David O. WallinDepartment of Environmental Sciences

Huxley College of the EnvironmentWestern Washington University

Bellingham, WAdavid.wallin@wwu.edu

360-650-7526

Tree removalTree removalRoadsRoads

Timber Harvest ImpactsTimber Harvest Impacts

Forest Hydrology: the basicsIn a forested In a forested

environment, with environment, with no disturbance, no disturbance, surface runoff is surface runoff is minimalminimal..

Forest Hydrology: the basicsIn a forested In a forested

environment, with environment, with no disturbance, no disturbance, surface runoff surface runoff does not occurdoes not occur

EvapotranspiratioEvapotranspiration (water loss to n (water loss to the atmosphere) the atmosphere) accounts for accounts for about 50% of about 50% of total annual total annual precipitationprecipitation

Forest Hydrology: the basicsIn a forested In a forested

environment, with no environment, with no disturbance, surface disturbance, surface runoff does not occurrunoff does not occur

Evapotranspiration Evapotranspiration (water loss to the (water loss to the atmosphere) atmosphere) accounts for about accounts for about 50% of total annual 50% of total annual precipitationprecipitation

Tree removal Tree removal significantly reduces significantly reduces water loss to the water loss to the atmosphereatmosphere

Forest Hydrology: Effects of Timber HarvestingTree removal reduces evapotranspiration Tree removal reduces evapotranspiration

resulting in much higher soil water content:resulting in much higher soil water content:Increased mass of soil profileIncreased mass of soil profileHigher pore water pressure increases lubricationHigher pore water pressure increases lubrication

Following tree removal, residual roots decay Following tree removal, residual roots decay resulting in reduced support for soil profileresulting in reduced support for soil profile

Net result is an increased risk of landslidesNet result is an increased risk of landslides

“Hydrologic Maturity”These recently harvested stands are referred to as being

“hydrologically immature.”

Based on the DNR, the effects described above persist for about 40 years following a timber harvest.

DNR manages their timber land on a 60 year rotation.

This means that, on lands that are actively managed for timber production, about 2/3rds (40/60) of the landscape will have an increased risk of landslides at any given time.

Hydrologic Maturity: How much area is “at risk.”The area proposed for reconveyance includes

about 8400 acres. Of this, about half is currently “off-limits” to timber harvesting under the Lake Whatcom Landscape Plan. Hence about 4200 acres are actively managed for timber production.

This means that, under the landscape plan, about 2700 acres (2/3rds of 4200) within the reconveyance area would always be maintained under conditions that have an elevated risk for landslides.

Roads and Flow Routing

A: Subsurface flow interceptionB: Surface flow on roadsC: Flow routing along ditches to streamD: Flow along roads to streamE: Flow from relief culverts can deliver water to streams

Roads and Slope Failure

A: Cutslope slidesB: Fillslope slidesC: Debris flow that pass roadsD: Fillslope or culvert failures that become debris flows

By how much is the risk increased?Over 30 years of research has shown that

timber harvesting and roads increase the risk of landslides by a factor of 2X to well over 100X.

Forest practices are constantly evolving and many changes have been implemented to reduce the risks.

Even the most recent publications (2007) document elevated risk even with improved timber management practices

How will reconveyance help?No new timber harvesting. Gradual

elimination of hydrologically immature stands.

Approximately 20 miles of new roads planned by DNR under the current landscape plan will not be constructed.

Approximately 9 miles of existing roads will be decommissioned.

What about Recreational Impacts Associated with Reconveyance?There is no scientific literature to support the

contention that recreational impacts will in any way come close to the known and well documented effects of timber harvesting.

There will be some minimal impacts associated with traffic and trail use but the current park plan takes steps to mitigate these impacts.

Slides triggered on slopes above buffered stream.

Note debris flow of sediment has passed through trees above and flowed down the stream channel.

Area of previous photograph.

Path of debris flow further down the slope. Small slides can cause huge sediment loading.

This slide destroyed two homes

Slides along logging road

Older slide

Slides along logging roads triggered a debris flow

Note multiple failures in young stand, but none in older mature stands.