fire and its effects on soil

8/10/2019 Fire and Its Effects on Soil

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Effects of Fire on Soil Microbes

and Structure

Nathaniel Tisdell


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Types of Wild Fire

Crown


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Types of Wild Fire

Brush


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Types of Wild Fire

Ground


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Factors Affecting Soil

Intensity

Duration

Leading to Severity


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Intensity

Heat of Fire

Duration

Length of heating

Severity

Amount of ecological

damage


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Depth of Heat Transfer

Thermal Diffusivity

Changes with

Moisture Content

Water Boiling Point

Vaporization begins

at 95C


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Depth of Heat Transfer

Surface Temp During Fire

200300C

With Heavy Fuel 500-700C

5cm Temp.


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Microbial Death

Intensity

Heat of Fire

Duration

Length of heating Clostridium botulinum thermal death

graph

Spores

Food Industry


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Intensity

Heat of Fire

Duration

Length of heating

Severity

Amount of ecological

damage


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Duration of Fire

Biggest variable

High heat, fast fire

Little soil heat transfer

Duration affects depth ofheat

Depth affects more

biomass


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Effects of Heat

Microbes

Carbon

Hydrophobicity Aggregate Stability


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Microbes: Immediate Effects

High temps Complete sterilization of topsoil (0-5cm)

50% biomass reduction in 5-10cm

Pollutants produced by combustion

Polychlorinated dibenzo-p-dioxins Dibenzofurans

polyaromatic hydrocarbons (PAH)

Modifies/Removes substrate

Moisture Content

Higher moisture, higher decline of biomass C Better Heat conduction

Fungi more sensitive to heat than bacteria


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Microbes: Long-Term Effects

Limited studiesMost done with prescribedburns

Some suggest increased heterogeneity

Aerobic Heterotrophs stimulated Cyanobacteria depressed

Fungi

Pyrophilous fungi

Quickly recolonize after low to moderate severity

Ascomycetes associated with recent burns

Other fungi take longer to recolonize


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Carbon: CO2

2008 Emissions

5,839 million metric tons

Forest Fire Emissions

290 million metric tons

Forest Fires Contribute 5% CO2Emissions


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Carbon: the Cycle


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Carbon: Fuel

Combustion

Starts at 200C

Complete at 460C

C6H12O6+6O2->6CO2+6H2O

Organic Carbon

Incomplete combustion

Myriad of other products


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Carbon: Byproducts

Pyrolysis

Heating Organics without O2

Occurs at moderate temp during wild-fire

220C 37% carbon lost

Rest pyrolysed

Produces Aromatic Rings

Removes Oxygenated Subgroups

Decreases Chain Length


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Carbon: Byproducts

High temp pyrolysis

250C - 500C

Black Carbon Production

Pure Carbon in Different forms

Very high temp produces graphite

If O2present, high temp produces CO2


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Hydrophobicity

Vaporization of Organics

from litter

Move down on temp gradient

Condense at cooler layer

175-200C

Strong Repellency

280-400C

Repellency destroyed


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Hydrophobicity


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Hydrophobicity: Chemistry

Compounds without Oxygen groups

Minimize H-bonding/polarity

No defined chemical structure

Infinite variety of carbon rearrangements


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Hydrophobicity: Practicality

Water Run-Off

Infiltration limitations

Erosion Bare Soil

Saturated

Run-off

Spatial variability on site


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Hydrophobicity: Hydrology

Uniform and Flat

Capillary Barrier

Wetting front slows through repellant layer

Infiltration speed increases as repellant layer

becomes wet

Shallow layer better at restricting infiltration


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Hydrophobicity: Hydrology

Heterogeneous and Micro topography

Produces wetting fingers

Rill Formation

Rain Drop Erosion


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Hydrophobicity: Wetting Fingers


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Hydrophobicity: Rill Formation


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Hydrophobicity: Rills


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Hydrophobicity: Rills


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Hydrophobicity: Rain Drop Erosion


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Erosion Prevention

Obstacles

Logs, mesh fences

Minimize overland movement

Mulching

Reseeding


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Hydrophobicity: Indirect Remediation

Masking Symptoms

Surfactants

Decrease surface tension

Adding Clay minerals

Masks Hydrophobic molecules

Biological

Introduce drought tolerant plants

Physical Cultivation

Compaction

Aeration


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Hydrophobicity: Direct Remediation

Reducing hydrophobic input/increasing

decomposition

Chemical

Liming

Increase pH, activates microbial communities

Slow Release Fertilizers

Promote Soil Biological Activity


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decomposition

Biological

Enriching specific bacterial populations

Wax degraders

Stimulating Earthworms

Mixing Soil

Microbial Priming Effect


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decomposition

Physical

High topsoil moisture

Irrigation

Reduce Drying


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Treatment

Expensive over large areas

Not performed unless land is of high value


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Hydrophobicity: Longevity

Depends on Severity of Fire

Low to Moderate

Short duration

Ex. Late spring burn in SW Oregon

Nearly normal infiltration in rainy season


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Aggregate Stability (AS)

Typically associated with OM

Biofilms, Hyphae

Water repellency increases AS to a point

Combustion decreases AS

Clay structure

Heating can fuse clays together Forms silt/sand fractions


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Bibliography

Bento-Goncalves, A., Vieira, A., Ubeda, X., & Martin, D. (2012). Fire and soils: Keyconcepts and recent advances. Geoderma, 191, 313.doi:10.1016/j.geoderma.2012.01.004

Certini, G. (2005). Effects of fire on properties of forest soils: a review. Oecologia,143(1), 110. doi:10.1007/s00442-004-1788-8

Mataix-Solera, J., Cerd, A., Arcenegui, V., Jordn, A., & Zavala, L. M. (2011). Fireeffects on soil aggregation: A review. Earth-Science Reviews, 109(1-2), 4460.doi:10.1016/j.earscirev.2011.08.002

McMullan-Fisher, S. J. M., May, T. W., Robinson, R. M., Bell, T. L., Lebel, T.,Catcheside, P., & York, A. (2011). Fungi and fire in Australian ecosystems: a reviewof current knowledge, management implications and future directions.Australian

Journal of Botany, 59(1), 70. doi:10.1071/BT10059

Mueller, K., & Deurer, M. (2011). Review of the remediation strategies for soil

water repellency.Agriculture Ecosystems & Environment, 144(1), 208

221.doi:10.1016/j.agee.2011.08.008

Shakesby, R. A., & Doerr, S. H. (2006). Wildfire as a hydrological andgeomorphological agent. Earth-Science Reviews, 74(3-4), 269307.doi:10.1016/j.earscirev.2005.10.006

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