Logging and Water Yield

Kim Raby GEOG 3511

Denver Post, 11/10/02

Coon Creek, WY 4,100 acre demonstration project illustrates patch cuts in lodgepole pine forest 1990s research says clearcut increased spring runoff by 17 percent

Is this the right decision for Colorado?

What’s happening: Snow collects in clearings instead of being intercepted and evaporating before it can become overland flow, yielding more runoff Can it work? Is it worth it?

Interception

• • Sublimation is greater from vegetation than from ground Higher temperature on leaf surface Greater surface area Trees radiate longwave radiation Higher air temperature surrounding snow Increase in SVP Cut trees to decrease interception Increase snowpack volume Increase water yield

Summary

Summary of 50 years of clearcutting and thinning experiments at small scale Fraser Experimental Forest The more area removed, the greater the SWE increase If 100 percent of basal area is removed, ~35 percent increase in water yield Yields have been long lived but clearcuts must be maintained Source: Meiman 1987

Large-Scale Replication

Goal of the Coon Creek Water Yield Augmentation Pilot Project: to test whether results demonstrated at small scale experimental basins (like Fraser Experimental Forest) can be duplicated to operational/large watershed scale Control: Upper East Fork Treatment: Coon Creek Maximum mean daily discharge comparison Daily mean flow increased 11% with treatment Source: Troendle et al. 2001

Increased Water Yield

Control: North Fork of Dry Creek Treatment: Brownie Creek Slopes are significantly different (p=0.0001) Flow during the two periods is significantly different ~70 percent increase in water yield relative to control after harvesting 25 percent of Brownie Creek 24% increase 91% increase Source: Troendle and Stednick 1999

Peak SWE Increases

Fraser Experimental Forest Increased accumulation after plot cut averaged 5.8 inches of water or 45 percent more than upwind plot No significant difference between upwind and downwind forest plots Source: Meiman 1987

Area of Clearcut

How large should the clearcut be?

•Very site-dependent •This representation is for the Fraser Experimental Forest (maximum snow depth at 5H (5x the canopy height)) •As the size of the opening increases, its efficiency in trapping snow decreases to the point (approximately 15H) where there is a net loss Loss is associated with increased wind scour and sublimation losses Source: Troendle and Meiman 1984

Influence of Wind

James River site, Alberta, Canada SWE is greatest on the leeward side of a clearing SWE is least on the windward side of a clearing Second peak occurs because right before the snow hits the far side of the forest, decrease in wind speed results in additional snow accumulation wind direction first peak clearing second peak Source: Golding and Swanson 1986

SWE Increases

clearing wind direction Fraser Experimental Forest Similar results Increased snow accumulation and SWE at leeward edge of forest Source: Gary 1974

Hydrograph

Fraser Experimental Forest, Fool Creek Watershed Total seasonal flow increased by 40 percent (longer duration of high flows) Peak flow increased by 20 percent Most of the detectable change occurred in May Source: Troendle and Olsen 1994

Hydrograph

Increases in peak discharge mean more erosion and flooding Results in a need for additional reservoirs to store water for low flows Generally, flows increased most during wet years as opposed to during droughts During drought (low antecedent moisture), snowmelt infiltrates and recharges groundwater, does not go to discharge  NEED RESERVOIRS Source: Troendle and Stednick 1999

Sedimentation

Appalachian catchment Logging-related activities (including road construction activities) increase erosion and sedimentation Sediment yield increased considerably as a result of road building and logging activities Source: Swank et al. 2001

Nutrient Loading

Appalachian catchment Logging activities increase nutrient loading, DOC, conductivity (ion concentrations) Sustained increases in nitrate concentrations after clearing and logging due to: •Reduction in nutrient uptake due to vegetation mortality •Nutrient release from decomposition of trees and logging residue •Increased soil N transformations Source: Swank et al. 2001

Wildfire mitigation?

• • • Proponents herald logging to increase water yield as a “forest health effort” Say it will serve a dual purpose • • Increase water yield Reduce fire risk However, logging trees at high elevation catchments will not reduce fire in high risk areas (at lower elevations) • Logging in high elevation areas could mean less money to spend on thinning fire-prone areas

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Other considerations for CO

Cutting lodgepole pine stands would remove habitat for federally threatened lynx and other interior forest species High cost, maintenance required to maintain yields Difficult to replicate Fraser results in other parts of Colorado • Study of runoff changes as a result of cutting ski runs at Eldora (Gaudagno)    deep snow collected in spruce-fir stands open runs scoured almost bare by high winds didn’t produce same results as Fraser experiments Other environmental costs • Erosion and sedimentation can stifle habitat for fish and aquatic insects Amount of water flowing off trees increases as they mature • Colorado’s middle-aged forests will soon become old-growth and capture more snowfall Shift focus from increasing supply  reducing demand?