Cedar River Fire Hazard Analysis: Assessment and Management Alternatives

Project Description

This project (1) characterized vegetation patterns and distribution, (2) described and quantified current and potential wildfire hazard, (3) developed and simulated potential thinnings and surface fuel treatments to identify options for addressing and minimizing fire hazard, and (4) made maps of current and predicted fire hazard.

The Fire and Fuels Extension to the Forest Vegetation Simulator (FFE-FVS) was used to quantify fuels for different forest classifications and to predict the characteristics and effects of a fire should one occur during warm, dry weather conditions.

Purpose and Scope

Fire hazards were assessed to help reconcile ecological restoration efforts and fire management with respect to fuel loadings across the landscape:

• Characterized vegetation patterns and distribution.
• Described and quantified current and potential wildfire hazard.
• Developed and simulated potential thinnings and surface fuel treatments to identify options for addressing and minimizing fire hazard.
• Developed maps of current and predicted fire hazard.

Fuel decomposition was measured to provide fine-scale temporal data on fuel succession that will inform the coarse-scale assessment of fire hazard for different management options.

• Quantify fuelbed characteristics (e.g., fuelbed loadings and fuelbed depth) in stands that were thinned at different times.
• Examine the effect of surface fuel treatments on fuelbed characteristics.
• Estimate fuel loading residence time.

Methods

The Fire and Fuels Extension to the Forest Vegetation Simulator (FFE-FVS) was used to quantify fuels for different forest classifications and to predict the characteristics and effects of a fire should one occur during warm, dry weather conditions.

Transects were done to measure fuelbed loading (i.e., tons per acre) and fuelbed depth in stands treated from 2001 to 2005. Mean loading per size class and mean fuelbed depth were calculated in DRA program (see figure below). A Pacific silver fir decomposition constant or fractional loss rate (percentage lost per year) was used to estimate the residence time of fuel loading after treatment.

Implementation

Specifically, the assessment (1) described vegetation patterns and distribution, (2) described and computed current and potential wildfire hazard, (3) developed and simulated potential thinning densities and surface fuel treatments to identify options for addressing and minimizing fire hazard, and (4) developed maps of current and predicted fire hazard.

The Fire and Fuels Extension to the Forest Vegetation Simulator (FFE-FVS) was used to estimate fuels for different forest types and to predict the characteristics and effects of a fire should one occur during warm, dry weather conditions.

Key Findings

• Fire hazard will increase in the many younger stands in the lower Cedar River Municipal Watershed (CRMW) over the next 30 years, or longer, as the forest understory becomes established and stand structure becomes stratified.
• Succession will lower canopy base heights, with predicted fire type gradually shifting from surface fire to passive or active crown fire.
• Fire hazard is high in the upper watershed and will remain high for the next 30 years, particularly in areas recently thinned by machines to remove trees that may have otherwise died naturally as a result of fires.
• It will take many decades for the height to the bottom of the tree canopy to increase and for surface fuels (including slash) to decompose to realize a significant reduction in fire hazard.
• Thinning to reduce stand densities alone generally does not decrease predicted postfire basal area mortality, although it may increase torching and crowning activity in some cases.
• Thinning, followed by removal of slash generated from thinning operations, usually causes models to predict a change from active crown fire down to passive crown fire or surface fire. There is no threshold thinning density that can be implemented to reduce basal area mortality projected in the CRMW.
• Management alternatives for treating slash and reducing the potential for fire-caused tree mortality include reduction of slash on site (e.g., chipping) or removal of slash from the site.

Project Deliverables

A final report was submitted to the city of Seattle.