Lolo National Forest
U.S. Forest Service
Missoula, MT 59804
PARK CREEK POST-FIRE BAER ASSESSMENT REPORT SUMMARY
FS-2500-8 Burned-Area Report: Watershed Analysis, Condition, and Response
The Park Creek Fire, which was ignited by a lightning strike on July 14, 2017, is located on the Lincoln Ranger District on the Helena-Lewis and Clark National Forest (NF), approximately two miles north of the town of Lincoln. It began as two separate fires: the Arrastra Creek fire and the Park Creek Fire. Driven by steep terrain, high temperatures, low relative humidity, high pre-existing tree mortality, and gusty winds, the fires spread and joined together when they burned into the Stonewall drainage on August 16, 2017. As of August 27, 2017, the fire burned 13,572 acres on Forest Service System (NFS) land, and 25 acres on private land. The fire continued to grow after this date, but areas that burned after August 27 will be addressed in future supplemental analyses.
The upper elevation areas of the fire are dominated by subalpine habitat types. Intermixed subalpine fire-white bark pine types occur in a small percentage of the high elevation areas. Douglas-fir habitat types dominate at mid-to-lower elevations. Within the fire area, species such as lodgepole pine, ponderosa pine, quaking aspen, western larch and whitebark pin occur as seral species. The rest of the fire area is covered by rock, grass, meadows and a small component of water.
This burned area was surveyed and assessed by a BAER team comprised of Forest Service scientists and specialists. The BAER team evaluated the burned watersheds to determine post-fire conditions, and identify values-at-risk such as threats to human life and safety, property, and critical natural and cultural resources. In addition to these critical values, other threats were also assessed, such as the risk for increased post-fire flooding, sediment flows, rock slides, hazard trees and noxious weed spread.
The BAER assessment team’s analysis of the burned area within the Park Creek Fire and recommended emergency treatments are documented in a Forest Service (FS) Burned-Area 2500-8 Report. This report was submitted to the Northern Region (Region 1) Regional Forester by the Forest Supervisor for the Helena-Lewis and Clark NF for review and funding. The following is a summary of the BAER team’s burned area analysis and report for the Park Creek Fire:
- 4 sub-watersheds were analyzed and modeled to compare pre-fire conditions to post-fire predicted response: Arrastra Creek, Beaver Creek, Copper Creek, and Keep Cool Creek.
- There are 18 miles of perennial stream, and 19.8 miles of intermittent streams.
- There are 23.5 miles of roads, 11.6 miles of trails.
- There are 1,321 acres with high hazard ratings for soil erosion, 7,766 acres with moderate ratings for soil erosion, and 2,426 acres with low hazard ratings for soil erosion.
- There are about 3,936 (31%) unburned acres, 5,108 (40%) acres of low soil burn severity, 3,153 (24%) acres of moderate soil burn severity and 653 (5%) acres of high soil burn severity.
- There are 3,806 acres of water repellent (hydrophobic) soils. Hydrophobic soil conditions are common within moderate and high burn severity areas and rare in the low burn severity areas.
Hydrophobic soil conditions may be the result of two processes; the first is a natural accumulation of waxy resins at the soil surface as plant litter and organic material decomposes. The second is a result of hot temperatures volatilizing organic compounds, destroying soil structure and redepositing water-resistant compounds deeper in the soil profile, and is common of areas of high and moderate severity burn. Increased run-off due to hydrophobic conditions is reflected in the peak flow analysis of the watersheds. Hydrophobic layers usually take 6 months to 2 years to break down. Plant root development, soil microbial activity, and freeze-thaw cycling all contribute to the degradation of hydrophobic conditions. Recovery of pre-fire slope stability and watershed hydrologic response is dependent on many factors and typically occurs within 3-5 years following the fire. Recovery of high burn severity areas is slower because little or no vegetative ground cover remains and soils may be susceptible to erosion.
The different soil burn severity categories reflect changes in soil properties and are a key element BAER specialists use to determine if post-fire threats exist. The distribution of unburned, low, moderate, and high soil burn severity levels become a baseline for resource specialists to monitor changes in soil hydrologic function and vegetative productivity as the burned watersheds recover.
High and moderate soil burn severity categories often have evidence of severe soil heating and the consumption of organic material. Soil seedbank and water infiltration characteristics are reduced in areas that have burned at high or moderate severity. Natural recovery is slower where little or no vegetative ground cover remains, and increased surface water runoff will result in increased soil erosion at these sites. Areas of moderate soil burn severity may have viable roots and some soil cover, but may still be vulnerable to erosion on steep slopes. The low to very low soil burn severity areas still have good surface soil structure, intact fine roots and organic matter, and should recover more quickly once revegetation begins and the soil cover is re-established.
With the high incidence of post-fire water repellency and fine soil textures, hillslopes are anticipated to be highly susceptible to post-fire run-off and reduced infiltration. Because much of the burned area is on steep slopes with large rock fragment amounts and shallow depths to bedrock, an increased post-fire run-off response and elevated erosion response can be expected if a strong rain event were to occur over the next 3-5 years. High soil rock content is expected to result in elevated but tolerable post-fire soil erosion, however steep slopes, surface hydrophobicity, and reduced vegetative cover and transpiration will likely result in substantially increased post-fire run-off and elevated stream flows.
Identified Values-at-Risk, Threats, and Emergency Conditions
Summer thunderstorms have the greatest likelihood of generating large run-off and soil erosion events. If large summer thunderstorms occur, the primary values-at-risk within the burned area are transportation infrastructure (roads, trails, and culverts), water quality, native fisheries (Bull trout and Westslope Cutthroat trout), native vegetation, and heritage sites. Several crossings affected by the fire have been recently upgraded in association with South West Crown of the Continent (SWCC) treatment and represent significant government investment in both Forest Service infrastructure and aquatic habitat improvement for Bull trout and Westslope Cutthroat trout.
Emergency post-fire conditions for the Park Creek Fire were identified by the BAER team for the following on-forest values-at-risk:
Human Life and Safety: There are potential impacts to the safety of Forest visitors and employees entering the burned area. Generally, increased risk occurs within or directly down-slope from high and moderate soil burn severity areas. Potential threats and risks for the general public to be impacted are from rolling rocks, flash flooding, flooding, debris flows, falling hazard trees, and loss of ingress/egress access.
Property: There are potential impacts and threats to Forest Service System roads (Road 4106 and Road 607), trails (Trail 418), and associated infrastructure. There is high potential for failure to road drainage due to increased post-fire flows and thus potential for erosion of trail surface tread and sediment delivery to streams. Soil deposition on trail surfaces from adjacent hillslopes may also occur. The potential threats are from increased water, sediment flows, soil erosion, loss of capacity, and overtopping and breaching during flood events.
Natural Resources: There are potential threats and risks to water quality, stream crossings, fish communities and habitat, native plant vegetation recovery, increased spread of noxious weeds, reduced soil productivity and hydrologic function from increased sediment flows and accelerated erosion.
Cultural/Heritage Resources: High risks potentially exist to historical and cultural resources due to the increased threat of flooding, deposition, and erosion from upslope burned areas due to loss of pre-fire ground cover.
Emergency Stabilization Treatments
The BAER assessment team’s emergency stabilization objectives for the burned areas are to protect, mitigate and reduce the potential for identified post-fire threats, including increased soil erosion/sediment yield and water run-off on steep slopes, for:
1. Human life, safety, and property within and downstream of the burned area;
2. Forest Service infrastructure and investments such as roads and trails;
3. Critical natural and cultural resources; and
4. Native and naturalized plant communities from new noxious weed infestations.
In addition to on-Forest efforts to reduce the threats to National Forest values and resources, the BAER team and the Forest will warn users of Forest Service roads and trails of hazards present in the burned area, and communicate and coordinate with other agencies such as the National Resource Conservation Service (NRCS), National Weather Service (NWS), State of Montana, local counties, and cities to assist private entities and communities including private residents and businesses to achieve post-fire recovery objectives.
The following post-fire emergency stabilizations measures and treatments have been approved:
- Conduct early detection surveys and rapid response eradication with herbicide of noxious weeds along areas disturbed by fire suppression activities, equipment concentration points, high and moderate soil burn severity areas near these fire suppression disturbed areas, and other high priority areas, to reduce the potential for impaired native vegetative recovery and the introduction and spread of invasive weeds. Total treatment area comprises 270 acres.
- Provide for worker safety during implementation of road and trail drainage improvements by removing hazard trees along the roads and trails where treatment crews are operating for extended periods of time.
- Storm-proof and stabilize Forest Service (FS) System transportation roads and crossings with improved water drainage structures and features to prevent damage resulting from post-fire watershed conditions such as soil erosion, storm water run-off, and public safety hazards to improve the safety of forest visitors and employees. Conduct storm patrol monitoring to ensure road treatments are functioning as intended.
- Storm-proof and stabilize approximately 9 miles of burned area FS trails with improved water drainage structures and features to prevent damage resulting from post-fire watershed conditions. Conduct post-storm inspection of problem areas and implement emergency repairs if needed.
- Install burned area warning signs to caution forest visitors traveling and recreating within the burned areas.
- Cultural resource concerns will be evaluated at a later time within the burned area to determine if future management actions are required.
- Continue to communicate risks to the public, community groups, and cooperating agencies.
- Continue to work and coordinate with interagency cooperators, partners, and affected parties and stakeholders.
- Assist cooperators, including local, state, and federal agencies with the interpretation of BAER assessment findings to identify potential post-fire impacts to communities and private land owners, domestic water supplies, and public utilities (such as power lines, state roads, county roads, and other infrastructure).
SPECIAL NOTE: Everyone near and downstream from the burned areas should remain alert and stay updated on weather conditions that may result in heavy rains over the burn scars. Flash flooding may occur quickly during heavy rain events. Current weather and emergency notifications can be found at the National Weather Service (www.weather.gov/mso/) website.