Risk Ratings for Soil Impacts from Wildfire and Ground-Based Logging Equipment

1. Risk Ratings for Soil Impacts from Wildfire and Ground-Based Logging Equipment

2. Introduction • Both wildfires and ground-based logging equipment can cause changes in soil properties that may aversely affect plant growth. • A decision support application has been developed that evaluates the risk and consequences of both wildfire and logging equipment to forest soils.

3. Application Details • Based on the Ecosystem Management Decision Support (EMDS) system • EMDS is an ArcMap extension that integrates logic based modeling into the geographic information systems (GIS) environment. • Ratings are based on a -1.0 to +1.0 scale • -1.0 rating indicates very low risk of soil damage, +1.0 indicates very high risk

4. Fire Risk Rating Assumptions • Based on loss of productivity from moderate to severe fires • Two major areas of risk: • Soil erosion processes • Sheet and rill • Ravel • Soil biochemical processes • Nutrient loss to volatilization • Nutrient loss to runoff • Coarse woody recruitment

5. Data Sources for the Fire Risk Ratings • NASIS soil properties and vegetation data, forest management interpretations, and SSURGO soil polygon spatial data. • Forest Service Land Type Associations • Fire regime and fuel condition class data • Slope and aspect derived from Digital Elevation Models (DEM’s)

6. Factors in the Risk Rating for Fire Damage • Sheet and rill erosion hazard • Dry ravel hazard (soil cohesion) • Surface runoff class • Root strength • Soil climate • Soil resilience • Aspect • Fire regime and condition class

7. Fire Damage – Sheet and Rill Erosion Hazard • Classified as low, moderate or high based on NASIS Kw factor for the surface mineral horizon and slope class derived from DEMs • Four slope classes are used: • O – 15% • 16 - 30% • 31 – 45% • 46 – 60% • >60%

8. Fire Damage – Dry Ravel Hazard • Uses Soil cohesion classes of low, moderate or high, based on clay content of the surface mineral horizon • Low: < 18% clay • Moderate: 18 – 35% clay • High: > 35% clay

9. Fire Damage – Surface Runoff Class • Based on the Forest Service surface runoff classes assigned to Land Type Associations • Factors considered: • Geomorphology • Stream density and pattern • Soils • Slope • Precipitation

10. Fire Damage – Root Strength • Interpreted from seven broad vegetation groups derived from NASIS vegetation data • Risk classes are assigned based on relative root strength of vegetation groups • Example: • Ponderosa pine – moderately low risk due to relative abundance or well-distributed roots and relatively slow decay rates

11. Fire Damage – Soil Climate • Interpreted from seven broad vegetation groups derived from NASIS and other soil survey vegetation data • Risk ratings are based on the rate of recovery of vegetation after fire • Examples: • Ponderosa pine – high risk • Douglas-fir/grand fir – moderate risk • Pacific silver fir/mountain hemlock – low risk • Western hemlock – very low risk

12. Fire Damage – Soil Resilience • Based on the ability of the soil to rebound and recover its functions after disturbance • Low, medium, or high classes assigned based on: • Soil depth and thickness of A-horizon • Organic matter content of the surface mineral horizon • Depth to root restrictive feature such as bedrock or densic material

13. Fire Damage – Fire Regime and Condition Class • Based on the modal fire regime for the soil polygon • Used to predict the expected amount of cover after fire • Includes an evaluation of the proportion on the soil polygon with a fire regime condition class greater than 1

15. Types of Soil Disturbance Considered in Equipment Risk Ratings • Compaction • Churning – incorporation of organic debris • Topsoil removal and displacement • Topsoil mixing with subsoil

16. Equipment Risk Rating Assumptions • Each soil is considered like a bank account. • Small withdrawals from a deep, fertile soil have small effects. • Large withdrawals from a shallow, infertile soil have large consequences. • Soils that support vigorous plant growth are assumed to be less affected by compaction or displacement than less favorable soils. • Impacts are more likely to reduce tree growth in stressful climatic conditions.

17. Data Sources for the Equipment Risk Ratings • NASIS soil properties data and SSURGO soil polygon spatial data • Official series descriptions (OSD’s) • Spatial data for Potential Vegetation Type from Forest Service Pacific Northwest Research Station • Slope and aspect derived from Digital Elevation Models (DEM’s)

18. Factors in the Risk Rating for Logging Equipment • Combined thickness of A and B horizons • Depth to which common or many fine and very roots are described in the official series description (OSD) • Rock fragment content in the A and B horizons • Thickness and type of tephra (ash mantle, mixed ash, pumice mantle, etc.)

19. Factors in the Risk Rating for Logging Equipment – cont. • Texture of A or AB horizon (sandy, loamy, or clayey • Texture of B horizon (sandy, loamy, or clayey) • Aspect • Slope class – same as fire hazard classes • Potential vegetation