replaced. |
| IV | 35 to 200 years | Replacement | High stand replacement-severity fires with greater than 75% of the dominant overstory vegetation replaced. |
| V | 200+ years | Replacement/any severity | High (stand replacement) severity. |
| Source: DOI and the Nature Conservancy 2008 | |||
Condition class describes ecosystem health as follows:
Condition Class 1 . For the most part, fire regimes in this Fire Condition Class are within historical ranges. Vegetation composition and structure are intact. Therefore, the risk of losing key ecosystem components from the occurrence of fire remains relatively low.
Condition Class 2 . Fire regimes on these lands have been moderately altered from their historical range by increased or decreased fire frequency. A moderate risk of losing key ecosystem components has been identified on these lands.
Condition Class 3 . Fire regimes on these lands have been substantially altered from their historical return interval. The risk of losing key ecosystem components from fire is high. Fire frequencies have departed from historical ranges by multiple return intervals. Vegetation composition, structure, and diversity have been substantially altered. Consequently, these lands have the greatest risk of ecological collapse.
The Planning Area is broken up into five Fire Management Units (FMUs) - Absaroka Front, Basin Bottom, Foothills Sagebrush, Nowater, and West Slope Bighorn. An FMU is a geographic area with similar plant communities and resource and fire management objectives. For example, portions of the Nowater, Foothills Sagebrush, and the lower elevations of the West Slope Bighorn FMUs have extensive areas of cheatgrass invasion in burned and unburned areas that are important greater sage-grouse habitat. For these reasons, the management prescription for these areas calls for aggressive fire suppression and rehabilitation of burned areas. In contrast, higher-elevation areas in the West Slope Bighorn FMU employ less aggressive suppression techniques because of inaccessible rugged terrain and the largely beneficial effects of fire on plant communities and overall watershed condition. General management guidelines for fire suppression are found in the Northern Zone FMP (BLM 2004a).
Table 3-20 provides a coarse-scale landscape-level assessment of condition classes for the area covered by the Northern Zone FMP based on University of Wyoming GAP Analysis Program Data (University of Wyoming 1994), ground-truthing, Risk Assessment Mitigation Strategy (RAMS) data, and expert input. Based on this assessment, it was estimated that nearly 35 percent of the FMUs in the Planning Area are in FRCC Classes 2 and 3.
Table 3.20. Acreages of Fire Regime Condition Classes by Fire Management Unit, 2007
| Fire Management Unit | Fire Management Unit Description | Condition Class 1 | Condition Class 2 | Condition Class 3 | Total Acres In FMU | |||
|---|---|---|---|---|---|---|---|---|
| Acres | Acres | Acres | ||||||
| Absaroka Front | Mountain lands bounded on the east by United States Highway 120, on the west by United States Forest Service-administered land, on the north by the state line, and on the south by the Wind River Reservation Desert lands west of the Bighorn River. | 667,352 | 64 | 273,193 | 26 | 108,595 | 10 | 1,049,140 |
| Basin Bottom | Largely Desert Salt Shrub lands east of the Bighorn River bounded on the north by the state land and the Foothills Sagebrush FMU to the south and west. | 796,943 | 78 | 206,346 | 20 | 16,960 | 2 | 1,020,249 |
| Foothills Sagebrush | Sagebrush zone east of United States Highway 120 and west of the Basin Bottom FMU. | 1,274,631 | 78 | 200,705 | 12 | 160,703 | 10 | 1,636,039 |
| Nowater | Bounded on the south by the Cooper Mountains, the west by the Bighorn River, and the north and west by the west slope of the Big Horn Mountains. | 347,034 | 33 | 388,071 | 37 | 313,525 | 30 | 1,048,630 |
| West Slope Bighorn | Lands bounded on the north, west, and east by the Bighorn and Nowood Rivers, and the south by the Copper Mountains. | 988,107 | 65 | 310,801 | 20 | 221,269 | 15 | 1,520,177 |
| Totals | 4,074,067 | 65 | 1,379,116 | 22 | 821,052 | 13 | 6,274,235 | |
| Source: BLM 2008c FMU Fire Management Unit | ||||||||
The challenges of fire and fuels management center on preventing wildfires and adequately addressing stabilization and rehabilitation efforts after wildfires. Fire size and frequency is likely to increase, due primarily to the spread of cheatgrass, but also due to mixed conifer forests affected by bark beetles and blister rust. The spread of cheatgrass, and the associated increase in wildfires, threatens greater sage-grouse and other sagebrush habitat-dependent species. Despite treatment efforts, cheatgrass has recently become more widespread and has extirpated native vegetation in some areas (BLM 2009b).