Post-Wildfire Forest Management: Soils and Soil Productivity

Transcription

1 Pre- and Post-Wildfire Forest Management Conference, 2010 Post-Wildfire Forest Management: Soils and Soil Productivity David Young, Zone Soil Scientist USDA Forest Service, Redding

2 Why YOU Should Care About Soils Soils are like a marriage... The ungrown 20%... Too big to fail...?

3 Loss of Productive Forest

4 Soils 101 Soil + Water + Sunlight = Vegetation Fundamental Productivity Trees compete for limited resources. Resources (nutrients and water) come from the soil.

5 Soils 101 Soil + Water + Sunlight = Vegetation Soil Hydrology How soil accepts, transmits, and stores water is of particular importance in the post-fire environment

6 Soils are Complex Pedogenesis = f (cl,o,r,p,t) Climate Organisms Relief (topography, slope and aspect) Parent material Time Natural History (disturbance regime) Hans Jenny, Factors of Soil Formation

7 Soils are Complex Soil Productivity = f : Soil Stability Hydrologic Function Soil Biology Nutrient Cycling Thermodynamics Filtering/Buffering Capacity All of these may be affected to varying degrees by wildfire.

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9 Soil Science Rocket Science Major Inherent Soil Properties: Texture Structure Depth Rock Content Clay Type & Content Horizonation

10 Soil Science Rocket Science Major Dynamic Soil Properties: Surface Structure Porosity OM Content Nutrient Content Infiltration Water Storage Cap. Nutrient Cycling

11 Direct Effects (Soil Properties & Qualities) Soil Cover PEAK TEMPERATURE RESIDENCE TIME Soil Physics Soil Biology Soil Chemistry Secondary Effects (Soil Processes & Functions) Infiltration & permeability Nutrient Supply & Cycling C-N Release/Retention Consequential Effects (Ecosystem Stability & Resilience) None Soil Erosion Watershed Hydrology Natural Regeneration Soil Productivity? Catastrophic? Magnitude and Longevity of Fire Effects Determined By: 1. Scale 2. Soil Burn Severity 3. Natural Recovery 4. Management Response

12 Direct Effects of Fire on Soil: Causal Mechanisms During Fire 1. Increased temperature 2. Loss of vegetation and OM combustion 3. Loss of matter - volatilization 4. Addition of substances - condensation Direct heating effects are in the surface 2-6 But... Fine roots, organisms, OM, nutrients are also concentrated toward the surface.

13 DEPTH (cm) Soil N Distribution Lowell Hill LTSP Site A1 A2 Bt Bt2 C1 C kg/ha in top meter TOTAL NITROGEN (kg/ha)

14 Direct Effects of Fire on Soil: Changes in Soil Properties and Processes Decreased: Structure Aggregate Stability Porosity OM Content Cation Exchange Capacity Infiltration Water Storage Capacity Increased: Bulk Density Erodibility Water Repellency ph Nutrient Availability (short-term ash fertilization ) Changes to what degree?? Soils, sites, and fires are all somewhat unique.

15 Direct Effects of Fire on Soil: Drivers of Soil Burn Severity 1. Fuel Properties 2. Fire Behavior 3. Antecedent Soil Moisture 4. Soil Texture & Porosity

16 Soil Burn Severity: Low Aboveground: Overstory crown largely intact Understory partially consumed Small branches/leaves remain Duff partially intact Belowground: Little soil heating evidence Structure/pores/roots intact Soil hydrologic function intact

17 Soil Burn Severity: Moderate Aboveground: Overstory brown crown (potential cover) Understory mostly consumed Large branches remain Duff mostly/wholly consumed Belowground: Shallow effects of soil heating Structure brittle Roots & pores largely intact

18 Soil Burn Severity: High Aboveground: Overstory consumed Understory consumed Stem/basal crowns remain Duff gone (white ash??) Belowground: Deep effects of soil heating Structure powdered Roots brittle/consumed Porosity & infiltration affected

19 Soil Burn Severity: High X High Aboveground: Copious CWD consumed Understory consumed Stem/basal crowns remain Belowground: Deeper effects of soil heating Heavily oxidized surface Structure powdered Roots consumed Porosity/infiltration destroyed

20 Soil Burn Severity and Water Repellency Low SBS usually unaffected Mod SBS extremely variable High SBS usually increased Very High temps destroyed Also depends somewhat on geology, texture, porosity, gravels. Hydrophobicity as a rule is highly variable spatially and temporally.

21 Post-Fire Management Intervention 1. Immediate response Suppression Repair & BAER 2. Short-Term Salvage Logging & Reforestation 3. Medium- to Long-Term Silviculture & Restoration How does management in the post-wildfire environment affect fragile soils??

22 Post-Fire Management Intervention Suppression Repair Nearly always done. Often have skips and quality problems. Potential Long-Term Sediment Source Areas.

23 Post-Fire Management Intervention BAER Burned Area Emergency Response Emergency soil stabilization treatments Usually used for non-soil VARs Very Expensive Range of Treatments & Effectiveness Mulch treatments are best Criticism can retard natural germinants

24 Post-Fire Management Intervention Salvage Logging Can have detrimental impacts Compaction Displacement Exacerbate Erosion Can have beneficial effects Increases surface cover Increases surface roughness Can help break up water repellency

25 Post-Fire Management Intervention Salvage Logging Bottom Line It s all in the application & soil sensitivity Helicopter Cable Tractor Operator Proficiency Soil Burn Severity Soil Texture & Resilience Mitigations & BMPs above the norm Landscape Location and Relative Scale Matter

26 Post-Fire Management Intervention Reforestation Can have detrimental impacts Tractor site-prep Can have beneficial effects Depends on land objectives Remember the Fountain Fire Controversies Competing vegetation management

27 Post-Fire Management Intervention Long-Term Restoration Chronic Sediment Source Stabilization Suppression Sores slow natural recovery Gullies

28 Take-Home Messages Soil-Specific Considerations Post Fire Mgmt Soil Burn Severity A-horizon depth Texture Clay content Rock content Topography Location Potential Erosion & Nutrient Loss Compaction Risk & Erodibility Sediment Delivery & Ecosystem Export

29 Encouraged reading:

30 Take-Home Messages Soils and Site Productivity Soils are complex, with massive variability. General soil principles are solid, complex interactions are largely unknown. Changes in belowground ecology are often expressed in aboveground ecology over long time scales.

31 Take-Home Messages Soils and Site Productivity High severity fire is not beneficial for soils. Repeated high severity fire can be destructive. Need research on cumulative effects of repeated fire (Rx and wild) on soils.

32 Take-Home Messages Soils and Site Productivity Effects to soils have ecosystem consequences. Scale and landscape context matter greatly they can be aggravators or mitigators. Soils are like a marriage... The ungrown 20%... Too big to fail...?

33 Why YOU Should Care About Soils Soils are like a marriage... The ungrown 20%... Too big to fail...?

34 Anyone who promotes absolutes about soils is surely not a Soil Scientist (Hauxwell, 1993). So, it kind of depends where you are in the world and what soils you have (Roath, 2007). The Answer Is: It Depends... David Young, Zone Soil Scientist USDA Forest Service, Redding daveyoung@fs.fed.us

35 VOLUME (m 3 ha -1 ) TERRACING, BITTERROOT NF Common 1960s Zlatnik et al WJAF Not Terraced Terraced 50 0 Spruce Ck Thunder Mtn Coal Ck Ck Mtn

36 Moonlight Fire, Plumas NF, 2007

37 Station Fire, Angeles NF, 2009

38 Delburn Fire Victoria, Australia 2009 Radiata pine plantation Churchill Fire Victoria, Australia 2009 Blue gum plantation

39 Soil Properties and Processes Erosional Process Universal Soil Loss Equation (USLE) A = RKLSCP where: A is average soil loss in tons/acre/year R is rainfall/runoff erosivity K is soil erodibility LS is slope length factor C is cover % P is practice being used

40 Bear Fire How Fire Affects Soils Burn severity effects on infiltration, runoff, and water quality:

41 How Fire Affects Soils Burn severity effects on nutrient release:

42 Adaptive Fire Management Practices Overall effects of fire on soils: Increase in ph, available N, P, K, Ca, Mg Decrease in wettability, total N, OM, S, C Moonlight Fire