United States

Department

of Agriculture

Forest Service

Rocky Mountain

Research Station

Proceedings

RMRS-P-44

March 2007

Volcanic-Ash-­Derived Forest 

Soils of the Inland Northwest: 

Properties and Implications for 

Management and Restoration

9-10 November 2005

Coeur d’Alene, ID
Page-Dumroese, Deborah; Miller, Richard; Mital, Jim; McDaniel, Paul; Miller, Dan, tech. eds. 2007. 

Volcanic-Ash-­Derived Forest Soils of the Inland Northwest: Properties and Implications 

for Management and Restoration. 9-10 November 2005; Coeur d’Alene, ID. Proceedings 

RMRS-P-44; Fort Collins, CO: U.S. Department of Agriculture, Forest Service, Rocky Mountain 

Research Station. 220 p.

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Abstract ________________________________________

Volcanic ash from the eruption of Mt. Mazama ~7,700 years ago has a strong influence on many forested landscapes of the Pacific Northwest and Intermountain regions 

of the USA and Canada. Because of the unique biological, physical and chemical 

properties of the ash, it is closely tied to plant communities and forest productivity, and 

should therefore be considered as a resource to protect when harvesting, burning, or 

site preparation activities occur on it. How did this symposium get started? There has 

been a steady stream of questions, problems, and research on volcanic ash-cap soils 

for many decades. This symposium was designed to assemble experts to discuss our 

state-of-knowledge about volcanic ash-cap soil management and restoration. About 200 

scientists and natural resource managers participated in this conference, which was held 

at the Coeur d’Alene Resort, Coeur d’Alene, ID in November 2005.

The Technical Committee __________________________

Deborah S. Page-Dumroese is a Research Soil Scientist and Project Leader, Rocky 

Mountain Research Station. Debbie’s research has focused on long-term soil productivity 

after management activities, including belowground chemical, physical, and biological 

properties. 

Richard E. Miller is a retired Research Soil Scientist from the Pacific Northwest Research 

Station. Dick is still actively involved in soil research and is currently working to address 

issues of soil quality and monitoring.

Jim Mital is the Forest Ecologist, Soil Scientist, and Weed Coordinator on the Clearwater 

National Forest. Jim has worked to help design “soil friendly” management options for 

resource managers.

Paul McDaniel is Professor of Soil Science in the College of Agricultural and Life Sciences at the University of Idaho. Paul’s research activities have included elucidating the 

unique chemical and physical properties of ash-cap soils.

Dan Miller is Silviculture Manager for Potlatch Forest Holdings, Inc., Lewiston, ID. Dan 

has been instrumental in working with logging contractors to reduce soil impacts during 

harvesting.
Contents______________________________________________________

Page

Properties, Characteristics, and Distribution of Ash-cap Soils .............................................. 1

Volcanic Ash-cap Forest Soils of the Inland Northwest Properties and 

Implications for Management and Restoration............................................................................... 3

Steven B. Daley-Laursen

Ecological and Topographic Features of Volcanic Ash-Influenced Forest Soils ............................. 7

Mark Kimsey, Brian Gardner, and Alan Busacca

Field Identification of Andic Soil Properties for Soils of North-central Idaho ................................ 23

Brian Gardner

Physical and Chemical Characteristics of Ash-influenced Soils of Inland Northwest Forests...... 31

P. A. McDaniel and M. A. Wilson

Assessing Quality in Volcanic Ash Soils....................................................................................... 47

Terry L. Craigg and Steven W. Howes

Past Activities and Their Consequences on Ash-cap Soils .................................................. 67

Effects of Machine Traffic on the Physical Properties of Ash-Cap Soils....................................... 69

Leonard R. Johnson, Debbie Page-Dumroese, and Han-Sup Han

Runoff and Erosion Effects after Prescribed Fire and Wildfire on Volcanic Ash-Cap Soils .......... 83

P. R. Robichaud, F. B. Pierson, and R. E. Brown

Management Alternatives for Ash-cap Soils ........................................................................... 95

Volcanic Ash Soils: Sustainable Soil Management Practices, With Examples of 

Harvest Effects and Root Disease Trends.................................................................................... 97

Mike Curran, Pat Green, and Doug Maynard

Restoring and Enhancing Productivity of Degraded Tephra-Derived Soils ................................ 121

Chuck Bulmer, Jim Archuleta, and Mike Curran

Ash Cap Influences on Site Productivity and Fertilizer Response in Forests of the 

Inland Northwest......................................................................................................................... 137

Mariann T. Garrison-Johnston, Peter G. Mika, Dan L. Miller, Phil Cannon, and Leonard R. Johnson

Economics of Soil Disturbance................................................................................................... 165

Han-Sup Han

Special Topic—Grand Fir Mosaic ........................................................................................... 173

The Grand Fir Mosaic Ecosystem—History and Management Impacts..................................... 175

D. E. Ferguson, J. L. Johnson-Maynard, and P. A. McDaniel

Chemical Changes Induced by pH Manipulations of Volcanic Ash-Influenced Soils.................. 185

Deborah Page-Dumroese, Dennis Ferguson, Paul McDaniel, and Jodi Johnson-Maynard

Summaries of Poster Papers .................................................................................................. 203

WEPP FuME Analysis for a North Idaho Site............................................................................. 205

William Elliot, Ina Sue Miller, and David Hall

Erosion Risks in Selected Watersheds for the 2005 School Fire Located Near 

Pomeroy, Washington on Predominately Ash-Cap Soils.............................................................211

William Elliot, Ina Sue Miller, and Brandon Glaza

Conference Wrap-up .................................................................................................................. 215

Richard E. Miller

Properties, Characteristics, and 

Distribution of Ash-cap Soils

Past Activities and Their 

Consequences on Ash-cap Soils

Management Alternatives

for Ash-cap Soils

Special Topic—

Grand Fir Mosaic

Summaries of Poster Papers

Properties, Characteristics, and 

Distribution of Ash-cap Soils

USDA Forest Service Proceedings RMRS-P-44. 2007 

Volcanic Ash-cap Forest Soils of the Inland 

Northwest Properties and Implications for 

Management and Restoration

Steven B. Daley-Laursen

In: Page-Dumroese, Deborah; Miller, Richard; Mital, Jim; McDaniel, Paul; Miller, Dan, tech. eds. 2007. 

Volcanic-Ash-­Derived Forest Soils of the Inland Northwest: Properties and Implications for Management 

and Restoration. 9-10 November 2005; Coeur d’Alene, ID. Proceedings RMRS-P-44; Fort Collins, CO: 

U.S. Department of Agriculture, Forest Service, Rocky Mountain Research Station.

Steven B. Daley-Laursen, Dean and Professor, College of Natural Resources, University of Idaho.

	 Good Morning and Welcome. My task today is to set the stage for a productive conference by

providing an historical context, an overview of the subject matter to be covered, and a challenge for

next steps by interested scientists and practitioners.

An Historical Perspective

	 Volcanoes have been part of the Earth’s history ever since it has had a solid surface. And, volcanoes have been a part of human culture for thousands of years. In some ways, our reactions to the

magnitude of a volcanic explosion haven’t evolved as much as one might think. Ranging from ancient

cultures who believed that victims should be sacrificed in response to volcanic eruption, to Harry

Truman who stubbornly sacrificed himself during the most recent eruption in the continental United

States, volcanoes have impacted our lives in many ways and will continue to do so in the future.

	 But disaster sometimes brings fortune. Here on the West Coast where some volcanoes erupt violently every 20-30 years or so, we live in one of the grandest ash-cap locations in the world. Soils

throughout the Inland Northwest region of the United States extending from the Cascade Mountains

of Oregon and Washington to Northern Idaho and Western Montana have been influenced and

overlain by tephra from cataclysmic eruptions of Mount Mazama.

	 About 6,850 years ago Mount Mazama, a strato-volcano, collapsed to produce Crater Lake, one of

the world’s best known calderas. The caldera is about 6 miles (10 km) wide. The catastrophic pyroclastic eruption released about 12 cubic miles (50 cubic km) of magma to the surface. It was one of

the largest eruptions in the last 10,000 years.

	 The Mazama eruption was followed by the May 18, 1980 eruption of Mount St. Helens in westcentral Washington. This eruption spread less than 1/100th of the Mazama ash volume over areas of

eastern Washington and Northern Idaho. The St. Helens ash plume carried by the jet stream took

2 weeks to circle the globe! Though considerably smaller in volume output than the Mazama eruption, the Mount St. Helens eruption and deposition had effects on soils and productivity in our region

that are still visible and proudly measurable.
USDA Forest Service Proceedings RMRS-P-44. 2007

Daley-Laursen Volcanic Ash-cap Forest Soils of the Inland Northwest Properties and Implications for Management and Restoration

On a personal note, these volcanoes and the consequence of their eruptions

have had a direct impact on my life and career in three ways. As an Oregonian by

birth I was a visitor to Crater Lake learning about local geology and forests. As a

resident of Moscow, Idaho during the May 1980 eruption of St. Helens (and the

nearly 1-year aftermath) I had the experience of being blanketedwith ash and having

life’s pace slow to a walk with a mask and goggles in a snowy white haze. And,

as a student of the Habitat Type at UI and a researcher developing stand growth

simulation models in the Grand fir, Douglas-fir and cedar hemlock systems of the

Inland Northwest, I learned first hand about the impact of ash on soil properties

and chemistry and site productivity and potential vegetation. So, I have for some

time been awed by the power of these profound phenomena—the volcanoes that

produce the ash, and the ash caps that add value to the region’s soils.

My experience with the aftermath of volcanic eruption was expanded and

deepened this past year, when I had the opportunity to tour Las Valles Caldera in

northern New Mexico. This is a 50 mile wide caldera that blew its top 1.2 million

years ago, leaving behind an inspiring landscape of biological diversity. I went

there to meet up with scientists from three New Mexico universities conducting

research on watershed dynamics and carbon-water relations. This is a remarkable

place at 10,000 feet in the Southern Rocky Mountains. Don’t miss your opportunity

to visit and learn about the past and present conditions of Las Valles Caldera.

These major volcanic eruptions and depositions all created the same wondrous

outcome; ash-cap soils. As a result of frequent volcanic activity, the soils of the

Northwest are unique and behave differently than anywhere else in the United

States. As you’ll hear from a dozen researchers and land managers over the next

2 days, we now know much about the properties and characteristics of these

deposited soils and the effects of our activity on them.

An Overview of Our State of Knowledge—

Preview of the Conference _______________________________________

We know the distribution of Andic soils, and Mark will tell you more. We

know about the chemical and physical properties of Andisols. They are light and

fluffy, low density and have remarkable water-holding capacity. Paul will tell us

more about all of this, drawing from his 2005 treatise on Andisols. We know

something about Andic soil quality and will hear more about that from Steve

later this afternoon.

We know that the most significant glass accumulations are found in forested

areas. It has been suggested that outside a forest structure like the Douglas-fir,

or the more mesic Grand fir and cedar hemlock ecosystems, volcanic ash is not

retained against erosion, certainly not under extreme conditions of management

that exacerbate erosion.

We also know there is a strong link between Andisol distribution and forest

productivity; reference my earlier comments about habitat type as a predictor

variable in stand growth simulation models. In the 1970s, Habitat Type was explaining much variation in our tree growth and forest stand simulation models,

acting as an effective integrator of slope, aspect, elevation, moisture and temperature in the prediction of species occurrence and abundance as well as tree

and shrub growth rate. At that time, many scientists and managers were beginning
USDA Forest Service Proceedings RMRS-P-44. 2007 

Volcanic Ash-cap Forest Soils of the Inland Northwest Properties and Implications for Management and Restoration Daley-Laursen

to believe that the one factor not adequately stratified in Daubenmire’s Habitat

Type scheme was soil type.

Ash-cap soils play a critical role in water relations and nutritional ecology, and

thus, plant diversity in forested ecosystems. Later attempts at habitat typing in the

United States have taken soil type much more seriously.

In more recent science on forest nutrition, soil parent material has taken on

celebrity status as a predictor variable in site productivity. Researchers and land

managers now speak of good and bad rocks (parent material) and acknowledge

through empirical and laboratory science the characteristics of ash soils and their

direct impact on nutritional ecology. Through cooperative research and outreach,

this has had a direct influence on management prescriptions on both public and

private forest ownerships.

From this body of research and practice, we know that properly managed

Andic soils can be some of the most productive on earth. Dennis and Larry will

share their knowledge on management regimes on forested systems with ash-cap

soils. Marianne will share ways to improve tree performance through nutritional

augmentation and site decisions. Pete will tell you about the effects of different

fire regimes on Andic soil types.

We know these soils are susceptible to compaction, and decrease in value and

volumeunderintense andfrequentfire anderosionfollowing irresponsible forest management practices. Han and Leonard will review the effects of machine traffic, plans

for a lighter footprint during forest operations, and the overall economics of timber

operationswithaneye toecological andeconomic sustainability.Chuckwillintroduce

us to restoration schemes for degraded soils. And, Mike will share best management

practices relating to insect and disease populations and harvest operations.

The Challenge to Scientists and Practitioners—

Where We Go From Here _________________________________________

We know much, and you’ve gathered an impressive crew of scientists and practitioners to share the current knowledge base. But, the conference is about more

than just dumping all the current knowledge on the table. It’s about synthesizing

current knowledge into a more coherent perspective on these soils and the management they can tolerate. And, just as important, it’s about framing the next set of

questions...laying out your science road map for the future, and doing it together.

In interviewing soils folks and managers in preparation for this presentation,

I was told by more than one person that most of the studies on Andisols have

occurred in the Midwest and overseas—in Japan, Iceland, and New Zealand for

example, and that the body of information available in the U.S. is fleeting and

incomplete. It would be good to organize a list of highest priority research to be

conducted on Andic soils in this region.

Most also agree that around the edges of this spotting science base, there are

mental volumes of endemic, practitioner knowledge about Andic soils stored in the

expert systems that are our experienced local forest managers. It would be useful to

all of you to organize this endemic knowledge and subject it to scientific scrutiny,

invalidation and confirmation. That’s why you’re here—to match the insights and

experience of forest managers with the curiosity of forest researchers...to develop

a coherent research agenda that will lead to best practices for protection and

sustainability of this important Andic soil resource.
 USDA Forest Service Proceedings RMRS-P-44. 2007

Daley-Laursen Volcanic Ash-cap Forest Soils of the Inland Northwest Properties and Implications for Management and Restoration

That’s the real reason I accepted the invitation to be with you today. Obviously, I can’t stand toe to toe with you on the science of soils or the intricacies

and art-form of management. But, I have spent my career straddling the research

and outreach worlds of academia, striving to bring the researcher and practitioner

together around a coherent and integrated science and management agenda. The

best outcomes of science are achieved when the scientist and practitioner conceptualize a problem and research question together and I’m passionate about

making this type of connection a reality. The rewards are profound for all who

subscribe.

So, my closing statement is an admonition in that spirit of collaboration and

coordination.

Soils are taken for granted and underrated by the average person. Just dirt,

you know—uncorruptable and forever static in the average mind’s eye. But, you

and I know this isn’t true. They are in fact the substrate on which most life and

biodiversity resides, they are the physical base on which the water system selfregulates, they are often the defining factor in what you can and cannot do well

on a particular site. And they are fragile, corruptible and degradable. In many

cases, if you screw them up once, you don’t get a second chance. In extreme

cases of erodibility, when they’re gone, they’re gone.

The Andic soil is particularly erodible. Studies of Andic soils can give clues to

other highly erodible soils in even more critical regions of biodiversity, like the

topics.

As we continue to grow our understanding of the working processes and functions of ecosystems, and as a society, we recognize and attempt to quantify, and

even trade, the values of natural capital, soil and it’s relationship to water and

carbon will be key areas of inquiry, value, credit and trade.

Most climate modelers and carbon scientists now agree that the Inland Northwest, in fact the Grand fir and cedar hemlock ecosystems with moist, relatively

warm temperature regimes and at low to mid elevations, may be one of North

America’s biggest carbon sponges. Andic soils definitely play a role in this equation. In the marketplace that characterizes our economy and society, our valuing

of these soils will follow on our understanding of these soils.

Scientists and managers in western North America have in their backyard a

living laboratory in which to study the Andic soil. You’re in the driver’s seat for

advancing the world’s knowledge on these soils, their properties and characteristics, their additions to ecological potential and production, and their responses

to the regimes of human activity. And, you’re gathered here to ponder this.

So, listen well to what you and your colleagues know and chart a course

together that will fill in the blanks. Identify the key management questions and

issues relating to ash cap soils. Identify the categories of inquiry that are important

to pursue. Identify areas where you need to go beyond anecdote to science and

make some plans to test and invalidate your mental models. Let the practitioners

influence the research agenda, and hold the scientists accountable for getting the

science out in usable form to managers on the ground.

The University of Idaho is a land grant institution with a mission to advance

both science and practice in natural resource management. We will be looking

for ways to partner in your noble pursuit.

Good luck with your meeting and thanks again for the invitation to participate.
USDA Forest Service Proceedings RMRS-P-44. 2007

In: Page-Dumroese, Deborah; Miller, Richard; Mital, Jim; McDaniel, Paul; Miller, Dan, tech. eds. 2007. 

Volcanic-Ash-­Derived Forest Soils of the Inland Northwest: Properties and Implications for Management 

and Restoration. 9-10 November 2005; Coeur d’Alene, ID. Proceedings RMRS-P-44; Fort Collins, CO: 

U.S. Department of Agriculture, Forest Service, Rocky Mountain Research Station.

Mark Kimsey is a Research Assistant, Department of Forest Resources, University of Idaho, Moscow, 

ID. Brian Gardner is a Soil Scientist, U.S. Department of Agriculture, Natural Resources Conservation 

Service, Moscow, ID. Alan Busacca is a Crop and Soil Scientist, Department of Crops and Soil Science, 

Washington State University, Pullman, WA.

Abstract

	 Volcanic ash distribution and thickness were determined for a forested region of north-central

Idaho. Mean ash thickness and multiple linear regression analyses were used to model the effect of

environmental variables on ash thickness. Slope and slope curvature relationships with volcanic ash

thickness varied on a local spatial scale across the study area. Ash distribution and aspect showed weak

correlation. Elevation and ecologically based plant associations accounted for about 54 percent of the

observed variation in volcanic ash thickness. Climax plant associations moister than grand fir/queen

cup beadlily (Abies grandis/Clintonia uniflora) had consistently thick ash mantles and soils that would

be classified as either Andisols or andic subgroups using Soil Taxonomy. The statistical model error of

10.7 cm was significantly lower than the >20 cm variation often found in local soil series. This model

quantitatively assesses ash distribution and can be integrated into other local ecological models. 

Ecological and Topographic Features of 

Volcanic Ash-Influenced Forest Soils

Mark Kimsey, Brian Gardner, and Alan Busacca

Introduction

	 Volcanic ash from eruptions along the Pacific Northwest Cascade Range has signifi­cantly

influenced forest soils of the Inland Northwest, U.S.A. (Mullineaux 1986; Shipley and

Sarna-Wojcicki 1983). The Holocene era eruption of Mt. Mazama (now Crater Lake, OR)

distributed >116 km3 of volcanic tephra across this region (Bacon 1983; Zdanowicz and others

1999). Soils influenced by the deposition of Mt. Mazama tephra can be found throughout

the western United States and into southwestern Canada (fig. 1). Soils formed in, or influenced by volcanic ash are important to forest management. Volcanic ash-influenced soils

have lower bulk density, higher porosity, and higher water infiltration and retention than

soils less influenced or unaffected by ash (McDaniel and others 2005; Nanzyo and others

1993; Nimlos 1980; Warkentin and Maeda 1980). Among the benefits of these properties is

the reduction in drought stress on plant communities during extended summer dry periods.
 USDA Forest Service Proceedings RMRS-P-44. 2007

Kimsey, Gardner, and Busacca Ecological and Topographic Features of Volcanic Ash-Influenced Forest Soils

Regional deposition following the eruption of Mt. Mazama was estimated at

approximately 15-20 cm thick in eastern Washington, with thinning in areas more

distal to the eruption (Busacca and others 2001). The current distribution pattern of volcanic glass derived from the Mazama event is much different than this

original deposition pattern. A map depicting the prevalence of volcanic glass in

modern surface soils of Eastern Washington indicates only weak tephra influence

in soils of the southwest Columbia Plateau even though these areas are closest

to the volcanic source of the tephra (fig. 2) (Busacca and others 2001). Instead,

glass content of the surface soils increases with increasing downwind distance

from the source volcano. Also, none of the modern tephra-influenced surface

soils are composed of pure volcanic ejecta. Soils of the Blue Mountains, OR, and

Clearwater Mountains, ID, have some of the best-expressed andic soil properties

Figure 1—Estimated spatial distribution of Mt. Mazama volcanic ash 

across the western United States and southwestern Canada. The study 

area for this research project is located within the boxed area of northcentral Idaho (Mt. Mazama ash distribution adapted from Williams and 

Goles 1968).
USDA Forest Service Proceedings RMRS-P-44. 2007

Ecological and Topographic Features of Volcanic Ash-Influenced Forest Soils Kimsey, Gardner, and Busacca

in the region, yet these soils generally have glass contents of 20 to 50 percent in

their surface layers.

Several mechanisms have been proposed as factors in the transformation of

the original tephra sheet into the mixed distribution patterns that we see. These

include: 1) a partial re-entrainment of ash by wind with resulting redeposition

further downwind (i.e. to the northeast); 2) burial of ash material by subsequent

episodes of loess deposition; 3) bioturbation of the tephra by soil fauna, which

served to mix the volcanic glass into the surrounding soil mass; and 4) reduced

erosion loss and enhanced capture ofremobilized air-fall material under coniferous

vegetation such as is found at the northern and eastern margins of the Columbia

Plateau (Busacca and others 2001; Hunter 1988).

Recent Natural Resource Conservation Service (NRCS) soil surveys have extensively mapped volcanic ash-influenced forest soils in portions of the Inland

Northwest. From these surveys, ash distribution and ecological/topographic

relationships can be assessed. However, these soil survey relationships are often

presented as a range in ash thickness. For example, volcanic ash thicknesses

in Hugus and Bouldercreek soil series commonly found in our study area have

mapped variations >20 cm (Soil Survey Division 2006). As more information is

gathered on the role of volcanic ash in forest productivity and management, forest managers may need finer resolution of ash distribution than a range in ash

thickness. The inherent variation of soil surveys may not provide the level of accuracy needed for decision support systems. A potentially workable alternative

is a statistical re-analysis of individual soil-site descriptions created during local

NRCS soil surveys.

Figure 2—Volcanic glass content of modern surface soils in eastern Washington (from Busacca 

and others 2001).
10 USDA Forest Service Proceedings RMRS-P-44. 2007

Kimsey, Gardner, and Busacca Ecological and Topographic Features of Volcanic Ash-Influenced Forest Soils

Based on the above rationale, our objective was to select a relatively small

geographic region within the Inland Northwest for which extensive soil and environmental data was available to 1) develop a dataset of volcanic ash depths, habitat

types, and terrain features; 2) conduct statistical analyses to assess relationships

between ash thickness and selected vegetative and topographic features; and 3)

determine the precision and fit of a statistical model to estimate the thickness of

volcanic ash across a landscape.

Materials and Methods __________________________________________

Study Area

The area chosen for this study is the NRCS ID-612 soil survey region of northcentral Idaho (fig. 1). This survey area encompasses about 336,250 ha of diverse

climatic factors, habitat types, and complex terrain attributes. Landscapes of this

region are generally characterized as mountainous in the north and east, while

the south and west are characterized as basalt plateaus/benchland incised with

deep canyons. Elevation ranges from 300 m in the southwest to >1700 m in the

north and east. Mean annual precipitation (MAP) roughly follows the elevational

gradient, with <300 mm MAP in the southwest and >1500 mm in the northeast.

Ponderosa pine (Pinus ponderosa) and Douglas-fir (Pseudotsuga menziesii var.

glauca) habitat types dominate the southern regions of the soil survey. Western

redcedar (Thuja plicata) and western hemlock (Tsuga heterophylla) dominate the

warm, moist upland regions; with Subalpine fir (Abies lasiocarpa) and mountain

hemlock (Tsuga mertensiana) predominant in the colder, higher elevations(Cooper

and others 1991).

Data Analysis

Nine hundred and twenty-one soil-site descriptions and their XY coordinates

were obtained from the Orofino, ID, NRCS field office. Field records composed

of volcanic ash thickness, terrain attribute, and habitat type observations were

entered into a database. The effective number of observations available for analyses

varied since it was not unusual for certain field observations to not be recorded

on the field form. A summary of the field descriptors and their potential influence

on volcanic ash distribution is presented in table 1.

The continuous variables elevation (ELE), slope (SLP), and aspect (ASP) were

grouped into discrete classes to facilitate the comparison of incremental changes

in ash thickness with terrain attributes. ELE was classed into 200-m intervals, SLP

at 10 percent breaks, and ASP in 45-degree quadrants. Curvature values were

derived from a United States Geological Survey (USGS) 30-m digital elevation

model (DEM) using grid algebra in a geographic information system (GIS). The

numerical curvature values were then grouped into their respective linear (L),

concave (C), and convex (C) classes.

Average ash thickness by class was computed for each of the variables described

above. Standard errors were computed and t-tests performed to test for significant

differences in ash thickness using an α-level of 0.1. Variables that showed significant class differences in volcanic ash thickness were subsequently tested for use

as predictor variables in a volcanic ash distribution model. A stepwise variable
USDA Forest Service Proceedings RMRS-P-44. 2007 11

Ecological and Topographic Features of Volcanic Ash-Influenced Forest Soils Kimsey, Gardner, and Busacca

Table 1—Selected ecological and topographic features used in this study and their potential significance in determining volcanic 

ash distribution patterns (Cooper and others, 1991; Gallant, 2000).

Ecological/Topographic Features Significance

Elevation (meters): ELE Climate, vegetation type, potential energy

200-400

400-600

 600-800

 800-1000

1000-1200

1200-1400

1400+

Slope (%): SLP Overland and subsurface flow, velocity, and runoff

0-10

10-20

20-30

 30-40

40-50

 50-60

 60+

Aspect (°): ASP Solar irradiation, wind erosion/deposition

Flat

N (342.6-27.5)

NE (27.6-72.5)

E (72.6-117.5)

SE (117.6-162.5)

S (162.6-207.5)

SW (207.6-252.5)

W (272.6-297.5)

NW (297.6-342.5)

Up/Across Slope Curvature: PRCU/PLCU Flow acceleration, erosion/deposition rate, converging/diverging 

Linear flow, soil water content

Concave

Convex

Plant Associations: Climate, topography, site productivity, disturbance

Vegetation Series: VS

 Pinus ponderosa (PIPO)

 Pseudotsuga menziesii (PSME)

 Abies grandis (ABGR)

 Thuja plicata (THPL)

 Tsuga heterophylla (TSHE)

 Tsuga mertensiana (TSME)

 Abies lasiocarpa (ABLA)

Habitat Type: HT

 Festuca idahoensis (FEID)

 Physocarpus malvaceus (PHMA)

 Symphoricarpus albus (SYAL)

 Linnaea borealis (LIBO)

 Clintonia uniflora (CLUN)

 Asarum caudatum (ASCA)

 Adiantum pedatum (ADPE)

 Gymnocarpium dryopteris (GYDR)
12 USDA Forest Service Proceedings RMRS-P-44. 2007

Kimsey, Gardner, and Busacca Ecological and Topographic Features of Volcanic Ash-Influenced Forest Soils

selection procedure was used within the framework of a general linear model

(GLM) to assess which variables explained the greatest variation in volcanic ash

thickness. Variables that were within the upper 0.1 percentile of a Type III sumsof-squares F-distribution were retained within the model. The prediction equation

was deemed reliable if it produced a high coefficient of determination (R2) and

low root mean square error (RMSE).

Results _________________________________________________________

Topographic and Vegetative Indicators

Volcanic ash is highly correlated with ELE (fig. 2). Each 200-m increment is

significantly different up to 1200 m (p <0.1). Above 1200 m, there is no significant

difference in mean ash thickness. Forest soils below 600 m in elevation have ash

thicknesses ≤10 cm. Many low elevation soils exhibit significant mixing of the

shallow ash mantle with underlying soil material. These lower elevation forest

soils are classified as vitrandic subgroups of a soil order (Soil Survey Staff 1999).

Forest soils located at elevations between 600 m and 1200 m have mean ash

thicknesses 24 to 35 cm. These soils are classified as andic subgroups. Volcanic

ash mantles have a mean thickness of about 45 cm above 1200 m elevation. Ash

mantles deeper than 36 cm that meet several other NRCS criteria are considered

members of the order Andisols (Soil Survey Staff 1999) or Andosols of the World

Reference Base (FAO/ISRIC/ISSS 1998).

Mean ash thicknessshowed no significant decreasewith increasing slope gradient

(fig. 3). Mean ash thickness showed relatively little variation with a small range of

25 to 34 cm across all slope classes. Slopes <10 percent showed significantly less

volcanic ash than all classes except the 60 percent class. Ash depth increases up

Figure 3—Mean volcanic ash thickness as a function of elevation (ELE) 

class. Y-axis bars represent standard errors, with letters indicating significant 

differences (p < 0.1).
USDA Forest Service Proceedings RMRS-P-44. 2007 13

Ecological and Topographic Features of Volcanic Ash-Influenced Forest Soils Kimsey, Gardner, and Busacca

to the 20 to 30 percent SLP class; after which, there are no significant differences

in ash thickness by SLP class. The 20 to 30 percent class had significantly greater

ash depths than all slope classes and was marginally greater than the 40 to 50

percent class (p = 0.12).

North aspects generally exhibit thicker ash mantles than south facing aspects

(fig. 4). N, NW, and SE aspects show mean ash depths >32 cm. NE and W facing

aspects have thinner ash caps (~30 cm), but are not significantly different than N,

NW, or SE aspects. S, SW, and E aspects have significantly thinner ash mantles

of about 27 cm.

Figure 4—Mean volcanic ash thickness as a function of slope (SLP) class. Y-axis bars represent 

standard errors, with letters indicating significant differences (p < 0.1).

Slope curvature shows that nonlinear surfaces retain a greater thickness of

volcanic ash compared to linear surfaces (fig. 5). Concave and convex surfaces

show mean ash depths >30 cm for both upslope (PRCU) and across slope (PLCU)

surface curvature. Linear surfaces in both PRCU and PLCU are significantly lower

(<25 cm) than either convex or concave surfaces. There was no statistical difference between concave and convex in either PRCU or PLCU slope curvature.

Vegetation series and habitat type plant associations showed the strongest relationship with volcanic ash thickness (fig. 6). Overall, the ponderosa pine (PIPO)

and Douglas-fir (PSME) vegetation series have very thin volcanic ash mantles

(<3 cm) and show no significant change by habitat type within series. Grand fir

(Abies grandis – ABGR) has the widest range in ash-influence of all vegetation

series. Mean ash thickness ranges from 0 to 40 cm depending on the underlying

habitat type within series. The moist twinflower (Linnaea borealis – LIBO) habitat
14 USDA Forest Service Proceedings RMRS-P-44. 2007

Kimsey, Gardner, and Busacca Ecological and Topographic Features of Volcanic Ash-Influenced Forest Soils

Figure 5—Mean volcanic ash thickness as a function of aspect (ASP) class. Y-axis bars represent 

standard errors, with letters indicating significant differences (p < 0.1).

Figure 6—Mean volcanic ash thickness as a function of upslope curvature (PRCU) class. Y-axis 

bars represent standard errors, with letters indicating significant differences (p < 0.1).
USDA Forest Service Proceedings RMRS-P-44. 2007 15

Ecological and Topographic Features of Volcanic Ash-Influenced Forest Soils Kimsey, Gardner, and Busacca

type of the ABGR vegetation series surprisingly shows no significant ash mantle

(mean = 0 cm). Ash thickness in ABGR habitat types can be described as a function of increasingly moist understory indicatorspecies, with the exception of LIBO.

Habitat type rankings for volcanic ash thickness would be LIBO < PHMA/SYAL 

< CLUN < ASCA, where PHMA, SYAL, CLUN, and ASCA represent ninebark

(Physocarpus malvaceus),snowberry (Symphoricarpus albus), queen-cup beadlily

(Clintonia uniflora), and wild ginger (Asarum caudatum), respectively. These rankings suggest that vitrandic intergrades would be more prevalent on PHMA/SYAL

and LIBO habitat types, andic intergrades on CLUN, and Andisols on ASCA.

Changing from an ABGR to a western redcedar (THPL) vegetation series is

accompanied by a 5-cm increase in mean ash thickness when comparing across

CLUN habitat types. This shift is not evident for the ASCA habitat type, which

shows no significant differences between ABGR and THPL vegetation series.

Maiden­hair fern (Adiantum pedatum – ADPE) and oak-fern (Gymnocarpium 

dryopteris – GYDR) habitat typesshow a reduction of >7 cm in mean ash thickness

over ABGR/THPL-ASCA. Mean ash thickness for CLUN and ADPE/GYDR habitat

types suggest that andic intergrades would be most common, with Andisols (in

other words, ash mantle >36 cm) occurring primarily under an ASCA habitat type.

Based on these observations, understory rankings of habitat type by increasing

ash thickness would be CLUN = ADPE/GYDR < ASCA.

The western hemlock (TSHE) series displayed the largest difference in volcanic

ash thickness between CLUN and ASCA habitat types (about 28 cm). TSHECLUN habitat types show at least a 6-cm decrease in mean ash thickness when

compared to THPL-CLUN; however, a TSHE-CLUN habitat type would still fall

within the andic intergrade classification associated with other CLUN habitat

types. Ash thickness in the ASCA habitat type is significantly greater for TSHE

vegetation series than for any other series with observed ASCA habitat types.

Mean ash depths on TSHE-ASCA are 54 cm, which would place them well within

the Andisol soil order.

Mountain hemlock (TSME) and subalpine fir (ABLA)series are typically found at

higher elevationswhere airtemperatures are relatively lowand annual precipitation

high. The warmer, moister ASCA habitat was not observed. Mean ash thickness

is greater on TSME-CLUN than ABLA-CLUN, but the difference is insignificant.

Volcanic ash-thickness on these vegetation series is >36 cm, thus placing them

into the Andisol order.

Volcanic Ash Distribution Modeling

The class variables listed in table 1 were added stepwise into a multiple linear

regression equation. Variables were assumed to be independent and normally

distributed. The final model, with selected variables acting as fixed effects on

volcanic ash thickness, is:

ATjklmno = μ + PRCUj + ASPk + SLPl + ELEm + VS*HTn + εjklmno

where,

ATjklmno is the predicted value for observation o with vegetation series*habitat

	 type interaction n at elevation m on slope l with aspect k and upslope

	 curvature j,
16 USDA Forest Service Proceedings RMRS-P-44. 2007

Kimsey, Gardner, and Busacca Ecological and Topographic Features of Volcanic Ash-Influenced Forest Soils

μ is overall volcanic ash thickness mean,

PRCUj is the fixed effect of upslope curvature (concave, convex, or linear),

ASPk is the fixed effect of aspect (N, NE, E, SE, S, SW, W, NW, or FLAT),

SLPl is the fixed effect of percent slope (0-10, 10-20, 20-30, 30-40, 40-50,

	 50-60,or 60+),

ELEm is the fixed effect of elevation in meters (200-400, 400-600, 600-800,

	 800-1000, 1000-1200, 1200-1400, 1400+),

VS*HTn is the fixed effect of vegetation series*habitat interaction (where, VS are

	 ponderosa pine, Douglas-fir, grand fir, western redcedar, western hemlock,

	 mountain hemlock, or subalpine fir; and HT are Idaho fescue, ninebark/

	 snowberry, twinflower, queen-cup beadlily, wild ginger, or maidenhair fern/

	 oak-fern),

εjklmno is the error term;

where, j = 3 for upslope curvature, k = 9 for aspect, l = 7 for slope, m = 7 for

elevation, n = 13 for vegetation series*habitat type interaction, and o = 1 for

number of observations per location.

All class variables, except PLCU, explained a significant portion of variation in

volcanic ash thickness (p < 0.1) (table 2). Variables ranked from least to most in

variance explained are PRCU < ASP < SLP < ELE < VS*HT. The interaction term,

VS*HT, accounted for the largest percentage of explained variance at 71.2 percent.

ELE wasthe second largest at 18.2 percent. SLP and ASP accounted for 8.9 percent

combined, and PRCU explained the least at 1.7 percent. The overall model was

significant (p <0.001) and accounted for 60 percent of the observed variation in

ash thickness. A model RMSE of 10.7 cm and CV of 36 percent indicate that there

is a significant amount of variation still unaccounted for; however, the predictive

error is significantly lower than the variation found in local soil series.

Table 2—General linear model variables retained in an ash prediction analysis. Partial variance 

indicates the percent of the model R2 explained by each retained variable.

 Upslope Vegetation Series*

Elevation Slope Aspect Curvature Habitat Type

Partial Variance (%) 18.2 4.7 4.2 1.7 71.2

Significancea <0.0001 0.006 0.04 0.03 <0.0001

aSignificance level tested at α = 0.1.

Discussion ______________________________________________________

Ecological and Topographic Indicators

It is evident from the broad relationships presented that volcanic ash distribution is strongly associated with vegetation patterns and less dependent on terrain

attributes. Elevation, although a topographic feature, shows strong collinearity

with local precipitation gradients and vegetative cover (data not shown). This

situation suggests that elevation serves locally as a proxy variable for interactions

between precipitation and vegetation patterns and their subsequent effect on ash

distribution.
USDA Forest Service Proceedings RMRS-P-44. 2007 17

Ecological and Topographic Features of Volcanic Ash-Influenced Forest Soils Kimsey, Gardner, and Busacca

Slope class did not have a negative impact on mean ash thickness with slopes

>60 percent showing no significant decline in ash depths (fig. 3). This result supports other research on slope stability of volcanic ash. In a review of volcanic ash

soils, Warkentin and Maeda (1980) note that volcanic ash on free-standing slopes

up to 70 degrees are common in regions of high rainfall. They attribute this high

degree of stability to the unique permeability of volcanic ash.

The significantly lower mean ash thickness in the 0-to-10 percent slope class

may be due to the geographic location of these observations. A majority of these

observations for nearly flat terrain were on the benchlands of the south and

southwest portion of the study area. This region is characterized by low elevation

PSME and ABGR vegetation series, which often exhibit thin or mixed volcanic

ash mantles.

The prevalence of thicker ash mantles on north aspects may be attributable to

several factors (fig. 4). North aspects typically support moister plant communities

in our study area (Cooper and others 1991). These moist plant communities may

provide greatersoilsurface cover,whichwould decrease the impact of precipitation

and overland water flow on volcanic ash redistribution. Additionally, the moisture

retained within the soils after precipitation events would be less susceptible to

evaporation from solar radiation. Giest and Strickler (1978) found volcanic ash

soils of Oregon to be susceptible to wind erosion once in a dry state. Assuming

that current southwesterly prevailing wind patterns were similar to historic posteruption patterns, dry volcanic ash on south-facing slopes would be expected to

be more susceptible to redistribution by wind than north aspects. The significant

increase in ash thickness on southeast slopes is anomalous to this theory and

suggests that the overall effect of aspect on ash distribution is local and intricately

tied with surrounding topographic and environmental factors.

The significant decrease in ash thickness on linear surfaces shown in figure 5

is partially correlated with the slope class these observations share. A review of

the dataset shows that about 67 percent of the linear surfaces occur on slopes

<10 percent with the remainder unevenly divided among several steeper slope

classes. As detailed in the previous discussion of slope classes, observations with

gradients <10 percent are found primarily in the drier benchland portions of the

study area. The correlation between slope steepness and slope surface curvature

within the dataset may mask local effects of slope curvature on ash thickness.

Surprisingly, convex surfaces in both upslope and across slope positions displayed

no significant decrease in mean ash thickness over concave surfaces. Other research on volcanic ash deposition after the eruption of Mt. St. Helens has shown

that concave surfaces support thicker ash mantles than convex (Zobel and Antos

1991). Our conflicting results may be due to the level of variation found within

these classes. Standard errors were small because of large sample sizes, but the

standard deviations were often large within the surface classes, reflecting significant variation within the data.

Cooper and others (1991) associate shifts in climax plant associations to distinctive soil and/or topographic microclimate features. Habitat type shifts and

differing soil ash depth are evident across the broad habitat type associations

observed in our study area (fig. 7). These strong relationships may be attributed

to many combinations of topographic, climatic, or edaphic factors. Steele and

others (1981) noted that the influence of volcanic ash contributed to distinct shifts

in Idaho plant communities. However, it is still an open question as to whether
18 USDA Forest Service Proceedings RMRS-P-44. 2007

Kimsey, Gardner, and Busacca Ecological and Topographic Features of Volcanic Ash-Influenced Forest Soils

the presence of volcanic ash is responsible for shifts in plant associations, or that

variations in plant community were responsible for differential ash retention.

Despite this uncertainty, volcanic ash thickness is highly correlated with plant

associations and can be used to assess ash distribution patterns.

PSME and PIPO vegetation series show the least ash thickness within our data.

Shifts to moister habitat types within these vegetation series show no significant

dependence on volcanic ash. It has been suggested that these vegetation series

now reside on landscapes that, post-Mazama eruption, were drier and did not

support forest vegetation cover. Lack of overstory cover and dry climatic conditions prevented these landscapes from retaining volcanic ash mantles subsequent

to the eruption.

Volcanic ash thickness in ABGR communities is highly variable. Unlike successively moister plant associations, an ABGR vegetation series does not always

indicate the presence of significant volcanic ash influence. This variability is

partly attributable to the transition zone that ABGR inhabits between xeric and

udic soil moisture regimes. Near the dry end of the spectrum, ABGR plant communities would be associated with minimal to no ash influence. This suggests

that an increase in plant available soil moisture would shift the understory plant

community towards moister habitat types. Thus, drier habitat types (PHMA/SYAL)

often exhibit less ash influence in the soil than the CLUN and ASCA types.

An exception to this pattern is the ABGR-LIBO association. LIBO is considered

to inhabit moister environments than PHMA, suggesting that volcanic ash might

be present on this habitat type. The absence of volcanic ash on LIBO habitat

types may be attributable to the fact that only five observations were collected

Figure 7—Mean volcanic ash thickness as a function of overstory (VS) and understory (HT) indicator 

plant species. Y-axis bars represent standard errors, with letters indicating significant differences 

(p < 0.1) (Cooper and others 1991).
USDA Forest Service Proceedings RMRS-P-44. 2007 19

Ecological and Topographic Features of Volcanic Ash-Influenced Forest Soils Kimsey, Gardner, and Busacca

within this habitat type, providing for a poor representation of the range in ash

thickness.

All remaining plant associations moister than ABGR show significant ash

influence in the soil. The presence of a thick ash mantle is often identified by the

presence of these climax species. Increasing ash thickness in the soil is evident

in the habitat type gradients within the THPL series; however, habitat type differences are minimal.

The TSHE vegetation series occupies a narrow ecological range in north Idaho

forests and primarily inhabits moist, moderate temperature sites and are intolerant to drought, excess moisture, and frost (Cooper and others 1991). The narrow

ecological range suggests that other edaphic and climatic factors might play a

larger role in TSHE distribution than volcanic ash influence in the soil. Such factors

may also explain why TSHE-CLUN plant associations have thinner ash mantles

than THPL-CLUN. TSHE-ASCA sites do show significant increases in volcanic ash

thickness. This result suggests that volcanic ash is associated with a shift to moister

understory plant communities within the TSHE vegetation series.

TSME and ABLA plant communities occupy high elevation sites with up to

1500 mm of annual precipitation within our study area. Vegetation series within

these zones are probably not dependent on the presence of volcanic ash for their

establishment. The high precipitation and dense vegetative cover of these plant

communities retained volcanic ash subsequent to original ash deposition.

Volcanic Ash Distribution Modeling

The strength of the relationships between elevation, plant communities, and

volcanic ash produces a strong predictive ability for our ash distribution model.

An R2 value of 0.6 is considered an excellent improvement over the limited regional volcanic ash modeling attempts (Nimlos and Zuuring 1982). Predictions

from this model allow quantitative ash assessments with a known error within

the study area. Forest managers can use this model to integrate the predictions

into a geographic information system (GIS). One motivation behind developing

a quantitative ash distribution model was to overcome the variation inherent

within mapping units generated through a soil survey. Volcanic ash thicknesses

in Hugus and Bouldercreek soil series commonly found in our study area have

mapped variations >20 cm (Soil Survey Division 2006). The predictive model’s

RMSE of 10.7 cm significantly improves on this level of variation, thus providing

a finer resolution support tool for local forest soil management.

Further research should be conducted to determine local affects of topographic

features on ash distribution despite the significant improvement this model provides in predicting ash depth and distribution. Global statistical procedures such

as multiple linear regression may mask local topographic influence. Adjusting a

statistical model to perform a more local analysis may yield improved results. A

more costly, but perhaps informative method, would be a detailed survey of a

finite landscape. Research at local levels may reveal topographic and volcanic

ash relationships otherwise masked by large conventional soil surveys. Regardless of which approach is used, modeling ash distribution seems to be inherently

a local exercise. The extrapolation of model results outside a study area is not

recommended. The concepts behind the model presented in this paper may be

applicable elsewhere, but the relationships as reflected in the model parameter

estimates are unique.
20 USDA Forest Service Proceedings RMRS-P-44. 2007

Kimsey, Gardner, and Busacca Ecological and Topographic Features of Volcanic Ash-Influenced Forest Soils

Summary ______________________________________________________

This study’s findings suggest that volcanic ash distribution is intricately linked

with elevation and plant community associations. Elevation increases precipitation, which in turn supports different climax plant communities. Increasing plant

density at each successive climax community may serve to retain ash deposits

subsequent to volcanic eruptions and entrap wind-transported volcanic ash from

drier, lower elevation sites. Topographic variables show relatively little impact

on ash thickness patterns. Several of the terrain attributes showed clustering by

geographic location within our study area. Gentler slopes, which were predominately found at drier, lower elevations, supported thinner ash mantles. The slope

curvature variable was also linked to geographic location. Nonlinear slopes were

most often found in the mountainous region of the study area. The strong effect

of elevation and vegetation habitat type series reduced the ability to distinguish

mean ash thickness differences between convex and concave surfaces.

Statistical modeling accounted for 60 percent of the observed variation in ash

thickness and returned an RMSE of 10.7 cm. These model statistics indicate a

significant development in the prediction capability of volcanic ash thickness.

Model error is significantly lower than the variation of >20 cm often observed in

local ash-influenced soil series. However, it became evident during our analyses

that ash distribution and thickness is heavily influenced by local ecological and

topographic attributes that cannot be assumed to affect ash depth uniformly

across a study area. Future ash modeling efforts must focus on assessing local

environmental influences and account for nonstationarity in the independent

variables. Such an analysis may clarify the ecological and topographic effects on

ash distribution and thickness that are otherwise generalized in a global regression analysis.

Literature Cited__________________________________________________

Bacon, C. R. 1983. Eruptive history of Mount Mazama and Crater Lake caldera, Cascade Range,

U.S.A. J. Volcanol. Geotherm. Res. 18: 57-115.

Busacca, A. J.; Marks, H. M.; Rossi, R. 2001. Volcanic glass in soils of the Columbia Plateau, Pacific

Northwest, U.S.A. Soil Sci. Soc. Am. J. 65: 161-168.

Cooper, S. V.; Neiman, K. E.; Roberts, D. W. 1991. Forest habitat types of northern Idaho: A second

approximation. Gen. Tech. Rep. INT-236. Ogden, UT: U.S. Department of Agriculture, Forest

Service, Intermountain Research Station. 143 p.

FAO/ISRIC/ISSS. 1998. World Reference Base for Soil Resources. Rome: Food and Agricultural

Organization of the United Nations, International Soil Reference and Information Centre, and

International Society of Soil Science.World Soil Resources Report No. 84.Available: http://www.

fao.org/docrep/W8594E/W8594E00.htm. Accessed July 7, 2006.

Geist, J. M.; Strickler, G. S. 1978. Physical and chemical properties of some Blue Mountain soils

in northeast Oregon. Res. Pap. PNW-236. Portland, OR: U.S. Department of Agriculture, Forest

Service, Pacific Northwest Forest and Range Exp. Station. 19 p.

Hunter, C. R. 1988. Pedogenesis in Mazama tephra along a bioclimatic gradient in the Blue

Mountains of southeastern Washington. Pullman, WA: Washington State University. 128 p.

Ph.D. Dissertation.

McDaniel, P. A.; Wilson, M. A.; Burt, R.; Lammers, D.; Thorson, T. D.; McGrath, C. L.; Peterson,

N. 2005. Andic soils of the Inland Pacific Northwest, U.S.A.: Properties and ecological significance. Soil Science. 170: 300-311.

Mullineaux, D. R. 1986. Summary of pre-1980 tephra-fall deposits erupted from Mount St. Helens,

Washington State, U.S.A. Bull. Volcanol. 48: 16-26.
USDA Forest Service Proceedings RMRS-P-44. 2007 21

Ecological and Topographic Features of Volcanic Ash-Influenced Forest Soils Kimsey, Gardner, and Busacca

Nanzyo, M.; Shoji, S.; Dahlgren, R. 1993. Physical characteristics of volcanic ash soils. In: Shoji,

S.; Nanzyo, M.; Dahlgren, R., eds. Volcanic ash soils: Genesis, properties, and utilization.

Amsterdam: Elsevier: 189-207.

Nimlos, T. J. 1980. Volcanic ash soils. Western Wildlands. 6: 22-24.

Nimlos, T. J.; Zuuring, H. 1982. The distribution and thickness of volcanic ash in Montana. Northwest Science. 56: 190-197.

Shipley, S.; Sarna-Wojcicki, A. M. 1983. Distribution, thickness, and mass of late Pleistocene

and Holocene tephra from major volcanoes in the northwestern United States: A preliminary

assessment of hazards from volcanic ejecta to nuclear reactors in the Pacific Northwest. U.S.

Geol. Surv. Misc. Field Studies Map. MF-1435. Washington, DC. 27 p.

Soil Survey Division. 2006. Officialsoilseries descriptions. NationalCooperative Survey.Available:

http://ortho.ftw.nrcs.usda.gov/cgi-bin/osd/osdname.cgi?-P. Accessed March 19, 2006.

Soil Survey Staff. 1999. Soil taxonomy. A basic system of soil classification for making and interpreting soil surveys. 2nd ed. U.S. Department of Agriculture, Natural Resources Conservation

Service. Agricultural Handbook No. 436. Washington, DC: U.S. Govt. Print. Office. 871 p.

Steele, R.; Pfister, R. D.; Ryker, R. A.; Kittams, J. A. 1981. Forest habitat types of central Idaho. Gen.

Tech. Rep. INT-114. Ogden, UT: U.S. Department of Agriculture, Forest Service, Intermountain

Research Station. 137 p.

Warkentin, B. P.; Maeda, T. 1980. Physical and mechanical characteristics of Andisols. In: Theng,

B. K. G., ed. Soils with variable charge. Palmerston North, NZ: Offset Publications: 281-301.

Williams, H.; Goles, G. 1968. Volume of the Mazama ash-fall and the origin of Crater Lake caldera: Andesite Conference Guidebook. Oregon Department of Geology and Mineral Industries

Bulletin. 62: 37-41.

Zdanowicz, C. M.; Zielinksi, G. A.; Germani, M. S. 1999. Mount Mazama eruption: Calendircal

age verified and atmospheric impact assessed. Geology. 27: 621-624.

Zobel, D. B.; Antos, J. A. 1991. 1980 tephra from Mt. St. Helens: Spatial and temporal variation

beneath forest canopies. Biol. Fertil. Soils. 12: 60-66.

USDA Forest Service Proceedings RMRS-P-44. 2007 23

In: Page-Dumroese, Deborah; Miller, Richard; Mital, Jim; McDaniel, Paul; Miller, Dan, tech. eds. 2007. 

Volcanic-Ash-­Derived Forest Soils of the Inland Northwest: Properties and Implications for Management 

and Restoration. 9-10 November 2005; Coeur d’Alene, ID. Proceedings RMRS-P-44; Fort Collins, CO: 

U.S. Department of Agriculture, Forest Service, Rocky Mountain Research Station.

Brian Gardner: U.S. Department of Agriculture, Moscow, Idaho.

Field Identification of Andic Soil Properties 

for Soils of North-central Idaho

Brian Gardner

Introduction

	 Currently, laboratory measurements are definitive for identifying andic soil properties in

both the USDA Soil Taxonomy (Soil Survey Staff 1999) and the World Reference Base for Soil

Resources(FAO/ISRIC/ISSS 1998). Andic soil properties, as described in Soil Taxonomy, result

mainly from the presence ofsignificant amounts of allophone, imogolite, ferrihydrite or aluminum-humus complexesin soils. The required properties are high acid-oxalate extractable aluminum and iron percentages, low bulk density, and high phosphate retention. In addition, glassis a

common component of andic soils of the Inland Northwestregion (McDaniel and others 2005).

	 A large body of work has been devoted to characterizing ash soils for classification

and management purposes. Summaries of this work include Shoji and others (1993) and

Dahlgren and others (2004). However none of these efforts have addressed the problem

of identifying soils with andic soil properties directly in the field. Most soil mapping professionals working with ashy materials are able to identify andic properties under field

conditions. However, there is currently no summary of the methods used by individuals to accomplish this identification. A procedure for recognizing andic materials using

field characteristics would assist both those lacking experience with these materials and

those assessing soils from written descriptions. Also, a logically derived set of selection criteria for detecting andic properties could help even experienced professionals

in areas where volcanic ash influence has been diluted by mixing with other materials.
24 USDA Forest Service Proceedings RMRS-P-44. 2007

Gardner Field Identification of Andic Soil Properties for Soils of North-central Idaho

This paper will examine two alternatives for detecting andic soil properties.

The first is the development of an empirical model using routinely observed soil

features as recorded in soil descriptions from north-central Idaho. The second is

the use of sodium-fluoride (NaF) pH to detect the presence of allophane or similar

amorphous materials in soils. The objectives of this project were to: 1) identify a

set of field-observable characteristics that can reliably identify soils derived from

Mount Mazama tephra; 2) develop a simple model using these characteristics to

evaluate samples as to whether they meet andic criteria or not; and, 3) evaluate

use of NaF-pH in this region as a test for recognizing ash influence.

Methods and Materials __________________________________________

Aset of 323 Natural ResourcesConservation Service (NRCS) pedon descriptions

(or 945 separate soil horizons) from Latah County, Idaho was used to evaluate how

well a set of field observations allows an observer to distinguish andic materials

from other soil materials. Only horizons having a complete set of observations

for all properties and occurring within 50cm of the soil surface were used. Each

horizon had been designated as ashy or non-ashy according to the expert opinion

of the NRCS soil scientist recording the soil description. The dataset contains 468

horizons designated as ashy and 477 horizons designated non-ashy.

The set of field observable characteristics proposed for recognizing andic

materials are soil color (dry and moist), structure, consistence (consistence is the

set of stickiness, plasticity, rupture resistance dry and rupture resistance moist),

and root abundance. Soil color is described using standard Munsell notation.

Structure, consistence and root abundance are described using the methods and

nomenclature found in Schoeneberger and others (2002).

Most of the soil properties are described using a number of component elements. For example, soil color is described by the six components of dry hue, dry

value, dry chroma, moist hue, moist value and moist chroma (see table 1). This

subdivision of properties resulted in a list of 17 properties and/or components

that could be used to distinguish between ashy and non-ashy soil horizons. Each

component of a property has been assigned one of several possible classes that

describe the component for a given soil. For example, dry soil hue could be 5YR,

7.5YR or 10YR. Tables 2 through 6 show the relative frequency distribution for

each class used to describe the components of each soil property by tephra or

non-tephra parent materials.

The relative frequencies observed for the classes describing the components of

each soil property were used to evaluate which components would be useful in

discriminating andic from non andic (or “other”) materials. A useful discriminator

was defined as one that showed: 1) a clustering of 60 percent or more of observations for the tephra material on one component class, and 2) less than 35 percent

of observations for the ‘other ‘ materials occurring in that same class.

The pH of a suspension containing 1 g soil in 50 mL 1 M NaF is used as a test

for the presence of short-range order minerals. These minerals are commonly

early products of the weathering of pyroclastic materials. The action of 1 M NaF

on these minerals releases hydroxide ions (OH–) to the soil solution and increases

the pH. A 1 M NaF pH of more than 9.4 at 2 minutes after the NaF solution is

added is a strong indicator (in non-calcareous soils) that short-range order minerals dominate the soil exchange complex (Burt 2004).
USDA Forest Service Proceedings RMRS-P-44. 2007 25

Field Identification of Andic Soil Properties for Soils of North-central Idaho Gardner

Table 1—Soil properties proposed as useful for field recognition of tephra derived soil materials with their component 

elements and descriptive classes.

Property Component elements Descriptive classes

Soil color dry hue 5YR, 7.5YR, 10YR

dry value 2, 2.5, 3, 4, 5, 6, 7

dry chroma 2, 3, 4, 6

moist hue 5YR, 7.5YR, 10YR

moist value 2, 2.5, 3, 4, 5, 6, 7

moist chroma 2, 3, 4, 6

Structure grade weak, moderate, strong

sizea 1, 2, 3, 4, 5

kindb abk, gr, pl, pr, sbk, massive

Consistence dry rupture resistance soft, slightly hard, moderately hard, hard, very hard

moist rupture resistance very friable, friable, firm

stickiness nonsticky, slightly sticky, moderately sticky, very sticky

plasticity nonplastic, slightly plastic, moderately plastic, very plastic

Root abundancec very fine and fine roots few, common, many

medium and coarse roots few, common, many

Textured none 1, 2, 3, 4 ,5 6, 7

a Structure size classes are: 1 = very fine, very fine and fine or fine; 2 = very fine to medium or fine and medium; 3 = medium; 4 = fine 

to coarse or medium and coarse; 5 = coarse.

b Structure kinds are: abk = angular blocky; gr = granular; pl = platy; pr = prismatic and sbk = subangular blocky.

c Root abundance classes are: few = <2%, common = 2 to 20% and many = >20%.

d Texture classes are: 1 = sil; 2 = l; 3 = fsl, vfsl; 4 = sicl; 5 = cl; 6 = sl; 7 = cosl, lcos for definitions of class terms see Schoenberger 

and others 2002.

Table 2—Observed frequencies for the components of soil color by moisture status and parent material.

 Moist Dry

Color tephra Other tephra Other

component Classes count Freq count Freq count Freq count Freq

 (no.) (no.) (no.) (no.)

Hue 10yr 145 0.39 120 0.73 240 0.74 138 0.90

 7.5yr 229 0.61 43 0.26 84 0.26 14 0.09a

yr 0 0 2 0.01 0 0 2 0.01

Value 2 0 0 3 0.02 0 0 0 0

 2.5 5 0.01 2 0.01 0 0 0 0

181 0.48 45 0.27 0 0 0 0

 4 184 0.49 101 0.60 2 0.01 11 0.07

0.01 16 0.10 127 0.39 19 0.12

0 0 1 0.01 181 0.56 104 0.68

 7 0 0 0 0 14 0.04 20 0.13

Chroma 2 2 0.01 4 0.03 3 0.01 5 0.03

2 0.14 63 0.41 21 0.07 66 0.43

 4 255 0.68 82 0.53 261 0.81 78 0.51

0.18 5 0.03 38 0.12 5 0.03

a Component meets criteria for useful ashy soil identifier.
26 USDA Forest Service Proceedings RMRS-P-44. 2007

Gardner Field Identification of Andic Soil Properties for Soils of North-central Idaho

Table 3—Observed frequencies for the components of soil structure by soil parent 

material.

Structure Tephra Other

component Classes count Freq count Freq

 (no.) (no.)

Structure grade weak 419 0.83 148 0.29a

 moderate 83 0.16 349 0.68

 strong 3 0.01 20 0.04

Structure size 1 261 0.52 125 0.24

 2 204 0.40 290 0.56

29 0.06 60 0.12

 4 1 0 29 0.06

9 0.02 11 0.02

Structure kind abk 0 0 2 0

 gr 196 0.39 91 0.17

 pl 0 0 11 0.02

 pr 0 0 16 0.03

 sbk 311 0.61 395 0.75

 massive 1 0.00 15 0.03

a Component meets criteria for useful ashy soil identifier.

Table 4—Observed frequencies for the components of soil consistence by soil parent 

material.

Consistence Tephra Other

component Classes count Freq count Freq

 (no.) (no.)

Dry consistence soft(so) 474 0.96 19 0.15a

 slightly hard (sh) 17 0.03 32 0.24

 moderately hard (mh) 1 0.00 32 0.24

 hard ( ha) 0 0.00 42 0.32

 very hard(vh) 1 0.00 6 0.05

Moist consistence very friable(vfr ) 507 0.98 25 0.19a

 friable(fr) 11 0.02 97 0.72

 firm(fi) 0 0.00 12 0.09

Stickiness nonsticky(so ) 474 0.93 34 0.25a

 slightly sticky(ss) 34 0.07 85 0.62

 moderately sticky(ms) 0 0.00 18 0.13

 very sticky(vs) 0 0.00 1 0.01

Plasticity nonplastic(po) 465 0.91 16 0.12a

 slightly plastic(sp ) 43 0.08 51 0.38

 moderately plastic(mp) 1 0.00 54 0.40

 very plastic(vp) 0 0.00 15 0.11

a Component meets criteria for useful ashy soil identifier.
USDA Forest Service Proceedings RMRS-P-44. 2007 27

Field Identification of Andic Soil Properties for Soils of North-central Idaho Gardner

Table 5—Observed frequencies for root abundance by root size class and soil 

parent material.

Root Tephra Other

abundance Classes count Freq count Freq

 (no.) (no.)

Very fine and fine roots none 2 0 4 0.01

few 12 0.03 33 0.07

common 93 0.20 223 0.47

many 366 0.77 216 0.45

Medium and coarse roots none 95 0.20 171 0.36

few 158 0.33 199 0.42

common 207 0.44 88 0.18

many 13 0.03 18 0.04

Table 6—Observed frequencies of soil textures (for the <2mm 

fraction) by parent material

 Tephra Other

Soil texture name count Freq count Freq

 (no.) (no.)

sil (1) 465 0.99 320 0.67

l (2) 3 0.01 112 0.23

fsl, vfsl (3) 0 0 10 0.02

sicl (4) 0 0 7 0.01

cl (5) 0 0 4 0.01

sl (6) 0 0 19 0.04

cosl, lcos (7) 0 0 5 0.01

While each of these variables is important in recognizing ash soils, the classification criteria allow for interaction between the two so that no single value

serves to discriminate andic from nonandic horizons. In an attempt to define such

a threshold value for NaF-pH, a dataset of laboratory measurementsfrom Clearwater County, Idaho was obtained for analysis. The dataset contained 267 horizons

with NaF-pH information. These were then grouped into andic (73 horizons) and

nonandic (194 horizons) soils. Table 7 reports the mean and standard deviation

for these two sample populations. Assuming a normal distribution, it is possible

to use these means and standard deviations to calculate a NaF-pH value that corresponds to the critical value for the Z statistic at a chosen level of probability.

Table 7 reports these critical values as NaF-pH values at P=.95 and P=.99.

Table 7—Mean, standard deviation and NaF-pH values that 

are equivalent to the critical values of Z at two 

levels of probability.

Standard NaF-pH NaF-pH

Mean deviation at P=.95 at P=.99

Nonandic 8.58 0.60 9.56 9.97

Andic 10.56 0.36 9.97 9.73
28 USDA Forest Service Proceedings RMRS-P-44. 2007

Gardner Field Identification of Andic Soil Properties for Soils of North-central Idaho

Results and Discussion___________________________________________

Soil color is strongly influenced by parent material (Richardson and Daniels

1993). Table 2 indicatesthat the only component ofsoil color useful forrecognizing

ash influenced soils in north-central Idaho is the moist hue. The ash-influenced

materials are noticeably redder in hue (7.5YR vs. 10YR) than other materials for

most samples. This is assumed to be a result of the prevalence of ferrihydrite in

ashy materials (Dahlgren and others 2004; Ugolini and Dahlgren 2002). Ferrihydrite-containing soils have hues of 5-7.5YR while soils with hues between 7.5YR

and 2.5Y tend to contain significant amounts of goethite (Schwertmann 1993).

Soil structure is a complex phenomenon that depends in part on factors such

as parent material, climate and the physical and biochemical processes of soil

formation (Brady and Weil 2001). Andic soils have a tendency to have weak

fine structure that is granular in A horizons and subangular blocky in B horizons

(table 3). Soils derived from other materials have similarstructure size and kind but

exhibitstronger development with a grade of moderate being dominant. Therefore,

structure grade is recognized as a suitable identifier for ash-influenced soils.

Consistence is a description of a soil’s physical condition at various moisture

contents as evidenced by the response of the soil to mechanicalstress or manipulation. The consistence of a soil is determined to a large extent by the particle-size

distribution of the soil, but is also related to other propertiessuch as organic matter

content and mineralogy (http://organiclifestyles.tamu.edu /soilbasics/soilphysical.

html). Andic soils have unique consistence properties displaying low rupture resistance (in both dry and moist states), little stickiness and low plasticity (table 4).

Each of these components of consistence is useful to separate ash influenced from

other materials. They are a reflection of the very low clay contents and unique

mineralogy of the ashy material.

Field observations have noted a high degree of root proliferation in ashy surface

horizons in north-central Idaho. While the data show a slight trend toward greater

root abundance in the ashy materials, the difference compared to the other parent

materials was not sufficient to allow use of this characteristic as a discriminator

(table 5). The recording of root abundance as broad classes rather than actual

counts per area may have reduced the usefulness of this comparison.

A series of simple models for recognizing ash-influenced soil materials were

created using the components identified as useful discriminators of ashy material.

They were tested through a process of trial and error. During this testing it was

discovered that soil texture could be used to help improve model performance.

This is true even though that property did not meet the criteria set for recognition as a useful discriminator. Soil texture proved to be a special case where the

high degree of clustering on the silt loam class (99.6 percent of observations)

for the ash-influenced material helped the model to recognize these materials.

This improved performance results from better separation of the ash-influenced

materials from low plasticity materials of other origins. During this phase, it was

also determined that moist rupture resistance would not be used in the final

model. Even though this component met the criteria for a useful discriminator, it

is strongly related to dry rupture resistance. The addition of moist rupture resistance did not improve the model. Dry rupture resistance was preferred because

it had more-easily recognized classes and greater consistency in application by

different observers.
USDA Forest Service Proceedings RMRS-P-44. 2007 29

Field Identification of Andic Soil Properties for Soils of North-central Idaho Gardner

A final model was created for evaluating whether a soil sample classifies as

andic material. The model scores a soil based on the six identified properties and

/or components as follows:

moist hue – 7.5YR=1, other=0;

structure grade – weak=1, other=0;

dry rupture resistance – soft=2, other=0;

stickiness – nonsticky=2, other=0;

plasticity – nonplastic=2, other=0;

texture – silt loam=2, other=0.

A score >= 8 is andic material while <8 is nonandic.

This model was used to evaluate the original dataset and returned an error rate

of 7.6 percent. There were approximately equal percentages of false positives and

false negatives. Of the 468 horizons designated ashy by the expert observers,

the model failed to recognize 37. These 37 false negatives were due primarily

to their lack of the expected moist hue and plasticity characteristics. Of the 477

horizons designated-non-ashy by expert observers, 35 were misidentified by the

model as andic materials. These 35 horizons are silt loams that are low in clay

and that have rupture resistance, stickiness and plasticity characteristics similar to

andic materials. The model correctly discriminated between andic and nonandic

materials in 92.4 percent of cases.

NaF-pH has been identified as a simple and convenient index for the presence

of andic materials (Fieldes and Perrott 1966). Work by Kimsey and others (2005)

found a strong (R2=.82) correlation between NaF-pH and acid oxalate extractable

Al and Fe. Another study by Brownfield and others (2005) reported a good correlation (R2 =.66) between tephra percent (based on grain counts) and NaF-pH.

A critical pH value of 9.4 has been suggested as the threshold for recognition of

tephra dominated materials (Soil Survey Staff 1995). The calculations shown in

table 7 indicate that, for the Clearwater County data, this threshold value is too

low. The table shows that 95 percent of the distribution of NaF-pH values for

andic horizons is greater than or equal to 9.97. Interestingly, the same NaF-pH

value of 9.97 is the upper bound below which 99 percent of the distribution of

nonandic values is found. Rounding to one decimal place gives a NaF-pH of 10.0

as a suggested threshold for recognizing andic materials. When applied to the

Clearwater County data, this threshold causes an error rate of about 10 percent (7

out of 73 horizons misidentified) for andic horizons and about 3 percent (6 out of

194 horizons misidentified) for nonandic horizons. Using a threshold pH value of

10.0 allowed for correct classification of horizons in about 95 percent of cases.

Summary ______________________________________________________

Two methods for field identification of volcanic ash influenced soil horizons

were explored. A simple empirical model was developed for ash recognition

using the easily observable qualitative properties of moist hue, structure grade,

dry rupture resistance, stickiness, plasticity and texture. This model successfully

discriminated between tephra and other materials in about 92 percent of cases.

A model like this can be used to help those not expert in soil classification to

recognize andic soil materials, to evaluate written descriptions when soil samples
30 USDA Forest Service Proceedings RMRS-P-44. 2007

Gardner Field Identification of Andic Soil Properties for Soils of North-central Idaho

are not available and to help more experienced soil classifiers in conditions where

the tephra is highly mixed with other materials. One principal weakness of this

model is that it is developed for Mount Mazama ash in north-central Idaho. Soils

formed in volcanic ejecta in other areas may have a different set of identifying

characteristics.

The second method for identification of andic materials was the use of NaF-pH.

While the analysis used here depended on laboratory measurements, the NaF-pH

can be readily measured in the field. Data from Clearwater County, Idaho showed

that using a threshold value of 10.0 pH units correctly classified soil horizons in

about 95 percent of cases. The use of NaF-pH to detect allophanic material has

broad application to many different volcanic materials. However, identification

of the most useful threshold value may be subject to regional variation.

Literature Cited__________________________________________________

Brady, N. C.; Weil, R. R. 2001. The Nature and Properties of Soils. 13th edition. Englewood, NJ:

Prentice Hall. 960 p.

Brownfield, S. H.; Nettleton,W. D.; Weisel, C. J.; Peterson, N.; McGrath, C. 2005. Tephra influence

on Spokane-flood terraces, Bonner County, Idaho. Soil Sci. Am. J. 69: 1422-1431.

Burt, R., ed. 2004. Soil Survey Laboratory Methods Manual. Soil Survey Investigations Report

No. 42. Version 4.0. Natural Resources Conservation Service, National Soil Survey Center,

Lincoln, NE.

Dahlgren, R. A.; Saigusa, M.; Ugolini, F. C. 2004. The nature, properties and management of

volcanic soils. In: Sparks, D., ed. Advances in Agronomy Vol. 82. Academic Press: 113-182.

FAO/ISRIC/ISSS. 1998. World Reference Base for Soil Resources. Rome: Food and Agricultural

Organization of the United Nations, International Soil Reference and Information Centre, and

International Society of Soil Science.World Soil Resources Report No. 84.Available: http://www.

fao.org/docrep/W8594E/W8594E00.htm.

Fieldes, M.; Perrott, K. W. 1966. The nature of allophane in soils. III. Rapid field and laboratory

test for allophane. New Zealand J. Sci. 9: 623-629.

Kimsey, Mark Jr.; McDaniel, Paul; Trawn, Dan; Moore, Jim. 2005. Fate of applied sulfate in volcanic

ash-influenced forest soils. Soil Sci. Soc. Am. J. 69: 1507-1515.

McDaniel, P. A.; Wilson, M. A.; Burt, R.; Lammers, D.; Thorson, T. D.; McGrath, C. L.;

Peterson, N. 2005. Andic soils of the Inland Pacific Northwest, USA: Properties and ecological

significance. Soil Science. 170: 300-311.

Richardson, J. L.; Daniels, R. B. 1993. Stratigraphic and hydraulic influences on soil color development. In: Bigham, J. M.; Ciolkosz, E. J., eds. Soil Color. SSA Special Pub. No. 31: 109-125.

Schoenberger, P. J.; Wysocki, D. A.; Benham, E. C.; Broderson, W. D., eds. 2002. Field book for

sampling and describing soils. Version 2.0. Natural Resources Conservation Service, National

Soil Survey Center, Lincoln, NE.

Schwertmann, U. 1993. Relations between iron oxides, soil color, and soil formation. In: Bigham,

J. M.; Ciolkosz, E. J., eds. Soil Color. SSA Special Pub. No. 31: 51-69.

Shoji, S.; Nanzyo, M.; Dahlgren, R. A. 1993. Volcanic ash soils: Genesis, properties, and utilization. In: Hartemink, A. E.; McBratney, A., eds. Developments in soil science, 21. Amsterdam,

The Netherlands: Elsevier.

Soil Survey Staff. 1995. Soil survey Laboratory Manual. Woil survey Investigations Report No. 45.

National Soil Survey Center. Soil Survey Laboratory, Lincoln, NE. 81 p.

Soil Survey Staff. 1999. Soil taxonomy. A basic system of soil classification for making and interpreting soil surveys. 2nd ed. U.S. Department of Agriculture, Natural Resources Conservation.

Ugolini, F. C.; Dahlgren, R. A. 2002. Soil development in volcanic ash. Available: http://www.

airies.or.jp/publication/ger/pdf/06-2-09.pdf.
USDA Forest Service Proceedings RMRS-P-44. 2007 31

In: Page-Dumroese, Deborah; Miller, Richard; Mital, Jim; McDaniel, Paul; Miller, Dan, tech. eds. 2007. 

Volcanic-Ash-­Derived Forest Soils of the Inland Northwest: Properties and Implications for Management 

and Restoration. 9-10 November 2005; Coeur d’Alene, ID. Proceedings RMRS-P-44; Fort Collins, CO: 

U.S. Department of Agriculture, Forest Service, Rocky Mountain Research Station.

P. A. McDaniel is a Professor of Soil Science, Soil & Land Resources Division, University of Idaho, 

Moscow, ID. M. A. Wilson is a Research Soil Scientist, U.S. Department of Agriculture, Natural Resources 

Conservation Service Soil Survey Center, Lincoln, NE.

Abstract

	 Holocene ash from the cataclysmic eruption of Mount Mazama (now Crater Lake) in south­eastern

Oregon is a major component of many forest soils that lie to the east of Cascade Mountains in the

Pacific Northwest region. The relatively high productivity of the region’s ecosystems is closely linked

to this volcanic ash component. This paper reports on the ecologically important properties of these

ash-influenced soils by examining soil characterization data from over 500 soil horizons of the region

contained in the National Soil Survey database. Volcanic ash-cap textures are generally silty in areas

distal to the eruption. Volumetric water-holding capacity of ash-cap horizons is as much as twice

that of underlying horizons and underscores the importance of ash caps in seasonally dry, forested

ecosystems of the Inland Northwest region. Cation exchange capacity (CEC) determined at field pH

(ECEC) averages 8.0 cmolc kg–1 and is less than one-third the CEC determined at pH 8.2, indicating

considerable variable charge. These data suggest that ash-influenced soils have limited ability to store

and exchange nutrient cations such as Ca, Mg, and K. In addition, strong sorption of SO4 and PO4

significantly limits the bioavailability of these nutrients. Erosion and compaction of ash caps are major

management concerns, but relationships between these processes and ash-cap performance remain

unclear.

Physical and Chemical Characteristics of 

Ash-influenced Soils of Inland Northwest Forests

P. A. McDaniel and M. A. Wilson

Introduction

	 Soils formed entirely or partially in volcanic ejecta such as ash (glassy particles <2mm in

size), cinders (glassy particles >2mm in size), and pumice (highly vesicular fragments) are

fundamentally different from other soils in terms of their physical, chemical, and mineralogical properties. Because of this, Andisols were established as the 11th soil order in U.S. Soil

Taxonomy in 1989. The World Reference Base of Soil Resources (WRB) also recognizes these

soils as Andosols, one of the 30 soil reference groups (FAO/ISRIC/ISSS 1998). Soils formed in

volcanic ash, such as the ash-cap soils found in the Pacific Northwest region, are characterized by what are referred to as andic properties in Soil Taxonomy (Soil Survey Staff 2003).

Andic properties refer to a combination of characteristics, including the presence of glass,

short-range-order or poorly crystalline weathering products with high surface reactivity, and

low bulk density.
32 USDA Forest Service Proceedings RMRS-P-44. 2007

McDaniel and Wilson Physical and Chemical Characteristics of Ash-influenced Soils of Inland Northwest Forests

Volcanic ashfromthe eruptionofMt.Mazama (nowCrater Lake,OR)~7,700 years

BP (Zdanowicz and others 1999) has influenced many mid- to high-elevation forest soils in the Pacific Northwest region. The unique properties of these ash-caps

are intricately linked to forest productivity across the region (Geist and Cochran

1991; Meurisse and others 1991). Assuch, these soilsrepresent a valuable regional

resource from both an economic and ecologic perspective. Moreover, ash-cap

soils respond differently to use and management than do soils formed in other

parent materials, and it is therefore important to recognize and understand the

basic differences in properties. In this paper, we describe some of the important

characteristics of volcanic ash-influenced soils.

We used the Natural Resources Conservation Service (NRCS) — Soil Survey

Laboratory characterization database forWashington, Oregon, Idaho, andMontana

to provide an overview of physical and chemical characteristics of volcanic ashcap soils of the region. The soils in this database are representative of the dominant mapping unit components in soil survey areas, and have properties that are

considered typical of soils across the region. For inclusion in the database, we

identified all horizons meeting either the criteria for andic soil properties or andic

subgroups in Soil Taxonomy (Soil Survey Staff 2003). All characterization data

were obtained using standard methods (Burt 2004) and have been summarized

in McDaniel and others (2005).

Soil Morphology________________________________________________

The thickness of ash caps across the Inland Northwest region is variable, but

follows a general trend of thinningwith increasing distance from Crater Lake (fig. 1a).

Data presented by McDaniel and others(2005)showed a range in thickness of 2 to

152 cm across the region, with an average thickness of 38 cm. It should be noted

that these reported thicknesses include ash caps thinned by erosion as well as

those in which other soil parent materials have been mixed with the volcanic ash

after initial deposition. In the latter case, the reported thicknesses represent those

of ash-influenced mantles rather than pure ash mantles. It is important to realize

that the ash caps found across the region have been mixed to varying degrees by

post-depositional processes and represent a range in composition. For purposes

of this paper and others contained in these proceedings, the term ash cap will be

used to include all ash mantles, regardless of degree of mixing.

Most of the official soil series descriptions (Soil Survey Division 2005) for ashcap soils of the region include forest litter layers that are underlain by A horizons

having thicknessestypically ranging from 2.5-7.5 cm (1-3 inches). The development

of A horizons formed in volcanic ash in the Inland Northwest is usually weak

despite the fact that ash-cap soils generally contain relatively large amounts of

organic matter compared to other mineral soils (Dahlgren and others 2004). This

weak development is probably due to the fact that most ash-influenced soils are

forest soils, where the majority of carbon is contained in litter layers and relatively

small quantities are added to A horizons in the form of roots. This factor results in

relatively thin, light-colored A horizons. Very dark-colored A horizons can form

in volcanic-influenced soils that support grasses or understory vegetation with

extensive rootsystems. Deep, dark A horizons have been described under bracken

fern (Pteridium aquilinum) communities in northern Idaho (Johnson-Maynard and

others 1997). These communities may have as much as 3,500 g/m2 of belowground

biomass in the form of rhizomes and fine roots (Jimenez 2005).
USDA Forest Service Proceedings RMRS-P-44. 2007 33

Physical and Chemical Characteristics of Ash-influenced Soils of Inland Northwest Forests McDaniel and Wilson

Figure 1—Change in (a) ash-cap thickness and (b) particle-size distribution of Mazama 

tephra as a function of distance from Crater Lake, OR. Particle-size data represent 

averages for the ash caps of Lapine, Angelpeak, Threebear, and Jimlake soils and 

are adapted from McDaniel and others (2005).

Underlying the A horizons are reddish- to yellowish-brown Bw horizons that

do not exhibit significant increases in clay content. Hues of these subsoil horizons

are typically 7.5YR to 10YR with chromas of 4 or 6. These characteristic colors

reflect the weathering of ash to form poorly crystalline Fe oxides such as ferrihydrite (McDaniel and others 2005).

In some higher-elevation areas, ash-cap soils may have undergone sufficient

podzolization to develop E-Bh, Bhs horizon sequences. These soils are typically

in high-precipitation environments and have extremely acid E horizons. In the

Selkirk Mountains of northern Idaho, pH values as low as 3.7 having been reported (McDaniel and others 1997), the lowest pH values found anywhere in the

region for native soils.
34 USDA Forest Service Proceedings RMRS-P-44. 2007

McDaniel and Wilson Physical and Chemical Characteristics of Ash-influenced Soils of Inland Northwest Forests

Physical Properties ______________________________________________

Particle-Size Distribution

Much of the tephra distributed throughout the Pacific Northwest was carried

in suspension by prevailing westerly winds, a process that has resulted in fairly

distinct ranges of particle sizes associated with ash caps. Examination of ash cap

textures across the region shows a decrease in overall particle size with increasing distance from the source (fig. 1b). The pumice regions of central Oregon are

in closer proximity to Crater Lake, and sand-sized pumice dominates in soils like

Lapine. However, ash capsfrom the Blue Mountains(e.g.Angelpeak soil), northern

Idaho (Threebear soil), and western Montana (Jimlake soil) are predominantly siltsized, reflecting the greater distance of transport. Fine-earth fractions of these ash

caps typically have silt loam or loam textures, which can substantially enhance

the water-holding capacity of soil profiles.

Bulk Density 

Bulk density of Andisols tends to be relatively low, and this is one of the defining

characteristics of these soils in Soil Taxonomy and the WRB. Of the 271 horizons

examined across the region, the average bulk density is 0.90 g cm–3 (fig. 2). However, only ~60 perecent of the horizons have bulk densities of <0.90 g cm–3, suggesting that mixing and/or compaction, both of which would tend to increase bulk

density, have occurred since deposition. Because bulk density is inversely related

to porosity, an ash cap with a bulk density of 0.90 g cm–3 may have ~40 percent

more porosity than a typical mineral soil with a bulk density of 1.3 g cm–3.

Figure 2—Bulk density data for andic soil horizons of the Pacific Northwest 

region. Taken from McDaniel and others (2005).
USDA Forest Service Proceedings RMRS-P-44. 2007 35

Physical and Chemical Characteristics of Ash-influenced Soils of Inland Northwest Forests McDaniel and Wilson

Water-Holding Capacity

Andisols typically are able to retain large amounts of water (Dahlgren and

others 2004). In the Inland Northwest region where extended dry periods often

occur during the growing season, this water-holding capacity is arguably the

most important property from an ecological standpoint. Additional water-holding

capacity associated with ash-cap soils may be critical to the establishment and

maintenance ofsome plant communities. The basisforthe additionalwater-holding

capacity imparted to soils by volcanic ash stems from three factors. First, as discussed previously, ash caps have relatively high porosity. Secondly, much of the

distal ash is silt-sized, which is desirable from the standpoint of water retention

characteristics. This is especially true in many mountainous areas where volcanic

ash overlies coarser-textured, often rocky soils with relatively little plant-availablewater-holding capacity. Finally, weathering of volcanic ash gives rise to a colloidal

fraction that has high surface area and is able to retain considerable quantities of

water (Wada 1989; Kimble and others 2000; Dahlgren and others 2004).

The effect of a volcanic ash cap on the water-holding capacity of a north Idaho

soil is illustrated in figure 3. The ash cap consists of the top two horizons, which

have more than twice the water-holding capacity (on a volume basis) of the underlying coarser-textured horizon that has formed in outwash. In this example,

the ash mantle contributes 8.6 cm (~3.4 inches) of plant-available water to the soil

profile. Ash-caps of the region have an average water retention of ~11 percent (by

weight) at 1,500 kPa of soil moisture tension (wilting point) (McDaniel and others

2005), or roughly twice that of sandy soils (Brady and Weil 2004).

Figure 3—Water retention difference in the top 50 cm of the Bonner series (86ID017002) from 

north Idaho. Bars represent the difference in water content between –1,500 and –33 kPa, 

expressed on a volume basis and corrected for rock fragment content. Shaded bars are for 

andic materials.
36 USDA Forest Service Proceedings RMRS-P-44. 2007

McDaniel and Wilson Physical and Chemical Characteristics of Ash-influenced Soils of Inland Northwest Forests

When comparing or interpreting water retention data, it is important to distinguish between data reported on a gravimetric (weight) and those reported on a

volume basis. Because soil horizons formed in volcanic ash typically have bulk

densities <1.0 g/cm3, water contents will be greater when expressed on a weight

basis rather than a volume basis. The opposite is true for other mineral soils with

bulk densities >1.0 g/cm3.

A mantle or cap of volcanic ash also contributes to a more-favorable soil

moisture regime through a mulching effect. Some of the increases in crop yields

observed after the 1980 Mount St. Helens eruption were attributed to the deposition of fresh ash and its role in reducing evaporative water losses (Dahlgren and

others 2004).

Other Physical Properties

Some Andisols exhibit thixotropy, which is described as a reversible gel-sol-gel

transformation (Nanzyo and others 1993b). Upon application of pressure or

vibration, a wet soil mass will experience a sudden reversible loss of strength

and begin to flow. It can easily be observed in a well-moistened ash-cap sample.

By applying pressure to the material between the thumb and forefinger, water

can be forced out of the soil mass; release of pressure will cause then water to

be re-absorbed. On a larger scale, thixotropy can result in soil collapse under

roadways and building foundations (Brady and Weil 2004). Thixotropy is most

pronounced in highly weathered soils formed in volcanic ash (Buol and others

2003), and therefore is not often well expressed in the relatively less-weathered

ash-cap soils of the Inland Northwest region. Soils formed in volcanic ash also

have a low bearing capacity because of their low bulk density (Kimble and others

2000), and this makes them susceptible to compaction and can create problems

for trafficking and building foundations.

Mineralogical Properties _________________________________________

Volcanic Glass

The principal component of Mazama volcanic ash is glass, which was formed

by the very rapid cooling of rhyodacitic magma as it was ejected from the volcano

during the climatic eruption (fig. 4) (Bacon 1983). The amount of glass in volcanic

ash mantles acrossthe region is variable, and most likely reflects post-depositional

redistribution. In the Blue Mountains of northeastern Oregon and southeastern

Washington, relatively undisturbed ash mantles contain 60-90 percent volcanic

glass and are found in moister landscape positions with lower fire frequency (Wilson and others 2002). In other areas with more active surficial processes such as

erosion after fire, glass contents ranges from 25-60 percent, and these are referred

to as mixed mantles (Wilson and others 2002). The glass content of 528 ash-cap

soil horizons of the region that meet andic soil requirements in Soil Taxonomy

averages ~42 percent and exhibits a bimodal distribution (McDaniel and others

2005). This suggests that mixed mantles are common across the region, and that

locally, underlying soils have at least some influence on ash cap properties.
USDA Forest Service Proceedings RMRS-P-44. 2007 37

Physical and Chemical Characteristics of Ash-influenced Soils of Inland Northwest Forests McDaniel and Wilson

Analysis of Mazama ash deposits shows an elemental composition of 70-

72 percent SiO2 (Bacon 1983). In addition, McDaniel and others (1997) reported

that the combined Al2O3 and SiO2 content of Mazama glass was ~87.5 percent,

with the CaO, MgO, and K2O contents comprising only 4.9 percent by weight.

For comparative purposes, Bohn and others (2001) report an average CaO, MgO,

and K2O content for a variety of igneous rocks of 12 percent. It is clear from these

data that volcanic glass is not a rich source of plant nutrients and should not

be thought of as a having remarkable fertility. Minor amounts of plant nutrients

such as SO4

2–, Ca2+, and PO42– present in the original Mazama ash fall may have

provided short-term fertility inputs, as was the case with the 1980 eruption of

Mount St. Helens (Fosberg and others 1982; Mahler and others 1984). However,

long-term fertility of the glass is relatively low.

Clay Mineralogy

Because of the lack of a crystalline structure, glass weathers relatively rapidly to

form poorly crystalline or non-crystalline minerals in the clay fraction. In slightly

to moderately weathered Andisols such as those found in the Pacific Northwest

region, there are three mineral assemblages that tend to dominate: (1) Al-humus

complexes, often with Al-hydroxy-interlayered 2:1 minerals; (2) allophane and

imogolite, and; (3) poorly crystalline Fe oxides (ferrihydrite) (Dahlgren and others

2004). As ash weathers, Al and Fe released into soil solution in surface horizons

can form stable organic complexes, especially at soil pH < 5 (Parfitt and Kimble

1989); these pH values are common under coniferous forest vegetation at higher

elevation in the Inland Pacific Northwest. Al-humus complexes represent active

Figure 4—Volcanic glass shard from north Idaho soil. Glass is from the Mazama eruption 

and measures ~0.1 mm across. Photo from University of Idaho. 
38 USDA Forest Service Proceedings RMRS-P-44. 2007

McDaniel and Wilson Physical and Chemical Characteristics of Ash-influenced Soils of Inland Northwest Forests

forms of Al and may contribute to Al toxicity (Dahlgren and others 2004). In the

relative absence of humus and less acid conditions, such as in B and C horizons,

Al and Si precipitate to form allophane and imogolite. These two aluminosilicate

minerals may have similar chemical composition, but allophane typically consists

of spherical units while imogolite appears as threads or tubes (Kimble and others

2000). Allophane and imogolite both have relatively high surface area. Using

data presented by Harsh and others (2002), White and Dixon (2002), and Malla

(2002), the surface area of imogolite is as much as 100 times greater than that of

kaolinite and 40 percent greater than that of vermiculite. This important property

is directly related to both the high water-holding capacity and chemical reactivity

of these minerals.

Chemical Properties _____________________________________________

Soil Reaction

The majority of andic soil horizons of the region are moderately to slightly acid.

Approximately 70 percent of the horizons examined have pH values between

5.6 and 6.5, with an average pH of 6.02 (fig. 5). This pH range is generally suitable

for plant growth, as many nutrients are present in plant-available forms within this

range and the potential for aluminum toxicity is low (Brady and Weil 2004).

Cation/Anion Exchange 

One of the important features of soils formed in volcanic ash is the variable

charge associated with the colloidal fraction. Variable charge, also sometimes

referred to as pH-dependent charge, means that the net surface charge depends

Figure 5—Soil pH data for ash-cap soil horizons from the Inland Pacific Northwest region.
USDA Forest Service Proceedings RMRS-P-44. 2007 39

Physical and Chemical Characteristics of Ash-influenced Soils of Inland Northwest Forests McDaniel and Wilson

on the pH of the soil solution (Soil Science Society of America 2001). It is this

net surface charge that determines the cation exchange capacity (CEC) of a soil

and its ability to retain and exchange nutrient cations such as Ca2+, Mg2+, and

K+. The CEC of andic soils decreases with decreasing pH, and may in fact, be

quite low at the acidic pH values that characterize many forest soils. Moreover,

some andic soils may have substantial anion exchange capacity (AEC) at acidic

field pH values (Kimble and others 2000), influencing the retention of ions such

as chloride and nitrate. Although PO4

2– and SO42– ions are sorbed through anion

exchange, fixation of these ions (described below) is much greater than this

exchange reaction.

The effect of variable surface charge is illustrated by CEC and base cation data

from ash-cap soils across the region. Table 1 shows CEC values determined for

515 horizons using three procedures. The lowest values are for effective cation

exchange capacity (ECEC), where the CEC is determined at the pH of the soil. The

highest values are for CEC determined at pH 8.2 (CECpH 8.2), which is considerably

higher than the soil pH of the region. Although this latter method overestimates

the CEC that exists in the field, the difference in ECEC and CECpH 8.2 values illustrates the potential variable charge that exists in these soils. On average, CECpH 8.2

values are approximately four times greater than ECEC values.

Table 1—Exchange properties of andic soil horizons of the Inland Northwest Region. Adapted from 

McDaniel and others (2005). 

Ca2+ Mg2+ K+ Base saturation1 ECEC2 CEC pH 7 CEC pH 8.2

- - - - (cmolc /kg) - - - - (%) - - - - - - - - (cmolc /kg) - - - - - - - -

Average 7.2 1.3 0.8 46.0 6.5 19.1 26.4

 n 515 515 514 514 113 515 513

Std. deviation 8.7 2.0 0.7 26.6 5.4 11.3 13.6

Minimum 0 0 0 1 0.5 3.4 7.0

Maximum 88.2 24.0 9.1 100 46.7 101.0 126.2

Another important characteristic of ash-cap soils is their ability to strongly

adsorb and immobilize plant-available forms of P and S. This process, known as

fixation, results in low concentrations of PO4

2– and SO42– in soil solution and

available for plant use (fig. 6). The ability to fix PO4

2– results from the strong attraction between PO4

2– and the edges of allophane, imogolite, and ferrihydrite,

and there are probably severalsorption mechanismsinvolved (Wada 1989). High

PO4

2– sorption is one of the characteristics used to define andic soil properties

in Soil Taxonomy and andic horizons in WRB.
40 USDA Forest Service Proceedings RMRS-P-44. 2007

McDaniel and Wilson Physical and Chemical Characteristics of Ash-influenced Soils of Inland Northwest Forests

Figure 6—Sorption isotherms for (a) phosphorus additions (adapted 

from Jones and others 1979), and (b) sulfate additions (adapted from 

Kimsey and others 2005). Data points represent the proportions of 

sorbed (plant unavailable) and soluble (plant available) forms with 

additions of increasing quantities of phosphorus and sulfate.

Allophanic and Non-allophanic Andisols __________________________

Because of the range in characteristics of volcanic ash-cap soils, a relatively

simple classification scheme has been devised that recognizes these differences

from a management perspective. This system classifies soils as either allophanic

or non-allophanic (Nanzyo and others 1993a; Dahlgren and others 2004). Allophanic Andisols are those that are dominated by inorganic weathering products

such as allophane and imogolite. In contrast, organically bound complexes are

much more important in non-allophanic Andisols. Properties of these two classes

of ash-derived soils are summarized in table 2. In general, non-allophanic soils

present more management challenges. These soils have several properties that

may inhibit plant growth — greater acidity and greater potential for Al3+ toxicity
USDA Forest Service Proceedings RMRS-P-44. 2007 41

Physical and Chemical Characteristics of Ash-influenced Soils of Inland Northwest Forests McDaniel and Wilson

are two of the most important. Most of the soils in the Inland Northwest region

are classified as allophanic (McDaniel and others 2005). However, research has

shown that shifts from allophanic to non-allophanic properties and vice versa

can occur relatively quickly with changes in vegetation. An example of this from

northern Idaho is described in the following section.

Response to Management _______________________________________

Erosion

The scientific literature contains sometimes-contradictory information about

susceptibility of ash-cap soils to erosion. Soils formed in volcanic ash are typically described as having strong resistance to erosion, largely as a function of

stable aggregation and high infiltration rates (Nanzyo and others 1993b; Dahlgren

and others 2004). However, because of their low bulk density they may be very

susceptible to wind and water erosion when vegetative cover is removed (Kimble

and others 2000; Arnalds and others 2001). In the Inland Northwest region,

maintenance of forest cover, including both canopy and litter layers, has been

an important factor in the retention of Mazama ash caps over the millennia since

deposition (McDaniel and others 2005). These factors suggest that erodibility of

volcanic ash caps is related to degree of disturbance; disturbance that destroys

or removes canopy and litter layers will likely lead to severe erosion.

Compaction

Perhaps one of the best-documented responses of ash-cap soils to land-use

activities is compaction. As described earlier, andic soils are defined in part by a

bulk density of <0.90 g/cm3. Numerous studies have shown significant increases

in ash-cap bulk density as a result of timber harvest trafficking. In the Blue Mountains of eastern Oregon and Washington, average bulk density increased from

0.669 g cm–3 in unharvested areas to 0.725 g cm–3 in harvested areas, representing an average increase of ~9 percent (Geist and others 1989). However, larger

Table 2—Comparison of properties of allophanic and non-allophanic Andisols (adapted from Dahlgren 

and others 2004; Nanzyo and others 1993a).

Property Allophanic Non-allophanic

pH slightly to moderately acid strongly acid

Dominant mineralogy allophane/imogolite Al-interlayered 2:1 layer

silicates and Al-organic complexes 

Organic matter content moderate moderate to high

Al toxicity rare common

Compaction potential slight moderate
42 USDA Forest Service Proceedings RMRS-P-44. 2007

McDaniel and Wilson Physical and Chemical Characteristics of Ash-influenced Soils of Inland Northwest Forests

bulk density increases were associated with skid trails and landings. Similarly,

Cullen and others (1991) reported significant increases in ash-cap bulk density in

moderately and severely trafficked areas as compared to non-harvested controls.

In addition, they were able to quantify changes in soil hydrologic properties

accompanying bulk density increases. Water content at relatively low soil moisture tensions decreased significantly in trafficked areas compared to the controls

(Cullen and others 1991) (fig. 7a). One-hour infiltration decreased as well, with

values decreasing from 38.5 cm in the control to 7.3 cm in the severely trafficked

areas (Cullen and others 1991).

Figure 7—Changes in (a) water content of ash-cap soils due to timber harvest 

trafficking, and (b) 1-hour infiltration in ash-cap soils due to timber harvest trafficking. *, ** indicate values that differ from the untrafficked controls at the 0.01 

and 0.05 significance levels, respectively. Data are adapted from Cullen and 

others (1991).
USDA Forest Service Proceedings RMRS-P-44. 2007 43

Physical and Chemical Characteristics of Ash-influenced Soils of Inland Northwest Forests McDaniel and Wilson

Chemical/Mineralogical Changes

Work by Johnson-Maynard and others (1997) in northern Idaho suggests that

development of non-allophanic properties accompanies establishment of bracken

fern communities after clearcutting in as little as 30 years and may contribute to

the observed lack of timber regeneration. This subject is discussed in more detail

by Ferguson and others (this proceedings). Recent literature suggests that this

mineralogical conversion is not irreversible. Takahashi and others (2006) reported

that additions of lime to non-allophanic soils will raise pH and reduce the active

forms of Al3+, thereby representing a potential reclamation strategy.

Knowledge Gaps________________________________________________

Two major questions related to the properties and management of ash-cap

soils in the Inland Pacific Northwest region remain. The first question is: How 

much ash is there and where is it? This seems like a basic question, yet it is one

for which a good answer does not currently exist. The National Cooperative Soil

Survey program has produced in ~1:24,000-scale soil surveys for parts of the

region, and these provide sufficient detail to assess the extent and spatial distribution of ash-cap soils. However, much of the forested land area where ash-cap

soils are found has not been subject to this type of soil mapping. As a result,

detailed information about the quantities and spatial distribution of ash across

the region is often lacking, poorly documented, and/or not readily accessible.

Development of models that predict ash cap depth and distribution will likely

be greatly enhanced by new technologies in remote sensing. However, in the

absence of more detailed mapping or predictive models, a test such as the NaF

pH measurement can provide a quick and easy indicator of ash-cap soils. An

NaF pH value >9.4 generally indicates the presence of weathered volcanic ash

(Fieldes and Perrott 1966; Wilson and others 2002) and serves as a guideline for

identifying ash-cap soils.

A second question is: What is the relationship between ash-cap soil properties 

and soil performance? The majority of research to date has focused on measurement of ash-cap properties rather than performance. For example, compaction

of ash-cap soils has been well documented, but compacted bulk densities are

typically well within the range considered to be acceptable for other mineral soils.

So with regard to performance, does an ash cap with bulk density 1.1 g cm3 behave differently than a soil without an ash cap having the same bulk density? An

answer to this question will require a better understanding of the changes in pore

size and connectivity that occur with compaction in ash-cap soils. Efforts should

be focused on determining critical thresholds in andic soil properties at which

tree growth and the hydrologic performance will be adversely affected. Long-term

studies will be needed to address these issues, and successful management will

ultimately require an understanding of the mechanisms involved.

References______________________________________________________

Arnalds, O.; Gisladottir, F. O.; Sigurjonsson, H. 2001. Sandy deserts of Iceland. J. Arid Environments. 47: 359-371.

Bacon, C. R. 1983. Eruptive history of Mount Mazama and Crater Lake caldera, Cascade Range,

USA. J. Volcanol. Geotherm. Res. 18: 57-115.
44 USDA Forest Service Proceedings RMRS-P-44. 2007

McDaniel and Wilson Physical and Chemical Characteristics of Ash-influenced Soils of Inland Northwest Forests

Bohn, H. L.; McNeal, B. L.; O’Connor, G. A. 2001. Soil chemistry. 3rd ed. New York: John Wiley

& Sons, Inc. 307 p.

Brady, N. C.; Weil, R. R. 2004. The nature and properties of soils. 13th ed. Upper Saddle River,

NJ: Prentice Hall. 960 p.

Buol, S. W.; Southard, R . J.; Graham, R. C.; McDaniel, P. A. 2003. Soil Genesis and Classification.

5th ed. Ames, IA: Iowa State Press - Blackwell Publ. 494 p.

Burt, R., ed. 2004. Soil Survey Laboratory Methods Manual. Soil Survey Investigations Report 42.

Version 4.0. Washington, DC: U.S. Government Printing Office. 700 p.

Cullen, S. J.; Montagne, C.; Ferguson, H. 1991. Timber harvest trafficking and soil compaction in

western Montana. Soil Sci. Soc. Am. J. 55: 1416-1421.

Dahlgren, R. A.; Saigusa, M.; Ugolini, F. C. 2004. The nature, properties, and management of

volcanic soils. In: Sparks, D. L., ed. Advances in Agronomy, vol. 82. Amsterdam: Elsevier Academic Press: 113-182.

FAO/ISRIC/ISSS. 1998. World Reference Base for Soil Resources. Available: http://www.fao.org/

documents/show_cdr.asp?url_file=docrep/W8594E/W8594E00.htm. Rome: Food and Agricultural Organization of the United Nations, International Soil Reference and Information Centre,

and International Society of Soil Science; World Soil Resources Report #84.

Fieldes, M.; Perrott, K. W. 1966. The nature of allophane in soils. III. Rapid field and laboratory

test for allophane. New Zealand J. Sci. 9: 623-629.

Fosberg, M. A.; Moody, U. L.; Falen, A. L.; Eisenger, D. L.; Clayton, J. [Submitted 1982]. Physical,

chemical, and mineralogical studies of tephra deposited on forested lands — northern Idaho

and western Montana. Boise, ID. Moscow, ID: University of Idaho. Final Rep. 216 p.

Geist, J. M.; Hazard, J. W.; Seidel, K. W. 1989. Assessing physical conditions of some Pacific

Northwest volcanic ash soils after forest harvest. Soil Sci. Soc. Am. J. 53: 946-950.

Geist, J. M.; Cochran, P. H. 1991. Influences of volcanic ash and pumice deposition on productivity of western interior forest soils. In: Management and productivity of western-montane forest

soils: proceedings; 1990 April 10-12; Ogden, UT: U.S. Department of Agriculture, Forest Service,

Intermountain Research Station: 82-88.

Harsh, J.; Chorover, J.; Nizeyimana, E. 2002. Allophane and imogolite. In: Dixon, J. B.; Schultze,

D. G., eds. Soil mineralogy with environmental applications. Book Series no. 7. Madison, WI:

Soil Science Society of America: 291-322.

Jimenez, J. 2005. Bracken fern communities of the Grand Fir Mosaic: Biomass allocation and

influence on selected soil properties. Moscow, ID: University of Idaho. 209 p. Thesis.

Johnson-Maynard, J. L.; McDaniel, P. A.; Ferguson, D. E.; Falen, A. L. 1997. Chemical and mineralogical conversion of Andisols following invasion by bracken fern. Soil Sci. Soc. Am. J. 61:

549-555.

Jones, J. P.; Singh, B. B.; Fosberg, M. A.; Falen, A. L. 1979. Physical, chemical, and mineralogical

characteristics of soils from volcanic ash in northern Idaho: II. Phosphorus sorption. Soil Sci.

Soc. Am. J. 43: 547-552.

Kimble, J. J.; Ping, C. L.; Sumner, M. E.; Wilding, L. P. 2000. Andisols. In: Sumner, M. E., ed.

Handbook of Soil Science. Boca Raton, Florida: CRC Press: E-209-224.

Kimsey, M.; McDaniel, P.; Strawn, D.; Moore, J. 2005. Fate of applied sulfate in volcanic ashinfluenced forest soils. Soil Sci. Soc. Am. J. 69: 1507-1515.

Malla, P. B. 2002. Vermiculites. In: Dixon, J. B.; Schultze, D. G., eds. Soil mineralogy with environmental applications. Book Series no. 7. Madison, WI: Soil Science Society of America:

501-529.

Mahler, R. L.; McDole, R. E.; Frederickson, M. K. 1984. The influence of Mount St. Helens ash

on wheat growth and phosphorus, sulfur, calcium, and magnesium uptake. J. Environ. Qual.

13: 91-96.

McDaniel, P. A.; Falen, A. L.; Fosberg, M. A. 1997. Genesis of non-allophanic E horizons in tephrainfluenced Spodosols. Soil Sci. Soc. Am. J. 61: 211-217.

McDaniel, P. A.; Wilson, M. A.; Burt, R.; Lammers, D.; Thorson, T. D.; McGrath, C. L.; Peterson,

N. 2005. Andic soils of the Inland Pacific Northwest, USA: Properties and ecological significance. Soil Science. 170: 300-311.

Meurisse, R. T.; Robbie, W. A.; Niehoff, J.; Ford, G. 1991. Dominant soil formation processes and

propertiesin western-montane forest types and landscapes—Some implicationsfor productivity

and management. In: Management and productivity of western-montane forest soils: proceedings; 1990 April 10-12; Boise, ID. Ogden, UT: U.S. Department of Agriculture, Forest Service,

Intermountain Research Station: 7-19.
USDA Forest Service Proceedings RMRS-P-44. 2007 45

Physical and Chemical Characteristics of Ash-influenced Soils of Inland Northwest Forests McDaniel and Wilson

Nanzyo, M.; Dahlgren, R.; Shoji, S. 1993a. Chemical characteristics of volcanic ash soils.

In: Shoji, S.; Nanzyo, M.; Dahlgren, R., eds. Volcanic ash soils — Genesis, properties, and

utilization. Amsterdam: Elsevier: 145-187.

Nanzyo, M.; Shoji, S.; Dahlgren, R. 1993b. Physical characteristics of volcanic ash soils. In: Shoji, S.;

Nanzyo, M.; Dahlgren, R., eds. Volcanic ash soils — Genesis, properties, and utilization.

Amsterdam: Elsevier: 189-207.

Parfitt, R. L.; Kimble, J. M. 1989. Conditions for formation of allophone in soils. Soil Sci. Soc.

Am. J. 53: 971-977.

Soil Science Society of America. 2001. Internet glossary of soil science terms. Available: http://

www.soils.org/sssagloss/. Madison, WI: Soil Science Society of America.

Soil Survey Division. 2005. Official Soil Series Descriptions. Available: http://ortho.ftw.nrcs.usda.

gov/osd/. U.S. Department of Agriculture, Natural Resources Conservation Service.

Soil Survey Staff. 2003. Keys to Soil Taxonomy. 9th ed. U.S. Department of Agriculture, Natural

Resources Conservation Service. Washington, DC: U.S. Govt. Print. Office. 332 p.

Takahashi, T.; Ikeda, Y.; Fujita, K.; Nanzyo, M. 2006. Effect of liming on organically complexed

aluminum of nonallophanic Andosols from northeastern Japan. Geoderma. 130: 26-34.

Soil Survey Staff. 2003. Keys to Soil Taxonomy. 9th ed. U.S. Department of Agriculture, Natural

Resources Conservation Service. Washington, DC: U.S. Govt. Print. Office. 332 p.

Wada, K. 1989. Allophane and imogolite. In: Dixon, J. B.; Weed, S. B., eds. Minerals in soil environments. 2nd ed. Madison, WI: Soil Science Society of America: 1051-1287.

White, G. N.; Dixon, J. B. 2002. Kaolin-serpentine minerals. In: Dixon, J. B.; Schultze, D. G., eds.

Soil mineralogy with environmental applications. Book Series no. 7. Madison, WI: Soil Science

Society of America: 389-414.

Wilson, M. A.; Burt, R.; Ottersburg, R. J.; Lammers, D. A.; Thorson, T. D.; Langridge, R. W.; Kreger,

A. E. 2002. Isotic mineralogy: Criteria review and application in Blue Mountains, Oregon. Soil

Sci. 167: 465-477.

Zdanowicz, C. M.; Zielinski, G. A.; Germani, M. S. 1999. Mount Mazama eruption: Calendrical

age verified and atmospheric impact assessed. Geology. 27: 621-624.

USDA Forest Service Proceedings RMRS-P-44. 2007 47

In: Page-Dumroese, Deborah; Miller, Richard; Mital, Jim; McDaniel, Paul; Miller, Dan, tech. eds. 2007. 

Volcanic-Ash-­Derived Forest Soils of the Inland Northwest: Properties and Implications for Management 

and Restoration. 9-10 November 2005; Coeur d’Alene, ID. Proceedings RMRS-P-44; Fort Collins, CO: 

U.S. Department of Agriculture, Forest Service, Rocky Mountain Research Station.

Terry L. Craigg, Soil Scientist, Deschutes National Forest, Sisters OR. Steven W. Howes, Regional Soil 

Scientist, U.S. Department of Agriculture, Forest Service, Pacific Northwest Region, Portland, OR.

Abstract

Forest managers must understand how changes in soil quality resulting from project implementation

affect long-term productivity and watershed health. Volcanic ash soils have unique properties that

affect their quality and function; and which may warrant soil quality standards and assessment techniques that are different from other soils. We discuss the concept of soil quality and how it may be

altered by activity-induced soil disturbances. A practical application of the use of soil disturbance

categories and physical soil indices used to perform operational soil monitoring on an ash cap soil

is also discussed.

Introduction

	 Soil disturbance resulting from forest management activities is of concern to both land

managers and the public. On National Forest System lands in the Northwest many current

projects are being administratively appealed or litigated based on the assumption they will

result in soil degradation. Some claim that when implementing ground disturbing activities,

the Forest Service commonly exceeds its own standards intended to maintain soil quality.

There is a need for objective and accurate measures of change in soil quality caused by

management activities. Assessing change in soil quality is difficult and can be influenced

by a number of complicating factors. Properties of volcanic ash soils may also require

development and application of unique soil quality standards and assessment protocols.

Properties of Volcanic Ash Soils that 

May Affect Quality and Function

	 Many soils in the Inland Northwest have been influenced by ashfall deposits from the

eruption of Mt. Mazama (now Crater Lake) as well as other Cascade volcanoes (Harward

and Youngblood 1969). These deposits are found in most soils of the Columbia Plateau of

central and eastern Oregon and Washington. Soils range in texture from “popcorn pumice”

Assessing Quality in Volcanic Ash Soils

Terry L. Craigg and Steven W. Howes
48 USDA Forest Service Proceedings RMRS-P-44. 2007

Craigg and Howes Assessing Quality in Volcanic Ash Soils

near Crater Lake to sands and silts as distance from source increases. Volcanic ash

soils have physical and chemical properties that affect their quality and function;

and that make them unique when compared to other soil parent materials.

A study conducted by Geist and Strickler (1978) compared some physical and

chemical properties of volcanic ash soilsto residualsoils derived from basalt in the

Blue Mountains of northeastern Oregon. In summary, volcanic ash soils had:

	 •	 Lower bulk density

	 •	 Higher porosity

	 •	 Weaker structural development

	 •	 Lower cohesion

	 •	 Lower coarse fragment (>2mm) content

Such properties are described in detail by others in these Proceedings.

This paper focuses on soils with a distinct “ash cap” or surface layer of volcanic ash deposits. Such deposits vary from a few centimeters to over a meter in

depth depending on distance from the source, topography, wind patterns and

subsequent erosion.

Volcanic ash soils have a relatively uniform undisturbed surface soil bulk density (0.67) and a disproportionate concentration of nutrients (total OM, N, K) in

the upper 30 cm of the soil profile. These properties tend to make volcanic ash

soils more susceptible to surface (sheet, rill, wind) erosion when exposed; and

to displacement by ground-based equipment. They store more water but yield a

larger proportion of it in the low suction ranges. Volcanic ash soils also seem to

compact to the same degree over a wide-range of moisture contents.

Pumice soils have many of the same properties as other volcanic ash soils.

Like other volcanic ash soils the low density, lack of cohesion, and concentration of soil nutrients in the upper soil profile of pumice soils, make pumice soils

susceptible to soil compaction and the loss of nutrients through soil displacement.

Because of their low cohesion between individual pumice particles, compaction

in pumice soils can result from both compression and vibration. Pumice soils also

have been found to be most susceptible to compaction when they are very dry

or at or near saturation. Soil moisture contents between these two extremes appear to provide some cohesion between soil particles reducing susceptibility to

compaction. Amounts of soil organic matter is also important when determining

their susceptibility to compaction.

When compaction does occur, soil strength (as measured by resistance to penetration) has been found to increase exponentially with an increase in soil bulk

density (Chitwood 1994). In compacted soils soil strength has also been shown

to increase quickly as the soil dries out over the growing season (Craigg 2006).

Thus measurements of soil strength and soil bulk density are providing different

information about changes occurring in the soil when compaction occurs. Since

there is not a simple linear relationship between measurements of soil strength

and soil bulk density when soil conditions change it would be difficult to readily

substitute one measurement for the other.

Consideration of these properties, along with ash/pumice depth and underlying

soil material, is important in developing soil management objectives/prescriptions, in evaluating potential impacts of proposed activities, and in establishing

meaningful soil quality standards.
USDA Forest Service Proceedings RMRS-P-44. 2007 49

Assessing Quality in Volcanic Ash Soils Craigg and Howes

Soil Disturbance and its Relationship to Soil Quality ________________

Definitions of soil quality differ greatly depending on whom one asks. Most

would say they recognize a high quality soil “when they see it” but when asked to

define soil quality, each would most likely provide a different answer depending

on their individual objectives and personal biases (Karlen and others 1997). The

quality of an individual soil may vary for differing purposes: a high quality soil

for production of trees or forage may have low quality for production of cotton

or wheat. To say that one soil is of higher quality or “better” than another is not

proper without qualification.

There are some who use the terms “soil quality” and “soil health” interchangeably (Warkentin 1995). Each soil has inherent physical, chemical, and biological

propertiesthat affect its ability to function as a medium for plant growth, to regulate

and partition water flow, or to serve as an effective environmental filter. When

any or a combination of these inherent factors is altered to a point where a soil

can no longer function at its maximum potential for any of these purposes, then

its quality or health is said to be reduced or impaired (Larson and Pierce 1991).

Many factors enter into making determinations of soil quality. Some of these

factors can be changed by disturbance (Larson and Pierce 1991; Seybold and

others 1997; Grossman and others 2001). Alteration of soil properties through

disturbance mechanisms is not necessarily harmful. Tillage is an extreme form

of soil disturbance often used to improve soil quality or “tilth” for production of

agricultural crops. In forestry applications, site preparation to improve regeneration success or soil restoration work often involve soil disturbance to some degree

(surface soil exposure, scalping, subsoiling). What sets these apart from other

forms of soil disturbance is that they are planned and are, or should be, carried

out with specific objectives in mind under prescribed conditions.

Management activities on forest and rangelands often result in various forms of

disturbance that can alter soil function. Commonly, land managers are concerned

about how changes in soil quality or function resulting from unplanned, activityinduced disturbance affect the long-term productivity and hydrologic response of

watersheds. In wildland situations, concern usually focuses on disturbance-related

departures from natural soil conditions (considered to be maximum potential or

best possible conditions), occurring as either legacy impacts or those caused by

current management activities. Understandably, there are differences of opinion

among soil scientists and land managers about when and where “significant”

thresholds are reached. This is complicated by the fact that soils differ in their

ability to resist and recover from disturbance effects (Seybold and others 1999).

Disturbance may have negative, neutral, or even positive effects on a soil

depending on its inherent properties. Meaningful soil disturbance standards or

objectives must be based on measured and documented relationships between

the degree of soil disturbance and subsequent tree growth, forage yield, or sediment production. Studies designed to determine these relationships are commonly

carried out as part of controlled and replicated research projects. The paucity

of such information has caused problems in determining threshold levels for, or

defining when, detrimental soil disturbance exists; and in determining how much

disturbance can be tolerated on a given area of land before unacceptable changes

in soil function (productive potential or hydrologic response) occur. Given natural

variability of soil properties across the landscape, a single set of standards for

assessing detrimental disturbance seems inappropriate.
50 USDA Forest Service Proceedings RMRS-P-44. 2007

Craigg and Howes Assessing Quality in Volcanic Ash Soils

Defining Detrimental Soil Disturbance _____________________________

Soil disturbance exists in a number of forms. In forest, range, and watershed

management applications, it most commonly occurs as compaction, displacement,

and puddling resulting from use of ground-based harvesting and slash disposal

equipment. The removal of above ground organic matter is also a result of this

type of disturbance. Soil disturbance can also occur in the form of sheet and rill

erosion or charred soil in intensely burned areas.

Effects of soil disturbance on site productivity or hydrologic function of watersheds is dependent on its degree, extent, distribution, and duration (Froehlich

1976; Snider and Miller 1985; Clayton and others 1987). Degree refers to the

amount of change in a particular soil property such as porosity, bulk density, or

strength and the depth to which that change occurs. Extent refers to the amount

of land surface occupied by that change expressed as a percentage of a specified 

area. Distribution of soil disturbance within a management area may likely be

more important than the actual estimated extent. Disturbance can occur as small

evenly-distributed polygons, or in large polygons in one or a few locations. Duration is the length of time disturbance effects persist. For example, compaction

effects have been measured over 30 years following timber harvest activities on

some soils (Froehlich and others 1985).

Degree and duration of effects are largely determined by inherent soil properties that influence resistance to, and ability to recover from, disturbance. Extent,

distribution, and, in some instances, degree of disturbance can be controlled by

imposing management constraints such as limiting season of operation, spacing

of skid roads and trails, and number of equipment passes.

A challenge has been to establish meaningful soil quality standards given the

inherent variability of soils across the landscape. Simply stating a single threshold

beyond which detrimental soil conditions are thought to exist may not be enough.

Most forest land managers do not wish to damage their productive base or cause

impaired watershed function. However, they also do not want to unnecessarily

limit management opportunities.

Current Status and Needs ________________________________________

Soil quality can be improved, maintained, or degraded by forest management

activities. In order to identify and quantify such changes, a scientifically rigorous

protocol isrequired. It must quantify types and amounts ofsoil disturbances within

a specified area; and identify areas of disturbance considered to be detrimental.

Protocols must be:

	 •	 Statistically valid

	 •	 Relatively easy to implement

	 •	 Cost effective

	 •	 Usable at different scales

	 •	 Able to determine if soil quality is being maintained, improved or degraded.

Numerous methods exist for sampling soil disturbance in both operational and

research settings. Methods differ with respect to sampling objectives,soil variables

considered, and assessment protocols. Inconsistent application of soil disturbance

measurement techniques across a variety of land ownerships has led, in some

cases, to unreliable and incomparable results. More effective and efficient (cost,
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Assessing Quality in Volcanic Ash Soils Craigg and Howes

utility of data) soil disturbance assessment and monitoring programs could be

achieved through use of common soil disturbance class definitions and consistent

use of statistically reliable sampling protocols (Curran and others 2005).

Defined soil disturbance categories must be related to physical indices of soil

quality and documented changes in vegetation growth or hydrologic function. A

determination needs to be made if, in fact or at what point, these disturbance categoriesrepresent “detrimental” changesin soil function. In orderto evaluate impacts

of forest management activities on soil quality, three distinct levels of information

are needed. The first two are commonly generated through agency or company

soil monitoring programs. The last one is primarily a research function.

Initial assessments can be as simple as determining if specified soil conservation or best management practices (BMP) have been implemented as planned or

if contractual/legal requirements relating to soil disturbance have been met. This

is often referred to as compliance or implementation monitoring.

After the initial compliance monitoring, soil disturbance assessment and

monitoring projects are commonly done to evaluate effectiveness of management

practices. These assessments evaluate pre-determined, usually provisional, soil

disturbance standards or objectives based on best available knowledge. This is

commonly referred to as operational or effectiveness monitoring.

Soil disturbance standards or objectives must also be tested or validated to

determine if they result in unacceptable reductions in productivity or watershed

function, are appropriate for local site conditions, or if adjustments are needed.

This process is usually referred to as validation monitoring. Validation is best

accomplished in a research environment under carefully controlled conditions.

Ideally, research would be completed before standards were developed and

implemented.

Cost-effective approaches are needed for operational soil disturbance assessments or monitoring that provides statistically valid and scientifically relevant

data. Monitoring must meet specified quality-control standards and contribute to

regional strategic databases relating tree growth or hydrologic function to defined

classes of disturbance. Our current ability to compare results from operational

and research studies requires more common or standardized soil disturbance

definitions and assessment protocols.

To be cost-effective, operational soil disturbance monitoring protocols must

meet several criteria. Protocols (1) must provide scientifically and technically

sound information, (2) must be reliable, pertinent, and obtained with minimum

investments, (3) must be clearly communicated and understood by all affected

parties, and (4) must be consistently and efficiently implemented (Curran and

others 2005).

USDA Forest Service Approach to Operational Soil Monitoring_______

In Forest Service Region 6, initial assessments of activity-induced changes in

soil quality are typically made through a stratification process in which visually

recognizable soil disturbance categories and disturbances that can be easily detected by probing the soil are described and quantified within an activity area.

This is commonly accomplished using a point grid system in combination with

point observations along a series of randomly oriented transects. This process is

described in detail by Howes and others (1983).

More recently, point observations are being replaced by visual soil disturbance

categories, developed and used to describe areas with a combination of soil
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Craigg and Howes Assessing Quality in Volcanic Ash Soils

disturbances that repeat across an activity area and which are likely large enough

in extent and distribution to affect soil function. Visual categories also account

for the fact that various forms of disturbance are not mutually exclusive. For example, compaction and displacement often occur together. An interim protocol

of this process that is based on procedures described by Scott and others (1979)

is currently being used on national forests in the Blue Mountains.

The process of quantifying different soil disturbance categories across a landscape provides a relatively rapid and inexpensive method for quantifying different types of soil disturbances over large acreages and is recognized by the FS as

an essential step in the soil assessment process. This process, however, is often 

stopped at this point and the incorrect assumption made that any soil disturbance is detrimental.

To avoid this potential problem, visualsoil disturbance categories must be further

evaluated to determine if they do, in fact, adequately represent detrimental soil

conditions. The first step in evaluating a disturbance category is to identify the

soil function(s) that may be negatively affected by a soil disturbance. For example,

if surface soils have been displaced, a soil’s ability to supply nutrients may be

reduced. In compacted skidroads and landings, changes in soil resistance to root

penetration as well as air and water movement in the soil may be the most important consideration. Identification of soil function(s) affected by disturbance allows

for the selection of the most appropriate soil indicators which can then be used

to assess a change in the ability of the soil to function. Care must be taken when

developing and interpreting such indices. Environmental factors such as macroand micro-climate can mask changes in soil function due to disturbance.

Soil indicators or indices are soil parameters that can be quantitatively measured using standardized methods and compared between disturbed and undisturbed sites. On National Forest System lands in the Northwest, soil disturbance

is considered to be detrimental when a soil index is either higher or lower than

a defined threshold.

Development and Application of Forest Service Soil Quality

Standards ______________________________________________________

The USDA Forest Service is directed by law to sustain productivity at current or

enhanced levels and to protect and improve the soils for which it is responsible.

Recognizing this responsibility, the Pacific Northwest Region (R6) issued a Forest

Service Manual Supplement dealing with soil productivity protection in 1979.

It has been revised a number of times since then (current version FSM 2520.

R-6 Supplement 2500.98-1, Effective August 24, 1998). This direction specifies

threshold values (degree) for estimating when detrimental soil disturbance occurs

and also sets area limits (extent) for detrimental soil disturbance on an activity

area basis. Most national forests within R6 have incorporated these values, with

minor modifications, as standards in their forest land and resource management

plans. Other Forest Service Regions subsequently developed similar policy and

direction (Powers and others 1998). Thresholds for estimating detrimental soil

compaction, displacement, puddling, and severely burned soils were developed

based on applicable research results available at the time.

Standards emphasize both observable and measurable soil characteristics

that field personnel can use to monitor effectiveness of activities in meeting
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Assessing Quality in Volcanic Ash Soils Craigg and Howes

soil management objectives. All forms of detrimental soil disturbance, including

permanent features of the transportation system such as roads and landings, are

limited in extent to no more than 20 percent of an activity area. In activity areas

that exceed this extent limit either as a result of previous or current activities,

restoration plans must be in place before new projects are implemented. These 

standards are applied to all soils regardless of their inherent properties and 

ability to resist or recover from disturbance. The only special consideration

given volcanic ash soils is an allowable 20 percent increase in soil bulk density

before they are considered detrimentally compacted. The reason for this is their

relatively low undisturbed bulk densities when compared to soils developed in

other parent materials.

Application of Operational Soil Monitoring Techniques _____________

The following is an example of the use of an operational soil monitoring procedure that was used to evaluate the effects of a forest thinning operation on the soil

resource. The procedure illustrates the application of soil disturbance categories

and physical soil indices.

Overview

During the winter of 2005, the Sisters Ranger District of the Deschutes National

Forest in central Oregon implemented a thinning project designed to reduce

hazardous fuels in pine stands within the wildland urban interface. A Timberjack

cut-to-length harvester and a Timberjack forwarder were used to remove trees

12 inches in diameter and smaller, resulting in a stand with irregular tree spacing

of about 20x20 ft.

Project objectives included:

	 •	 Reduce risk of wildfire to the nearby community of Black Butte Ranch.

	 •	 Promote residual tree growth and move stand toward larger diameter trees.

	 •	 Produce a biomass product that could be used to help offset the cost of the

thinning operation.

Thinning operations occurred during February and March of 2005. During much

of this time, the surface 2 to 4 inches of soil was frozen. There were, however,

times when temperatures rose and soils were moist but not frozen. Several snow

storms also occurred during this period, depositing from a few inches to over a

foot of snow. Soil conditions were favorable for most of the two month period

during which operations occurred.

Soil functions potentially affected by the project included:

	 •	 Ability of the soil to supply water and nutrients to residual trees.

	 •	 Ability of the soil to absorb and transmit water.

	 •	 Ability of the soil to resist other detrimental soil impacts including

displacement, puddling, severe burning, and surface erosion.

Mitigation measures used to reduce potentially detrimental soil impacts included operating over frozen ground, snow, and slash; use of harvest equipment

designed to have low ground pressure; designating spacing of equipment trails;

and hand piling slash.
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Craigg and Howes Assessing Quality in Volcanic Ash Soils

Forest managers wished to know if these practices were effective in meeting

soil quality objectives on this and other similar projects. In this case, managers

wished to know if soil disturbance resulting from the above suite of practices

exceeded 20 percent of the activity area. They also wished to know if different

categories of disturbance contained detrimental soil impacts as defined in (FSM

2520. R-6 Supplement 2500.98-1).

Project Area Soils

Soils in the project area were mapped as part of the Soil Survey of the Upper

Deschutes River Area, Oregon (NRCS 2002). They are described as the SistersYapoah complex 0-15 percent slopes. Soils are classified as:

Sisters soil series – Ashy over loamy, mixed, frigid Humic Vitrixerands

Yapoah soil series – Ashy-skeletal, frigid Humic Vitrixerands

Harvester/Forwarder Transportation System

The Timberjack cut-to-length harvester used in this operation was equipped

with a cutting head mounted on a 30 foot boom. This allowed the harvester to

cut and process materials while making parallel passes across the harvest unit at a

spacing of approximately 60 feet. Harvested materials are positioned so they can

be reached from alternate harvester trails by the forwarder machine. This results

in two types of trails within the harvest unit (1) those that been driven across only

one time by the harvester (ghost trails) and (2) trails that have been driven across

by the harvester followed by the forwarder (harvester-forwarder trails). Because

trees are limbed and topped at the time of felling there are no landings within

the harvest unit. Once the forwarder has collected harvested materials they are

piled next to a haul road prior to loading on log trucks.

Description of Visual Soil Disturbance Categories

A combination of visual observations and probing of the soil with a tile spade

or metal rod was used to identify and describe four categories of soil disturbance

within activity areas. These categories are:

Condition Class 1: Undisturbed state, natural.

	 •	 No evidence of past equipment operation.

	 •	 No wheel tracks or depressions evident.

	 •	 Litter and duff layers intact.

	 •	 No soil displacement evident.

Condition Class 2: Trails used by the harvester machine only. Ghost trails.

	 •	 Two track trails created by one pass of a Timberjack cut-to-length harvester.

	 •	 Faint wheel tracks with a slight depression evident and are < 4 inches deep.

	 •	 Litter and duff layers intact.

	 •	 Surface soil has not been displaced and shows minimal mixing with

subsoil.

Condition Class 3: Trails used by both harvester and forwarder.

	 •	 Two track trails created by one or more passes of a Timberjack cut-to-length

harvester and one or more passes of a Timberjack forwarder.
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Assessing Quality in Volcanic Ash Soils Craigg and Howes

	 •	 Wheel tracks evident and are 4 to 6 inches deep with the exception of

areas where operator was able to lay down enough slash to mitigate soil

impacts.

	 •	 Litter and duff layers are partially intact or missing.

Condition Class 4: Skid trails from previous entries. All were re-used during

current entry.

	 •	 Old skid trails created in the early part of 20th century when selective harvest occurred.

	 •	 Trails appear to have high levels of soil compaction across the entire trail.

	 •	 Evidence of topsoil removal.

Soil Functions Affected by Soil Disturbances

Based on visual observations described above, it was determined that soil

compaction was the most prevalent form of soil disturbance within the harvested

area. When compaction occurs, there are alterations of basic soil properties such

as soil density, total pore volume, pore size distribution, macropore continuity,

and soil strength (Greacen and Sands 1980). Soils vary in their susceptibility to

compaction (Seybold and others 1999). Once a soil becomes compacted, the

condition can persist for decades (Froehlich and others 1985). This, in turn, affects soil function.

Anumber ofresearchers have measured reductionsin site productivity attributed

to soil compaction (Froehlich and others 1986; Cochran and Brock 1985; Helms

and Hipken 1986). Effects of soil compaction on site productivity, however, are

not universally negative. Gomez and others (2002) looked at a range of forest soil

types in California and found compaction to be detrimental, neutral, or beneficial

depending on soil texture and water regime.

Quantifying Visual Soil Disturbance within an Activity 

Area

To assist with quantifying the amount of soil compaction, a recording penetrometer was used to determine the average width of compacted soils across

both the ghost trails and the harvester-forwarder trails (figs. 1 and 2). A threshold

level for the increased soil strength of 2.5 MPa was used to identify compacted

areas. Soil strengths beyond this level were considered to be high enough to begin

to inhibit plant root growth. Based on results harvester ghost trails were initially

considered to consist of two detrimentally compacted tracks, each approximately

three feet in width. Harvester forwarder trails were considered to consist of two

detrimentally compacted tracks, each approximately four feet wide.

A randomly oriented square grid with one grid intersection every two acres was

next overlain on the activity area and used to locate sample points for determining areal extent of soil disturbance categories (fig. 3). At each of the grid intersections, a randomly oriented, 100-ft transect was established. The four defined

disturbance categories were measured along each transect and lengths occupied

by each category recorded. A mean for each category was then computed for the

entire activity area. Sampling in this manner ensured an unbiased, representative

sample. It was determined that 17 percent of the activity area was occupied by

soil disturbance (total of categories 2-4). A 95 percent confidence interval around

this estimate was calculated to be plus or minus 2 percent.
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Craigg and Howes Assessing Quality in Volcanic Ash Soils

Figure 1—Average soil resistance measured 

for the 10 to 25 cm soil depth. Measurements 

were made perpendicular to the harvester ghost 

trails.

Figure 2—Average soil resistance measured 

for the 10 to 25 cm soil depth. Measurements 

were made perpendicular to the harvester 

forwarder trails.

Use of Soil Indices to Interpret Visual Soil Disturbance 

Categories

Three physical soil indices used by the Forest Service to assess changes in soil

physical properties attributed to compaction are increases in soil bulk density,

increases in soil strength (resistance to penetration), and changes in soil pore

size distribution.

Soil Bulk Density

Soil bulk density is defined as the mass per unit volume of soil and represents

the ratio of the mass of solids to the total or bulk volume of the soil (Soil Survey

Staff 1996). The direct measurement of an increase in soil bulk density from soil

compaction requires a minimum amount of sampling equipment and is the most

commonly made measurement of soil compaction used by the Forest Service.

Physical factors that affect soil bulk density and compactability include soil
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Assessing Quality in Volcanic Ash Soils Craigg and Howes

Figure 3—Example of a pre-established grid (randomly oriented) with transects oriented along 

random azimuths.

particle sizes and density, organic matter content, and mineralogy (Howard and

others 1981).

Soil bulk density samples were collected in the spring of the year using a hammer-driven soil core sampler. Table 1 shows soil bulk densities reported for both

the whole soil and for the fine fraction of soil (soil particles <2mm removed).

Determining soil BD based on the fine fraction of soil results in a lower BD value

compared to that determined on a whole soil basis. Thisis due to the higher weight

to volume ratio of soil coarse fragments in the soil core, compared to an equal

volume of soil material. When determined on a whole soil basis, soil compaction

resulted in a significant increase in soil bulk density in both the ghost trails and

the forwarder trails. Soil bulk densities determined for the fine fractions of soil

were significantly greater in the forwarder trails but not in the ghost trails.

Table 1—Soil bulk density measurements determined based on the whole soil (including soil coarse fragments 

>2mm) and based on the fine fraction of soil.

% Volume Soil Soil Bulk Density Soil Bulk Density

Soil Condition Class Coarse Fragments Whole Soil (Mg/m3) Fine Fraction Soil (Mg/m3)

1 1 0.93a 0.92a

2 2 1.02b 1.00ab

 3 2 1.08b 1.06b

Columns within a soil bulk density analysis method are not significant at p = 0.05 if followed by the same letter.

n = 3
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Craigg and Howes Assessing Quality in Volcanic Ash Soils

In this case, few coarse fragments were encountered and there was little difference in soil BD between results obtained using cores with and without coarse

fragments. If there had been more coarse fragments in cores or a large variation

in coarse fragments between cores, it would have had a greater influence on

calculated soil bulk densities and on the way in which the soil functions. To correctly interpret soil bulk density measurements, it is necessary to report soil bulk

densities for whole soil and the fine fraction of soil. It is also necessary to know

the amounts of coarse fragments in the soil cores.

Forest Service soil quality standards identify a change in soil bulk density of 20

percent or more above undisturbed levels as a threshold for determining detrimental

compaction in Andisols (soils derived from volcanic ash). When calculated on

both a whole soil and fine fraction of soil basis, no measured increases in soil bulk

density exceeded the 20 percent relative increase threshold. Therefore, none of

the soil bulk density changes in any of the visual soil disturbance categories met

the Forest Service definition of a detrimentally compacted soil table 2.

Soil Strength

Soil strength describes the soil hardness or the soils resistance to penetration.

Soil probes and spades can be used to detect changes in soil strength resulting

from soil compaction. This technique can be quantified by using a recording soil

penetrometer. Measured soil strengths can vary depending on soil particle size

distribution and shape, clay and organic matter content (Byrd and Cassel 1980).

Within a soil type changes in soil water content and structure can also affect soil

strength (Gerard 1965).

Changes in soil strength resulting from soil compaction were measured within

different disturbance categories using a recording soil cone penetrometer, which

is capable of recording, at predetermined intervals, the force required to push

a cone into the ground (Miller and others 2001). Measurements were made in

early spring, shortly after harvest operations were complete. Field measurements

of gravimetric soil moisture, based on the fine fraction of soil, ranged from 0.19

to 0.22 g/g and were slightly less than the 0.23 g/g estimate of soil field capacity

that was obtained from soil core samples used to determine soil pore size distribution. The penetrometer was set to record soil resistance at 1.5 cm increments

between 0 and 60 cm soil depth. Readings were then down loaded to a Microsoft

Excel Spreadsheet for analysis.

Table 2—Absolute and relative percentage increase in soil bulk density as a result of soil compaction.

Absolute Increase Relative % 

Soil Bulk Density Soil Bulk in Soil Bulk Increase in 

Soil Condition Class Determination Method Density (Mg/m3) Density (Mg/m3) Soil Bulk Density

1 Whole Soil 0.93 

2 Whole Soil 1.02 0.09 10

 3 Whole Soil 1.08 0.15 16

1 Fine Fraction 0.92

2 Fine Fraction 1.00 0.08 9

 3 Fine Fraction 1.06 0.14 15
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Assessing Quality in Volcanic Ash Soils Craigg and Howes

Soil texture and seasonal changes in soil moisture can greatly influence soil

strength measurements. Resistance to penetration has been shown to increase

for both uncompacted and compacted soils as they dry out over the growing

season. The increase in resistance to penetration with decreasing soil moisture,

however, tends to occur more rapidly in compacted soils than in uncompacted

soils (Craigg 2006). Therefore, soil moisture relationships should be considered

when interpreting soil resistance measurements.

Measurements of soil resistance in the undisturbed areas gradually increased

with soil depth reaching a resistance of 1 MPa in the first 10 cm and a final soil

resistance of 2 MPa at approximately 60 cm soil depth. In the forwarder trails soil

resistance increased much faster, reaching a resistance of 3 MPa within the first

10 cm soil depth and retaining that high strength throughout the 60 cm depth.

Increases in soil resistance in the ghost trails were higher than the undisturbed but

less than the forwarder trails (fig. 4). During the thinning operation efforts were

made to limb harvested trees on the equipment trails and then drive on the slash

mat to mitigate soil compaction. Soil penetrometer measurementsindicated that the

slash mat did have at least some affect on mitigating soil compaction (fig. 5).

Currently, Forest Service Region 6 does not have a soil quality index threshold for increases in soil resistance resulting from compaction. Research results

suggest that soil resistances of 2 MPa and greater can begin to affect plant root

growth (Siegel-Issem and others 2005). Thus these results suggest differences in

soil function between the different soil condition classes, in particular the ability

of roots to penetrate compacted soils.

Figure 4—Soil strength measured in the spring of 2005 for different soil 

disturbance classes. Horizontal bars indicate one standard error. n = 30.
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Craigg and Howes Assessing Quality in Volcanic Ash Soils

Soil Pore Size Distribution

Soil pore space accounts for approximately half of the total volume of mineral

soil. Changes in total soil porosity and pore size distribution that may result from

soil compaction can affect soil functions by altering air and water flow into and

through the soil. Changes in soil porosity can also affect the amounts of water

storage in the soil (Scott 2000).

Measuring a full range of soil pore sizes requires relatively sophisticated laboratory equipment compared to that needed for measuring soil bulk density or soil

strength. Although total soil porosity can be estimated from bulk density and soil

particle density, this calculation provides no information about pore size distribution changes occurring in the soil. To better understand changes in soil pore

size distribution resulting from soil compaction, a relatively simple method was

used which does not require the use of sophisticated laboratory equipment. This

technique measures mainly the porosity changes occurring in the larger soil pore

sizes (soil pores > 30μm).

Intact soil cores for measuring soil pore size distribution were collected using

the same hammer-driven core sampler used to sample soil bulk density. Following collection of intact soil cores, soil pore size distribution was determined using a modification of the water desorption method described in (Danielson and

Sutherland 1986). Briefly, a hanging water column was created by connecting a

Buchner funnel with a porous ceramic plate in the bottom to approximately 3

meters of plastic tubing with a burette connected to the other end. A soil core

was then placed in the funnel and saturated with water by raising the burette

Figure 5—Soil strength measured in the spring of 2005 for different soil disturbance classes with measurements on harvester forwarder trails separated 

depending upon whether or not slash was present. Horizontal bars indicate 

one standard error. n = 30 (undisturbed and ghost trails)

n = 15 (forwarder trails)
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Assessing Quality in Volcanic Ash Soils Craigg and Howes

and creating a slight head of water. A series of suctions were next applied to the

saturated soil core by raising the funnel above a predetermined mark on the burette. Volumes of water removed from the soil cores were recorded for a series

of applied suctions and the equivalent radius of the largest soil pores filled with

water determined by the capillary equation (Scott 2000).

Results indicated a shift in soil pore size distribution from larger pore sizes or

macropores (soil pores > 30μm) to smaller pore sizes (soil pores < 30μm) when

soils became compacted (fig. 6). While soil compaction did result in a significant

decrease in macropores and a significant increase in smaller soil pore sizes, there

was not a significant change in totalsoil porosity between the different disturbance

categories (table 3). Although standards have been established in Forest Service

Region 6 for macropore space reductions in residual soils, none have yet been

established for ash-derived soils.

Figure 6—Shift in soil pore size distributions for different soil disturbance classes 

following soil compaction.

Table 3—Changes in soil pore size distribution and total soil porosity resulting from soil compaction.

Pore volume Pore volume Total pore volume

Soil condition Class >30μm (cm3/cm3) <30μm (cm3/cm3) (cm3/cm3)

1 0.36a 0.24a 0.59a

2 0.29b 0.27b 0.55a

 3 0.25b 0.30c 0.55a

n = 3

Columns within a pore size class are not significant at p = 0.05 if followed by the same letter.
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Craigg and Howes Assessing Quality in Volcanic Ash Soils

Interpretation of Results

Extent of soil disturbance within the project area was initially determined by

first describing and quantifying visual soil disturbance categories and then measuring a suite of indices within each category. Soil index measurements that were

made within disturbed areas were then compared to those measurements made in

undisturbed areas. Degree of change in specified soil indices was next compared

to defined thresholds for determining if the change is considered “detrimental”

or “undesirable.”

All measured increasesin soil bulk density were below threshold values defined

by the Pacific Northwest Region for soils derived from volcanic ash. Although increases in soil strength were measured for ghost trails and for harvester-forwarder

trails, no threshold value or soil quality standard has yet been established in the

Pacific Northwest Region for soil strength. Reductions in macropore space were

also measured in ghost trails and for harvester-forwarder trails. Forest Service

Region 6 does not currently have a soil quality index threshold established for

macropore space reductions in ash-derived soils. Soil strength and reductions in

macropore space appear to be reliable and easily measurable indices of soil function. They also provide additional information about changes occurring in the soil

when compaction occurs. Validation work needs to be completed to determine

appropriate thresholds for each of these indices.

Summary ______________________________________________________

Soil quality can be defined in a number of ways depending on one’s point

of view. For forest practitioners, management-induced changes in soil quality

are of concern when site productivity is measurably reduced or water quality

is impaired. Soil disturbance can be accurately described and quantified using

consistent visual categories and sound, cost-effective sampling protocols. Assessments of soil quality must relate visual disturbance categories to changes in the

ability of the soil to provide nutrients or to absorb and transmit water. A number

of physical soil indices (soil bulk density, soil strength, soil pore size distribution)

are available to help define such relationships.

Soils vary across the landscape and respond differently to management practices. Care must be taken when making soil quality assessments to select the most

appropriate soil indices, to follow proper sampling protocols, and to interpret

results correctly. Finally, without knowing effects of soil disturbance on site productivity and sediment yield, meaningful assessments of soil quality cannot be

made. Validation of such cause and effect relationships is a step in the process

that is often never completed.

References______________________________________________________

Byrd, C. W.; Cassel, D. K. 1980. The effect of sand content upon cone index and selected physical

properties. Soil Science. 129: 197-204.

Chitwood, L. 1994. Soil compaction study phase A, Deschutes National Forest. DRAFT report.

Clayton, J. L.; Kellogg, G.; Forrester, N. 1987. Soil disturbance-tree growth relations in central

Idaho clearcuts. Research Note INT-372. Ogden, UT: U.S. Department of Agriculture, Forest

Service, Intermountain Research Station. 6 p.

Cochran, P. H.; Brock, T. 1985. Soil compaction and initial height growth of planted ponderosa

pine. Pacific Northwest Extension Publication-PNW 434. 3 p.
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Assessing Quality in Volcanic Ash Soils Craigg and Howes

Craigg, T. L. 2006. Soil Sciences. Unpublished. Davis, CA: University of California, Davis. Masters

Thesis.

Curran, M. P.; Miller, R. E.; Howes, S. W.; Maynard, D. G.; Terry,T. A.; Heninger, R. L.; Niemann,

T.; van Rees, K.; Powers, R. F.; Schoenholtz, S. H. 2005. Progress toward more uniform assessment and reporting of soil disturbance for operations, research, and sustainability protocols. J.

For. Ecol. Manage. 220: 7-30.

Danielson, R. E.; Sutherland, P. L. 1986. Porosity. In: Klute, A., ed. Methods of soil analysis. SSSA

Book Series: 5 Part 1 – Physical and mineralogical methods. Madison, WI: SSSA.

Froehlich, H. A. 1976. The influence of different thinning systems on damage to soil and trees.

Proceedings; XVI IUFOR World Congress Division IV; Norway: UUFRO: 333-334.

Froehlich, H. A.; Miles, D. W. R.; Robbins, R. W. 1985. Soil bulk density recovery on compacted

skid trails in central Idaho. Soil Sci. Soc. Am. J. 53: 946-950.

Froehlich, H. A.; Miles, D. W. R.; Robbins, R. W. 1986. Growth of young Pinus ponderosa and

Pinus contorta on compacted soil in central Washington. Forest Ecology and Management. 15:

285-294.

Geist, J. M.; Strickler, G. S. 1978. Physical and chemical properties of some Blue Mountain soils

in northeast Oregon. Res. Pap PNW-236. Portland, OR: U.S. Department of Agriculture, Forest

Service, Pacific Northwest Forest and Range Experiment Station. 19 p.

Gerard, C. J. 1965. The influence of soil moisture, soil texture, drying conditions, and exchangeable cations on soil strength. Soil Sci. Soc. Amer. J. 29: 641-645.

Gomez, A.; Powers, R. F.; Singer, M. J.; Horwath, W. R. 2002. Soil compaction effects on growth

of young ponderosa pine following litter removal in California’s Sierra Nevada. Soil Science

Soc. Amer. J. 66: 1334-1343.

Greacen, E. L.; Sands, R. 1980. Compaction of forest soils. Aust. J. Res. 18: 163-189.

Grossman, R. B.; Harms, D. S.; Seybold, C. A.; Herrick, J. E. 2001. Coupling use-dependent and useinvariant data for soil quality evaluation in the United States. J. Soil Water Conserv. 56(1): 63-68.

Harward, M. E.; Youngberg, C. T. 1969. Soils from Mazama ash in Oregon: identification, distribution and properties. Pedology and quaternary research symposium: proceedings; 1969 May

13-14, Edmonton, AB: University of Alberta: 163-178.

Helms, J. A.; Hipken, C. 1986. Effects of soil compaction on height growth of a California ponderosa pine plantation. West. J. Appl. For 1: 121-124.

Howard, R. F.; Singer, M. J.; Franz, G. A. 1981. Effects of soil properties, water content, and

compactive effort on compaction of selected California forest and range soils. Soil Sci. Soc.

Amer. J. 45(2): 231-237.

Howes, S.; Hazard, J.; Geist, J. M. 1983. Guidelines for sampling some physical conditions of

surface soils. R6-RWM-146-1983. Portland, OR: U. S. Department of Agriculture, Forest Service,

Pacific Northwest Region.

Karlen, D. L.; Mausbach, M. J.; Doran, J. W.; Cline, R. G.; Harris, R. F.; Schuman, G. E. 1997. Soil

Sci. Soc. Am. J. 61(1): 139-49.

Larson, W. E.; Pierce, F. J. 1991. Conservation and enhancement of soil quality. In: Evaluation of

Sustainable Land Management in the Developing World. Int. Bangkok, Thailand: Board for Soil

Res. and Management: 175-203.

Miller, R. E.; Hazard, J.; Howes, S. 2001. Precision, accuracy, and efficiency of four tools for

measuring soil bulk density or strength. Gen. Tech. Rep. PNW-RP-532. U.S. Department of

Agriculture, Forest Service, Pacific Northwest Research Station. 16 p.

Natural Resources Conservation Service (NRCS). 2002. Soil Survey of upper Deshutes river area,

Oregon, including parts of Deschutes, Jefferson, and Klamath Counties. Report. U.S. Department of Agriculture, Natural Resources Conservation Service. 515 p.

Powers, R. F.; Tiarks, A. E.; Boyle, J. R. 1998. Assessing soil quality: practical standards for sustainable forest productivity in the United States. In: The contribution of soil science to the

development and implementation of criteria and indicators of sustainable forest management.

SSSA Spec. Publ. 53. Madison, WI: SSSA: 53-80.

Scott, W.; Gillis, G. C.; Thronson, D. 1979. Ground skidding soil management guidelines. Weyerhaeuser Company Internal Report. Federal Way, WA: WTC. 34 p.

Scott, D. H. 2000. Soil physics agricultural and environmental applications, Iowa State University

Press, First Edition. 421 p.

Seybold, C. A.; Mausbach, M. J.; Karlen, D. L.; Rogers, H. H. 1997. Quantification of Soil Quality. In: Stewart, B. A.; Lal, R., eds. Advances in Agronomy. Proceedings from an International

Symposium on Carbon Sequestration in Soil. Lewis Publ. 53-68.
64 USDA Forest Service Proceedings RMRS-P-44. 2007

Craigg and Howes Assessing Quality in Volcanic Ash Soils

Seybold, C. A.; Herrick, J. E.; Bredja, J. J. 1999. Soil resilience: a fundamental component of soil

quality. Soil Sci. 164(4): 224-234.

Siegel-Issem, C. M.; Burger, J. A.; Powers, R. F.; Ponder, F.; Patterson, S. C. 2005. Seedling root

growth as a function of soil density and water content. Soil Sci. Soc. Am. J. 69: 215-226

Snider, M. D.; Miller, R. F. 1985. Effects of tractor logging on soils and vegetation in eastern Oregon. Soil Science Society of America Journal. 49: 1280-1282.

Soil Survey Staff. 1996. Soil survey laboratory methods manual. Soil Survey Investigations Report

No. 42 version 3.0.

Warkentin, B. P. 1995. The changing concept of soil quality. J. Soil Water Cons. 50: 226-228.

Timberjack cut-to-length harvester

Timberjack forwarder machine
USDA Forest Service Proceedings RMRS-P-44. 2007 65

Assessing Quality in Volcanic Ash Soils Craigg and Howes

Harvester forwarder trail

Quantification of soil disturbance 

categories using randomly oriented 

100 foot transects.
66 USDA Forest Service Proceedings RMRS-P-44. 2007

Craigg and Howes Assessing Quality in Volcanic Ash Soils

Measuring soil resistance using the recording soil penetrometer.
Past Activities and Their 

Consequences on Ash-cap Soils

USDA Forest Service Proceedings RMRS-P-44. 2007 69

In: Page-Dumroese, Deborah; Miller, Richard; Mital, Jim; McDaniel, Paul; Miller, Dan, tech. eds. 2007. 

Volcanic-Ash-­Derived Forest Soils of the Inland Northwest: Properties and Implications for Management 

and Restoration. 9-10 November 2005; Coeur d’Alene, ID. Proceedings RMRS-P-44; Fort Collins, CO: 

U.S. Department of Agriculture, Forest Service, Rocky Mountain Research Station.

Leonard R. Johnson and Han-Sup Han are faculty in the area of forest operations in the College of 

Natural Resources at the University of Idaho. Debbie Page-Dumroese is a Research Scientist with 

the Rocky Mountain Research Station, U.S. Department of Agriculture, Forest Service and is based 

in Moscow, Idaho. 

Abstract

	 With pressure and vibration on a soil, air spaces between soil particles can be reduced by displaced

soil particles. Activity associated with heavy machine traffic increases the density of the soil and can

also increase the resistance of the soil to penetration. This paper reviewsresearch related to disturbance

of forest soils with a primary focus on compaction in ash-cap soils. The general process of compaction is described along with physical properties of ash-cap soils that relate to compaction. Ash-cap

soils have physical soil properties most closely aligned to silt-loam soils. Undisturbed ash-cap soils

often have low bulk densities to variable depths. Under moisture conditions near field capacity, these

soils are susceptible to significant disturbance from machine traffic, and when the disturbance causes

increases in bulk density, the soils are not likely to recover from this disturbed condition for many

years. Machine traffic on forest soils generally occurs as a result of some form of active stand management including precommercial thinning, intermediate and final timber harvest, and site preparation

activities involving slash disposal and treatment. The direct contact between equipment and the forest

soil will result in some type of soil disturbance. The degree and extent of the soil disturbance is most

often controlled through guidelines on the selection and operation of equipment and by restricting

the location and operating season for equipment.

Effects of Machine Traffic on the Physical 

Properties of Ash-Cap Soils

Leonard R. Johnson, Debbie Page-Dumroese and Han-Sup Han

Introduction

General Process of Compaction

	 Compaction ofsoilsis created through the energy exerted on the soil, usually through vehicular

traffic in harvesting and site preparation operations. It results in the reduction of air spaces in

the soil with a corresponding increase in the bulk density of the soil (weight per unit of volume).

Erosion can also result from forest operations. Erosion generally occurs as a result ofsoil displacement and is most often associated with harvest and site preparation activities on steeperslopes.

	 Although generally viewed in a negative contextwith respect to forestsoils, compaction is often

a desirable processin construction activities. Many engineering projectsinvolving earthwork in

earthen dams,structural foundations, and roadsrequire predictable strength in the soilsthat are at
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Johnson, Page-Dumroese and Han Effects of Machine Traffic on the Physical Properties of Ash-Cap Soils

the foundation of the construction projects. Various compaction methods have

been developed to achieve a desired level of soil strength and density. Some of

the principles derived from research in civil engineering and soil mechanics on

achieving desired levels of compaction can also be applied to forest soils in determining conditions where natural soils are at the greatest risk of compaction.

Cullen and Montagne (1981) conducted an extensive summary of literature on

the general relationships between soil properties and compaction. Their review

includes the general relationship between the soil properties of texture, fragment

content,structure, moisture content at the time of compaction, and organic matter

and the susceptibility of the soil to compaction. A more recent review by Miller

and others (2004) summarized current literature on the effects of heavy equipment on soils and productivity. The discussion in this section draws heavily on

these literature reviews.

Engineering Compaction Methods

Compression or kneading compaction is generally achieved in the field with

equipment that exerts gradually increasing pressure on the soil. Pressure is gradually increased to a maximum and then is gradually decreased. A device commonly

used to accomplish this task in construction is called a sheepsfoot roller. Rubber

tired rollers also exhibit the characteristics of this kneading action. The interaction

of the tires of rubber-tired skidders used in forest operations with the soil seems

to resemble that of kneading compaction machines, but with far less pressure

than the equipment designed for that purpose.

Vibratory compactors usually combine pressure on the soil with vibration.

Hand-held models utilize a vibrating plate. Larger versions combine a large steel

roller with a vibratory impulse. There is some conjecture that tracked equipment

used in forest operations can duplicate this action, but, again, with far less compactive energy than equipment designed for that purpose.

Engineering properties of soils are important to compaction. In addition to

moisture content, important factors include initial soil strength or bulk density,

distribution of particle sizes, percent organic matter, rock-fragment content, and

percent sand, silt or clay (soil texture). The presence and influence of clay in the

soil will usually determine whetherit is classified as cohesive or non-cohesive.Clay

influences the susceptibility of soils to compaction because of the small particle

sizes of clay, clay mineralogy, and through its effect on shear strength. With small

clay particles, the shearstrength on soils can be partially attributed to the chemical

bonding and electro-chemical resistance between particles (Brown 1977).

Soil type, texture and structure will influence the equipment that is most effective in achieving the highest level of compaction. Means and Parcher (1963)

found that “maximum densities for soils with coarse texture were achieved with

a heavy smooth-wheeled roller with some vibratory effects.” Coarse textured

soils, usually those very low in clay content, are non-cohesive and these generally

require vibratory compactors. Fine-textured soils and soils with a high content of

clay are usually not compacted well through vibratory compactors and require

the kneading action of a mechanism similar to a sheepsfoot roller (Ingersoll-Rand

1975). Kryine (1951) noted that, in general, the maximum soil densities achieved

by several methods of laboratory and field compaction decrease with decreasing

soil particle size. The highest densities generally occur in soils with a wide range

in particle sizes where particles can be reoriented in ways that allow the small
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Effects of Machine Traffic on the Physical Properties of Ash-Cap Soils Johnson, Page-Dumroese and Han

particles to pack into the voids between the larger particles (Li 1956; Cullen and

Montagne 1981; Miller and others 2004).

Ash-cap soils have unique characteristicsthat affect theirresponse to the various

compaction methods. While the particle size is relatively small, ash-cap soils are

also considered non-cohesive and non-plastic (Cullen and others 1991). Because

of their non-cohesive nature, they are likely to be susceptible to vibratory compaction (Cullen and Montagne 1981). While the kneading action of a sheepsfoot

roller would probably exceed the shear strength of ash-cap soils and would not be

effective for compaction, the pressure and more subtle kneading action produced

by rubber-tired and tracked vehicles could increase bulk densities.

Froehlich and others (1980) completed a general report for the Equipment

Development Center of the U.S. Forest Service to provide a basis for predicting

soil compaction on forested land. Observed soil types included sandy loam, clay

loam and loam. The study developed equations to predict absolute and percent

changes in bulk density with vehicular traffic. While specific values associated

with the equations may not be useful in a broad sense, the statistically significant

factors are of interest. These include the number of trips by equipment, initial soil

strength (cone index), initial soil density, machine derived pressure of the vehicle

in kilograms per square centimeter, soil organic matter in percent, soil moisture

content in percent, and forest floor depth. The most significant of these factors

were number of trips and the initial cone index of the soil, reflecting a measure

of initial soil strength and the level of machine activity as two primary factors in

determining changes in soil characteristics.

Optimum Moisture Content

The optimum moisture content for compaction isrelated to the energy generated

in the compaction effort. As compaction effort increases, soils will be compacted

to higher soil strength and bulk density. The maximum bulk density will also occur

at lower optimum moisture content. Soils below the optimum moisture content

will not be compacted to as high a bulk density as when they are at the optimum

moisture content (Håkansson and Lipiec 2000). Up to and including the optimum

moisture content, water can lubricate particles and allow their reorientation with

respect to each other. Most compaction is seen in wet conditions, particularly

near soil field moisture capacity (Alexander and Poff 1985). When soil moisture

exceeds the optimum moisture content of the soil, soils begin to become plastic

or the incompressibility of the water prevents reorientation and packing of the

soil particles. According to the review by Cullen and Montagne (1981), optimum

moisture content for compaction tends to increase as soil texture becomes finer

(Felt 1965). The less dense the initial soil sample, the greater the moisture content required to reach maximum soil density for a given compactive effort (Lull

1959).

Optimum moisture content for compaction is determined for engineering

purposes by a laboratory analysis called the Proctor test. The standard proctor

test involves 25 blows of a 2.5 kg hammer dropped from a height of 30.5 cm.

Because this test did not generate sufficient energy to predict compaction efforts

of most modern construction equipment, a modified proctor test was developed.

The modified test increased the compaction energy, using 25 blows of a 4.5 kg

hammer dropped from a height of 45.7 cm. Both the standard and modified Proctor tests created too much compaction energy to effectively predict compaction
72 USDA Forest Service Proceedings RMRS-P-44. 2007

Johnson, Page-Dumroese and Han Effects of Machine Traffic on the Physical Properties of Ash-Cap Soils

from equipment used in forest operations (Froehlich and others 1980). A light

proctor test using 8% of the energy of the standard Proctor test appeared to be

effective in predicting the compaction effort of harvesting and site preparation

equipment. It involved 10 blows of a hammer weighing 0.5 kg dropped from a

height of 30.5 cm. The general relationship between optimum moisture content,

maximum bulk density and level of compaction effort are illustrated in Figure 1.

As compaction energy increases, the optimum moisture content for compaction

decreases.

Soil texture can also affect the response of the soil to compaction efforts and

its sensitivity to moisture content. Figure 2 illustrates theoretical differences in

maximum bulk density and sensitivity to moisture for well graded and uniform

soils when other factors of the soil are held constant. Although the light Proctor

test could be used to predict maximum bulk densities that might result from forest

operations for some soil types, it also showed that the soils were less sensitive

to moisture content when there was less compaction energy applied. The compaction curve was flatter and, in some cases, U-shaped as illustrated in Figure 3

(Froehlich and others 1980).

Davis (1992) used the light Proctor test in his studies of bulk density changes

in two central Oregon soils. He found the light proctor test to be adequate for

describing a cobbly loam soil, but found a test using the heavier hammer of the

standard proctor test with 5 to10 blows of the hammer (rather than 25) to be more

accurate in predicting compaction for the ash-cap soil with sandy loam texture.

His Proctor tests showed gradually increasing bulk densities as compaction effort

increased, but there was not a high sensitivity to soil moisture content.

Total organic matter content in the soil is closely related to aggregate size and

stability. Thus a reduction in organic matter content will result in a loss of aggregate stability and a subsequent increase in a soil’s potential for compaction

(Alderfer and Merkle 1941). Working with four soils in New York, Free and others

(1947) concluded that soil samples containing the most organic matter would be

compacted the least at given moisture contents and compactive efforts. This relationship between organic matter and compactibility of soils was also confirmed

in the review conducted by Miller and others (2004).

Figure 1—General relationships between moisture content, compaction effort and 

maximum bulk density.
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Effects of Machine Traffic on the Physical Properties of Ash-Cap Soils Johnson, Page-Dumroese and Han

Methods and Limitations of Measuring Compaction ________________

There are several methods available to measure compaction, but all have limitations in forest soils. Two of the most common include: (1) the bulk density of the soil

and (2) soil strength as often measured by the resistance of the soil to penetration

with a calibrated penetrometer. While measurement of bulk density or soil strength

before and after vehicular traffic is ideal because it reduces sampling error, it is seldom done. Most often the measurements are taken “on and off” compacted areas.

If the soil disturbance has also displaced soils in compacted areas, this leads to the

risk of comparing soil characteristics in one soil horizon with those in another.

Figure 3—Proctor test results on light soil gravelly sandy loam soil with initial bulk density near 

0.70 g/cm3 (Mg/m3 ) and 2% clay content adapted from Froehlich and others (1980).

Figure 2—General relationships of optimum moisture content and maximum bulk 

density for well graded and uniform textured soils.
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Johnson, Page-Dumroese and Han Effects of Machine Traffic on the Physical Properties of Ash-Cap Soils

Bulk Density

Bulk density, the dry mass of a unit volume of soil (Blake and Hartge 1986),

is commonly used to measure soil compaction. Bulk density and rock content

measurements are required to convertsoil nutrient, water, and microbial measures

to a mass-per-area basis to compare between sites with different bulk densities

and within-site processes (McNabb and others 1986). Although rocks are often

not a large component of ash-cap soils, roots and steep slopes make it extremely

difficult to accurately determine soil bulk density. A number of different methods have been used to determine bulk density in soils. These can generally be

categorized as (1) core sampling, (2) excavation and volume displacement and

(3) radiation.

Core sampling is a simple, straightforward method for measuring bulk density.

Cylinders of a known volume are driven into the soil and the resultant soil core

dried and weighed. In some cases, narrow and small core samplers may overestimate bulk density by compacting soil into the cylinder when it is hammered

into the soil.

Volume excavation is an appealing alternative to core techniques because it

allows for flexibility in volume of soil sampled based on the size of soil coarsefragments, roots or hardpans. A hole is excavated to the desired depth and width,

all soil material is removed and collected for weight determination and the volume of the hole measured. Various methods have been used to measure hole

volume including known quantities of sand or styrofoam balls, water as measured

in a plastic bag lining the hole (Kohl 1988), and expanding polyurethane foam

(Page-Dumroese and others 1999).

Radiation methods are instantaneous, produce minimal soil disturbance, allow

accessibility to subsoil measurements without excavation, do not have to be on

a level site, and have the option of continuous or repeated measurements of the

same point (Blake and Hartge 1986). With a nuclear moisture-density gauge, the

source probe is lowered to selected soil depths through access tubes and the

average density between the source and surface-located detector is obtained.

However, using a nuclear gauge is not common on forest sites far from a road

since it weighs about 18 kg. In addition, the equipment operator much be certified

to handle and transport radioactive material (Flint and Childs 1984).

Penetrometer

Soil penetrability is a measure of the ease with which a probe can be pushed

or driven into the soil (Vaz and others 2001). The resistance to penetration is related to the pressure required to form a spherical cavity in the soil, large enough

to accommodate the cone of the penetrometer, and allowing for the frictional

resistance between the cone and its surrounding soil. Ease of penetration by the

probe is influenced by both soil and probe characteristics. Soil-to-probe friction

is governed by probe factors such as cone angle, diameter, roughness and rate of

penetration. Soil factors influencing penetration resistance are matric water potential (water content), bulk density, soil compressibility, soil texture, and organic

matter content (Smith and others 1997; Vaz and others 2001).

Major factors that limit the use and interpretation of penetrometers as field indicators of excessive compaction are the influences of water content and initial bulk

density, mostly because there is an insufficient data base to allow adjustments for
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Effects of Machine Traffic on the Physical Properties of Ash-Cap Soils Johnson, Page-Dumroese and Han

these factors(Gupta andAllmara 1987; Bennie and Burger 1988).A widely accepted

method is to measure penetrometer resistance at or near field moisture capacity.

Penetrometer-measured soil strength has been principally linked with soil bulk

density, water content, clay content, and organic carbon. Usually soil strength

increases with increasing bulk density and decreasing water content, except at

lower levels of compaction when soil strength declines as soils dry out (Smith

and others 1997). Since soil strength is strongly related to water content, it varies

considerably throughout the year with each wetting and drying cycle (Busscher

and others 1997). This relationship is also influenced by the degree of compaction (Mirreh and Ketcheson 1972). Increasing clay contents appears to reduce the

rate at which soil strength increases as soils dry to wilting point. With increasing

organic matter content, soil strength values are high at field capacity, especially

at higher bulk densities (Smith and others 1997).

Correlation between methods of measuring compaction

Increasesin bulk density generally have a positive correlation to increasesin the

resistance to penetration as measured by a penetrometer, but specific, statistical

relationships between these two types of measurement have been much more

difficult to establish. Effortsto correlate bulk density measurementsto penetrometer

readings through regression analysis have often failed or resulted in an extremely

low correlation coefficient (Landsberg and others 2003; Froese 2004). Allbrook

(1986) was reasonably successful in developing a statistical relationship between

bulk density and soil strength (R2=0.67) when the soil strength was measured at

or near field capacity moisture content. The study was conducted on volcanic

soils in central Oregon and compared bulk densities and soil strength in skid ruts

and in adjacent undisturbed areas. Soils had initial soil bulk densities averaging

0.80 Mg/m3. At the 5 cm depth he found a 23.2% increase in bulk densities measured with a nuclear densimeter and a 143% increase in soil strength as measured

with a penetrometer. It appears that the soil strength measurements were more

sensitive and responsive to changes in soil conditions, but it is also clear that a

standard of detrimental soil disturbance that dictates less than a 15% change in

bulk density will not be the appropriate percentage standard when comparing

soil strength (penetrometer) readings. The USDA Forest Service uses a threshold

value of a 15% increase in bulk density for determining when soil compaction

has reached a level that is detrimental to biomass production (Powers and others

1998).

Characterization of Ash-Cap Soils _________________________________

Soils characterized as ash-cap soils are often derived from a variety of volcanic

eruptions, the most common being the eruption of Mount Mazama at Crater Lake,

Oregon. These soils are often considered surficial deposits, overlaying the soil

derived from the base rock by depths that vary from 15 cm to several meters. They

are frequently characterized in the silt loam or sandy loam textural categories of

soils. Most ash-cap soils are characterized by low bulk densities, generally less

than 0.75 g/cm3, and by high porosity and low shear strength (Page-Dumroese

1993; Cullen and Montagne 1981; Davis 1992). The predominance of silica (glass

fragments) in the soil contributes to the water holding capacity of the soil. The

distribution of micro- and macro-pore spaces provides many areas for holding
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Johnson, Page-Dumroese and Han Effects of Machine Traffic on the Physical Properties of Ash-Cap Soils

water, especially in the micro- pore spaces. One effect of compaction may be

to decrease the macro-pore space that is easily assessable to plants, but not the

micro-pore space. Ash-cap soils can also be characterized by relatively low clay

content. This generally means that there will be very little cohesion and internal

bonding in the soil. Without clay, there will be very little shrinking and swelling

and this may affect the rate of soil recovery from compaction.

Although ash-cap influenced soils are non-cohesive, they do notseem to recover

easily from compaction. Froehlich and others (1985) observed compaction on

and off skid trails on several harvested sites in central Idaho. For soils of volcanic

origin, there was a reduction in the percent difference in density on and off trails

with time, but they also found that soil bulk density on volcanic soils were still

26% higher at 15 cm depth in the trails than off trails 20-25 years after harvesting. One risk with soil recovery studies that consider bulk densities in disturbed

and undisturbed areas is that they may not be comparing the same soil types

and texture. For example, if the disturbance also displaced soil on a skid trail, the

comparison may be between the surface horizon of the undisturbed soil and a

sub-horizon of the soil on the skid trail.

There are several hypotheses on why ash-cap soils do not recover more quickly.

One is that the compaction activity breaks down the soil particles and/or realigns

them into more of a platy structure that allows them to fit closer together after

traffic. Another is that the jagged edges of the silica dominated ash-cap soil particles are physically locked during compaction. Since clay content is low, there

is little natural shrinkage and swelling in the soil. Other factors may be related

to the high initial percent change in bulk density that generally occurs and the

lack of a significant freeze-thaw cycles in the drier regions of the intermountain

western USA.

Cullen and others (1991) characterized two ash-cap soils in their work in

western Montana. Using a standard Proctor test they determined the optimum

moisture content for compaction of ash cap soils to be about 228 g/kg (22.8%)

and 256 g/kg (25.6%) in the surface layer with a projected maximum bulk density

at this moisture content of 1.50 Mg/m3 and 1.36 Mg/m3 for ash over quartzite or

limestone till, respectively. These bulk densities are much higher than those encountered in even heavily compacted forest soils as a result of forest operations.

Given the results of the work of Froehlich and others (1980), one would expect

the optimum water content for compaction from forest operations to be higher

than the value observed in the Montana tests and the resulting maximum compaction to be lower. Field observations in the Montana soils showed their severely

compacted sites to have average bulk densities at the 5 cm depth of 1.01 Mg/m3

and 0.97 Mg/m3 for ash over quartzite or limestone till, respectively.

Although the relatively low bulk densities of ash cap soils make them very

susceptible to compaction, the resulting bulk densities of compacted soils seldom exceed 1.0 Mg/m3. The impact of this degree of change in bulk density on

future forest productivity is not the subject of this paper but the general impact

of compaction on tree growth has been studied in a number of different settings

over the years (Froehlich 1979; Davis 1992; Powers and others 2004). While increased bulk density associated with machine traffic has generally been shown

to reduce tree growth, the extent of the growth reduction in ash-cap soils is not

well documented. Growth reduction can possibly be attributed to a reduction

in the water holding capacity of the soil, but the change in pore-size distribution
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Effects of Machine Traffic on the Physical Properties of Ash-Cap Soils Johnson, Page-Dumroese and Han

within the ash-cap soils after compaction may also affect tree growth (Powers

and others 2004). The use of 15% percent change that is used as a threshold

value for determining detrimental soil compaction by the USDA Forest Service

may be ineffective for all soils since each soil textural class varies in initial bulk

density value and biological significance of that change (Williamson and Neilsen

2000). Block and others (2002) suggest that combining soil bulk density or soil

strength measurements with a surface disturbance regime can be a useful method

for monitoring harvesting impacts on soil.

Case Studies of Operations on Ash-Cap Soils _______________________

Compaction on some ash-cap soils has been found to persist for long periods

of time, particularly at depths of 15 cm and greater. Geist and others (1989) found

significant compaction on study sites sampled 14 to 23 years after harvest in the

Blue Mountains of Oregon. Although average bulk densities did not vary greatly

between harvested and undisturbed area for mostsites, 0.67 Mg/m3 on undisturbed

versus 0.71 Mg/m3 on harvested, there was a much wider range of bulk densities

in the disturbed areasindicating areas ofsignificant compaction and areas of likely

displacement. In the most disturbed unit, average bulk density was 0.66 Mg/m3

on the undisturbed area and 0.80 Mg/m3 on the harvested area, but the range of

observed bulk densities on the disturbed sites was even wider.

Davis(1992) observed difference in bulk densities on disturbed and undisturbed

areas in an ash-cap soil with sandy loam texture. He found the average bulk

density of disturbed volcanic ash soils to be 35% higher than the undisturbed,

0.73 g/cm3 versus 0.98 g/cm3. He conducted standard and light Proctor tests on

the soil and determined a maximum bulk density with the standard Proctor test

of 1.07 g/cm3 at a moisture content of about 35%. He also found a relatively flat

curve across a range of moisture contents for lighter Proctor tests.

Another study conducted in the Blue Mountains of Oregon (Snider and Miller

1985) illustrates the impact of soil moisture content on operational results. They

established a statistical split-plot design to look at soil characteristics on skid trails,

on berms of trails, in obvious fire rings where slash had been piled and burned,

in areas with some general disturbance, and in undisturbed areas five years after

the last harvest/site preparation activity. Bulk densities in the control area averaged 0.68 Mg/m3 at the 3.2 cm depth, 0.89 Mg/m3 at the 10.8 cm depth and

0.92 Mg/m3 at the 18.4 cm depth. Generally there were no significant differences

in bulk densities at any depth among the four variations and the control. The

authors suggest that the reduced level of compaction may have been a function

of dry soil conditions during the period of operations.

An experiment on the Colville National Forest in northeastern Washington involved analysis of harvesting economics and soil impacts for a number variations

in harvesting systems and trail spacing for harvesting equipment on both steep and

gentle slopes. The steep slope units involved use of a cable yarding system coupled

with mechanized harvesting equipment. One unit allowed downhill forwardingwith

a ground-basedcut-to-lengthforwarder.Gentle slopeunitsweredesignedwithvariations in the designated trail spacing with some allowance for the felling machine to

travel off trail in some units (Johnson 1999; Keatley 2000; Johnson 2002).

Soil analysis involved bulk density and penetrometer measurements before and

after harvest operations (Landsberg and others 2003). Study conclusions suggest
78 USDA Forest Service Proceedings RMRS-P-44. 2007

Johnson, Page-Dumroese and Han Effects of Machine Traffic on the Physical Properties of Ash-Cap Soils

that compaction resulting from an earlier fire-salvage harvesting operation has

remained for at least 70 years. Conclusions note that compaction was not as

great on steep terrain where the cable based systems were used, but also note

that the soils were sandier in that area and were likely to be more resistant to

changes in soil strength. Changes in soil strength, as measured with a recording

penetrometer, showed an average of 127% increase in resistance to penetration

in the surface layer (0 to 10 cm) and an 89% increase in resistance to penetration

at depths of 15 to 25 cm on skid trails in the ground based units. This contrasts

to changes of –3% for the surface layer and 43% at depths of 15 to 25 cm in the

steeper units. Differences on and off skid trails at the 0 to 10 cm depth averaged

63% in the ground based units and 10% in the steep slopes. Differences at the

15-25 cm depth averaged 26% for both units. There were significant differences

between the types of harvesting system, however. For example, the differences

between on and off trail resistance to penetration for the cut-to-length system

was 15% at the 0 - 10 cm depth and 3% at the 15 - 25 cm depth. Soil conditions

after harvesting that remained within limits of the specified guidelines, but results

also reflected difficulties associated with interpretation of penetrometer results

when readings are taken over a full field season that includes significant changes

in soil moisture content (Landsberg and others 2003).

In one study, ash-cap soils in northern Idaho were shown to reach their maximum bulk density after 4 trips with a rubber-tired skidder. Subsequent trips did

not result in further increases in bulk density. However, pore-size distribution

continued to change after 4 or more trips (Lenhard 1986). Although bulk density

does not appear to change after several passes, other physical properties may

continue to change to the detriment of soil productivity. If soil pore-size distribution continues to change, then plant-water relationships are likely to be altered

or soil puddling will occur for longer periods of time.

The resultsreported on dry soilsin northern Idaho by Froese (2004) were similar

to those reported in northeastern Oregon (Snider and Miller 1985). Froese’ thesis

work involved study of a cut-to-length system operating on ash cap soils. Bulk

densities in the control averaged 0.95 Mg/m3 at the 10 cm depth, 1.10 Mg/m3 at

the 20 cm depth and 1.21 Mg/m3 at the 30 cm depth. These values are higher

than typical bulk densities for ash-cap soils with minimal disturbance and may

have contributed to the lack of change after operations. They are also typical of

bulk densities measured on skid trails after machine operations as illustrated in

the case study for Western Montana (Cullen and others 1991). There was virtually

no change in bulk density after the passage of the harvester and one pass of the

forwarder. Some increase in bulk density was detected at the surface layer with

increased numbers of forwarder passes. Operations were also conducted in late

summer when soils were quite dry.

Cullen and others (1991) reported changes in bulk density as a result of traffic

at three soil depths on soils in Western Montana. Bulk density in the surface

layer of ash over a limestone till at 5 cm changed from 0.61 Mg/m3 with no traffic to 0.84 Mg/m3 with moderate traffic and to 0.97 Mg/m3 with severe traffic.

The changes at 15 cm were also significant, changing from 0.53 Mg/m3 in the

undisturbed case to 0.97 Mg/m3 and 0.93 Mg/m3 for moderate and severe traffic

respectively. In their conclusions they note that the volcanic surface horizon

overlying the glacial till soils was well-graded, cohesionless, and was prone to

vibratory compaction.
USDA Forest Service Proceedings RMRS-P-44. 2007 79

Effects of Machine Traffic on the Physical Properties of Ash-Cap Soils Johnson, Page-Dumroese and Han

Controlling Compaction __________________________________________

Methods of limiting compaction impacts on soils generally involve control of

the traffic patterns of equipment, restriction of vehicles to designated trails and

areas, and control over the seasons of operation. Since topography plays a major

role in the redistribution of water on a site, depressions in the landscape may have

higher moisture content and be more prone to compaction damage than areas

higher on the landscape. Designated trails can avoid these sites when needed.

The use of low ground pressure machines and covering of trails with slash mats

such as those generated with cut-to-length systems can limit the consequences of

one or two passes of equipment, but do not appear to be effective in minimizing

soil compaction when equipment must use trails multiple times(Froese 2004; Han

2005). In several studies of mechanized equipment, one pass of the harvesting

machine did not appear to significantly change bulk density in the soils (Froese

2004; Han 2005). Subsequent passes of the skidding or forwarding equipment

did increase soil bulk densities, but compaction was limited to the percent of the

area in major trails or just in the ruts of well defined forwarder trails.

Increasing spacing between operational trails can decrease the overall impact

on an area, but can also have negative economic consequences because of the

increased cost of moving cut logs and trees increased distances to the operational

trails(Johnson 2002). Careful operational planning can mitigate some of the higher

costs associated with increased trail spacing, however. It may also be possible to

allow the felling equipment to operate in a limited fashion off established trails

and to bunch harvested material to the trail for processing and/or forwarding.

Limiting operations during periods of high soil moisture content will also limit

soil impacts. This generally will translate into seasonal restrictions on equipment,

with most operations taking place in late summer and early fall. Dry soils (<15%

soil moisture content) can effectively support higher ground pressures and result

in more limited soil compaction to the surface mineral soil (>10 cm) (Han 2005).

Winter operations may be possible with minimal soil impact if the ground is

frozen to depths of 10 to 15 cm (Flatten 2002) or has sufficient snow cover (at

least 15 cm).

Another option for minimizing soil compaction, but which can also have

significant economic consequences is to shift from ground-based harvesting to

cable or helicopter harvesting systems. Both of these options can be structured

to have minimal soil impacts, but will generally incur higher costs than groundbased systems.

Summary and Suggested Areas of Future Research ________________

Ash-cap soils are derived from a variety of volcanic eruptions and are most often

classified in the silt or sandy loam categories. They are also characterized with

low bulk density, high porosity, and high water holding capacity. They tend to be

non-cohesive and because of their relatively low strength, are highly susceptible

to both vibratory and compressive compaction. Compaction is generally viewed

in a negative context with respect to long-term site productivity and sustainable

forest management. The results of several studies in the intermountain west illustrate that both bulk density and soil strength values were significantly increased

during ground-based harvest operations, but that the resulting bulk densities of

compacted ash-cap soils are often below the initial bulk densities of other soil
80 USDA Forest Service Proceedings RMRS-P-44. 2007

Johnson, Page-Dumroese and Han Effects of Machine Traffic on the Physical Properties of Ash-Cap Soils

textures. The long-term effects of the changes in factors on site productivity still

need to be studied through controlled experiments.

Since ash-cap soils have relatively low bulk densities before operations, they

may experience a very high percent change in soil strength and bulk density. In

setting standards, it is not clear whether the focus should be on the final bulk

density or soil strength reading, the absolute amount of change, or the percent

change. If soil strength, as measured by the penetrometer, is recommended as a

standard method for soil measurement, corresponding threshold levels of percent

and absolute change will need to be established.

The process of soil compaction can be explained by engineering properties

of soils, but the degree of soil compaction created in field settings is highly influenced by a variety of factors including distribution of particle sizes, presence

of organic matter, soil moisture content, and soil texture. Bulk density and soil

strength are commonly used to measure the degree of soil compaction, but the

statistical correlations between two variables can be very low when soil strength

is not measured near field capacity of the soil. The relationships between bulk

density and soil strength and the other critical soil factors such as water holding

capacity is less clear, however. Additional work is also needed to determine the

effect of the depth of the ash-cap on soil response to machine traffic.

Although ash-cap soils are susceptible to both vibratory and compression

forces, the specific vibratory and compressive force potential of the equipment

operating in various harvesting and site preparation functions (cutting, transporting) is not known. Research on the vibratory effects of equipment and whether

changes in machine design could reduce this effect would be very useful to forest

management strategies.

Several studies also found that changes in bulk density and soil strength in

ash-cap are long term (>70 years) and that recovery time for ash-cap soils is expected to be slow. These studies noted that soil compaction was generally limited

to skid trails and top soil layers (<30 cm). Harvesting equipment used, season of

operation and harvest planning were major factors in affecting soil compaction.

Controlling compaction often involves use of low impact equipment selection,

use of designated skid trails, and limitation of operations to dry seasons or when

the ground is frozen. The use of low ground pressure machines and covering trails

with slash in a cut-to-length logging may help reduce impacts on soils, especially

soil displacement.

References______________________________________________________

Alexander, E.; Poff, R. 1985. Soil disturbance and compaction in wildland management. U.S.

Department of Agriculture, Forest Service, Pacific Southwest Region, Earth Resources Monograph B. 158 p.

Alderfer, R. B.; Merkle, F. G. 1941. Structural stability and permeability of native forest soils compared with cultivated areas of the same soil type. Soil Sci Soc Am Proc. 6: 98-103.

Allbrook, R. F. 1986. Effect of skid trail compaction on a volcanic soil in central Oregon. Soil Sci.

Soc. Am. J. 50: 1344-1346.

Bennie, A. T. P.; Burger, R. D. T. 1988. Penetration resistance of fine sandy apedal soils as affected

by relative bulk density, water content and texture. S. Afr. J. Plant Soil 5: 5-10.

Blake, G. R.; Hartge, K. H. 1986. Bulk Density. In: Klute, A., ed. Methods of soil analysis. Part 1.

Agronomy Mongr. 9. Madison, WI: ASA: 363-375.

Block, R.; K.; VanRees, C. J.; Pennock, D. J. 2002. Quantifying harvesting impacts using soil compaction and disturbance regimes at a landscape scale. Soil Sci. Soc. Am. J. 66: 1669-1676.
USDA Forest Service Proceedings RMRS-P-44. 2007 81

Effects of Machine Traffic on the Physical Properties of Ash-Cap Soils Johnson, Page-Dumroese and Han

Brown, K. W. 1977. Shrinking and swelling of clay, clay strength, and other properties of clay soils

and clays. In: Minerals in soil environments. Soil Sci. Soc. of Am. 948 p.

Busscher, W. J.; Bauer, P. J.; Camp, C. R.; Sojka, R. E. 1997. Correction of cone index for soil water

content differences in a coastal plain soil. Soil Tillage Res. 43: 205-217.

Cullen, S.; Montagne, C. 1981. Final Report to the United States Forest Service (Region 1) — Soil

Compaction Study. Unpublished report on file at: U.S. Department of Agriculture, Forest

Service. 243 p.

Cullen, S. J; Montagne, C.; Ferguson, H. 1991. Timber harvest trafficking and soil compaction in

western Montana. Soil Sci. Soc. Am. J. 55: 1416-1421.

Davis, S. 1992. Bulk density changes in two central Oregon soils following tractor logging and

slash piling. Western Journal of Applied Forestry. 7(3): 86-88.

Felt, E. J. 1965. Compactibility. In: Black, C. A. and others, eds. Methods of soil analysis. Part 1.

Agronomy. Madison, WI: Am. Soc. of Agron. 9: 400-412.

Flatten, B. 2002. Determining appropriate winter logging conditions for protection of the soil

resource. Presented to SALHI-W (Sale Area Layout & Harvesting Institute - West) Ground-based

Systems Session; 2002 June; Moscow, ID. 14 p.

Flint, A. L.; Childs, S. 1984. Development and calibration of an irregular hole bulk density sampler.

Soil Sci. Soc. Am. J. 48: 374-378.

Free, G. R.; John, Lamb, J. Jr.; Carleton, E. A. 1947. Compactibility of certain soils as related to

organic matter and erosion. J. Am. Soc. of Agron. 39:1068-1076.

Froehlich, Henry A. 1979. Soil compaction from logging equipment: effects on growth of young

ponderosa pine. Journal of Soil and Water Conservation. 34: 276-278.

Froehlich, H. A.; Azevedo, J.; Cafferata, P.; Lysne, D. 1980. Predicting soil compaction on forested

land. Final Project Report. Missoula, MT: U.S. Department of Agriculture, Forest Service. Equipment Development Center. 120 p.

Froehlich, H. A.; Miles, D. W.; Robbins, R. W. 1985. Soil bulk density recovery on compacted

skid trails in central Idaho. Soil Sci Soc Am J. 49: 1015-1017.

Froese, K. 2004. Bulk density, soil strength, and soil disturbance impacts from a cut-to-length

harvest operation in north central Idaho. Unpublished: Moscow, ID: University of Idaho. 72 p.

M.S. Thesis.

Geist, J. M.; Hazard, J. W.; Seidel, K. W. 1989. Assessing physical conditions of some pacific

northwest volcanic ash soils after forest harvest. Soil Sci. Soc. Am. J. 53: 946-950.

Gupta, S. C.; Allmaras, R. R. 1987. Models to assess the susceptibility of soils to excessive compaction. Adv. Soil Sci. New York: Springer-Verlag.

Håkansson, I.; Lipiec, J. 2000. A review of the usefulness of relative bulk density values in studies

of soil structure and compaction. Soil & Tillage Research. 53: 71-85.

Han, H.-S. 2005. Compaction of forest soils. Presented at: 22nd Inland Empire Forest Engineering

Conference; 2005 March 8-9; Moscow, ID.

Ingersoll-Rand. 1975. Compaction data handbook. Ingersoll-Rand Co. Shippensburg, PA. 68 p.

Johnson, L. R. 1999. Combining cut-to-length and cable yarding systems. In: Proceedings of the

International Mountain Logging and 10th Pacific Northwest Skyline Symposium; 1999 March;

Corvallis, OR: Oregon State University: 43-52.

Johnson, L. R. 2002. Adapting conventional harvesting equipment to small diameter stands – the

Fritz experiments. Unpublished report on file at: College of Natural Resources, University of

Idaho, Moscow, ID. 16 p.

Keatly, T. A. 2000. Harvesting options in small diameter stands operating on gentle slopes. Moscow, ID: University of Idaho. 199 p. M.S. Thesis.

Kohl, K. D. 1988. Mechanics of rill headcutting. Ames, IA: Iowa State University. PhD. Dissertation.

Krynine, D. P. 1951. Some comments on earth compaction. National Resource Council Highway

Research Board Bulletin. 42: 14-20.

Landsberg, J. D.; Miller, R. E.; Anderson, H. W.; Tepp, J. S. 2003. Bulk density and soil resistance

to penetration as affected by commercial thinning in northeastern Washington. Research Paper

PNW-RP-551. Portland, OR: U.S. Department of Agriculture, Forest Service, Pacific Northwest

Research Station. 35 p.

Lenhard, R. J. 1986. Changes in void distribution and volume during compaction of a forest soil.

Soil Sci. Soc. Am J. 50: 462-464.

Li, C. Y. 1956. Basic concepts on the compaction of soil. Proceedings of the American Society of

Civil Engineers, Journal of Soil Mechanics and Foundations Division. Paper 862. 82: 1-20.
82 USDA Forest Service Proceedings RMRS-P-44. 2007

Johnson, Page-Dumroese and Han Effects of Machine Traffic on the Physical Properties of Ash-Cap Soils

Lull, H. W. 1959. Soil compaction on forest and range lands. Misc Pub No 768. U.S. Department

of Agriculture. 33 p.

McNabb, D. H.; Cromack, K. Jr.; Fredricksen, R. L. 1986. Variability of nitrogen and carbon in

surface soils of six forest types in the Oregon Cascades. Soil Sci. Soc. Am. J. 50: 1037-1041.

Means, R. E.; Parcher, J. V. 1963. Physical properties of soils. Columbus, Ohio: Charles E. Merrill

Books, Inc. 464 p.

Miller, R. E.; Colbert, S. R.; Morris, L. A. 2004. Effects of heavy equipment on physical properties of soils and on long-term productivity: a review of literature and current research. NCASI

Technical Bulletin 887. National Council for Air and Stream Improvement.

Mirreh, H. F.; Ketcheson, J. W. 1972. Influence of bulk density and matric pressure on soil resistance to penetration. Can. J. Soil Sci. 52: 477-483.

Page-Dumroese, D. S. 1993. Susceptibility of volcanic ash-influenced soil in Northern Idaho to

mechanical compaction. Research Note INT-409. Ogden, UT: U.S. Department of Agriculture,

Forest Service, Intermountain Research Station. 5 p.

Page-Dumroese, D. S.; Jurgensen, M. F.; Brown, R. E.; Mroz, G. D. 1999. Comparison of methods

for determining bulk densities of rocky forest soils. Soil Sci. Soc. Am. J. 63: 379-383.

Powers, R. F.; Tiarks, A. E.; Boyle, J. R. 1998. Assessing soil quality: Practicable standards for sustainable forest productivity in the United States. In: Davidson, E. A.; Adams, M. B.; Ramakrishna,

K., eds. The contribution of soil science to the development of and implementation of criteria

and indicators of sustainable forest management. Madison, WI: SSSA Spec. Publ. 53: 53-80.

Powers, R. F.; Sanchez, F. G.; Scott, D. A.; Page-Dumroese, D. 2004. The North American LongTerm Soil Productivity Experiment: coast-to-coast findings from the first decade. RMRS-P-34.

U.S. Department of Agriculture, Forest Service, Rocky Mountain Research Station. 191-206.

Smith, C. W.; Johnston, M. A.; Lorentz, S. 1997. Assessing the compaction susceptibility of South

African forest soils. I. The effect of soil type, water content, and applied pressure on uniaxial

compaction. Soil Tillage Res. 41: 53-73.

Snider, M. D.; Miller, R. F. 1985. Effects of tractor logging on soils and vegetation in eastern Oregon. Soil Sci. Soc. Am. J. 49: 1280-1282.

Vaz, C. M. P.; Bassoi, L. H.; Hopmans, J. W. 2001. Contribution of water content and bulk density

to field soil penetration resistance as measured by a combined cone penetrometer-TDR probe.

Soil & Tillage. 60: 35-42.

Williamson, J. R.; Neilsen, W. A. 2000. The influence of forest site on rate and extent of soil

compaction and profile disturbance of skid trails during ground-based harvesting. Can. J. For.

Res. 30: 1196-1205.
USDA Forest Service Proceedings RMRS-P-44. 2007 83

In: Page-Dumroese, Deborah; Miller, Richard; Mital, Jim; McDaniel, Paul; Miller, Dan, tech. eds. 2007. 

Volcanic-Ash-­Derived Forest Soils of the Inland Northwest: Properties and Implications for Management 

and Restoration. 9-10 November 2005; Coeur d’Alene, ID. Proceedings RMRS-P-44; Fort Collins, CO: 

U.S. Department of Agriculture, Forest Service, Rocky Mountain Research Station.

P. R. Robichaud, U.S. Department of Agriculture, Forest Service, Rocky Mountain Research Station, 

Moscow, ID. F. B. Pierson, U.S. Department of Agriculture, Agricultural Research Service, Northwest 

Watershed Research Center, Boise, ID, . R. E. Brown, U.S. Department of Agriculture, Forest Service, 

Rocky Mountain Research Station, Moscow, ID. 

Abstract

	 After prescribed burns at three locations and one wildfire, rainfall simulations studies were completed

to compare postfire runoff rates and sediment yields on ash-cap soil in conifer forest regions of northern

Idaho and western Montana. The measured fire effects were differentiated by burn severity (unburned,

low, moderate, and high).

	 Results indicate that this dry, undisturbed ash-cap soil exhibits high runoff rates and is naturally water

repellent at the surface. However, the unburned, undisturbed ash-cap soil is not highly erodible due

the protective duff layer on the surface. When ash-cap soil was exposed to prolonged soil heating (high

severity burn), surface water repellency was destroyed and a strong water repellent layer occurred a

few centimeters beneath the soil surface. With the simulated rainfall, the non-water repellent surface

layer became saturated; thus making the soil above the water repellent layer highly erodible—especially

during high intensity rainfall. 

Keywords: water repellent soils, rainfall simulation, burn severity, runoff, erosion.

Runoff and Erosion Effects after Prescribed 

Fire and Wildfire on Volcanic Ash-Cap Soils

P. R. Robichaud, F. B. Pierson, and R. E. Brown

Introduction

	 Fire is a natural and an important part of disturbance regime for forest ecosystems and many

landscapes are well-adapted to this natural fire cycle. Wildfire suppression has dominated

forest management for the past century and has interfered with these natural fire regimes

causing unnatural accumulations of forest fuels. Although managed forests burn lessfrequently

than the unmanaged forests, the wildfires that do occur are larger and more severe than in

the past, causing more severe and long-lasting effects. Fire effects on forest soil may include

fire-induced soil water repellency, reduced infiltration rates, increased overland flow, and

increased peak flow, which often result in increased water and sediment yields.
84 USDA Forest Service Proceedings RMRS-P-44. 2007

Robichaud, Pierson, and Brown Runoff and Erosion Effects after Prescribed Fire and Wildfire on Volcanic Ash-Cap Soils

Burn Severity

Burn severity, a qualitative measure of the effects of fire on site resources, is a

useful concept for comparing fires (Hartford and Frandsen 1992; Ryan and Noste

1983). A range of fire and postfire conditions, such as fire intensity, fire duration,

crown consumption, soil color, and proportion of litter remaining, are typically

used to classify burned areas into discrete classes of high, moderate, or low burn

severity. Although some aspects of burn severity can be quantified, no single

number can be determined to measure ‘resource impact’.

The component of burn severity that results in the most damage to soils is fire

duration, because duration generally determines the temperature and depth of

soil heating. Ryan and Noste (1983) created a burn severity classification system

(expanded by Jain (2004)) that estimates the amount of soil heating that likely occurred during the fire based on postfire litter amounts and mineral soil coloration.

Because it is specific to soil, the Ryan and Noste (1983) definition of burn severity

was used to evaluate burn severity at research sites discussed in this paper.

Water Repellency

Naturally occurring water repellent soils occur in every continent and have

different infiltration properties than wettable soils (Letey 2005). Fire creates or

enhances water repellency in soils (Doerr and others 2000). As surface vegetation

is burned and the soil is heated, organic matter in and on the soil is volatilized,

and a significant fraction of these vaporized organic compounds move from the

surface into the soil profile (DeBano and others 1976). These aliphatic hydrocarbon vapors condense on soil particles in the cooler layers beneath the surface

to form a water repellent layer. This water repellent layer is generally within the

top 5 cm of the soil profile, non-continuous, and roughly parallel to the surface

(Clothier and others 2000; DeBano 2000). In general, coarse soils (low clay content) are more susceptible to becoming water repellent than finer soils (high clay

content) due to the lower specific surface area of coarse soil particles. However,

when water repellency is established in fine-grained soils, it can be equally or

more severe than in a coarse-textured soil (Doerr and others 2000; Robichaud

and Hungerford 2000).

Fire-induced soilwaterrepellency has high temporal and spatial variability (Letey

2005). The degree and depth of postfire water repellency is related to soil heating

during the fire, which, because of its dependence on antecedent soil moisture,

forest floor thickness, burn duration, postfire smoldering, etc., is highly variable.

Fire-induced soil water repellency has been found to vary both in the horizontal

and the vertical directions at the 1 cm scale (Hallett and others 2004; Gerke and

others 2001). Fire-induced water repellency is most often detected at 1 to 3 cm

below the surface (Huffmann and others 2001). In addition, soil water repellency

is transient and is related to soil moisture. Generally, both natural and fire-induced

soil water repellency is lost during long wet periods and is re-established upon

drying, causing short-term or seasonal variations (Robichaud and Hungerford

2000). Fire-induced soil water repellency is temporary because the hydrophobic

substances responsible for water repellency are slightly water-soluble and slowly

dissolve such that water repellent soil conditions are broken up or washed away

within several years after the fire.
USDA Forest Service Proceedings RMRS-P-44. 2007 85

Runoff and Erosion Effects after Prescribed Fire and Wildfire on Volcanic Ash-Cap Soils Robichaud, Pierson, and Brown

Infiltration

In water repellent soils, water may move through a wettable surface layer, and

upon reaching a water repellent layer, flow laterally below the surface (DeBano

1981). Given the spatial variability of water repellency, water may flow preferentially, via columns, or ‘fingers,’ through the less water repellent areas forming

an uneven wetting front (Ritsema and Dekker 1994, 1995). Infiltration on water

repellent soils is also dependent on the type and distribution of plants over the

surface (Shakesby and others 2000). Some plants, such as chaparral, decrease

infiltration by adding hydrophobic compoundsto the soil directly underthe canopy

(DeBano 1981). Conversely, infiltration can be enhanced by root channels and

macropores (remaining after roots decay or burn) that can act as pathways for

infiltrating water through water repellent layers (Meeuwig 1971; Sevink and others

1989; Burch and others 1989; Shakesby and others 2000).

Overland Flow and Erosion

Overland flow and soil erosion rates are dependent on a range of inter-related

factors that include rainfall (e.g., amount, intensity, duration), soil (e.g., erodibility,

particle size, pore size, bulk density, water repellency), topography (e.g., slope,

aspect), and biotic (e.g., vegetation, ground cover, animal use, natural and human

disturbances). Because of the reduction in infiltration capacity in water repellent soils, postfire increases in overland flow and erosion are often attributed to

fire-induced water repellency (Doerr and others 2000). However, it is difficult to

determine the proportion of postfire increased erosion that can be attributed to

soil water repellency. Fire can also increase the erodibility of soil through reduction of protective ground cover and soil organic matter, sealing of soil pores, loss

of water storage capacity in the litter and duff, loss of soil moisture, break down

soil aggregates, and reduction of soil particle size (DeBano and others 1998).

Thus, the contribution of soil water repellency on total postfire erosion is often

difficult to separate from other fire impacts.

Caution must be used when extrapolating measurements of overland flow from

small plots to determine the potential runoff on the hillslope- or catchment-scale

where differential flow patterns may have significantly more effect (Shakesby and

others 2000; Imeson and others 1992). After a Eucalyptus forest fire in Australia,

Prosser and Williams (1998) found that small plots produced greater runoff and

sediment transfer than was observed at the hillslope catchment outlet. The lack of

spatial contiguity in soil water repellency and the existence of differential infiltration flow patterns may create scattered ‘sink’ areas across a hillside where water

infiltrates and, as a result, does not reach the base of a catchment as overland

flow (Imeson and others 1992; Prosser and Williams 1998).

Study Objectives

Small plot rain simulation data from three prescribed burns (northern Idaho)

and one wildfire (western Montana) are used to compare fire effects on runoff

and erosion of ash-cap soils. The two studies (prescribed fire study and the wildfire study) had common site characteristics (conifer forested environments and

ash-cap soil types) and test procedures (rainfall simulation), which facilitated
86 USDA Forest Service Proceedings RMRS-P-44. 2007

Robichaud, Pierson, and Brown Runoff and Erosion Effects after Prescribed Fire and Wildfire on Volcanic Ash-Cap Soils

the comparison of first year postfire data from the four fires to: 1) examine fireinduced and natural ash-cap soil water repellency; 2) compare runoff rates; and

3) compare sediment concentrations and sediment yields.

Methods _______________________________________________________

Prescribed Fire

Site Description—The prescribed fire study was conducted in the Fernan

Ranger District, Idaho Panhandle National Forest in the Coeur d’Alene Mountains

(48°15’ N, 116°15’ W). Study plots were located between 950 to 1500 m elevation on 14 to 46 percent slopes. The predominant soil type is Typic Vitrandepts,

a silt loam derived from volcanic ash-influenced loess 28 to 45 cm thick, over an

Eutirc Glossoboralfs, a mixed loamy-skeletal formed from Precambrian Belt rock.

Average annual precipitation is 34 inches with about one third of that falling as

snow in the winter months (Abramovich and others 1998). Vegetation of the area

istypical of the western hemlock/queencup beadlily (Tsuga heterophylla/Clintonia 

uniflora) habitat type (Cooper and others 1991).

Ignition of the first harvested unit was in the spring on April 25 (Bumble Bee).

Ignition of the second burn occurred in the fall two years later on September 30

(Buckskin I). The third harvest unit was ignited in the summer on August 25

(Buckskin II). For each of the three prescribed burns, a helitorch-ignited strip

headfire was started at the top of the slope with fire strips placed about every

30-40 m down the slope. Ignition was generally very rapid, and the entire unit

ignited within 30 min.

Plots—Before each prescribed fire, six paired 1-m2 plots were systematically

selected in the study areasto represent the average fuel condition and average slope,

with one plot designated for rainfall simulation and the other for soil temperature

measurements. Four steel pins were installed flush with the forest floor surface in

each plot to estimate forest floor consumption. In the temperature-measurement

plots, these forest floor pins were located near thermocouples. Temperatures

during the fire were recorded with eight chromel-alumel thermocouples located

at the litter surface, in the humus, at the humus-mineral soil interface, and in the

mineral soil at 1, 2, 4, 8, and 10 cm below the interface. Temperatures during

the burn were first recorded when the surface temperature reached 80 °C and

continued every minute thereafter for 36 h. Immediately before burning, samples

of the woody fuels, forest floor, and mineral soil were collected to determine

moisture content.

On each of the rainfall simulation plots, a four-sided sheet metal frame was

installed. Three frame sides were 15 cm tall and installed with 5 cm inserted into

the mineral soil, and the fourth, downslope side of the frame was 5 cm tall and

inserted fully into the soil (no extension above the surface of the soil) allowing

runoff and sediment to leave the plot.

Rain Simulation—Within days of the prescribed fire, a 30-min rain simulation was conducted at the existing soil moisture condition as determined from a

composite soil sample was taken near the edge of the plot frame. The simulated

rainfall was applied to each plot using a USDA-Forest Service modified Purduetype oscillating nozzle rainfallsimulator with specifications as described by Meyer
USDA Forest Service Proceedings RMRS-P-44. 2007 87

Runoff and Erosion Effects after Prescribed Fire and Wildfire on Volcanic Ash-Cap Soils Robichaud, Pierson, and Brown

and Harmon (1979). The rainfall simulator produced an average rainfall intensity of

38 mm h–1 for the Bumble Bee (spring 92) burn site. After the Bumble Bee simulations, the simulated rainfall intensity was increased to ensure that the rainfall rate

exceeded the infiltration capacity of the soil. Rainfall intensity was 100 mm h–1

for the Buckskin I (autumn 94) and Buckskin II (summer 95) burn sites. Seven rain

gauges located around the 1 m2 plots verified the rainfall amount.

A covered trough at the lower end of each plot conducted runoff (water and

sediment) through a pipe fittedwith a valve that allowed fortimed volume sampling.

The samples were manually collected in 1000 ml bottles at 1-min intervals. At the

end of the simulation run, any sediment remaining in the trough was washed into

a sample bottle. All runoff samples were weighed and oven-dried to determine

runoff rates and sediment concentrations.

Wildfire Study

Site Description—The wildfire study was conducted in the Bitterroot National Forest (46°4’ N, 114°0’ W) of western Montana where, in the summer of

2000, lightning strikes ignited the Bitterroot Complex Fires. These fires burned

101,000 ha—40 percent at high burn severity as determined by postfire appearance (USDA 2000). The predominant soil is derived from volcanic ash over highly

weathered granite and is classified as a sandy skeletal Andic-Dystrocryept. The

mean elevation is approximately 1,950 meters with slopes ranging from 25 to

55 percent and dominantly west-southwestern aspects. Vegetation of the area is

typical of the subalpine fir/menziesii (Abies lasiocarpa/Menziesia ferruginea h.t.)

forest habitat type.

Plots—Within an area of high burn severity, four study sites were selected

based on comparable slope, aspect, and ground cover characteristics. On each

of the four sites, 15 plots of 0.5 m2 were randomly located and delineated by a

four-sided sheet metal frame as previously described. Approximately 3 km north

of the burned study area, three unburned sites were selected such that the slope,

aspect, and soil type were comparable to the burned area sites and, in addition,

the vegetative characteristics were comparable among the unburned study sites.

In each of the three unburned sites, 7 plots of 0.5 m2 were randomly located and

defined by the installation of sheet metal plot frames as described above.

Directly adjacent to each plot frame, water repellency was measured using the

water drop penetration time (WDPT) adapted from DeBano (1981). Eight water

drops were placed on an exposed surface of the mineral soil and the time to

infiltrate into the soil is observed. The degree of water repellency is determined

by the length of time the water drop sits on the soil without being absorbed: 0

to 5 sec = none; 6 to 60 sec = slight; 61 to 180 sec = moderate; 181 to 300 or

more = severe. The maximum observation time was limited to 5 minutes. If the

water drops infiltrated in less than 5 seconds, the test was repeated at 1 cm depth

below the surface. This process was repeated at 1 cm increments to a maximum

depth of 5 cm.

Near the edge of the plot frame, a composite soil sample was taken to assess

soil moisture. Ground cover within each plot was determined.

Rainfall Simulation—Within days after the fire was contained, a simulated

rainfall event with a mean rainfall intensity of 100 mm h–1 was applied to each of

the 102 plotsfor 60 min using the USDA-Forest Service and the USDA-­Agricultural
88 USDA Forest Service Proceedings RMRS-P-44. 2007

Robichaud, Pierson, and Brown Runoff and Erosion Effects after Prescribed Fire and Wildfire on Volcanic Ash-Cap Soils

Research Service oscillating-arm rainfallsimulatorswith specifications as described

by Meyer and Harmon (1979). Data from the first 30 minutes of each simulation

were used for comparisons and analysis. During the rainfall simulation, samples

of runoff and sediment were collected through a covered trough at the downslope

edge of each plot as described for the prescribed burns above. The samples were

manually collected at 1-min intervals for the first 14 min, then at 2-min intervals

for the remainder of the 60-min run. All runoff samples were weighed and ovendried to determine runoff volume for each interval, total runoff volume, sediment

concentrations.

Analytical Methods

The data from the Bumble Bee prescribed fire site were not included in the

statistical analysis because the rainfall application rate of 38 mm h–1 was much

less than 100 mm h–1 rainfall application rate applied at all other sites. The total

runoff and dry suspended sediment weight were calculated for the first 29 to 30

min of the first simulation for the Buckskin I and II sites and for the first 29 to 31

min of the year 2000 simulations at the Bitterroot sites. Runoff and suspended

sediment were normalized by area to account for the different plot sizes. Runoff

ratios are total runoff (mm) divided by total rainfall applied (mm) for each simulation; the rainfall is adjusted for the plot size.

Results and Discussion___________________________________________

Burn Severity

Varied antecedent conditions for the three prescribed burns resulted in differential soil heating and a range of fire effects on the soil. Bumble Bee, a spring

burn, had the highest pre-fire soil and duff moisture contents (61 to 69 percent

and 125 percent, respectively) and the lowest mineral soil temperatures (20 to

80 °C) and proportion of duff consumed (28 percent) during the fire (table 1).

Bumble Bee was a low burn severity fire. Buckskin I was burned in the fall with

the driest conditions of the three prescribed burns (table 1) and was classified

moderate burn severity. Buckskin II, a summer burn, had slightly higher pre-burn

fuel and soil moisture conditions than Buckskin I and was also classified moderate burn severity (table 1). The study areas within the Bitterroot Complex Fire

area were in unburned and high burn severity areas. These four fires on ash-cap

soils provided four burn severity conditions—unburned (Bitterroot), low burn

severity (Bumble Bee), moderate burn severity (Buckskin I and II), and high burn

severity (Bitterroot).

Moisture Content and Water Repellency

Soil moistures immediately prior to the rainfall simulations were higher in the

prescribed fire sitesthan the wildfire sites(table 2), but probably not high enough to

change the soil water repellency response (Robichaud and Hungerford 2000). Soil

water repellency was directly assessed in the Bitterroot study, where both burned

and unburned soils had strong water repellent responses at different depths. The

unburned soil was severely water repellent at the surface while the burned soil
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Runoff and Erosion Effects after Prescribed Fire and Wildfire on Volcanic Ash-Cap Soils Robichaud, Pierson, and Brown

Table 1—Measured conditions before, during, and after three prescribed burns in 

northern Idaho.

Pre-prescribed Burn

Fuel and soil moisture

contents and weather conditions Bumble Bee Buckskin I Buckskin II

Fine fuels (0-76 mm) (%) 20 9 10

Large fuels (77-300 mm) (%) 41 11 28

Litter (%) 64 13 11

Humus (%) 125 45 48

Soil 0-2 cm (%) 69 40 49

Soil 2-5 cm (%) 61 29 40

Ambient temperature (oC) 22 20 18

Wind speed (kph) 8-15 2-8 0-11

Relative humidity (%) 15 30 57

Prescribed Burn

Maximum soil temperatures (°C) Bumble Bee Buckskin I Buckskin II

Mineral soil surface 20-80 40-300 90-260

1 cm below min. soil surface 40-70 40-270 70-120

2 cm below min. soil surface 20-60 40-80 60-80

Post-prescribed Burn

Organic material remaining (%) Bumble Bee Buckskin I Buckskin II

Fine fuels 12 5 0

Duff 72 27 38

Table 2—Pre-rainfall simulation mean ground cover and 

gravimetric soil moisture content by location.

Gravimetric soil

Locations Ground cover water content

- - - - - - - - - - - - (%) - - - - - - - - - - -

Unburned Bitterroot 100 15

Bumble Bee 100 29

Buckskin II 98 25

Buckskin I 70 30

Burned Bitterroot 10 17

had a water repellent layer at 1 to 2 cm below the surface (fig. 1). The creation

of a fire-induced water repellent layer has been observed by other researchers

(e.g., McNabb and others 1989; Brock and DeBano 1990; Scott and Van Wyk

1990; Doerr and others 2000). However, the high burn severity fire appeared to

destroy the natural surface water repellency, and create a water repellent layer

at depth. Doerr and others (in press) observed the same affect after wildfires in

eucalyptus forests in Australia.
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Robichaud, Pierson, and Brown Runoff and Erosion Effects after Prescribed Fire and Wildfire on Volcanic Ash-Cap Soils

Runoff

The highest runoff ratio rates (fig. 2) and mean runoff amounts (33 and 32

mm) and runoff ratios (0.71 and 0.67) were measured on the high and moderate

severity burn sites—Bitterroot-burned and Buckskin I, respectively (table 3). The

unburned-Bitterroot sites and the moderate burn severity Buckskin II site had

similar runoff ratio rates (fig. 2) and mean runoff amounts (26 and 24 mm) and

runoff ratios (0.54 and 0.53) (table 3). This unexpectedly large runoff response in

the unburned-Bitterroot sites is likely due to the short time frame of the simulation and the resistance to wetting of the dry organic duff material as well as the

naturally water repellent dry surface soil. The Bumble Bee prescribed burn site

had low runoff ratio rates (fig. 2) and a low mean runoff amount (4.7 mm) and

runoff ratio (0.12) (table 3). However, these data are not directly comparable to

the other sites as the lower rainfall application rate may not have exceeded the

infiltration capacity of the soil.

Sediment Concentrations and Yields

Sediment concentrations and mean sediment yields generally increased with

increasing burn severity (fig. 3 and table 3). Sediment concentrations in the rain

simulation runoff tended to peak in the first 5 min, rapidly decrease during the

second 5 min, and slowly decrease during the remaining 20 minutes of the simulation (fig. 3). The unburned-Bitterroot sites and the Bumble Bee site (low burn

severity) had the lowest concentrations, peaking at 7 and 4 g L–1, respectively and

decreasing to less than 1 g L–1 at 30 min (fig. 3). These concentrations resulted

in mean sediment yields of 0.027 and 0.0091 kg m–2, respectively (table 3). The

lower rainfall application rate on the Bumble Bee site probably had little affect

on mean sediment yield (table 3) due to the high ground cover remaining after

Figure 1—On the Unburned- and Burned-Bitterroot wildfire sites, the portion of water

repellent soil, as measured by the Water Drop Penetration Time (WDPT) tests, are

indicated for the soil surface and 1, 2, 3, 4, and 5 cm depths. The shading/hatching

within each bar indicate the severity of the measured water repellency.
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Runoff and Erosion Effects after Prescribed Fire and Wildfire on Volcanic Ash-Cap Soils Robichaud, Pierson, and Brown

Table 3—Mean runoff, runoff ratio, and suspended sediment yield by location. Standard errors are in parentheses. Different letters within a column indicate significant differences at α=0.05. Comparative statistics do not include 

the Bumble Bee data due to the lower applied rainfall at that site.

Location Disturbance type n Runoff Runoff ratio Sediment yield

 (mm) (kg m–2)

Unburned-Bitterroot Undisturbed 21 26 (1.8) a 0.54 (0.032) a 0.027 (0.039) a

Bumble Bee Prescribed fire 4 4.7 (1.4) 0.26 (0.043) 0.0091 (0.0028)

Buckskin II Prescribed fire 6 24 (2.5) a 0.53 (0.049) a 0.26 (0.90) ab

Buckskin I Prescribed fire 6 32 (1.3) ab 0.67 (0.19) ab 0.50 (0.80) ab

Burned-Bitterroot Wildfire 60 33 (0.60) b 0.71 (0.12) b 0.85 (0.61) b

Figure 2—The runoff ratio

(runoff / rainfall) rate for

all study sites are plotted.

The Bumble Bee sites

received a lower amount

of rainfall as compared to

other sites.

Figure 3—The sediment concentration rate for all study sites

are plotted. The Bumble Bee sites received a lower amount

of and less intense rainfall as compared to other sites.
92 USDA Forest Service Proceedings RMRS-P-44. 2007

Robichaud, Pierson, and Brown Runoff and Erosion Effects after Prescribed Fire and Wildfire on Volcanic Ash-Cap Soils

the spring burn (table 2). The Buckskin I and II, both moderate burns, peaked at

47 and 36 g L–1, respectively and decreased to about 1 g L–1 at 30 min. (fig. 3),

resulting in mean sediment yields of 0.50 and 0.26 kg m–2, respectively (table

3). The high severity burned-Bitterroot sites peaked at 38 g L–1, and remained

higher than any of the other sites through out most of the 30 min simulation, and

decreased to 20 g L–1 at 30 min. (fig. 3), resulting in a 0.85 kg m–2 mean sediment

yield, an order of magnitude greater than the unburned-Bitterroot sites (table 3).

The higher sediment yields for the wildfire sites reflect the higher consumption

of organic material during a wildfire (longer fire duration and higher soil temperatures) as compared to a prescribed fire. This difference in fires is reflected

in the postfire, pre-rainfall mean ground covers, with the Burned-Bitterroot sites

having 10 percent ground cover and the Buckskin I and Buckskin II sites having

70 percent and 98 percent, respectively (table 2).

Conclusions_____________________________________________________

A strong natural soil water repellency was detected at the surface of the mineral

soil in the unburned, undisturbed ash-cap soil with low soil moisture content.

The high burn severity wildfire appeared to destroy the surface water repellency, and cause a strong water repellent layer to develop 1 to 2 cm below the

surface of the mineral soil. Soil water repellency, at the surface or slightly below

the surface, increased runoff; however, below-surface water repellency results

in a much larger sediment response than surface water repellency. When there

is fire-induced, below-surface soil water repellency, rainfall is readily absorbed

by the non-repellent surface soil (0 to 1-2 cm) which becomes saturated down

to the more resistant water repellent layer. This saturated surface layer is easily

detached and entrained within the subsequent overland flow. Additionally, fine

roots that bind the surface soil together were likely partially consumed during the

fire, making soil particles vulnerable to detachment.

Even in steep forest environments with dry conditions (i.e., severe surface

water repellency), the undisturbed, unburned site with its intact duff layer was

not highly erodible, despite high runoff rates. During the 30 min of high intensity

rainfall, the dry duff did not absorb much water and the rainfall flowed through

the duff layer and atop the water repellent mineral soil to the outlet of the plots.

Consequently, the runoff rates for the unburned-Bitterroot sites were similar to

those found on the moderate burn severity Buckskin II site. However, the sediment concentrations and sediment yields were less than the Buckskin II due to

the protective layer of duff material. The Bumble Bee low severity prescribed

fire also had minimal sediment response because of the charred, but intact, duff

remaining after the fire. The fire effects on sediment concentrations and sediment

yields increased with increasing burn severity.

Management Implications

Ash-cap soils are known as highly productive forest soils, and protecting this

soil resource is an important land management consideration. Prescribed fires

should be ignited when duff moisture content will prevent total consumption of

the protective duff layer. Ash-cap soils burned at high severity are highly erodible

and postfire rehabilitation decisionsshould take into account the potential postfire

hydrological and sediment response from potential rain events.
USDA Forest Service Proceedings RMRS-P-44. 2007 93

Runoff and Erosion Effects after Prescribed Fire and Wildfire on Volcanic Ash-Cap Soils Robichaud, Pierson, and Brown

References______________________________________________________

Abramovich, R.; Molnau, M.; Craine, K. 1998. Climates of Idaho. University of Idaho, College of

Agriculture, Moscow, ID. 216 p.

Brock, J. H.; DeBano, L. F. 1990. Wettability of an Arizona chaparral soil influenced by prescribed

burning. Gen. Tech. Rep. RMRS-191. Fort Collins, CO: U.S. Department of Agriculture, Forest

Service, Rocky Mountain Research. 206-209.

Burch, G. J.; Moore, I. D.; Burns, J. 1989. Soil hydrophobic effects on infiltration and catchment

runoff. Hydrological Processes. 3: 211-222.

Clothier, B. E.; Vogeler, I.; Magesan, G. N. 2000. The breakdown of water repellency and solute

transport through a hydrophobic soil. Journal of Hydrology. 231-232, no. 1-4, 255-264.

Cooper, S. V.; Neiman, K. E.; Steele, R.; Roberts, D. W. 1991. Forest habitat types of northern

Idaho: a second approximation. Gen. Tech. Rep. INT-GTR-236. Ogden, UT: U.S. Department

of Agriculture, Forest Service, Intermountain Research Station. 143 p.

DeBano, L. F. 2000. Fire-induced water repellency: an erosional factor in wildland environments.

In: Proceedings of Land stewardship in the 21st century: the contributions of watershed management. 2000 March 13-16; Arizona. Fort Collins, CO: U.S. Department of Agriculture, Forest

Service, Rocky Mountain Research Station: 307-310.

DeBano, L. F. 1981. Water repellent soils: a state-of-the-art. Gen. Tech. Rep. PSW-46. Berkeley,

CA: U.S. Department of Agriculture, Pacific Southwest Research Station.. 21 p.

DeBano, L. F.; Neary, D.G.; Ffolliott, P. F. 1998. Fire’s effects on ecosystems. New York: John

Wiley & Sons. 333 p.

DeBano, L. F.; Savage, S. M.; Hamilton,A. D. 1976. The transfer of heat and hydrophobic substances

during burning. Proceedings of the Soil Science Society of America. 40: 779-782.

Doerr, S. H.; Shakesby, R. A.; Blake, W. H.; Chafer, C. J.; Humphreys, G. S.; Wallbrink, P. J. [In

press]. Effects of differing wildfire severities on soil wettability and implications for hydrological

response. Journal of Hydrology.

Doerr, S. H.; Shakesby, R. A.; Walsh, R. P. D. 2000. Soil water repellency: its causes, characteristics

and hydro-geomorphological significance. Earth-Science Reviews. 15: 33-65.

Gerke, H. H.; Hangen, E.; Schaaf, W.; Huttl, R. F. 2001. Spatial variability of potential water repellency in a lignitic mine soil afforested with Pinus nigra. Geoderma. 102: 255-274.

Hallett, P. D.; Numan, N.; Douglas, J. T.; Young, I. M. 2004. Millimeter-scale spatial variability

in soil water sorptivity: scale, surface elevation, and subcritical repellency effects. Soil Science

Society of America Journal. 68: 352-358.

Hartford, R. A.; Frandsen, W. H. 1992. When it’s hot, it’s hot—or maybe it’s not (surface flaming

may not portend extensive soil heating). International Journal of Wildland Fire. 2: 139-144.

Huffmann, E. L.; MacDonald, L. H.; Stednick, J. D. 2001. Strength and persistence of fire-induced

hydrophobicity under ponderosa and lodgepole pine, Colorado Front Range. Hydrological

Processes. 15: 2877-2892.

Imeson, A. C.; Verstraten, J. M.; Van Mulligen, E. J.; Sevink, J. 1992. The effects of fire and water

repellency on infiltration and runoff under Mediterranean type forests. Catena. 19: 345-361.

Jain, T. B. 2004. Tongue-tied. Wildfire, July-August 2004: 22-26.

Letey, J. 2005. Water-repellent soils. In: Hillel, D., ed. Encyclopedia of Soils in the Environment.

Oxford: Elsevier Ltd. 301-306.

McNabb, D. H.; Gaweda, F.; Frohlich, H. A. 1989. Infiltration, water repellency, and soil moisture

content after broadcast burning in a forest site in southwest Oregon. Journal of Soil and Water

Conservation. 44(1): 87-90.

Meeuwig, R. O. 1971. Infiltration and water repellency in granitic soils. Research Paper INT-111.

Ogden, UT: U.S. Department of Agriculture, Forest Service, Intermountain Research Station.

20 p.

Meyer, L. D.; Harmon, W. C. 1979. Multiple-intensity rainfall simulator for erosion research on row

sideslopes. Transactions of the American Society of Agricultural Engineers. 22: 100-103.

Prosser, I. P.; Williams, L. 1998. The effect of wildfire on runoff and erosion in native Eucalyptus

forest. Hydrological Processes. 12: 251-265.

Ritsema, C. J.; Dekker, L. W. 1995. Distribution flow: a general process in the top layer of water

repellent soils. Water Resources Research. 31(5): 1187-1200.

Ritsema, C. J.; Dekker, L. W. 1994. How water moves in a water repellent sandy soil: 2. Dynamics

of fingered flow. Water Resources Research. 30(9): 2519-2531.
94 USDA Forest Service Proceedings RMRS-P-44. 2007

Robichaud, Pierson, and Brown Runoff and Erosion Effects after Prescribed Fire and Wildfire on Volcanic Ash-Cap Soils

Robichaud, P. R.; Hungerford, R. D. 2000. Water repellency by laboratory burning of four northern

Rocky Mountain forest soils. Journal of Hydrology. 231-232(1-4): 207-219.

Ryan, K. C.; Noste, N. V. 1983. Evaluating prescribed fires. In: Lotan, J. E.; Kilgore, B. M.; Fischer,

W. C.; Mutch, R. W., tech. coords. Proceedings of the symposium and workshop on wilderness fire. Gen. Tech. Rep. INT-182. Ogden, UT: U.S. Department of Agriculture, Forest Service,

Intermountain Research Station: 230-238.

Scott, D. F.; Van Wyk, D. B. 1990. The effects of wildfire on soil wettability and hydrological

behaviour of an afforested catchment. Journal of Hydrology. 121: 239-256.

Sevik, J.; Imeson, A. D.; Verstratun, J. M., 1989. Humus form development and hillslope runoff,

and the effects of fire and management, under Mediterranean forest in N.E. Spain. Catena. 16:

461-475.

Shakesby, R. A.; Doerr, S. H.; Walsh, R. P. D. 2000. The erosional impact of soil hydrophobicity:

current problems and future research directions. Journal of Hydrology. 231-232, 178-191.

USDA Forest Service. 2000. Valley phase I: burned area emergency rehabilitation (BAER) report

FS-2500-8—funding request. Missoula, MT: U.S. Department of Agriculture, Forest Service,

Bitterroot National Forest. 253 p.
Management Alternatives

for Ash-cap Soils

USDA Forest Service Proceedings RMRS-P-44. 2007 97

The Practice of Sustainable Soil Management

	 Sustainable soil management can be defined as ensuring the biological, chemical and physical integrity of the soil remains for future generations. Sustainability should be addressed

throughout all facets of forest management including implementation of individual harvest

or stand-tending plans, development of agency or company standards and best management

practices (BMPs), and third-party certification. Demonstration of sustainable soil management

In: Page-Dumroese, Deborah; Miller, Richard; Mital, Jim; McDaniel, Paul; Miller, Dan, tech. eds. 2007. VolcanicAsh-­Derived Forest Soils of the Inland Northwest: Properties and Implications for Management and Restoration. 9-10 

November 2005; Coeur d’Alene, ID. Proceedings RMRS-P-44; Fort Collins, CO: U.S. Department of Agriculture, Forest 

Service, Rocky Mountain Research Station.

Mike Curran, Corresponding author, Research Soil Scientist, B.C. Ministry of Forests and Range, Forest Sciences Program, Kootenay Lake Forestry Centre, Nelson B.C., Canada. (also Adjunct Professor, Agroecology, University of B.C.). 

Pat Green, Forest Ecologist, Nez Perce National Forest, Grangeville, Idaho. Doug Maynard, Research Scientist, Natural 

Resources Canada, Canadian Forest Service, Victoria BC, Canada.

Abstract

	 Sustainability protocols recognize forest soil disturbance as an important issue at national and international levels.

At regional levels continual monitoring and testing of standards, practices, and effects are necessary for successful

implementation of sustainable soil management. Volcanic ash-cap soils are affected by soil disturbance and changes

to soil properties influence ecosystem responses such as productivity and hydrologic function. Soil disturbance from

timber harvesting, reforestation, or stand tending is mainly a result of moving equipment and trees. Compaction and

organic matter removal are of primary concern. The severity and extent of disturbance depend on the harvest system,

soil and climatic conditions. Ash-cap soils can be susceptible to disturbance and schemes to predict compaction,

displacement and erosion hazards are useful for planning forest management operations. On-site effects range from

permanent loss of growing sites because of roads, to more subtle changes in soil properties that ultimately influence

site productivity. Off-site effects may include erosion and landslides. Soil disturbance during operations should be

regulated and monitored to minimize both on- and off-site effects, which can take years or decades to appear. Forest

health issues vary on volcanic ash-cap soils. An analysis of Armillaria root disease incidence across the National Forests of the Inland Northwest indicates some potential relationships among root disease, and soil and site factors. The

strong relations between presence of susceptible host and development of fungal biomass may be the strongest causal

agent, with the soil and site factors supporting the presence of the pathogen and susceptible host. Thicker ash soils

of more northerly areas are related to habitat types that historically supported white pine and a higher diversity of less

susceptible species. After root disease mortality occurs, these more mesic environments also fill in with other species

rapidly, so higher levels of root disease are more difficult to discern. Recommendations are made for soil management

and about information needs for soil disturbance and root disease relations.

Key words: volcanic ash-cap soils, forest health, Armillaria, root disease, criteria and indicators, organic matter depletion, soil disturbance, soil compaction, sustainability protocols

Volcanic Ash Soils: Sustainable Soil 

Management Practices, With Examples of 

Harvest Effects and Root Disease Trends

Mike Curran, Pat Green and Doug Maynard
98 USDA Forest Service Proceedings RMRS-P-44. 2007

is promoted through reporting procedures required by applicable sustainability

protocols,and by having third-party certification of forest practices and products

(Curran and others 2005a).

Sustainability protocols exist at international and national levels. At the international level, the Montreal Process (MP) includes a Working Group on Criteria

and Indicators for the Conservation and Sustainable Management of Temperate

and Boreal Forests (Montreal Process Working Group 1997). Some countries

have developed their own protocols and procedures designed to track and report

progress toward meeting requirements of international protocols such as the MP.

For example, the Canadian Council of Forest Ministers recently developed revised

criteria and indicators for sustainable forest management (CCFM 2003).

Third-party (eco)certification of forest practices and resulting wood products

arose in response to sustainability protocols and the greening of the global marketplace. Organizations such as Sustainable Forestry Initiative (American Forest and

Paper Association), Canadian Standards Association, Forest Stewardship Council

(FSC), and ISO 1400.1 all have documented review processes and procedures for

certification. Protecting streams and natural drainage patterns, maintaining slope

stability, and regulating soil disturbance are common elements considered. In

addition, most require some adaptive management process to ensure continuous

improvement of practices on the ground.Compliance with currentsoil disturbance

standards is often used as a proxy for ensuring sustainability; however, a common

approach to standards, and validation of the standards through research are important steps that must not be overlooked when these are used as proxies. Some

certification schemes also call for more restrictive standards (e.g., FSC in British

Columbia calls for lower disturbance levels than Provincial regulations).

At the local level, when managing harvest-effects on soils, tree growth and longterm productivity,soil disturbance from mechanical operationsis of most concern.

Soil disturbance occurring at time of operations can have negative, positive, or no

detectable effect on growth or hydrologic function. Soil disturbance at the time

of operations is often an indicator used in regulating long-term productivity and

hydrologic effects. This is because in many NA ecosystems, we need at least 10

to 20 years data to draw conclusions about the effects of various practices on

growth or hydrologic function. In discussing evidence for long-term productivity

changes, Morris and Miller (1994) indicated slow-growing stands require 20 or

more years of growth before long-term productivity consequences can be ascertained. Soil disturbance is the proxy that we can observe and regulate at the time

of harvesting and site preparation. However, this proxy also needs to be validated

and revised over time in an adaptive management processthat includes standards,

best management practices, monitoring (compliance, effectiveness and validation),

further research and strategic direction and revision over time (Curran and others

2005b). A common approach is needed for describing soil disturbance so that

results achieved in different areas are comparable (Curran and others 2005c).

Management and Communication Frameworks for Sustainable 

Soil Management _______________________________________________

Just like ecosystem classification schemes (e.g., Braumandl and Curran 1992)

in neighboring BC, organizing soil into mappable or otherwise describable units

provides an important framework for communicating management experience,

Curran, Green, and Maynard Volcanic Ash Soils: Sustainable Soil Management Practices, With Examples of Harvest Effects and Root Disease Trends
USDA Forest Service Proceedings RMRS-P-44. 2007 99

research results, and conservation efforts. Detailed soil or land type maps are

available for much of the ash-cap soils in the United States, and reconnaissancelevel soil mapping is available in southern BC. Maps designate soil units (e.g., soil

series in detailed mapping and soil or land type associations in reconnaissance

mapping) based on soil-forming factors of parent material, topography, climate and

vegetation, all acting over time, which varies due to geologic events like glaciation

and volcanic eruptions. As discussed above,soil disturbance can also be classified

and we are working towards a common classification there as well.

Perhaps the most useful way of organizing soil units for forest management is

a consideration of their risk of damage from soil disturbance. The most common

disturbance of concern in forest management is from machine traffic during harvesting, site preparation, or fuel management treatments. The biggest concerns

associated with machine traffic are soil compaction, soil displacement, and soil

erosion. In addition, slope stability is a concern on steeper and wetter sites. To

identify and mitigate the potential for landslides, terrain mapping and/or terrain

stability field assessments are used on sites that exceed certain slope gradients

or have indicators of potential slope instability.

Determining the soil disturbance hazards on a given site provides a framework

for developing harvesting strategies by alerting the prescription developer to the

specific soil disturbance concerns on that site. For example, in BC, soil disturbance default standards under the Forest and Range Practices Act (FRPA) permit

up to 5 or 10% net disturbance within a cutblock area (excluding permanent

access). In the Interior, the trigger for 5% is when one of the key hazards is Very

High. A High rating for any hazard is primarily intended to alert the prescription

developer and the operational staff of a hazard that may require special treatment

to prevent problems (manage and mitigate the hazard). High compaction hazard

also results in more equipment traffic disturbance types being “counted”1 under

FRPA disturbance criteria. The soil disturbance hazards also help identify site

conditions that are suitable for construction of excavated and bladed trails (skid

roads or backspar trails), and/or temporarily exceeding soil disturbance levels and

rehabilitating slope hydrology and forestsite productivity. The hazards are defined

below, including brief discussions of why they are of concern.2

Soil Compaction Hazard

Soil compaction is the increase in soil bulk density that results from the rearrangement of soil particles in response to applied external forces. Soil puddling

is the destruction of soil structure and the associated loss of macroporosity that

1 In BC, the term “counted” is used in reference to soil disturbance to recognize the fact that

soil disturbance types or their severity vary with soil sensitivity to disturbance. More disturbance

types are of concern on more sensitive soils, and less are of concern on more resilient soils (e.g.,

sandy soils). The net result is that more disturbance types are “counted” towards the total cumulative allowable limit on more sensitive soils.

2 Soil degradation hazard rating keys for soil compaction, displacement, and erosion are found

in Land Management Handbook 47 (Curran et al. 2000) and the Forest Practices Code of British 

Columbia, Hazard Assessment Keys for Evaluating Site Sensitivity to Soil Degrading Processes 

Guidebook. The general BCMOF Web site where these and other FPC information can be located is: http://www.for.gov.bc.ca/ (look under legislation).

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results from working the soil when wet. Organic matter is often incorporated

during puddling and because organic matter is lighter than mineral particles, soil

bulk density may not increase; however, the other properties described below are

still negatively affected. The science and rationale for the BC compaction hazard

key are laid out in Carr and others (1991).

Soil moisture content is probably the best determinant of compaction hazard

at any given time. In British Columbia, the soil compaction hazard key ranks the

potential compaction hazard by grouping soil textures that are most susceptible

to structural degradation from compaction and puddling, and are most likely to

hold moisture and remain wet for longer periods. The soil compaction hazard

key is a tool to help with planning of an operation, while careful monitoring of

equipment effects on the soil, and hand tests for soil moisture content are the

tools that help guide the operation.

Soil compaction and puddling are of concern in timber harvesting operations

because of effects on roots and site water relations. Compacted soils have higher

penetration resistance that can impede root growth. Compacted and puddled

soils both have lower aeration porosity and lower hydraulic conductivity and

infiltration rates; however, in some coarser textured soils, compaction may actually increase water holding capacity (these soils typically have lower compaction

hazard ratings).

Lower aeration porosity results in reduced gas exchange that can adversely

affect oxygen levels in the soil air; this reduces physiologic function of roots,

which in turn can lead to root die off under wetter conditions. Lower hydraulic

conductivity and infiltration rates of the compacted or puddled soil can result in

increased runoff during rainfall and snowmelt events. This can lead to increased

net export of water from a cutblock, which can affect downslope sites, natural

drainage features, and other resource values due to erosion and sedimentation.

Increased water export also means less water may be stored on site to support

tree growth during summer drought. Compacted soils can also remain wetter

longer, thereby further affecting seedlings because the soil may be colder and

have poor aeration.

Monitoring of traditional spring harvesting on three ash-cap influenced soils in

the southern Rocky Mountain Trench near Cranbrook indicated that significant

declines in aeration porosity occured when evidence of equipment traffic was

visible on the ground (e.g., wheel lugmarks on the soil or slight impressions with

track grouser marks) (Utzig and others 1992). These sites were typical Trench

soils: silt loam to silty clay loam textured surface soils low in coarse fragments,

underlain by denser subsoils with more coarse fragments.

The undisturbed soils had aeration porosity values at or above the threshold

recommended by the United States Forest Service (USFS) in some of its policy

for the Pacific Northwest (i.e., 15% at 10 J/kg water tension referred to in Boyer

1979). Regardless of the severity of disturbance, aeration porosities were less

than 15% (fig. 1). Effects on saturated hydraulic conductivity (i.e., water relations) were similar (fig. 2). Bulk density increased in a similar but opposite trend

to the aeration porosity and saturated conductivity, as would be expected. The

concern about these effects is how extensive the machine traffic disturbance is

on fully mechanized harvesting. On the three sites studied, the combined total

of the light ruts, 5-cm ruts, and main trail disturbance ranged from 52 to 64% of

the entire cutblock area, with lighter machine disturbance covering from about

30 to over 45% (fig. 3).

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Figure 1—Aeration porosity at 10 J/kg tension for two sample depths at three sites in the southern 

Rocky Mountain Trench near Cranbrook, BC (Utzig and others 1992). U (undisturbed), VL (very 

light ruts, <5 cm deep), 1 (ruts 5 cm or deeper), HT (heavy [main] trails).

Figure 2—Saturated hydraulic conductivity for two sample depths at three sites in the southern 

Rocky Mountain Trench near Cranbrook, BC (Utzig and others 1992). U (undisturbed), VL (very 

light ruts, <5 cm deep), 1 (ruts 5 cm or deeper), HT (heavy [main] trails), from Curran (1999).

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These results are consistent with monitoring studies of nearby sites in northern

Washington, Idaho, and Montana (Kuennen and others 1979; Laing and Howes

1988, Svalberg 1979). In the Washington study, based on the literature at the

time, Laing and Howes (1988) predicted a “conservative estimate of 35% volume

reductions over the next rotation” for detrimentally compacted areas (42% of the

cutblock area in their study). On similar sites in Northern Idaho and Montana,

Kuennen and others (1979) suggested that changes in soil physical properties

resulting from compaction can decrease the ability of trees to compete with pine

grass. It is not clear whether these type of effects would be realized on our soils;

however, in the absence of long-term data to the contrary, we need to continue

to monitor tree growth on these sites. Light compaction is also being studied as

part of the North American Long-term Soil Productivity Study (LTSP).

In summary, the implications for site water storage, runoff, and tree growth

are of concern when random skidding causes these types of disturbances. It is

therefore inferred that, under certain soil conditions (e.g., harvesting under wetter

than optimum soil conditions), detrimental compaction can occur before soil disturbance criteria for ruts or trails are reached. Harvesting strategiesrecommending

dispersed skidding traffic need to recognize this risk and “tread lightly.” Compaction is a long-lived phenomenon; natural freeze-thaw and wet-dry cycles have

Figure 3—Aerial extent of soil disturbance at three sites in the southern Rocky Mountain Trench 

near Cranbrook, BC (Utzig and others 1992). LL (very light ruts, <5 cm deep), HL (heavy [main] 

trails), 1&2 (ruts 5 cm or deeper), and L (very light and heavy, combined) from Curran (1999).

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not been observed to ameliorate machine-induced compaction at depth. In the

ash-cap soil locations, where summer drought is one of the factors most limiting

to tree growth, and in the absence of long-term data to the contrary, prevention

of widespread “below the FRPA depth limit” compaction is probably the best bet

and can be achieved economically.

Soil Displacement Hazard

Soil displacement is the mechanical movement of soil materials by equipment

and movement of logs. It involves excavation, scalping, exposure of underlying

materials, and burial of fertile surface soils. Three aspects of displacement can

produce soil degradation:

	 •	 Exposure of unfavourable subsoils, such as dense parent material, gravelly

subsoil, and calcareous (high pH) soils.

	 •	 Redistribution and loss of nutrients.

	 •	 Alteration ofslope hydrology, which can lead to hydrologic effects(discussed

under compaction, above).

Soil development is often shallow and many of the nutrients that are limiting

to tree growth are often biocycled and concentrated in the upper soil horizons

throughout the British Columbia Interior. A similar affect occurs on shallow ashcap soils that overlay less fertile subsoils. Most of the soil nutrients are often

concentrated in the forest floor and top 20 cm of mineral soil (table 1). Therefore,

we don’t want to displace this fertile topsoil away from seedlings, or reduce the

rooting volume of these vital topsoil layers.

Table 1—Typical nutrient distribution in British Columbia Interior soils.

 Nutrients in kg ha–1 (% of total)

Soil layer Nitrogen Phosphorus Potassium

Forest floor 1450 (44%) 112 (82%) 224 (73%)

0-20 cm 1050 13 56

20-40 cm 820 8 25

Total 3320 133 305

Forest Floor Displacement Hazard

Forest floor displacement is the mechanical movement of the upper organic

materials by equipment and movement of logs. It involves excavation, scalping,

mineral soil exposure, and burial of the forest floor. The effects of forest floor

displacement range from beneficial to detrimental, depending on site factors

(e.g. mineral soil characteristics) and how far the forest floor is displaced from

the seedlings.

Forest floors typically represent a major component of the nutrient capital on a

forest site. In the British Columbia Interior, it is not uncommon for the forest floor

to contain over 50% of the soil nitrogen and 80% of the phosphorus (table 1).

Given that many Interior sites are considered nitrogen deficient, conservation of

the forest floor is important. On deeper ash-cap or older, richer soils, much of

the nutrient capital occurs in the mineral topsoil and forest floor displacement

may be of less concern.

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Two aspects of forest floor displacement can produce soil degradation:

	 •	 Redistribution and loss of nutrients (e.g. chemically bound and unavailable

in the mineral soil, and accelerated decomposition of organic matter).

	 •	 Exposure of unfavourable rooting medium.

A review of forest floor displacement and implications for tree growth in the

Southern British Columbia Interior found that while there were a few trends in

soil nutrient levels, it was difficult to relate displacement to any negative effects

on tree growth (Hickling 1997). In cooperation with Pope and Talbot Ltd., we

installed long-term monitoring plots on various disturbance types including some

associated with stumping (Hickling 1998).

Most forest operations were well below the forest floor displacement limits

originally set in the FPC, so determining the forest floor displacement hazard is

no longer officially required for harvest planning and permitting. However, use of

this hazard interpretation is supported and recommended for planning dispersed

skidding on steeper slopes, rehabilitation of soil disturbance, and root rot treatments. Forest floor displacement is also more of a concern on calcareous soils

due to the higher pH of the mineral soil

Surface Soil Erosion Hazard

Surface soil erosion is the wearing away of the earth’s surface by water and

includes splash, rill, and gully erosion. It has on-site impacts (soil loss, nutrient

loss, lower productivity) and off-site impacts(water quality,sedimentation, habitat

impacts). The surface soil erosion hazard key focuses on on-site erosion and conservation of the fertile topsoil layers near developing seedlings. The science and

rationale for the British Columbia key were laid out in Carr and others (1991), and

the rating weightings tested in the Nelson Forest Region by Commandeur (1994),

resulting in modifications to the final key currently in use. Other assessments

may be used for haul road erosion and sediment delivery to streams. Haul roads

and landings are of concern because erosion and drainage diversions can lead to

sedimentation and stability problems. They require careful layout and attention to

erosion hazard on haul roads and minimizing erosion and sedimentation during

construction and maintenance.

Defining Soil Disturbance

A technical definition of soil disturbance is any disturbance that changes the

physical, chemical, or biological properties of the soil (Lewis and others 1991). It

is not always negative. Foresters commonly prescribe purposeful soil disturbance

as site preparation for seedling planting and establishment; these disturbance

types are often not counted in standards (e.g., under FRPA in British Columbia).

By controlling how we harvest a site, we can create more “site preparation” type

disturbance and keep most of the potentially detrimental disturbance confined

to travel corridors; these main trails may then be rehabilitated after harvesting, as

appropriate. Whenever planning soil disturbance, the preservation and restoration

of natural drainage patterns should be the primary goal (necessary repetition).

The strategies described in this documentstrike a balance between “favourable”

and “detrimental” disturbance by limiting the amount of “counted” soil disturbance.

Regionally applicable soil disturbance standards recognize that some level of

disturbance is necessary to permit access to timber. Counted disturbance usually

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includes main trails and ruts/impressions of certain dimensions, and under some

schemes(e.g., FRPA in British Columbia) also include wide or deep gougesinto the

soil. Those developing and implementing a harvesting strategy need to recognize

that on more sensitive sites, disturbance types that “count” may be created more

easily and may be counted sooner (e.g., in Interior British Columbia 5-cm ruts and

impressions on High and Very High Compaction hazard, as opposed to 15 cm on

other soils; when Erosion, Displacement, or Compaction hazards are Very High).

On sites with lower hazard ratings, less disturbance categories may be counted.

The actual effect of a given soil disturbance on tree growth will depend on the

most growth-limiting factors on a given site and how these factors change over

the course of a rotation. In the British Columbia Interior, common growth-limiting factors include: competing vegetation, soil moisture (drought or excess), soil

temperature, summer frost, rooting substrate (volume), soil nutritional problems

(e.g., calcareous soils), and root rot. The net effect on growth will also depend on

whether soil disturbance has introduced a new limitation, such as reduced soil

aeration from compaction. Long-term effects could include increased susceptibility

to blowdown because of poor rooting in detrimentally disturbed soil.

Regional ecology guides often summarize common growth-limiting factors

for various ecosystems (Braumandl and Curran 1992), and a model has been

developed for comparing disturbance effects on growth-limiting factors when

deciding on site preparation prescriptions (Curran and Johnston 1992; Sachs and

others 2004).

Regardless of the actual tree growth effects, a number of soil disturbance types

are also of concern because of potential effects on site and slope hydrology and

the potential for downslope impacts. On-site hydrology changes are difficult to

study but we need to err on the conservative side considering that much of British

Columbia is not flat and summer drought is often one of the most growth-limiting factors on many sites (effects on hydrology may confound tree growth on

apparently “undisturbed” microsites in tree growth studies). Similar hydrologic

concerns have been voiced by other researchers in the local area (Kuennen and

others 1979).

Synthesis of Above Knowledge and Principles in 

Our Forest Practices _____________________________________________

Machine-Based Practices

Forest harvest,site preparation, and fuel management treatments are most commonly accomplished through the use of machinery. In the case of timber harvest or

fuels, this may occur through aerial, cable, or ground-based equipment. Because

ground-based harvesting typically creates the most disturbance, it is discussed

below but the principles remain the same for the other methods.

Based on the environmental framework described in the preceding section, a

given harvesting strategy should meet the following four requirements:

	 1.	 Be site specific and responsive to the soil sensitivities on site and downslope.

	 2.	 Offer a reasonable amount of independence from climatic interruptions,.

	 3.	 Incorporate rehabilitation, if necessary, to lower disturbance below guidelines.

	 4.	 It must instill enough confidence at all levels of approval and operations.

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In the 1990s we worked on a number of trials with Industry and District staff,

to address concerns about managing harvesting soil disturbance. Trials have addressed tree growth on rehabilitated skid roads (Dykstra and Curran 1999), haul

roads(Curran, unpublished data), and landings(Bulmer andCurran 1999a). Memos

were circulated and a special publication (Curran 1999) summarized simple field

tests developed during operational trials of seasonal harvesting constraints (i.e.,

“how wet is too wet?” and “how much frost is enough frost?”). Other research

trials have been successful in demonstrating the feasibility of rehabilitating soil

disturbance (Bulmer and Curran 1999b). Combined, these trials were designed to

test tree growth on rehabilitated disturbance and develop strategies to reduce the

dependency on weather conditions and reduce shutdown of operations during

wetter conditions. Research and practical innovation are still ongoing, and further

field guides will be produced as warranted (e.g., we are developing a simpler soil

texture key at this time).

Based on industry innovation, practical experience, and research trials, we have

identified four key strategies that we feel meet the above criteria:

	 a)	 close trail spacing with rehabilitation,

	 b)	 closely spaced temporary spur (haul) roads with rehabilitation,

	 c)	 combination designated and dispersed (random) skidding, and

	 d)	 hoe-chucking, Interior style (i.e., forwarding to wider spaced trails).

These strategies may or may not include fully mechanized harvesting, either with

cut-to-length feller-processors and forwarders, or with feller-bunchers and grapple

skidders. The strategies also may offer the opportunity to reduce site preparation

costs by creating disturbance during the harvesting or rehabilitation phases. Each

strategy is described in more detail in Curran (1999). Other harvesting strategies

have been described for meeting soil disturbance standards under site conditions

in western Washington and Oregon by Heninger and others (1997). Again, the

objective is to match equipment capabilities to site sensitivity to disturbance.

Ground-based equipment may be restricted to designated trails or allowed to

travel overland depending on the soil and climatic conditions.

Studies on ash-cap influenced and similar soils in southern Interior British

Columbia have shown that large amounts of soil disturbance can occur during

mechanicalrootremoval forroot disease management (Quesnel andCurran 2000;

Curran, unpublished data). Tree growth responses to these disturbances vary

with site growth limiting factors and over time. On two sites on similar climate in

southern British Columbia, stump removal treatments had differing effects (fig. 4).

On an ash-cap influenced soil at Phoenix, soil disturbance either increased or

did not negatively affect tree growth; whereas on a soil on the Gates Creek site

that had more clay (12% versus 4%), there was a clear negative trend with tree

growth and disturbance severity. The long-term growth trend at the Gates Creek

site is interesting as it clearly demonstrates the need for long-term tree growth

response data (fig. 5).

Insect and Disease

Some forest insects and pathogens are opportunistic organisms that cause

primary damage to stressed host trees. Stress may occur due to soil disturbance

effects on tree growing environment, climate change resulting in temperature or

moisture stress, other biotic or abiotic environmental factors, or multiple interacting factors. Interacting factors that contribute to pest outbreak are complex. For

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Figure 4—Fifteen-year volume of Douglas-fir 

seedlings growing in different disturbance types 

on the Canadian Forest Service Gates Creek and 

Phoenix stumping trial sites in southern British 

Columbia, which are gravelly sandy loam textured 

with 12% clay at Gates Creek and 4% clay at 

Phoenix (Curran and others 2005a adapted from 

Wass and Senyk 1999).

Figure 5—Comparison of relative 

growth of Douglas-fir on a stump 

removal trial in southern British 

Columbia at 3, 10 and 15 years 

since treatment. All data is relative 

to the undisturbed condition(Curran 

and others 2005a adapted from 

Wass and Senyk 1999).

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108 USDA Forest Service Proceedings RMRS-P-44. 2007

example, large areas of bark beetle infestations are sometimes attributed to climate

change and/or root disease interactions (Partridge and Miller 1972). However,

insect attack is also dependent upon inherent dynamics of insect behavior. The

following text focuses on root disease organisms in Inland Northwest.

Environmental Factors Affecting the Distribution and 

Activity of Root Diseases

Biophysical Setting—Armillaria root disease (primarily caused by Armillaria 

ostoyae) and Annosus root disease (caused by Heterobasidion annonsum) are

widely distributed in western conifer forests. Off-site plantings, wounded trees,

and trees growing on compacted soils or in areas with drainage problems are

particularly likely to be affected by Armillaria root disease (Goheen and Otrosina

1998; Wiensczyk and others 1997). Douglas-fir dominated stands in northern

and central Idaho and northeastern Washington experience substantial mortality

from Annosus root disease, especially on dry sites (Schmitt and others 2000).

However, in southern interior BC, Morrison and others (2000), found significantly

higher rates of Armillaria sp. infection on dry sites than moist or wet sites; and

once infected, trees on drier sites were less able to resist infection and were more

likely to show aboveground symptoms.

Laminated root rot, (caused by Phellinus weirii), occurs mainly in hemlock,

western red cedar and grand fir habitat types on the Lolo National Forest, but

infrequently in Douglas-fir and subalpine fir habitat types, while Armillaria and

Annosum root disease are distributed more widely (Byler and others, 1990). Hagle

and others(1994)similarly found root disease mostsevere in grand fir habitat types,

and low severity disease ratings occurred most often on Douglas-fir habitat types.

Declines in disease severity were noted after 160 years as the more susceptible

species died out of the stand. They suggest that grand fir habitat types are most

likely to support grand fir and Douglas-fir as seral and climax species, and these

are the most susceptible species.

On the Lolo National Forest, Byler and others (1990), found higher probabilities of Armillaria root disease on Douglas-fir habitat types on southerly aspects.

Moderate slopes had a higher incidence than either flat or very steep slopes.

Soil Physical Properties—In another study, Armillaria spp. infection levels decreased with increasing clay content, which is correlated with moisture-holding

ability (Wiensczyk and others, 1997). This is consistent with the hazard rating

system of Froelich and others (1977). In the Wiensczyk study, sandy soils were

more highly correlated with Armillaria spp. activity in black spruce than were

silty soils, and as moisture regime increased (based on mottles and gleying), Armillaria spp. frequency decreased. This may be due to reduced growth of Armillaria rhizomorphs in finer textured and moister soils, or to improved tree vigor.

Sand, large soil pores, and high bulk density were also positively correlated with

Annosum root disease in loblolly pine plantations (Alexander and others, 1975).

It is thought that rapid infiltration in sandy soils allowed easy translocation of

root rot spores. Baker and others (1993) also found that low silt in the A horizon

was an important predictor of H. annosum infection. Blenis and others (1989)

also found clay loam to be least favorable for Armillaria root disease and sandy

loam the most favorable. The pathogen is known to be sensitive to low levels of

oxygen and high levels of carbon dioxide.

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Soil Chemical Properties—Armillaria ostoyae infection levels were found to

increase with increasing phosphorous in the A horizon (Wiensczyk and others

1997). However, phosphorous in ash-cap surface soils is often held in unavailable

form and may not locally contribute to infection. Reduced phosphorous may limit

tree root elongation, which could reduce the likelihood of underground contact

with A. ostoyae.

Rishbeth (1951) found H. annosum infection rates from stumps to be lower in

acid than alkaline soils. He attributes this to competing fungi in more acid soils.

Baker and others (1993) found H. annosum infection incidence to be lower in

acid soils, as did Blenis and others (1989).

Soil Microbiology—Root microflora, such as Actinomycetes and fungi (e.g.,

Trichoderma spp., Phlebiopsis spp., Bjerkandera spp., Hypholoma sp., etc.), can

have fungistatic effects on root pathogens (Hagle and Shaw 1991; Holdenreider

and Greig 1998; Nelson 1964, 1973;Nelson and Thies 1985, 1986; Raziq 2000).

It has been suggested that mixed stands with fewer potential host species, and

interruption of succession with shrub and other non-susceptible species reduce

H. annosum inoculum (Johansson and Marklund, 1980) by supporting enhanced

populations of Actinomycetes. Chapman and Xiao (2000) confirmed the ability

of a saprophytic fungus, Hypholoma fasciculare, to out-compete A. ostoyae on

a variety of nonliving substrates, such as stumps. Veech and Boyce (1964) also

found higher levels of soil fungi, Actinomycetes, and bacteria than in areas of

higher H. annosum infection. Greig (1962) also found development of Annosum 

root disease to be lower in plantations established on areas formerly occupied

by hardwoods than on second-rotation conifer plantations. This “diversity of soil

microflora” is hypothesized to be more typical of natural disturbance regimes

than stands affected by fire suppression and emphasis on one or two susceptible

crop species, like grand fir and Douglas-fir.

Ectomycorrhizal fungi associated with tree roots are known to be important

for moisture and nutrient relationships of the host tree (Harvey and others 1986,

1987). Decayed soil wood promotes this association. Root pathogens may interact

directly with mycorrhizae so that biomass and energy reserves of all parties are

reduced (Graham 2001; Sharma and others 1992), butsometimes pathogen effects

on the host tree are reduced (Morin and others 1999). This complex interaction

suggests we need to sustain a continuous supply of the organic materials that

support healthy mycorrhizal populations.

Relation to Properties of Volcanic Ash—Surface soils formed in volcanic

ash tend to be silty in texture, have high porosity, and low bulk density, and low

inherent nutrient status, and low nutrient-holding capacity (McDaniel and others

2005). They may adsorb phosphorus and hold it in an unavailable form. Acidity is typically slightly acid to neutral. Tree roots are often concentrated in the

volcanic ash layer, suggesting that root contact could be common and distance

from stump inoculation point to live root would be short. This would make it

easier for infections to spread. High moisture-holding capacity suggests that

drought-induced stress during summers would be somewhat mitigated, but that

this capacity would be reduced by compaction or displacement. Volcanic ash is

highly correlated with grand fir, cedar, hemlock, and subalpine fir habitat series,

and to a lesser extent with Douglas-fir.

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Management Effects—Fire exclusion, harvest of lesssusceptible pine and larch,

and declines in white pine due to exotic blister rust (Cronartium ribicola) have

all contributed to the increase in more susceptible Douglas-fir and grand fir, and

moisture and nutrient stress, increasing the prevalence of root disease in the range

of volcanic ash soils. More studes are needed to determine the effects of partial

harvest and soil compaction/displacement on root disease in managed stands.

Climate Change, Root Disease, and Management on 

Volcanic Ash-cap Soils

Climate change can result in mature trees that are maladapted to their environment, which can increase vulnerability to pathogens (Ayres and Lombardero,

2000), as well as other disturbances like fire or insects. In the Interior Northwest,

increasing temperatures and reduced summer moisture (McKenzie and others

2004; Mote and others 2003) increase stress on trees in marginal sites (thin ashcap, compacted soils), which may make them more susceptible to root diseases.

Physiological modelsto predict how tree defenses would alter with climate change

are lacking. Effects of climate change on root disease and competing organisms

are not known.

Fire suppression and subsequently more severe fires may increase the rate of root

disease by providing more fire-scarred tree wounds as entrance points (Otrosina

and Garbelotto 1997). Fire exclusion leading to dominance of susceptible true firs

and high levels of root disease would also lead to increased susceptibility to fire and

large insect outbreaks. Higher density stands due to fire exclusion could increase the

likelihood of belowground spread of the pathogen from tree to tree. Longer periods

of high heat and drought could suppress spore germination and stump colonization

for longer periodsin the summer, although Bendz-Hellgren and Stenlid (1998) found

no effect of temperature on stump colonization by H. annosum.

Management Opportunities:

	 •	 Limit management induced stress by confining soil compaction and displacement to limited areas and rehabilitating them after use.

	 •	 Provideconnectionsforspeciestomove inresponse tochangedclimaticcontext

(maintaining continuity of species in space, while allowing for movement).

	 •	 Use species and density management to allow forest species to use disturbance as stepping stones for migration.

	 •	 Introduce and sustain species resistant to root disease.

	 •	 Root removal has been proposed to control Armillaria root disease (Roth

and others 2000), but some studies have concluded that inoculum removal

cannot be complete enough to change the dynamics of root disease development (Reaves and others 1993). The associated soil disturbance, particularly

in ash-cap soils, is likely to have deleterious physical effects.

The issue of soil restoration to recover suitable moisture and air relationships

is complicated by other factors. Soil disturbance associated with roads, skid

trails, and precommercial thinning (Hessburg and others 2001) was correlated

with incidence of black stain root disease (caused by Leptographium wageneri)

in southwest Oregon. Alternatively, subsoiling to alleviate soil compaction may

result in root damage and dieback of any residual trees, attracting root feeding

beetles that carry black stain root disease. Kliejunas and Otrosina (1997) and

Curran, Green, and Maynard Volcanic Ash Soils: Sustainable Soil Management Practices, With Examples of Harvest Effects and Root Disease Trends
USDA Forest Service Proceedings RMRS-P-44. 2007 111

Otrosina and others (1996) found higher levels of ergosterol in subsoiled areas,

which indicated higher levels of fungal decomposer activity. This was attributed

to soil displacement and root severing. This suggests managers should limit the

extent of compacted areas as much as possible and avoid subsoiling near trees to

avoid both above and below ground damage. Stump removal could have similar

effects in adjacent live trees.

Analysis of North Idaho Root Disease Trends in Relation 

to Soil and Site Factors

Sue Hagle (Pathologist, USDA Forest Service, Region 1) rated stands within

randomly selected subcompartmentsforroot disease activity using photo interpretation on a scale of 0 to 9 (Hagle and others 2000). On the three Idaho National

Forests (Idaho Panhandle, Clearwater, and Nez Perce) analyzed here, 1,204 plots

were available, but 11 of these did not have geologic information and 29 did not

have soil survey information. The stand polygons were interacted with geospatial layers including soil survey map units, lithology, mean annual precipitation,

elevation, aspect, latitude, longitude, and slope.

Soil survey map units were classified into four classes based on volcanic ash

depth:

	 1:	No described volcanic ash influence

	 2:	Thin or mixed ash

	 3:	Andic subgroups

	 4:	Thick ash (Andosols)

Where soil type varied by aspect, aspect was used to refine the ash depth

factor.

Geologic groups were developed based on literature describing associations

between root disease and rock type (Garrison and Moore 1998; Moore and others

2004). This process was complicated by different scales, notation, and depth of

description of available geologic maps. We tried to identify potential strong associations by spatial exploration of root disease activity and geologic formation.

Patterns that appeared strong in one area were not consistent in other areas. The

resulting groups used are:

	 2	 = Granitics, predominantly Cretaceous, but also Jurassic (292 samples).

	 3	 = Recent metamorphics (younger than Belt Age) (21 samples).

	 4	 = Belt age metamorphics, but not including Belt quartzites described under

11. (666 samples). These were expected to have higher inherent fertility.

	 5	 = Tertiary and more recent sediments (3 samples).

	 6	 = Seven Devils volcanics of Triassic and Permian age (20 samples). These sites

were omitted from this analysis because they are thought to be anomalous.

They had very high root disease activity ratings. Trends and significance

were similar with and without these samples.

	 7	 = Undifferentiated, such as glacial deposits or alluvium (65 samples).

	 8	 = Other volcanics (2 samples).

	 9	 = Limestone no samples.

	 10	 = Belt age sediments no samples.

	 11	 = Belt quartzites (Middle Wallace quartzites, Striped Peak formation, Revett

quartzite, and Prichard quartzite (94 samples). These were expected to

have the lowest inherent fertility.

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112 USDA Forest Service Proceedings RMRS-P-44. 2007

Each stand was additionally assigned to a moisture and temperature gradient

class after McDonald and others (2000) using the habitat type information associated with each stand polygon:

Understory: Moisture Regime

No data	 0

Dry grass	 1

Dry shrub	 2

Dry herb	 3

Moist herb	 4

Wet herb	 5

Wet fern	 6

Wet shrub	 7

Overstory: Temperature Regime

No data	 0

Cold fir	 1

Cool fir	 2

Cedar hemlock	 3

Douglas-fir	 4

Ponderosa pine	 5

Pinyon juniper	 6

The following tables and plots display exploratory analysis of the association of

root disease activity (using an 8 classranking system) and categorical environmental variables. Shown are the median, interquartile range, extremes, and possible

outliers. No pattern is apparent for aspect class and root disease ranking,

Root Disease and Ash Depth

Thin or mixed ash is associated with higher incidence of root disease (table 2).

Low root disease activity associated with areas of no volcanic ash are usually in

very dry steep slopes or poorly drained areas where soils are formed in mixed

alluvium.

Soils with no ash influence have significantly lower root disease activity, but

Andic soils and Andosols do not differ significantly.

Table 2—Ash-cap depth as related to root disease ranking.

Ash Depth N

Mean Root

Disease

Ranking* 95% C.I.

1 – None 25 2.2 1.5-2.9

2 – Thin or mixed 198 3.6 3.3-3.9

3 – Andic 247 3.2 2.9-3.4

4 – Andosol 638 3.0 2.9-3.2

*See Hagle and others (2000) for detailed root disease activity scale.

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Geologic Group

No strong trends were noted, however there were some differences among 

lithologic groups.

Recent metamorphics showed greater root disease activity than in undifferentiated deposits (table 3). The great variability in recent sediments (group 5) suggests

a need forfurtherrefinement of this class. Belt age metamorphics(group 4)showed

relatively low root disease activity, with numerous samples, and were significantly

less than granitics, recent metamorphics, and Belt quartzites. Undifferentiated

rock types (recent deposits) also showed low root disease activity. The Belt Age

quartzites, anticipated to be naturally low in potassium and with high levels of

root disease activity, were significantly higher than other Belt metamorphics and

undifferentiated rock types, but did not differ from granitics, recent sediments,

or recent metamorphics.

Table 3—Influence of geologic group on disease incidence. 

Geologic Group N

Mean Root

Disease

Ranking* 95% C.I.

2 – Granitics 292 3.5 3.3-3.7

3 – Metamorphics

(not Belt Age)

21 3.9 2.8-4.9

4 – Belt Age

Metamorphics/not

quartzites

666 2.9 2.8-3.0

5 – Tertiary and

more recent

sediments

3 4.3 .5-8.1

7 – Undifferentiated

(recent glacial

deposits or alluvium)

65 2.9 2.5-3.3

8 – Other volcanics 2 3.5 NA

11 – Belt quartzites 94 3.5 3.1-3.9

*See Hagle and others (2000) for detailed root disease activity scale.

Root Disease and Forest

The Idaho Panhandle National Forest had the lowest disease ranking, followed

by the Clearwater National Forest, and then Nez Perce National Forest (table 4).

These differences could be caused by drier soils, changes in geology, soil nutrition, or other inherent site physical, chemical, or biological properties.

Table 4—National Forest and incidence of disease.

National Forest N

Mean Root

Disease

Ranking* 95% C.I.

4 – Idaho Panhandle 639 2.7 2.6-2.9

5 – Clearwater 331 3.4 3.2-3.6

17 – Nez Perce 173 4.0 3.7-4.3

*See Hagle and others (2000) for detailed root disease activity scale.

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114 USDA Forest Service Proceedings RMRS-P-44. 2007

Root Disease and Potential Vegetation (Habitat Type Group)

Potential Vegetation is an indicator of soil moisture and temperature regimes

and constrains whether susceptible species are likely to occur as seral or climax

on the site. When habitat types (Cooper and others 1991) are grouped according to Jones (2004), it is evident that those habitat types most likely to support

susceptible grand fir or Douglas-fir and show higher levels of root disease activity

(data not shown). The occurrence and severity of root disease depends strongly

on the abundance of a susceptible host. Sites with a longer history of dominance

by suitable host species will likely have accrued higher levels of fungal biomass.

Drier grand fir and Douglas-fir habitat types, which are more likely to support

more ponderosa pine, show lower levels of root disease activity. It is interesting

to note that some extremely high values of root disease activity are associated

with more moist cedar or western hemlock habitat type groups. It is possible that

these sites are capable of very high levels of inoculum where seral white pine has

been eliminated for long periods.

Moisture and Temperature Regime

Using the moisture and temperature indices defined by McDonald and others (2000), we compared disease ranking against moisture indicator (understory

association) and temperature indicator (overstory series).

Sites with moderately dry moisture regimes (dry shrub) had the highest root

disease activity, and differed from dry grass and dry shrub, but not moist herb

(table 5). This may be due to the high incidence of susceptible Douglas-fir on

these moisture settings.

Sites with moderately warm temperature regimes (Douglas-fir) had the highest

root disease activity, and differed significantly from cold fir and ponderosa pine.

Cool fir temperature regimes had higher root disease than cold fir, cedar hemlock,

and ponderosa pine (table 6). Again, the presence of susceptible host species is

highly correlated with these temperature regimes.

Table 5—Root disease ranking as related to understory moisture indicator. 

Moisture Regime N

Mean Root

Disease

Ranking* 95% C.I.

1 – Dry grass 12 2.2 1.1-3.2

2 – Dry shrub 89 3.4 2.9-3.8

3 – Dry herb 303 2.9 2.7-3.1

4 – Moist herb 734 3.2 3.1-3.3

5 – Wet herb 1 3 NA

6 – Wet fern 1 0 NA

7 – Wet shrub 1 1 NA

*See Hagle and others (2000) for detailed root disease activity scale.

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Table 6—Root disease ranking as related to temperature regime.

Temperature Regime N

Mean Root

Disease

Ranking* 95% C.I.

1 – Cold fir 366 3.0 2.8-3.2

2 – Cool fir 153 3.6 3.3-3.9

3 – Cedar hemlock 528 3.1 2.9-3.2

4 – Douglas-fir 90 3.5 3.0-3.9

5 – Ponderosa pine 3 1.3 0-4.2

*See Hagle and others (2000) for detailed root disease activity scale.

Association of Root Disease Ranking with Numeric 

Variables

The most ecologically significant correlations appear to be that root disease

activity is positively associated with steep slopes, southerly latitude, westerly

longitude, potential for host species (based on habitat type cover tables), and

decreasing annual precipitation.

Conclusions_____________________________________________________

Ash-cap soils are susceptible to disturbance; schemes to predict compaction,

displacement, and erosion hazards are useful in forest management application.

Whether more or less disturbance should be permitted on ash-cap soils is a

controversial topic and it is likely more important to focus on the individual site

hazards because ash-cap soils can vary considerably in their state of weathering, texture, depth and inter-mixing with other soil materials. Machine traffic can

be managed and as demonstrated in Bulmer and others (this proceedings), and

mitigated through rehabilitation in a set of harvest (machine-traffic) strategies that

consider site.

Regarding root disease on ash-cap soils, this preliminary coarse-scale investigation suggests some potential relationships among root disease (primarily

Armillaria in Idaho) and soil and site factors. The strong relationship between

presence of susceptible host and development of fungal biomass may be the

strongest causal agent, and the soil and site factors promote the presence of the

susceptible host.

Thicker ash soils of more northerly areas are related to habitat types that historically supported white pine and a higher diversity of less susceptible species.

These more mesic environments also fill in with other species rapidly after root

disease mortality occurs, so higher levels of root disease activity are more difficult

to discern (Hagle, personal communication, 2006).

Recommendations ______________________________________________

Sustainable soilmanagementonash-capsoilsneedstofollowprotocolsdeveloped

for all sites whereby an adaptive management / continuous improvement process

needsto be supported by research, best management practices, and strategiesthat

include all types of monitoring (compliance, effectiveness and validation).

Volcanic Ash Soils: Sustainable Soil Management Practices, With Examples of Harvest Effects and Root Disease Trends Curran, Green, and Maynard
116 USDA Forest Service Proceedings RMRS-P-44. 2007

Development of a common approach to describing soil disturbance and soil

disturbance hazards will go a long way toward more effective sharing of management experiences on ash-cap soils.

More work is needed on the long-term effects of cumulative aerial extent of

soil disturbance and on soil disturbance categories to refine these and hazard

rating systems.

For the root disease work, more site-specific evaluation of soil properties,

stand history, and geologic parent materials, both mineralogical composition and

weathering state, would help to sort out these relationships.

Acknowledgments ______________________________________________

The authors thank Dr. R.E. Miller, emeritus research scientist at USDA Forest

Service, Pacific Northwest Research Station for his review of the manuscript, and

Sue Hagle, pathologist for USDA Forest Service Region 1 for her helpful advice

and review of the root disease part of this paper.

References______________________________________________________

Alexander, S. A.; Skelly, J. M.; Morris, C. L. 1975. Edaphic factors associated with the incidence

severity of disease caused by Fomes annosus in loblolly pine plantations in Virginia. Phytopathology. 65(5): 585-591.

Ayres, M. P.; Lombardero, M. J. 2000. Assessing the consequences of global change for forest

disturbance from herbivores and pathogens. The Science of the Total Environment. 262(3):

263-286.

Baker, F. A.; Verbyla, D. L.; Hodges, C. S.; Ross, E. W. 1993. Classification and regression tree

analysis for assessing hazard of pine mortality caused by Heterobasidion annosum. Plant Disease. 77(2): 136-139.

Bendz-Hellgren, M.; Stenlid, J. 1998. Effects of clear-cutting, thinning, and wood moisture content

on the susceptibility of Norway spruce stumps to Heterobasidion annosum. Canadian Journal

of Forest Research. 28: 759-765.

Blenis, P. V.; Mugala, M. S.; Hiratsuka, Y. 1989. Soil affects Armillaria root rot of lodgepole pine.

Canadian Journal of Forest Research. 19: 1638-1641.

Boyer, D. 1979. Guidelines for soil resource protection and restoration for timber harvest and

post-harvest activities. Portland, OR: U.S. Department of Agriculture, Forest Service, Pacific

Northwest Region, Watershed Management.

Braumandl, T. F.; Curran, M. P., eds. 1992. A field guide for site identification and interpretation for

the Nelson Forest Region. Victoria, BC Min. Forests, Land Management Report No. 20. 311 p.

Bulmer, C.; Curran, M. 1999a. Retrospective evaluation of log landing rehabilitation on coarser

textured soils in southeastern British Columbia. BC Min. Forests, Nelson Forest Region Extension Note No. EN-042. 4 p.

Bulmer, C; Curran, M. 1999b. Operational trials of soil rehabilitation. BC Min. Forests, Nelson

Forest Region Draft Extension Note. 10 p.

Byler, J. W.; Marsden, M. A.; Hagle, S. 1990. The probability of root disease on the Lolo National

Forest, Montana. Canadian Journal of Forest Research. 20: 987-994.

Carr, W. W.; Mitchell, W. R.; Watt, W. J. 1991. Basic soil interpretations for forest development

planning: Surface soil erosion and compaction. BC Min. Forests, Land Management Report

No. 63. 17 p.

Canadian Council of Forest Ministers. 2003. Defining sustainable forest management in Canada.

Criteria and indicators. 2003. Available: http://www.ccfm.org/2000pdf/CI_Booklet_e.pdf. Accessed November 2003.

Chapman, B.; Xiao, G. 2000. Inoculation of stumps with Hypholoma fasciculare as a possible

means to control Armillaria root disease. Canadian Journal of Botany. 78: 129-134.

Commandeur, P. 1994. Rainfall simulation, soil infiltration, and surface erosion on skidroad surfaces, Nelson Forest Region. BC Min. Forests, Research Branch. Canada - BC FRDA Report

228. 28 p.

Curran, Green, and Maynard Volcanic Ash Soils: Sustainable Soil Management Practices, With Examples of Harvest Effects and Root Disease Trends
USDA Forest Service Proceedings RMRS-P-44. 2007 117

Cooper, S. V.; Neiman, K. E.; Steele, R.; Roberts, D. W. 1991. Forest Habitat Types of Northern

Idaho: a Second Approximation. INT-GTR-236. U.S. Department of Agriculture, Forest Service,

Intermountain Research Station. 143 p.

Curran, M. 1999. Harvest systems and strategies to reduce soil and regeneration impacts and

costs. In: Impact of machine traffic on soil and regeneration. Proceedings of FERIC’s Machine

Traffic/Soil Interaction Workshop; 1999 February; Edmonton, Alberta. FERIC Special Report

No. SR-133: 75-11.

Curran, M .P.; Johnston, M. A. 1992. Overview of the SYTEPREP computer-based system (System To

Evaluate Prescription Effects on potential Productivity). BC Min. Forests, Nelson Forest Region,

Research Summary (Extension Note) RS-006. 2 p.

Curran, M.; Davis, I.; Mitchell, B. 2000. Silviculture prescription data collection field handbook:

Interpretive guide for data collection, site stratification, and sensitivity evaluation for silviculture

prescriptions. B.C. Min. Forests Land Management Handbook No. 47. 156 p. Includes forms

FS39A and B. Available: http://www.for.gov.bc.ca/hfd/pubs/Docs/Lmh/Lmh47.htm. Accessed

December 2004.

Curran, M. P.; Heninger, R. L.; Maynard, D. G.; Powers, R. F. 2005a. Harvesting effects on soils,

tree growth and long-term productivity. In: Productivity of Western Forests: A Forest Products

Focus.GTR-PNW-642.U.S.Department ofAgriculture, Forest Service, PacificNorthwest Station:

3-15. Available: http://www.fs.fed.us/pnw/publications/GTR-642/GTR642a.pdf.

Curran, M. P.; Maynard,D.G.;Heninger, R. L.; Terry, T.A.;Howes, S.W.; Stone,D. M.;Niemann, T.;

Miller, R. E.; Powers, R. F. 2005b. An adaptive management process for forest soil conservation.

Forestry Chronicle. 81: 717-722.

Curran, M. P.; Miller, R. E.; Howes, S. W.; Maynard, D. G.; Terry, T. A.; Heninger, R. L.; Niemann, T.;

Van Rees, K.; Powers, R. F.; Schoenholtz, S. H. 2005c. Progress towards more uniform assessment and reporting of soil disturbance for operations, research, and sustainability protocols.

J. For. Ecol. Mange. 220(1-3): 17-30.

Dykstra, P. R.; Curran, M. P. 1999. Tree Growth on Rehabilitated Skid Roads in Southeastern British

Columbia.. BC Min. Forests, Nelson Forest Region, Extension Note EN-046. 6 p.

Froelich, R. C.; Kuhlman, E. G.; Hodges, C. S.; Weiss, M. J.; Nichols, J. D. 1977. Fomes annosus

root rot in the South: guidelines for prevention. U.S. Department of Agriculture, Forest Service,

Southern Forest Experiment Station, Southeastern Forest Experiment Station and Southeastern

Area, State and Private Forestry. 17 p.

Garrison-Johnston, M.; Moore, J. A. 1998. Nutrient management: a summary and review. Intermountain Forest Tree Nutrition Cooperative. Supplemental Report 98-5. 47 p.

Goheen , D. J.; Otrosina, W. J. 1998. Characteristics and consequences of root diseases in forests

of western North American. PSW-GTR-165. U.S. Department of Agriculture, Forest Service,

Southern Research Station: 3-7.

Graham, J. H. 2001. What do root pathogens see in mycorrhizas? New Phytologist. 149: 357-359.

Greig, B. J. W. 1962. Fomes annosus (Fr.) Cke. and other root-rotting fungi in conifers on exhardwood sites. Forestry. 35(2): 164-182.

Hagle, S.; Byler, J.; Jeheber-Matthews, S.; Bath, R.; Stock, J.; Hansen, B.; Hubbard, C. 1994. Root

disease in the Coeur d’Alene River Basin: an assessment. In: Proceedings of Interior CedarHemlock White Pine Forests: Ecology and Management; 1993 March 2-4; Spokane Washington.

Pullman, WA: Washington Date University: 335-344.

Hagle, S.; Johnson, T. L.; Stipe, L. E.; Schwandt, J. W.; Byler, J. W.; Kegley, S. J.; Bell Randall, C. S.;

Taylor, J. E.; Lockman, I. B.; Sturdevant, N. J.; Williams, S. B.; Marsden, M. A.; Lewis, L. G.

2000. Succession function of forest pathogens and insects, Volume 1: Methods. FHP Report

No. 00-10. U.S. Department of Agriculture, Forest Service, Forest Health Protection, Northern

Region. 97 p.

Hagle, S. K.; Shaw, C. G. III.1991. Avoiding and reducing losses from Armillaria root disease. In:

Shaw, C. G. III; Kile, G. A., eds. Armillaria Root Disease. Agricultureal Handbook No. 691. U.S.

Department of Agriculture, Forest Service, Washington, DC: 157-173.

Harvey, A. E.; Jurgensen, M. F.; Larsen, M. J.; Schlieter, J. A. 1986. Distribution of active mycorrhizal

short roots in forest soils of the Inland Northwest: Effects of site and disturbance. Research paper

INT-374. U.S. Department of Agriculture, Forest Service, Intermountain Research Station. 8 p.

Harvey, A. E.; Jurgensen, M. F.; Larsen, M. J.; Graham, R. T. 1987. Decaying organic materials and

soil quality in the Inland Northwest: a management opportunity. Gen. Tech. Rep. INT-225. U.S.

Department of Agriculture, Forest Service, Intermountain Research Station. 15 p.

Volcanic Ash Soils: Sustainable Soil Management Practices, With Examples of Harvest Effects and Root Disease Trends Curran, Green, and Maynard
118 USDA Forest Service Proceedings RMRS-P-44. 2007

Heninger, R .L.; Terry, T.; Dobkowski, A.; Scott, W. 1997. Managing for sustainable site productivity: Weyerhaeuser’s forestry perspective. Biomass and Bioenergy. 13(4/5): 255-267.

Hessburg, P. F.; Goheen, D. J.; Koester, H. 2001. Association of black stain root disease with

roads, skid trails, and precommercial thinning in Southwest Oregon. Western Journal of Applied

Forestry. 16(3): 127-135.

Hickling, J. S. 1997. Some effects of forest floor displacement on soil properties and lodgepole

pine productivity in the Boundary Forest District. University of Vancouver, British Columbia.

Thesis.

Hickling, J. S. 1998. Effects of forest floor displacement on soil properties and seedling productivity

in the Boundary Forest District: Long-term productivity plots. Year two Establishment Report.

Prepared for Forest Renewal BC, Pope and Talbot Ltd., and BCMOF, Nelson Region. 35 p.

Holdenreider, O.; Greig, B. J. W. 1998. Biological methods of control. In: Woodward, S.; Stenlid,

J.; Karjalainen, R.; Hüttermann, A., eds. Heterobasidion annosum: Biology, Ecology, Impact and

Control. CAB International, Wallingford, Oxon, UK. Chapter 13.

Johansson, M.; Marklund, E. 1980. Antagonists of Fomes annosus in the rhizosphere of gray alder

(Alnus incana) and Norway spruce (Picea abies). European Journal of Forest Pathology. 10(80):

385-395.

Jones, J. 2004. Potential natural vegetation types for Idaho. Data on file at Nez Perce National

Forest headquarters.

Kliejunas, J. T.; Otrosina, W. J. 1997. Progress report: effects of subsoiling study, Milford Ranger

District, Plumas, National Forest. Report Number R97-01. U.S. Department of Agriculture, Forest

Service, Pacific Southwest Region. Forest Pest Management, State and Private Forestry. 10 p.

Kuennen, L.; Edson, G.; Tolle, T. V. 1979. Soil compaction due to timber harvesting activities. Soil,

Air, and Water Notes 79-3. U.S. Department of Agriculture, Forest Service, Northern Region.

Laing, L. E.; Howes, S. W. 1988. Detrimental soil compaction resulting from feller buncher and

rubber-tired skidder harvest operation: a case study. In: Degradation of forested lands: “Forest

soils at risk” Proc. 10th BC Soil Sci. Workshop; 1986 February; BC Min. Forests, Land Management Report 56: 191-195

Lewis, T., Carr, W. W.; Timber Harvesting Subcommittee. 1989. Developing timber harvesting

prescriptions to minimize site degradation - Interior sites. BC Min. Forests Land Management

Handbook - Field Guide Insert. BC Min. Forests Land Management Report No. 62.

McDaniel, P. A; Wilson, M. A.; Burt, R.; Lammers, D.; Thorson, T. D.; McGrath, C. L.; Peterson, N.

2005. Andic soils of the Inland Pacific Northwest, USA: properties and ecological significance.

Soil Science. 170: 300-311.

McDonald, G. I.; Harvey, A. E.; Tonn, J. R. 2000. Fire, competition and forest pests: landscape treatment to sustain ecosystem function. In: Neuenschwander, L. F.; Ryan, K. C.; Gollberg, G. E.; Greer,

J. D., eds. The Joint Fire Science Conference and Workshop, Vol. II. Boise, ID, USA: 195–211.

McKenzie, E.; Gedalof, A.; Peterson, D. L.; Mote, P. 2004. Climate change, wildfire, and conservation. Conservation Biology. 18(4): 890-902.

Montréal Process Working Group. 1997. First approximation report on the Montréal Process, 1997.

The Montréal Process Liaison Office, Canadian Forest Service, Ottawa, ON.

Moore, J. A.; Hamilton Jr., D. A.; Xiao, Y.; Bryne, J. 2004. Bedrock type significantly affects individual tree mortality for various conifers in the Inland Northwest, U.S.A. Canadian Journal of

Forest Research. 34: 31-42.

Morin, C.; Samson, J.; Dessureault, M. 1999. Protection of black spruce seedlings against Cylindrocladium root rot with Ectomycorrhizal fungi. Canadian Journal of Botany. 77: 169-174.

Morris, L. A.; Miller, R. E. 1994. Evidence for long-term productivity changes as provided by field

trials. p. 41-48 In: Dyck, W. J. and others, eds. Impacts of forest harvesting on long-term site

productivity. London: Chapman and Hall: 41-48.

Morrison, D. J.; Pellow, K. W.; Norris, D. J.; Nemec, A. F. L. 2000. Visible versus actual incidence

of Armillaria root disease in juvenile conifer stands in the southern interior of British Columbia.

Canadian Journal of Forest Research. 30: 405-414.

Mote, P. W.; Parson, E. A.; Hamlet, A. F.; Keeton, W. S.; Lettenmaier, D.; Mantua, N.; Miles, E. L.;

Peterson, D. W.; Peterson, D. L.; Slaughter, R.; Snover, A. K. 2003. Preparing for climate change:

the water, salmon, and forests of the Pacific Northwest. Climatic Change. 61: 45-88.

Nelson, E. E. 1964. Some probable relationships of soil fungi and zone lines in the survival of Poria 

weirii in buried wood blocks. Phytopathology. 54: 120-121.

Nelson, E. E. 1973. Observations on the formation of zone lines in wood by Poria weirii. Res. Note

PNW-210. Portland, OR: U.S. Department of Agriculture, Forest Service, Pacific Northwest

Forest and Range Experiment Station. 4 p.

Curran, Green, and Maynard Volcanic Ash Soils: Sustainable Soil Management Practices, With Examples of Harvest Effects and Root Disease Trends
USDA Forest Service Proceedings RMRS-P-44. 2007 119

Nelson, E .E.;Thies,W.G.1985.ColonizationofPhellinus weirii-infestedstumpsbyTrichoderma viride.

1: Effect of isolate and inoculum base. European Journal of Forest Pathology. 15: 425-431.

Nelson, E. E.; Thies, W. G. 1986. Colonization of Phellinus weirii-infested stumps by Trichoderma

viride. 2: Effects of season of inoculation and stage of wood decay. European Journal of Forest

Pathology. 16: 56-60.

Otrosina, W. J.; Sung, S.; White, L. M. 1996. Effects ofsubsoiling on lateral roots,sucrose metabolizing enzymes, and soil ergosterol in two Jeffrey pine stands. Tree Physiology. 16: 1009-1013.

Otrosina, W. J.; Garbelotto, M. 1997. Root disease and exotic ecosystems: implications for longterm site productivity. In: Proceedings of the 9th International Conference on Root and Butt

Rots of Forest Trees; 1997 September 1-7; Carcans-Maubuisson, France : Institut National de la

Recherche Agronomique: 275-283.

Partridge, A. D.; Miller, D. L. 1972. Bark beetles and root rots related in Idaho conifers. Plant

Disease Reporter. 58: 498-500.

Quesnel, H.J.; Curran, M.P. 2000. Shelterwood harvesting in root-disease infected stands - postharvest soil disturbance and compaction. Forest Ecology and Management: 62: 89-113.

Raziq, F. 2000. Biological and integrated control ofArmillaria rootrot. In: Fox, R. T.V., ed.Armillaria

root rot: Biology and control of honey fungus. Andover, Hants., UK: Intercept Ltd: 183-201.

Reaves, J. L; Shaw, C. G.; Roth, L. F. 1993. Infection of ponderosa pine trees by Armillaria ostoyae:

residual innoculum versus contagion. Northwest Science. 67: 156-162.

Rishbeth, J. 1951. Observations of the biology of Fomes annosus, with particular reference to

East Anglian pine plantations. II. Spore production, stump infection, and saprophytic activity

in stumps. Annals of Botany. 5(57): 14-21.

Roth, L. F.; Shaw III, C. G.; Rolph, L. 2000. Inoculum reduction measures to control Armillaria

root disease in a severely infested stand off ponderosa pine in south-central Washington: 20

year results. Western Journal of Applied Forestry. 15: 92-100.

Sachs, Don; Heineman, Jean; Mather, Jean;Curran, Mike; Simard, Suzanne. 2004. Expertsystem for

site preparation and vegetation management in southern Interior British Columbia. Model. Available: http://www.myacquire.com/spvegman/expertsystem/. Accessed November 17, 2005.

Schmitt, C. L.; Parmeter, J. R.; Kliejunas, J. T. 2000. Annosusroot disease of western conifers. Forest

Insect and Disease Leaflet 172. U.S. Department of Agriculture, Forest Service. 9 p.

Sharma, A. K.; Johri, B. N.; Gianinazzi, S. 1992. Vesicular-arbuscular mycorrhizae in relation to

plant disease. World Journal of Microbiology and Biotechnology. 8(6): 559-563.

Svalberg, T. 1979. Compaction study results, Preliminary draft. (Unpublished mimeo.) Libby,

Montanta: U.S. Department of Agriculture, Forest Service, Kootenai National Forest.

Utzig, G. F.; Thompson, S. R.; Curran, M. P. 1992. Soil compaction from random skidding in

southeastern British Columbia. Contract report to BCMOF, Nelson Forest Region. 45 p.

Veech. J .A.; Boyce Jr., J. S. 1964. Soil microorganisms in two Georgia slash pine plantations with

annosus root rot. Plant Disease Reporter. 48(11): 873-874.

Wass, E. F.; Senyk, J. P. 1999. Tree growth for 15 years following stumping in interior British Columbia. Technology Transfer Note 13, Nat. Res. Victoria, British Columbia, Canada: Can. For.

Serv., Pacific Forestry Center.

Wiensczyk, A. M.; Dumas, M. T.; Irwin, R. N. 1997. Predicting Armillaria ostoyae infection levels

in black spruce plantations as a function of environmental factors. Canadian Journal of Forest

Research. 27: 1630-1634.

Volcanic Ash Soils: Sustainable Soil Management Practices, With Examples of Harvest Effects and Root Disease Trends Curran, Green, and Maynard

USDA Forest Service Proceedings RMRS-P-44. 2007 121

In: Page-Dumroese, Deborah; Miller, Richard; Mital, Jim; McDaniel, Paul; Miller, Dan, tech. eds. 2007. 

Volcanic-Ash-­Derived Forest Soils of the Inland Northwest: Properties and Implications for Management 

and Restoration. 9-10 November 2005; Coeur d’Alene, ID. Proceedings RMRS-P-44; Fort Collins, CO: 

U.S. Department of Agriculture, Forest Service, Rocky Mountain Research Station.

Chuck Bulmer is a Soil Scientist, BC Ministry of Forests and Range, Vernon B.C. Mike Curran is a Soil 

Scientist, BC Ministry of Forests and Range, Nelson, B.C. Jim Archuleta is a District Soil Scientist, Diamond Lake District, Umpqua National Forest, Idleyld Park, OR.

Abstract

	 Soilrestoration (sometimestermed enhancement) is an importantstrategy forsustaining the productivity

of managed forest landscapes. Tephra-derived soils have unique physical and chemical characteristics

that affect their response to disturbance and restoration. A variety of factors reduce forest productivity

on degraded soils. Site-specific information on soil physical conditions, organic matter, and nutrient

status is required for efficient soil restoration, but only limited research is available to help interpret

such information and guide efforts to restore tephra-derived soils. Based on site-specific conditions,

reclamation treatments can be identified to control water, till compacted soils, restore organic matter,

and revegetate disturbed areas. Successful reclamation investments will often involve simple treatments

focusing on low cost options such as decompaction, topsoil replacement, fertilization, and tree planting. Avoiding difficult sites such those in high elevation environments, wet areas or fine textured soils

is recommended where possible, as treatments to overcome such problems are likely to be expensive

and have uncertain outcomes. Restoration efforts in volcanic terrain likely need to be accompanied

by programs to monitor the beneficial effects of treatments on forest productivity, in relation to their

costs.

Restoring and Enhancing Productivity of 

Degraded Tephra-Derived Soils

Chuck Bulmer, Jim Archuleta, Mike Curran

Introduction

	 Soil restoration (sometimes termed enhancement) is an important strategy for sustaining the

productivity of managed forested landscapes (Richardson and others 1999), and ecosystems

(Cairns 1999). Restoration techniques play a role as (a) planned activities for improving the

efficiency of accessing and harvesting timber while meeting soil conservation goals, or (b) a

means to repair unanticipated damage to soils caused by harvesting, or where previous management approaches have been superseded by strategies that reduce the need for soil disturbance,

and allow restoration of previously disturbed areas.

	 Tephra-derived soils have unique physical and chemical characteristics that affect their

response to disturbance and restoration. Volcanic materials have undeveloped crystalline

structure and weather rapidly in humid environments, producing soils that are characterized

by high water holding capacity (Moldrup and others 2003) and cation exchange capacity,
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Bulmer, Archuleta, and Curran Restoring and Enhancing Productivity of Degraded Tephra-derived Soils

the ability to stabilize soil organic matter, and high reactivity towards phosphate.

In the Pacific Northwest, mountainous topography leads to strong redistribution

of ash fall materials that were likely deposited in fairly uniform layers throughout

these landscapes. Strong environmental gradients also create diverse weathering

and pedogenic environments in Pacific Northwest forest soils. For these reasons,

the expression of andic soil characteristicsshows great variation within landscapes,

creating a wide range of conditions in tephra-affected soils, and a similar range

of responses to soil disturbance and subsequent restoration or enhancement

efforts.

In general, the goal of forest soil restoration is to recreate pre-disturbance

growing conditions, so that tree growth rates on the reclaimed soil will approximate those of trees on undisturbed soils on similar sites. Effective soil restoration

employs techniques that alleviate growth-limiting conditions on sites that have

suffered degrading soil disturbance. Degraded soils are defined here as soils that

have experienced disturbance leading to a loss in productivity. Forest productivity on degraded soils can be reduced by compaction that causes plant roots to

experience limiting conditions of soil mechanical resistance, water availability,

and aeration. Removal of surface soil layers may cause similar effects because

organic matter may be depleted from the site, or because unproductive subsoil

materials may be exposed. Degraded soils may also be more susceptible to erosion

which can cause further loss of nutrients and organic matter that are essential for

maintaining site productivity. Erosion can also cause serious off-site consequences

for aquatic and terrestrial systems.

Site-specific information on soil physical conditions, organic matter, and nutrient status is required for efficient soil restoration, but only limited research is

available to help interpret such information and guide efforts to restore degraded

soils derived from tephra.

Restoration techniques aimed at controlling erosion include (a) those aimed at

stabilizing soils such as slope recontouring, (b) those aimed at managing water

such as ditching or outsloping and (c) those aimed at preventing soil detachment

such as revegetation. For compacted soils, tillage is often required to restore

conditions conducive for productive root growth. Restoration of organic matter,

where appropriate, may be accomplished through replacing displaced topsoil

materials, by mulching with organic materials such as logging debris, or through

the soil building action of seeded cover crops.

This manuscript outlines the role of soil restoration in maintaining the productivity of managed forest landscapes, reviews the principles that govern how the

unique characteristics of tephra-derived soils affectrestoration planning in volcanic

terrain, discusses how information available from elsewhere appliesto reclamation

techniques in volcanic terrain of the Pacific Northwest, and provides management

recommendations to guide restoration and enhancement efforts.

Soil Restoration to Conserve and Enhance Productivity in Forested 

Landscapes _____________________________________________________

Minimizing degrading soil disturbance (Page-Dumroese and others 2000) is an

important first step to ensure that soils are maintained in a productive condition,

and that forest management is sustainable. Throughout North America, regulatory systems are in place for preventing soil degradation during forest harvesting,
USDA Forest Service Proceedings RMRS-P-44. 2007 123

Restoring and Enhancing Productivity of Degraded Tephra-derived Soils Bulmer, Archuleta, and Curran

access development, and other management activities (Powers and others 1998;

USDA Forest Service Standards and Guidelines 2521.1 and 2521.2; CCFM 2002;

BC Ministry of Forests 2001). These systems generally specify site specific limits

for defined forms of degrading soil disturbance, and may also provide incentives

for restoring soils that have been degraded by forest management activities.

In British Columbia, soil conservation policy allows more soil disturbance on

sites with low sensitivity to soil-degrading processes(BC Ministry of Forests 2001).

In the northwestern United States, higher intensity of soil compaction (i.e. 20%

increase in bulk density) is considered acceptable on volcanic-ash derived soils

(Powers and others 1998), compared to those developed on other parent materials

(maximum 15% increase). These differencesrecognize that many undisturbed tephraderived soils have low bulk density, but may also imply that they are less sensitive

than other soils to modest changes in density. Tephra-derived soils may also respond

differently than others to reclamation treatments.

Restoring degraded soils improves forest productivity. On access structures that

are no longer needed,restoration and reforestation increasesthe land base available

for growing trees, and can thereby increase future timber supplies. On areas that

have suffered degrading soil disturbance, restoration can improve establishment

success and productivity of planted trees compared to areas where soils are left

in a degraded state. Achieving full benefit from soil restoration practices depends

on the development of cost-effective reclamation techniques, and their application to sites where the cost of reclamation will be offset by improved productivity

from the reclaimed lands (Richardson and others 1999).

Reclamation work should be subjected to cost benefit analysis the same as

any other management activity. Such an approach avoids wrongly thinking of

rehabilitation as an intrinsically good activity, where the true costs of reclamation

work can be discounted or ignored. Costs of restoration work include dollar costs,

diversion ofscarce resourcesfrom other activities, consumption of fossil fuels, and

risk to workers or property, along with potential negative consequences which

may not be anticipated such as water diversion, erosion, slope failure, and weed

infestation. At the same time, the potential benefits of reclamation work may also

be understated if the analysis is restricted traditional economic measures (dollar

costs only), or if inappropriate discount rates are applied to timber production.

The social and environmental benefits of carrying out reclamation activities may

have been neglected in the past, but recent evaluations have shown the important

role that healthy ecosystems play in maintaining economies and societies (Hillel

1991). Such considerations are likely to become even more important as globalization and population growth exert increased pressure on natural environments

all over the world.

In general, given the almost universal scarcity of resources, the uncertainty of

cost benefit analyses, and the risks associated with undertaking any activity that

imposes significant disturbance to a natural system, a prudent approach would

focus reclamation efforts on sites where simple techniques have been shown to

have success. Treatment of high risk sites and use of expensive or exotic treatments

are likely best left to special situations where potential values are high, social

factors warrant, or where such efforts are treated as an operational trial or where

detailed monitoring will improve our overall understanding of rehabilitation and

its role in forest management.
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Bulmer, Archuleta, and Curran Restoring and Enhancing Productivity of Degraded Tephra-derived Soils

Characteristics of Tephra-Derived Soils as They Affect Growth-Limiting 

Conditions and Restoration Efforts ________________________________

Variation in soil properties and growth-limiting factors in tephra-derived soils

arise from (a) ecological characteristics of the site associated with climate, topography, parent materials, and vegetation, (b) chemical and physical characteristics

of the tephra as it was deposited, and (c) redistribution and alteration of tephra

in the landscape in response to topography, moisture etc.

Strategies for reclaiming soils without tephra influence have been developed

in the Pacific Northwest and elsewhere, and specify different approaches for a

range of soils in diverse geographic settings. The applicability of these to tephraderived soils depends on the differences in soil properties brought about by the

presence of tephra. Some questions to consider include:

	 •	 Have natural depositions of tephra led to improved soil fertility by providing

a supply of readily available inorganic nutrients?

	 •	 What is the weathering state of the tephra? Tephra materials weather rapidly

in humid surface environments, but in the Pacific Northwest there are many

examples of relatively unweathered materials either because of dry climates

or short duration of weathering since deposition.

	 •	 What is the particle size of the tephra materials? In the Pacific Northwest,

variation in physical and chemical properties as they affect plant growth

primarily results from particle size effects (including distance from the

source) and post depositional alteration including organic matter retention

and weathering.

	 •	 For a given particle size, tephra-derived soils tend to have physical characteristics (i.e. water holding capacity; specific surface; organic matter retention) that reflect those of other soil materials with finer texture (i.e. sandy

tephra materials may behave more like loams derived from other parent

materials).

Morphological Characteristics of Tephra-Derived Soils

Tephra-derived soils include those where minor amounts of tephra were deposited to soil, but are no longer discernable as a distinct layer. In other soils, a

distinct layer of tephra is present as an “ash-cap’ of varying depth (fig. 1). Finally,

some soils may be exclusively derived from volcanic materials to the depth of

rooting, with little or no influence from other parent materials on the vegetation.

Many soils will display intermediate characteristics to these idealized categories,

especially where tephra layers become intermixed with subsoils during construction and use of access structures. Depending on the proportion of tephra, and

characteristics such as particle size, special considerations may or may not be

needed when developing reclamation strategies.

Physical Characteristics of Tephra-Derived Soils

The presence of weathering products with highly reactive surfaces lead to

the common characteristics noted for weathered volcanic materials, including

high water retention, organic matter stabilization, and well developed aggregate

structure. The characteristics are inter-related as organic matter is partly stabilized

because of the surface reactivity, while the presence of organic matter results in
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Restoring and Enhancing Productivity of Degraded Tephra-derived Soils Bulmer, Archuleta, and Curran

additional reactive surfaces. The expression of Andic characteristics depends on

the degree of weathering of the material.

A key characteristic affecting reclamation is the low bulk density observed in

many tephra-derived soils, owing in part to their low particle density but also to

the tendency to develop well aggregated structures. Miller and others (1996) found

that even after a substantial increase in bulk density of ash derived soils in central

Washington, the bulk density was still less than 1000 kg m–3. For this reason,

threshold values for growth-limiting conditions need to be determined specifically

for ash derived soils, rather than using values derived for other soils.

Figure 1—Ash cap overlying ultramafic soil material in the Shulaps Range: interior 

British Columbia.
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Bulmer, Archuleta, and Curran Restoring and Enhancing Productivity of Degraded Tephra-derived Soils

Relationships between soil texture and management impactsreflect the variable

effects of ash characteristics and soil environments. For example, poorly crystalline

weathering products act as a cement to create very stable aggregates in Andisols

that occupy wet sites. Also, the weathering products of volcanic parent materials

have high surface area compared to the clay minerals found in most other soils

(Moldrup and others 2003). In addition, tephra particles often consist of porous and

fragile materials, so coarse-grained tephra soils are often less resistant to fracture

compared to non-tephra soils, and particle size distribution may shift towardsfiner

size fractions following mechanical disturbance (Sahaphol and Miura 2005).

Tephra-derived soils retain large amounts of water compared to soils derived

from other parent materials. Conversely, they are also subject to changes upon

drying, which can include the development of water repellency (Poulenard and

others 2004) and irreversible structural collapse (Poulenard and others 2003)

which is most likely for soils formed in wet environments (Shoji and others 1996).

In considering the impact of this characteristic on disturbance and reclamation,

the high water retention may lead to a soil with low bearing strength, and high

susceptibility to rutting when wet. It may also make tillage operations difficult

when soils are moist. Despite this, the materials are expected to provide a good

growing medium for plant roots, especially on mesic sites.

Unweathered tephra materials are often non-cohesive and prone to erosion

by wind and water (Basher and Painter 1997; Arnalds and Kimble 2001), and this

susceptibility may last for some time in unvegetated areas. For this reason, planning should consider measures for rapid revegetation of exposed tephra materials

resulting from disturbance and reclamation. Tephra-derived materials with coarse

particle sizes have also been used as a water conserving mulch (Tejedor and others

2002, 2003). This characteristic may also present challenges when considering

the seedbed characteristics of coarse-textured tephra soils.

The unique physical conditions provide both challenges and opportunities,

and both need to be considered when planning restoration treatments for tephraderived soils.

Chemical Characteristics of Tephra-Derived Soils

The chemical characteristics of tephra vary depending on the geologic environment, and these characteristics are inherited by the soils derived from volcanic

materials. In general, the composition of tephra materials in the Pacific Northwest

are similar to those of rhyolite, which is expected to provide adequate supplies of

mineral-bound plant available nutrients in unweathered or moderately weathered

soils. The weathering products of volcanic ash have a high affinity for organic

matter, and this characteristic accounts for many of the unique properties, including high cation exchange capacity, and high availability of organically bound

plant nutrients. Anion exchange capacity derives from the creation of poorly

crystalline oxides of Fe and Al, and also from short range order aluminosilicates

like allophane. The anion exchange capacity accounts for the high reactivity of

tephra-derived soils to phosphate. Despite these features, recent tephra deposits

which characterize much of the Pacific Northwest may have similar fertility to

other parent materials (McDaniel, this proceedings).

The presence of large amounts of organic matter in weathered ash deposits is

expected to lead to soil materialsthat are resilient to disturbance, but unweathered

materials in cold or dry environments, may have low levels of organic matter.
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Restoring and Enhancing Productivity of Degraded Tephra-derived Soils Bulmer, Archuleta, and Curran

Reclamation planning should consider the need for organic matter and nutrient

additionsin consideration ofsoil conditions and forest productivity in undisturbed

soils on similar site types in the area.

Planning Considerations for Restoring and Enhancing 

Productivity of Tephra-Derived Soils

The unique chemical and physical characteristics of soils derived from tephra

play an important role in determining what treatments should be considered for

rehabilitating or enhancing a degraded soil. To develop the most appropriate

restoration approach, the following general questions need to be answered by

collecting field information:

	 1.	 Is the soil degraded to the point that forest productivity or other values are

likely to be significantly affected?

	 2.	 What growth-limiting conditions (e.g. compaction, organic matter loss) or

other issuessuch as erosion,sediment delivery to streams, or visual concerns

are present that require amelioration?

	 3.	 Are there site conditions or otherfactors(e.g. culturalresources) that preclude

or favor the use of one rehabilitation technique or combination of treatments

over another for addressing the growth limiting factor(s)?

	 4.	 Are proven treatments likely to increase site productivity to an extent where

the associated costs will be returned?

Several research efforts in northwestern North America and elsewhere have

recently focused on evaluating the effectiveness of commonly used soil rehabilitation techniques.Although research specifically addressing degraded tephra-derived

soils in the Pacific Northwest is limited, the principles governing the success or

failure of such work are expected to be similar to those from elsewhere, and on

different soil types.

For tephra-influenced soils in coastal Washington, Miller and others (1996) observed that trees on compacted skid trails were growing at the same rate as trees

in undisturbed soils and trails where soils were decompacted. They concluded that

site specific factors determined the response to soil disturbance and rehabilitation.

Where climatic factors were favorable, and soil properties of compacted soils

remained within thresholds for growth limiting factors, productive forests could

develop on disturbed soils. For the tephra-influenced soils studied by Miller and

others(1996), despite a 50 percent increase in bulk density after harvest and values

of bulk density that were 20 percent higher after 8 years, the disturbed soils still

had bulk density below 1000 kg m–3. Partly because of the results, the authors

concluded that the relationship between pre-disturbance and post-­disturbance

bulk density, which has been used as an indicator of soil degradation in the United

States, was not a good predictor of productivity effects.

The complex processes affecting seedling response to disturbance and rehabilitationwere furtherillustratedby resultsfrom PriestRiver, Idaho,where soil compaction

effects on tree root growth were studied on a soil derived from Mazama tephra.

Douglas-fir and western white pine seedlings growing in compacted soils for one

year had fewer nonmycorrhizal root tips compared to soils without compaction

(Amaranthus and others 1996). Ectomycorrhizal root tip abundance and diversity

was reduced by compaction for Douglas-fir, but not western white pine. Despite

these results, seedling growth response was not significantly affected. Thus the
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Bulmer, Archuleta, and Curran Restoring and Enhancing Productivity of Degraded Tephra-derived Soils

initial response to compaction, and the need for rehabilitation treatments, not

only varies for different soil and disturbance types, but also may depend on the

tree species under management.

Recent results in British Columbia on a range of soil types and climatic conditions have shown that relatively simple rehabilitation treatments such as subsoiling followed by planting with lodgepole pine often produce well-stocked new

forests (Plotnikoff and others 2002; Bulmer and Krzic 2003), but on wet sites,

fine-textured soils, or where topsoil retrieval and replacement were not carried

out, growth rates may lag those of undisturbed areas of adjacent plantations.

Lodgepole pine is often planted on rehabilitated sites in British Columbia owing

to high survival rates and rapid early growth. In contrast to the previous results,

soil decompaction without tree planting led to unsatisfactory stocking on 100

sites in BC’s southern interior (Bulmer and Staffeldt 2004), indicating that natural

regeneration should only be relied on as a reforestation strategy after carefully

evaluating the availability of a seed source.

These research studies show that it is difficult to generalize when predicting the

response to disturbance and rehabilitation. Site-specific information is essential for

determining which research efforts and conclusions apply to a particular site, and

therefore which course of action is likely to be most successful and cost-effective.

The following critical site factors can affect the response to soil disturbance and

rehabilitation on a particular site:

	 •	 Climatic conditions such as temperature and annual water deficit affect

the rooting characteristics of trees, and the extent to which they are limited

by moisture availability, cold temperatures, short growing season, or other

factors.

	 •	 Slope characteristics and surface drainage patterns affect the potential for

erosion or slope failure that could affect resources on and off the site.

	 •	 Soil texture and tephra influence affect the response of the soil to the

disturbance and subsequent rehabilitation treatments because fine textured materials have low strength when wet and are highly susceptible to

compaction, while the pore system in coarse-textured materials is generally

resistant to compaction, and less likely to suffer soil degradation associated

with machine traffic.

	 •	 Moisture regime strongly affects the tree growth limiting factors, and the

likelihood of realizing suitable conditions for tillage equipment. Wet sites in

particular often sufferincreased soil disturbance because of low soilstrength,

and restoration efforts face challenges because of poor soil structure resulting from tillage of wet soils.

	 •	 Presence of unfavorable subsoils and the extent to which surface soil displacement has exposed them or may force plant roots to grow in them.

	 •	 Rooting depth in undisturbed soils, potential rooting depth on the disturbed

site, and the depth of soil disturbance affect the response of trees.

The expected loss of forest productivity if the site was left alone needs to be

balanced against the benefits of intervention to improve conditions on the site. In

cases where the expected benefits are small, no treatment would be indicated, and

planted trees could simply be monitored to evaluate the need for fertilizer inputs

or other activities to maintain growth rates at desirable levels. In such cases, site
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Restoring and Enhancing Productivity of Degraded Tephra-derived Soils Bulmer, Archuleta, and Curran

productivity may be slightly lowerthan ifsoil disturbance had not occurred, but the

loss in productivity may be small compared to cost of restoration treatments.

In summary, reclamation treatments will likely deliver the most benefit when:

•	 Climatic and other site conditions favour productive tree growth

	 •	 Severe soil disturbance will likely prevent seedling establishment and significantly reduce growth without intervention

	 •	 Proven and relatively inexpensive treatments such as decompaction, topsoil

replacement, and revegetation are applied to mesic sites with medium and

coarse textured soils

	 •	 Difficult sites, wet areas and fine-textured soils are avoided, as treatments

to overcome these challenges are expensive and benefits unproven.

Restoration Treatments and Unique Aspects of Their Application to 

Tephra-Derived Soil______________________________________________

Where soil disturbance is likely to reduce tree growth to an unsatisfactory

degree, and treatments are indicated, a basic approach to rehabilitation would

involve attempting to create site conditions approximating those of undisturbed

soils on similar sites in the area, even though this may not always be possible

(e.g. where surface soils have been displaced and their retrieval is not feasible).

The conditions on undisturbed sites likely reflect what is conducive to productive forest growth in the area. To develop a cost effective plan for implementing

reclamation treatments, there is a need to consider:

	 •	 The extent to which conditions on the site are expected to exceed thresholds of growth limiting factors such as aeration porosity, soil mechanical

resistance, water availability, and nutrient content.

	 •	 Availability of displaced surface soil that could be retrieved and nature of

surface soils in nearby undisturbed soils on similar sites

	 •	 Stones, stumps or other factors that may affect the operation of equipment

	 •	 Presence of existing vegetation, and likely seed sources for preferred crop

trees and other species to be re-established on the site

	 •	 Expected wildlife or cattle use that may affect the success of reforestation

or revegetation efforts

Based on site-specific conditions, reclamation treatments can be identified to

address each of four objectives.

Managing Water and Preventing Erosion

Water management and erosion control is the first step in reclamation planning.

Without a stable substrate that is free of erosion, the beneficial effects of restoration

treatments could be destroyed by removal of organic rich surface soil layers, or by

exposure of lessfertile subsoils. In addition, the high costs of potential off-site effects

on water quality, fish, and property require that water and erosion control is given

highest priority. Site water management is also essential for correcting detrimental

effects of soil disturbance on the soil drainage class and moisture regime.

Water management may be as simple as building a ditch to divert surface

water away from a road or landing, or could involve more expensive options

such as slope recontouring designed with internal drainage to restore the flow of

subsurface water.
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Bulmer, Archuleta, and Curran Restoring and Enhancing Productivity of Degraded Tephra-derived Soils

Erodibility may be related to poor cohesion of recently deposited tephra materials, high water retention, and low internal strength of deposits. These factors

may be offset by high porosity. The characteristics of the subsoils and other site

attributes need to be considered before selecting treatments.

Localized erosion was observed in Diamond Lake District, Umpqua National

Forest, when surface water flow patterns were disturbed by compaction of deep

pumice soils, routing water to the edge of the unit. Routed water affected residual

topsoil left post-harvest, and, where compaction endures for long periods, water

routing and erosion would continue into the future without tillage.

Treatments to control erosion include:

	 •	 outsloping decompaction

	 •	 slope recontouring

	 •	 diverting / managing surface water

	 •	 revegetation

Where water management, erosion, slope stability issues do not pose severe

restrictions, the next step is to proceed with efforts to restore site productivity.

Tillage to Restore Soil Physical Conditions

For compacted soils with high soil strength or those that have suffered deterioration of the pore system, restoring soil physical conditions is an essential part of

reclamation. Compaction affects the pore system mostly by reducing the number

of large pores. This leads to increased water retention and reduced infiltration,

and may lead to soils with insufficient air for plant roots.

There are reasons to believe that trees growing in some soils rich in volcanic

ash may respond differently to compaction than for other parent materials. The

highly developed aggregate structure of weathered and developed soils derived

from volcanic materials in other areas has been well documented, suggesting that

stable aggregates in such soils may survive the compaction process, and provide

stability for large pores. For the Pacific Northwest, recent tephra deposits likely

have relatively stable macrostructure where particle strength is high enough to

resist particle breakage. On mesic and dry sites, these characteristics may lead to

a soil that is able to withstand compaction and still provide a productive environment for plant roots, and/or one that is able to naturally regenerate soil conditions

suitable for productive forest growth following disturbance. Despite this, some

specific challenges could include:

	 •	 Water retention: On wetter sites, the high water retentivity of tephra soils

may lead to similar problems as identified for fine-textured soils, and could

be especially problematic in low-lying landscape positions. The major

problems would include excessive soil water, and lack of aeration.

	 •	 Particle breakage: Some volcanic materials are susceptible to particle breakage when disturbed, which increases the proportion of fines in the particle

size distribution. Particle breakage may be a factor in poor performance of

regeneration on some sites in Oregon.

	 •	 Irreversible drying: Cementation may lead to massive structure with high

soil strengths that plant roots are incapable of penetrating. Although this

phenomenon is not expected to be widespread in the Pacific Northwest, it
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Restoring and Enhancing Productivity of Degraded Tephra-derived Soils Bulmer, Archuleta, and Curran

could affect results in low lying landscape positions with weathered soils

and where soilstructure has been destroyed (puddling) by repeated machine

traffic, and where sites are subject to occasional drying in summer.

Where tillage isrequired, a variety of implements are available, includingwinged

subsoilers, rock ripper, excavators with brush rakes, mulching heads, or custom

attachments such as the subsoiling grapple rake and subsoiling excavating bucket.

The best implement for the job likely depends on factors such as required depth,

soil strength, water status, and logistics (e.g. availability of prime movers).

An example of an implement that was purpose-built for decompacting soils in

volcanic terrain is the subsoiling grapple rake, which was developed and used

in the Diamond Lake Ranger District, Umpqua National Forest (Archuleta and

Karr 2004). This implement is a grapple rake fitted with subsoiling shanks and

wings. It was designed to mitigate either legacy compaction or newly created

harvest impacts, and is best employed when used in concert with an ongoing

activity, such as post-harvest slash reduction. At Diamond Lake, the combination

of these activities reduced the overall cost of individual projects with a minor

increase to either slash piling or subsoiling costs. The subsoiling excavator bucket

is another implement that is also equipped with shanks, and allows cost-effective decommissioning of roads. This implement also reduces the subsoiling rate

on small tillage projects and makes additional equipment (i.e. dozer and tillage

implement) redundant.

Tillage is aimed at alleviating the effects of detrimental compaction, which

include increases in soil strength, reduced aeration, and excessive water retention. Although the effectiveness of tillage has been questioned on fine-textured

soils in central Alberta where subsoils stayed wet and soft for long periods during

the year (McNabb 1994), such issues may be less of a concern in fine-textured

tephra-derived soils in the Pacific Northwest because of (a) the strong aggregation expected in fine-textured soils derived from volcanic materials, and (b) dryer

climates. For relatively fresh volcanic parent materials, particle sizes may be coarse

and water infiltration and aeration may not be limiting.

In summary, for successful tillage, consider:

	 •	 tillage is used to reduce soil strength and restore the pore system,

	 •	 a variety of implements are available,

	 •	 use the rooting depth in natural forests on similar sites as a guide to tillage

depth

	 •	 for dispersed disturbance, and to reduce costs, consider spot tillage

	 •	 the effects of tilling wet volcanic soils, which may be subject to irreversible

drying or consolidation, need to be evaluated through monitoring

Restoring Organic Matter and Nutrients

In general, the most effective means of restoring surface soil organic matter

is to retrieve and replace displaced topsoil. In situations where recovery of displaced surface soil is not practical, other potential strategies include distributing

green logging slash from harvesting operations over the reclaimed area. In central

BC, chipped waste logs enhanced soil properties and contributed to successful

establishment and early growth of white spruce seedlings (Sanborn and others

2004). Despite their benefits, organic amendments are generally only suitable if

they are locally available, as they are expensive to transport.
132 USDA Forest Service Proceedings RMRS-P-44. 2007

Bulmer, Archuleta, and Curran Restoring and Enhancing Productivity of Degraded Tephra-derived Soils

Since tephra derived materials are known to have a high affinity for soil organic matter, a cost-effective alternative could involve revegetation with grasses

and legumes that can build soil organic matter through decomposition of their

root systems. In one study (not an ash soil), Bendfeldt and others (2001) showed

that vegetation inputs of C were an important source of surface soil organic matter levels after sixteen years on reclaimed mine soil that also received an initial

amendment with wood waste.

In summary, to restore organic matter and nutrients, consider:

	 •	 Organic matter is an essential component of productive soil, but forest

ecosystems vary in the amount present in surface soils.

	 •	 Retrieval of displaced topsoil is a cost effective approach for restoring suitable growing conditions.

	 •	 Use the characteristics of surface soils on similar sites as a guide to what

surface soil organic matter levels are appropriate, and its distribution as a

surface layer or incorporated into surface soils.

	 •	 Revegetation with agronomic grasses and legumes can contribute significant

quantities of organic matter over time.

	 •	 Organic amendments can effectively restore soil conditions, but are expensive to transport.

Revegetation

Successful revegetation and reforestation of disturbed areas is an important

final step in reclamation efforts. In many cases, the objective for the reclamation

is defined by the type of vegetation cover desired. For example, grass and legume

cover may be prescribed to prevent erosion, forest restoration provides for timber,

or other values may have priority such as wildlife, watershed values, and aesthetics.

Tree planting is the most common and effective means to establish a new forest,

but natural regeneration could be effective if a seed source and suitable seedbed

conditions were present.

For successful and cost-effective revegetation, consider

	 •	 Revegetation is essential for erosion control in sloping terrain.

	 •	 Seeding agronomic grasses and legumes are proven means to prevent

erosion.

	 •	 Seedbed characteristics are often best immediately after tillage operations

are complete.

	 •	 Droughtiness; may hamper revegetation efforts in coarse-textured tephras

where low water retention results in a lack of seedbed moisture. Seeding

treatments in such soils would have to be considered carefully, and consider

the timing in relation to expected precipitation, along with the possible need

for mulches to conserve moisture.

	 •	 Ingress of native vegetation may occur without intervention where disturbances are small (e.g. roads and trails).

	 •	 Natural regeneration of tree seedlings may be a low cost alternative to

planting where a seed source is available and slightly longer regen delay is

acceptable.
USDA Forest Service Proceedings RMRS-P-44. 2007 133

Restoring and Enhancing Productivity of Degraded Tephra-derived Soils Bulmer, Archuleta, and Curran

Information and Research Needs _________________________________

The published information base is limited and provides few specific examples

of the effects of soil disturbance, enhancement and restoration on forest site productivity in volcanic terrain in western North America. The lack of information

partly reflects the difficulty and expense in designing and implementing studies

that are relevant to the wide range of site types, soil conditions, and tree species

that occur in the region. Despite this, there is considerable information on soil

disturbance and restoration effectsfor othersoil typesin similar climates and much

of this information can likely be extrapolated to volcanic soils in the Northwest.

In addition, soil scientists and forest managers in the region have considerable

experience with how the soils respond to management.

To address the lack of specific published information, a useful approach would

be to combine existing research from elsewhere with local knowledge of the soils

response to management through retrospective study, monitoring, and operational

trials. Although these approaches have their limitations for resolving detailed questions, they are extremely useful for answering the broad questions that arise during

the initial stages of a detailed research program. Specific questions to be addressed

(and suggested approach to study) include:

	 •	 Identifying sites mostsusceptible to degradation, and those where restoration

or enhancement provide the greatest benefit (monitoring and retrospective 

study)

	 •	 Evaluating a range of treatment options for restoring and enhancing productivity (monitoring results and operational trials)

	 •	 Characterizing the effect of typical operations on soil properties such as

bulk density, penetration resistance, and organic matter (research)

	 •	 Determining thresholds for unacceptable productivity decline on the most

common site types (research)

Management Recommendations _________________________________

1. Evaluate costs and benefits: Soil restoration and enhancement should be

considered investments where the expected benefits, costs and risks are carefully

evaluated. In general, it is best to focus efforts on sites with the best expected

return on restoration dollars, and use low cost, reliable methods for restoration.

The benefits of restoration and enhancement efforts typically include:

	 •	 increased timber supply,

	 •	 reduced environmental liability associated with roads,

	 •	 improved watershed, wildlife, and aesthetic values.

2. Have a site-specific plan: Evaluate limitations to productivity, risk of erosion, and other site specific factors, and then set realistic objectives for the work.

Where legacy impacts are present, combination machines such as the subsoiling

grapple rake and subsoiling excavator bucket may allow restoration to be blended

into other work such as brush piling or road decommissioning.

3. Start simple (and cheap): Try the simple solution first. Consider treatments

in the following order:

	 •	 do nothing (i.e. rely on natural regeneration to recolonize lightly disturbed

areas)
134 USDA Forest Service Proceedings RMRS-P-44. 2007

Bulmer, Archuleta, and Curran Restoring and Enhancing Productivity of Degraded Tephra-derived Soils

	 •	 tree planting

	 •	 fertilization

	 •	 decompaction / tillage plus topsoil recovery

	 •	 organic amendments

	 •	 re-establishing native species by planting

4. Keep learning: Monitor the results of your efforts and those of others.

Acknowledgments ______________________________________________

Research described here was supported by British Columbia’s Forest Science

Program and other funding sources. Umpqua National Forest supported work

of J. Archuleta. Mike Karr provided work on the subsoiling equipment on the

Umpqua National Forest.

References______________________________________________________

Amaranthus, M. P.; Page-Dumroese, D.; Harvey, A.; Cazares, E.; Bednar, L. F. 1996. Soil compaction and organic matter affect conifer seedling nonmycorrhizal and ectomycorrhizal root tip

abundance and diversity. PNW-RP-494. Portland, OR: U.S. Department of Agriculture, Forest

Service, Pacific North West Station. 12 p.

Archuleta, J. G.; Karr, M. 2004. Multipurpose subsoiling excavator attachments. Tech. Tip. San

Dimas technology development Center. U.S. Department of Agriculture, Forest service.

Arnalds, O.; Kimble, J. 2001. Andisols of deserts in Iceland. Soil Sci. Soc. Am. J. 65: 1778-1786.

Basher, L. R.; Painter, D. J. 1997. Wind erosion in New Zealand. In: Proceedings of the International Symposium on Wind Erosion; 1997 June 3-5; Manhattan, Kansas: U.S. Department of

Agriculture, ARS: 1-10.

Bendfeldt, E. A.; Burger, J. A.; Daniels, W. L. 2001. Quality of amended mine soil after sixteen

years. Soil Sci. Soc. Am. J. 65: 1736-1744.

British Columbia Ministry of Forests. 2001. Soil conservation guidebook. BC Min. For. Victoria.

Available: http://www.for.gov.bc.ca/tasb/legsregs/fpc/fpcguide/soil/soil-toc.htm. Accessed

October 2005.

Bulmer, C. E.; Krzic, M. 2003. Soil properties and lodgepole pine growth on rehabilitated landings

in northeastern British Columbia. Can. J. Soil Sci. 83: 465-474.

Bulmer, C. E.; Staffeldt, P. 2004. Salmon Arm landing rehabilitation monitoring report. Unpublished

technical report available from the author.

Cairns, J. Jr. 1999. Ecological restoration: A major component of sustainable use of the planet.

Renewable Resources Journal: 7-11.

Canadian Council of Forest Ministers. 2002. Technical working group draft recommendations

for improved CCFM indicators for sustainable forest management draft compiled by the C&I

secretariat October 2, 2002. TWG Chairs meeting; 2002 October 9 – 11; Edmonton, Alberta.

CCCFM Secretariat 8th Floor, 580 Booth Street Ottawa.

Hillel, D. 1991. Out of the earth. Berkeley, CA: University of California Press. 322 p.

McNabb, D. H. 1994. Tillage of compacted haul roads and landings in the boreal forests of Alberta,

Canada. For. Ecol. Mgmt. 66: 179-194.

Miller, R. E.; Scott, W.; Hazard, J. W. 1996. Soil compaction and conifer growth after tractor yarding at three coastal Washington locations. Can. J. For Res. 26: 225-236.

Moldrup, P.; Yoshikawa, S.; Olesen, T.; Komatsu, T.; Rolston, D. E. 2003. Gas Diffusivity in Undisturbed Volcanic Ash Soils: Test of Soil-Water-Characteristic-Based Prediction Models. Soil

Sci. Soc. Am. J. 67: 41–51.

Page-Dumrose, D.; Jurgensen, M.; Elliot, W.; Rice, T.; Nesser, J.; Collins, T.; Meurisse, R. 2000.

Soil quality standards and guidelines for forest sustainability in northwestern North America.

For. Ecol. Manage. 138: 445-462.

Plotnikoff, M. R.; Bulmer, C. E.; Schmidt, M. G. 2002. Soil properties and tree growth on rehabilitated forest landings in the interior cedar hemlock biogeoclimatic zone: British Columbia.

For. Ecol. Mgmt. 170: 199-215.
USDA Forest Service Proceedings RMRS-P-44. 2007 135

Restoring and Enhancing Productivity of Degraded Tephra-derived Soils Bulmer, Archuleta, and Curran

Poulenard, J.; Podwojewski, P.; Herbillona, A. 2003. Characteristics of non-allophanic Andisols

with hydric properties from the Ecuadorian paramos. Geoderma. 117: 267–281.

Poulenard, J.; Michel, J. C.; Bartoli, F.; Portal, J. M. 2004. Water repellency of volcanic ash soils

from Ecuadorian paramos: effect of water content and characteristics of hydrophobic organic

matter. European Journal of Soil Science. 55: 487–496.

Powers, R. F.; Tiarks, A. E.; Boyle, J. R. 1998. Assessing soil quality: Practicable standards for

sustainable forest productivity in the United States. In: The contribution of soil science to the

development of and implementation of criteria and indicators of sustainable forest management.

Soil. Sci. Soc. Am. Spec. Pub. no. 53. Madison, WI: Soil Science Society of America: 53-79.

Richardson, B.; Skinner, M. F.; West, G. 1999. The role of forest productivity in defining the sustainability of plantation forests in new Zealand. For. Ecol. Manage. 122: 125-137.

Sahaphol, T.; Miura, S. 2005. Shear moduli of volcanic soils. Soil Dyn. Earth. Eng. 25: 157-165.

Sanborn, P.; Bulmer, C.; Coopersmith, D. 2004. Use of wood waste in rehabilitation of landings

constructed on fine-textured soils, central interior British Columbia, Canada. West. J. Appl.

For. 19: 175–183.

Shoji, S.; Nanzyo, M.; Dahlgren, R. A.; Quantin, P. 1996. Evaluation and proposed revisions of

criteria for Andosols in the world reference base for soil resources. Soil Sci. 161: 604-615.

Tejedor, M.; Jimenez, C. C.; Dıaz, F. 2002. Soil Moisture Regime Changes in Tephra-Mulched

Soils: Implications for Soil Taxonomy. Soil Sci. Soc. Am. J. 66: 202–206.

Tejedor, M.; Jimenez, C. C.; Dıaz, F. 2003. Volcanic materials as mulches for water conservation.

Geoderma. 117: 283–295.

USDA Forest Service Proceedings RMRS-P-44. 2007 137

In: Page-Dumroese, Deborah; Miller, Richard; Mital, Jim; McDaniel, Paul; Miller, Dan, tech. eds. 2007. 

Volcanic-Ash-­Derived Forest Soils of the Inland Northwest: Properties and Implications for Management 

and Restoration. 9-10 November 2005; Coeur d’Alene, ID. Proceedings RMRS-P-44; Fort Collins, CO: 

U.S. Department of Agriculture, Forest Service, Rocky Mountain Research Station.

Mariann T. Garrison-Johnston and Peter G. Mika are research scientists and Leonard R. Johnson is 

the director for the Intermountain Forest Tree Nutrition Cooperative, University of Idaho, Moscow, 

ID. Dan L. Miller is a silviculture manager for Potlatch Corporation, Lewiston, ID. Phil Cannon is the 

productivity manager for Forest Capital, North, Monmouth, OR.

Abstract

	 Data from 139 research sites throughout the Inland Northwest were analyzed for effects of ash cap

on site productivity, nutrient availability and fertilization response. Stand productivity and nitrogen (N)

fertilizer response were greater on sites with ash cap than on sites without. Where ash was present,

depth of ash had no effect on site productivity or N fertilizer response. Site productivity increased

with increasing potentially available soil water. Potentially available soil water, in turn, increased with

increasing ash depth. Decreasing availability of magnesium (Mg) and calcium (Ca) in the upper 12

inches of soil may have constrained site productivity with increasing ash depth. Soil mineralizable N

and ammonium N were unaffected by ash presence or depth but did vary by underlying parent material.

Site productivity and N fertilizer response varied by underlying parent material even after accounting

for ash presence. Stand volume response to sulfur (S) fertilization decreased with increasing ash depth,

suggesting possible S adsorption by ash cap. No growth response or change in foliar K status was

discerned following K fertilization. Management recommendations by parent material are provided.

Ash Cap Influences on Site Productivity and 

Fertilizer Response in Forests of the Inland 

Northwest

Mariann T. Garrison-Johnston, Peter G. Mika, Dan L. Miller, Phil Cannon, and 

Leonard R. Johnson

Background

	 Availability to plants of most nutrients besides nitrogen (N) is related primarily to mineral

weathering rates and soil physical and chemical properties. Common parent materials of soils

in the Inland Northwest include the Columbia River basalt flows, Belt Series metasedimentary

rocks, granites, and various glacial deposits. Characteristics that these materials impart to forest soils significantly affect forest nutrition, productivity and response to fertilization (Moore

and Mika 1997; Moore and others 2004). However, surficially deposited parent materials are

often neglected during analyses of parent rock effects on forest nutrition. This is particularly

true for widespread volcanic ash resulting from the eruption of Mount Mazama (now Crater

Lake) in southwestern Oregon. The effects of surficially deposited parent materials on forest

nutrition, productivity and response to fertilization are poorly understood.
138 USDA Forest Service Proceedings RMRS-P-44. 2007

Garrison-Johnston, Mika, Miller, Cannon, and Johnson Ash Cap Influences on Site Productivity and Fertilizer Response in Forests of the Inland Northwest

Ash-cap soils common to the Inland Northwest are known for their capability

to hold ample available moisture, which in turn is thought to enhance site productivity (Brown and Lowenstein 1978; Mital 1995). Because of the improved

soil moisture status, forest stands growing on ash-cap soils are generally expected

to show greater growth response to nitrogen (N) fertilization than stands on

soils without ash cap, at least so long as some other factor is not more limiting

than moisture and/or N. In a study of 90 Douglas-fir fertilization trial stands

across the Inland Northwest, Mital (1995) found a positive correlation between

Douglas-fir growth response to N fertilization and ash depth at an application rate

of 400 lb ac–1, while the relationship was less strong when the application rate

was 200 lb ac–1. In another study, Geist (1976) reported that forage production

on volcanic ash soils showed strong fertilization response on forested range sites

in eastern Oregon and Washington.

Without fertilizers or blending with organic matter, unweathered ash-cap soils

are not particularly fertile, being comprised largely of poorly crystalline aluminosilicates and iron (Fe) and aluminum (Al) oxides. Their nutrient cation storage

capacity is low, suggesting that supply of the nutrient cations potassium (K),

calcium (Ca) and magnesium (Mg) may be poor (McDaniel and others 2005).

Furthermore, strong anion adsorption capacity by volcanic ash may impede tree

fertilization response. In a study of sulfur (S) adsorption properties of andic soils in

the Inland Northwest, Kimsey and others (2005) suggest that applied S fertilizers

may be ineffective in increasing S-availability to trees unless a threshold sorption

capacity of the ash cap is exceeded. Similar interactions may be expected for

the anionic forms of other elements, including N, phosphorus (P) and boron (B).

Such a phenomenon may explain, in part, the variable relationship between ash

cap depth and N-fertilization rates described by Mital (1995), if some threshold

sorption capacity had to be met (such as at the 400 lb rate) before the applied N

became available to the forest vegetation. The ash cap may take on nutritional

characteristics of underlying residual soils, though this perception has not been

scientifically tested.

A statistical analysis of data from nutritional research conducted by the Intermountain Forest Tree Nutrition Cooperative (IFTNC) from 1980 to the present was

undertaken to determine whether ash deposits affected tree and soil nutrition, forest productivity and fertilization response. We hypothesized that site productivity

and fertilizer response would be greater on ash sites than non-ash sites and that

productivity and response would increase with increasing ash depth.

Methodology ___________________________________________________

Data Compilation

Data from 139 IFTNC research sites were compiled. The data set included

94 sites from the 1980-1982 Douglas-fir Study, 8 sites each from the 1991 and

1993 Mixed Conifer Studies, and 29 sites from the 1994-1996 Forest Health and

Nutrition Study (table 1). Soil profile descriptions were used to estimate organic

horizon depth, surficial deposit depth and residual soil depth to 36 inches. Surficial deposits were categorized as ash, loess, glacial deposits, other modern

(quarternary era) deposits, and tertiary deposits. Residual soils were those derived

from the base geology. The division between surficial deposits and base geology
USDA Forest Service Proceedings RMRS-P-44. 2007 139

Ash Cap Influences on Site Productivity and Fertilizer Response in Forests of the Inland Northwest Garrison-Johnston, Mika, Miller, Cannon, and Johnson Table 1—List of selected fertilization studies established by the Intermountain Forest Tree Nutrition Cooperative between 1980 and 2000. Regions refer to northeastern Oregon (NE OR), central Washington (C WA), northeastern Washington (NE WA), central Idaho (C ID), northern Idaho (N ID) and western Montana (W MT). No. of Year(s) Stand Trial name sites established composition Region Treatments and ratesa Douglas-fir trials 94 1980-1982 Douglas-fir C ID, C WA, control; 200 lb N; 400 lb N NE WA, NE OR, N ID, W MT Umatilla mixed conifer 8 1991 Mixed conifer NE OR control; 200 lb N; 200 lb N + 100 lb S Okanogan mixed conifer 8 1993 Mixed conifer C WA control; 200 lb N; 200 lb N + 170 lb K Forest health and 29 1994-1996 Mixed conifer C ID, C WA, NE 1994 (12 sites): control; 300 lb N; 170 lb K; 300 lb N + 170 lb K nutrition WA, NE OR, N ID 1995 (12 sites): control; 300 lb N; 170 lb K; 300 lb N + 170 lb K; 300 lb N + 170 lb K + 100 lb S 1996 (7 sites): control; 300 lb N; 170 lb K; 300 lb N + 170 lb K; 300 lb N + 170 lb K + 100 lb S + 5 lb B + 10 lb Cu +10 lb Zn + 0.1 lb Mo All years: Additional N+K combinations ranging from 0 lb N and 0 lb K to 600 lb N and 512 lb K, per experimental design

a Rates in lb ac–1 as broadcast application
140 USDA Forest Service Proceedings RMRS-P-44. 2007

Garrison-Johnston, Mika, Miller, Cannon, and Johnson Ash Cap Influences on Site Productivity and Fertilizer Response in Forests of the Inland Northwest

was not always clear. Because the soil depth parameter for this study was limited

to 36 inches, deep surficial deposits were often the only parent material noted.

Therefore, the base geologic parent material categories for this paper included

basalt, granite, sedimentary rock, metasedimentary rock, glacial deposit, tertiary

sediments and modern sediments. Ash was considered present if it was continuous and measurable to a depth of 1 inch or greater. Admixtures of ash and other

materials were also counted as ash cap if the ash was a predominant and identifiable component of the mix.

Soil water-holding capacity was determined for the upper 24 inches of the

soil profile on 110 sites. Potential plant-available water was calculated as the

difference in moisture-holding capacity between 1/3 and 15 bars for those sites.

Conventional laboratory soil tests were performed on the upper 12 inches of soil

for all 139 sites, though some tests were performed on only a subset of the sites.

Available P and K were tested using sodium acetate extraction, while NH4

+ and

NO3

– were analyzed using 2M KCl extraction with analysis by colorimetry (Case

and Thyssen 1996a; Case and Thyssen 1996d). Sulfate-sulfur was analyzed by

calcium phosphate extraction and ion chromatography, and B was analyzed

by calcium chloride extraction and spectrophotometric determination (Case

1996; Case and Thyssen 1996c). Extractable Ca, Mg, K and Na were analyzed

by 1N ammonium acetate extraction and ICP, and micronutrients Cu, Zn, Mn

and Fe by DTPA (Case and Thyssen 1996b; Case and Thyssen 2000).

Two different approaches were used to estimate site productivity. The first approach utilized Douglas-fir site index (SI, Monserud 1984), available for 110 of

the 139 sites. We also selected control plot growth rate (CGR) as an easily calculated productivity estimate available for all sites included in the study. Control

plot growth rate was estimated as the average growth rate in ft3 ac –1 yr –1 over the

first 6 years of each study. Fertilization response was based on 6-year cubic foot

volume response (ft3 ac –1 yr –1) to N fertilizers applied at 200 to 300 lb N ac –1.

Limited data were available for examination of volume response to S fertilizers

applied at 100 lb S ac –1 and K fertilizers applied at 170 lb K ac –1.

Tree nutrition was assessed by chemical analysis of foliage collected one year

after fertilization from the upper third of the crown on dominant or co-dominant

trees. Because foliage chemistry differs for different tree species, Douglas-fir was

selected for inclusion in this analysis as the species most commonly occurring

across the selected test sites. Nutrient deficiencies were identified by the critical

levels method, defined as the point on a yield curve where an increase in nutrient concentration no longer results in increased yield. Thus, the “critical level”

is the optimum nutrient concentration at which maximum yield is obtained with

minimum nutrient input. Currently accepted critical levels for Inland Northwest

Douglas-fir foliage are shown in table 2.

Data Analysis

Sites were arrayed in a matrix by geographic region, rock type, vegetation

series and ash cap presence or absence to evaluate sample sizes in each category.

Analysis of variance was used to detect the effects of region, rock type, vegetation

series and ash presence on site productivity, soil and foliage characteristics and

fertilization response. The basic statistical model used for this analysis was:

Yijk = μ + αj + βk + (αβ)jk + εijk (1)
USDA Forest Service Proceedings RMRS-P-44. 2007 141

Ash Cap Influences on Site Productivity and Fertilizer Response in Forests of the Inland Northwest Garrison-Johnston, Mika, Miller, Cannon, and Johnson

Table 2—Nutritional critical levels for Douglas-fir foliage. Adapted 

from Webster and Dobkowski (1983).

Nutrient Unit of concentration Critical level

Nitrogen (N) % 1.40

Phosphorus (P) % 0.12

Potassium (K) % 0.60

Sulfur (S) % 0.11

Calcium (Ca) % 0.15

Magnesium (Mg) % 0.08

Manganese (Mn) ppm 15

Iron (Fe) ppm 25

Zinc (Zn) ppm 10

Copper (Cu) ppm 2

Boron (B) ppm 10

Where:

Yijk = the productivity, soil or foliage characteristic measured at each site

μ = population grand mean for productivity, soil or foliage characteristic

αj = effect of region, parent material or vegetation series

βk = effect of ash presence or absence (dummy variable)

(αβ)jk = effect of region, parent material or vegetation series by ash cap interaction

εijk = the error term ~ NID (0, σ2)

Because CGR was a function of initial volume, analyses of CGR included initial

volume as a covariate in the above model. Similarly, because fertilization response

depended on starting volume and stand growth rate, those variables were used

as covariates for that analysis. Ash depth as a continuous variable was also incorporated into the above model to perform regression analysis of the effects of ash

depth on all variables examined in this study. Results were considered significant

at the 90% confidence level (p=0.10).

Results _________________________________________________________

Ash Distribution

SitesinnorthIdaho,northeastWashingtonandnortheastOregonweremore likely

to have ash than sites in central Washington, Montana and central Idaho (table 3).

Sites on tertiary deposits, metasedimentary rocks and glacial deposits were more

likely to have ash than those on basalt, granite, modern sedimentary deposits and

sedimentary rocks. Almost all western red cedar and western hemlock vegetation

series occurred on sites with ash, while only about half the grand fir series and a

quarter of the Douglas-fir series occurred on sites with ash cap. The statistical term

for this pattern whereby ash occurs in conjunction with certain characteristics and

not others is known as “confounding.” Confounding between ash presence and

other site characteristics make statistical analysis difficult because we cannot determine whether productivity or response differences between sites are due to the ash

presence/absence or the other site characteristic (vegetation series, parent rock or

geographic region). The occurrence of ash in conjunction with certain parent rocks
142 USDA Forest Service Proceedings RMRS-P-44. 2007

Garrison-Johnston, Mika, Miller, Cannon, and Johnson Ash Cap Influences on Site Productivity and Fertilizer Response in Forests of the Inland Northwest

or geographic regions is likely coincidental, while the occurrence of ash in conjunction with certain vegetation series is more suggestive of a causal relationship.

Site Productivity

Douglas-fir SI was analyzed for 110 sites (SI information was not available for

the Forest Health and Nutrition Study sites). Overall, SI was 10.6% greater on

sites with ash cap than sites without. Base parent material explained a significant

amount of SI variation (R2=0.18), and the addition of ash presence to this model

explained some additional variation in SI (R2=0.28; fig. 1a). On all parent material

types except basalt, the presence of ash cap somewhat increased site productivity

compared to the non-ash sites. However, given ash presence, a subsequent regression analysis revealed no significant influence of ash depth on SI (fig. 1b). Average

SI did vary by geographic region (fig. 1c); however, ash presence or absence did

not further explain variation in SI once the geographic region was known. Similarly,

while a significant amount of variation in SI was explained by vegetation series

alone (fig. 1d), ash presence did not explain any further variation.

Control plot growth rate was available for all 139 sites included in the analysis,

and was highly correlated with SI (R2=0.59). Overall, CGR was 29.0% greater

on ash versus non-ash sites. Ash depth did not affect CGR (fig. 2a). Control plot

growth rate was significantly affected by geographic region (R2=0.58; fig. 2b),

Table 3—Number of research sites with and without ash cap by region, underlying 

geology and vegetation series.

Ash cap present? Percent sites

Region no yes Total with ash cap

North Idaho 5 26 31 84%

Northeast Washington 6 17 23 74%

Northeast Oregon 7 10 17 59%

Central Washington 23 11 34 32%

Montana 14 2 16 13%

Central Idaho 17 1 18 6%

 

Underlying geology

Tertiary deposits 1 6 7 86%

Metasedimentary rocks 8 20 28 71%

Glacial deposits 8 17 25 68%

Basalt 25 13 38 34%

Granite 18 9 27 33%

Modern deposits 7 2 9 22%

Sedimentary rocks 5 0 5 0%

Vegetation series

Western red cedar 1 22 23 96%

Western hemlock 1 5 6 83%

Grand fir 29 24 53 45%

Subalpine fir 3 2 5 40%

Douglas-fir 38 14 52 27%

 

Total sites with and without ash cap: 72 67 139 48%
USDA Forest Service Proceedings RMRS-P-44. 2007 143

Ash Cap Influences on Site Productivity and Fertilizer Response in Forests of the Inland Northwest Garrison-Johnston, Mika, Miller, Cannon, and Johnson

Figure 1a—Douglas-fir site index by base parent 

material and ash cap presence. Parent materials 

include basalt, glacial deposit (glacial), granite, 

metasedimentary (metased), sedimentary (sed), 

modern sedimentary deposits (mod sed) and 

tertiary sedimentary deposits (tert sed).

Figure 1b—Douglas-fir site index (ft at 50 years) by 

ash cap depth for sites with ash cap.

Figure 1d—Douglas-fir site index by vegetation series. 

Vegetation series include Douglas-fir (DF), grand fir 

(GF), subalpine fir (SAF), western hemlock (WH) and 

western red cedar (WRC).

Figure 1c—Douglas-fir site index by geographic region. 

Regions include central Idaho (C ID), central Washington 

(C WA), Montana (MT), north Idaho (N ID), northeast 

Oregon (NE OR) and northeast Washington (NE WA).
144 USDA Forest Service Proceedings RMRS-P-44. 2007

Garrison-Johnston, Mika, Miller, Cannon, and Johnson Ash Cap Influences on Site Productivity and Fertilizer Response in Forests of the Inland Northwest

vegetation series (R2=0.59; fig. 2c) and dominant parent material (R2=0.46;

fig. 2d). Ash presence did not explain any additional variation for the geographic

region or the vegetation series models. However, ash presence did explain some

additional variation in CGR in the parent material model (R2=0.57; fig. 2e). The

results were similar to those for SI, with ash presence somewhat increasing CGR

for most parent materials. Also similar to SI, once ash was present CGR did not

change with ash depth.

Site Fertility

Soil moisture—Site productivity increased with increasing potentially available

water (fig. 3a). Potentially available water, in turn, increased with increasing ash

depth. When arrayed by vegetation series, potentially available water was greater

Figure 2a—Control plot growth rate by ash cap depth for sites with 

ash cap.

Figure 2b—Control plot growth rate (ft3ac –1yr –1) by geographic 

region. Regions include central Idaho (C ID), central Washington 

(C WA),Montana (MT), north Idaho (N ID), northeast Oregon (NE OR) 

and northeast Washington (NE WA).
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Figure 2e—Control plot growth rate ft3ac –1yr –1) by base parent material 

and ash cap presence. Parent materials include basalt, glacial deposit 

(glacial), granite, metasedimentary (metased), sedimentary (sed), modern sedimentary deposits (mod sed) and tertiary sedimentary deposits 

(tert sed).

Figure 2c—Control plot growth rate (ft3ac –1yr –1) by vegetation series. 

Vegetation series include Douglas-fir (DF), grand fir (GF), subalpine fir 

(SAF), western hemlock (WH) and western red cedar (WRC).

Figure 2d—Control plot growth rate ft3ac –1yr –1) by base parent material. 

Parent materials include basalt, glacial deposit (glacial), granite, metasedimentary (metased), sedimentary (sed), modern sedimentary deposits 

(mod sed) and tertiary sedimentary deposits (tert sed).
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on sites on western red cedar series compared to sites on Douglas-fir and grand

fir series (fig. 3b). When arrayed by parent material (fig. 3c), sites with ash caps

on basalt and metasedimentary parent materials averaged higher potential water

availability than those on granite and glacial till parent materials. However, when

ash was absent, sites on glacial till parent materials had higher potentially available water than sites on metasedimentary or granitic rocks.

Soil Acidity—Soil pH data were available for 135 sites. Overall, pH increased

with increasing ash depth. Vegetation series had a significant effect on pH, with

sites on subalpine fir series less acid than those on grand fir or Douglas-fir series,

which in turn were less acid than sites on western red cedar or western hemlock

series (fig. 4a). Parent material also affected soil pH, but interacted with ash

Figure 3a—Control plot growth rate

ft3ac –1yr –1) and Douglas-fir site index 

(ft at 50 years) as a function of potential 

available water (inches) in the upper 24 

inches of soil.

Figure 3c—Potentially available water 

(inches) in the upper 24 inches of soil as 

a function of ash depth (inches), by base 

parent material. Parent materials include 

basalt, glacial deposit (glacial), granite and 

metasedimentary (metased).

Figure 3b—Potential available water 

(inches) in the upper 24 inches of soil 

as a function of ash depth (inches), by 

vegetation series. Vegetation series 

include Douglas-fir (DF), grand fir (GF) 

and western red cedar (WRC).
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depth (fig. 4b). Soil acidity decreased with increasing ash depth on granite and

perhaps basalt parent materials, and increased with increasing ash depth on tertiary sediments, but showed little variation with ash depth on other underlying

parent materials. In the absence of ash, soil acidity was about the same for all

underlying parent materials.

Nitrogen—Soil mineralizable N data were available for 119 sites, while

ammonium-N data were available for 45 sites and nitrate-N data for 44 sites.

None of these three measures of soil-available N varied with ash presence or

depth. However, two of the variables, soil mineralizable N and ammonium-N,

varied by parent material (fig. 5a and 5b). Both measures showed higher values

on metasedimentary and tertiary deposit parent materials, and lower values on

Figure 4a—Soil pH by vegetation series. Vegetation series 

include Douglas-fir (DF), grand fir (GF), subalpine fir (SAF), 

western hemlock (WH) and western red cedar (WRC).

Figure 4b—Soil pH as a function of ash depth (inches) and base parent 

material. Parent materials include basalt, glacial deposit (glacial), granite, 

metasedimentary (metased), sedimentary (sed), modern sedimentary deposits 

(mod sed) and tertiary sedimentary deposits (tert sed).
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granitic and basaltic materials. In an effort to determine why parent material would

affect soil mineralizable N, several additional statistical analyses were performed

using data on percent organic matter (29 sites) and percent carbon (90 sites). Mineralizable N was strongly and positively correlated with both soil organic matter

(R2=0.69) and soil carbon (R2=0.68), suggesting that parent material could affect

soil mineralizable N by affecting soil organic matter and/or carbon content.

Foliar N concentrations of unfertilized Douglas-fir trees were below the critical

level of 1.4% for most sites, and were generally unaffected by ash presence or

depth. However, foliar N was affected by underlying parent material, with trees

on basalt parent materials showing higher foliar N concentrations than trees on

other parent material types (fig. 5c). Examination of SI as a function of foliar N

showed a positive relationship (R2=0.28; fig. 5d). The slope of the relationship did

not vary by underlying parent material, but SI was higher on tertiary sediments

and metasedimentary rocks. Foliage N concentrations were also analyzed as a

function of soil-available (mineralizable) N, with the expectation that foliage N

levels would increase with increasing soil mineralizable N levels. However, the

correlation was very weak (R2=0.05). A model combining the effects of rock type,

mineralizable N and elevation better described variation in foliage N (R2=0.27),

with foliage N positively related to mineralizable N and negatively related to elevation. Interestingly, this model showed that trees on basalt, sedimentary rock

or modern sediments had higher foliar N concentrations than those on glacial

tills or metasedimentary rocks. Other site factors including soil fertility, soil water

potential, aspect and slope were not related to foliage N, and foliage N did not

vary by vegetation type or geographic region. This suggested that underlying rock

did somehow influence foliage N nutrition.

Cations—Extractable cation data from soilsamplesfrom 119 sitesindicated that

extractable K was not affected by ash cap presence or depth, but was affected by

underlying parent material (fig. 6a). Extractable Ca and Mg both decreased with

increasing ash depth (Ca: R2=0.30, fig. 6b and Mg: R2=0.33, fig. 6c). Given the

same depth of ash, Ca and Mg were lowest on sites with granitic parent materials and highest on basalt and metasedimentary parent materials. In contrast to

Figure 5a—Soil mineralizable nitrogen (N, ppm) by base parent material. 

Parent materials include basalt, glacial deposit (glacial), granite, metasedimentary (metased), sedimentary (sed), modern sedimentary deposits 

(mod sed) and tertiary sedimentary deposits (tert sed).
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Figure 5b—Soil ammonium-nitrogen (NH4-N, 

ppm) by base parent material. Parent materials 

include basalt, glacial deposit (glacial), granite, 

metasedimentary (metased), sedimentary (sed), 

modern sedimentary deposits (mod sed) and 

tertiary sedimentary deposits (tert sed).

Figure 5d—Site index (ft3ac –1yr –1) as a function of 

ash depth (inches), by base parent material. Parent 

materials include basalt, glacial deposit (glacial), 

granite, metasedimentary (metased), sedimentary 

(sed), modern sedimentary deposits (mod sed) and 

tertiary sedimentary deposits (tert sed).

Figure 5c—Douglas-fir foliar nitrogen (N) concentration (percent) as a function of ash depth 

(inches), by base parent material. Parent materials 

include basalt, glacial deposit (glacial), granite, 

metasedimentary (metased), sedimentary (sed), 

modern sedimentary deposits (mod sed) and tertiary 

sedimentary deposits (tert sed).
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soil K, Douglas-fir foliar K was unaffected by underlying parent rock, but was

consistently higher in the presence of ash (fig. 6d). Once ash was present, ash

depth had no effect on foliar K. Douglas-fir foliar Ca (fig. 6d) and Mg (fig. 6e)

concentrations behaved similarly to soil availability in that both decreased with

increasing ash depth. Underlying parent material did not affect foliar Ca or Mg

values. Foliar K, Ca and Mg concentrations were generally above nutritional critical levels (table 2).

Phosphorus—Soil-available P datawere available for only 45 sites. Soil-available

P was not affected by ash presence or depth, but was affected by parent material

(fig. 7a), with glacial deposits showing the highest P availability and metasedimentary rocks the lowest. Douglas-fir foliar P values were generally above critical levels (table 2), and were also unaffected by ash presence or depth. Foliar P

concentrations differed by parent material, and were highest on glacial deposits

Figure 6a—Extractable potassium (K, cmol kg–1) by base 

parent material. Parent materials include basalt, glacial 

deposit (glacial), granite, metasedimentary (metased), 

sedimentary (sed), modern sedimentary deposits (mod 

sed) and tertiary sedimentary deposits (tert sed).

Figure 6b—Extractable calcium (Ca, cmol kg–1) as a 

function of ash depth (inches), by base parent material. 

Parent materials include basalt, glacial deposit (glacial), 

granite, metasedimentary (metased), sedimentary (sed), 

modern sedimentary deposits (mod sed) and tertiary 

sedimentary deposits (tert sed).

Figure 6c—Extractable magnesium (Mg, cmol kg–1) 

as a function of ash depth (inches), by base parent 

material. Parent materials include basalt, glacial deposit (glacial), granite, metasedimentary (metased), 

sedimentary (sed), modern sedimentary deposits (mod 

sed) and tertiary sedimentary deposits (tert sed).
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Figure 6f—Douglas-fir foliar magnesium (Mg) concentration (percent) 

as a function of ash depth (inches), by base parent material. Parent 

materials include basalt, glacial deposit (glacial), granite, metasedimentary (metased), sedimentary (sed), modern sedimentary deposits 

(mod sed) and tertiary sedimentary deposits (tert sed).

Figure 6d—Douglas-fir foliar potassium (K) concentration (percent) 

as a function of ash depth (inches), by base parent material. Parent 

materials include basalt, glacial deposit (glacial), granite, metasedimentary (metased), sedimentary (sed), modern sedimentary deposits 

(mod sed) and tertiary sedimentary deposits (tert sed).

Figure 6e—Douglas-fir foliar calcium (Ca) concentration (percent) as a 

function of ash depth (inches), by base parent material. Parent materials include basalt, glacial deposit (glacial), granite, metasedimentary 

(metased), sedimentary (sed), modern sedimentary deposits (mod sed) 

and tertiary sedimentary deposits (tert sed).
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Garrison-Johnston, Mika, Miller, Cannon, and Johnson Ash Cap Influences on Site Productivity and Fertilizer Response in Forests of the Inland Northwest

and lowest on metasedimentary rocks (fig. 7b). Neither foliar P concentrations

nor soil P tests suggested any effect of ash on P availability during this study.

Sulfur, B and Cu—Sufficient data were available to perform statistical analyses

for available B and S (45 sites) and Cu (29 sites). Given ash presence, available

B increased with increasing ash depth (fig. 8a). There was no evidence that parent material or vegetation series affected soil B availability. In contrast, available

Cu was not affected by ash presence or depth, but did vary by parent material,

ranging from 0.46 ppm on granitic sites to 1.03 ppm on modern sedimentary

Figure 7a—Available phosphorus (P, ppm) by base parent material. 

Parent materials include basalt, glacial deposit (glacial), granite, 

metasedimentary (metased), sedimentary (sed), modern sedimentary 

deposits (mod sed) and tertiary sedimentary deposits (tert sed).

Figure 7b—Douglas-fir foliar phosphorus (P) concentration (percent) 

as a function of ash depth (inches), by base parent material. Parent 

materials include basalt, glacial deposit (glacial), granite, metasedimentary (metased), sedimentary (sed), modern sedimentary deposits 

(mod sed) and tertiary sedimentary deposits (tert sed).
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deposits (fig. 8b). Sulfate-S availability was not affected by ash, parent material

or vegetation series.

Douglas-fir foliar B values increased with increasing ash depth, showing good

agreement with soil-available B tests (fig. 8c). Foliar B was also affected by parent material, ranging from about 23 ppm on granitic rocks to about 29 ppm on

tertiary sediments in the absence of ash. Foliar Cu values, in contrast, were not

affected by parent material or ash presence or depth. Foliar B and Cu values were

generally above nutritional critical levels (table 2). While foliar S concentrations

were at or above critical level most of the time, S was the next most likely element, after N, to show deficiency levels.

Figure 8a—Soil available boron (B, ppm) as a function of ash 

depth (inches).

Figure 8b—Available copper (Cu, ppm) by base parent material. Parent materials include basalt, glacial deposit (glacial), 

granite, metasedimentary (metased), sedimentary (sed), modern sedimentary deposits (mod sed) and tertiary sedimentary 

deposits (tert sed).

Figure 8c—Douglas-fir foliar boron (B) concentration (ppm) 

as a function of ash depth (inches), by base parent material. 

Parent materials include basalt, glacial deposit (glacial), granite, metasedimentary (metased), sedimentary (sed), modern 

sedimentary deposits (mod sed) and tertiary sedimentary 

deposits (tert sed).
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Garrison-Johnston, Mika, Miller, Cannon, and Johnson Ash Cap Influences on Site Productivity and Fertilizer Response in Forests of the Inland Northwest

Fertilization Response

Nitrogen Fertilizer Response—Across all geographic regions, base parent materials and vegetation series, 6-year gross volume response to N fertilizer of stands

on ash-cap sites was 49.6% greater on average than fertilizer response of stands

on non-ash sites. However, once ash was present, ash depth had no effect. The

combined effect of parent material and ash presence more effectively described

variation in response than ash cap alone. Ash presence increased volume response

by 87% on glacial deposits, 76% on tertiary sediments, 48% on modern sediments

and 34% on basalts (fig. 9a). Ash presence did not affect volume response on

metasedimentary or granitic parent materials. Vegetation series did not describe

any additional fertilization response once ash presencewas accounted for.A model

combining parent material and vegetation series was more effective at explaining variation in response (fig. 9b) than the parent material and ash model. Sites

on western red cedar vegetation series and basalt or glacial till parent materials

showed the highest N fertilizer response, while sites on Douglas-fir vegetation

series and metasedimentary parent materials showed the lowest response, with

other sites falling in between. Even though this relationship between response and

vegetation seriessuggested thatsoil moisture may affect response, the relationship

between volume response to N fertilization and potentially available water in the

upper 24 inches of soil was statistically nonsignificant.

Volume response to N fertilizer decreased with increasing soil mineralizable N

(R2=0.34; fig. 9c) and ammonium-N. However, volume response to N fertilizer

showed no relationship to unfertilized foliar N levels. Changes in foliar N concentration caused by N fertilization were inversely related to unfertilized foliar N

concentrations (fig. 9d). In other words, the lower the untreated foliar N levels, the

greater the change in foliar N resulting from N fertilization. Neither ash presence

nor depth influenced this change, thus the presence of ash did not appear to affect

the availability of applied N to trees. Furthermore, neither vegetation series nor

rock type affected the fertilization-induced change in foliar N concentration.

Figure 9a—Six-year nitrogen (N) fertilization response (ft3ac –1yr –1) by 

base parent material and ash cap presence. Parent materials include 

basalt, glacial deposit (glacial), granite, metasedimentary (metased), 

sedimentary (sed), modern sedimentary deposits (mod sed) and tertiary 

sedimentary deposits (tert sed).
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Figure 9d—Change in Douglas-fir foliar nitrogen (N) concentration 

(percent) following N fertilization as a function of control plot (unfertilized) foliar N concentration (percent).

Figure 9b—Six-year nitrogen (N) fertilization response (ft3ac –1yr –1) by 

base parent material and vegetation series. Parent materials include 

basalt, glacial deposit (glacial), granite and metasedimentary (metased). 

Vegetation series include Douglas-fir (DF), grand fir (GF) and western 

red cedar (WRC).

Figure 9c—Six-year nitrogen (N) fertilization response (ft3ac –1yr –1) as 

a function of soil mineralizable nitrogen (N, ppm).
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Garrison-Johnston, Mika, Miller, Cannon, and Johnson Ash Cap Influences on Site Productivity and Fertilizer Response in Forests of the Inland Northwest

Discussion ______________________________________________________

Ash distribution

Ash presence generally explained the same variation as geographic region, parent material and vegetation series. The confounding with vegetation series was not

unexpected. It has long been known, for example, that western red cedar habitat

types are highly likely to have ash cap. It is also known that ash cap is more widely

distributed in north Idaho, northeast Washington and northeast Oregon and less

commonly found in central Washington and central Idaho. The confounding of

ash presence with underlying parent material type is perhaps less intuitive, but is

likely related to the geographic distribution of those parent materials. Sites located

on tertiary sedimentary deposits, metasedimentary rocks and glacial deposits are

more likely to occur in north Idaho and northeast Washington, while sites located

on basalts, granites, modern deposits and sedimentary rocks are more likely to

occur in central Washington and central Idaho.

Site Productivity

While SI was available for only 110 sites and CGR for all 139 sites, the two

variables were highly correlated (R2=0.59),suggesting that both variables behaved

similarly as descriptors of site productivity. For both variables, ash presence at

a depth of 1 inch or greater significantly increased site productivity relative to

non-ash sites. The increase was greater for CGR, suggesting that this variable

was a more sensitive indicator of the effect of ash presence on site productivity.

However, additional ash depth had no effect on either of the site productivity

variables. Thus, once ash was present, it did not appear to matter how deep the

ash was in terms of predicting site productivity.

Even though potentially available water was positively correlated with ash

depth and site productivity, site productivity was unaffected by increasing ash

depth. This meant thatsomething about the ash besides potentially available water

was affecting site productivity. Decreased nutrient availability was one possible

factor limiting site productivity. Foliage and soil-available Mg and Ca generally

decreased with increasing ash depth. Decreased availability of these elements

on sites with deeper ash caps could help explain the lack of a corresponding

increase in site productivity even though potentially available water was higher

on such sites. Positive relationships between ash and nutrient availability of B,

P and K suggested that these elements were not likely growth-limiting in the

presence of ash.

Site Fertility

Soil Moisture—Potential available water is a descriptor of the capability of a

site to retain and supply moisture to the plants growing on that site. Potentially

available water increased with increasing ash depth, as seemed reasonable based

on our experience with ash-cap soils. The finding that potentially available water

was greater on western red cedar series than on grand fir or Douglas-fir series

also seemed reasonable, given that most western red cedar sites occurred in

conjunction with ash-cap soils. However, variation in potentially available water

by vegetation series and ash depth (fig. 3b) suggested that sites on western red
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cedar vegetation series still had higher available water than sites on grand fir or

Douglas-fir series even after accounting for ash. Thus, something besides ash

presence and depth affected potentially available water and the resulting vegetation series. Factors besides ash likely to affect soil moisture and vegetation series

are climate, soil temperature regime, soil depth, soil texture, parent material and

topographic position (slope, aspect, and elevation).

Some of the variation in potentially available water among parent materials in

the presence of ash likely reflected differences in underlying soil texture as well

as ash depth. Basalt and metasedimentary rocks weather to finer size-class soils

with inherently higher potential moisture availability compared to the coarsergrained and more permeable soils derived from granitic rocks and glacial deposits. However, the interaction between ash presence and parent material was

less easily explained. Sites on granitic rocks and glacial deposits showed higher

moisture availability in the absence of ash than in the presence of a shallow ash

layer (fig. 3c). Sites on granitic rocks needed about 7 inches of ash and glacial

sites about 16 inches of ash to achieve the same potentially available moisture as

the non-ash sites on these same rock types. After meeting these threshold levels,

potentially available moisture continued to increase with increasing ash depth on

both rock types. Perhaps some degree of soil mixing occurred between ash and

the underlying residual soils that negatively impacted moisture-holding capacity

at the shallower ash depths.

Soil Acidity—Soil pH tended to increase with increasing ash depth. However,

a complex relationship between parent material and ash depth suggests that this

increase was driven primarily by data from sites on granitic and basaltic substrates,

where increasing ash depth led to increased pH. On all other parent materials,

which were sedimentary in origin, ash depth had no effect on soil pH. The reasons for this behavior are not entirely clear. Soil pH levels of the research sites

included in this study were within a range where nutrient availability and uptake

of applied fertilizer elements should not be adversely affected.

Nitrogen—Foliar and soil measures of N availability suggested that N was

affected by parent material, but unaffected by ash presence or depth. Soil mineralizableN and available ammonium-N were consistently higher on metasedimentary

and tertiary deposit sites and lower on granitic and basaltic sites. In contrast,

foliar analyses suggested that N uptake was greatest on sites with basalt parent

materials. This suggests that trees growing on basalt parent materials were better able to take advantage of soil-available N than trees on other rock types,

or conversely that trees on metasedimentary and tertiary sedimentary deposits

were less able to utilize soil-available N.

Reasons for the contrasting effects of parent material on soil-available N pools

were not clear from this analysis. Parent material could positively affect N supply

by imparting soil textural or chemical conditions that are conducive to increased

N-mineralization rates. Conversely, parent material may negatively affect plant

uptake of N through introduction of a more significant growth-limiting factor,such

as low moisture availability (affected by soil texture) or low nutrient availability

(affected by parent material mineralogy). Either scenario could contribute to an

increase in the soil mineralizable N pool. Mineralizable N was strongly correlated

with soil organic matter and soil carbon, suggesting that N-mineralization rates

were also governed by organic matter availability. Climatic conditions may affect

organic matter production by affecting productivity and/or by affecting conditions
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Garrison-Johnston, Mika, Miller, Cannon, and Johnson Ash Cap Influences on Site Productivity and Fertilizer Response in Forests of the Inland Northwest

conducive to N mineralization. While foliar N was only weakly correlated with

mineralizable N, it was negatively correlated with elevation, suggesting greater

N availability on warmer, lower elevation sites. Other site factors including site

fertility, soil water potential and topographic factors had no effect on foliage N

concentrations.

Cations—Like N, cations were also affected by base parent materials, though

in a more predictable fashion. In the absence of ash, soil-extractable Ca and Mg

concentrationsin the upper 12 inches ofsoil were higher on basalt parent materials

and lower on granites. Because basalts are higher in Ca- and Mg-bearing minerals

than granites, this finding is plausible. However, once ash was present, available

Ca and Mg decreased with increasing ash depth on both basalts and granites. This

suggests that Ca and Mg storage in ash is poor even in the presence of Ca- and

Mg-rich underlying parent materials, and that soil Ca and Mg availability may be

lower on sites with deeper ash caps. This may reflect the dilution of residual soils

with increasing ash presence, and a resulting dilution of Ca and Mg pools in the

upper 12 inches of soil. Foliar chemistry also suggested that plant uptake of both

elements decreased at increasing ash depths.

In contrast to Ca and Mg, soil-extractable K was unaffected by ash presence

or depth, and was only affected by parent material. The parent material effect

was driven by basalt, which showed higher extractable K than other rock types.

However, foliar K was unrelated to parent material, and was positively affected

by ash presence (but not affected by depth). The lack of a relationship between

soil-extractable K and foliar K could indicate that either the soil or foliar test for

K was inadequate. These results could also suggest that ash presence somehow

facilitated tree uptake of K, even though soil-extractable K appeared unaffected

by ash presence. This may also be an indicator of low cation retention by ash

soils and the high mobility of the K+ ion.

Phosphorus—Despite concerns of possible P adsorption by ash soils, soil and

foliartestssuggested that P availability and uptake were unaffected by ash presence

or depth. On all sites, foliar P concentrations were at or above nutritional critical

levels, suggesting that sufficient P was available for tree growth and function.

Boron, Cu and S—Boron showed increasing soil availability and foliar concentration with increasing ash depth. This positive relationship suggests that ash may

provide efficient storage for B, and also that ash does not adsorb B to an extent

that makes the B unavailable for plant uptake. Ash did not affect soil or foliar Cu

values. Soil-available Cu showed some variation by parent material that was likely

related to trace minerals in the various parent materials. However, there was poor

agreement between soil-available and foliar Cu concentrations in that foliar Cu

showed no corresponding parent material effect. Soil-available S was unaffected

by ash presence or depth, or by parent material.

Fertilization Response

Nitrogen—Overall, volume growth response to N fertilization was much better

on sites with ash than on sites without. Including base parent material in the model

with ash contributed an additional degree of predictability of volume response to

N fertilization. Ash was particularly valuable in increasing fertilization response

on the sedimentary deposits (including glacial deposits) and somewhat less so on

the basalt, granite and metasedimentary rocks.
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The relationship of fertilization response to soil mineralizable N suggested that

the lower the mineralizable N, the higher the fertilization response. This supports

the idea that N-deficient sites should show a higher degree of response to N

fertilization. Similarly, the change in foliar N concentration following fertilization

should indicate the effectiveness of the fertilization treatment in changing the

amount of N available to the trees for growth. However, unfertilized foliar N concentrations, while inversely proportional to the change in foliar N concentration

following N application, did not show any relationship to fertilization response.

Thus, while lower foliar N levels were predictive of a greater increase in foliar N

after fertilization, they were not necessarily predictive of a greater N fertilization

response. Increases in foliar biomass following N fertilization have been shown

to be more predictive of future volume response than changes in N concentration

alone (Weetman and Fournier 1986; Hasse and Rose 1995; Brockley 2000).

Sulfur and K—Sites with ash generally responded better to S fertilization than

those without. However, once ash was present, the trend was decreasing response

with increasing ash depth, suggesting possible S adsorption by ash-cap soils. No

evidence was found to suggest that ash presence affected growth response or

foliar K status following K fertilization.

Nutritional Characteristics of Ash

Anion adsorption may be an issue of concern in ash soils due to the characteristic variable charge of ash (McDaniel and others 2005; Kimsey and others 2005).

The decrease in tree growth response to S fertilization with increasing ash depth

suggests possible sulfate retention by ash soils. However no evidence of nitrate

retention appeared following N application as urea or ammonium. Foliar tests

suggested that applied N was taken up by the trees, and 6-year growth response

suggests that N-fertilization did increase biomass and volume production. Phosphorus and B were not applied during these fertilization trials because foliage

tests indicated that these elements were not deficient. Our results also suggested

that ash did not have any effect on soil-available or foliar P, implying that P is not

likely a growth-limiting element on ash-cap soils. Boron availability appeared to

increase with increasing ash depth according to both soil-available and foliage

tests. While insufficient data were available to test for the fate of B following application, B adsorption did not seem to be a growth-limiting characteristic of ash

soils during this analysis.

The inability of pure, unweathered ash to store and supply cations may also be an

issue of concern in andic soils (McDaniel and others 2005). Despite the degree of

mixing andweathering exhibited by the ash-cap soilsin ourstudy,storage and supply

may still have been an issue for Mg2+ and Ca2+. Both elements showed decreased

soil availability and foliar concentration with increasing ash depth. This occurred

even when the underlying parent materials were high in Ca and Mg, suggesting

possible dilution of residual soil nutrient pools by ash. In contrast, soil-extractable

K was unaffected by ash presence or depth, and was only affected by parent material. Thus, ash soils appeared capable of taking on the K characteristic of underlying

parent material, but not the Ca or Mg characteristic. This could occur because K+

is a more mobile ion and is likely to be taken up by plants and deposited on the

soil surface. Also, foliar K was positively affected by ash presence, suggesting that

ash soils were better able to supply K, though not necessarily store it, compared

to non-ash soils. Thus, cation storage and supply or nutrient pool dilution of the
160 USDA Forest Service Proceedings RMRS-P-44. 2007

Garrison-Johnston, Mika, Miller, Cannon, and Johnson Ash Cap Influences on Site Productivity and Fertilizer Response in Forests of the Inland Northwest

divalent cations appeared potentially problematic in ash soils, while the monovalent

K ion was less affected by ash retention and dilution issues.

Management Recommendations _________________________________

Site Nutrition and Nutrient Management

“Nutrient management” refers to silvicultural activities as they affect the

nutrient capital of a forest stand. It can include fertilization treatments and activities that retain nutrients on site during silvicultural activities. Because most

nutrients are held in limbs and foliage (Cole and others 1967; Pang and others

1987; Miller and others 1993; Moller 2000), a conservative nutrient management strategy would be to leave the tops and limbs of harvested trees on-site

through a variety of bole-only harvesting techniques. Whole-tree operations in

late fall and winter, when breakage is more likely, should also be effective at

retaining some nutrients on the site. Species differ in nutrient demand (Gordon

1983; Gower and others 1993; Miller and others 1993; Moore and others 2004).

Therefore, planting nutritionally challenged sites with less-demanding species

and favoring less-demanding species during silvicultural operations are also

conservative nutrient management strategies.

Tests of foliage and soil chemistry may be performed as site specific indicators

of productivity and potential fertilization response. Foliar N was a better predictor

of site productivity, while soil mineralizable N was a better predictor of fertilizer

response. Ifsatisfactory information on site productivity is available and the parent

material/ash combination suggests that the site may be responsive to fertilization,

managers should consider focusing on tests of soil mineralizable N. If mineralizable N is below 70 ppm, the site should show a 6-year volume response of 10%

or more, with the potential response increasing as mineralizable N decreases.

Foliar N may be tested as an indicator of overall site productivity; however, the

effort and expense of this test make it less desirable than performing simple site

height/age measurements.

Nutrient Management Recommendations by Parent 

Material and Ash Presence

Basalts, Glacial and Modern Deposits—Sites on basalts, glacial deposits and

modern sedimentary deposits showed no change in site productivity in terms

of CGR in the presence of ash. However these sites did show moderate (basalt

and modern sedimentary) to high (glacial deposit) increases in volume growth

responses to N fertilization when ash was present. This suggests that sites on these

parent materials should respond reasonably well to N fertilization without ash,

and respond even better when ash is present. There was weak evidence that on

basalt parent materials, the presence of ash inhibited volume response to S fertilization. However, other IFTNC studies have shown that S is sometimes necessary to

stimulate a growth response to N fertilization on basalt parent materials (Garrison

and others 2000). While all parent materials in this category should respond well

to fertilization with N only, stronger growth responses might be induced by multinutrient fertilization that includes S. Conservative nutrient management strategies

should be evaluated, but may be less crucial on these parent materials compared

to other parent materials.
USDA Forest Service Proceedings RMRS-P-44. 2007 161

Ash Cap Influences on Site Productivity and Fertilizer Response in Forests of the Inland Northwest Garrison-Johnston, Mika, Miller, Cannon, and Johnson

Metasedimentary and Granite—Metasedimentary parent materials showed

relatively lower site productivity and granites showed moderate productivity

compared to other parent materials. Site productivity increased in the presence of

ash on both parent material types, with metasedimentary productivity doubling in

terms of CGR. However, N-fertilizer response was unaffected by ash presence for

either parent material. This suggests that (1) trees grow better on metasedimentary

and granitic rocks when ash is present, and (2) fertilization with N alone will not

increase productivity on ash sites over that of non-ash sites on metasedimentary

or granitic rocks. There was weak evidence that metasedimentary and granitic

sites with ash may respond positively to S fertilization. Preliminary results of recent fertilization screening trials on both parent material types showed generally

poor growth response to fertilization with N alone, and stronger response to a

combined treatment of N, K, S, and B when ash was present (Garrison-Johnston

and others 2005, unpublished data). Thus, multinutrient fertilization is more likely

to stimulate growth response on ash soils on metasedimentary and granitic parent

materials. General nutritional challenges of these sites suggest use of conservative

nutrient management strategies.

Tertiary Sedimentary Deposits—Tertiary sedimentary parent materials behaved

somewhat differently than the other parent materials in that both site productivity and N fertilization response were enhanced in the presence of ash. Because

the available data for tertiary sedimentary sites was sparse, these results for this

deposit type should be viewed cautiously. However, this suggests that if stands

on tertiary sediments are growing well, they should respond well to N fertilization

in the absence of ash, and even better when ash is present. Some caution should

be exercised in applying fertilizer, however, as field experience has also shown

that tertiary sedimentary deposits can inherently be quite variable in composition.

Pending further investigation, use of conservative nutrient management strategies

is also recommended.

Conclusions_____________________________________________________

Stand productivity was greater on sites with ash cap than on sites without; however once ash was present, changes in ash depth did not affect site productivity.

Because ash presence or absence tended to coincide with particular vegetation

series and geographic regions, ash presence did not further explain variation in

site productivity beyond that described by those variables. While ash presence

also tended to coincide with particular parent material types, ash presence still

explained some variation in site productivity beyond that explained by parent

material. Ash presence was most likely to increase site productivity on metasedimentary rocks, granites and perhaps tertiary sediments.

Although site productivity was positively correlated with potentially available

water and potentially available water was positively correlated with ash depth,

there was no correlation between site productivity and ash depth. This suggests

that something else about the ash, such as poor nutrition, affected productivity.

Soil-available and foliar Mg and Ca decreased with increasing ash depth. Thus,

while increasing ash depth may have a positive effect on soil moisture potential,

it may have a negative effect on nutrient availability, particularly for Mg and Ca,

and therefore on site productivity.
162 USDA Forest Service Proceedings RMRS-P-44. 2007

Garrison-Johnston, Mika, Miller, Cannon, and Johnson Ash Cap Influences on Site Productivity and Fertilizer Response in Forests of the Inland Northwest

Soil N availability (mineralizable and ammonium) and foliage N concentrations were not affected by ash presence or depth, but were affected by parent

material. Reasons for the parent material effect were not entirely clear, however

the site productivity and soil textural and chemical conditions associated with

particular underlying parent materials likely affected organic matter production

and cycling. Soil organic matter and carbon content were highly correlated with

soil N availability. Climate and elevation likely interacted with parent materials

to have an effect on N availability, as well.

Possible nutrient adsorption and supply by ashwere also considered.Adsorption

of applied N did not appear to occur in ash-cap soils in this study. In contrast,

decreasing growth response to S-fertilization at greater ash depths suggested

that adsorption of applied S may have occurred. Foliage and soil-availability of P

and B either showed no change (P) or increased availability (B) with increasing

ash depth, suggesting that availability of these elements may not be an issue of

concern in ash-cap soils. Lack of soil Mg and Ca storage and supply at greater

ash depths, or perhaps dilution of Mg and Ca supply by increasing quantities of

ash, did appear to occur. Soil K was unaffected by ash presence or depth, while

foliar K concentrations increased when ash was present, suggesting that K supply

was perhaps enhanced by ash presence.

Average volume response to N fertilization was almost 50% greater on ash

compared to non-ash sites. However changes in ash depth did not further affect

volume response. Ash presence increased volume response to N fertilization on

glacial deposits, tertiary sediments, modern sediments and basalts, but not on

granite or metasedimentary parent materials. Volume response was greatest on

western red cedar vegetation series, followed by grand fir and then Douglas-fir

vegetation series. However ash presence or depth did not further affect volume

response once vegetation series was known. Parent material combined with vegetation series best described volume response to N-fertilization.

References______________________________________________________

Brockley, R. P. 2000. Using foliar variables to predict the response of lodgepole pine to nitrogen

and sulphur fertilization. Canadian Journal of Forest Research. 30: 1389-1399.

Brown, H. G.; Lowenstein, H. 1978. Predicting site productivity of mixed conifer stands in northern Idaho from soil and topographic variables. Soil Science Society of America Journal. 48:

910-913.

Case, T. E. 1996. Sulfate-sulfur in soils. Analytical Sciences Laboratory Standard Methods

SMM.85.090.03. Moscow, ID: University of Idaho. 4 p.

Case, T. E.; Thyssen, B. C. 1996a. Available phosphorus and potassium in soils sodium acetate

method. Analytical Sciences Laboratory Standard Methods SMM.85.050.04. Moscow, ID:

University of Idaho. 6 p.

Case, T. E.; Thyssen, B. C. 1996b. Extractable and exchangeable cations. Analytical Sciences

Laboratory Standard Methods SMM.85.100.03. Moscow, ID: University of Idaho. 4 p.

Case, T. E.; Thyssen, B. C. 1996c. Soil boron, pouch method. Analytical Sciences Laboratory

Standard Methods SMM.85.060.02. Moscow, ID: University of Idaho. 5 p.

Case, T. E.; Thyssen, B. C. 1996d. Soil nitrate and ammonium nitrogen extraction method. Analytical Sciences Laboratory Standard Methods SMM.85.080.03. Moscow, ID: University of Idaho.

6 p.

Case, T. E.; Thyssen, B. C. 2000. Zn, Mn, Cu, Fe, Pb, Cd, Ni and As in soils — DTPA Method.

Analytical Sciences Laboratory Standard Methods SMM.85.110.04. Moscow, ID: University of

Idaho. 4 p.
USDA Forest Service Proceedings RMRS-P-44. 2007 163

Ash Cap Influences on Site Productivity and Fertilizer Response in Forests of the Inland Northwest Garrison-Johnston, Mika, Miller, Cannon, and Johnson

Cole, D. W.; Gessel, S. P.; Dice, S. F. 1967. Distribution and cycling of nitrogen, phosphorus, potassium and calcium in a second-growth Douglas-fir ecosystem. In: Symposium on the primary

productivity and mineral cycling in natural ecosystems: proceedings: 1967; Ecological Society

of America, American Association for the Advancement of Science Annual Meeting: 197-232.

Garrison, M. T.; Moore, J. A.; Shaw, T. M.; Mika, P. G. 2000. Foliar nutrient and tree growth response of mixed-conifer stands to three fertilization treatments in northeast Oregon and north

central Washington. Forest Ecology and Management. 132: 183-198.

Geist, J. M. 1976. Forested range fertilization in eastern Oregon and Washington. Rangeman’s

Journal. 3: 116-118.

Gordon, A. G. 1983. Nutrient cycling dynamics in differing spruce and mixed wood ecosystems

in Ontario and the effects of nutrient removals through harvesting. In: Wein, R. W.; Riewe,

R. R.; Methven, I. R. Resources and Dynamics of the Boreal Zone: proceedings; 1982 August;

Thunder Bay, Ontario. Ottawa, Canada: Association of Canadian Universities for Northern

Studies: 97-118.

Gower, S. T.; Reich, P. B.; Son, Y. 1993. Canopy dynamics and aboveground production of five

tree species with different leaf longevities. Tree Physiology. 12: 327-345.

Hasse, D. L.; Rose, R. 1995. Vector analysis and its use for interpreting plant nutrient shifts in

response to silvicultural treatments. Forest Science. 41: 54-66.

Kimsey, M.; McDaniel, P.; Strawn, D.; Moore, J. 2005. Fate of applied sulfate in volcanic ashinfluenced forest soils. Soil Science Society of America Journal. 69: 1507-1515.

McDaniel, P. A.; Wilson, M. A.; Burt, R.; Lammers, D.; Thorson, T. D.; McGrath, C. L.; Peterson,

N. 2005. Andic soils of the Inland Pacific Northwest, USA: properties and ecological significance. Soil Science. 170(4): 300-311.

Miller, J. D.; Cooper, J. M.; Miller, H. G. 1993. A comparison of above-ground component

weights and element amounts in four forest species at Kirkton Glen. Journal of Hydrology.

145: 419-438.

Mital, J. M. 1995. Relating soil, vegetation, and site characteristicstoDouglas-firresponse to nitrogen

fertilization in the Inland Northwest. Moscow, ID: University of Idaho. PhD Dissertation.

Moller, I. S. 2000. Calculation of biomass and nutrient removal for different harvesting intensities.

New Zealand Journal of Forest Science. 30(1/2): 29-45.

Monserud, R .A. 1984. Height growth and site index curves for inland Douglas-fir based on stem

analysis data and habitat type. Forest Science. 30: 943-965.

Moore, J. A.; Mika, P. G. 1997. Influence of soil parent material on the nutrition and health of

established conifer stands in the Inland Northwest. In: Haase, D. L.; Rose, R. Forest Seedling

Nutrition From the Nursery to the Field: proceedings; Corvallis, Oregon: Nursery Technology

Cooperative, Oregon State University: 144-153.

Moore, J. A.; Mika, P. G.; Shaw, T. M.; Garrison-Johnston, M. T. 2004. Foliar nutrient characteristics of four conifer species in theInterior Northwest United States. Western Journal of Applied

Forestry. 19(1): 13-24.

Pang, P. C.; Barclay, H. J.; McCullough, K. 1987. Aboveground nutrient distribution within trees and

stands in thinned and fertilized Douglas-fir. Canadian Journal of Forest Research. 17: 1379-1384.

Webster, S. R.; Dobkowski, A. 1983. Concentrations of foliar nutrients for trees and the dosage

frequency of fertilizer trials. Weyerhaeuser Research Report No. 1; Project 050-3920/3. 25 p.

Weetman, G. F.; Fournier, R. M. 1986. Construction and interpretation of foliar graphical diagnostic

technique. In: Interior forest fertilization workshop: proceedings; Kamloops, British Columbia:

55-76.

USDA Forest Service Proceedings RMRS-P-44. 2007 165

In: Page-Dumroese, Deborah; Miller, Richard; Mital, Jim; McDaniel, Paul; Miller, Dan, tech. eds. 2007. 

Volcanic-Ash-­Derived Forest Soils of the Inland Northwest: Properties and Implications for Management 

and Restoration. 9-10 November 2005; Coeur d’Alene, ID. Proceedings RMRS-P-44; Fort Collins, CO: 

U.S. Department of Agriculture, Forest Service, Rocky Mountain Research Station.

Han-Sup Han is an academic faculty, Forest Products Department, College of Natural Resources, 

University of Idaho, Moscow.

Abstract

	 Economic implications of soil disturbance are discussed in four categories: planning and layout,

selection of harvesting systems and equipment, long-term site productivity loss, and rehabilitation

treatments. Preventive measures are more effective in minimizing impacts on soils than rehabilitation

treatments because of the remedial expenses, loss of productivity until mitigation occurs, and the

possibility that original soil conditions may not be restored. Alternative harvesting practices that are

designed to minimize impacts on soils, such as use of designated skid trails and wide trail-spacing,

increase overall harvesting costs. Sites with high risk for soil disturbance may require use of expensive

wood extraction methods(e.g.,skyline yarding), as opposed to lower cost options(e.g. ground skidding).

Tillage treatments in severely compacted areas appear to be cost effective if properly implemented.

An accurate estimation of economic consequences from long-term site productivity losses is difficult,

although there is a general consensus that soil disturbance at some locations can reduce tree growth.

Economics of Soil Disturbance

Han-Sup Han

Introduction

	 Questions on the economics of soil disturbance are often raised regarding long-term productivity losses, efforts to minimize soil impacts, and rehabilitation of damaged soils. What

are potential financial impacts from site productivity losses? Should we require every groundskidding machine on high-risk sitesto use designated skid trails and how doesthis affect logging

costs? Would it be cost-effective to ameliorate compacted soils? Are we financially getting a

significant benefit from soilrehabilitation treatments? These questions have not been extensively

answered because of the difficulty in obtaining appropriate data about tree responses to site

disturbance across an entire rotation, the value of offsite impacts, and other pertinent information such as preventive and remediation measures (Lousier 1990; Miller and others 2004).
166 USDA Forest Service Proceedings RMRS-P-44. 2007

Han Economics of Soil Disturbance

Lack of information on the economics of soil disturbance limits forest practioners from attempting to develop harvesting plans and timber sales. A harvesting

plan needs to account for soil disturbance risks, previous impacts on soils, and

preventive measures that minimize further damage to soils. Preventive measures

may require cable logging systems on gentle slopes(<30 percent) or widerspacing

of designated skid trails, but these often result in higher logging costs. Lack of

compelling evidence to justify these high logging options often causes disagreements among forest managers, although there is a general consensus that soil

disturbance may reduce tree growth at some locations (Miller and others 2004).

One would also wonder if these preventive measures would financially benefit

landowners in the long run.

This paper summarizes economic information related to soil impacts in four

categories: planning and layout, selection of harvesting systems and equipment,

long-term site productivity loss, and rehabilitation treatments. In this paper,soil disturbances include soil compaction, scalping, puddling, and soil displacement.

Planning and Layout: Measures to Prevent Soil Disturbance _________

Soil disturbance from timber harvesting may not be avoidable, but can be minimized through careful planning and operations. Preventive measures are more

effective in minimizing impacts on soils than remedial mitigation because of the

remedial expenses, loss of productivity until mitigation occurs, and the possibility

that original soil conditions may not be restored (Miller and others 2004). Existing guidelines and requirements for soil protection should always be observed

when the harvesting plan is developed. A good harvest plan can minimize soil

disturbance by recognizing and identifying the risk of soil disturbance. Some

important factors determining “risk rating” include soil texture, moisture content,

slope, and organic materials at the top soil.

Planning and layout components for timber harvesting include locations for

roads and landings, marking trees to cut or leave, and flagging skid trails or skyline corridors. These vary with different harvesting systems. For example, skyline

yarding requires locating anchors for rigging and ground-profile analysis for available deflection, causing higher planning and layout costs for cable logging than

ground-based harvesting system. Kellogg and others (1998) compared planning

and layout cost for logging contractors in various silvicultural treatments. They

found that a CTL system using a mix of random and designated skid trails (60-ft

spacing) had the lowest cost, followed by the tractor-based winching system for

hand-felled trees that used 130-ft spacing designated skid trails. The skyline systems had the highest cost.

Use of designated skid trails has been recommended in past soil compaction

studies because it effectively reduces the skid trail areas in a harvesting unit and

facilitates rehabilitation efforts (Andrus and Froehlich 1983). Designated skid trails

at a wide spacing increase logging costs. In an earlier study (Bradshaw 1979), the

harvest unit with pre-planned skid trails and winching had a 29 percent higher skid

cost than the conventionally harvested unit. However, only 4 percent of its area was

in skid trails, compared to 22 percent for the conventionally harvested unit.

There are other planning and layout components that increase costs, but are

difficult to estimate. These include expenses related to evaluating soil disturbance risks, identifying areas in the field that pose a high risk for soil damage
USDA Forest Service Proceedings RMRS-P-44. 2007 167

Economics of Soil Disturbance Han

and erosion, and development strategies and guidelines to minimize soil impact.

Delaying logging operations to dry seasons or winter season logging and strict

requirements for best management practices (BMP) are examples for preventive

efforts at a planning stage. These expenses usually occur in the form of overhead

or administrative cost and can be estimated based on companies or agencies’

indirect cost rates.

Selection of Harvesting Systems and Equipment ___________________

Because harvest equipment creates ground pressures and soil disturbance

types (e.g., compaction and scalping), choice of harvesting systems and equipment type can greatly affect the degree and extent of soil impacts. Cable systems

are often preferred over ground-based systems because cable logging does not

require heavy machines moving on harvesting areas. Logs are fully or partially

suspended to the skyline and pulled to the landings. Allen (1997) reported that

a skyline thinning operation in western Oregon left only 2 percent of soil disturbance while a single entry of cut-to-length (CTL) system caused 25 percent of

the harvest area compacted.

However, cable logging istypically more expensive than a ground-based system:

cable yarding costs are 65 to 160 percent higher than conventional ground-based

logging (Lousier 1990). For example, Keegan and others (1995) surveyed stumpto-truck harvest costs in the Montana and northern Idaho region and found that

the cost for ground-based systems was lowest ($87 to $124/thousand board feet

(MBF)), followed by cable systems ranging from $13 to $164/MBF. Helicopter

systems were most expensive at $233/MBF. Compared to mechanized groundbased systems, cable logging requires more labor to manually handle trees or

logs on steep grounds (typically >30 percent slope) as well as to set-up and tear

down an entire yarding system, which results in low daily production of timber.

Time spent changing skyline roads and rigging also contributes to high costs in

cable logging. High logging costs in cable logging becomes more noticeable

when handling small-diameter trees. At average 10-inch diameter at breast height

(DBH), skyline and helicopter stump-to-truck logging and chipping costs were

about 3 and 6 times more expensive, respectively, compared with a mechanized

whole-tree harvesting system that showed the lowest cost at $34.23/100 cubic

feet (Han and others 2004).

Cable yarding, combined with mechanized felling and processing, has been

considered as a way of reducing soil compaction and other types of soil disturbance from the ground skidding or forwarding phase of timber harvesting.

Although mechanized felling and in-woods processing using a feller-buncher or

a harvester have insignificant impacts on soils, subsequent ground skidding and

forwarding cause significant increase in soil bulk density (Allen 1997). The question is how much more expensive it is to use skyline yarding than ground-based

skidding. Johnson (1999) reported that cable yarding ($0.51/ft3) resulted in 113

percent cost increase over forwarding ($0.24/ft3) of logs felled and processed

by a CTL harvester. However, the average forwarding distance (212 ft) for cable

yarding was much longer that the one (129 ft) with forwarding. This may lower

the road density required for timber harvesting activities and reduce the area

of soils disturbed. In eastern Oregon, a skyline yarder was used to extract logs

processed by a CTL harvester in an effort to avoid further damage to soil from
168 USDA Forest Service Proceedings RMRS-P-44. 2007

Han Economics of Soil Disturbance

fuel reduction thinning on slopes that averaged 12 percent or less on all units,

with maximums of 25 percent (Drews and others 2000). They reported that the

harvester-yardersystem averaged much higher($80/green ton)stump-to-mill costs

than the harvester-forwarder system ($46/green ton).

Low ground-pressure machines, such as log loaders and wide-tired skidders,

for wood extraction from stump to landing are also often considered to minimize

soil compaction. Shovel logging uses a hydraulic log loader to repeatedly swing

the logs to reach the road or landing area, and has been used as an alternative

to a cable system on moderate grounds (20 to 40 percent slope) or a groundbased system on gentle slopes (<20 percent). The average unit production cost

for shovel logging in western Washington was 40 percent less than the one with

cable logging at an average external yarding distance of 600 feet (Fisher 1999).

Use of a skidder equipped with wide tires to reduce ground pressure has been

used by machinery manufacturers as machines have increased in size and weight

(Brinker and others 1996). Past studies indicated that wider tires resulted in 13 to

23 percent increase (Meek 1994) or no significant difference (Klepac and others

2001) in skidding cost. Klepac and others (2001) also noted that loggers are reluctant to use wide tires because of additional overhang during machine transport

from one site to another, and requirement for a higher torque, heavy-duty rear

axle in the skidder.

When selecting a mechanized, ground-based system fortimber harvesting, aCTL

system is often compared with a whole tree system consisting of a feller-buncher,

skidder, a processor, and a loader for its harvesting productivity and cost. While

production rates and costs for these two systems are comparable (Hartsough and

others 1997; Lanford and Stokes 1996; Gingras 1994), impacts on sites can differ significantly (Lanford and Stokes 1995; Gingras 1994). A CTL system is often

favored over a whole-tree harvesting system because a harvester processes trees

to log length at the stump, leaving all branches and tree tops on site. A forwarder

drives over the slash mat, and this helps to minimize impacts on soils.

Long-term Site Productivity Losses _______________________________

Aconcern forsite productivity losses aftersoil disturbance from timber harvesting

activities is a primary reason for imposing strict requirements for soil protection in

the context of sustainable forestry. Some studies have shown that soil compaction

adversely impact tree growth.However, estimation of actual or possible productivity

losses resulting from soil disturbance is a complicated issue because of difficulties

of accurate estimation of soil disturbances consequences on tree growth (Miller

and others 2004; Heninger and others 2002; Lousier 1990; Helms and others

1986). Miller and others (2004) suggested that forecasts of reduced timber yield

from degraded soils are uncertain because tree response to soil disturbance is

greatly affected by other site-specific, growth-determining factors.

In addition to tree’s biological and physical responses to soil disturbances,

discount rates also have significant impact on the overall economic analysis of

soil disturbances; the analysis performs over the entire tree rotation period and

discount rates are greatly sensitive to time. Stewart and others (1988) developed

an economic model that addressed financial impacts of soil compaction on a

long-term basis. The model used a stand-growth simulator and included various scenarios of management options. At a 4 percent discount rate, net-present

value analysis showed positive values, thus encouraging preventive efforts (wide
USDA Forest Service Proceedings RMRS-P-44. 2007 169

Economics of Soil Disturbance Han

trail spacing) and indicating higher affordability for careful logging. Under an assumption that tree yield was reduced on 100 percent of skid trail areas, the net

present value (NPV) with 4 percent was $504/ac while it was $144/ac with 8

percent discount rate. One could afford to spend an extra $144/ac to avoid these

yield reductions.

Rehabilitation___________________________________________________

Soil rehabilitation involves mechanical measures (e.g. tillage) to break up severely compacted soils. It helps promote water and air movement (Andrus and

Froehlich 1983) and increase nutrient availability (Miller and others 2004) in a

compacted soil. The efficacy of tillage in loosening compacted soils depends on

equipment types used and soil properties (Unger and Cassel 1991; Andrus and

Froehlich 1983), number of machine passes (Andrus and Froehlich 1983), and

tillage depth (McNabb and Hobbs 1989). The overall cost of tilling is directly

influenced by these factors.

Andrus and Froehlich (1983) studied production rates and costs for skid-trail

tillage at selected sites in Oregon and Washington. Four types of tillage equipment

were evaluated in the study: disk harrow, rock ripper, brush blade, and winged

subsoiler. Production rates were highest when tilling with one pass of the machine.

Uphill tilling on steep grounds required a large crawler tractor at a higher machine

cost. The winged subsoiler lossened more than 80 percent of the compacted

soil in a single pass and was the most cost-effective tillage method (fig. 1). The

authors indicated that tillage results for these sites would have improved if the tillage improvement had made additional passes along the skid trails, but additional

passes would increase the cost of tilling.

Figure 1—Tillage costs and rates for various type of tillage equipment (Andrus and 

Froehlich 1983)
170 USDA Forest Service Proceedings RMRS-P-44. 2007

Han Economics of Soil Disturbance

If properly implemented, tillage may be cost-effective under the most extreme

compaction situations, such as landing areas and heavily traveled skid trails.

Stewart and others (1988) estimated the justifiable increased cost for high-cost

logging or rehabilitation per harvest entry with 125-ft skid trail spacing. The net

financial benefit from tillage was notably affected by discount rates and site index

and ranged from $86/ac to $284/ac. This range of justifiable costs is far more

than a cost estimate ($20/ac or $176/mile) for skid trail restoration with a winged

subsoiler mounted behind Cat D6C crawler tractor (Froehlich and Miles 1984).

Conclusion______________________________________________________

Economics ofsoil disturbance is complicated and requires measuring economic

consequences from long-term site productivity losses and expenses for preventive

and rehabilitation measures. An accurate estimation of soil disturbances consequences on tree growth is difficult because the tree’s response to soil disturbance

is affected by other site-specific, growth-determining factors. Many assumptions

are needed to estimate future growth and yield and these greatly affect overall

financial analyses. Although direct costs for prevention and rehabilitation can be

estimated, direct and indirect financial benefits from these practices are not well

documented. Major uncertainties originate from the requirement for long-term

economic analysis of unknown biological impacts from soil disturbance and inconsistent discount rates used in the analysis.

Preventive measures are more effective in minimizing impacts on soils than

rehabilitation treatments because of remedial expenses, loss of productivity until

mitigation occurs, and the possibility that original soil conditions may not be

restored. Careful planning and layout and selection of harvesting systems and

equipment often increase overall harvesting costs. Alternative harvesting practices that are designed to minimize impacts on soils, such as use of designated

skid trails and wide trail spacing, increase overall harvesting costs. Rehabilitation

expenses are additional to these increased costs. However, these initial expenses

can be justified when preventive and rehabilitation measures are focused on high

risk sites and severely disturbed areas. Expenses for careful planning and layout,

alternative logging practices and rehabilitation measures should be recognized as

part of overall logging cost estimation to support the idea of minimizing impacts

on soils.

Literature Cited__________________________________________________

Allen, M. M. 1997. Soil compaction and disturbance following a thinning of second-growth

Douglas-fir with a cut-to-length and a skyline system in Oregon cascade. Corvallis, OR: Oregon

State University. 105 p. MS thesis.

Andrus, W. C.; Froehlich, H. A. 1983. An evaluation of four implements used to till compacted

forest soils in the Pacific Northwest. Res. Bulletin 45. Corvallis, OR: Oregon State University.

12 p.

Bradshaw, G. 1979. Preplanned skid trails and winching versus conventional harvesting on a partial

cut. Res. Note 62. Corvallis, OR: Oregon State University. 4 p.

Brinker, R.W.; Klepac, J. F.; Stokes, B. J.; Roberson, J. D. 1996. Effect of tire size on skidder productivity. In: Proceedings of a Joint Conference of the Canadian Woodlands Forum, the Canadian

Pulp and Paper Association, and the International Union of Forest Research Organizations;

1996 September 9-11; Quebec City, Quebec. Montreal, Quebec: Canadian Pulp and Paper

Association: 85-89.
USDA Forest Service Proceedings RMRS-P-44. 2007 171

Economics of Soil Disturbance Han

Drews, E. S.; Doyal, J. A.; Hartsough, B. R.; Kellogg, L. D. 2000. Harvester-forwarder and

harvester-yarder systems for fuel reduction treatments. Int. J. of For. Eng. 12(1): 81-91.

Fisher, J. 1999. Shovel logging: cost effective systems gains ground. Proceedings of International

Mountain Logging and 10th Pacific Northwest Skyline Symposium; 1999 March 28-April 1;

Corvallis, Oregon: 61-67.

Froehlich, H. A.; Miles, D. W. R. 1984. Winged subsoiler tills compacted forest soil. For. Ind.

111(2): 42-43.

Gingras, J.-F. 1994. A comparison of full-tree versus cut-to-length systems in the Manitoba Model

Forest. Forest Engineering Institute of Canada. Special Report, SR-92. 16 p.

Han, H.-S.; Lee, H. W.; Johnson, L. R. 2004. Economic feasibility of an integrated harvesting system

for small-diameter trees in southwest Idaho. For. Prod. J. 54(2): 21-27.

Hartsough, B. R.; Drews, E. S.; McNeel, J. F.; Durston, T. A.; Stokes, B. J. 1997. Comparison

of mechinized systems for thinning ponderosa pine and mixed conifer stands. For. Prod. J.

47(11/12): 59-68.

Helms, J. A.; Hipkin, C.; Alexander, E. B. 1986. Effects of soil compaction on height growth of a

California ponderosa pine plantation. West. J. Appl. For. 1(4): 104-108.

Heninger, R.; Scott, W.; Dobkowski, A.; Miller, R.; Anderson, H.; Duke, S. 2002. Soil disturbance

and 10-year growth response of coast Douglas-fir on nontilled and tilled skid trails in the Oregon

Cascades. Can. J. For. Res. 32: 233-246.

Johnson, L. R. 1999. Combining cut-to-length and cable yarding operation. Proceedings of International Mountain Logging and 10th Pacific Northwest Skyline Symposium; 1999 March 28-

April 1; Corvallis, Oregon: 42-52.

Keegan, C. E.; Fiedler, C. E.; Wichman, D. P. 1995. Costs associated with harvest activities for

major harvest systems in Montana. For. Prod. J. 45(7/8): 78-82.

Kellogg, L. D.; Milota, G. V.; Stringham, B. 1998. Logging planning and layout costs for thinning:

experience from the Willamette Young Stand Project. Res. Contribution 20. Oregon State University, College of Forestry. 12 p.

Klepac, J.; Stokes, B.; Roberson, J. 2001. Effect of tire size on skidder productivity under wet

conditions. Int. J. of For. Eng. 12(1): 61-69.

Lanford, B. L.; Stokes, B. J. 1995. Comparison of two thinning systems. Part 1. Stand and site

impacts. For. Prod. J. 45(5): 74-79.

Lanford, B. L.; Stokes, B. J. 1996. Comparison of two thinning systems. Part 2. Productivity and

cost. For. Prod. J. 46(11/12): 47-53.

Lousier, J. D., comp. 1990. Impacts of forest harvesting and regeneration on forest sites. Land

Management Report 67. Victoria: British Columbia Ministry of Forests. 90 p.

McNabb, D. H.; Hobbs, S. D. 1989. Shallow tillage fails to increase 5-year growth of ponderosa

pine seedlings. Northwest Science. 63: 241-245.

Meek, P. 1994. A comparison of two skidders equipped with wide and extra-wide tires. Field Note

No.: Skidding/Forwarding-28. Forest Engineering Institute of Canada. 48 p.

Miller, R. E.; Colbert, S. R.; Morris, L. A. 2004. Effect of heavy equipment on physical properties

of soils and on long-term productivity: A review of literature and current research. Technical

Bulletin No. 887. Research Triangle Park, NC: National Council for Air and Stream Improvement (NCASI), Inc. 76 p.

Stewart, R.; Froehlich, H.; Olsen, E. 1988. Soil compaction: an economic model. West. J. Appl.

For. 3(1): 20-22.

Unger, P. W.; Cassel, D. K. 1991. Tillage implement disturbance effects on soil properties related

to soil and water conservation: A literature review. Soil and Tillage Research. 19: 363-382.

Special Topic—Grand Fir Mosaic

USDA Forest Service Proceedings RMRS-P-44. 2007 175

In: Page-Dumroese, Deborah; Miller, Richard; Mital, Jim; McDaniel, Paul; Miller, Dan, tech. eds. 2007. 

Volcanic-Ash-­Derived Forest Soils of the Inland Northwest: Properties and Implications for Management 

and Restoration. 9-10 November 2005; Coeur d’Alene, ID. Proceedings RMRS-P-44; Fort Collins, CO: 

U.S. Department of Agriculture, Forest Service, Rocky Mountain Research Station.

D. E. Ferguson is a research forester, Rocky Mountain Research Station, Moscow, ID. 

J. L. Johnson-Maynard and P. A. McDaniel are soil scientists, Soil & Land Resources Division, University 

of Idaho, Moscow, ID.

Abstract

	 The Grand Fir Mosaic (GFM) ecosystem is found on ash-cap soils in some mid-elevation forests

of northern Idaho and northeastern Oregon. Harvesting on GFM sites results in successional plant

communities that are dominated by bracken fern (Pteridium aquilinum) and western coneflower

(Rudbeckia occidentalis), andhave largepopulationsofpocket gophers(Thomomys talpoides). Succession

to trees and shrubs is very slow on disturbed GFM sites. Four factors contribute to the protracted stages

of bracken fern plant communities and the slow rate of succession to woody plants: (1) competition

among plants for site resources, (2) allelopathy from bracken fern and western coneflower, (3) pocket

gopher activity, and (4) a nonallophanic soil forming process. Nonallophanic soils occur under the

bracken fern successional plant communities — they are dominated by Al-humus complexes, have

strongly acid pH, have high KCl-extractable Al, and may cause Al toxicity to plants. Allophanic soils

occur under forested conditions — they are dominated by allophane and imogolite, have weakly to

moderately acid pH, and have low Al availability. Allophanic and nonallophanic soils exist side-byside in the GFM, with mineralogy being dependent upon the dominant vegetation. Bracken fern and

western coneflower, with below-ground carbon inputsfrom their well-developed rootsystems, provide

a mechanism that promotes the shift from allophanic to nonallophanic soils. Recommendations for

reforesting GFM sites are provided.

The Grand Fir Mosaic Ecosystem—History 

and Management Impacts

D. E. Ferguson, J. L. Johnson-Maynard, P. A. McDaniel

Introduction

	 Imagine a moist forest environment in the northern Rocky Mountains where supposedly seral

plant communities dominated by bracken fern (Pteridium aquilinum) and western coneflower

(Rudbeckia occidentalis) are really climax plant communities that persist within a matrix of

overmature grand fir (Abies grandis) and western redcedar (Thuja plicata) forests. There are

few wildfires here, so natural succession has reduced the occurrence of seral conifers such

as lodgepole pine (Pinus contorta), Douglas-fir (Pseudotsuga menziesii), western white pine

(Pinus monticola), and western larch (Larix occidentalis). Late successional,shade-tolerantspecies like grand fir, western redcedar, Pacific yew (Taxus brevifolia), and sometimes mountain
176 USDA Forest Service Proceedings RMRS-P-44. 2007

Ferguson, Johnson-Maynard, and McDaniel The Grand Fir Mosaic Ecosystem—History and Management Imacts

hemlock (Tsuga mertensiana) and subalpine fir (Abies lasiocarpa), are common

along with mid-successional Engelmann spruce (Picea engelmannii). Regeneration

of conifers in forest canopy openings is a slow and unreliable process in these

low pH volcanic ash-cap soils that have abundant populations of pocket gophers

(Thomomys talpoides). Disjunct and rare plant species occur in and near these

forests, including evergreen synthyris (Synthyris platycarpa), Oregon bluebell

(Mertensia bella), Dasynotus (Dasynotus daubenmirei), and Case’s corydalis (Corydalis caseana). These moist forests are collectively called the Grand Fir Mosaic

(GFM) ecosystem.

Grand Fir Mosaic forests occur on productive volcanic ash-cap soilsin and near

the Clearwater, Nez Perce, and southern St. Joe National Forestsin northern Idaho,

and the Umatilla National Forest in northeastern Oregon. The name for the GFM

comes from the dominant conifer (grand fir) and the variety of sizes and shapes

of natural openings in the forest canopy. The GFM encompasses approximately

500,000 acres at elevations primarily between 4,500 and 5,500 ft, but is found as

low as 4,200 ft and as high as 6,000 ft (Ferguson and Johnson 1996). The most

common habitat type is Abies grandis/Asarum caudatum (grand fir/wild ginger),

a cool, moist habitat defined by Cooper and others (1991).

Successional plant communities in the GFM are dominated by bracken fern and

western coneflower. Bracken fern is usually present in low densities under forest

canopies, but rapidly expands following disturbance, and can reach heights of 6

ft and densities of 116,000 fronds per acre (Znerold 1979). Below-ground bracken

biomass, primarily rhizomes and fine roots, may be as much as 27,280 lbs per

acre (Jimenez 2005).

Bracken fern glades are plant communities dominated by bracken fern and

western coneflower that appear to persist for millennia. Charcoal samples found

at or near the lower boundary of GFM ash-caps were found to be 1,335±75 and

7,755±75 cal. yrs BP using radiocarbon dating (Jimenez 2005). These charcoal

samples suggest that woody vegetation has been absent for thousands of years,

perhaps dating back to the time of ash deposition during the eruption of Mt.

Mazama (Crater Lake, OR) ~7,600 yrs BP (Zdanowicz and others 1999).

Pocket gophers also alter the course of secondary succession in the GFM,

particularly for planted conifers. Entire plantations of seedlings can be killed by

pocket gophers. Smallseedlings are usually pulled from below ground into tunnels

where the whole tree is eaten. Gophers may eat all or most of the root system of

larger seedlings and saplings.

Our investigations on the GFM were initiated because of difficulty in regenerating harvested areas in the GFM. The first task was to define key ecological

processes that might account for the lack of regeneration and the absence of other

woody species. Research was planned and implemented to study competition

and allelopathy from bracken fern and western coneflower, effects of pocket

gophers, environmental characteristics of the GFM relative to adjacent forests,

and soil development.

Bracken Fern, Western Coneflower, Pocket Gopher, and 

Environmental Research

There is abundant research on bracken fern from around the world dealing

with allelopathy, competition, encroachment rates, and harm to crops, livestock,
USDA Forest Service Proceedings RMRS-P-44. 2007 177

The Grand Fir Mosaic Ecosystem—History and Management Impacts Ferguson, Johnson-Maynard, and McDaniel

and humans. The allelopathic potential of bracken fern has been demonstrated by

severalresearchers, including Stewart (1975) andGliessman (1976). The allelopathic

potential of bracken fern in the GFM was demonstrated by Ferguson and Boyd

(1988), who found that most of the seeds that germinated on soil dominated by

bracken fern died before the seedcoat was shed. Ferguson (1991) demonstrated

allelopathic potential for western coneflower in laboratory tests. Volatile compounds (vapors) from western coneflower reduced or delayed seed germination,

and water extracts reduced growth of the seedling radicle.

Growth and mortality of planted conifers at GFM sites wasreported by Ferguson

and Adams (1994) and Ferguson (1999). Hand weeding of bracken fern and

western coneflower from planting sites increased height growth of planted conifer

seedlings. Pocket gophers killed from 24 to 59 percent of the seedlings, depending

on species. Of the seedlings killed by pocket gophers, 77 percent were killed the

first summer (following spring planting) and the first or second winter, but few

seedlings were killed the second or third summers.

Environmental conditions were studied by Ferguson and Byrne (2000) to see

if they differed between GFM and non-GFM sites in the same vicinity. Remote

monitoring stations were used to sample harvested areas at a GFM site and three

adjacent habitat types (non-GFM grand fir, subalpine fir, and western redcedar).

Variables sampled were wind speed and wind direction at 9 ft above the soil

surface; precipitation; solar radiation; relative humidity at 4.5 ft; air temperature

at 4.5 ft; soil temperature on the soil surface, 1 inch, and 8 inches depth; soil

water potential at 1 inch and 8 inches; and soil pH at 1 inch.

Comparison of the GFM site to non-GFM sites in the same vicinity showed

that the GFM site had a shorter growing season, even though one of the sites was

a subalpine fir habitat type 140 ft higher in elevation than the GFM site. Snow

melted at the GFM site an average of 9 days later than at the subalpine fir habitat

type, 24 days later than at the non-GFM grand fir habitat type, and 52 days later

than at the western redcedar habitat type.

Average GFM soil temperatures at 1 and 8 inches were cooler than the nonGFM sites in April and May because of late snowpacks at the GFM site. During

the rest of the growing season, the GFM site was warmer than the subalpine fir

habitat type, but cooler than the grand fir and western redcedar habitat types.

Summer soil moisture at the GFM site did not dry to the permanent wilting

point as often as the non-GFM sites. Soils at 8 inches dried to a water potential

of –15 bars in only 2 of 6 years of monitoring at the GFM site, while –15 bars

was reached during 4 of the 6 monitoring years at the non-GFM grand fir habitat

type, 4 of 5 years at the western redcedar habitat type, and 5 of 5 years at the

subalpine fir habitat type.

The most insightful variable measured was soil pH at 1-inch depth. The GFM

site was different from the other three sites because soil pH cycled from about

6.0 in the spring to 4.0 in the summer and back to 6.0 in the fall (fig. 1). Each

year for 7 years, soil pH was lower than 5.0 for several weeks to a few months.

A soil pH below 5.0 is a commonly cited threshold where Al toxicity is common to many crops (Shoji and others 1993). A laboratory study has shown that

exchangeable Al increases exponentially in GFM soils as pH decreases below

5.0 (Page-Dumroese and others, this proceedings).
178 USDA Forest Service Proceedings RMRS-P-44. 2007

Ferguson, Johnson-Maynard, and McDaniel The Grand Fir Mosaic Ecosystem—History and Management Imacts

Ash-cap Soil Relationships _______________________________________

Allophanic and Nonallophanic Andisols

The Andisol soil order includes soils that are characterized by andic soil

properties that arise from the presence of significant amounts of noncrystalline

aluminosilicates such as allophane and imogolite, Al-humus complexes, and/or

poorly crystalline Fe oxides (Soil Survey Staff 2003). A lack of illuvial B horizons

indicates that the process of translocation is not significant within the Andisol

order (Ugolini and others 1988; Dahlgren and others 1991) and clearly separates

Andisols from other soil orders with similar mineralogical components.

Andisols are commonly described as being allophanic or nonallophanic, depending on the nature of the minerals present. Allophanic Andisols are dominated

by allophane, imogolite, and clay minerals; are weakly to moderately acid; and

have low KCl-extractable Al and low Alsaturation (table 1) (Shoji and others 1985;

Nanzyo and others 1993). Nonallophanic Andisols have Al-humus complexes and

crystalline clay minerals astheir dominant mineralogical components, and contain

Figure 1—Average daily soil pH at 1 inch for 

a GFM site, 1989 through 1995 (Ferguson 

and Byrne 2000). Each line is a different year 

of data, and discontinuous lines are periods 

of time when soils were too dry to collect pH 

measurements. The horizontal line at pH 5

shows a commonly cited threshold where 

plants start to experience Al toxicity.

Table 1—Comparative characteristics of allophanic and nonallophanic Andisols.

Characteristic Allophanic Nonallophanic

Mineralogy More allophane and imogolite; Less allophane and imogolite: 

less Al-humus complexes more Al-humus complexes

Soil acidity Weakly to moderately acid Strongly acid

Exchangeable Al Low High

Al toxicity Rare Common
USDA Forest Service Proceedings RMRS-P-44. 2007 179

The Grand Fir Mosaic Ecosystem—History and Management Impacts Ferguson, Johnson-Maynard, and McDaniel

a substantially smaller proportion of allophane and imogolite as compared to allophanic Andisols. In addition, nonallophanic soils are strongly to very strongly

acid, have high KCl-extractable Al, and commonly exhibit Al toxicity (table 1)

(Shoji and others 1985; Nanzyo and others 1993). Al-humus complexes and

high concentrations of exchangeable Al in nonallophanic Andisols result in rapid

dissolution and equilibrium between Al in solid and solution phases. Allophanic

Andisols are dominated by allophane and imogolite, which have slower dissolution rates and, therefore, result in slower release of Al into soil solution (Dahlgren

and Saigusa 1994; Dahlgren and others 2004). The rapid release rates of Al in

nonallophanic Andisols provide a source of Al for plant uptake. Due to the possibility of Al toxicity, the distinction of allophanic and nonallophanic Andisols is

important for management purposes.

Because of the impact of Andisol mineralogy on plant productivity (Dahlgren

and others 2004), it is important to understand the factors that control mineral

formation and weathering within the order. Differences in parent material such

as tephra age, geochemistry, hydraulic properties, and additions of exogenous

materials such as loess (Inoue and Naruse 1987; Vacca and others 2003) have

been reported to influence the development of certain mineralogical components

within ash-influenced soils. Other factors that are more influenced by management include organic matter and pH (Shoji and Fugiwara 1984; Johnson-Maynard

and others 1997). The formation of allophanic Andisols tends to be favored in

environments where pH is greater than 5. In contrast, nonallophanic Andisols are

predominately found in more acidic (pH < 5) environments with higher concentrations of organic matter (Shoji and Fujiwara 1984; Shoji and others 1993).

The relationship between organic matter, pH, and Al availability indicates that

plant communities may play a role in influencing Andisol properties. Specific

examples of the impact of vegetation and vegetation conversion on Andisol

morphology and chemistry have been reported. Japanese pampas grass (Miscanthus sinensis), for example, is associated with the formation of dark, humus-rich,

surface horizons known as melanic epipedons (Shoji and others 1990). Biomass

production by Japanese pampas grass was estimated to be 4,840 lbs per acre above

ground and 15,500 lbs per acre below ground. With all of the above-ground and

one-quarter of the below-ground parts added to the soil each year, Japanese pampas grass creates conditions that promote accumulation and humification of soil

organic matter resulting in the formation of melanic epipedons (Shoji and others

1993). Dahlgren and others (1991) reported lowering of soil solution pH with a

corresponding increase in Al concentrations in A horizons of Alic Melanudands

where Japanese oak (Quercus serrata) replaced Japanese pampas grass. The accumulation of organic matter was a distinguishing feature between soils under the

two vegetation types. Another example of the effect of plants on Andisols can be

found on the North Island of New Zealand where Andisols rarely display thick

dark humus horizons except where native podocarp forest has been converted to

bracken fern (Pteridium aquilinum var. esculentum) (Leamy and others 1980).

Andisols in the Grand Fir Mosaic

Sommer (1991) sampled soils and foliage in three GFM plant communities:

mature forest, natural bracken fern glade, and bracken-invaded clearcut. Soil pH

waslower and exchangeable Al was higher in bracken-dominated plant communities than in the mature forest. Soil and foliar nutrients were adequate for conifer
180 USDA Forest Service Proceedings RMRS-P-44. 2007

Ferguson, Johnson-Maynard, and McDaniel The Grand Fir Mosaic Ecosystem—History and Management Imacts

growth, although Al was approaching levels known to be toxic to some plant

species. Small sample size and high variability prevented conclusive results, but

evidence suggested that disturbed forest sites in the GFM are invaded by bracken

fern plant communities and become more like bracken fern glades.

The important documentation of both allophanic and nonallophanic Andisols

in the GFM was reported by Johnson-Maynard and others (1997). Soil chemical and mineralogical properties were studied in adjacent mature forest, natural

bracken fern glade, and bracken-invaded clearcut. Retrospective comparison of

the 30-year-old clearcut to the mature forest and bracken fern glade showed a

conversion from allophanic to nonallophanic soils (fig. 2). Soils in the forest were

dominated by short-range-orderAl-Fe minerals, had low exchangeableAl, and had

pH >5, all of which are consistent with characteristics of allophanic soils (table 1).

Soils in the bracken-invaded clearcut and bracken fern glade were dominated by

Al-humus complexes, had high exchangeable Al, and pH <5, which is consistent

with nonallophanic soils. Johnson-Maynard and others (1997) were the first to

report nonallophanic Andisols in northern Idaho. Also, they were the first, to our

knowledge, to report a conversion from allophanic to nonallophanic mineralogy.

Allophanic and nonallophanic soils exist side-by-side in the GFM, their expression

being dependent upon the dominant plant community.

The chemistry of soil water moving through soils of the GFM has also been

studied in the GFM (Johnson-Maynard and others 1998), using the same study

sites as Johnson-Maynard and others (1997). Soil water chemistry was consistent

with the preferential formation of Al-humus complexesin bracken-dominated sites

that had once been forested. Soil solution was also collected from a weeded area

in a bracken fern glade where bracken fern and western coneflower were hand

weeded for 6 years prior to sampling (Ferguson 1999). Soil water pH, Al, and

dissolved organic carbon in the weeded area were more similar to the forest than

to soil water collected from under the bracken fern glade. Weeding appeared to

result in soil water with chemical composition more similar to that measured in

Figure 2—Depth distribution of Al in soil fractions as determined by 

selective dissolution techniques (adapted from Johnson-Maynard 

1995).
USDA Forest Service Proceedings RMRS-P-44. 2007 181

The Grand Fir Mosaic Ecosystem—History and Management Impacts Ferguson, Johnson-Maynard, and McDaniel

the undisturbed forest, suggesting that the growth of bracken fern and western

coneflower play an important role in the conversion from allophanic to nonallophanic soils.

Although soil water Al concentrations were highest in bracken-dominated plant

communities, they were lower than published toxicity levels for other conifer

species. More work is indicated to determine toxic levels for plant species in the

GFM and to determine the different forms and toxicity of Al in soil solution.

Discussion ______________________________________________________

Research on the GFM ecosystem has identified four factors that, individually

and collectively, may account for the slow rate of secondary succession to woody

vegetation following disturbances that create openings in the forest canopy. The

first factor is competition among plants for site resources such as light, water,

nutrients, and growing space. Competition can be intense because forb communities dominated by bracken fern and western coneflower expand rapidly into

previously forested openings.

The second factor is allelopathy. Direct and indirect effects of phytotoxins

released by plants can reduce the successful establishment and growth of other

species. The allelopathic potential of bracken fern andwestern coneflower has been

demonstrated (Stewart 1975; Gliessman 1976; Ferguson 1991). The quantification

of the individual effects attributable to allelopathy and competition is difficult

because removal of a plant from its natural environment simultaneously removes

the source of allelopathy and competition. Ecologists use the term “interference”

to refer to the combined effects of allelopathy and competition (Muller 1969).

The third factor is large populations of pocket gophers. Gophers can cause

a substantial amount of mortality to planted and natural seedlings in the GFM.

Most gopher-caused mortality to planted seedlings takes place the first summer

after planting and during the first and second winters (Ferguson 1999; Ferguson

and others 2005). Partial removal of the overstory canopy allows enough light

to reach planted seedlings so they can survive and grow — albeit slower than in

full sunlight — and also reduces abundance of pocket gophers, bracken fern, and

western coneflower (Ferguson and others 2005).

The fourth factor is a nonallophanic soil forming process. The data collected

by Johnson-Maynard and others (1997, 1998) demonstrate the conversion of allophanic to nonallophanic mineralogy based on the criteria summarized in table

1. In the undisturbed forest, the dominant secondary mineralogical component of

soils is inorganic, short-range order minerals, which is consistent with allophanic

type Andisols. In bracken/coneflower dominated areas, Al-humus complexes are

the dominant component of soils, consistent with what has been described in

nonallophanic soils.

Allophanic and nonallophanic soils existside-by-side in the GFM, with mineralogy dependent upon the dominant vegetation (fig. 2). Allophanic conditions occur

when vegetation is dominated by coniferous trees, but nonallophanic conditions

occur when sites are dominated by bracken fern and western coneflower (Johnson-Maynard and others 1997). When bracken fern and western coneflower are

removed,soilwater chemistry issimilarto that under allophanicGFMsoils(JohnsonMaynard and others 1998), indicating that bracken fern and western coneflower

are a mechanism in promoting nonallophanic soils. It is likely that bracken fern

and western coneflower are not only sources of large annual additions of carbon
182 USDA Forest Service Proceedings RMRS-P-44. 2007

Ferguson, Johnson-Maynard, and McDaniel The Grand Fir Mosaic Ecosystem—History and Management Imacts

to the soil, thus favoring the formation of Al-humus complexes, but also sources

of organic acids that lower soil pH (Johnson-Maynard and others 1998).

Reforesting GFM Sites____________________________________________

In this section, we discuss management strategies for reforesting GFM sites as

they relate to the nonallophanic soil forming process. The most important point to

remember is that natural regeneration of woody plant species will be a slow and

unreliable process within the GFM. We know of many examples of cutover GFM

forests that have little woody vegetation after 20 to 30 years. Seeds that germinate

in openings in the GFM forest canopy are subject to competition, allelopathy,

pocket gophers, and Al toxicity. These four factors can combine to virtually eliminate the natural establishment of trees and other woody plant species.

Prompt planting following a disturbance will help seedlings become established before the site has abundant bracken fern, western coneflower, and pocket

gophers. Planting larger vs. smaller seedlings helps increase survival and growth

rates. Planted seedlings in clearcuts need to be protected from pocket gophers

until the third spring after they are planted.

Partial cuttings, where only a portion of the overstory trees are removed, retain the shrub component better than clearcuts, and result in less bracken fern,

western coneflower, and gopher-caused damage to seedlings (Ferguson and others 2005). Planted trees do not need protection from pocket gophers in partial

cuttings; however, they will not grow as fast as in clearcuts. After seedlings are

established (5 to 10 years), all or part of the remaining overstory trees can be

removed to improve growth of seedlings.

The overall performance of some planted conifer species was better in trial

plantings on GFM sites (Ferguson 1999; Ferguson and others 2005). Engelmann

spruce and western white pine grew well, had little mortality from non-gopher

causes, and had little top damage from snow or senescing bracken fern fronds.

Douglas-fir also did quite well, especially if larger seedlings were planted. Lodgepole pine grew rapidly, but thisspecies often suffered severe snow damage to tops,

limbs, and stems. Western larch had very high overall mortality, both from gopher

and non-gopher causes, but surviving trees grew rapidly. Another concern with

western larch is top damage and severe lean caused by snowloads in the GFM.

Research Questions _____________________________________________

Much has been learned about ash-cap soils and management options for the

GFM, and additional research would help fill the gaps in our knowledge. Research

studies show that allophanic and nonallophanic soil forming processes exist sideby-side in the GFM. Allophanic processes occur where conifers dominate the site,

and nonallophanic processes occur where bracken fern and western coneflower

dominate. It would be helpful to study allophanic vs. nonallophanic mineralogy

across a range of overstory densities, and determine how quickly allophanic

processes turn into nonallophanic processes following harvest or other activities

that reduce the density of the forest canopy.

Another key research topic is to understand why pH is cyclic in GFM sites

dominated by bracken/coneflower successional plant communities (fig. 1). Comparisons ofseasonal patternsin pH under bracken fern gladesto undisturbed grand

fir forests may shed light on the mechanisms behind this observation.
USDA Forest Service Proceedings RMRS-P-44. 2007 183

The Grand Fir Mosaic Ecosystem—History and Management Impacts Ferguson, Johnson-Maynard, and McDaniel

Soil pH values cycle below 5.0 during part of the growing season, which could

result in Al toxicity (Page-Dumroese and others, this proceedings). However,

little is known about Al toxicity thresholds for plant species and their mychorrhizal associations in the GFM. We would expect that Al toxicity varies with Al

concentration, the various Al compounds that exist in ash-cap soils, and size/age

of plant species. The cyclic nature of soil pH in the GFM may also interfere with

nutrient availability (see Page-Dumroese and others, these proceedings). More

information is needed on availability of nutrients other than Al, especially nitrogen. Recent work has suggested that additions of lime are effective in raising

pH and reducing levels of bioavailable Al in nonallophanic Andisols (Takahashi

and others 2006). Liming experiments could therefore be used to provide valuable information about the role of pH and active forms of Al in tree regeneration

problems observed in the GFM.

The allelopathic potential of bracken fern has been demonstrated by several

researchers around the world, but we only have rudimentary knowledge of allelopathy in western coneflower. Ferguson (1991) demonstrated the allelopathic

potential of western coneflower in laboratory tests, but additional research is

needed under field conditions.

The answers to these research questions would improve our knowledge of the

mechanisms that delay secondary succession to woody plant species in the GFM,

thereby helping refine management recommendations for GFM ash-cap soils.

References______________________________________________________

Cooper, S. V.; Neiman, K. E.; Roberts, D. W. 1991 (revised). Forest habitat types of northern Idaho:

a second approximation. Gen. Tech. Rep. INT-236. Ogden, UT: U.S. Department of Agriculture,

Forest Service, Intermountain Research Station. 143 p.

Dahlgren, R. A.; Saigusa, M. 1994. Aluminum release rates from allophanic and nonallophanic

Andosols. Soil Science and Plant Nutrition. 40: 125-136.

Dahlgren, R. A.; Saigusa, M.; Ugolini, F. C. 2004. The nature, properties and management of

volcanic soils. Advances in Agronomy. 82: 113-182.

Dahlgren, R. A.; Ugolini, F. C.; Shoji, S.; Ito, I.; Sletten, R. S. 1991. Soil-forming processes in Alic

Melanudands under Japanese pampas grass and oak. Soil Science Society of America Journal.

55: 1049-1056.

Ferguson, D. E. 1991. Allelopathic potential of western coneflower (Rudbeckia occidentalis).

Canadian Journal of Botany. 69: 2806-2808.

Ferguson, D. E. 1999. Effects of pocket gophers, bracken fern, and western coneflower on planted

conifers in northern Idaho — an update and two more species. New Forests. 18: 199-217.

Ferguson, D. E.; Adams, D. L. 1994. Effects of pocket gophers, bracken fern, and western coneflower on survival and growth of planted conifers. Northwest Science. 68: 241-249.

Ferguson, D. E.; Boyd, R. J. 1988. Bracken fern inhibition of conifer regeneration in northern Idaho.

Res. Pap. INT-388. Ogden, UT: U.S. Department of Agriculture, Forest Service, Intermountain

Research Station. 11 p.

Ferguson, D. E.; Byrne, J. C. 2000. Environmental characteristics of the Grand Fir Mosaic and adjacent habitat types. Res. Pap. RMRS-RP-24. Fort Collins, CO: U.S. Department of Agriculture,

Forest Service, Rocky Mountain Research Station. 20 p.

Ferguson, D. E.; Byrne, J. C.; Coffen, D. O. 2005. Reforestation trials and secondary succession

with three levels of overstory shade in the Grand Fir Mosaic ecosystem. Res. Pap. RMRS-RP-53.

Fort Collins, CO: U.S. Department of Agriculture, Forest Service, Rocky Mountain Research

Station. 16 p.

Ferguson, D. E.; Johnson, F. D. 1996. Classification of Grand Fir Mosaic habitats. Gen. Tech.

Rep. INT-GTR-337. Ogden, UT: U.S. Department of Agriculture, Forest Service, Intermountain

Research Station. 16 p.

Gliessman, S. R. 1976. Allelopathy in a broad spectrum of environments as illustrated by bracken.

Linnean Society Botanical Journal. 73: 95-104.
184 USDA Forest Service Proceedings RMRS-P-44. 2007

Ferguson, Johnson-Maynard, and McDaniel The Grand Fir Mosaic Ecosystem—History and Management Imacts

Inoue, K.; Naruse, T. 1987. Physical, chemical and mineralogical characteristics of modern eolian

dust in Japan and rate of dust deposition. Soil Science and Plant Nutrition. 33: 327-345.

Johnson-Maynard, J. L. 1995. Alteration of Andisols in the Grand Fir Mosaic ecosystem following

invasion by bracken fern successional plant communities. Moscow: University of Idaho. 91 p.

Thesis.

Johnson-Maynard, J. L.; McDaniel, P. A.; Ferguson, D. E.; Falen, A. L. 1997. Chemical and mineralogical conversion of Andisols following invasion by bracken fern. Soil Science Society of

America Journal. 61: 549-555.

Johnson-Maynard, J. L.; McDaniel, P. A.; Ferguson, D. E.; Falen, A. L. 1998. Changes in soil solution chemistry of Andisols following invasion by bracken fern. Soil Science. 163: 814-821.

Jimenez, J. 2005. Bracken fern communities of the Grand Fir Mosaic: biomass allocation and influence on selected soil properties. Moscow, ID: University of Idaho. 209 p. Thesis.

Leamy, M. L.; Smith, G. D.; Colmet-Daage, F.; Otowa, M. 1980. The morphological characteristics

of Andisols. In: Theng, B. K. B., ed. Soils with variable charge. Palmerston North, New Zealand:

Offset Publications: 17-34.

Muller, C. H. 1969. Allelopathy as a factor in ecological process. Vegetatio. 18: 348-357.

Nanzyo, M.; Dahlgren, R.; Shoji, S. 1993. Chemical characteristics of volcanic ash soils. In: Shoji,

S.; Nanzyo, M.; Dahlgren, R., eds. Volcanic ash soils: genesis, properties, and utilization. Amsterdam, The Netherlands: Elsevier Science Publishers: 145-187.

Shoji, S.; Fugiwara, T. 1984. Active aluminum and iron in the humus horizons of Andosols from

northeastern Japan: their forms, properties, and significance in clay weathering. Soil Science.

137: 216-226.

Shoji, S.; Ito, T.; Saigusa, M.; Yamada, I. 1985. Properties of nonallophanic Andisols from Japan.

Soil Science. 140: 264-277.

Shoji, S.; Kurebayashi, T.; Yamada, I. 1990. Growth and chemical composition of Japanese pampas

grass (Miscanthus sinensis) with special reference to the formation of dark-colored Andisols in

northeastern Japan. Soil Science and Plant Nutrition. 36: 105-120.

Shoji, S.; Nanzyo, M.; Dahlgren, R. A. 1993. Volcanic ash soils: genesis, properties, and utilization. Amsterdam, The Netherlands: Elsevier Science Publishers: 288 p.

Soil Survey Staff. 2003. Keys to Soil Taxonomy. 9th ed. U.S. Department of Agriculture, Natural

Resources Conservation Service. U.S. Government. Printing Office, Washington, DC: 331 p.

Sommer, M. R. 1991. Soils of the Grand Fir Mosaic. Moscow, ID: University of Idaho. 97 p.

Thesis.

Stewart, R. E. 1975. Allelopathic potential of western bracken. Journal of Chemical Ecology. 1:

161-169.

Takahashi, T.; Ikeda, Y.; Fujita, K.; Nanzyo, M. 2006. Effect of liming on organically complexed

aluminum of nonallophanic Andosols from northeastern Japan. Geoderma. 130: 26-34.

Ugolini, F. C.; Dahlgren, R. A.; Shoji, S.; Ito, T. 1988. An example of andosolization and podzolization as revealed by soil solution studies, S. Hakkoda, N.E. Japan. Soil Science. 145: 111-125.

Vacca, A.; Aamo, P.; Pigna, M.; Violante, P. 2003. Genesis of tephra-derived soils from the Roccamonfina volcano, south central Italy. Soil Science Society of America Journal. 67: 198-207.

Zdanowicz, C. M.; Zielinski, G. A.; Germani, M. S. 1999. Mount Mazama eruption: calendrical age

verified and atmospheric impact assessed. Geology. 27: 621-624.

Znerold, R. M. 1979. Western bracken control with asulam. Pullman, WA: Washington State University.

36 p. Thesis.
USDA Forest Service Proceedings RMRS-P-44. 2007 185

In: Page-Dumroese, Deborah; Miller, Richard; Mital, Jim; McDaniel, Paul; Miller, Dan, tech. eds. 2007. 

Volcanic-Ash-­Derived Forest Soils of the Inland Northwest: Properties and Implications for Management 

and Restoration. 9-10 November 2005; Coeur d’Alene, ID. Proceedings RMRS-P-44; Fort Collins, CO: 

U.S. Department of Agriculture, Forest Service, Rocky Mountain Research Station.

Deborah Page-Dumroese and Dennis Ferguson are Research Scientists at the Rocky Mountain Research 

Station, U.S. Forest Service in Moscow, ID; Paul McDaniel and Jodi Johnson-Maynard are faculty in 

the Department of Plant, Soil, and Entomological Sciences, University of Idaho, Moscow, ID. 

Abstract

	 Data from volcanic ash-influenced soils indicates that soil pH may change by as much as 3 units during a year. The effects of these changes on soil chemical properties are not well understood. Our study

examined soil chemical changes after artificially altering soil pH of ash-influenced soils in a laboratory.

Soil from the surface (0-5 cm) and subsurface (10-15 cm) mineral horizons were collected from two

National Forests in northern Idaho. Soil collections were made from two undisturbed forest stands,

a partial cut, a natural bracken fern (Pteridium aquilinum [L.] Kuhn) glade, an approximately 30-yearold clearcut invaded with bracken fern, and a 21-year-old clearcut invaded with western coneflower

(Rudbeckia occidentalis Nutt.). Either elemental sulfur (S) or calcium hydroxide (Ca(OH)2) were added

to the soil to manipulate pH. After 90 days of incubation, pH ranged from 3.6 to 6.1 for both National

Forests and all stand conditions. Total C, total N, and extractable base cations (Ca, Mg, and K) were

generally unaffected by pH change. Available P increased as pH dropped below 4.5 for both depths

and all soil types. Nitrate was highest at pH values greater than 5.0 and decreased as pH decreased

indicating that nitrification is inhibited at lower pH. Contrary to nitrate, potentially mineralizable N

increased as pH declined. Total acidity and exchangeable aluminum increased exponentially as pH

decreased, especially in the uncut and partial cut stands. Data from this laboratory study provides

information on the role of pH in determining the availability of nutrients in ash-cap soils.

Chemical Changes Induced by 

pH Manipulations of Volcanic 

Ash-Influenced Soils

Deborah Page-Dumroese, Dennis Ferguson, Paul McDaniel, and 

Jodi Johnson-Maynard

Introduction

	 In north-central Idaho, some forests are characterized by conifer regeneration problems despite favorable

climatic conditions(udic moisture and frigid soil temperature regimes). Foreststands at mid-elevations are most

at risk after timber harvest or other disturbance because they are quickly invaded by bracken fern (Pteridium 

aquilinum [L.] Kuhn), western coneflower (Rudbeckia occidentalis Nutt.), and pocket gophers (Thomomys 

talpoides). These sites are collectively known as the Grand Fir Mosaic (GFM) and are named for the dominant

conifer, grand fir (Abies grandis [Dougl. ex D. Don] Lindl.), that occurs in a mosaic pattern with shrub and

forb communities (Ferguson 1991a; Ferguson and others, this proceedings).
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Page-Dumroese, Ferguson, McDaniel, and Johnson-Maynard Chemical Changes Induced by pH Manipulations of Volcanic Ash-Influenced Soils

Timber harvesting began in the GFM in the 1960s and it soon became evident

that regeneration problems existed. Woody vegetation is still infrequent on many

of these sites 30 years after clearcutting, even with repeated plantings (Ferguson

and Adams 1994). Clearcut stands were quickly invaded by forbs (predominately

bracken fern and western coneflower) and rodents. The allelopathic potential of

both bracken fern and western coneflower has been well documented (Stewart

1975; Ferguson and Boyd 1988; Ferguson 1991b). In addition to invading forbs,

pocket gophers also cause substantial seedling mortality (Ferguson and others

2005). Competition for light, moisture, and nutrients within the GFM is high.

While the combination of competition, pocket gophers, and allelopathy contribute

to the arrested state of secondary succession (Ferguson and Adams 1994), these

factors do not appear to entirely explain reforestation failures.

Soils throughout the GFM are strongly influenced by volcanic ash in the

surface horizons. The ash was deposited approximately 7,700 years ago when

Mt. Mazama erupted (Zdanowicz 1999). Volcanic ash-influenced soils have

unique parent materials and secondary mineral assemblages that, in general, are

not as well understood as those in other mineral soils. Volcanic ash-influenced

soils are classified as either allophanic or nonallophanic, depending on the relative abundance of organic matter and inorganic short-range-order minerals (Shoji

and others 1993). Nonallophanic soils have more organic matter, lower pH,

higher levels of KCl-extractable aluminum (Al), and lower levels of calcium (Ca)

relative to allophanic soils (Shoji and others 1993). Low soil pH may increase

concentrations of extractable (potentially plant available) Al, leading to Al toxicity to woody vegetation (Dahlgren and others 1991). Clearcutting and intensive

utilization (whole tree harvesting) of forest biomass may accelerate soil acidification processes (Ulrich and others 1980; Nosko and Kershaw 1992). In addition to

acidification from harvest activities, vegetation-induced acidification appears to

occur under bracken fern and western coneflower plant communities (JohnsonMaynard and others 1997). These acidified volcanic ash-influenced soils, which

are high in exchangeable Al, may release Al into soil solution at levels toxic to

woody vegetation (Anderegg and Naylor 1988).

Two soil factors have become a concern in GFM forest openings. First, soil

pH drops below 5.0 after harvest operations and the subsequent invasion of

bracken fern and western coneflower (figs. 1 and 2). At this pH, Al can reach

toxic levels and low soil pH can inhibit growth of some seedling species (Nosko

and Kershaw 1992). Second, there are seasonal pH fluctuations of 2-3 pH units

that are not typically found in bulk mineral soil unless heavily impacted by acid

rain or, occasionally, harvest activities (Mroz and others 1985; Brais and others

1995; Alewell and others 1997). Winter pH values average around 6, but drop

below 4 during the growing season. These seasonal pH fluxes could be correlated

with inputs of acid litter from bracken fern and western coneflower, increasing

root respiration during the growing season, or decreases in soil moisture content.

In addition, these two species likely take up high amounts of nutrients from the

soil, which may also contribute to acid conditions (Gilliam 1991). Many factors

influence forest soil pH (for example, precipitation, nutrient exchange, and soil

age), but harvest activity can particularly influence it (Staaf and Olsson 1991).

Although forest harvesting can lower pH, subsequent invasion by bracken fern

and western coneflower appears to contribute to and maintain low pH relative

to undisturbed forest soils.
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Chemical Changes Induced by pH Manipulations of Volcanic Ash-Influenced Soils Page-Dumroese, Ferguson, McDaniel, and Johnson-Maynard

Figure 2—Average soil pH at 2.5 cm for the Clearwater National 

Forest fern-invaded clearcut (unpublished data collected as 

described in Ferguson and Byrne 2000). The bold line is 1997 

and the thin line is 1995.

Figure 1—Average soil pH at 2.5 cm for the Nez Perce National 

Forest coneflower-invaded clearcut (from Ferguson and Byrne 

2000). The bold line is 1994, which was a dry growing season. 

The thin line is 1993, which was a wet growing season. Discontinuous parts of the line are from removal of the pH probe 

during the driest part of the growing season. Soil pH at this site 

was assessed in situ using pH probes (model 613, IC controls 

Orangeville, Ontario, Canada) buried 2.5 cm below the mineral 

soil surface.
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Page-Dumroese, Ferguson, McDaniel, and Johnson-Maynard Chemical Changes Induced by pH Manipulations of Volcanic Ash-Influenced Soils

The slow forest regeneration process in the GFM has decreased management

options for fuel reductions and biomass production, biodiversity of native flora

and fauna, and aesthetic values in and near these areas. Low soil pH and its cyclic

nature over a growing season may be altering soil chemistry, nutrient cycling

processes, and preventing establishment of woody vegetation. Consequently,

our objective was to artificially alter pH of ash-influenced forest soils from the

GFM by additions of sulfur (S) or calcium hydroxide (Ca(OH)2) to better evaluate

potential in situ chemical changes within these soils.

Study Site Description ___________________________________________

Two study sites, one on the Clearwater National Forest and one on the Nez

Perce National Forest of north-central Idaho, were selected to provide a north/

south range of plant community cover types for soil collection. There are thicker

deposits of volcanic ash in the northern part of the GFM where these soils are

classified as Andisols. Inceptisols dominate in the southern part of the GFM where

ash deposits are thinner and more highly mixed. Bracken fern dominates forb

communities in the northern part of the GFM and western coneflower dominates

in the southern part, although both species occur together throughout the GFM.

Table 1 lists study site locations, vegetation types, and soil classifications.

Clearwater National Forest soil samples were collected in 1994 near Eagle

Point (elevation 1,400 m, eastern aspect, 20 percent slope, T40N, R7E, S35). The

dominant soil feature of this study area is approximately 60 cm of Mt. Mazama

volcanic ash underlain with colluvium or residuum derived from fine-grained

igneous rock. To assess the importance of vegetation community structure, soil

samples were collected from adjacent areas with similar slope, aspect, and parent material, but different vegetation cover. Soil samples were collected from

the undisturbed forest (46 m2 ha–1 basal area of overstory), a partial cut (approximately 30 m2 ha–1 of overstory remaining), a naturally occurring bracken

fern glade (present when the adjacent areas were harvested), and a ~30-year-old

bracken fern-invaded clearcut (invaded by bracken fern and western coneflower

after harvesting between 1965 and 1968).

Nez Perce National Forestsoilsamples were collected in 1994 at Dogleg (elevation 1,740 m, southern aspect, 5 percent slope, T31N, R6E, S34). The dominant

soil feature is approximately 40 cm of Mt. Mazama volcanic ash underlain with

deeply weathered mica schist (Sommer 1991). Vegetation types at this site were

undisturbed forest (45 m2 ha–1 basal area of overstory) and a 21-year-old western

Table 1—Location, vegetation type, and soil classification of study sites.

National Forest Vegetation type Soil classification‡

Clearwater Undisturbed forest Typic Hapludand

Nez Perce Undisturbed forest Vitrandic Cryumbrept

Clearwater Partial cut Typic Hapludand

Clearwater Natural bracken fern glade Alic Fulvudand

Clearwater 30-year-old bracken fern-invaded clearcut Alic Hapludand

Nez Perce 21-year-old western coneflower-invaded clearcut Vitrandic Cryumbrept

‡ Clearwater National Forest soil classifications from Johnson-Maynard and others (1997)

Nez Perce National Forest soil classifications from Sommer (1991).
USDA Forest Service Proceedings RMRS-P-44. 2007 189

Chemical Changes Induced by pH Manipulations of Volcanic Ash-Influenced Soils Page-Dumroese, Ferguson, McDaniel, and Johnson-Maynard

coneflower-invaded clearcut (invaded bywestern coneflower and bracken fern after

harvesting in 1973). Vegetation types were adjacent to each other, having similar

slope, aspect, and parent material. There were no natural western coneflower

glades dating to pre-harvest activities and no partial cut stands in the vicinity.

Methods _______________________________________________________

Field Collection Methods

In each forest and vegetation type, mineral soil was collected from the 0-5 cm

and 10-15 cm depths. Soil samples were brought to the USDA Forest Service,

Moscow Laboratory, air dried, and passed through a 2-mm sieve. Initial pH was

measured electrometrically in a 2:1 water:soil suspension.

Laboratory Methods

Depending on initial soil pH, we chose five treatments to raise or lower soil pH

in an attempt to establish a range of pH values from 3.5 to 6.0. For each vegetation type and depth, S at rates of 0.45, 0.90, 1.80, 2.70, or 3.6 g kg–1 or Ca(OH)2

at rates of 0.45, 0.90, or 1.80 g kg –1 were added to provide a range of pH values.

In addition, there was a control (no chemical added) for each vegetation type

and soil depth. Each S or Ca(OH)2 soil addition rate and the control from each

vegetation type was replicated three times. Soil was placed in 655 cm3 plastic

tubes with nylon screen over the bottom openings to prevent soil loss.

Soil water potential was brought to –0.033 MPa by the addition of deionized

water. The tubes were randomly located on a greenhouse bench and incubated at

a daytime temperature of 25 °C and a nighttime temperature of 18 to 20 °C until

the pH stabilized (90 days). When soil water potential dropped below –0.10 MPa,

additional deionized water was added until the soil reached field capacity. After

pH stabilized (unchanged for 5 days), soil was air dried for chemical analyses.

Final pH was measured as described above after the incubation period.

Total carbon (C) and nitrogen (N) were analyzed in a LECO induction furnace

operated at 1050 °C (LECO Corp, St. Joseph, MI). Total acidity and exchangeable Al were extracted with 1N KCl (Bertsch and Bloom 1986). Exchangeable

calcium (Ca), magnesium (Mg), and potassium (K) were extracted using 1N NH4Cl

(Palmer and others 2001). Calcium and Mg were analyzed by atomic absorption

spectroscopy, and K was analyzed by flame emission. Nitrate-N (NO3-N) was

determined on moist samples using 1N KCl extract and an Alpkem Rapid Flow

Analyzer (Mulvaney 1996). Potentially mineralizable N (PMN) was estimated using the 7-day anaerobic incubation technique on moist samples (Powers 1980).

Extractable phosphorus (P) was determined using either the Bray 1 method (for

samples with a pH<6.0) or the Olsen method (for samples with a pH >6.0) (Kuo

1996). Organic matter was determined by weight loss after combustion at 375 °C

for 16 h (Ball 1964).

Statistical Analyses

Regression equations were developed using PROC MIXED in SAS (Littell and

others 1996), at the 0.05 significance level, and LSMEANS was used to compare

vegetation types within soil depths. When analyzing results for Ca, we excluded
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Page-Dumroese, Ferguson, McDaniel, and Johnson-Maynard Chemical Changes Induced by pH Manipulations of Volcanic Ash-Influenced Soils

treatments to raise soil pH because the Ca(OH)2 would have artificially elevated

Ca levels. Transformations of variables were explored to achieve homogeneity

of error variance, normality and independence of error and block effects, and to

obtain additivity of effects (Littell and others 1996).

Results and Discussion___________________________________________

Soil pH Changes

Field studies in the GFM indicate that substantial pH fluxes occur throughout

the year (figs. 1 and 2) (Ferguson and others, this proceedings). Results of our

controlled study confirm our initial observation that changes in vegetation type

influence forest soil pH (table 2). Before treatment with S or Ca(OH)2, the 0-5 cm

soil pH waslowest in the natural bracken fern glade (5.0) and fern-invaded clearcut

(4.7) on the Clearwater National Forest, intermediate on the Nez Perce National

Forest undisturbed area (5.4) and coneflower-invaded clearcut (5.4), and highest

on the Clearwater National Forest undisturbed forest (6.3) and partial cut (6.4)

(table 2). Soil pH at the 10-15 cm depth followed the same trends. After treatment

with S or Ca(OH)2 and 90 days of incubation, final pH values ranged from 3.6 to

6.1 (table 2). Most pH changes occurred within 45 days of starting the incubation

period, but the lowest pH values were achieved after 85 days.

Interestingly, untreated soils from the Clearwater National Forest undisturbed

and partial cut treatments exhibited a decline in soil pH during incubation in the

greenhouse. For example, the initial average pH in the undisturbed forest was

6.3, but at the end of the incubation period, the highest pH value was 5.4. This

“natural” decrease in the absence of vegetation and biotic processes is similar to

the pH decreases shown in figures 1 and 2. In these two figures, winter pH values

average around 6, but drop below 4 during the growing season. These seasonal

pH fluxes may be driven by inputs of acid litter from bracken fern and western

coneflower. In addition, these two specieslikely take up high rates of nutrientsfrom

Table 2—Initial and final soil pH ranges after treatment with S or Ca(OH) 2.

National Forest Vegetation type Initial pH Final pH range

- - - - - -0-5 cm depth- - - - - - - -

Clearwater Undisturbed forest 6.3 3.7 - 5.4

Nez Perce Undisturbed forest 5.4 3.8 - 5.3

Clearwater Partial cut 6.4 3.6 - 5.0

Clearwater Natural bracken fern glade 5.0 3.7 - 5.0

Clearwater 30-year-old bracken fern-invaded clearcut 4.7 3.7 - 5.6

Nez Perce 21-year-old coneflower-invaded clearcut 5.4 3.8 - 5.8

- - - - - - 10-15 cm depth - - - - - -

Clearwater Undisturbed forest 5.8 3.6 - 5.3

Nez Perce Undisturbed forest 5.3 3.8 - 5.5

Clearwater Partial cut 6.2 3.8 - 5.2

Clearwater Natural bracken fern glade 4.9 3.9 - 5.1

Clearwater 30-year-old bracken fern-invaded clearcut 4.3 3.7 - 5.1

Nez Perce 21-year-old coneflower-invaded clearcut 5.6 3.8 - 6.1
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Chemical Changes Induced by pH Manipulations of Volcanic Ash-Influenced Soils Page-Dumroese, Ferguson, McDaniel, and Johnson-Maynard

the soil, which may also contribute to acid conditions (Gilliam 1991). Although

forest harvesting can lower pH, subsequent invasion by bracken fern or western

coneflower appears to contribute to and maintain low pH relative to undisturbed

forest soils. However, the laboratory data indicates that some pH changes within

these soil types are possible even without vegetation facilitating the change.

Carbon and Nitrogen

There were significant differencesin totalCconcentration among the vegetation

types (table 3). Soil C concentration was highest under the fern-invaded clearcut

at both depths (11.27 percent 0-5 cm depth; 10.00 percent 10-15 cm depth).

Total C was lowest at the 10-15 cm depth where conifers were present (both

undisturbed forests and partial cut). The soils that support the highest vegetation

turnover rates (bracken fern and western coneflower) had similar C concentrations

at both depths, while vegetation types with conifers present had about twice as

much C in the surface soil compared to the 10-15 cm depth.

The fern-invaded clearcut has approximately 390 g/m2 of bracken frond biomass

added to the soil annually (Znerold 1979). On the Clearwater National Forest,

rhizome and fine root biomass in the fern-invaded communities averaged

4000 g/m2 (Jimenez 2005); in the natural glade, rhizome and fine root biomass

averaged 3200 g/m2. It is not surprising that this vegetation type has higher C concentrations. We expected that the natural bracken fern glade would have as much

C as the fern-invaded clearcut, but this was not the case. The natural bracken fern

glade soil appears to be at an intermediate point between the undisturbed forest

and the fern-invaded clearcut. These results are similar to C and N data collected

from nearby sites within the GFM (Johnson-Maynard and others 1997). One explanation may be that the natural bracken fern glade has reached a steady state.

Table 3—Mean C, N, Ca, Mg, and K in the control treatment, by vegetation type and depth. Each mean is an average of three 

replications. 

National Vegetation

Forest type Carbon Nitrogen Calcium Magnesium Potassium

- - - - - - percent - - - - - - - - - mg/kg - - -

 0-5 cm depth

Clearwater Undisturbed forest 6.60 a‡ 0.40 a 12.21 d 1.12 b 1.54 b

Nez Perce Undisturbed forest 7.87 b 0.74 c 14.16 e 1.14 b 0.99 a

Clearwater Partial cut 6.23 a 0.36 a 7.86 b 0.74 a 0.99 a

Clearwater Natural bracken fern glade 7.93 b 0.61 b 6.88 a 3.29 d 2.77 c

Clearwater Bracken fern-invaded clearcut 11.27 c 0.69 bc 6.70 a 2.34 c 2.89 c

Nez Perce Coneflower-invaded clearcut 6.17 a 0.35 a 9.16 c 0.92 a 1.02 a

 10-15 cm depth

Clearwater Undisturbed forest 3.17 a 0.24 a 5.41 c 0.74 d 1.22 c

Nez Perce Undisturbed forest 3.90 b 0.22 a 5.38 c 0.41 a 0.71 b

Clearwater Partial cut 3.63 ab 0.25 a 3.79 b 0.49 c 0.71 b

Clearwater Natural bracken fern glade 5.90 c 0.48 c 4.25 b 1.38 e 2.20 e

Clearwater Bracken fern-invaded clearcut 10.00 d 0.67 d 2.72 a 0.77 d 1.30 d

Nez Perce Coneflower-invaded clearcut 6.27 c 0.34 b 5.66 c 0.45 b 0.46 a

‡ Within soil depth, means followed by different letters are significantly different (p = 0.05) using LSMEANS.
192 USDA Forest Service Proceedings RMRS-P-44. 2007

Page-Dumroese, Ferguson, McDaniel, and Johnson-Maynard Chemical Changes Induced by pH Manipulations of Volcanic Ash-Influenced Soils

Because bracken fern produces high levels of allelopathic chemicals (Ferguson

and Boyd 1988), it is perhaps becoming autotoxic (Gliessman and Muller 1978),

which results in less frond biomass (natural glade 678 g/m2; fern-invaded clearcut

916 g/m2 (Jimenez 2005)) and less organic C incorporated into the soil. These

two types of bracken fern stands (natural glade and invaded clearcut) may also

be at different lifecycle stages (Atkinson 1986).

Higher soil C concentrations in the fern-invaded clearcut are consistent with

the development of nonallophanic soil characteristics following invasion (Nanzyo

and others 1993; Johnson-Maynard and others 1997; Dahlgren and others 2004).

Increased levels of C in the bracken fern sites, as compared to undisturbed soils,

may increase the potential for preferential formation of Al-humus complexes

(Dahlgren and others 1993).

Forest sites invaded by western coneflower maintained moderate levels of C

throughout the sampling depths. At the 10-15 cm depth the coneflower-invaded

clearcut had nearly twice as much C as the undisturbed forest soil (table 3). Carbon was distributed deeper in the soil profile in the coneflower-invaded clearcut

than on the bracken fern sites. This may be because the coneflower-invaded site

had greater surface and subsoil mixing caused by pocket gophers (Ferguson and

Adams 1994) or because of slightly less surface volcanic ash deposition (Sommer

1991).

For each vegetation type, there was generally more N in the 0-5 cm depth than

in the 10-15 cm depth, with two notable exceptions. Both the fern-invaded clearcut

and the coneflower-invaded clearcut soils had as much N in the 10-15 cm depth

as the surface soil. This is likely caused by the large annual inputs of forb biomass

that usually occur in newly invaded clearcuts (Attiwill and others 1985).

Regression analyses showed that total C and N were unchanged after altering

pH. This result was not unexpected since we did not add organic matter.

Base Cation Concentrations

Based on the control samples, vegetation type does influence soil Ca, Mg, and

K concentrations in these volcanic ash soils (table 3). For both soil depths, the

fern glade and the fern-invaded clearcut had significantly more K and Mg than

soils from under the other vegetation types. In contrast, Ca content was greatest

in soils under both undisturbed forests.

Regression analysis showed that base cation concentrations (Ca, Mg, and K)

did not change as a result of pH changes (data not shown). Our results differ from

those of Mohebbi and Mahler (1988) who found a strong correlation between pH

and cation concentration after artificially changing pH in a loessal soil. In their

study, as pH increased, both K and Mg decreased; however, Ca sharply increased

from pH 5 to 7. It also increased after pH dropped below 3.5. It is unusual that

soil consisting of volcanic-ash influenced materials, which have a variable charge,

did not show a marked reduction in the retention of exchangeable bases with

decreasing pH. This indicates there may be enough permanent charge minerals

to maintain base concentrations. In the fern glade and the fern-invaded clearcut,

soils may be developing properties typical of nonallophanic Andisols (JohnsonMaynard and others 1997).

Lack of pH-driven changes in cation concentration in our study may be related

to high organic C content of the ash-influenced soil (Shoji and others 1993).

Theoretically, once these sites are harvested, substantial losses of basic cations are
USDA Forest Service Proceedings RMRS-P-44. 2007 193

Chemical Changes Induced by pH Manipulations of Volcanic Ash-Influenced Soils Page-Dumroese, Ferguson, McDaniel, and Johnson-Maynard

possible. Both loss of nutrients from aboveground pools (Boyle and others 1973;

Federer and others 1989) and increased leaching losses have been reported after

harvesting (Hendrickson and others 1989). However, cations may be redistributed into new, immediate regrowth of bracken fern or western coneflower after

harvesting and not lost from the site (Johnson and others 1997).

Available Phosphorus

Phosphorus (P) amounts varied significantly among vegetation types and soil

depths. The mean values for P in the control treatment are shown in table 4. The

largest P means are in the 0-5 cm depth under the undisturbed forests (Nez Perce

National Forest 3.17 μg/g and Clearwater National Forest 3.03 μg/g). The fern

glade (2.73 μg/g) and fern-invaded clearcut (2.20 μg/g) were intermediate in P,

and the lowest means were in the coneflower-invaded clearcut (1.87 μg/g) and

partial cut (1.70 μg/g).

Regression analyses showed that P increased with decreasing pH. Response of

soil P was similar at both soil depths; therefore, regression equations are shown

only for the 0-5 cm depth (table 5). The vegetation types had similar response

Table 4—Mean P, potentially mineralizable N (PMN), nitrate (NO3-N), aluminum (Al), and total acidity in the control treatment, by vegetation type and soil depth. Each mean is the average of three replications.

National Vegetation

Forest type P PMN NO3-N Al Total acidity

 μg/g - - - - - - mg/kg - - - - - - - - - - - -cmol/kg - - - - -

0-5 cm depth

Clearwater Undisturbed forest 3.03 c‡ 100.41 b 87.73 a 0.17 a 0.28 a

Nez Perce Undisturbed forest 3.17 c 60.16 ab 172.01 b 0.22 a 0.41 ab

Clearwater Partial cut 1.70 a 14.96 a 105.18 a 0.34 ab 0.58 bc

Clearwater Natural bracken fern glade 2.73 c 7.56 a 230.07 bc 0.54 b 0.78 c

Clearwater Bracken fern-invaded clearcut 2.20 b 55.32 ab 246.99 c 1.14 c 1.77 d

Nez Perce Coneflower-invaded clearcut 1.87 ab 2.14 a 97.51 a 0.23 a 0.34 ab

10-15 cm depth

Clearwater Undisturbed forest 1.80 c 6.55 a 24.03 a 0.18 a 0.31 a

Nez Perce Undisturbed forest 2.10 d 38.85 a 36.51 a 0.81 ab 0.95 ab

Clearwater Partial cut 1.40 b 28.04 a 51.68 ab 0.50 a 0.61 a

Clearwater Natural bracken fern glade 1.50 b 3.97 a 136.94 c 1.38 b 1.70 b

Clearwater Bracken fern-invaded clearcut 2.53 e 192.30 b 127.45 bc 3.55 c 4.22 c

Nez Perce Coneflower-invaded clearcut 0.93 a 29.31 a 47.61 ab 0.21 a 0.31 a

‡ Within each soil depth, means followed by different letters are significantly different (p = 0.05) using LSMEANS.

Table 5—Regression equations for 0-5 cm depth (bold lines on figs. 3, 5, 

and 6).

Y= exp (βo +β1*pH) and Y, βo, and β1 take on the following values:

	 Definition	 Dependent (Y)	 βo	 β1

P concentration PHOS 2.6789 –0.3612

Potentially mineralizable N PMN 10.4498 –1.4457

NO3-N concentration NO3-N –7.1482 2.2212

KCl-extractable Al ALUM 10.5408 –2.2514

Total acidity ACID 9.9878 –2.0526
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Page-Dumroese, Ferguson, McDaniel, and Johnson-Maynard Chemical Changes Induced by pH Manipulations of Volcanic Ash-Influenced Soils

surfaces (fig. 3). Soil from the Clearwater National Forest undisturbed forest had

the highest available P when pH dropped below 4.0. Both humus and allophane

content in volcanic ash-influenced soils affect P availability and the high level of

C in the fern-invaded clearcut soil may be sorbing P (Wada 1985). These results

are quite different from the loessal soils that have a strong linear increase in available P as pH increases (Mohebbi and Mahler 1988). For volcanic ash-influenced

soils, the pH dependency of phosphate sorption is highest between pH 3 and 4,

and generally decreases with increasing pH (Nanzyo 1987). This is especially true

for allophanic ash-influenced soils as compared to nonallophanic ash-influenced

soils (Nanzyo and others 1993).

In soils consisting of weathered volcanic ash, P sorption is a major soil fertility

problem (Andregg and Naylor 1988). In most mineral soils, organic matter is an

important reservoir for P. However, in many volcanic ash-influenced soils, organic

matter protects P from sorption (Moshi and others 1974). This appears to be the

case for these soils as well.

Figure 3—Regression equations for available P concentration (μg/g) of the 

0‐5 cm depth as affected by pH manipulation by vegetation type. The bold line 

is the regression for all vegetation types.
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Chemical Changes Induced by pH Manipulations of Volcanic Ash-Influenced Soils Page-Dumroese, Ferguson, McDaniel, and Johnson-Maynard

Potentially Mineralizable N and Nitrate-N

Potentially mineralizable N (PMN) concentrations varied widely among vegetation types and soil depths (table 4). For example, in the control soil for the

0-5 cm depth, PMN ranged from a low of 2.14 mg/kg in the coneflower-invaded

clearcut to 100.41 mg/kg in the undisturbed forest on the Clearwater National

Forest. Amounts of PMN at the 0-5 cm soil depth was low in the fern glade, but

intermediate in the fern-invaded clearcut.

Nitrate-N (NO3-N) also varied among vegetation and soil depths. The largest

means at the 0-5 cm depth for the control soil (table 4) were in the fern-invaded

clearcut (246.99 mg/kg) and fern glade (230.07 mg/kg), and the lowest mean was

87.73 mg/kg in the undisturbed forest soil from the Clearwater National Forest.

Means for NO3-N at the 10-15 cm depth were lower than the 0-5 cm depth, but

the trends were similar.

Analysesshowed that PMN concentrations declined rapidly assoil pH increased

above 5.0 and, in contrast, soil NO3-N concentration increased rapidly above

pH 5.0, except in the fern glade and fern-invaded clearcut where this change in

N form occurred below pH 4.5 (fig. 4a-f). While the soils in both undisturbed

forests and the partial cut forests exhibited a threshold level of pH 5.0 for substantial changes in the quantity of available N, the two sites with bracken fern

vegetation types and the coneflower-invaded clearcut had steady changes in N as

pH increased. Both soil depths have similar regression curves for each vegetation

type; therefore, only the 0-5 cm soil depth is shown (table 5).

The sharp decline in PMN from these ash-influenced sites is different from

the northern Idaho loessal soils, which had a significant increase in PMN as pH

increased from 3.0 to 7.0 (Mohebbi and Mahler 1988). This may indicate a difference in organic matter concentration from loess-grassland areas to ash-forested

areas, and suggests that organic N in volcanic ash-influenced soils may be fairly

resistant to microbial decomposition because of the Al-organic complexes that

are formed (Shoji and others 1993).

While soil from most of the vegetation types show a crossover in relative abundance of PMN and NO3-N around pH 5.0, the bracken-fern dominated vegetation

types change below pH 4.5. Increased NO3 -N and decreased PMN at higher pH

values is consistent with results of acid rain and soil nutrition studies (Schier 1986;

Marx 1990).Nitrogen mineralization often increaseswhen soil pHisraised (Montes

and Christensen 1979), but occasionally has been shown to decrease (Adams and

Cornforth 1973). Nitrification is also pH sensitive and generally increases as pH

is raised from very acid to moderately acid (Robertson 1982). In this study, the

clearcuts invaded with either bracken fern or western coneflower likely exhibit

this N change each year as pH changes (Binkley and Richter 1987).

Aluminum and Total Acidity

KCl-extractable Al (which reflects exchangeable Al) and total acidity varied

significantly among vegetation types and soil depths. Mean values in the control

treatments are shown in table 4. Aluminum and total acidity are significantly

higher in the fern glade and fern-invaded clearcut, for both depths. Mean Al and

acid values are generally higher in the 10-15 cm depth soil as compared to the

0-5 cm depth.
196 USDA Forest Service Proceedings RMRS-P-44. 2007

Page-Dumroese, Ferguson, McDaniel, and Johnson-Maynard Chemical Changes Induced by pH Manipulations of Volcanic Ash-Influenced Soils

Figure 4—Soil NO3-N and PMN concentration (mg/kg) in the 0-5 cm depth as affected by pH manipulation, by vegetation 

type (a) Clearwater National Forest, undisturbed, (b) Nez Perce National Forest, undisturbed, (c) Clearwater National Forest, 

partial cut, (d) Clearwater National Forest, bracken fern glade, (e) Clearwater National Forest, bracken fern-invaded clearcut, 

(f) Nez Perce National Forest, coneflower-invaded clearcut.

(a) (b)

(c) (d)

(e) (f)
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Chemical Changes Induced by pH Manipulations of Volcanic Ash-Influenced Soils Page-Dumroese, Ferguson, McDaniel, and Johnson-Maynard

Regression analyses showed that Al was highly correlated with changes in pH

(table 5) in all vegetation types. Aluminum increased exponentially when the pH

decreased below 4.5 (fig. 5). Both 0-5 cm and 10-15 cm depths had similar curves;

therefore, only the 0-5 cm soil depth regression lines are shown. Volcanic ashinfluenced soils contain high levels of Al-containing materials that can undergo

dissolution under acidic (less that pH 5.0) conditions (Tisdale and others 1993).

In these soils, very little exchangeable Al was detected above pH 5.0. Based on

continuous soil measurements of pH (figs. 1 and 2), soils under bracken fern and

coneflower vegetation have a pH below 5.0 each growing season. Soil pH 5.0 is

generally considered to be the critical point for Al toxicity to woody vegetation

(Wolt 1994).

In general, woody plant species appear to be more tolerant of Al than agriculture crops (McCormick and Steiner 1978; Ryan and others 1986), and there is

considerable variation in Al tolerance among tree species(McCormick and Steiner

1978; Steiner and others 1984; Arp and Ouimet 1986; Hutchinson and others

1986; Schaedle and others 1989; Raynal and others 1990). Aluminum toxicity

alters tree root anatomy, which first occurs in the roots (Hutchinson and others

1986; Schaedle and others 1989; McQuattie and Schier 1990; Nosko and Kershaw 1992; Schier 1996). The result of Al toxicity is impaired root development,

resulting in reduced root length and formation of a shallow root system. At high

Figure 5—Exchangeable Al concentration (cmol/ kg) in the 0-5 cm depth as affected by 

pH, by vegetation type. The bold line is the regression for all vegetation types.
198 USDA Forest Service Proceedings RMRS-P-44. 2007

Page-Dumroese, Ferguson, McDaniel, and Johnson-Maynard Chemical Changes Induced by pH Manipulations of Volcanic Ash-Influenced Soils

Al levels, mitosis is almost completely inhibited. Leamy (1988) noted that in volcanic ash-influenced soils, Al toxicity may occur at concentrations of 2 cmol/kg

soil, and this value is used as a threshold in Soil Taxonomy for identifying those

Andisols in which Al phytotoxicity may occur (Soil Survey Staff 2003). Aluminum

levels found in this laboratory study are much higher than 2 cmol/kg when pH

decreased below 5.0 and indicates a strong potential for Al toxicity in these ashinfluenced soils as pH values decline.

The variousstudies onAl toxicity in tree species are difficult to compare because

of different study methods, units of measure, growth media, length of experiments, and age of trees (Schaedle and others 1989; Nosko and Kershaw 1992).

However, one important finding is that young seedlings are more sensitive to Al

toxicity than older seedlings. For example, Schier (1996) found that Al concentrations of 0.32 mM/l inhibited root biomass in newly germinated red spruce (Picea 

rubens) seedlings, while the threshold was 2.1 mM/l in 1-year-old seedlings. It

seems reasonable to assume that conifer seed germinating on GFM sites could

be impacted by low concentrations of Al. Aluminum toxicity, allelopathic compounds, and competition could combine to eliminate the natural establishment

of trees and other woody plant species on these sites.

Regression analyses for total acidity followed the same trend as extractable

Al (fig. 6), and only the 0-5 cm soil regression lines are shown. The regression

equation for total acidity is shown in table 5. Most of the acidity in these soils

Figure 6—Total acidity (cmol/kg) in the 0-5 cm depth as affected by pH manipulation 

by, vegetation type. The bold line is the regression for all vegetation types.
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Chemical Changes Induced by pH Manipulations of Volcanic Ash-Influenced Soils Page-Dumroese, Ferguson, McDaniel, and Johnson-Maynard

occurs as Al. The relationship between exchangeable Al and total acidity is not

unusual since most of the exchangeable acidity is derived from Al and H on

the exchange sites (Binkley and Richter 1987). Changes in exchangeable acidity

generally occur over a long period of time and are due to acidification through

weathering, leaching, cation uptake, or atmospheric deposition (Richter 1986).

Rapid changes in acidity occur occasionally by other H-ion inputs. In the GFM,

both bracken fern and western coneflower vegetation have the potential to input

H-ions via organic acid production or additions of high amounts of organic C

through yearly vegetation cycles.

 Summary______________________________________________________

Analysis of unaltered soil samples supporting undisturbed grand fir forest

and bracken fern/western coneflower plant communities suggests that chemical

properties of GFM forest soil are altered through invasion of successional plant

species after timber harvest or other disturbance. Changes in soil conditions are

similar to a depth of 15 cm. Seasonal decreases in soil pH under bracken fern and

western coneflower vegetation types most likely cause a release of exchangeable

Al at levels toxic to woody vegetation. High levels of C, exchangeable Al, and

total acidity under these two vegetation types may also be facilitating a localized

conversion of these ash-influenced soils from allophanic to nonallophanic Andisols. Forested soils in the GFM are capable of exhibiting these same characteristics

once disturbed.

Results of this study also provide insights into the chemical changes that may

occur in volcanic ash-influenced soils as pH fluctuates. Mechanisms that contribute to forb-dominated secondary successional plant communities have been

identified. For example, the apparent change in N between PMN and NO3-N

has implications in determining which species can grow on these sites, as does

the exponential increase of Al below pH 5.0. Clearly, this laboratory study points

out the potential for Al toxicity that may accompany seasonal pH fluctuations.

These laboratory study findings are consistent with in situ soil solution data, which

indicate that soils invaded by bracken fern and western coneflower undergo

conversion from allophonic to nonallophanic properties (Johnson-Maynard and

others 1997). However, altering the pH of ash-influenced soils differed from altering loessal soils (Mohebbi and Mahler 1988). These soil-type differences are

likely attributable to the unique physical, chemical, and biological properties of

ash-influenced soils as compared to those derived from other parent materials

(Dahlgren and others 2004).

This laboratory study highlights important characteristics of ash-influenced

soils that may contribute to changes in vegetation. This type of study, combined

with field work, will help in the development of practical management recommendations.

Literature Cited__________________________________________________

Adams, S. N.; Cornforth, I. S. 1973. Some short-term effects of lime and fertilizers on a Sitka

spruce plantation II. Laboratory studies on litter decomposition and nitrogen mineralization.

Forestry. 46: 39-47.

Alewell, C.; Bredemeier, M.; Matzner, E.; Blanck, K. 1997. Soil solution response to experimentally

reduced acid deposition in a forest ecosystem. J. Environ. Qual. 26: 658-665.
200 USDA Forest Service Proceedings RMRS-P-44. 2007

Page-Dumroese, Ferguson, McDaniel, and Johnson-Maynard Chemical Changes Induced by pH Manipulations of Volcanic Ash-Influenced Soils

Anderegg, J. C.; Naylor, D. V. 1988. Phosphorus and pH relationships in an andic soil with surface

and incorporated organic amendments. Plant and Soil. 107: 273-278.

Arp, P. A.; Ouimet, R. 1986. Uptake of Al, Ca and P in black spruce seedlings: Effect of organic

versus inorganic Al in nutrient solutions. Water Air Soil Pollution. 31: 367-375.

Atkinson, T. P. 1986. Bracken on the Malvern Hills: the influence of topographic and management

factors on early-season emergence and biomass. In: Smith, R. T.; Taylor, J. A., eds. Bracken:

ecology, land use and control technology. Proceedings of Bracken ’85; 1985 July 1-5; University

of Leeds, England: The Parthenon Publishing Group Limited: 195-204.

Attiwill, P. M.; Turvey, N. D.; Adams, M. A. 1985. Effects of mound-cultivation (bedding) on concentration and conservation of nutrients in a sandy podzol. For. Ecol. Manage. 11: 97-110.

Ball, D. F. 1964. Loss-on-ignition as an estimate of organic matter and organic carbon in noncalcareous soils. J. Soil Sci. 15: 84-92.

Binkley, D.; Richter, D. 1987. Nutrient cycles and H+ budgets of forest ecosystems. Adv. Ecol.

Res. 16: 1-49.

Boyle, J. R.; Phillips, J. J.; Ek, A. R. 1973. Whole-tree harvesting: nutrient budget evaluation. J.

For. 71: 760-762.

Brais, S.; Camiré, C.; Paré, D. 1995. Impacts of whole-tree harvesting and winter windrowing on soil

pH and base status of clayey sites of northwestern Quebec. Can. J. For. Res. 25: 997-1007.

Dahlgren, R. A.; Saigusa, M.; Ugolini, F. C. 2004. The nature, properties and management of

volcanic soils. Advances in Agronomy. 82: 113-182.

Dahlgren, R. A.; Shoji, S.; Nanzyo, M. 1993. Mineralogical characteristics of volcanic ash soils. In:

Shoji, S.; Nanzyo, M.; Dahlgren, R., eds. Volcanic ash soils—Genesis, properties, and utilization. Amsterdam: Elsevier: 101-144.

Dahlgren, R. A.; Ugolini, F. C.; Shoji, S.; Ito, T.; Sletten, R. S. 1991. Soil-forming processes in Alic

Melanudands under Japanese pampas grass and oak. Soil Sci. Soc. Am. J. 55: 1049-1056.

Federer, C. A.; Hornbeck, J. W.; Tritton, L. M.; Martin, C. W.; Pierce, R. S.; Smith, C. T. J. 1989.

Long-term depletion of calcium and other nutrients in eastern U.S. forests. Environ. Manage.

13: 593-601.

Ferguson, D. E. 1991a. Investigations on the Grand Fir Mosaic Ecosystem of northern Idaho. Moscow, ID: University of Idaho. 255 p. Ph.D. dissertation.

Ferguson, D. E. 1991b. Allelopathic potential of western coneflower (Rudbeckia occidentalis).

Can. J. Bot. 69: 2806-2808.

Ferguson, D. E.; Adams, D. L. 1994. Effects of pocket gophers, bracken fern, and western coneflower on survival and growth of planted conifers. Northwest Sci. 68: 242-249.

Ferguson, D. E.; Boyd, R. J. 1988. Bracken fern inhibition of conifer regeneration in northern Idaho.

Res. Pap. INT-RP-388. Ogden, UT: U.S. Department ofAgriculture, Forest Service, Intermountain

Research Station. 11 p.

Ferguson, D. E.; Byrne, J. C. 2000. Environmental characteristics of the Grand Fir Mosaic and adjacent habitat types. Res. Pap. RMRS-RP-24. Fort Collins, CO: U.S. Department of Agriculture,

Forest Service, Rocky Mountain Research Station. 20 p.

Ferguson, D. E.; Byrne, J. C.; Coffen, D. O. 2005. Reforestation trials and secondary succession

with three levels of overstory shade in the Grand Fir Mosaic ecosystem. Res. Pap. RMRS-RP-53.

Fort Collins, CO: U.S. Department of Agriculture, Forest Service, Rocky Mountain Research

Station. 16 p.

Gilliam, F. S. 1991. Ecosystem-level significance of acid forest soils. In: Wright, R. J. and others,

eds. Plant-soil interaction at low pH. proceedings; 1990 June 24-29; Beckley, WV. Dordrecht,

the Netherlands: Kluwer Acad. Publ.: 187-295.

Gliessman, S. R.; Muller, C. H. 1978. The allelopathic mechanisms of dominance in bracken

(Pteridium aquilinum) in southern California. J. Chem. Ecol. 4: 337-362.

Hendrickson, O. Q.; Chatarpual, L.; Burgess, D. 1989. Nutrient cycling following whole-tree and

conventional harvest in a northern mixed forest. Can. J. For. Res. 19: 725-735.

Hutchinson, T. C.; Bozic, L.; Munoz-Vega, G. 1986. Responses of five species of conifer seedlings

to aluminum stress. Water, Air and Soil Pollution. 31: 283-894.

Jimenez, J. 2005. Bracken fern communities of the Grand Fir Mosaic: Biomass allocation and influence on selected soil properties. Moscow, ID: University of Idaho. 209 p. M.S. thesis.

Johnson, C. E.; Romanowicz, R. B.; Siccama, T. G. 1997. Conservation of exchangeable cations

after clear-cutting of a northern hardwood forest. Can. J. For. Res. 27: 859-868.

Johnson-Maynard, J. L.; McDaniel, P. A.; Ferguson, D. E.; Falen, A. L. 1997. Chemical and mineralogical conversion of Andisols following invasion by bracken fern. Soil Sci. Soc. Am. J. 61:

549-555.
USDA Forest Service Proceedings RMRS-P-44. 2007 201

Chemical Changes Induced by pH Manipulations of Volcanic Ash-Influenced Soils Page-Dumroese, Ferguson, McDaniel, and Johnson-Maynard

Kuo, S. 1996. Phosphorus. In: Methods of soil analysis. Part 3. Chemical methods. Madison, WI:

Soil Science Society of America: 869-919.

Leamy, M. L. 1988. International committee on the classification of Andisols (ICOMAND). Circular

letter no. 9. New Zealand Soil Bureau, DSIR, Lower Hutt.

Littell, R. C.; Milliken, G. A.; Stroup, W. W.; Wolfinger, R. D. 1996. SAS system for mixed model.

Cary, NC: SAS Institute, Inc. 633 p.

Marx, D. 1990. Soil pH and nitrogen influence Pisolithus ectomycorrhizal development and growth

of loblolly pine seedlings. For. Sci. 36: 224-245.

McCormick, L. H.; Steiner, K. C. 1978. Variation in aluminum tolerance among six genera of trees.

Forest Science. 4: 565-568.

McQuattie, C. J.; Schier, G. A. 1990. Response of red spruce seedlings to aluminum toxicity in

nutrient solution: alterations in root anatomy. Can. J. For. Res. 20: 1001-1011.

Mohebbi, S.; Mahler, R. L. 1988. The effect of soil pH manipulation on chemical properties of an

agricultural soil from northern Idaho. Comm. in Soil Sci. and Plant Anal. 19: 1795-1812.

Montes, R. A.; Christensen, N. L. 1979. Nitrification and succession in the Piedmont of North

Carolina. For. Sci. 25: 287-297.

Moshi, A. O.; Wild, A.; Greenland, D. J. 1974. Effect of organic matter on the charge and phosphate

adsorption characteristics of a Kikuyu red clay from Kenya. Geoderma. 11: 275-285.

Mroz, G. D.; Jurgensen, M. F.; Frederick, D. J. 1985. Soil nutrient changes following whole-tree

harvesting on three northern hardwood sites. Soil Sci. Soc. Am. J. 49: 591-594.

Mulvaney, R. L. 1996. Nitrogen-inorganic forms. In: Methods of Soil Analysis. Part 3. Book Ser. 5.

Madison, WI: Soil Sci. Soc. Am. J.: 1123-1184.

Nanzyo, M. 1987. Formation of noncrystalline aluminum phosphate through phosphate sorption

on allophanic Ando soils. Commun. Soil Sci. Plant Anal. 18: 735-742.

Nanzyo, M.; Dahlgren, R.; Shoji, S. 1993. Chemical characteristics of volcanic ash soils. In: Shoji,

S.; Nanzyo, M.; Dahlgren, R., eds. Volcanic ash soils-Genesis, properties, and utilization. Amsterdam: Elsevier: 145-187.

Nosko, P.; Kershaw, K. A. 1992. The influence of pH on the toxicity of a low concentration of

aluminum to white spruce seedlings. Can. J. Bot. 70: 1488-1492.

Palmer, C. J.; Dresback, R.; Amacher, M. C.; O’Neill, K. P. 2001. Forest inventory and analysis soil

quality monitoring: Manual of soil analysis methods (2001 Edition). Available: http://socrates.

lv-hrc.nevada.edu/fia/ia/IAWeb/Soil.htm.

Powers, R. F. 1980. Mineralization of soil N as an index of nitrogen availability to forest trees. Soil

Sci. Soc. Am. J. 44: 1314-1320.

Raynal, D. J.; Joslin, J. D.; Thornton, F. C.; Schaedle, M.; Henderson, G. S. 1990. Sensitivity of tree

seedlings to aluminum: III. Red spruce and loblolly pine. J. Environ. Qual. 19: 180-187.

Richter, D. D. 1986. Sources of acidity in some forested Udults. Soil Sci. Soc. Am. J. 50:

1584-1589.

Robertson, G. P. 1982. Nitrification in forested ecosystems. Phil. Trans. R. Soc. Lond. 296:

445-457.

Ryan, P. J.; Gessel, S. P.; Zasoski, R. J. 1986. Acid tolerance of Pacific Northwest conifers in solution culture, 1: Effect of high aluminum concentration and solution acidity. Plant and Soil. 96:

239-257.

Schaedle, M.; Thornton, F. C.; Raynal, D. J.; Tepper, H. B. 1989. Response of tree seedlings to

aluminum. Tree Physiology. 5: 337-356.

Schier, G. A. 1996. Effect of aluminum on growth of newly germinated and 1-year-old red spruce

(Picea rubens) seedlings. Can. J. For. Res. 26: 1781-1787.

Schier, G. A. 1986. Seedling growth and nutrient relationships in a New Jersey Pine Barrens soil

treated with “acid rain.” Can. J. For. Res. 16: 136-142.

Shoji, S.; Nanzyo, M.; Dahlgren, R. A. 1993. Volcanic ash soils-Genesis, properties, and utilization. Amsterdam: Elsevier. 288 p.

Soil Survey Staff. 2003. Keys to soil taxonomy, Ninth Edition. Washington, DC: U.S. Department

of Agriculture, Natural Resources Conservation Service. 331 p.

Sommer, M. R. 1991. Soil of the Grand Fir Mosaic. Moscow, ID: University of Idaho. 97 p.

M. S. thesis.

Staaf, H.; Olsson, B. A. 1991. Acidity in four coniferousforestsoils after different harvesting regimes

of logging slash. Scand. J. For. Res. 6: 19-29.

Steiner, K. C.; Barbour, J. R.; McCormick, L. H. 1984. Responses of Populus hybrids to aluminum

toxicity. For. Sci. 30: 404-410.
202 USDA Forest Service Proceedings RMRS-P-44. 2007

Page-Dumroese, Ferguson, McDaniel, and Johnson-Maynard Chemical Changes Induced by pH Manipulations of Volcanic Ash-Influenced Soils

Stewart , R. E. 1975. Allelopathic potential of western bracken. J. Chem. Ecol. 1: 161-169.

Tisdale, S. L.; Beaton, J. D.; Nelson, W. L.; Havlin, J. L. 1993. Soil fertility and fertilizers. New

York, NY: MacMillan Publishing Company. 754 p.

Ulrich, B.; Mayer, R.; Khanna, P. K. 1980. Chemical changes due to acid precipitation in a loessderived soil in Central Europe. Soil Sci. 130: 193-199.

Wada, K. 1985. The distinctive properties of Andosols. Adv. Soil Sci. 2: 173-229.

Wolt, J. D. 1994. Soil Solution Chemistry: applications to environmental science and agriculture.

New York: John Wiley & Sons, Inc. 456 p.

Zdanowicz, C. M.; Zielinski, G. A.; Germani, M. S. 1999. Mount Mazama eruption: Calendrical

age verified and atmospheric input assessed. Geology. 17: 621-624.

Znerold, R. M. 1979. Western bracken control with asulam. Pullman, WA: Washington State

University. 36 p. M. S. thesis.
Summaries of Poster Papers

USDA Forest Service Proceedings RMRS-P-44. 2007 205

In: Page-Dumroese, Deborah; Miller, Richard; Mital, Jim; McDaniel, Paul; Miller, Dan, tech. eds. 2007. 

Volcanic-Ash-­Derived Forest Soils of the Inland Northwest: Properties and Implications for Management 

and Restoration. 9-10 November 2005; Coeur d’Alene, ID. Proceedings RMRS-P-44; Fort Collins, CO: 

U.S. Department of Agriculture, Forest Service, Rocky Mountain Research Station.

William Elliot is Project Leader, Ina Sue Miller is Hydrologist, and David Hall is IT Specialist, Soil and 

Water Engineering Research Work Unit, Rocky Mountain Research Station, Moscow, ID.

WEPP FuME Analysis for a North Idaho Site

William Elliot, Ina Sue Miller, and David Hall

Introduction

	 A computer interface has been developed to assist with analyzing soil erosion rates associated with fuel management activities. This interface uses the Water Erosion Prediction Project

(WEPP) model to predict sediment yields from hillslopes and road segments to the stream

network. The simple interface has a large database of climates, vegetation files and forest

soil properties to support this and other interfaces, including Disturbed WEPP for forests and

WEPP:Road for road segment analyses. The soil databases for roads and disturbed forested

hillslopes are based on rainfall simulation and natural rainfall studies.

	 The WEPP FuME interface carries out erosion prediction runs for six forest conditions:

	 1. Undisturbed mature forest

	 2. Wildfire

	 3. Prescribed fire

	 4. Thinning

	 5. Low traffic roads

	 6. High traffic roads

	 The climate, soil texture, topography, road density, wildfire return interval, prescribed fire

cycle and thinning cycle are specified by the user.

	 The WEPP FuME interface can be used anywhere within the United States using the existing

climate database. The interface is intended to provide an overview of the sources of sediment

on a given fuel management site. Sediment predictions from WEPP FuME are for surface

erosion only.
206 USDA Forest Service Proceedings RMRS-P-44. 2007

Elliot, Miller, and Hall WEPP FuME Analysis for a North Idaho Site

Hillslope Method and Parameters _________________________________

The example in this paper is an area within the Yellowpine timber sale in

northern Idaho (fig. 1). The watershed hillslope boundaries were delineated using

GeoWEPP (a geo-spatial interface tool for WEPP) (fig. 2). Each hillslope from the

example watershed was examined using the FuME model. Only one hillslope can

be run at a time and in this instance, hillslope number 22 is displayed (fig. 2).

FuME was run for an individual hillslope (number 22, fig. 2). The conditions

of the model were sandy loam soil texture, hillslope length of 708 feet, hillslope

gradient starting with the top of the hill 25, 36, and 20 percent, a 40 ft buffer

length and the default road density, fire and thinning cycles.

Figure 1—Unit 4 of the Yellowpine timber sale in northern Idaho.
USDA Forest Service Proceedings RMRS-P-44. 2007 207

WEPP FuME Analysis for a North Idaho Site Elliot, Miller, and Hall

Figure 2—The WEPP-FuME model windows for hillslope 22.
208 USDA Forest Service Proceedings RMRS-P-44. 2007

Elliot, Miller, and Hall WEPP FuME Analysis for a North Idaho Site

Table 1—WEPP FuME summarized results and weighted averages.

Thinning + Rx 

Background Thinning Rx Fire Thinning + Rx fire fire w/moderate 

Hill slope sedimentation effects effects w/high severity fire severity fire

- - - - - - - - - - - - - (ton/mi 2)- - - - - - - - - - - (ton/mi 2)* (ton/mi 2)**

22 139 141.6 152.1 155.6 52.92

23 97.2 98.2 99.1 100.2 30.52

 31 92.2 92.8 93.2 93.8 28.48

 32 120.8 122.8 126.6 129.7 55.94

 33 118.3 119.6 120.2 121.6 39.46

41 104.1 105.1 105.1 106.2 31.38

42 144.3 145.6 144.3 145.9 48.32

43 93.3 94.3 94.6 106.1 29.02

Weighted averages

for the example

watershed 113.7 115.2 117.9 120.3 39.9

* The projected background rate in this column assumes fuel management activities did not reduce the fire hazard by removing excess fuel. The estimated background rate for this column was calculated with a high severity fire value.

** The projected background rate in this column assumes fuel management activities reduce the fire hazard by removing 

excess fuel. Therefore, the estimated background rate for this column was calculated with a moderate severity fire value.

Note: All sedimentation estimates displayed above are calculated from the low end erosion rates of the road network.

The high severity fire value was used in the background sedimentation rate calculation unless stated otherwise.

Cumulative Watershed Results ____________________________________

All hillslopes from the example watershed were analyzed with WEPP FuME.

The summarized results and weighted averages for the example watershed are

displayed in table 1 below.

From the table we can observe that if a moderate fire scenario occurs every

40 years for the watershed, in combination with the prescribed fire and thinning

management activities, including erosion from roads, there is a 65 percent decrease

of erosion occurring when compared to the background rate. In the event of a

high severity fire, in combination with the prescribed fire and thinning management activities including the erosion from roads, the total watershed results in a

6 percent increase of predicted erosion. For both examples, the background rate

includes low impact roads and the high severity fire scenario.
USDA Forest Service Proceedings RMRS-P-44. 2007 209

WEPP FuME Analysis for a North Idaho Site Elliot, Miller, and Hall

References______________________________________________________

Covert, S. A.; Robichaud, P. R.; Elliot, W. J.; Link, T. E. 2005. Evaluation of runoff prediction from

WEPP-based erosion models for harvested and burned forest watersheds. Transactions of the

ASAE. 48(3): 1091-1100.

Elliot, W. J. 2004. WEPP internet interfaces for forest erosion prediction. Jour. of the Amer. Water

Res. Assoc. 40(2): 299-309.

Elliot, W. J.; Hall, D. E. 1997. Water Erosion Prediction Project (WEPP) forest applications. General

Technical Report INT-GTR-365. Ogden, UT: U.S. Department of Agriculture, Forest Service,

Intermountain Research Station. 11 p.

Elliot, W. J.; Hall, D. E. 2005. Water Erosion Prediction Project (WEPP) Fuel Management (FuME)

tool. Fuels planning: science synthesis and integration; environmental consequences fact sheet

12. Res. Note RMRS-RN-23-12-WWW. Fort Collins, CO: U.S. Department of Agriculture, Forest

Service, Rocky Mountain Research Station. 2 p.

Elliot, W. J.; Robichaud, P. R. 2004. The effectiveness of postfire mitigation treatments. Presented

at the 2004 BAER Training Workshop; 2004 April 30; Denver, CO.

Elliot, W. J.; Robichaud, P. R. 2004. Evaluating sediment risks associated with fuel management.

Fuels planning: science synthesis and integration; environmental consequences fact sheet 8.

Res. Note RMRS-RN-23-8-WWW. Fort Collins, CO: U.S. Department of Agriculture, Forest

Service, Rocky Mountain Research Station. 2 p.

Elliot, W. J.; Miller, I. S. 2002. Estimating Erosion Impacts from Implementing the National Fire

Plan. 2002 ASAE annual international meeting/CIGR XVth world congress; 2002 July 28-31;

Chicago, IL. St. Joseph, MI: ASAE: ASAE meeting paper no. 02-5011.

Elliot, W. J.; Miller, I. S. 2004. Measuring Low Rates of Erosion from Forest Fuel Reduction

Operations, 2004 ASAE/CSAE Annual International Meeting; 2004 August 1-4; Ottawa, Ontario,

Canada: ASAE paper number 045018.

Laflen, J. M.; Elliot, W. J.; Flanagan, D. C.; Meyer, C. R.; Nearing, M. A. 1997. WEPP–Predicting

water erosion using a process-based model. Journal of Soil and Water Conservation. 52(2):

96-102.

McDonald, G. I.; Harvey, A. E.; Tonn, J. R. 2000. Fire, competition and forest pests: Landscape

treatment to sustain ecosystem function. In: Neuenschwander, L. F.; Ryan, K. C., eds. Proceedings from the Joint Fire Science Conference and Workshop; 1999 June 15-17; Boise, ID. Online

at < http://jfsp.nifc.gov/conferenceproc/T-11McDonaldetal.pdf > . Accessed June, 2004: 17 p.

Spigel, K. M. 2002. First year postfire erosion rates in Bitterroot National Forest, Montana.

Madison, WI: University of Wisconsin. 147 p. MS Thesis.

USDA Forest Service Proceedings RMRS-P-44. 2007 211

In: Page-Dumroese, Deborah; Miller, Richard; Mital, Jim; McDaniel, Paul; Miller, Dan, tech. eds. 2007. 

Volcanic-Ash-­Derived Forest Soils of the Inland Northwest: Properties and Implications for Management 

and Restoration. 9-10 November 2005; Coeur d’Alene, ID. Proceedings RMRS-P-44; Fort Collins, CO: 

U.S. Department of Agriculture, Forest Service, Rocky Mountain Research Station.

William Elliot is Project Leader, Ina Sue Miller is Hydrologist, and Brandon Glaza is Civil Engineer, 

Soil and Water Engineering Research Work Unit, Rocky Mountain Research Station, Moscow, ID.

Erosion Risks in Selected Watersheds for the 

2005 School Fire Located Near Pomeroy, 

Washington on Predominately Ash-Cap Soils

William Elliot, Ina Sue Miller, and Brandon Glaza

Geo-WEPP Spatial Analysis

	 A limited erosion potential analysis was carried out on the 50,000 acre School Fire. Three

WEPP interfaces were used for the analysis, a GIS wizard, an online interface and a windows interface. Ten watersheds within the fire area were modeled with the GeoWEPP tool (a

geo-spatial interface for WEPP, Water Erosion Predication Project). The watersheds covered

18,823 acres, or about 38 percent of the total burned area. Hillslopes were specified high,

moderate or low burn severity by examining the BAER (Burned Area Emergency Response)

severity map.

	 By consulting with the BAER specialists, watersheds of greatest interest were identified. One

set included four watersheds discharging into the Tucannon River from the western side, including School Creek, which flowed into the Tucannon River at the Tucannon Guard Station.

A second set included three watersheds flowing into the Tucannon River from the east side,

south of the Tucannon Guard Station. The third set of watersheds were larger and incorporated

Dry Creek (a tributary to Cummings Creek), Cummings Creek and Pataha Creek.
212 USDA Forest Service Proceedings RMRS-P-44. 2007

Elliot, Miller, and Glaza Erosion Risks in Selected Watersheds for the 2005 School Fire Located Near Pomeroy, Washington...

ERMiT Hillslope Analysis – Online Interface________________________

The ERMiT (Erosion Rehabilitation Management Tool; August, 2005 version)

results for a single storm erosion prediction are given in table 1 below. Table 2

provides an overall average of all ERMiT runs. Hillslopes were specified high,

moderate or low severity from the BAER severity map. An average of about 12

randomly selected hillslopes or 5 percent of the hillslopes on larger watersheds,

were run with ERMiT for each watershed, with the exception of upper Pataha.

In the upper Pataha watershed, only 10 hillslopes were identified as moderate or

severely burned. The mulching treatment assumed an application role of 0.9 tons/

acre following the fire. On average, there is a 20 percent chance that the erosion

rate in the watershed will be greater than 7 tons per acre if left untreated, and only

a 10 percent probability that erosion will exceed 10 tons/ac if left untreated.

Table 1—ERMiT single storm erosion predictions – August-2005 version.

Untreated Seeded Mulched

Year Year Year

Drainage Exceedance 1 2 1 2 1 2

 - - - - - - - - - - - - - - - - - (tons/ac) - - - - - - - - - - - - - - - - - -

Tucannon West 3 10% Mean 12.98 9.00 12.98 4.98 1.34 3.11

Std Dev 8.00 5.97 8.00 3.32 0.85 2.16

20% Mean 8.57 5.78 8.57 2.27 0.00 0.92

Std Dev 5.56 3.93 5.56 1.76 0.00 0.79

Tucannon West 2 10% Mean 10.05 7.24 10.05 3.95 0.99 2.43

Std Dev 8.40 6.30 8.4 4.08 1.02 2.50

20% Mean 6.56 4.67 6.56 1.73 0.00 0.70

Std Dev 6.22 4.71 6.22 2.09 0.00 0.86

Tucannon West 1 10% Mean 14.14 9.61 14.14 5.27 1.36 3.16

Std Dev 8.11 5.95 8.11 3.79 1.33 2.51

20% Mean 9.23 6.25 9.23 2.21 0.00 0.90

Std Dev 5.79 4.44 5.79 1.99 0.00 0.87

School Canyon 10% Mean 6.00 4.15 6.00 2.21 0.53 1.34

Std Dev 7.00 5.24 7.00 3.33 0.74 2.04

20% Mean 3.77 2.51 3.77 0.92 0.00 0.37

Std Dev 5.13 3.84 5.13 1.64 0.00 0.67

Grub Creek 10% Mean 10.71 7.70 10.71 4.38 1.10 2.67

Std Dev 8.31 6.23 8.31 3.87 0.93 2.37

20% Mean 7.31 5.18 7.31 1.93 0.00 0.78

Std Dev 6.02 4.65 6.02 1.95 0.00 0.84

Hixon Creek 10% Mean 6.71 4.49 6.71 2.06 0.65 1.39

Std Dev 8.31 5.78 8.31 3.41 1.34 2.41

20% Mean 4.10 2.48 4.10 0.95 0.00 0.37

Std Dev 5.78 4.08 5.78 2.00 0.00 0.75

(continued)
USDA Forest Service Proceedings RMRS-P-44. 2007 213

Erosion Risks in Selected Watersheds for the 2005 School Fire Located Near Pomeroy, Washington... Elliot, Miller, and Glaza

Table 2—Average of ERMiT runs.

Untreated Seeded Mulched

Year Year Year

Drainage Exceedance 1 2 1 2 1 2

 - - - - - - - - - - - - - - - - - (tons/ac) - - - - - - - - - - - - - - - - - -

Means of ten sets of 10% Mean 10.82 7.53 10.82 4.38 1.51 2.95

ERMiT runs Std Dev 2.50 1.68 2.50 1.24 1.08 1.24

20% Mean 7.06 4.80 7.10 1.99 0.15 0.85

Std Dev 1.68 1.11 1.68 0.72 0.31 0.40

Tucannon East 10% Mean 8.22 5.72 8.22 2.90 0.72 1.82

unnamed Std Dev 8.44 6.24 8.44 3.93 0.89 2.35

20% Mean 5.28 3.44 5.28 1.22 0.00 0.51

Std Dev 5.94 4.49 5.94 1.97 0.00 0.83

Upper Cummings 10% Mean 10.23 6.94 10.23 3.99 1.04 2.34

Creek Std Dev 6.08 4.42 6.08 2.62 1.03 1.71

20% Mean 6.70 4.73 6.70 1.56 0.00 0.51

Std Dev 4.16 3.07 4.16 1.25 0.00 0.56

Dry Creek 10% Mean 11.32 7.77 11.33 5.25 3.08 4.38

Std Dev 8.59 6.05 8.58 4.28 2.75 3.59

20% Mean 6.87 4.61 7.30 2.70 0.73 1.51

Std Dev 5.78 4.07 5.77 2.71 1.05 1.67

Upper Pataha 10% Mean 13.88 9.48 13.88 6.54 3.89 5.59

Std Dev 6.17 4.15 6.17 3.10 1.93 2.75

20% Mean 9.02 5.60 9.02 3.40 0.76 1.55

Std Dev 3.90 2.65 3.90 1.70 0.54 0.81

Table 1 (Continued).

Untreated Seeded Mulched

Year Year Year

Drainage Exceedance 1 2 1 2 1 2

 - - - - - - - - - - - - - - - - - (tons/ac) - - - - - - - - - - - - - - - - - -

WEPP Windows Analysis ________________________________________

The WEPP windows interface was run for each watershed to estimate return

periods for peak runoff rates. These results were combined with other methods

to make final runoff predictions.

Conclusions_____________________________________________________

The GeoWEPP tool allows the user to quickly estimate hillslope parameters

for use in the ERMiT program. The results from the ERMiT program show that

mulching will have major benefits in reducing erosion, especially on the high

severity areas. On the other hand, erosion risks on low severity burned slopes

were projected as being minimal.
214 USDA Forest Service Proceedings RMRS-P-44. 2007

Elliot, Miller, and Glaza Erosion Risks in Selected Watersheds for the 2005 School Fire Located Near Pomeroy, Washington...

References______________________________________________________

Elliot, W. J.; Cuhaciyan, C. O.; Robichaud, P. R.; Pierson, F. B.; Wohlgemuth, P. M. 2001. Modeling

Erosion Variability after Fire. Presentation at the 2001 ASAE International Meeting; 2001 July 30-

August 1; Sacramento, CA. 

Foltz, R. B.; Elliot, W. J. 1999. Forest erosion probability analysis with the WEPP Model. Presented

at the 1999 ASAE/CSAE Annual International Meeting, Paper No. 995047. St. Joseph, MI: ASAE.

Laflen, J. M.; Elliot, W. J.; Flanagan, D. C.; Meyer, C. R.; Nearing, M. A. 1997. WEPP–Predicting water

erosion using a process-based model. Journal of Soil and Water Conservation. 52(2): 96-102.

Renschler, C. S. 2004. The Geo-spatial interface for the Water Erosion Prediction Project (GeoWEPP).

Online at < http://www.geog.buffalo.edu/~rensch/geowepp/ >. Accessed June, 2004.

Robichaud, P. R.; Elliot, W. J.; Pierson, F. B.; Hall, D. E.; Moffet, C. A. 2006. Erosion Risk Management

Tool (ERMiT) Ver. 2006.01.18. Online at <http://forest.moscowfsl.wsu.edu/fswepp/ >. Moscow, ID:

U.S. Department of Agriculture, Forest Service, Rocky Mountain Research Station.

USDA ARS National Soil Erosion Research Laboratory. 2004. WEPP Software. Online at < http://

topsoil.nserl.purdue.edu/nserlweb/weppmain/wepp.html >. Accessed June, 2004.
USDA Forest Service Proceedings RMRS-P-44. 2007 215

In: Page-Dumroese, Deborah; Miller, Richard; Mital, Jim; McDaniel, Paul; Miller, Dan, tech. eds. 2007. 

Volcanic-Ash-­Derived Forest Soils of the Inland Northwest: Properties and Implications for Management 

and Restoration. 9-10 November 2005; Coeur d’Alene, ID. Proceedings RMRS-P-44; Fort Collins, CO: 

U.S. Department of Agriculture, Forest Service, Rocky Mountain Research Station.

Richard E. Miller, USDA Forest Service, PNW Research Station (retired), Olympia, WA.

Conference Wrap-up

Richard E. Miller

	 My purpose is twofold: to review key messages from previous speakers and to offer some

concepts that may help you link recently acquired information.

	 When Mt. Mazama erupted about 7,000 years ago, its airborne ash and pumice fell on a

wide variety of existing soils. This Mazama tephra was a new parent material for soil development (fig. 1). At some locations, the original deposition was redistributed by: gravity, wind,

water, plants, or animal activities, including those of humans. Soil at any specific location in

the Inland West is a result of these soil-forming factors and their many possible interactions.

Figure 1—Soil-forming factors (Jenny 1941).
216 USDA Forest Service Proceedings RMRS-P-44. 2007

Miller Conference Wrap-up

Major Take-Home Messages _____________________________________

	 1.	Ash-derived soils are extensive, variable, and different from soils derived

from other parent materials.

	 2.	Activities (equipment, fire) can change soil properties and functions.

	 3.	Consequences of soil changes for vegetative growth or soil erosion are

uncertain, because they are seldom quantified.

	 4.	Hence, optimum allocation of preventative or restorative efforts is

uncertain.

What is a Forester to do? ________________________________________

Assuming your intent is to protect and manage soil at specific locations, how

will you use information gained at this conference? Can you state facts and explain relationships among these facts? Will this new information change or affect

your future decisions about prescribing or controlling activities on ash-derived

or ash-influenced soils?

Most foresters and land managers are concerned about yield...of wood, forage

and protective vegetation. Most recognize that yield at a specific location depends

on numerous factors and their interactions (fig. 2). Several speakers reviewed the

effects on soil properties of either heavy equipment used in harvesting or of wild

and prescribed fire. You should recognize that a change in soil properties is a

change in one of several factors that contributes to yield. Despite visually apparent

or measured changes in soil characteristics (for example, bulk density, resistance,

organic matter) or functions, however, yield may not change. Other factors that

also affect yield at a given location can be enhanced by or compensate for the

Figure 2—Factors that set productivity or yield (Jenny 1941).
USDA Forest Service Proceedings RMRS-P-44. 2007 217

Conference Wrap-up Miller

potentially negative effects of soil changes on yield. Factors controlling yield also

interact. For example,soil disturbance may reduce vegetative competition fortrees.

Consequently, this indirect effect of soil disturbance on competing vegetation

can enhance tree growth or compensate for direct, potentially negative effects

of disturbance on tree growth.

When you propose to harvest trees or prescribe fire, can you predict likely

consequences on soil properties and subsequent plant yield? The components

of this practical and important question are displayed in figure 3. You, as the

agent, propose to use ground based equipment at location Y. Do you recognize

that each location has a unique combination of soils, climate, and other factors

that determine the severity of soil disturbance and the practical consequences for

tree or vegetative growth? Therefore, do not anticipate the same effects on soil

or growth at all locations. Refer to current research results and explanations, for

example, Gomez and others (2002); Powers and others (2005) for justification of

your decisions and remember your A, B, C’s (fig. 4).

The concept of ecological stability also applies to soil stability (fig. 5). Soils

differ in their initial resistance to heavy equipment traffic. For example, compare

visual effects of traffic on a sandy soil containing 70- to 90-percent gravel and

cobbles by volume in the top 3 feet with that on a deep silt loam soil that is

stone-free. These two soils differ in their weight-bearing capacity and in shear

strength, especially when moist or wet. Soils also differ in their resilience or rate

of recovery after disturbance. Rate of recovery of soil properties and functions

depends largely on interactions among climate, above-and-below ground organisms, and soil properties. For example, recovery is hastened in climates that cause

soil to have cycles of thawing and freezing, wetting and drying, or climates that

promote rapid growth of plants and other organisms.

Figure 3—A general concept of actions and consequences.
218 USDA Forest Service Proceedings RMRS-P-44. 2007

Miller Conference Wrap-up

Figure 4—Locations (sites) differ: Remember your A, B, C’s.

Figure 5—Ecological stability: response depends on resistance; recovery depends on 

resilience.
USDA Forest Service Proceedings RMRS-P-44. 2007 219

Conference Wrap-up Miller

Figure 6—Soils and site differ in resistance and resilience.

Among the many combinations of soils and micro- and macro-climates in the

Inland West, we need to identify our A-, B-, C-locations. Recall a similar urging

by our after-dinner speaker, Larry Ross: “go forth and stratify forestland;” then fit

the practice to the soil.

Soils andclimatesdiffer. Soils andclimatesinteracttocreate varying consequences

of soil disturbance or fire for yield (fig. 6). Your considering differences in soil

depth like differences in bank accounts will be helpful: Equate shallow soils to a

$100 account and deep soils to a $1,000 account. Thus, your prescribing groundbased equipment or fire to reduce fuels will most likely result in reduced growth

and subsequent yield on shallow soils or soils with shallow ash caps. Moreover,

presence of coarse, non-weathered rock fragments further reduce effective soil

depth or the “bank account.” Finally, remember interactions: where equipment or

fire degrade soil for plant growth, anticipate stronger reductions in plant growth

where climate is harsh and less favorable for plant growth.

Final Take-Home Messages ______________________________________

	 1.	Do not assume negative “consequences” for vegetation yield on all soils

and locations (soils differ... climates differ...hence, tree response differs).

	 2.	Help others to identify Case A, B, C locations by measuring tree response

to disturbance.

	 3.	Know your A-, B-, C-soils/sites.

	 4.	Allocate time and dollars at Case A locations (where activities reduce growth).

	 5.	Save time and dollars at Case B and C locations (where activities have no

effect or improve growth).

	 6.	In short, allocate your protective and restorative efforts... to achieve favorable benefit/cost ratios.
220 USDA Forest Service Proceedings RMRS-P-44. 2007

Miller Conference Wrap-up

Literature Cited__________________________________________________

Gomez, A.; Powers, R. F.; Singer, M. J.; Horwath, W. R. 2002. Soil compaction effects on growth

of young ponderosa pine following litter removal in California’s Sierra Nevada. Soil Sci. Am.

J. 66: 1334-1343.

Jenny, H. 1941. Factors of Soil Formation. A System of Quantitative Pedology. New York, NY:

McGraw-Hill.

Powers, R. F.; Scott, D. A.; Sanchez, F. G.; Voldseth, R. A.; Page-Dumroese, D.; Elioff, J. D.; Stone,

D. M. 2005. The North American long-term soil productivity experiment: Findings from the first

decade of research. Forest Ecology and Management. 20: 31-50.

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