Controls on Fire in the Pacific Northwest: Climate, Fuels, and Land

Management

Dave Peterson & Don McKenzieForest Service – PNW Research Station

Pacific Wildland Fire Sciences LabUW College of Forest Resources

Assumptions about fire and fuels

“Historic data show that wildfires are getting larger and becoming more intense.” – Forest Service Southwest Region web site

Assumption 1: Fires are larger and more intense than earlier in the 20th century

Assumption 2: The size and intensity of wildfires are controlled by fuel accumulations

What causes large and severe fires?

Annual area burned – 11 Western states

1945 decrease Effective suppression?

1975 increase Fuel build-up?

Acr

es b

urn

ed

1945 decrease Effective suppression?

1980 increase Fuel buildup?

Annual area burned – 11 Western states

1945 decrease Effective suppression?

1975 increase Fuel build-up?

Acr

es b

urn

ed

cool warm cool warm cool?

Pacific Decadal Oscillation phase

Years with fire area > 80,000 hectares

National Forest data, 1916-2002

Warm-phase PDO Cool-phase PDO

Idaho 14 7

Oregon 14 5

Washington 10 2

TOTAL 38 (73%) 14 (27%)

Climatology affects wildfire in the Pacific Northwest

Extreme wildfire years are forced at least in part by antecedent drought and summer blocking in the 500-hPa height field.

From Gedalof et al. (2004), Ecological Applications in press

M ay

Septem ber

August

July

June

Limiting factors vary by ecosystem

Fuels

Clim

ate

Boreal Subalpine Lodgepole pine Ponderosa pine (PNW) Calif. mixed conifer Ponderosa pine (SW) Oak woodland Chaparral

Traditional perspective:pyrophobia

Revisionist perspective:pyrophilia

But many are still in denial

Managing fire and fuels is mostly a sociocultural challenge

Federal fire suppression cost in 2002 = $1.6 billion (~$500 per ha burned)

Fuel structures can be complex

Current conditions Target (historical) conditions

Silviculture meets fire science

Scientific principles of fuel treatment:

• Raise canopy base height

• Reduce canopy bulk density

• Reduce canopy continuity

AND reduce surface fuels

Principle #1 – Canopy base height

Dense stand with understory

-------- Canopy base height < 2 m

Treated stand after thinning from below

-------- Canopy base height > 6 m

Principle #2 – Canopy bulk density

Dense stand with understory

Canopy BD > 0.30 kg m-3

Treated stand after thinning from below

Canopy BD < 0.10 kg m-3

Principle #3 – Canopy continuity

Dense stand with understory

Treated stand after thinning from below

Surface fuels must be treated following removal of trees

Analysis of stand development assists treatment scheduling

2005 2010 2015 2020

No treatment

Thinning

Silviculture meets fire science

Many constraints to effective fuel treatments

Need lots of tree removal

Lack of markets for small wood

EIS, EA and other review

Litigation

Risk of escaped fire

Scheduling (~20-year cycle)

A rational approach to fire management and fuel reduction: Focus on the wildland-urban interface

Benefits

Focus fuel treatment area

Protect high economic value

Reduce fire suppression cost

Respond to political concern

Create defensible zones

Reduce liability

Toward science-based firemanagement and policy

Develop guidelines that quantify the effects of fuel treatments on fire behavior

Integrate scientific information and human values(ecological + cultural restoration)

Develop a rational economic approach

Educate the public on living with fire

The restoration pathway will vary