FOR 426. Mineral and organic matter on the Earth s surface. Chad Hoffman and Penny Morgan

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Fire Effects on Soils: An Introduction Chad Hoffman and Penny Morgan What is Soil?

biological processes functioning on geological parent material a continuous

components of the environment James Henderson, Gulf South Research Corporation,

waterholding capacity, nutrient cycling, soil structure, habitat Soil Particle

arrangement Particles are bounded together into units called aggregates David J.

Soil Pores The pores between the particles are the soil s ventilation system,

Fire effects on soils Organic matter Source of nutrients Holds water Adds to soil

1 Fire Effects on Soils: An Introduction Chad Hoffman and Penny Morgan What is Soil? Mineral and organic matter on the Earth s surface physical, chemical and biological processes functioning on geological parent material a continuous interaction between the soil system and the biotic, climatic, and topographic components of the environment James Henderson, Gulf South Research Corporation, Organic Matter in Soils Living and dead biomass Very important to soil function: waterholding capacity, nutrient cycling, soil structure, habitat Soil Particle Size and Organization Soil texture particle size Soil Structure particle arrangement Particles are bounded together into units called aggregates David J. Moorhead, University of Georgia, Roger Lopez-Chaves, Universidad de Costa Rica, Soil Pores The pores between the particles are the soil s ventilation system, water intake system, water storage and drainage system. Fire effects on soils Organic matter Source of nutrients Holds water Adds to soil structure P t t il f Protects soil surface If is a source of heat into soil, otherwise can insulate soil from heating Holds roots, seeds, etc. 1

Soil temperature (C) Ash color and appearance Black (charred litter)

Moderate 300-400 200-300 40-50 White and fluffy ash, red soil at

or Duff intact Woody debris is scorched to lightly charred Mineral

al. 1979 Moderate depth of burn Litter Duff deeply charred or

mostly Logs deeply charred High depth of burn Duff Surface mineral

structure Char layer (dark color) may extend several centimeters t

2 Soil temperature (C) Ash color and appearance Black (charred litter) Depth of burn Surface 1-2 cm 5 cm Light <100 None Bare soil Moderate White and fluffy ash, red soil at surface Severe >100 Low depth of burn Litter charred or Duff intact Woody debris is scorched to lightly charred Mineral soil unchanged Small twigs and some leaves remain on plants Wells et al Moderate depth of burn Litter Duff deeply charred or Mineral soil visibly unchanged Ash light colored Twigs and branches mostly Logs deeply charred High depth of burn Duff Surface mineral soil oxidized (reddish or orange) with visibly altered texture and structure Char layer (dark color) may extend several centimeters t into mineral soil Logs deeply charred or Almost no small diameter wood remains 2

Mosaic of depth of burn Light Moderate Mosaic of depth of burn

Water-Repellent (hydrophobic) Soils Table Adapted from Neary et al

increase in the density of the soil Reduced soil porosity

2005 Found in both fire and nonfire environments Can be caused by

microbial byproducts intermixing of soil particles and organic

Fire affects water infiltration in two ways: Burned soil is

3 Mosaic of depth of burn Light Moderate Mosaic of depth of burn Moderate Deep Effects of Temperature on Soil Properties Water-Repellent (hydrophobic) Soils Table Adapted from Neary et al 2005 Changes to the soil structure due to heating: Collapse and increase in the density of the soil Reduced soil porosity Hydrophobic soils Soil erosion Figure from Neary et al Found in both fire and nonfire environments Can be caused by irreversible drying leachates from organic materials Hydrophobic microbial byproducts intermixing of soil particles and organic matter Fire-Induced Hydrophobic Soils Hydrophobic Soils and Erosion Fire affects water infiltration in two ways: Burned soil is unprotected from rain drop impact Fire may cause a water-repellent layer within the soil Figure from dartmoor-npa.gov.uk 3

Raindrop Splash Fire Effects on Soil Chemistry Fire affects individual soil chemical characteristics,

impact and the organic matter helps to absorb water Table from Neary et al 2005 Fire Effects on Soil

nutrient recycling is altered by combustion and accelerated decomposition post-fire Soil nutrients and fire

4 Raindrop Splash Fire Effects on Soil Chemistry Fire affects individual soil chemical characteristics, chemical reactions, and chemical processes Work by Robichaud and others suggests that when there is >60% cover on soil surface (e.g. from plants, duff, and litter), There is little risk of erosion because the soil is protected from Raindrop impact and the organic matter helps to absorb water Table from Neary et al 2005 Fire Effects on Soil Chemistry In between fires, nutrient recycling depends upon decomposition During and immediately after fire, nutrient recycling is altered by combustion and accelerated decomposition post-fire Soil nutrients and fire Total N declines, available N can increase; effects depend on temperature and organic matter consumption When foliage, roots and small stems are, the cations (e.g. Ca, Mg, K) are in the highly soluble ash Ash can be moved by wind and water More cations are deposited where there was more biomass that was ; most are left on site after logging because most are in tree crowns Fires Affect Soil Biology Fires Affect Soil Biology 4

through combustion Surface organic matter can help protect soil from erosion Organic matter in and on the soil helps increase capacity of

5 Many fire effects on soils depend on whether organic matter is or not Soil heating can occur if duff and litter burn; if not duff and litter can help to insulate soil Organic matter contains many nutrients that can be released slowly through decomposition or rapidly through combustion Surface organic matter can help protect soil from erosion Organic matter in and on the soil helps increase capacity of soil to hold water and nutrients (cation exchange capacity of OM is high) OM is source of water repellency C:N ratio is important to microbial activity 5

FOR 433. Fire Effects on Soils: An Introduction. Chad Hoffman

FOR 433. Fire Effects on Soils: An Introduction. Chad Hoffman Fire Effects on Soils: An Introduction Chad Hoffman During this weeks lecture we will be discussing the effects of fire on soils, and you will review the WEPP-FUME model. One point I would like to reemphasize