In southwestern ponderosa pine forests, wildfires have become unnaturally damaging because of decades of fire exclusion and the increased density of forest stands. Large, severe fires are well known to be destructive to forest vegetation and wildlife, but an additional, often-unseen effect of fires is on and in the ground the disruption of soil structure and properties that can have a cascade of effects throughout forest systems. Forest soils supply air, water, nutrients, and mechanical support for plants, and provide habitat for decomposers, nitrogen-fixing bacteria, and symbiotic fungi. Whether forest managers are looking to rehabilitate forests after wildfire or conduct restoration treatments intended to prevent severe wildfire, it is important to protect soils

Minard, A.E.

OpenKnowledge@NAU

5
Ecological Restoration Institute
Northern Arizona University
P.O. Box 15017
Flagstaff, AZ 86011-5017
www.eri.nau.edu
Working Papers in Southwestern 
Ponderosa Pine Forest Restoration 
Limiting Damage 
to Forest Soils 
During Restoration
August 2003 
Working Papers in Southwestern Ponderosa Pine Forest Restoration
The Ecological Restoration Institute at Northern Arizona University is a pioneer in
researching, implementing, and monitoring ecological restoration of southwestern pon-
derosa pine forests. These forests have been significantly altered through more than a
century of fire suppression, livestock grazing, logging, and other ecosystem changes. As a
result, ecological and recreational values of these forests have decreased, while the threat
of large-scale fires has increased dramatically. The ERI is helping to restore these forests
in collaboration with numerous public agencies. By allowing natural processes such as
fire to resume self-sustaining patterns, we hope to reestablish healthy forests that provide
ecosystem services, wildlife habitat, and recreational opportunities.
Every restoration project needs to be site-specific, but the detailed experience of field
practitioners may help guide practitioners elsewhere. The Working Papers series presents
findings and management recommendations from research and observations by the ERI
and its partner organizations.
This publication would not have been possible without significant staff contributions and
funding from the Bureau of Land Management. The views and conclusions contained in
this document are those of the authors and should not be interpreted as representing the
opinions or policies of the U.S. Government. Mention of trade names or commercial
products does not constitute their endorsement by the U.S. Government.
1: Restoring the Uinkaret Mountains: Operational Lessons and Adaptive 
Management Practices
2: Understory Plant Community Restoration in the Uinkaret Mountains, Arizona
3: Protecting Old Trees From Prescribed Fire
4: Fuels Treatments and Forest Restoration: An Analysis of Benefits  
Limiting Damage to Forest Soils During Restoration a
Introduction
In southwestern ponderosa pine forests, wildfires have become unnaturally damaging
because of decades of fire exclusion and the increased density of forest stands. Large,
severe fires are well known to be destructive to forest vegetation and wildlife, but an
additional, often-unseen effect of fires is on and in the ground—the disruption of soil
structure and properties that can have a cascade of effects throughout forest systems.
Forest soils supply air, water, nutrients, and mechanical support for plants, and provide
habitat for decomposers, nitrogen-fixing bacteria, and symbiotic fungi. Whether forest
managers are looking to rehabilitate forests after wildfire or conduct restoration treat-
ments intended to prevent severe wildfire, it is important to protect soils.
Fire Effects on Soils
Only about 10 to 15 percent of a fire’s heat is typically directed downward (DeBano et al.
1998), but this can still cause considerable changes in soils. Beginning at 48 degrees
Celsius (118 degrees Fahrenheit), heat destroys the biological components in soils,
including microbes and plants. These effects are most obvious in the top centimeter or
two of soil, and the most common result is the loss of top organic layers to erosion after
fires. At higher temperatures, though, damage can result from the fire itself, especially
during intense, stand-replacing fires.
When heat dries out organic components irreversibly, or they leach out to coat soil’s
mineral components, a hydrophobic (water-repellent) layer can form. This is most likely
to happen when soil temperatures rise to between 176 and 204 degrees Celsius (350 to
400 degrees Fahrenheit). Soil temperatures can reach this level when thick layers of
ground litter or accumulations of woody debris burn for long periods. Because it resists
infiltration by rain, a hydrophobic layer puts the forest floor at risk of runoff and ero-
sion.
When soils heat to temperatures between 200 and 500 degrees Celsius (390 to 900
degrees Fahrenheit), solid organic matter is destroyed. While this can provide ready
nutrients for plants growing immediately after a fire, these conditions destroy soil struc-
ture. In the long run, this can affect archaeological or other cultural resources, nutrient
cycling, and ecosystem productivity. Arid soils, such as those in some southwestern pon-
derosa pine forests, recover more slowly from these effects than soils in which organic
matter is replaced more quickly.
1
Limiting Damage to Forest Soils During Restorationa
Proactive Restoration Treatments Can Benefit Soils
Many of fire’s negative effects on soils can be minimized with efforts to prevent cata-
strophic fires. Thinning and controlled burns can clear out accumulated brush and other
fuels from forests. Then, when a fire does start, it is likely to burn cooler and with shorter
duration in a forest that has undergone restoration treatments, thereby preventing many
of the deleterious effects of prolonged, hot fires.
However, even prescribed burns and mechanical thinning projects introduce their own
damage to forest soils, especially soil compaction. Compaction can reduce soil porosity
and decrease the rate of water infiltration. These effects can lead to increased runoff and
erosion similar to that seen following fires. Careful planning and treatment implementa-
tion can minimize these impacts.
Forest Restoration: Effects on Soils
Mineral soil can be lost during restoration thinning efforts in the same way as during
traditional logging operations: directly through the removal of surface layers by mecha-
nized equipment, or indirectly through compaction. Either type of damage can lead to
erosion, retardation of plant recovery, and impeded root growth. Various factors affect
the degree to which a particular soil type or site is vulnerable to soil compaction and loss
(Selmants et al. 2003):
• Fine-textured soils are more at risk of compaction.
• Wet soils are more likely to sustain damage from both compaction and mechanical soil
removal than dry soils.
• Organic matter and surface rock fragments can buffer soils from compaction.
The same factors can influence the speed at which soil recovers, although no studies to
date have documented complete recovery from machine-induced compaction.
In addition, prescribed fires after restoration thinning can cause extensive soil heating
and, when burning in thick litter, can damage roots and cause tree mortality (see
Working Paper 3: Protecting Old-Growth Trees From Prescribed Fire). Slash pile fires can
cause intense soil heating, destroying the soil seed bank and mycorrhizal fungi (Korb and
Springer 2003). For these reasons, soil effects should be considered when planning post-
thinning burns.
Minimizing Soil Loss and Compaction
Soil impacts should be considered during all stages of a restoration project: in the plan-
ning process, during implementation, and after thinning is completed. The following
steps can aid in minimizing impacts.
2
Limiting Damage to Forest Soils During Restoration a
3
Planning
• Make prescriptions reasonable for easier cutting. Leaving a few small trees where a
dense doghair thicket stands, for example, makes it difficult for the logger to cut the
rest down, resulting in more time needed for the job and greater impacts to soil. If a
thicket is to be retained for wildlife habitat, it may be better to cut trees from its edge
while retaining the thicket’s integrity.
• Designate skid trails ahead of time. Use a pattern, such as a zigzagging line, that occu-
pies as little surface area as possible (Garland 1997). Take advantage of areas least sus-
ceptible to compaction, such as areas with some surface rocks.
• Consider manual treatments such as hand felling, especially in ecologically sensitive
areas.
• Consider a mosaic of treatments that leaves some areas undisturbed.
Implementation
• Work when soils are least sensitive. Avoid wet periods. One good option is to work
when soil is frozen or dry. A layer of snow can provide an additional buffer against
compaction.
• Maintain soil organic matter and keep surface soil, litter, and slash in place while har-
vesting. This can increase resistance to com-
paction and protect soils from erosion. The
tradeoff is that this can also increase the severity
of burns, controlled or otherwise, that follow
mechanical treatments—so removing slash
before burning may be a good idea.
• Use a cut-to-length (CTL) harvesting system
that processes trees in the woods. The resulting
slash can be disposed of in front of the machine
and driven on to buffer soils from compaction.
The use of a CTL system also reduces the need
to drive to each individual tree by harvesting
those within a set radius of the machine, as
opposed to harvesting requirements for a drive-
to-tree feller buncher.
• Use a forwarding system rather than a log skid-
ding system in conjunction with a CTL har-
vester to collect logs piled in the woods by driv-
ing on the same slash mats. Later, the forwarder
may be used to collect and remove the slash
itself.
• Fell trees to skid trails in order to minimize skidding distances, soil disturbance, and
damage to vegetation (Figure 1; Garland 1997).
Figure 1. Felling trees to skid trails can
reduce the difficulty of winching and
minimize soil impacts. Reprinted with
permission from Garland 1997.
Limiting Damage to Forest Soils During Restorationa
4
• Consider hot loading, or loading logs directly onto trucks rather than decking them
first.
• Consider ripping skid trails to rehabilitate them after use.
After Thinning
• Burn slash where soil is already disturbed, such as on loading areas or roads.
• Lop and scatter slash before burning in order to prevent intense soil impacts under
slash piles. The tradeoff is that excessive broadcast slash can greatly increase the inten-
sity of prescribed fires and make them difficult to control. In particular, hot spots may
occur under larger branches.
• Consider alternatives to burning slash. It can be removed for chipping, or transported
to a biomass or pellet plant. If they are to be removed, slash piles should be placed
along roads or skid trails for easy loading.
• One new approach that shows promise is remediation of severely disturbed areas—
such as former roads and sites of slash pile fires—with native fungus. Spreading
chipped wood and bark on such areas after inoculating it with fungi speeds the ecolog-
ical recovery process and may help prevent the spread of noxious plants.
• Construct fire control lines with an eye toward minimizing soil compaction and ero-
sion problems. Locate control lines away from erosive soils. Minimize the time control
lines are in place, and rehabilitate them quickly after burning. Install water bars on
steep slopes. Strike a careful balance between the straight control lines preferred by fire
managers and zigzagging lines that may better prevent soil compaction and erosion.
• Seeding with native herbaceous plants can help stabilize soils after fire. Applying seed
into the ash bed immediately after burning helps hold the seed in place, reducing the
need to drill or otherwise disturb the surface.
• Carefully consider the frequency of future prescribed fires. They are crucial in main-
taining forest structure but, if repeated as often as every two years, may cause declines
in soil nitrogen available to plants (Wright and Hart 1997). Somewhat longer intervals
may be preferable.
For More Information
For information about forest restoration, contact the ERI at 928-523-7182 or
www.eri.nau.edu.
To learn more about remediation of disturbed areas with fungus, contact Jim Bell at com-
posttrees@yahoo.com or visit www.fungi.com/mycotech/roadrestoration.html.
Written by Anne Minard
Reviewed by Dennis Becker, Sat Sansar Best, Kevin Boness, Charlie Denton, Tori Derr, Tim
Duck, Taylor McKinnon, Jeff Morton, Steve Overby, and Todd Schulke.
Series Editor Peter Friederici  
Northern Arizona University is an Equal Opportunity/Affirmative Action Institution   
NAU Creative Communications/A49866/1M/11-02
References
DeBano, L. F., D. G. Neary, and P. F. Ffolliott. 1998. Fire’s effects on ecosystems. New York:
Wiley.
Garland, J. J. 1997. Designated skid trails minimize soil compaction. Oregon State
University Extension Service publication EC1110.
http://eesc.orst.edu/agcomwebfile/edmat/EC1110.pdf.
Korb, J. E., and J. D. Springer. 2003. Understory vegetation. Pp. 233–250 in Ecological
restoration of southwestern ponderosa pine forests, ed. P. Friederici. Washington, D.C.:
Island Press.
Selmants, P. C., A. Elseroad, and S. C. Hart. 2003. Soils and nutrients. Pp. 144–160 in
Ecological restoration of southwestern ponderosa pine forests, ed. P. Friederici. Washington,
D.C.: Island Press.
Wright, R. J., and S. C. Hart. 1997. Nitrogen and phosphorus status in a ponderosa pine
forest after 20 years of interval burning. Ecoscience 4:526–533.
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Working Paper 05: Limiting Damage to Forest Soils During Restoration

5Ecological Restoration InstituteNorthern Arizona UniversityP.O. Box 15017Flagstaff, AZ 86011-5017www.eri.nau.eduWorking Papers in Southwestern Ponderosa Pine Forest Restoration Limiting Damage to Forest Soils During RestorationAugust 2003 Working Papers in Southwestern Ponderosa Pine Forest RestorationThe Ecological Restoration Institute at Northern Arizona University is a pioneer inresearching, implementing, and monitoring ecological restoration of southwestern pon-derosa pine forests. These forests have been significantly altered through more than acentury of fire suppression, livestock grazing, logging, and other ecosystem changes. As aresult, ecological and recreational values of these forests have decreased, while the threatof large-scale fires has increased dramatically. The ERI is helping to restore these forestsin collaboration with numerous public agencies. By allowing natural processes such asfire to resume self-sustaining patterns, we hope to reestablish healthy forests that provideecosystem services, wildlife habitat, and recreational opportunities.Every restoration project needs to be site-specific, but the detailed experience of fieldpractitioners may help guide practitioners elsewhere. The Working Papers series presentsfindings and management recommendations from research and observations by the ERIand its partner organizations.This publication would not have been possible without significant staff contributions andfunding from the Bureau of Land Management. The views and conclusions contained inthis document are those of the authors and should not be interpreted as representing theopinions or policies of the U.S. Government. Mention of trade names or commercialproducts does not constitute their endorsement by the U.S. Government.1: Restoring the Uinkaret Mountains: Operational Lessons and Adaptive Management Practices2: Understory Plant Community Restoration in the Uinkaret Mountains, Arizona3: Protecting Old Trees From Prescribed Fire4: Fuels Treatments and Forest Restoration: An Analysis of Benefits  Limiting Damage to Forest Soils During Restoration aIntroductionIn southwestern ponderosa pine forests, wildfires have become unnaturally damagingbecause of decades of fire exclusion and the increased density of forest stands. Large,severe fires are well known to be destructive to forest vegetation and wildlife, but anadditional, often-unseen effect of fires is on and in the ground—the disruption of soilstructure and properties that can have a cascade of effects throughout forest systems.Forest soils supply air, water, nutrients, and mechanical support for plants, and providehabitat for decomposers, nitrogen-fixing bacteria, and symbiotic fungi. Whether forestmanagers are looking to rehabilitate forests after wildfire or conduct restoration treat-ments intended to prevent severe wildfire, it is important to protect soils.Fire Effects on SoilsOnly about 10 to 15 percent of a fire’s heat is typically directed downward (DeBano et al.1998), but this can still cause considerable changes in soils. Beginning at 48 degreesCelsius (118 degrees Fahrenheit), heat destroys the biological components in soils,including microbes and plants. These effects are most obvious in the top centimeter ortwo of soil, and the most common result is the loss of top organic layers to erosion afterfires. At higher temperatures, though, damage can result from the fire itself, especiallyduring intense, stand-replacing fires.When heat dries out organic components irreversibly, or they leach out to coat soil’smineral components, a hydrophobic (water-repellent) layer can form. This is most likelyto happen when soil temperatures rise to between 176 and 204 degrees Celsius (350 to400 degrees Fahrenheit). Soil temperatures can reach this level when thick layers ofground litter or accumulations of woody debris burn for long periods. Because it resistsinfiltration by rain, a hydrophobic layer puts the forest floor at risk of runoff and ero-sion.When soils heat to temperatures between 200 and 500 degrees Celsius (390 to 900degrees Fahrenheit), solid organic matter is destroyed. While this can provide readynutrients for plants growing immediately after a fire, these conditions destroy soil struc-ture. In the long run, this can affect archaeological or other cultural resources, nutrientcycling, and ecosystem productivity. Arid soils, such as those in some southwestern pon-derosa pine forests, recover more slowly from these effects than soils in which organicmatter is replaced more quickly.1Limiting Damage to Forest Soils During RestorationaProactive Restoration Treatments Can Benefit SoilsMany of fire’s negative effects on soils can be minimized with efforts to prevent cata-strophic fires. Thinning and controlled burns can clear out accumulated brush and otherfuels from forests. Then, when a fire does start, it is likely to burn cooler and with shorterduration in a forest that has undergone restoration treatments, thereby preventing manyof the deleterious effects of prolonged, hot fires.However, even prescribed burns and mechanical thinning projects introduce their owndamage to forest soils, especially soil compaction. Compaction can reduce soil porosityand decrease the rate of water infiltration. These effects can lead to increased runoff anderosion similar to that seen following fires. Careful planning and treatment implementa-tion can minimize these impacts.Forest Restoration: Effects on SoilsMineral soil can be lost during restoration thinning efforts in the same way as duringtraditional logging operations: directly through the removal of surface layers by mecha-nized equipment, or indirectly through compaction. Either type of damage can lead toerosion, retardation of plant recovery, and impeded root growth. Various factors affectthe degree to which a particular soil type or site is vulnerable to soil compaction and loss(Selmants et al. 2003):• Fine-textured soils are more at risk of compaction.• Wet soils are more likely to sustain damage from both compaction and mechanical soilremoval than dry soils.• Organic matter and surface rock fragments can buffer soils from compaction.The same factors can influence the speed at which soil recovers, although no studies todate have documented complete recovery from machine-induced compaction.In addition, prescribed fires after restoration thinning can cause extensive soil heatingand, when burning in thick litter, can damage roots and cause tree mortality (seeWorking Paper 3: Protecting Old-Growth Trees From Prescribed Fire). Slash pile fires cancause intense soil heating, destroying the soil seed bank and mycorrhizal fungi (Korb andSpringer 2003). For these reasons, soil effects should be considered when planning post-thinning burns.Minimizing Soil Loss and CompactionSoil impacts should be considered during all stages of a restoration project: in the plan-ning process, during implementation, and after thinning is completed. The followingsteps can aid in minimizing impacts.2Limiting Damage to Forest Soils During Restoration a3Planning• Make prescriptions reasonable for easier cutting. Leaving a few small trees where adense doghair thicket stands, for example, makes it difficult for the logger to cut therest down, resulting in more time needed for the job and greater impacts to soil. If athicket is to be retained for wildlife habitat, it may be better to cut trees from its edgewhile retaining the thicket’s integrity.• Designate skid trails ahead of time. Use a pattern, such as a zigzagging line, that occu-pies as little surface area as possible (Garland 1997). Take advantage of areas least sus-ceptible to compaction, such as areas with some surface rocks.• Consider manual treatments such as hand felling, especially in ecologically sensitiveareas.• Consider a mosaic of treatments that leaves some areas undisturbed.Implementation• Work when soils are least sensitive. Avoid wet periods. One good option is to workwhen soil is frozen or dry. A layer of snow can provide an additional buffer againstcompaction.• Maintain soil organic matter and keep surface soil, litter, and slash in place while har-vesting. This can increase resistance to com-paction and protect soils from erosion. Thetradeoff is that this can also increase the severityof burns, controlled or otherwise, that followmechanical treatments—so removing slashbefore burning may be a good idea.• Use a cut-to-length (CTL) harvesting systemthat processes trees in the woods. The resultingslash can be disposed of in front of the machineand driven on to buffer soils from compaction.The use of a CTL system also reduces the needto drive to each individual tree by harvestingthose within a set radius of the machine, asopposed to harvesting requirements for a drive-to-tree feller buncher.• Use a forwarding system rather than a log skid-ding system in conjunction with a CTL har-vester to collect logs piled in the woods by driv-ing on the same slash mats. Later, the forwardermay be used to collect and remove the slashitself.• Fell trees to skid trails in order to minimize skidding distances, soil disturbance, anddamage to vegetation (Figure 1; Garland 1997).Figure 1. Felling trees to skid trails canreduce the difficulty of winching andminimize soil impacts. Reprinted withpermission from Garland 1997.Limiting Damage to Forest Soils During Restorationa4• Consider hot loading, or loading logs directly onto trucks rather than decking themfirst.• Consider ripping skid trails to rehabilitate them after use.After Thinning• Burn slash where soil is already disturbed, such as on loading areas or roads.• Lop and scatter slash before burning in order to prevent intense soil impacts underslash piles. The tradeoff is that excessive broadcast slash can greatly increase the inten-sity of prescribed fires and make them difficult to control. In particular, hot spots mayoccur under larger branches.• Consider alternatives to burning slash. It can be removed for chipping, or transportedto a biomass or pellet plant. If they are to be removed, slash piles should be placedalong roads or skid trails for easy loading.• One new approach that shows promise is remediation of severely disturbed areas—such as former roads and sites of slash pile fires—with native fungus. Spreadingchipped wood and bark on such areas after inoculating it with fungi speeds the ecolog-ical recovery process and may help prevent the spread of noxious plants.• Construct fire control lines with an eye toward minimizing soil compaction and ero-sion problems. Locate control lines away from erosive soils. Minimize the time controllines are in place, and rehabilitate them quickly after burning. Install water bars onsteep slopes. Strike a careful balance between the straight control lines preferred by firemanagers and zigzagging lines that may better prevent soil compaction and erosion.• Seeding with native herbaceous plants can help stabilize soils after fire. Applying seedinto the ash bed immediately after burning helps hold the seed in place, reducing theneed to drill or otherwise disturb the surface.• Carefully consider the frequency of future prescribed fires. They are crucial in main-taining forest structure but, if repeated as often as every two years, may cause declinesin soil nitrogen available to plants (Wright and Hart 1997). Somewhat longer intervalsmay be preferable.For More InformationFor information about forest restoration, contact the ERI at 928-523-7182 orwww.eri.nau.edu.To learn more about remediation of disturbed areas with fungus, contact Jim Bell at com-posttrees@yahoo.com or visit www.fungi.com/mycotech/roadrestoration.html.Written by Anne MinardReviewed by Dennis Becker, Sat Sansar Best, Kevin Boness, Charlie Denton, Tori Derr, TimDuck, Taylor McKinnon, Jeff Morton, Steve Overby, and Todd Schulke.Series Editor Peter Friederici  Northern Arizona University is an Equal Opportunity/Affirmative Action Institution   NAU Creative Communications/A49866/1M/11-02ReferencesDeBano, L. F., D. G. Neary, and P. F. Ffolliott. 1998. Fire’s effects on ecosystems. New York:Wiley.Garland, J. J. 1997. Designated skid trails minimize soil compaction. Oregon StateUniversity Extension Service publication EC1110.http://eesc.orst.edu/agcomwebfile/edmat/EC1110.pdf.Korb, J. E., and J. D. Springer. 2003. Understory vegetation. Pp. 233–250 in Ecologicalrestoration of southwestern ponderosa pine forests, ed. P. Friederici. Washington, D.C.:Island Press.Selmants, P. C., A. Elseroad, and S. C. Hart. 2003. Soils and nutrients. Pp. 144–160 inEcological restoration of southwestern ponderosa pine forests, ed. P. Friederici. Washington,D.C.: Island Press.Wright, R. J., and S. C. Hart. 1997. Nitrogen and phosphorus status in a ponderosa pineforest after 20 years of interval burning. Ecoscience 4:526–533.Ecological Restoration InstituteNorthern Arizona UniversityP.O.Box 15017Flagstaff,AZ 86011-5017www.eri.nau.edu2ERI 35AENON-PROFIT ORG.U.S. POSTAGEPAIDNORTHERNARIZONAUNIVERSITY

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