Silvicultural Research 

and the Evolution of

Forest Practices in the

Douglas-Fir Region

Robert O. Curtis, Dean S. DeBell, Richard E. Miller,

Michael Newton, J. Bradley St. Clair, William I. Stein

United States 

Department of 

Agriculture

Forest Service

Pacific Northwest

Research Station

General Technical 

Report

PNW-GTR-696

June 2007
Authors

Robert O. Curtis and Richard E. Miller are emeritus scientists and Dean S. DeBell is a 

research forester (retired), U.S. Department of Agriculture, Forest Service, Forestry Sciences

Laboratory, Olympia, WA 98512; Michael Newton is an emeritus professor, Department

of Forest Science, College of Forestry, Oregon State University, Corvallis, OR 97331; 

J. Bradley St. Clair is a research geneticist and William I. Stein is an emeritus scientist,

U.S. Department of Agriculture, Forest Service, Pacific Northwest Research Station, Forestry

Sciences Laboratory, 3200 SW Jefferson Way, Corvallis, OR 97331.

The Forest Service of the U.S. Department of Agriculture is dedicated to the principle of 

multiple use management of the Nation’s forest resources for sustained yields of wood, water,

forage, wildlife, and recreation. Through forestry research, cooperation with the States and 

private forest owners, and management of the National Forests and national grasslands, it

strives—as directed by Congress—to provide increasingly greater service to a growing

Nation.

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activities on the basis of race, color, national origin, age, disability, and where applicable sex,

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and TDD).

To file a complaint of discrimination, write USDA, Director, Office of Civil Rights, 1400

Independence Avenue, S.W. Washington, DC 20250-9410 or call (800) 795-3272 (voice) 

or (202) 720-6382 (TDD). USDA is an equal opportunity provider and employer.
Abstract

Curtis, Robert O.; DeBell, Dean S.; Miller, Richard E.; Newton, Michael; St. Clair,

J. Bradley; Stein, William I. 2007. Silvicultural research and the evolution of forest

practices in the Douglas-fir region. Gen. Tech. Rep. PNW-GTR-696. Portland, OR:

U.S. Department of Agriculture, Forest Service, Pacific Northwest Research Station.

172 p.

Silvicultural practices in the Douglas-fir region evolved through a combination of formal 

research, observation, and practical experience of forest managers and silviculturists, and

changing economic and social factors. This process began more than a century ago and still

continues. It has had a great influence on the economic well-being of the region and on the

present characteristics of the region’s forests. This long history is unknown to most of the

public, and much of it is unfamiliar to many natural resource specialists outside (and even

within) the field of silviculture. We trace the history of how we got where we are today and

the contribution of silvicultural research to the evolution of forest practices. We give special

attention to the large body of information developed in the first half of the past century that

is becoming increasingly unfamiliar to both operational foresters and—perhaps more importantly—to those engaged in forestry research. We also discuss some current trends in silviculture and silviculture-related research.

Keywords: Forest history, silviculture, Douglas-fir, forest research, Pseudotsuga 

menziesii. 
Contents

1 Chapter 1: Introduction

3 Chapter 2: Historical Background

3 European Experience

6 United States Beginnings

9 Chapter 3: The Douglas-Fir Region

9 The Forests

10 Early History

13 Chapter 4: Forestry Research—Origin and 

Direction

13 Initial Explorations

13 Early Research: 1881–1920

16 Research: 1921–1960

18 Research: 1961–1985

19 Research: 1986 to the Present

21 Chapter 5: Regeneration Systems

21 Natural Regeneration

25 Artificial Regeneration

26 Seed Characteristics and Testing

26 Determining Seed Characteristics

28 Seed Testing

29 Seed Production

29 Seed Source

29 Crop Forecasting and Stimulation

30 Collection and Processing

31 Seed Storage

31 Seedling Production

31 Bare-Root Seedlings

33 Containerized seedlings

34 Seedling Storage

35 Planting and Seeding

35 Direct Seeding

37 Planting

39 Reforestation Evaluation

39 Overview

41 Site Preparation and Control of Competing 

Vegetation

41 Site Preparation

43 Control of Competing Vegetation

51 Chapter 6: Stand Density Control

51 Plantation Spacing

51 Wind River Spacing Trial

52 University of British Columbia Spacing Trials

52 Other Spacing Trials

53 Early Thinning Research: Pre-World War II

53 Wind River: Martha Creek and Lookout Mountain

Road

53 Mount Walker (Olympic National Forest)

54 Schenstrom Thinning (Cowichan Lake, 

British Columbia)

54 Kugel Creek (Olympic National Forest)

55 Summary of Early Trials

55 Thinning Research: Post-World War II to the 

Present

55 Precommercial Thinning

55 Commercial Thinning

61 Chapter 7: Genetics and Tree Improvement

61 Exotic Species

61 Provenance Trials, Geographic Variation, 

and Seed Zones

63 Tree Improvement Programs in Douglas-Fir

65 Tree Improvement Programs in Other Species

67 Chapter 8: Forest Fertilization and Long-Term 

Productivity

67 Forest Fertilization

69 Long-Term Site Productivity

73 Chapter 9: Growth and Yield/Mensuration

73 Volume Tables and Equations

73 Site Index Estimates

73 Normal Yield Tables

73 Methodology

74 Douglas-Fir Yield

75 Sitka Spruce and Western Hemlock Yield

75 Red Alder Yield

75 Adjustment of Normal Yield Tables

75 Managed-Stand Yield Estimates

76 Permanent-Plot Data

76 Early Managed-Stand Yield Estimates

76 Simulation Models

78 Model Limitations

78 Stand-Density Measures
81 Chapter 10: Silvicultural Influences on Wood 

Quality

81 Background

81 General Overview

81 Brief History of Wood Quality Research

82 General Influences of Silvicultural Practices

83 Pruning

85 Initial Spacing and Thinning

85 Fertilizer Application

86 Genetic Improvement

86 Rotation Age

87 Simulation Estimates of the Effects of Silviculture 

on Wood Quality

89 Chapter 11: Silviculture of Associated Species

89 Western Hemlock

90 Western Redcedar

92 High-Elevation True Fir–Hemlock

93 Red Alder

93 Red Alder as a Timber Species

94 Red Alder as a Soil Improver

95 Oregon White Oak

96 Black Cottonwood and Hybrid Poplars

99 Chapter 12: Changes in Society, Forest 

Management Objectives, and Supporting

Silivicultural Research

99 Social Change and Silviculture

103 Sustained Yield, Multiple Use, Ecosystem 

Management, and Sustainable Forestry

104 Visual Effects and Public Perceptions

105 Green-Tree Retention

106 Nontraditional Thinning

107 Forest Health Issues

108 Nontimber Forest Products

108 Growth Trends, Rotations, and Carbon

109 Riparian Silviculture

111 Comparisons of Silvicultural Systems and 

Management Regimes

115 Chapter 13: Evolution of Applied Forest 

Management Practices

115 Forest Management Changes: 1900–1925

116 Forest Management Changes: 1925–1950

118 Forest Management Changes: 1950–1985

119 Forest Management Changes: 1985 to the Present

121 Chapter 14: In Conclusion

123 Acknowledgments

123 Literature Cited

171 Appendix
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Silvicultural Research and the Evolution of Forest Practices in the Douglas-Fir Region

Forestry is the science, art, and practice of creating,

managing, using, and conserving forests and associated

resources for human benefit to meet desired goals, needs,

and values (Helms 1998). Silviculture is that portion of the

field of forestry that deals with the knowledge and techniques used to establish and manipulate vegetation and to

direct stand and tree development to create or maintain

desired conditions. It is the application of knowledge of 

forest biology and ecology to practical forestry problems.

Modern forestry evolved over more than a century in

the United States and over several centuries in Europe and

elsewhere in the world. This long history is not well known

to many people interested in forestry, and many natural

resource professionals—including a good many foresters—

know little of the scientific and social background that

influenced the historical development of forestry and forest

science. Yet, many modern questions and controversies are

merely variations on those of the past. Any balanced consideration of current problems and possible solutions

requires an understanding of how we got where we are

today.

In the United States, a large body of information that

was developed in the first half of the 20th century is becoming increasingly unfamiliar to both operational foresters

and—perhaps more importantly—those engaged in forestry

research. It is not unusual to see published papers whose

authors are apparently unaware of pertinent information

published many years ago, or who cite as sources recent

papers without acknowledging original work done by

researchers long before. This tendency is perhaps in part a

result of generational turnover, but also stems from reliance

on computerized bibliographic searches of relatively recent

databases that do not include older work. The monumental

Selected Bibliography of North American Forestry (Munns

1940)—largely unknown to the current generation of

researchers—contains 21,413 North American forestryrelated references prior to 1940. Most of these publications

are not found in existing databases, yet some are of great

value to anyone working in forest history, forest policy, or

forest biology and silviculture.

A complete and detailed history of North American

forestry and forestry research would be an enormous undertaking, far beyond our capabilities. We here confine ourselves to the much more limited subject of the development

of silvicultural research and practice in the Douglas-fir

region of the Pacific Northwest. In doing so, we take a

broad view of silviculture, including silvics, nursery practice, seeding and planting, forest genetics, and those aspects

of forest mensuration related to stand development. Our

discussion will deal primarily with Douglas-fir as it occurs

in western Washington and Oregon, but will also touch on

important associated species. We concentrate on events and

research in Washington and Oregon, only briefly touching

on more or less parallel developments in adjacent Canada

and California. We delve very lightly into the enormously

important topic of fire and its effects. Likewise, we touch

only briefly on the important role of silviculture in forest

health issues such as prevention and control of root diseases, insect attacks, animal damage, and similar matters.

We consciously bypass much of the large body of related

work in physiology and ecology. Our main focus will be on

the silvicultural research bearing on stand regeneration and

stand management. 

We give special attention to the period before World

War II (WWII) and treat subsequent years in less detail, in

part because the pre-WWII period is least familiar to the

current generation of foresters. Most research in this early

period was carried out by the U.S. Forest Service, the number of people involved was small, and they often worked 

on a variety of topics. The early researchers included some

truly remarkable people who made enormous contributions.

The memory of these people and their contributions should

not be lost. 

1

Chapter 1: Introduction1

1 By R.O. Curtis.
2

GENERAL TECHNICAL REPORT PNW-GTR-696

After WWII, there was a great expansion in the number

of people involved in forestry research and in silvicultural

research in particular (which peaked about 1975), and a

broadening of activity by universities and a number of

industrial organizations. In recent years, there has been a

great increase in forest ecology research—some of it rather

far removed from practical application—and a declining

emphasis on research in practical silviculture. Boyce and

Oliver (1999) described the history of the interplay between

ecology and silviculture. It is impracticable to cover in

detail the many individuals and individual studies involved.

From about 1950 onward, we identify general trends, the

major silvicultural research results, and a sampling of studies that are directly related to stand establishment and stand

management. We also discuss their effects on current and

future forest management practices. 

We have organized our presentation into (1) historical

background, (2) a brief outline in more or less chronological

order of the general trends in silviculture-related research

over time, (3) a series of more detailed chapters covering

research on particular silvicultural or silviculture-related

topics, and (4) a discussion of concurrent developments in

practical forest management and the way in which they

were influenced by formal forest research. 

We also give an extensive list of references, which

includes most of the important work prior to about 1950. 

It is impractical to list all of the greatly expanded literature

from subsequent years, but we provide enough to indicate

the general direction of research and to serve as entry points

to the literature for those interested in particular topics.
Silvicultural Research and the Evolution of Forest Practices in the Douglas-Fir Region

European Experience

We do not know when forestry began any more than we can

answer such a question for agriculture. Both agriculture and

forestry initially evolved through practical experience, long

before the days of land-grant colleges and professional publications. Some forms of intentional management of trees

and forests probably antedate the written word. Both agriculture and forestry have been practiced in one form or

another in different locations and at different times, with

results strongly influenced by physical conditions and existing cultural, political, and economic factors.

The prerequisites for development and systematic

application of forestry and silviculture are (1) a climate

favorable to the establishment and growth of forests; (2) a

stage of population and economic development in which

pressure on forest resources creates an awareness of present

or anticipated scarcity; (3) sufficient prosperity that concern

for the future is not completely overshadowed by immediate problems of survival; and (4) a degree of cultural, political, and economic stability and social organization that

makes concerted action possible.

Fragmentary evidence shows that techniques such as

planting, coppicing, and thinning were known and practiced

in the ancient Mediterranean world, together with some

governmental efforts to control forest use (Mather 1990).

But a climate not particularly favorable to forests, repeated

wars and invasions and associated political and social instability, population pressures, and the goat combined over the

millennia to destroy much of the region’s forests. 

The moist temperate climate of western and central

Europe is much more favorable for establishment and

growth of forests, and resembles the climate of portions of

the Eastern United States. The roots of modern forestry and

silviculture stem from developments in western Europe,

from the late Middle Ages onward. We do not have a good

up-to-date comprehensive history of European forestry in

English; the closest to this is still Fernow (1911). There are

a number of more recent publications in English that treat

specific limited topics. Among these are Freeman (1994),

James (1996), Klose (n.d.), Linnard (1974, 1999), Lowood

(1990), Mantel (1964), Osmaston (1968) Smout (1997),

Thirgood (1971, 1989), and Watkins (1998). This list is by

no means comprehensive, and the synopsis given below is

necessarily an incomplete and broad-brush treatment of the

subject.

Like our North American forests, the composition 

of European forests changed over time in response to the

changing climate of the glacial and postglacial period and

to the effects of human activities. By the late medieval 

period, most of the forests of western Europe south of

Scandinavia are thought to have been broad-leaved, primarily oaks (Quercus sp.) and beech (see appendix for scientific names of species). Higher elevations in Switzerland

and the mountains of Germany and France contained much

spruce and silver fir. Scots pine was abundant on drier sites

in Germany, in the Scottish highlands, and in Scandinavia

and the Baltic countries, whereas spruce and birch were

extensive in northern Scandinavia. 

The Europe of late medieval and early modern times

was composed of numerous political and economic units,

which gradually became consolidated. Wood was the only

energy source for cooking and heating. Mining, glass 

making, brick making, and the metal working industries

were dependent on wood or on charcoal made from wood.

Shipbuilding and general construction all depended on

wood. Transportation was rudimentary, and heavy or bulky

commodities could only be transported by water. Consequently, timber shortages soon developed in the vicinity of

population and industrial centers, even though there might

be abundant supplies in other areas.

Timber was not the only or even the priority product of

forests. The nobility put great value on their hunting privileges—both for sport and meat—and these privileges frequently took precedence over the interests of the majority

3

Chapter 2: Historical Background1

1 By R.O. Curtis.
4

GENERAL TECHNICAL REPORT PNW-GTR-696

of the population. Cattle grazing was important. The widespread oak forests were valued for mast production, which

supported numerous herds of swine. 

Because fuel- and charcoal-wood and oak mast were

two of the primary products in demand, much of the broadleaved forest was managed from an early date under coppice (regeneration by sprouts) or coppice with standards

(some trees reserved to grow to large sizes) systems. The

standards also provided some large timber for shipbuilding

and construction as well as mast for swine production.

These were relatively simple regimes, well adapted to the

needs of the time, and continued in many areas until the

introduction of coal in the late 18th century and the coming

of the railroads in the early 19th century reduced markets

for fuel wood while improving transportation and, hence,

markets for large and formerly inaccessible timber. This, 

in turn, led to a gradual conversion of many forests from

coppice or coppice with standards to high forest (originating from seed rather than sprouts), managed under several

silvicultural systems. 

Fragmentary records exist, dating at least from the 

13th century, of the systematic forest management of some

monastic and communal forests. By the 17th and 18th centuries, closely controlled forest administrative organizations

had developed for royal and community forests in France

and the German principalities, with timber production as a

major objective.

Thus, in France, an ordinance of 1376 provided for

regulation of cut and reservation of standards (trees held 

for further growth) on felled areas in the royal forests. The

ordinance of 1669 reformed the forest administration and

established a new and more comprehensive forest code for

the royal and communal forests. After the disruptions of the

revolutionary period, the present Ecole National des Eaux

et Forêts was established at Nancy in 1824 and a new Code

Forestier was introduced in 1827. The majority of French

forests remained in hardwoods (beech and oak). Regeneration was primarily by coppice or by natural seeding, and

there was a gradual conversion from coppice or coppice

with standards to some form of the shelterwood system in

most royal and communal forests (James 1996, Thirgood

1989).

Parts of Germany (such as the Black Forest) and

France had large areas of derelict forest and poor pasture

land (reminiscent of our eastern Appalachians of the early

1900s), and much of this passed into state ownership in the

late 18th and early 19th centuries. There were extensive

planting programs in the early 19th century, mostly with

spruce in the mountains, Scots pine on poorer lowland sites,

and maritime pine in the Landes region of southwestern

France. 

A number of texts on silviculture and forest management appeared in the late 18th and early 19th centuries, and

the scientific study of forests and formal forestry education

began in France and Germany. This, in turn, led to the

establishment of specialized forest research institutions in

the latter half of the 19th century. Similar developments

took place in Denmark and Austria, and somewhat later in

the Scandinavian countries. Various techniques for regulation of cut were introduced, aiming at the objective of sustained yield and establishment of a uniform (“normal”)

distribution of age classes. Thinning became a common

practice in France, Denmark, and Germany. By the late 19th

century, yield tables for the major species (which portray

expected stand development and timber production) were 

in common use. 

Of course, there was not a smooth continuum of

progress everywhere. Major disruptions of forest management and damage to the resource accompanied the social

and economic upheavals associated with events such as

plagues, the Thirty-Years War, the French Revolution, and

the Napoleonic wars. 

In Britain, the early forest laws of 1184 and later were

primarily concerned with protecting game for the use of

king and nobility. An act of 1543 under Henry VIII was the

first that defined a positive policy for timber production

(Osmaston 1968), including provision for regeneration and

reservation of standards. John Evelyn’s Sylva (1664) is

often cited as the first silvicultural text in English (Dengler
Silvicultural Research and the Evolution of Forest Practices in the Douglas-Fir Region

1964), along with other early writings. In the 1700s, tree

planting became a common practice on estates. 

Despite these early efforts, Britain had no overall forest

policy. After a start in the 17th and 18th centuries, stimulated by the needs of naval construction and early industry,

timber production forestry declined in the 19th century, with

an increasing emphasis on land use for shooting grounds

and amenities. Factors responsible included the availability

of cheap imported timber from North America and the

Baltic, the substitution of coal for wood as an energy

source, the shift from wood to iron in ship construction, the

absence of any overall government forest policy, and the

fact that many large landowners came to derive their

income primarily from investments in manufacturing industries and overseas development rather than from their lands

in Britain. Timber production forestry was resumed in

Britain on a large scale only with the establishment of the

Forestry Commission and an extensive afforestation program in 1919, as a response to wartime shortages. This was

greatly expanded after World War II, with afforestation of

large areas of poor grazing land and nonproductive moor

land.

In contrast to the neglect of forestry in 19th century

Britain, an effective forest policy and administration was

established comparatively early in British-ruled India and

Burma. This work began in the 1850s and developed under

three German foresters, Brandis, Schlich, and Ribbentrop

(Fernow 1911). Professional staff were trained at Oxford

and at the forestry college (and research institute) established in 1878 at Dehra Dun.

Forest management was introduced on some communal

and other forests in Switzerland by the 17th century, but

was far from universal. Government was highly decentralized until the early 1800s. By the mid-1800s, severe flood

problems were recognized, and toward the end of the century (1876) federal forestry programs were put in place that

emphasized watershed protection on mountain lands. In

1902, federal oversight was extended to all forest lands.

Further clearing of forests was restricted, and efforts were

made to reforest poor mountain pasturelands. Most forests

were and are managed under selection and shelterwood 

systems, with predominantly natural regeneration. 

In the more remote and less accessible areas of northern Scandinavia and Finland, forest management remained

largely extractive until the beginning of the 20th century.

By 1900, German forestry was widely viewed as an

outstanding success and a model for other countries to follow. Highly productive forests under systematic planned

management had replaced the degraded forests of earlier

times. Plantation forestry, particularly with spruce, was

emphasized because of its high yields and favorable financial returns. But there were some rumblings of discontent,

which have increased over time. A decline in growth of

planted spruce stands occurred in some areas, now attributed to the attempt to grow spruce on warmer and drier

sites than those on which it occurred naturally. Pure spruce

stands suffered from windfall. Rising labor costs made the

traditional dense planting and intensive early thinning

increasingly questionable. There were movements in favor

of mixed species, more “natural” regeneration methods, and

more emphasis on amenity values (Plochmann 1992, Troup

1952: 193–207).

Public regulation of forest practices in varying degree

has long been established in many European countries, and

is often combined with extensive public assistance to private and communal owners through technical services, 

marketing services, owner cooperatives, and various forms

of subsidy for socially beneficial activities that are not 

otherwise financially attractive to an owner (Gilfillan and

others 1990; Grayson 1993; Klose, n.d.; Plochmann 1974).

Although European species are not identical with those

of the United States, most of them are close relatives of and

similar in behavior to those of the Northern United States.

A number of species from the Pacific Northwest, including

Douglas-fir, Sitka spruce, and lodgepole pine, have been

introduced in Europe and have done extremely well.

Weetman (1996) provided a useful discussion of European

silvicultural experience and recent parallels with Pacific

Northwest experience and problems.

5
6

GENERAL TECHNICAL REPORT PNW-GTR-696

Several lessons can be drawn from European forest 

history:

• Forestry and silviculture have a much longer history

than most people realize.

• Objectives and practices evolve with changes in the

social and economic environment.

• Forests have been managed for multiple objectives

throughout history, although the emphasis has been 

different in different places and at different times.

• The moist temperate forests of central and northern

Europe have shown great resilience and remain 

highly productive after 2000+ years of relatively 

dense human occupation and intensive use and 

abuse. Extensive areas that had been reduced to 

nonproductive wasteland have been successfully 

rehabilitated.

• Many of our present activities and problems have 

parallels in the past. 

United States Beginnings2

The indigenous peoples of the Eastern and Southern United 

States cleared and cultivated substantial areas, but there

were also vast areas of forest. The early European settlers

were mainly agriculturists, who viewed forests as obstacles

to be removed. It was the policy of both colonial governments and the later government of the United States to

transfer public lands into private ownership as rapidly as

possible, in the belief that agricultural development would

naturally follow. This policy was not seriously questioned

until the latter part of the 19th century.

The transfer of lands to private ownership was accomplished by large land grants to private parties in the colonial

period; by direct sale; by the Homestead Act of 1862,

which gave 160 acres (65 ha) of land to any citizen willing

to cultivate it; by huge land grants to railroad companies in

lieu of cash subsidies; various grants to the states; and

assorted other acts, such as the Timber and Stone Act of

1878, the Timber Culture Act of 1873, and the Mining Act

of 1872. Administration of the various laws governing land

disposals was unavoidably loose and sometimes corrupt.

Fraud and speculation were common and led to a number of

scandals toward the end of the 19th century.

Results of this overall policy were reasonably satisfactory in the fertile lands of the Midwest and the Mississippi

Valley. But it gradually became evident that agriculture on

the eastern pattern would never be feasible in much of the

arid West or in the rugged terrain of the Rocky Mountain

and Pacific coast regions. Future values lay in timber, minerals, grazing, and the water that could make agriculture

feasible.

By the latter half of the 19th century, a large lumber

industry had developed that provided materials for the burgeoning economy as population grew and industrialization

proceeded. At the time, this was a migratory industry that

viewed the forests as fixed assets to be mined. Competition

among numerous firms was intense, and the industry was

highly cyclical. The center of activity shifted from New

England to Pennsylvania to the Lake States as the resource

was exhausted, then to the South and to a beginning on the

west coast. These lumbering operations and the fires that

often accompanied them left behind a trail of derelict lands

and ghost towns. 

From the Civil War onward, repeated warnings were

voiced of the calamitous consequences of the progressive

destruction of North American forests. An approaching timber famine, floods, and water supply problems were predicted. Notable figures in the efforts to obtain congressional

action included George P. Marsh, Carl Schurz, Franklin 

B. Hough, and John A. Warder (who was instrumental in

formation of the American Forestry Association in 1875). 

A committee of the American Association for the

Advancement of Science, with Hough as chairman, prepared a statement asking Congress to address the issue

(Hough 1873). President Grant presented this to Congress

in 1874. As one result, Hough was appointed as forestry

agent in the Department of Agriculture, in which capacity

2 This section and related discussion are drawn from Dana (1953), Miller

(2000), Rodgers (1991), and Steen (1977).
Silvicultural Research and the Evolution of Forest Practices in the Douglas-Fir Region

he prepared several extensive reports on the U.S. forest 

situation and recommendations for action (Hough 1913,

Miller 2000, Steen 1977). His book The Elements of

Forestry was the first general forestry text published in the

United States (Hough 1882).

Efforts for reform and congressional maneuvering continued over subsequent years. We will not attempt to follow

the details, but merely point out the results:

• A Forestry Division was established in the Department of Agriculture in 1881 with Hough as its first

chief. He was succeeded for a brief period by 

Nathaniel Eggleston, and the division (later renamed

the Bureau of Forestry) was made permanent in 

1886, under Bernhard E. Fernow as Chief (Rodgers

1991). Fernow in turn was succeeded by Gifford

Pinchot in 1898.

• The Forest Reserve Act of 1891 gave the President

authority to establish forest reserves from the public

lands. Presidents Harrison and Cleveland set aside

some 40 million acres over the next few years, with

protection and management responsibility assigned to

the General Land Office in the Interior Department.

• The Organic Act of 1897 provided extended authority

for creation and administration of the forest reserves,

and established their purposes as “to improve and 

protect the forest. . . .to secure favorable conditions 

of water flows, and to furnish a continuous supply of

timber for the use. . . .of citizens of the United States.”

• In 1905, the Interior Department functions in administration of the forest reserves were combined with 

the Department of Agriculture’s Bureau of Forestry 

to form the U.S. Forest Service and National Forest

System, located in the Department of Agriculture, 

with Gifford Pinchot as Chief.

• The national forests were greatly expanded under 

the Theodore Roosevelt administration.

The Society of American Foresters was established in 

1900, with an initial membership that included a number 

of people who were prominent leaders in American forest

policy, forest science, and forestry education over the next

several decades. 

A forestry education program was established at

Cornell University in 1898 under Fernow, but fell victim 

to political difficulties in 1903. Carl Schenck (a German

forester) established and ran the independent Biltmore

School from 1898 to 1913. The Yale School of Forestry was

established as a graduate school in 1900, under Henry S.

Graves, previously assistant to Pinchot in the Bureau of

Forestry. A number of other professional programs were

established at various universities within the next few years,

including that at Oregon State in 1906 and at the University

of Washington in 1907. These provided the cadres for the

developing federal, state, and private forestry organizations.

Fernow and Schenck were German foresters who

immigrated to the United States. Pinchot, Graves, and some

others had studied forestry in France and Germany. Thus,

they came to their tasks with a considerable knowledge of

the European experience and the practices in use in Europe.

Although American social and economic conditions were

markedly different, their European forestry background had

a considerable and generally beneficial influence on their

thinking and choice of measures.

7
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Silvicultural Research and the Evolution of Forest Practices in the Douglas-Fir Region

As we use the term, the “Douglas-Fir Region” is the region

lying between the crest of the Cascade Mountains and the

Pacific Ocean in western Washington and western Oregon,

plus a considerable area of similar conditions in southwestern British Columbia including Vancouver Island. This

geographic area encompasses most of the range of coast

Douglas-fir (Pseudotsuga menziesii (Mirb.) Franco var.

menziesii), which extends southward more narrowly into

northern California.

Annual rainfall is moderate in the Puget Sound basin 

and Willamette Valley (about 100 centimeters, 40 inches),

somewhat lower in southwest Oregon, and very high along

the Pacific coast and at higher mountain elevations (200 

to 300 centimeters, 80 to 120 inches). Rainfall is strongly

seasonal, with dry summers. Temperatures are mild and 

relatively equable although the climate becomes more

severe with much greater snowfall at the higher elevations.

The Forests

The predominantly coniferous forests of the coastal Pacific 

Northwest are complex and are probably the most productive natural temperate forests in the world. The region takes

its name from Douglas-fir, the most abundant and economically most important species. However, the region also

includes a number of other important species and forest

types, which have received considerably less attention. 

Popular mythology has it that at the coming of

Europeans, the region was an unbroken expanse of giant

old-growth trees that had been present from the distant past.

This is far from the truth. We cannot know exactly how

much of the region was “old growth,” but several estimates

suggest it may have been about 50 percent (Ripple 1994).

The proportion of old growth must have fluctuated considerably because of the periodic huge fires that we know

occurred in presettlement as well as postsettlement times.

The Native Americans of the region were not agriculturists

and settled mainly along the seacoast and major rivers. The

forests were therefore less affected by pre-European human

activities, excepting fire, than those of the Eastern United

States. Nonetheless, accidental and intentional burning by

Natives had major effects. Camas (Camassia quamash)

was a major food source, and extensive lowland areas were

intentionally burned to promote growth of this plant as well

as to facilitate hunting. These fires, combined with relatively low rainfall and excessively drained glacial outwash

soils in some areas around Puget Sound, produced extensive areas of open prairie and oak woodland in the Puget

Sound trough and Willamette Valley. Similarly, intentional

as well as accidental fires in the mountains produced extensive huckleberry fields, much valued by the Natives.

Glaciers covered the northern part of the region 

until about 12,000 years ago. Pollen analyses and dating 

of organic debris indicate marked changes in climate and 

in species composition of the forests since retreat of the 

glaciers. The forests are thought to have reached approximately their present species composition only some 6,000

years ago (Brubaker 1991). 

Present forest composition is closely related to elevation and rainfall. The forest can be subdivided into zones

(adapted from Franklin and Dyrness 1973) more or less as

follows:

• Western hemlock (Tsuga heterophylla) zone.

• Sitka spruce (Picea sitchensis) zone.

• Pacific silver fir (Abies amabilis) zone.

• Mountain hemlock (Tsuga mertensiana) zone.

• Willamette Valley.

• Mixed-conifer and mixed-evergreen zones (southwest 

Oregon and adjacent California).

Of these, the western hemlock zone is by far the most 

important in terms of both area and productivity. Despite

the name (based on the successional “climax” species),

most of the zone is dominated by Douglas-fir. This dominance is the combined result of past fires (historical and

prehistoric), clearcut timber harvesting, and planting of

burned or harvested areas; all of which favor the relatively

shade-intolerant Douglas-fir. Important associated species

9

Chapter 3: The Douglas-Fir Region1

1 By R.O. Curtis.
10

GENERAL TECHNICAL REPORT PNW-GTR-696

include western hemlock, western redcedar (Thuja plicata),

and red alder (Alnus rubra), plus a considerable number 

of others common in parts of the zone. Productivity varies

from moderate to extremely high, according to rainfall, elevation, and soils. The majority of research studies and most

of the discussion in later portions of this paper are primarily

concerned with Douglas-fir as it occurs in the western hemlock zone. We touch only briefly on the associated species

and adjacent zones.

The Sitka spruce zone is a narrow belt along the

Pacific Ocean, with mild temperatures, very high rainfall,

and high productivity. It is a southern continuation of the

extensive spruce-hemlock forests of southeastern Alaska

and western Vancouver Island. Although it takes its name

from the characteristic presence of Sitka spruce, western

hemlock is the most abundant species. Other commercially

important species present in lesser amounts include red

alder, western redcedar, and Douglas-fir. This zone has

received less research attention than the western hemlock

zone, probably because western hemlock was seen as a 

relatively low-value species until quite recently.

The silver fir and mountain hemlock zones are at 

higher elevations, in which timber harvesting has a short

history and in which relatively little silvicultural research

has been done. Sites range from moderately productive to

clearly noncommercial. Species composition is mixed,

including—in addition to the Pacific silver fir and mountain

hemlock that give the zones their names—Douglas-fir at

the lower margins and such other species as western hemlock, western redcedar, Engelmann spruce (Picea engelmannii), western white pine (Pinus monticola), noble fir

(Abies procera), lodgepole pine (Pinus contorta), and

Alaska yellow-cedar (Chamaecyparis nootkatensis).

The Willamette Valley is an area of lesser rainfall, in

the rain shadow of the Oregon Coast Range. At the time of

settlement it consisted largely of prairie and open Oregon

white oak (Quercus garryana) woodland. Associated

species include Douglas-fir, grand fir (Abies grandis), 

ponderosa pine (Pinus ponderosa), and bigleaf maple 

(Acer macrophyllum).

The mixed-conifer and mixed-evergreen forests of

southwestern Oregon and adjacent California (which

include Douglas-fir as an important component) have considerable differences from forests to the north; the forests in

the southern part of the region are associated with a warmer

and drier climate and more frequent fire-return intervals.

Early History

The first permanent European settlements were the furtrading posts of the Hudson’s Bay Company and its U.S.

competitors, established shortly after the Lewis and Clark

expedition reached the Northwest coast in 1805. By the

1840s, there was substantial continuing immigration from

the Eastern United States. A major area of settlement was

the Willamette Valley, which attracted settlers because of its

good agricultural soils and open prairie and oak woodland.

The second and somewhat later area of settlement was the

Puget Sound region, which was less attractive to the agriculturist but had the advantage of sheltered harbors and

easy water transport on Puget Sound.

The California gold rush of 1849 suddenly created a

large demand for lumber. Most of Puget Sound was bordered by forests, easily accessible to water transportation.

The immediate result was establishment of a lumber industry shipping its products to California; a trade that soon

expanded to include exports to Hawaii, Australia, and South

America. This quickly became the principal industry in the

area. A similar but considerably later development occurred

in Oregon, where transport and access to shipping was

much more of a problem. Completion of the transcontinental railroads in the 1870s, and the opening of the Panama

Canal in 1914 provided access to Eastern U.S. markets.

Logging began at tidewater, and gradually moved

inland up the valleys and lower slopes. The horse and ox

teams that were originally used quickly proved inadequate

for handling large timber over any distance. There was

rapid development of an elaborate logging technology

based on the steam engine, logging railroad, and cable 

yarding systems (Gibbon 1918).
Silvicultural Research and the Evolution of Forest Practices in the Douglas-Fir Region

In this early period, timber was obtainable either without cost (bluntly, by theft from public lands) or at minimal

cost through the various land grants and land disposal laws

(Ficken 1987, Yonce 1980). Timber was regarded as a fixed

asset to be mined. No value was placed on future use of the

land other than possible use for agriculture or town sites in

some favorable locations. There was no effort at fire control

beyond the immediate vicinity of mills and established

communities. The combination of large-scale unregulated

logging and repeated fires produced large areas of

unstocked and derelict land, much of which (but not all)

eventually restocked through natural processes.

11
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Silvicultural Research and the Evolution of Forest Practices in the Douglas-Fir Region

Initial Explorations

The scientific study of Douglas-fir and associated vegetation started with the description of the species in 1792 by

Archibald Menzies at Nootka Sound on the west coast of

Vancouver Island (Hermann 1982). Doubtless, Native people had earlier knowledge of the ecology of Douglas-fir and

other species. Slightly more than a decade after Menzies,

the Lewis and Clark expedition made systematic notes on

Northwest flora (Moulton 1983).

Other expeditions that included systematic observations

of vegetation soon followed. David Douglas observed and

collected plant and animal specimens in exploratory trips

throughout the Pacific Northwest from 1825 to 1827, and

1830 to 1833 (Harvey 1947). John Fremont’s expeditions

from 1844 to 1852 involved some observations and collections in forest types of the Pacific Northwest (Welsh 1998).

Railroad surveys followed, and as settlers arrived, systematic land surveys were begun that recorded the most

prominent species present (Habeck 1961). Much information on forest types and conditions was developed by

Leiberg, Plummer, and others during surveys of the forest

reserves in the Pacific Northwest (Gannett 1900). These

early observations for various purposes provided the first

knowledge about species distribution and characteristics.

Early Research: 1881–1920

The Division of Forestry established in 1881 (renamed 

the Bureau of Forestry in 1901) in the Department of

Agriculture was authorized to undertake a variety of work,

including making forest plans for private timberland owners, tree planting, and forest investigations. Its assigned

functions thus combined education, forestry extension, and

forestry research. Its chiefs, Hough and Fernow (chapter 2),

both had a research orientation, and a large part of their

activities were concerned with fact-gathering and research.

Within a rather short period, the organization produced a

considerable number of publications, despite (by present

standards) a small staff and minuscule appropriations. 

These activities continued after the Bureau of Forestry

was merged with the forest reserve administration of the

Public Lands Office to create the U.S. Forest Service within

the Department of Agriculture under Pinchot, although

Pinchot’s efforts appear to have emphasized the promotion

of forestry among landowners and the problems of organizing and administering the public forests. Raphael Zon 

promoted establishment of a series of forest experiment 

stations, the first of which was established in 1908 at Fort

Valley, Arizona. 

In 1908, a Section of Silvics was established in the

newly organized District Forester’s office in Portland. Its

leader, Thornton T. Munger (fig. 1), soon became one of

the outstanding figures in Northwestern forestry research.

13

Chapter 4: Forestry Research—Origin and Direction1

1 By R.O. Curtis.

Figure 1—Thornton T. Munger came to the Pacific

Northwest in 1908, became the first Director of the 

Pacific Northwest Forest Experiment Station (1924–38),

and retired in 1946. He had a great influence on

Northwestern forestry and forestry research. 
14

GENERAL TECHNICAL REPORT PNW-GTR-696

In 1913, the Wind River Experiment Station was established near Carson, Washington. (Herring and Greene, in

press, give a detailed history). The location was originally

chosen for its proximity to the recently established Wind

River nursery (fig. 2), primarily because of the belief that

the most pressing problems concerned nursery practice and

reforestation of the extensive burned areas (fig. 3). This

emphasis was soon replaced as the paramount interests by

problems of slash disposal, fire control, and natural regeneration after cutting (Munger 1955). From 1913 to 1924, most

silvicultural research was conducted at Wind River (fig. 4)

by staff working there under Julius V. Hofmann. In 1915,

160 acres (65 hectares) of new plantations and young natural regeneration was set aside as the first unit of an experimental forest (Munger 1955: 229). This was later greatly

expanded (1932) to form the present Wind River

Experimental Forest. In 1926, a 280-acre (113-hectare) 

natural area was established in the Trout Creek drainage. 

In 1932, this was enlarged to 1,180 acres (480 hectares) to 

form the Wind River Natural Area within the Wind River

Experimental Forest, later (1977) renamed the T.T. Munger

Research Natural Area.

In 1915, Henry S. Graves, successor to Pinchot as

Chief of the Forest Service, appointed Earle H. Clapp as

chief of the newly established Branch of Research, a post

he held until 1935. He established the position of research

(including the Wind River Experiment Station) as an activity

Figure 2—Beginnings of the Wind River Nursery, about 1910. 

Figure 4—Wind River Nursery and Wind River Forest Experiment

Station, 1919. 

Figure 3—The great Yacolt Fire and others prompted early

emphasis on reforestation of burned areas. This 1913 photo of the

1902 Yacolt Burn was taken by Julius V. Hofmann near the Wind

River Forest Experiment Station.
Silvicultural Research and the Evolution of Forest Practices in the Douglas-Fir Region

independent of national forest administration and responsible to the Washington Office rather than the regional

foresters. He laid the groundwork for the McSweeneyMcNary Act, discussed below.

Many of the small staff involved in research activities

of the Bureau of Forestry and in the early years of the

Forest Service went on to play prominent regional and

national roles in forestry research, policy, education, and

administration. Hereafter, we mention only those individuals, studies, and publications directly pertinent to the

Douglas-fir region. 

A major activity in the initial years was preparation of

a series of monographs on the silvics and general characteristics of important timber species, as understood at the time.

Among of the first of these was a bulletin on western hemlock by E.T. Allen2 (1902), who later played a prominent

role in the Western Forestry and Conservation Association

(still extant) and in the promotion of industrial forestry. He

also wrote a lengthy report on Douglas-fir,3 which, among

other things, recognized the role of fire in creating and perpetuating Douglas-fir forests, and the possibilities of future

management of these forests.

Sudworth published (1908) Forest Trees of the Pacific

Slope, a comprehensive text on the dendrology and silvics

of Pacific Northwest species. This provided the first compiled information on seeding characteristics and reproduction of western trees and specifics about the geographic

occurrence of individual species.

Another major early publication was Frothingham’s

(1909) monograph on Douglas-fir. Frothingham recognized

the distinction between coast and Rocky Mountain forms,

gave some information on European experience with introduced Douglas-fir, and discussed its geographic distribution

and silvical characteristics in different parts of the region.

He recognized the role of fire in perpetuating Douglas-fir,

its inability to reproduce and grow under shade, and recommended clean (clear) cutting with burning of slash to

expose mineral soil as the most appropriate form of management on the Northwest coast. Reading this today, one is

impressed by the author’s understanding and generally correct observations.

The first large field study was on growth and yield of

Douglas-fir, and involved extensive field measurements in

existing second-growth stands. The results were published,

along with much other information, in The Growth and

Management of Douglas-Fir in the Pacific Northwest

(Munger 1911). This discussed silvics of the species, the

possibilities of future production from logged-off land, the

measures needed to ensure regeneration, associated costs,

and prospective yields. It presented a volume table and a

yield table, based on field measurements in the previous

several years; these were the first of many such tables prepared in the Northwest. Munger argued that satisfactory

regeneration could be secured with some fairly minor modifications of prevailing logging methods. He recommended: 

• Clean (clear) cutting the area (except that 

provision must be made for seed trees),

• Clearing the area of debris by fire to prepare 

the seedbed,

• Protecting the area from subsequent fires.

In 1911, Allen published Practical Forestry in the 

Pacific Northwest, through the newly established Western

Forestry and Conservation Association. This was a lengthy

discussion of the problems and opportunities for forestry in

the Pacific Northwest and a plea for action, based in part on

the recently acquired silvicultural knowledge, in part on the

economics of the lumber industry, and in part on extrapolation from European experience. From the standpoint of the

15

2 E.T. Allen began as a ranger in Washington state under the Public Lands

Office, joined the Division of Forestry in 1899, served briefly (1905–07)

as State Forester of California, and was then appointed District Forester

for District 6 in Portland, Oregon. He resigned in 1909 to become manager of the newly organized Western Forestry and Conservation Association.

3 Allen, E.T. 1899. Red fir in the Northwest. 94 p. Unpublished manuscript. On file with R.O. Curtis. 
16

GENERAL TECHNICAL REPORT PNW-GTR-696

present discussion, his two most important points were (1)

the overriding importance of establishing adequate fire protection as a prerequisite for any type of forest management

and (2) the importance of regeneration.

An early long-term research project was a provenance

trial of Douglas-fir, begun in 1912 (chapter 7). Seed was

collected at widely scattered locations in western Oregon

and Washington, grown in the nursery, and then planted at

five locations ranging from 1,000 to 4,600 feet (300 to

1400 meters) in elevation. Major differences among seed

sources were found in survival, growth rate, and sensitivity

to differences in local climate (Hofmann 1921, Morris

1934, Munger and Morris 1936). 

A worldwide search for fast-growing exotic trees began

in 1912, and specimens were planted to form the Wind

River Arboretum. This work was initiated by T.T. Munger,

continued by E.L. Kolbe, and later by Leo Isaac, and

reported in detail by Silen and Olson (1992). Results demonstrated the superiority of native species over exotics. The

progressive failure of initially promising exotics showed

that long-term forest research findings can be very different

from initial results.

From 1910 through 1940, a series of permanent sample

plots was established in young-growth Douglas-fir stands

(first reported in Munger 1915). The original purpose was

to provide a foundation for growth and yield estimates for

pure, well-stocked stands of Douglas-fir. These formed 

the basis for a number of publications, discussed later.

Williamson (1963) described those plots still surviving in

1963. Several are still extant and have recently been used

by university scientists interested in development of older

unmanaged stands (Acker and others 1998).

In 1920, a set of three experimental thinning plots was

established on Martha Creek at Wind River, in a 9-year-old

naturally regenerated stand. One plot was left unthinned,

and two were thinned to 8- by 8-foot spacing (2.4- by2.4-meter) (chapter 6).

On the national scale, knowledge of artificial regeneration had accumulated to the point that J.W. Toumey published a detailed textbook on the subject (Toumey 1916),

subsequently rewritten and considerably expanded (Toumey

and Korstian 1931).

In this early period, there was debate over the use of

natural vs. artificial regeneration methods. Rehabilitation of

the extensive burned areas (Yacolt Fire of 1902 and others)

was an urgent problem, and the Wind River nursery had

been established (1910) to provide for this. There was little

question about the need for planting such areas. But there

was some difference of opinion over desirable practice for

regenerating freshly logged areas. Munger (1912), in rebuttal of Kirkland’s (1911) opinion that artificial regeneration

would be both cheaper and more satisfactory than natural

regeneration, advocated general use of natural seeding by

the scattered seed tree method, after burning slash to expose

mineral soil. He (optimistically) estimated that one large

seed tree per 2 acres might be sufficient. As these could be

selected from among damaged and defective trees, the cost

would be materially less than with artificial regeneration.

Greeley (1912) sided with Munger on the practical grounds

that limited financial resources would be best directed at

reforesting the huge existing area of nonstocked land.

Research: 1921–1960

The increased level of research activity and wide variety of 

topics make it impractical to adhere to a strictly chronological presentation in discussing this and subsequent periods,

and instead we will review progress in a number of silviculture-related topics in a series of subsequent chapters.

In general, silviculture research in this period was

directed primarily at the problem of securing prompt and

adequate regeneration of cut areas mainly, though not

exclusively, by natural seeding. There was also much work

on Douglas-fir yield tables and growth prediction and a

beginning on extensive thinning research. 

A number of major events and organizational and technical changes in this period affected the course of forestry

research. These included:

• The Pacific Northwest Forest and Range Experiment

Station (now Pacific Northwest Research Station,

PNW) was established in 1924 and absorbed the 
Silvicultural Research and the Evolution of Forest Practices in the Douglas-Fir Region

former Wind River Experiment Station. Headquarters

was in Portland, Oregon, with Thornton T. Munger 

as its first Director. Extensive records of events at 

the Station are given in unpublished reports by 

Cowlin4 and Wertz.5

• The McSweeney-McNary Act of 1928, for which 

Earle Clapp was largely responsible, established 

essentially the present system of forest experiment 

stations under USDA Forest Service. The act greatly

elaborated research authorization and increased funding. The act provided clear direction that Forest 

Service research should serve the needs of all forest

landowners and of the public, rather than functioning

as a support organization for national forest administration. It also established the Forest Survey (now

Forest Inventory and Analysis), as a continuing 

national inventory of forest resources.

• Although the Great Depression of 1929–1940 

severely impacted the timber industry, the Civilian

Conservation Corps program improved research 

infrastructure and provided manpower in support of

research.

• The introduction of truck transport and tractor 

skidding provided increased flexibility in application of silviculture.

• Statistical methods were increasingly used, as a 

result of developments in applied statistics, education, and the introduction of mechanical calculating devices. The methods pioneered by R.A. Fisher 

in agronomy were introduced to forestry research 

(primarily through training efforts within the USFS

research organization) by people such as Donald 

Bruce, F.X. Schumacher, J.G. Osborne, R.A. 

Chapman, and others (Bruce 1999).

• World War II shifted most research personnel to the

military or to war-related work for the duration.

• After the war, forestry education expanded and the 

role of the universities in forestry research increased.

• Support for forestry research increased markedly as 

a result of postwar changes in the economy and the

timber-related industries.

In 1934, the Forest Service established the Cascade 

Head Experimental Forest on the Siuslaw National Forest,

north of Lincoln City on the Oregon coast. This experimental forest was primarily Sitka spruce and western hemlock.

It was the site of considerable research in the type, including precommercial thinning trials in hemlock (Hoyer and

Swanzey 1986) and in Sitka spruce comparing a range of

spacings; work on spruce-hemlock regeneration; and harvest methods. Walter Meyer established 11 long-term

growth plots in spruce and hemlock. In 1940, Briegleb

added three Douglas-fir long-term plots at Cascade Head 

in the series begun by Munger. In 1935–37, a study was

installed comparing growth of red alder and alder-conifer

mixtures (Berntsen 1961a). In the late 1930s, experimental

plantings were made of a number of introduced species,

none of which were successful. Cascade Head Experimental

Forest has also been the site of a considerable amount of

more recent work in various aspects of forest ecology, by

both PNW Research Station and Oregon State University. 

Three experimental forests were established in 1947–

49, specifically to study commercial thinning, and will be

discussed further under that topic. These three—the

Hemlock, McCleary, and Voigt Creek Experimental Forests

—were established on industrial land under cooperative

leases.

In 1948, the H.J. Andrews Experimental Forest was

established on the Willamette National Forest, east of

Eugene, Oregon. It has been the site of much research by

PNW Research Station, Oregon State University, and others

that continues to the present. Early work was concerned 

primarily with old-growth harvesting techniques, including

17

4 Cowlin, R.W. 1988. Federal forest research in the Pacific Northwest 

Research Station. 244 p. Unpublished manuscript. On file with R.O. Curtis.

5 Wertz, J.H. 1940. A record concerning the Wind River Forest Experiment 

Station, July 1, 1924–December 30, 1938, with supplements 1939 

through 1943. Unpublished documents. On file with R.O. Curtis. 
18

GENERAL TECHNICAL REPORT PNW-GTR-696

various forms of strip cutting, small group cuts, seed tree

cuts, and conventional staggered settings. Emphasis then

shifted to forest ecology and watershed questions, and in

recent years there has also been work on thinning regimes

and related topics.

Munger (1927), in Timber Growing and Logging

Practice in the Douglas-fir Region, summarized thenexisting information and recommendations for harvest and

regeneration of old stands and protection of regeneration

from fire.

In 1947, the PNW Forest and Range Experiment

Station published Management of Second-Growth Forests

in the Douglas-Fir Region (USDA FS 1947). This was a

compendium of existing knowledge on all aspects of

Douglas-fir silviculture and stand management prepared by

a committee that included many individuals prominent in

public and private forestry and in both research and administration. It had a major influence on the transition to permanent long-term management on industrial and other

private lands.

In the late 1950s to early 1960s, there were substantial

changes in the Forest Service research organization, under

the leadership of V.L. Harper. The former geographically

based research center organization adopted after World War

II was abandoned in favor of a project organization that

grouped people working on particular topics. Promotion of

scientists was no longer dependent on acceptance of administrative responsibilities. Pioneering research units were

established to provide wide scope for the abilities of selected outstanding researchers (Steen 1998). Research funding

was increased and a laboratory construction program was

undertaken.

Research: 1961–1985

Research in this period emphasized increasing growth rates 

of established young stands through such practices as density control and fertilization. There was also much work on

artificial regeneration and the associated problems of site

preparation and brush control. Extensive work was undertaken in genetics and tree improvement.

University research underwent a great expansion, supported in part by funding under the McIntire-Stennis Act 

of 1962. A number of corporations established substantial

forestry research organizations (Staebler 1999). Forest

research was no longer solely or even primarily a function

of the federal government. Most foresters and much of the

public saw the needs of public and private owners as broadly

similar, and there was much cooperation and mutual support between the public and private sectors. This cooperation included establishment of a number of research cooperatives involving industry, public agencies, and educational

and research organizations. The first cooperatives were in

tree improvement and forest fertilization, but the approach

expanded to other silvicultural and forestry matters.

Efforts in several research areas were greatly increased

in the 1950s and 1960s. These included the initiation of

comprehensive genetics studies in Douglas-fir, installation

of numerous thinning studies, and expansion of artificial

regeneration and vegetation management studies. Outputs

from these programs had profound effects on silvicultural

practices and on the conduct of future research.

Statistical designs were evolving rapidly, as were calculators and computer technology for handling large data

sets. Statistical methods and designed experiments became

routine. The advent of the electronic computer brought a

revolution in data management and analysis, including the

development of computer models to predict stand and tree

growth and response to treatment. These became an important means of summarizing silvicultural knowledge and an

important management tool. The new capabilities enabled

scientists to address problems in ways that were not previously possible. They also had drawbacks in that they led

some to place undue reliance on computer-generated numbers as substitutes for direct field observation and experience.

Some of the early experiments in nursery technology

revealed needs for major changes in seedling density management, fertilization, and soil maintenance. Research in

artificial regeneration showed that competition from native
Silvicultural Research and the Evolution of Forest Practices in the Douglas-Fir Region

and invasive exotic plants, and herbivory by wildlife were

major obstacles that needed regional attention. Agricultural

chemicals adapted for selective weed control in agronomic

crops were found to have major roles in controlling forest

composition. By the 1970s, these early programs had developed the basis for large, well-designed experiments that

have greatly strengthened the data base underlying many

decisions in forest management, and provided the basis for

using silvicultural strategies to accomplish a wide range of

management goals.

Research: 1986 to the Present

The pressures associated with the rise of the environmental 

movement, the Endangered Species Act (1973), and the

growing opposition of segments of an urbanized public to

cutting trees and to clearcutting in particular, produced

major changes in research direction in this period. Objectives

and interests of private and industrial owners now often

diverged from those of the public land managing agencies.

The federal agencies, in particular, no longer saw commodity production as a primary objective.

Accordingly, research directed at enhancement of 

timber production was deemphasized by the Forest Service.

The Northwest Forest Plan of 1994 placed the longestablished Wind River and Cascade Head Experimental

Forests in late-successional reserves, thus effectively halting any form of manipulative experimentation on these

areas. Emphasis shifted to various aspects of forest ecology

and to alternatives to the long-established clearcutting 

system that might be used to enhance wildlife habitat and

scenic values. 

In contrast, industrial and state ownerships remained

strongly interested in practices to increase timber growth

rates, an interest that was enhanced by impending timber

supply shortages and the prospect of more caused by the

Northwest Forest Plan’s withdrawal of most Forest Service

land from timber harvest. Nursery practices for producing

seedlings with good storage tolerance, rapid early growth,

and competitive ability emerged from a combination of

research by commercial nursery interests and cooperative

nursery technology programs. Research continued on

aspects of production forestry such as fertilization, plantation density, and control of vegetative competition. There

was a decline in in-house research by industry that was at

least partially offset by the work of university-based cooperatives, which were financed mainly by industrial and 

state landowners.

19
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Silvicultural Research and the Evolution of Forest Practices in the Douglas-Fir Region

Natural Regeneration1

In the early days of Northwestern forestry, the priority 

problem (after fire control) was that of securing prompt and 

adequate regeneration. It was soon realized that most of the

existing forest consisted of more-or-less even-aged stands

that had originated after fire, and that Douglas-fir

(Pseudotsuga menziesii (Mirb.) Franco) was a moderately

intolerant species that grew best with full overhead light.

There was consensus at the time within the Forest Service

that natural seeding was the most economical and, in most

cases, the only feasible means of regenerating harvested

areas, with artificial regeneration to be used mainly on

burns or other areas that were not restocking adequately.

It was initially assumed by almost everyone that the

regeneration often found on logged or burned areas was

from wind-borne seed produced by whatever few surviving

trees were present. Hofmann conducted extensive surveys

of the distribution of regeneration on old burns and logged

areas, and found regeneration in locations far removed from

any existing seed source (fig. 5). He concluded (Hofmann

1920, 1924) that Douglas-fir seed could survive for considerable periods in the duff, and that this was the main source

of regeneration. 

In 1918, Hoffmann installed a 1.5-mile (2.4-kilometer)

transect across the Wind River Valley in a large freshly

clearcut and burned area. Small plots located at intervals

along this transect were periodically assessed (1919–46) for

establishment of regeneration (Steele 1953), and aspect,

topographic position and distance from uncut timber were

recorded. Results showed that under favorable conditions,

adequate regeneration could become established within 10

years for up to 4 mile (400 meters) from uncut timber.

Final results (as updated by DeBell2 in 2003) showed that

most of the area eventually restocked naturally. 

Hofmann left the Wind River Experiment Station soon

after this transect was established, and went on to an academic career in the East.

In 1924, Leo Isaac came to Wind River, and thence to

the newly formed Pacific Northwest Experiment Station

(fig. 6). He devoted most of his working life to Douglas-fir

silviculture, primarily research on the problems of natural

21

Chapter 5: Regeneration Systems

1 By R.O. Curtis.

2 DeBell, D.S. 2003. Historic transect across Wind River Valley. 4 p.

Unpublished note. On file with R.O. Curtis.

Figure 5—Natural regeneration in 1918 on a burn in the Wind

River Valley. Natural regeneration at considerable distances from

any existing seed source led Hofmann to conclude that regeneration originated principally from seed stored in the duff.

Figure 6—Leo A. Isaac joined

the PNW Forest Experiment

Station in 1924. He became the

authority on natural regeneration

and provided early impetus for

tree improvement.
22

GENERAL TECHNICAL REPORT PNW-GTR-696

regeneration. He became the recognized authority on the

subject, and his findings are still relevant.

Hofmann’s conclusion—that Douglas-fir seeds that 

survived for extended periods in the forest floor and germinated following cutting were the principal source of regeneration—was questioned by others who pointed to

numerous large open areas that were not restocking.

Isaac conducted two experimental studies that settled

the question of seedling origin. The first (Isaac 1930, Isaac

and Fry 1972) consisted of experimental dispersal trials of

seed released from a container attached to a kite or balloon,

with varying altitudes of release and varying wind velocities. Results showed that dispersion was greater from the

edge of uncut old (tall) timber than from second-growth

timber, and was strongly related to wind velocity and

topography. Most seed fell within 200 feet (60 meters) of

the source, but substantial quantities could travel up to 1/4

mile (400 meters), and sometimes considerably more under

favorable conditions. There were also differences among

species, with hemlock seed traveling the farthest. 

The second study (Isaac 1935) was a series of germination trials using Douglas-fir seeds stored in containers

placed in soil or the duff for varying periods, under existing

stands and in the open. In all cases there was negligible germination after the first year, refuting Hofmann’s (1924)

conclusions.

These results together with the Wind River transect

observations provided the basis for Forest Service standards

for maximum size of clearcut blocks.

In 1933, McArdle and Isaac briefly summarized available knowledge on natural regeneration, a subject covered

in much greater detail in Isaac’s later publications.

Isaac conducted extensive work on factors affecting

establishment and early growth of Douglas-fir seedlings

(Isaac 1938). Among the major conclusions reached were

(1) high surface-soil temperatures following germination

are a major cause of first-year mortality; (2) maximum temperatures are higher in the open than in shade, and higher

on a fire-blackened soil surface than on an unburned surface; (3) frost is also an important cause of early mortality;

(4) low soil moisture in summer is a major cause of mortality; (5) partial shading is favorable to early establishment

because of its mitigation of high temperatures in summer

and frost in spring; and (6) hot slash fires should be avoided

where feasible, particularly on south slopes. “Dead” shade

from slash and stumps was more favorable to initial establishment and early survival than shade from other vegetation, because of competition from the latter.

In 1943, Isaac published Reproductive Habits of

Douglas-Fir, which summarized results of his and others’

many years of research. It remains definitive. He recapitulated earlier results and also gave much quantitative

information on other aspects of natural regeneration and

associated recommendations. He estimated that about 8

pounds of seed per acre (9 kilograms per hectare) is needed

for successful restocking within a reasonable time. Seed

crops are sporadic, with complete failures in some years.

He concluded that slash burning should be limited to that

necessary for fire protection, and severe burns are best

avoided as they have unfavorable effects on soils and

aggravate heat mortality. Rodents are an important cause of

mortality and seed predation. Partial shade is favorable to

initial establishment but not to later growth. There are pronounced variations in local climate and soils within the

Douglas-fir region, and these have a marked influence on

behavior of regeneration and severity of brush competition.

Height growth of regeneration is related to number of seed

trees retained, with a noticeable slowing of growth at 11

reserve trees per acre (27 per hectare) and a pronounced

difference at 20 trees per acre (49 or more per hectare).

(Note: these were old-growth trees; numbers cited are not

necessarily applicable to young-growth stands). Mortality

of old-growth seed trees is erratic and very high, with more

than half occurring in the first 5 years. If the seed-tree

method is used, 6 to 10 seed trees per acre (15 to 25 per

hectare) were recommended rather than the 2 per acre (5

per hectare) that had been common Forest Service practice.

Clearcut blocks should be so arranged that no part of the

area is more than a quarter mile (400 meters) from uncut

timber.
Silvicultural Research and the Evolution of Forest Practices in the Douglas-Fir Region

Isaac also gave extensive attention to the effect of

shade on Douglas-fir survival and growth. After observing

shade effects on natural regeneration, he initiated a controlled test of light requirements of Douglas-fir seedlings.

Seven shade conditions were tested: in the open, under

three 16- by 16-foot (4.9- by 4.9-meter) shade frames in the

Wind River Arboretum, in light shade under young growth,

under heavy shade of young growth, and under virgin timber. Light, medium, and heavy shade was achieved by varying the spacing of wooden slats making up the sides and

tops of the shade frames. Sectional tops were removed each

year before snow fell and put back on after snowmelt. Twoyear-old seedlings were planted, and seeds were sown in

spots in the spring of 1939. More spots were sown in 

fall 1939 and spring 1940. Early survival was best in light

shade, but height growth of survivors was best by far in the

open (Isaac 1943, 1963) (fig. 7). From these measurements

and other information, he concluded that satisfactory development of Douglas-fir natural regeneration requires

removal of 50 percent or more of the overwood or groupwise removals providing openings of 1 acre (0.4 hectare) or

larger. Isaac (1955) gave a brief summary of these findings

plus a variety of recommendations for practical application.

Although Isaac was the outstanding individual working

on natural regeneration in this period, others were also

active. We note a few without attempting a complete coverage.

Munger (1930) summarized the factors affecting establishment of second-growth forests. 

Worthington (1953) compared natural regeneration 5

years after cutting in old-growth Douglas-fir in western

Washington on six small group cuts ranging from 1.2 to 4

acres (0.47 to 1.6 hectares), and a nearby large clearcut.

Stocking of Douglas-fir and hemlock was satisfactory on 

all group cuts, and seedlings were more vigorous than on

the clearcut. The clearcut had satisfactory stocking within

500 feet (150 meters) of the timber edge, somewhat less at

greater distances, with a reduced proportion of Douglas-fir

at the greater distances. Slash burning apparently favored

reproduction of both species.

Garman (1955) summarized results from extensive

research in coastal British Columbia over a considerable

period of years. This report is generally comparable to Isaac

(1943), and very similar in many respects in its results and

recommendations. There are some differences, possibly

reflecting the more northerly location: the British Columbia

work had somewhat better results with reserved seed trees,

and slash burning had a generally favorable effect on

Douglas-fir establishment, except on south slopes.

Lavender and others (1956) examined a series of

clearcuts in western Oregon, that were less than 160 acres

(65 hectares) and that ranged in time since cut from 4 to 11

years. They found little correlation between size of unit and

regeneration, but some units contained scattered seed trees,

and little of the area was more than 800 feet (240 meters)

from uncut timber. Established regeneration was most abundant on areas that were unburned, on north aspects, with

light slash and light herbaceous cover, and correspondingly,

less on burned areas, south aspects, and with heavy slash or

heavy herbaceous or woody plant cover.

23

Figure 7—William I. Stein examining 9-year-old Douglas-fir

transplants grown in the Wind River Arboretum under (A) 25 

percent of full sunlight and (B) in the open. 

A

B
24

GENERAL TECHNICAL REPORT PNW-GTR-696

Franklin (1963) compared seedling establishment in

various strip and small patch cuttings, a seed-tree cut, and a

conventional large clearcut. He found best establishment in

east-west strips, small patch cuts, and in the one seed-tree

cut examined. Differences in initial establishment were

attributed to the effects of intermittent shading in mitigating

high surface temperatures.

Prior to the late 1930s, most cutting on private land

was essentially liquidation. Although often loosely referred

to in popular writing as “clearcutting,” this was quite different in motivation and practice from the clearcutting system

long recognized in silviculture (a silvicultural system is a

planned series of operations for tending, harvesting, and

reproducing a stand or forest). However, if subsequent fires

were excluded, defective trees and inaccessible groups of

trees frequently provided an approximation to the seed-tree

method. 

Harvests on national forest land before the 1930s most

commonly used the scattered seed tree method, with a

rough standard of at least 2 seed trees left per acre (5 per

hectare). Experience showed that seed trees were often lost

to wind, and that seed production was often insufficient.

The method was not dependable.

By 1930, the introduction of the motor truck and

crawler tractor made partial cuts feasible on gentle terrain.

This capability combined with the economic pressures of

the Great Depression led to introduction of what was then

termed “selective cutting.” Logging cost studies showed

that under the conditions of the time, small and low-quality

logs could only be handled at a net loss, and profitability

would be improved by removing only those trees that could

more than pay the costs of logging and milling. Such selective cutting was simply high-grading (removal of the most

valuable trees with little regard to the future), driven by the

economic fact that under the depressed markets of the time,

only the finest trees could be handled at a profit. Operators

hoped to be able to return for the remaining trees when 

conditions improved.

Kirkland and Brandstrom (1936) advanced a considerably more sophisticated proposal in a detailed prospectus

entitled Selective Timber Management in the Douglas-Fir

Region. They proposed a light initial cut removing primarily defective and low-vigor trees and providing for establishment of a road system. Then, after one or more cycles

of such light cutting, there would follow a gradual move

into small patch cuts of the order of 2 to 10 acres (0.8 to 

4.0 hectares) to obtain regeneration. Regional forester C.J.

Buck and others adopted this idea as an alternative to

clearcutting, and attempted to apply it in a series of sales 

in the mid to late 1930s.

There was considerable skepticism and controversy at

the time, and apparently heated personal conflict between

Buck on the one hand, and Munger and Isaac on the other.

Some modifications were made in the Kirkland and

Brandstrom proposal before publication, in response to

objections raised by Munger. Buck in turn attempted to

block publication of a critique by Munger (1938), a critique

that today seems fair and restrained. 

Isaac and others established a series of plots and transects in national forest sale areas, which were remeasured

over a period of about 10 years. Results showed no growth

response by the residual trees, heavy losses to wind and

bark beetles, much logging damage, and no regeneration.

The effort was judged a failure (Isaac 1956, Munger 1950,

Smith 1970) and was often cited in later years as proof that

under most circumstances there was no feasible alternative

to clearcutting in management of Douglas-fir.

In retrospect, failure stemmed less from defects in the

basic idea than in unavoidable (at the time) practical difficulties in application. These included (1) attempted application in over-mature stands of low vigor; (2) economic

conditions that made removal of small, defective, and lowquality trees impractical; (3) equipment not well suited to

the task; and (4) total reliance on natural regeneration. In

effect, the attempt quickly degenerated into high-grading

and never progressed to the small patch cuts that Kirkland

and Brandstrom recognized as necessary for Douglas-fir

regeneration (Curtis 1998). Munger (1938), although

opposed to individual-tree selection cuts, recognized that

large-scale clearcutting was not the only or necessarily the
Silvicultural Research and the Evolution of Forest Practices in the Douglas-Fir Region

best way in all situations and specifically stated that group

selection, area selection, and strip cutting should have a

large place in Douglas-fir silviculture. Kirkland and

Brandstrom’s proposal had some similarities to several

recently established experiments (chapter 12), and might

well have been successful if applied in younger and more

vigorous stands under more favorable economic conditions. 

In the meantime, Isaac’s work of the 1920s and 1930s

had shown that scattered seed trees were generally an inadequate seed source and that wind dispersal of seed from

uncut stands could extend up to 1,500 feet (460 meters)

from old-growth stands and 1,000 feet (300 meters) from

second-growth stands. These facts coupled with feasibility

considerations in high-lead logging led to general adoption

of the “staggered setting” system. “Staggered settings” were

simply moderate-size clearcuts, often about 40 acres (16

hectares) interspersed with blocks of uncut timber that

served as a seed source. Cut areas were so shaped and

placed that no part of the area was more than the specified

distance from the margin of the uncut stand. Slash was normally burned, primarily as a fire-protection measure but

also for the presumed benefits of exposure of mineral soil

and partial control of brush competition. This was the most

common procedure in the 1940s and 1950s (fig. 8) and was

a marked improvement over previous practices.

It was not, however, the final word. Prolonged delays

or failures of regeneration occurred at times, because of the

sporadic nature of Douglas-fir seed crops, damage by seedeating rodents, and the effects of high surface temperatures

on some sites. Summaries of age-class distribution from

1850 to 1940 (Teensma and others 1991) demonstrated the

general recovery of Coast Range forests following fire or

early cutting, all of which relied on natural regeneration.

But, there were also major gaps in conifer distribution that

were filled by noncommercial species when natural processes were left alone. During the 1950s, there was a general

shift to planting in place of reliance on natural regeneration.

It soon became standard procedure to clearcut, burn, and

plant (usually Douglas-fir). This was relatively simple, not

unduly expensive, and under most circumstances produced

prompt and adequate regeneration. It also removed the need

to retain seed blocks and allowed use of large harvest areas,

which reduced logging and management costs. The regeneration problem seemed to be solved. Everybody (almost)

was happy, and many soon came to believe that this was 

the only way to do things. There was a corresponding loss

of interest in alternative systems, other than some limited

work with shelterwood on difficult-to-regenerate sites

(Tesch and Mann 1991, Williamson 1973). Research and

practice concentrated on fine-tuning the method of clearcutting with artificial regeneration. This concentration on a

single system later came to severely hamper efforts to mitigate conflicts between timber production forestry and the

environmental movement (chapter 12).

Although planting has largely replaced reliance on natural regeneration, the latter is still a factor. Natural seeding

provides profuse regeneration of hemlock in some localities. Some natural fill-in occurs in many plantations and 

can lead to overstocking. Advance regeneration (mostly of

shade-tolerant species) can sometimes be used as an important supplement to planting.

Artificial Regeneration3

Although natural regeneration was the first choice in the 

early years of the 20th century, planting and seeding were

25

Figure 8—Excellent natural regeneration on a clearcut block,

Cedar River Watershed, 1954. 

3 By W.I. Stein.

R.O. Curtis
26

GENERAL TECHNICAL REPORT PNW-GTR-696

used to speed reforestation after large wildfires. Research

on natural and artificial regeneration of Douglas-fir began

and progressed concurrently in the early years. After midcentury, artificial regeneration and supporting research

became dominant. From the earliest times onward, informal

studies and trials in the nursery and field provided many of

the improvements in reforestation practices. Key formal

studies, however, provided new direction or the insight as

to why some practices improved or impeded progress. 

Research to support artificial regeneration efforts in the

Pacific Northwest did not start from scratch. Researchers

and practicing foresters alike drew guidance from a substantial body of published information, notably Toumey’s

manual on Seeding and Planting (1916 and subsequent editions). Early U.S. Forest Service publications such as Cox

(1911) and Tillotson (1917a, 1917b) also made available the

nationwide experiences from reforestation research and

operations.

Components of artificial regeneration include seed

characteristics and testing, seed and seedling production,

and seeding and planting techniques. Needs and circumstances triggered uneven emphasis on these components at

different times. We here consider the development of each

component separately.

Seed Characteristics and Testing

Determining Seed Characteristics

Seed collection and trade in seeds of Northwest species 

developed long before formal regeneration research began

in the Pacific Northwest. Knowledge was sought on seed

quality, purity, and the intrinsic germination characteristics

of each species. As domestic and international uses expanded, source identity, genetic traits, testing methods, storage,

stratification, and other attributes were also investigated.

The need for high-quality seed intensified when limited

numbers were sown per container and when scarce genetically improved seeds were used. Despite recognized needs,

no sustained program of seed research developed in the

Pacific Northwest. Instead, individual researchers responded to particular interests or demands to produce, in the

aggregate, a substantial array of information. Locally developed information was supplemented by results of many

studies conducted in other parts of the world.

The earliest systematic methods for determining seed

weight, purity, germination capacity, and germination rate

of Northwest species appears attributable to Johannes 

Rafn (1915). He founded the Scandinavian Forest Seed

Establishment in 1887 and reported on a 25-year accumulation of information gained from seed lots tested. Rafn’s

comments about the characteristics of Northwest species

are remarkably insightful for those early times, and even

include some performance comparisons of seed produced in

Denmark and other European sources with seed of the same

species collected in the Pacific Northwest.

The next data summary from testing commercial lots of

Northwest species was reported by Toumey and Stevens in

1928. Seed weight, purity, apparent viability, and course of

germination were determined systematically. Germination

tests were conducted at Yale in soil and between wick-fed

moist blotters. Slightly higher germination resulted from

tests made in the germinator than in the soil—a result

reported repeatedly in various studies over the years. Great

variability was found between seed lots, as Rafn had also

experienced.

Several more sets of summary statistics on seeds per

pound, purity, germination percentage, and seed preparation

and treatment that include Northwest species have since

been compiled. To facilitate conservation plantings by the

U.S. Soil Conservation Service, Swingle (1939) assembled

information from 78 references in an unpublished report

entitled Seed Propagation of Trees, Shrubs, and Forbs for

Conservation Plantings. This report included much unpublished data from various Bureau of Plant Industry and Soil

Conservation Service sources. Swingle’s compilation and

the contemporary publications by Mirov and Kraebel (1937,

1939) and Mirov (1940) are among the earliest sources to

include data for shrubs and for less prominent tree species.

The Woody-Plant Seed Manual (USDA FS 1948) 

provided seed information known by 1941 on 444 species

and varieties of trees and shrubs nationwide. In 1974, this
Silvicultural Research and the Evolution of Forest Practices in the Douglas-Fir Region

manual was superseded by a greatly expanded Agriculture

Handbook 450, Seeds of Woody Plants in the United States

(Schopmeyer 1974). The handbook included a major compilation of test results from the Oregon State University

Seed Testing Laboratory. A third edition is now in press 

and available on the Worldwide Web (http://nsl.fs.fed.

us/wpsm/). Much seed information developed for some

species during the lengthy intervals between compilations,

and in one instance, an update based on the 1974 handbook

was made and published privately (Young and Young

1992).

The statistics on seed purity, weight, germination

capacity, and germination rate in the three seed manuals

and their predecessors are broadly informative. They provide a general understanding of achievable purity, range in

number of seeds per unit weight, likely germination rate,

and total germination by species. However, these are pooled

averages, based on good lots and poor lots from often undefined locations, subjected to various processing, storage,

and testing methods. For species where data are limited,

such summaries are the best available. But, for species

where samples are abundant, averages based on best practices or developed for specific stands or populations are

more useful and informative. A minor start in that direction

is given in the statistics for Douglas-fir in the third edition

of the seed manual.

Seed characteristics have also been studied for individual trees or for carefully defined populations or stands.

The first and one of the most comprehensive studies for

Douglas-fir was started at the Wind River Experiment

Station in 1912 (Willis and Hofmann 1915). Cones were

collected from all parts of the crown from 127 trees of different sizes and ages, growing on different soils on the west

side of the Cascade Range from north-central Washington

to south-central Oregon. Individual tree lots provided information on cone size, seed size, and seed quality. Data were

developed for each lot as well as pooled averages for elevation, latitude, etc.—83 tables in all. Seedlings were grown

from each lot, and provided the stock for the first genetic

study of Douglas-fir. This single pioneering study, planned

by Thornton T. Munger, provided the concepts and basic

supporting data that guided cone collection, seed tree selection, and other genetic considerations for decades (discussed further in chapter 7), as well as practical knowledge

on seed processing and seedling germination.

Several other early investigators contributed to knowledge of seed characteristics and testing. In California, Show

(1917) determined rate and total germination for ponderosa

pine, sugar pine, Jeffrey pine, and incense-cedar seeds subjected to various pretreatments. Boerker (1916) made extensive greenhouse studies of germination of many species

under several levels of shade, soil moisture, soil texture,

seeding depth, and seed size at Lincoln, Nebraska. These

studies included Douglas-fir, Sitka spruce, and western

hemlock from western Oregon and Washington. He found

that Douglas-fir and ponderosa pine from west coast

sources differed in germination characteristics from sources

farther inland and that large seeds produced a better seedling crop than small seeds of the same lot.

Surprisingly little was formally published on seed characteristics and seed testing of Northwest species from 1920

to 1950, even though seed use continued. Three researchers

reported on the effect of heat on germination: Hofmann

(1925) found that neither Douglas-fir nor western white

pine seeds remained viable when subjected to high temperatures for lengthy periods, Wright (1931) demonstrated that

some shrub seeds withstand high temperatures better than

several conifers and grasses, and Morris (1936) determined

the combined effect of moisture content with level and

duration of temperature on germination of Douglas-fir and

ponderosa pine. His study yielded basic information on

seed characteristics as well as early guidelines for kilndrying cones. Three publications reported on testing procedures: Heit and Eliason (1940) in New York provided

information on many species, Flemion (1948) compared

seed viability as determined by excised embryo and germination tests, and Allen (1941b) advocated a standard germination test for Douglas-fir. In subsequent decades, both

Allen and Heit contributed repeatedly on the seed characteristics and testing of Northwest species.

27
28

GENERAL TECHNICAL REPORT PNW-GTR-696

Seed Testing

The first general instructions for testing seed of Northwest 

species were included in the bulletin Forest Planting in the

Douglas-fir Region (Kummel and others 1944) that summarized available information gained from research and practical experience. Similar information for individual species

was published in the Woody-Plant Seed Manual (USDA FS

1948).

Demand for information on seed characteristics and

testing increased greatly as large reforestation projects, such

as the Tillamook Burn, and increased harvesting accelerated

the use of direct seeding and nursery stock. Common interests triggered formation of the Northwest Forest Tree Seed

Committee in 1953, later titled the Western Forest Tree

Seed Council (Stein 1975) and currently named the Western

Forest and Range Seed Council, affiliated with the Western

Forestry and Conservation Association. Improvement and

standardization of forest tree seed testing was one of the

committee’s primary concerns. A consensus was reached

eventually on some processing standards and testing techniques for Northwest tree seeds entitled Rules for Service

Testing Forest Tree Seed of the Pacific Northwest (Bever

1959).

George S. Allen (fig. 9) was by far the most prolific

individual contributor of seed information on Northwest

species during the 1950s and 1960s. While at the University

of British Columbia, he published on seed maturity and 

viability, stratification (moist prechilling), germination temperatures and moisture levels, processing effects, testing

standards, and seed storage (Allen 1958, 1960, 1962b,

1962c; Allen and Bientjes 1954). Allen concluded that 

25 °C (77 °F) provided the most satisfactory constant 

temperature for testing viability of Douglas-fir seeds.

Meanwhile, at the Oregon State University (OSU) Seed

Laboratory, where service testing Northwest conifers began

in 1939, results of many comparison tests led to adoption 

of an alternating temperature regime for testing Douglasfir–16 hours at 20 °C (68 °F) and 8 hours at 30 °C (86 °F)

with light (Jensen and Noll 1959). In the early 1960s, while

Director of the Weyerhaeuser Research Center at Centralia,

Washington, Allen guided a collaborative test to identify the

best testing method for Douglas-fir. The same tests were

conducted on the same seed lots by six cooperating laboratories. These showed that the alternating temperature

regime provided the most consistent results. This test procedure was recommended to the Association of Official Seed

Analysts, who adopted and published rules for testing

Northwest tree species in 1965. The new information was

included in a booklet Sampling and Service Testing Western

Conifer Seeds (Western Forest Tree Seed Council 1966).

Because of variability among Douglas-fir lots in response

to cold moist pretreatment (stratification) before germination, testing of dual samples, one prechilled and one not

prechilled, continues to be part of the standard germination

test.

For more than half a century, the OSU Seed Laboratory

has been the focal point for information on seed testing and

related studies. The laboratory conducted comparison studies to identify better methods for service-testing tree seeds.

To find faster alternatives to germination tests, “quick tests”

focused attention on hydrogen peroxide (Ching 1959, Ching

and Parker 1958), tetrazolium (TZ), and excised embryo

Figure 9—George S. Allen did extensive research on forest tree

seed, served as dean of the Faculty of Forestry at the University 

of British Columbia, and became Director of Forestry Research

for the Weyerhaeuser Company 1961–1966. 

Weyerhaeuser Archives
Silvicultural Research and the Evolution of Forest Practices in the Douglas-Fir Region

(Heit 1955) methods of determining seed viability. Primary

development of several alternative methods occurred elsewhere, but the OSU laboratory kept abreast of improvements and made comparative tests. Laboratory Director, Ed

Hardin (Hardin 1981) concluded that the hydrogen peroxide, tetrazolium, and x-ray tests, . . .“when properly performed and evaluated, can predict viability which correlates

with the standard germination tests on the same sample

(Douglas-fir, pines, spruce, bitterbrush), except in Abies

species.”

In recent decades, new information on seed characteristics and testing originated primarily from research with a

genetic orientation, and from seed investigations in British

Columbia. In Oregon, Sorensen (1980, 1996) reported that

date of cone collection, seed stratification period, and sowing date affected coastal Douglas-fir germination and

growth. Seed collected early was smaller and produced

smaller seedlings. Sorensen and Campbell (1981, 1993)

found that Douglas-fir seed orientation in the germination

test can affect germination rate, and determined the genetic

and environmental components affecting seed weight and

seedling size. Seed research in British Columbia produced

information on the interactive effects of light, temperature,

and stratification on seed germination of many species

(Leadem 1988, Li and others 1994). Information on seed

characteristics of Northwest species continues to originate

from other parts of the world.

Seed Production

Seed Source

Whenever tree seed is collected and used, questions arise 

regarding appropriate sources and parentage. The pioneering study of seeds and seedlings at Wind River (Willis and

Hofmann 1915) produced the first information guiding 

use of Douglas-fir seed sources in the Pacific Northwest.

Munger and Morris (1936) reported on continuing aspects

of the same study. Soon afterward, broad zones or provenances were suggested by Munger and others to guide seed

collection and use (Kummel and others 1944). Concentrating on the topic during a sabbatical, Isaac developed

specific guidelines for choice of seed. He incorporated the

available results of the Wind River study, domestic and foreign experience, and great personal knowledge to produce

Better Douglas-Fir Forests From Better Seed (Isaac 1949).

Isaac suggested tentative rules or limitations for collection

and use of Douglas-fir seed and advocated seed certification and a research program to genetically improve the

species.

The next step was geographic delineation of seed zones

to provide guidance for seed collection and use. Preliminary

statewide seed zone maps for the Pacific Northwest were

produced by a committee of the Western Forest Tree Seed

Council in 1966, and improved maps in 1973. The zones

were based on latitude, longitude, temperature, moisture,

and coniferous species composition, with seed lots identified by species within 500-foot elevation bands. Subsequent

efforts to improve seed zones and seed transfer guidelines

are covered in chapter 7.

Certification of species and origin of tree seed soon

followed. Again, the Western Forest Tree Seed Council was

the sponsoring group where the merits of certification were

hotly debated and the mechanics of implementation developed. In 1966, the Northwest Forest Tree Seed Certifiers

Association was founded (Hopkins 1968) and has since

guided certifying efforts and standards. By late in the century, seeds, seedlings, and other reproductive materials were

being certified (Schrumpf and Pfeifer 1993). The implementation of standards based on research and experience

continues to have significant effects on all artificial regeneration in the Pacific Northwest.

Crop Forecasting and Stimulation

As demand for seed increased, forecasting and the evaluation of seed crops gained attention. George Allen (1941a)

had an early and lifelong interest in seed-crop forecasting,

particularly in flower initiation and development of seed

maturity in Douglas-fir. After Allen’s death, his detailed

information was prepared for publication by John Owens

who also drew on his own extensive experience in the

monograph, The Life History of Douglas-Fir (Allen and

Owens 1972).

29
30

GENERAL TECHNICAL REPORT PNW-GTR-696

Seed crops in the Pacific Northwest are cyclical or

erratic. Causes of crop failures and means for better predicting seed crops have been sought occasionally by investigators (Eis 1973, Griffith 1968, Lowry 1966, Owens and

others 1991, Silen 1967). Other authors documented the

periodic nature of seed crops (Isaac 1943, McDonald 1992,

Reukema 1982). Stimulation of seed production in ordinary

young stands by thinning, fertilization, or other cultural

means has received very limited study (Reukema 1982,

Steinbrenner and others 1960), whereas means of stimulating seed production in tended orchards have been studied

extensively in recent years (for example, Copes 1973, Ross

and Currel 1989, Ross and others 1980, Wheeler and others

1985). Today most Douglas-fir seed and some of that for

other conifers used in the Pacific Northwest comes from

seed orchards. 

Research on means to protect developing seed crops

proceeded concurrently with studies aimed at crop stimulation. It was established early that insect depredation ruined

many promising seed crops (Miller 1914). Subsequent

information on cone and seed damage was summarized in

Insect Enemies of Western Forests (Keen 1938), revised in

1952. Furniss and Carolin (1977) provided the most recent

summarization of insect damage to cones and seeds. Topics

of recent emphasis concerning insects and seeds include

techniques for damage prediction, infection relationships,

and physical and chemical means of reducing insect damage. Many of the research results appear in the proceedings

of the second and third Cone and Seed Insects Working

Party conferences held in Briancon, France, and Victoria,

British Columbia, respectively, or in the Journal of

Economic Entomology or Canadian Entomologist.

Collection and Processing

Among the components of artificial regeneration, seed 

collection, processing, and storage have received the least

formal study. Following the preliminary guidelines by

Willis and Hofmann (1915) and Willis (1917) for cone collection, drying, and extraction, little published information

was added for several decades. Reports on planting and

seeding provide evidence that collections were made and

seed was used, but the technology developed mostly from

practical experience rather than from research. 

Willis (1917) provided the first insight on timing of

collections by making weekly collections from nine

Douglas-fir trees from early August until cone opening.

Decades later, Finnis (1950) also made weekly collections

and determined that specific gravity of Douglas-fir cones

gave no guidance on initiation of seed maturity but length

of embryo might. Subsequently, Allen (1958) studied periodic collections of both Douglas-fir and western hemlock

and illustrated tree-to-tree variation in seed maturity.

Studies and observations by Allen and Owens (1972) and

others produced a good description of cone and seed maturity to guide timing of collections (Brown 1983).

Methods for after-ripening seeds in immature cones

were investigated by Silen (1958), and collection time differences in Douglas-fir seed weight and germination were

reported in a mass collection that spanned the entire season

(Olson and Silen 1975). Seed lots collected within 10 days

of seedfall yielded the best results; after-ripening in damp

storage somewhat mitigated the effects of immature collection.

Winjum and Johnson (1962) seem to be the only ones

who devised and tested a method for estimating the number

of cones on young Douglas-firs. Cone crops of Northwest

species have been rated in broad terms for many years, and

those in the collection business have their individual estimation methods developed from practical experience and

perhaps informal studies.

Only in the last half of the 20th century were improvements made in the time-honored ways of collecting cones

by climbing the tree, felling it, or resorting to squirreldropped cones and caches. Power lifts of various kinds

were tried and used in seed orchards and other machineaccessible locations. Successful tests were made of mechanical tree shakers under the direction of the U.S. Forest

Service’s Equipment Development Center in Missoula

(USDA FS 1972) with later tests in an Oregon seed orchard

(Copes 1985, Copes and Randall 1983). Cost-effective
Silvicultural Research and the Evolution of Forest Practices in the Douglas-Fir Region

methods have been devised in Canada to aerially rake

crowns or clip tops by helicopter (Camenzind 1990). A

field guide for collecting cones in British Columbia by F.T.

Portlock (1996) is the most recent and by far the most comprehensive regional guide to cone and seed collection.

Techniques for drying cones of Northwest species,

extracting the seeds, and then dewinging and removing

inert matter also progressed with limited research attention.

In 1912, a USDA circular described the general sequence

from cone storage to seed storage and discussed various

options (USDA 1912). Willis and Hofmann (1915) were 

the first to describe cone drying and extraction techniques

specific to Douglas-fir. Willis (1917) tested drying cones in

a small kiln and concluded that 35 to 51 percent of the wet

weight must be lost for Douglas-fir cones to fully open.

Early studies on effects of heat on seed by Wright

(1931), Hofmann (1925), and Morris (1936) have already

been noted under seed characteristics. The collection and

extraction technology developed in the early years is

described by Kummel and others (1944) and the major

developments in the next 30 years by Stein and others

(1974). 

As seed use increased, various aspects of cone and seed

processing received limited attention. Seed viability after

prolonged storage in the cone was tested by Lavender

(1958). Shea and Rediske (1964) and others examined the

effect of fungal development in stored cones. Allen (1958)

determined that commercial processing or blows simulating

those that might occur in processing damaged or killed

Douglas-fir seeds, altered germination, and produced weakened seedlings. He demonstrated that tree seeds are relatively fragile, hence the now-accepted dictum that cones

and seeds need to be handled and processed as gently as

possible. Silen and Osterhaus (1979) determined that separating seed by sizes can undesirably reduce the genetic base

of a bulked lot. In recent decades, application of the flotation method of separating full and empty seeds has been

applied to remove seeds infested with the seed chalcid

(Megastigmus spermotrophus Wachtl) from Douglas-fir

seed lots (Sweeny and others 1991).

Seed Storage

Seeds of Northwest conifers and some hardwoods have 

retained high viability for years when stored near 0 °F 

(-18 °C) at moisture contents of 5 to 9 percent. Again, 

current storage practices were arrived at largely from accumulated experience aided by some insights provided by

research. Early experience with cellar storage of seeds of

Northwest conifers is briefly described by Kummel and

others (1944). The very rapid loss of viability by true fir

seeds in room or cellar storage caused Isaac (1934) to

investigate their storage at 15 °F (-9 °C). His favorable

results were the first evidence that Northwest conifers store

well at subfreezing temperatures. Barton (1954) added more

insight on above- and below-freezing storage and packeting

of Douglas-fir and western hemlock at different moisture

contents. Allen (1957, 1962a) conducted storage tests at

room temperature, 0 °F (-18 °C) and 32 °F (0 °C) of

Douglas-fir seeds in sealed containers and when vacuum

packed. Schubert (1954) showed that some conifer species

and seed lots retain viability for 5 years or longer when

stored at 41 °F (5 °C), but viability eventually declines to

low levels. Forest nurseries and other organizations that

maintain subfreezing seed storages retest lots in storage on

a scheduled basis, and have extensive but unpublished

records of long-term viability. 

Storage of stratified (prechilled) Douglas-fir seed has

recently gained attention (Malavasi and others 1985, Muller

and others 1999). Stratified seeds have been re-dried and

held as long as 17 months with better seedling performance

reported than for seeds sown immediately after stratification.

Seedling Production

Bare-Root Seedlings

Organized production of bare-root nursery stock in the 

Pacific Northwest began with the establishment of the

Silverton Nursery on the Snoqualmie National Forest in

1909 and the Wind River Nursery on the Gifford Pinchot

(Columbia) National Forest a year later (Cameron 1979).

Forest Service production was soon consolidated at Wind

31
32

GENERAL TECHNICAL REPORT PNW-GTR-696

River, which continued as the sole source of stock until the

1920s when four lumber companies operated small nurseries for several years. The city of Seattle built a forest

nursery in 1925 to produce stock for the Cedar River

Watershed, and the British Columbia Forest Service started

an experimental nursery in 1926 that became the Green

Timbers Forest Nursery in 1930 (Wells 1940). Federally

aided nurseries were established in Pullman, Washington,

Corvallis, Oregon, and later in Olympia, Washington.

During the same period, small nurseries were operated 

by other federal agencies (Kummel and others 1944). The

forest industries’ first large cooperative nursery was established at Nisqually in 1942. In early years as well as in

recent decades, nurseries were started and eventually closed

as a result of technological advances and changing demands

for nursery stock.

There is little in the published literature to indicate the

role played by research during the first 50 years of nursery

technology development. Because of its unique climate and

soil, each nursery site poses its own set of problems and

challenges. Nursery personnel tend to be innovators and

experimenters. Thus, comparative trials and informal studies were a regular feature at many nurseries. Results were

put to use, technology improved, and the information

shared, but little was published. The first efforts at Silverton

described by Cameron (1979) and the full chapter in

Kumme and others (1944) probably provide the best insight

into technological levels in the first 30 years. From 1948

on, nurserymen shared developing insights and experiences

primarily at biennial nurserymen’s meetings and in their

proceedings, with Tree Planter’s Notes a primary publication outlet.

Greatly expanded production and often less than 

desirable field performance triggered research studies on

bare-root seedling technology from the 1950s onward. The

physiology as well as the physical characteristics and condition of nursery stock received attention. Foremost early

examples include (1) Edward C. Stone’s studies in Berkeley

on the absorption of dew (Stone and Fowells 1954) and

investigations of root regeneration and lifting time on the

survival of Douglas-fir, ponderosa pine, and other species

(Stone and Schubert 1959, Stone and others 1962); (2) 

studies by Weyerhaeuser Company researchers in Centralia,

Washington, on lifting date and storage of bare-root stock

(Winjum 1963) and on seedling growth in controlled 

environments (Steinbrenner and Rediske 1964); and (3)

Kenneth W. Krueger’s research on food reserves and seasonal growth of Douglas-fir (Krueger and Trappe 1967),

effect of packing material (Krueger 1968), seedling mineral

content (Krueger 1967), and comparative photosynthesis

and respiration (Krueger and Ferrell 1965, Krueger and

Ruth 1969). Other early studies included effect of lifting

date on survival of Douglas-fir seedlings (Lavender 1964)

and the effect of mycorrhizae (Wright 1964).

Many aspects of bare-root seedling production have

since been studied, involving numerous researchers and

professionals at different laboratories and nurseries. Weed

control, a large part of production costs in many nurseries,

received particular attention. Control of weeds was first

achieved by a combination of mechanical and manual

means (Owston and Abrahamson 1984). For several

decades, a petroleum distillate and other organic and inorganic chemicals, including fumigation for disease control,

helped prevent weed emergence and early development. 

In the early 1970s, some promising herbicide treatments

exhibited selective value in Douglas-fir bare-root operations

(Newton and others 1976). As suitable herbicides became

available, a large cooperative study was made involving 14

nurseries and 9 species to evaluate 6 herbicides for nursery

weed control and conifer phytotoxicity (Stewart and others

1978). This screening test and subsequent followup studies

formed the registration basis for use of several herbicides in

Western forest nurseries. 

In the early 1980s, van den Driessche (1984) published several articles involving fertilization, spacing, root

wrenching, and their relation to field performance of

Douglas-fir and other species grown in British Columbia

nurseries. Seedling physiology was the focus of an entire

technical session at the 1983 Society of American Foresters

meeting in Portland (Duryea and Brown 1984). In the same
Silvicultural Research and the Evolution of Forest Practices in the Douglas-Fir Region

year, a manual was published on the production of bare-root

seedlings (Duryea and Landis 1984), and a workshop was

held on evaluating seedling quality (Duryea 1985). In these

publications, Northwest species are the primary but not

exclusive backdrop to the technical presentations.

Research emphasis on bare-root seedling production

peaked in the 1980s, but substantial new information has

been produced since. Frost hardiness, involving hardening

and dehardening of Douglas-fir seedlings, received attention (Schuch and others 1989a, 1989b). Widespread emphasis on seedling attributes led to the Target Seedling

Symposium (Rose and others 1990). The accumulated

experience from many studies at the Humboldt nursery 

was summarized by Jenkinson and others (1993). In recent

years, the Nursery Technology Cooperative at Oregon State

University has been in the forefront of supporting bare-root

seedling research (Rose and others 1993, 1997).

Containerized Seedlings

In the Pacific Northwest, large-scale production of containerized seedlings became a reality in the past 40 years.

Unlike the technology for bare-root production that developed as much from practical experience as from research,

container seedling technology developed from the start on

the basis of forest and horticulture research information.

Incentives for use of container stock included better control

of the production environment, easier establishment and

more flexibility of production facilities, and quicker production of stock not tied directly to local weather conditions (fig. 10).

Container stock was already in common use in other

parts of the world before sustained interest developed in the

Pacific Northwest. John Walters of the University of British

Columbia stimulated local interest with his imaginative trials of bullet containers planted by gun or dropped aerially

(Walters 1961, 1971). Although later trials proved seedlings

developed best if removed from the container before planting, Walters’ initial results stimulated sustained research on

all facets of container seedlings—design and controls in the

production facility, irrigation and fertilization schedules,

size and shape of container, and sowing, storage, transport,

and planting techniques.

The Canadian Forestry Service and British Columbia

Forest Service worked cooperatively to rapidly advance 

and test the container seedling concept, leading to primary

reliance on container stock in western Canada. In Oregon,

Peyton Owston at the Pacific Northwest Research Station

collaborated with the Siuslaw National Forest in investigating container production capabilities (Owston 1974,

Owston and Kozlowski 1981). Private companies also

investigated the technology and rapidly increased container

seedling production. Information on container technology

developed so rapidly in the Pacific Northwest and elsewhere that the North American Containerized Forest Tree

Seedling Symposium (Tinus and others 1974) was organized to bring together and exchange available information,

viewpoints, and thoughts.

Subsequent research that advanced production of 

containerized seedlings originated from many sources.

Growing regimes are largely independent of local weather

and site, and information developed in one location is often

33

Figure 10—Container seedlings growing in a greenhouse (A) and

outdoors under shade (B).

A

B
34

GENERAL TECHNICAL REPORT PNW-GTR-696

readily transferable to other regions or even other countries.

Accumulated knowledge was summarized in the fivevolume publication of the Container Tree Nursery Manual

(Landis and others 1989, 1990a, 1990b, 1992, 1995). Since

publication of the Container Tree Nursery Manual, container technology (and also bare-root technology) has expanded

into the production of native shrubs, grasses, and other 

nontimber species (Steinfeld 1997).

The use of cuttings and other forms of vegetative 

propagation span facets of bare-root and container seedling

technology. Plantations of black cottonwood established in

1893 (Brandstrom 1957) and 1901 (Kummel and others

1944) represent the probable first use of cuttings in the

Pacific Northwest. Local research studies on poplar propagation appear to have started in the 1950s with determination of the effect of crown position and size of cutting on

subsequent rooting and growth (Smith and others 1956).

Subsequently, the culture and genetics of black cottonwood

received much more research attention than its reproductive

aspects, but occasional articles did appear (Heilman and

Ekuan 1979).

In recent decades, efforts have been made to propagate

Douglas-fir and other conifers by rooted cuttings (Copes

1992) and micropropagation (Hutzell and Durzan 1993),

mainly to advance genetic objectives. Somatic embryogenesis, the production of plants from minute tissues, is getting

substantial attention (Taber and others 1998). The results

provide alternate methods to propagate conifer seedlings

but have not led to commercial success.

Seedling Storage

Packing, storage, and shipment of nursery stock also 

evolved to meet local conditions and needs. Seedling 

storage was a minor consideration in the early days–most

seedlings were shipped soon after lifting. Seedlings were

packed for transport by railroad, wagon, and horseback.

There was strong emphasis on packing seedlings with the

tops toward the outside of the bundle or crate for good ventilation. Tillotson (1917a) summarized the packing techniques and variations then used at Forest Service nurseries.

Kummel and others (1944) described bundling techniques used at Wind River. Bundles were to be protected

from sun and wind, and if held for more than a few days

they were to be placed in a refrigerated building or cold

cellar at temperatures between 35 and 40 °F (2 and 4 °C).

A typical record was given of storage temperatures in the

cellar at Wind River, and of moisture loss in storage from

baled stock packed in tree moss or shingle tow. If transported in an open truck, bundles were to be covered by

canvas, but were to be uncovered if the truck was stationary for any length of time.

The earliest research studies on seedling storage

involved field comparisons of stored and nonstored stock.

No growth differences were found for Douglas-fir seedlings

stored in a cold room for 2 months at the Oregon Forest

Nursery (Ruth 1953) or for 6 months in several tests at the

Wind River Nursery (Deffenbacher and Wright 1954).

These results formed the early basis for extensive and often

lengthy storage of nursery stock. With improved storages

and controls, temperatures were held between 33 and 35 °F

(1 and 2 °C) and 90 percent or more humidity.

Introduction of polylined multiwall kraft bags or lined

boxes for packaging tree seedlings (Duffield and Eide

1959) brought about major changes in storage and shipping

methods. Packing in closed containers represented a major

departure from the long-held tenet that seedling tops need

“open air,” and maintained better moisture conditions in

and around seedlings. 

Several decades after cold storage of conifer nursery

stock in lined containers became common practice, storage

of stock below freezing temperatures gained consideration.

Weyerhaeuser company employees conducted the first

broad-scale research on below-freezing storage of western

conifer nursery stock (Gutzwiler 1978), although small 

trials or effects of accidental freezing may have been

observed by others. Comparison trials of cold and freezer

storage were accompanied by a careful look at how cold

storage affects seedling physiology (Ritchie 1987). By

1986, Weyerhaeuser storage of bare-root and containerized

conifer seedlings at -2 °C (28 °F) was a routine practice
Silvicultural Research and the Evolution of Forest Practices in the Douglas-Fir Region

(Hee 1987). Soon thereafter, guidelines for the cold storage

of seedlings were issued in British Columbia, since updated

(British Columbia Forest Service 2002). A recent study

showed that variations in thawing regime did not affect

container seedling survival or growth during two growing

seasons (Rose and Haase 1997).

Over the past century, numerous improvements in the

technology of growing seedlings have been accompanied

by a complete change in how seedlings are stored, shipped,

and handled at destination before being planted. Initially, it

was common practice to lift seedlings, pack them in the

field, and soon ship them; later, cellar or cold-room storage

of short duration was used; then, short to lengthy storage in

near freezing temperature was the norm; and now, belowfreezing storage is used. Throughout, keeping seedlings

cool and preventing desiccation has been emphasized. This

is still the goal; the means of achieving it have become

immeasurably better. Changes in shipping, made with little

investigative research, amply illustrate the contrast—from

open-ended bundles or crates shipped by railroad, wagon,

or open truck and stored at destination in shade or even in a

handy snowbank to shipment in closed, often refrigerated,

trucks with storage at destination in coolers until the day of

planting.

Planting and Seeding

Planting and seeding have been integral parts of reforestation efforts in the Pacific Northwest for nearly a century. In

early decades, these were supplemental to natural regeneration, whereas today, artificial regeneration has the dominant

role. Most early planting and seeding was done on federal

land, where efforts to reforest denuded areas started soon

after establishment of the national forests. Early accounts

allude to experiments preceding large-scale reforestation,

but little published information can be found on field comparisons of methods or techniques. 

Direct Seeding

Numerous trials of broadcast seeding and spot seeding were

made on the national forests starting in 1908 and concluding

about 1913 (Kummel and others 1944), when early plantings proved to be more successful and reliable. A second

peak of direct seeding studies and trials occurred at midcentury, triggered by the push to reforest the Tillamook

Burn and meet more demanding regeneration requirements

on a rapidly expanding acreage of cutovers. Again, use of

direct seeding decreased as planting proved more reliable.

Published accounts of the earliest seedings are fragmentary,

being more in the nature of summaries of several trials,

without specifics about exact location, site conditions, techniques employed, and level of data collection. 

Rodent depredation of seed was a common hindrance

in direct seeding, and C.P. Willis (1914) rather humorously

described his futile efforts to protect seed in field and laboratory experiments. Munger (1917) briefly reported successful establishment of maritime pine (probably Pinus

pinaster Ait.) in broadcast seeding, seed spotting, and planting trials to afforest coastal sand dunes on the Siuslaw

National Forest. Reforestation bulletins by Cox (1911) and

Tillotson (1917b) summarized experiences gained in early

seeding and planting trials nationwide, including some

specifics for the Pacific Northwest. The latter author provided a striking photo of a crew broadcast seeding in deep

snow on the Siuslaw National Forest, as well as photos 

of reforestation efforts on several other sites. Summary

accounts of forest planting by Kummel and others (1944)

and of animal damage by Moore (1940) provide the most

(but still limited) insight on early seeding trials in the

Pacific Northwest. Apparently, Schenstrom’s (1930) report

on a seeding trial near Cowichan Lake in British Columbia

was the first detailed published account of an experimental

direct seeding.

Limited trials of direct seeding preceded the 1940s

expansion as reported by Garman and Orr-Ewing (1949) for

British Columbia and by Bever (1952) and Quintus (1952)

for Oregon. A few trials yielded good stands of established

seedlings, but most did not, with rodent depredation a primary cause of failure. These limited studies did identify

problems and improve field techniques.

35
36

GENERAL TECHNICAL REPORT PNW-GTR-696

The ease of broadcasting rodent bait and tree seeds

from the air stimulated a number of large aerial seeding 

trials in the Pacific Northwest around the mid-1900s. Early

state of Oregon tests centered in the Cochran area that had

burned repeatedly (Kallander and Berry 1953) and elsewhere in the Tillamook Burn (Woods and Bever 1952).

There was also a U.S. Forest Service trial on the recent

Forks Burn (Shaw 1953a) and a trial by MacMillan and

Bloedel, Ltd. on an older burned area, Ash River (Allen 

and others 1955). Results on study areas indicated sufficient

success to warrant further use of aerial seeding with suggestions for improvements in study and application techniques.

Direct seeding trials generally included concomitant

evaluation of rodent populations and population control

techniques. Members of the U.S. Biological Survey, notably

Ned Dearborn and A.W. Moore (Moore 1940) made early

studies of rodent populations and means to reduce seed

depredation. Personnel of the Oregon State Board of

Forestry that studied rodent control aspects of seeding trials

included Edward Hooven (1958, 1966) and Denis Lavender

(1952).

The accelerated use of direct seeding, especially by air,

with attendant large-scale use of poison baits raised great

concerns and demand for more selective baits and improved

rodent control techniques or repellents. In response, the

U.S. Fish and Wildlife Service established a temporary 

field headquarters in 1950 at the Wind River Experimental

Forest, Carson, Washington, in cooperation with the Pacific

Northwest (PNW) Forest and Range Experiment Station.

Donald Spencer was the leader for the Fish and Wildlife

Service assisted by Fred Eggert and later by Nelson

Kverno, with Robert Steele and William Stein of the PNW

assisting. Rodent census studies were started on local

cutovers and in adjacent timber, as well as baiting and feeding trials. Meanwhile, screening of potential baits and

repellents was accelerated at the Wildlife Research

Laboratory in Denver. The project soon became a broad,

cooperative regeneration research effort, regional or wider

in scope, with many organizations and researchers participating. Seeding trials were conducted, rodent populations

censused, existing poison baits evaluated, and several new

candidates tested, with the eventual introduction of

tetramine and then endrin applied directly on the tree seed.

A series of publications (Spencer and others 1950, Spencer

1951, Spencer and Kverno 1952, 1953) reported the

progress of this concentrated effort, and later publications

by many authors reported different parts of the investigations (Dick and others 1958; Dimock 1957; Gashwiler

1959, 1969; Radwan and Ellis 1971; Shaw 1953b; Shea

1959; Stewart 1966).

Meanwhile, spot seeding received renewed but more

limited attention. Good results were reported for spot seeding trials of ponderosa and sugar pine in southwestern

Oregon. (Stein 1955b, 1957) and ponderosa and Jeffrey

pine in central Oregon (Wagg 1958), though in later smallplot trials, artificial seeding in central Oregon was judged

unreliable (Wagg and Hermann 1962).

The value of a nurse crop to aid establishment of newly

germinated Douglas-fir seedlings also received attention.

Some effects of India mustard (Brassica juncea (L.)

Czern.), often used to quickly reestablish cover on burned

areas, were evaluated, but the few studies provided only

limited insights on the positive and negative aspects of a

mustard nurse crop on seedlings and soil moisture levels

(Chilcote 1957, McKell and Finnis 1957).

Despite reports of substantial successes for both broadcast and spot seeding, seeding use and supporting research

soon declined. Planting could shorten the regeneration 

period and bypass many hazards to which tender young

seedlings are subjected. Even though planting was more

costly, the changing economics of timber production and

increased restraints on rodent control increased the attractiveness of more rapid stand establishment by planting with

attendant close control of genetic source and spacing. 

But interest in direct seeding never completely ceased.

Its status was summarized in a direct seeding symposium

(Cayford 1974), and a historical perspective is provided in 

a summary publication on animal damage management

(Black and Lawrence 1992). Studies on various aspects of

direct seeding continue to appear with the most sustained

effort by Thomas Sullivan in British Columbia investigating
Silvicultural Research and the Evolution of Forest Practices in the Douglas-Fir Region

deer mouse populations and alternate foods to reduce

depredation of conifer seeds (Sullivan 1979, Sullivan and

Sullivan 1984).

Planting

Published results of field plantings in the early years are 

mostly summarized results of trials and experiences.

Tillotson (1917b) described planting methods then in use 

on the national forests and suggested site priorities for

planting or seeding Douglas-fir, noble fir, and ponderosa

pine. Factors to consider in field planting were comprehensively covered by Kummel and others (1944). Included

tables provide brief results of planting on good or rocky

soil, survival by aspect, monthly moisture content at various soil depths, air and soil temperatures, and moisture 

content on denuded and brush-covered areas, and survival

in brush and in the open. These limited data provide clear

evidence that environmental factors were carefully considered in early planting trials.

The Douglas-Fir Heredity Study begun in 1912 was the

first study that provided substantial information on growth

and other long-term aspects of plantation development at

different sites (Munger and Morris 1936) as well as evidence of genetic variation (see chapter 7). Munger (1943)

pointed out that mortality continues in plantations after the

initial losses: among 12 plantations, 1 was destroyed by

fire, 2 were effectively eliminated by mountain beaver, and

mortality in the other 9 averaged 35 percent 26 years after

planting. Silen (1964) reported little correlation between

seedling height and 50-year height. He wrote “Our experience, our techniques, and our concepts have changed in 30

years about as much as the plantations themselves.” The

development of these plantations continues to draw

research attention. 

The Wind River Arboretum, another unique field trial,

was initiated by Munger in 1912 to test the suitability of

trees from all parts of the world for forest plantings in

Oregon and Washington. Over time, it became clear that

native species far surpass introduced species in sustained

vigor and growth, and that good early growth of a species is

not necessarily assurance of its continued vigor and wellbeing (see chapter 7). Other early plantations that have

yielded long-term results include a regional study of ponderosa pine races started in 1926 (Squillace and Silen 1962)

and several spacing studies (see chapter 6). 

The Oregon State Board of Forestry also initiated

planting trials in 1912.4 The first efforts involved introduction of new tree species for windbreaks, fence-posts, and

fuel purposes in the eastern part of the state. Additional

plantings were made in 1926 and 1927 using seedlings

from the first crop produced at the state forest nursery in

Corvallis. Some plantings of maritime pine were made at

Coos Head in cooperation with the U.S. Coast Guard. Very

successful plantings of Port Orford cedar were made in central Lincoln County in 1935 and 1937, with many trees

measuring 14 to 16 inches in diameter in 1953. Over half a

million seedlings, representing 23 species were planted in

the late 1930s in the Hamlet State Experimental Forest

located in Clatsop County. As with most early plantings, 

the results of these trials were not published; perhaps some

reports exist in archives.

In an extensive research effort beginning in 1913, S.B.

Show developed much information on planting stock performance of Douglas-fir, ponderosa pine, sugar pine,

Jeffrey pine, incense-cedar, and white fir. Although stock

was from seed of northern California sources and also compared there, much information was equally applicable to

those same species in Oregon. Show compared age classes

of planting stock, adaptability of species to various soils,

influence of brush cover, survival in burned and unburned

brush, relation of brush cover to rodent damage, and influence of slopes. After observation and testing in the nursery,

seedlings of the same stock were field tested. In addition,

repeated extensive observations were made on staked

seedlings in numerous operational plantings. He reported

that spring planting provided somewhat better survival than

37

4 Lyon, H.G., Jr.; Berg, A.B. 1953. A forest history of Oregon. Salem, OR:

Oregon Department of Forestry. 173 p. Unpublished manuscript. On file

with: R.O. Curtis.
38

GENERAL TECHNICAL REPORT PNW-GTR-696

fall planting, and that large stock generally survived better

than small stock of the same age class. Show’s research

constitutes the first and single largest effort to determine 

the stock characteristics and field capabilities of these six

species. It is likely, but not documented, that his results

undergirded early nursery and planting practices in the

Pacific Northwest (Show 1924, 1930).

Isaac’s shade study (described in “Natural Regeneration” section) showed very clearly that both planted and

seeded Douglas-firs make their best growth and development in full sunlight. Strothmann (1972) repeated a modern-day version of Isaac’s shade study under northern

California conditions and arrived at essentially the same

broad conclusions.

From the early 1950s onward, many researchers and

organizations made short-term field studies with bare-root

seedlings to serve a variety of objectives. One of the first

was a survival and growth comparison of conifer species

native to the Hemlock Experimental Forest in Gray’s

Harbor County, Washington (Worthington 1955). Among

many other trials, plantings were made to evaluate timing

effects of lifting or planting, and the influence of various

nursery practices on seedling field performance (Duryea

and Omi 1987, Jenkinson and others 1993, Owston and 

others 1986, Stein 1988, Strothmann 1971, Tanaka and 

others 1976, Walters and Soos 1961, Winjum 1963). Other

plantings investigated the effect of seedling size and supplemental treatment on subsequent field performance (Edgren

1977, Newton and others 1993, Strothmann 1980, Van den

Driessche 1992, Walters and Kozak 1965). The interaction

between stock size and animal damage was also determined

in a variety of studies (Hartwell and Johnson 1983, Newton

and Black 1965, Schaap and DeYoe 1986, Staebler 1954).

Test plantings were made to solve problems experienced 

on specific sites such as planting on steep slopes (Berntsen

1958), on droughty sites in southern Oregon (Hermann

1965), and to overcome severe conditions on the Dead

Indian plateau (Williamson and Minore 1978). Strong interest led to a 1978 symposium on root form of planted trees

in Victoria, British Columbia (Van Eerden and Kinghorn

1978).

Beginning in the late 1960s, field trials of container

stock and comparisons with bare-root seedlings became

part of the research effort. Early studies included a comparison of survival, growth, and root form of containerized

Douglas-fir and noble fir (Owston and Stein 1978), how

container and root treatments affected growth of ponderosa

pine (Owston and Seidel 1978), and a regionwide effort to

compare performance of bare-root and containerized

seedlings (Owston 1990, Owston and Stein 1974). And, in

British Columbia, the concerted effort to evaluate container

seedling performance continued.

Several large retrospective investigations were also

made in problem areas, generally to evaluate the success of

both plantations and natural regeneration. Many cutovers

were sampled by Halverson and Emmingham (1982) in the

Pacific silver fir zone, by Minore and others (1982, 1984)

and Stein (1981, 1986) in southern Oregon, and by

Strothmann (1979) in the Klamath Mountains, to learn

where regeneration succeeded or failed and identify the

probable causes. 

In recent decades, large-scale integrative studies 

spanning 5 years or more have been made to determine 

the combined effects of variables such as site preparation,

stock type and species, protection, and competition on the

survival and growth of planted trees. Perhaps the earliest 

of these is Strothmann’s (1976) 10-year results of planting

Douglas-fir by four methods in northwestern California.

Michael Newton and associates, doing research in many

aspects of site preparation and stock types, have reported

results of two long-term studies (Newton and others 1993).

In a unique retrospective effort, Richard Miller compared

35- to 38-year-old Douglas-fir stands on matched planted

and naturally regenerated plots established on seven slashburned areas in the Cascade Range (Miller and others

1993). William Stein and associates conducted three integrative studies in the Coast Range of Oregon. The first

compared survival and growth of five Douglas-fir and two

western hemlock stock types with and without protection
Silvicultural Research and the Evolution of Forest Practices in the Douglas-Fir Region

after four site preparation treatments (Stein 1990a) (fig. 11).

The second determined growth of Douglas-fir and associated species for 10 years with and without protection after six

site preparation treatments (Stein 1995), and the third, 6-

year growth of Douglas-fir after manual or chemical release

from competition (Stein 1999). Data from these studies and

others underway have been the basis for predictive models

(Knowe and Stein 1995, Knowe and others 1997). 

Reforestation Evaluation

In all planting or seeding or natural reproduction there 

comes a time to ask if an area can be considered sufficiently stocked. Stocking can be determined by counting 

all qualifying trees on sample plots and then determining

the average number per acre, or by determining presence 

or absence of one qualifying tree per plot of designated

size, and then determining percentage of stocking and the

distribution of stocked plots per acre. The stocked quadrat

method, suggested by early researchers (Haig 1931,

Lowdermilk 1927) has often been used, sometimes incorrectly. The strengths and weaknesses of the stocked quadrat

and full count methods and possible alternatives have been

considered and investigated over the years (Stein 1992).

Once stocking percentage or trees per acre has been

determined, what do the numbers mean? The first attempt

at defining stocking was produced by a subcommittee of

the Western Forestry and Conservation Association

(McKeever and Munger 1950). Consensus was reached by

a committee that defined four classes of stocking by number of trees per acre, or by stocking percentage based on

milacre (4.05-square-meter) or 4-milacre (16.2-squaremeter) plots (Reynolds and others 1953). For several

decades, these defined parameters for good, medium, and

poor stocking were in general use, but they are seldom 

used today.

As state and provincial forest conservation laws 

were enacted, revised, and implemented, methods were 

prescribed for determining if minimum stocking requirements had been met. Designated standards for countable

tree, sampling technique, and summary procedures differ

greatly among states and provinces and change over time.

Individual national forests as well as private companies set

regeneration standards consistent with their management

objectives. Not all evaluation methods in use are conceptually sound nor do they produce comparable data. 

Unfortunately, there is at present no consensus on sampling methods and stocking standards. Therefore, broad

comparisons of stocking percentage or numbers across or

even within organizations involve a high risk of comparing

noncompatible data. Valid comparisons are possible only

when the countable tree, the sampling technique, and the

summary procedures are comparable.

Overview

The literature cited and the many uncited publications of 

recent decades represent a vast store of knowledge and

experience on artificial regeneration in the Pacific Northwest.

This research has been summarized and interpreted periodically in comprehensive publications. The first of these 

modern summaries that merits attention is Reforestation

Practices for Conifers in California (Schubert and Adams

39

Figure 11—Stein (1990a) compared survival and growth of five

Douglas-fir and two western hemlock stock types with different

protection and site preparation treatments. 
40

GENERAL TECHNICAL REPORT PNW-GTR-696

1971). These authors delved deeply into reforestation publications for the entire Pacific Coast and provided good leads

to many early publications.

The next summary, Regenerating Oregon’s Forests

(Cleary and others 1978), was the product of coordinated

efforts involving many authors. A summary specific to the

Klamath Mountains of Oregon and California was prepared

by Strothmann and Roy (1984). Fire effects that relate to

reforestation are covered in Natural and Prescribed Fire in

Pacific Northwest Forests (Walstad and others 1990), and

animal relationships in Silvicultural Approaches to Animal

Damage Management in Pacific Northwest Forests (Black

1992). The output of the Forestry Intensified Research

(FIR) Program was made available in many individual 

publications and in a comprehensive book, Reforestation

Practices in Southwestern Oregon and Northern California

(Hobbs and others 1992). Similarly, the reforestation

aspects of the cooperative Coastal Oregon Productivity

Enhancement Program (COPE) are included in the book

Forest and Stream Management in the Oregon Coast Range

(Hobbs and others 2002a). Regenerating British Columbia

Forests (Lavender and others 1990) provided a guide 

specific for Canadian conditions.

Throughout most of the past century, reforestation

efforts were aimed at achieving satisfactory results at minimum cost, and the supporting research was confined to the

same objective. Initially, natural regeneration was expected

to reforest denuded areas, and was only given a helping

hand when very large denuded areas needed quick attention. Nature’s uncertain timetable for regeneration establishment was good enough until land managers, and later forest

practice regulations, set stocking goals to be achieved in

specified lengths of time. Direct seeding then got much

attention because it appeared to provide great flexibility at

lower cost than production and planting of nursery stock.

As the uncertainties and shortcomings of direct seeding 

surfaced and the reforestation targets became ever more

pressing, primary emphasis shifted to bare-root nursery

stock, and eventually also to container stock.

For far too many years, reforestation success was

judged solely on the survival of an adequate number of

seedlings. Eventually, both survival and actual or potential

growth of seedlings was given attention. Only in recent

decades, however, has maximizing both seedling survival

and growth become an accepted reforestation objective. The

knowledge, first reported by Show in 1930 and more

recently affirmed by Van den Driessche, Newton, Stein and

others, that large stock of good quality outgrows small

stock in many reforestation situations is now being applied

in practice. Likewise, much effort now goes to providing

planted seedlings with nearly competition-free conditions.

Increasing forest values, broader management objectives,

and strong social pressures continue to drastically broaden

the horizons and objectives of research on artificial regeneration.

The current state of nursery technology makes it possible to produce seedlings with specific physical (height,

stem diameter, root density) and physiological (bud dormancy, cold-hardiness, root growth potential) characteristics as implied by the term “target seedling.” The concept of

a “target” seedling (Rose and others 1990) aims to provide

silviculturists the seedling best suited to thrive in conditions

on specific sites. This is a comprehensive, far-reaching concept that raises many challenges. The field performance of

different-sized seedlings in various conditions has been

determined in general terms. There is yet much to be done

to learn how key characteristics, particularly the nonvisible

physiological ones, govern seedling performance on specific sites.

The progress made in advancing reforestation practices

through research, development, and experience is starkly

illustrated by a comparison of the short, colorless planting

instructions prepared by Munger (1942) versus the lengthy

and colorful reforestation guide by Rose and Morgan in

2000.
Silvicultural Research and the Evolution of Forest Practices in the Douglas-Fir Region

Site Preparation and Control of 

Competing Vegetation5

Site preparation involves disposing of slash and unwanted 

vegetation and sometimes additional steps to prepare the

seedbed. Control of competing vegetation may involve

removing trees, shrubs, or herbaceous vegetation by various

means to foster growth of the desired tree seedlings.

Site Preparation

The highest priorities in the early years of forest management were reduction of fire risk and provision for regeneration. Both objectives drove development of site preparation

techniques. Requirements for meeting these needs eventually became part of forest practice regulations.

In the early years, most harvest operations were in old

and often highly defective timber under economic conditions that prevented utilization of small and poor quality

material. Defective logs and large branches produced slash

accumulations in the hundreds of tons per acre. Because of

the explosive nature of fires in heavy slash and the physical

obstacles to regeneration represented by slash, early legislation required that slash be burned unless the landowner was

granted permission by the state forester to do otherwise. 

On the steep terrain in most of the Douglas-fir Region, few

alternatives were available. Snag felling within harvest

units and in surrounding stands was also required in most

circumstances. Broadcast burning was nearly universal 

(fig. 12). Burning greatly reduced short-term fire hazard,

and exposed bare mineral soil for seedling establishment.

Broadcast slash burns also reduced live brush and destroyed

most weed seeds (Isaac 1963), although they also stimulated germination of many seeds in the sclerophyll brush

areas of southwestern and central Oregon (Gratkowski

1962).

Movement of heavy logs and logging equipment

caused soil disturbance in harvest of old-growth stands.

Except for mass failures, soil disturbance was regarded as

favorable to natural regeneration. Bare soil was an excellent

medium for Douglas-fir, but also for red alder (Trappe and

others 1968), and where hard-seeded species such as snowbrush (Ceanothus velutinus Doug. ex Hook.) had been present, the heat from slash burning stimulated seeds that had

long lain dormant (Gratkowski 1962, Zavitkovski and

Newton 1968). The herbaceous cover developing after

either broadcast burning or clearcutting without burning

was another major obstacle to seed or seedling survival and

growth (Dyrness 1973, Krueger 1960, Petersen and others

1988, Yerkes 1960).

In general, natural regeneration was assumed to follow

clearcutting with or without burning if some trees (usually

culls) were left as a seed source. In many, but not all cases,

this sequence produced adequate although irregular stocking of Douglas-fir, and is the source of most of the secondgrowth volume harvested in recent decades. It also initiated

invasion by hardwoods and shrubs that could remain dominant for long periods (Newton and others 1968, Tappeiner

and others 1991). Near the coast, hemlock also regenerated

well after clearcutting and burning. 

Considerable research was done in the 1920s and

1930s on fire danger, including rate of spread and resistance

to control in slash burned vs. unburned conditions. There

41

5 By M. Newton and W.I. Stein.

Figure 12—Until recently, broadcast burning was the usual 

method of fire hazard reduction and site preparation.
42

GENERAL TECHNICAL REPORT PNW-GTR-696

was concomitant work on the ecological effects of fire and

vegetative succession after burning (Isaac 1940, Munger

1930) and on effects of fire on forest soils (Isaac and

Hopkins 1937). This and other work was summarized by

Munger and Matthews (1941), who made a variety of management recommendations. In the years 1946–52, Morris

(1970) installed an extensive series of paired burned and

unburned plots on national forest lands. Changes in vegetation cover and species were generally similar to those

reported earlier, but the reduction in fire risk was of longer

duration than reported by Munger and Matthews (1941),

possibly reflecting the generally higher elevations sampled.

Although there was often little alternative to burning

for site preparation and hazard reduction, it was shown that

hot fires had some undesirable effects on soils and on establishment of reproduction (Isaac 1963, Isaac and Hopkins

1937). Reduction in fire danger usually lasted 15 years or

less; thereafter, vegetative cover became the most important

factor in fire risk, with continued low fire danger depending

largely on successful establishment of conifers sufficient to

shade out flammable brush species. Large freshly logged

areas are much more hazardous than small units. There are

large differences in fire danger and in the importance of

slash burning within the region, associated with variations

in climate: fire risk increases from north to south, and west

to east away from the coastal fog belt.

Several variations of broadcast burning have been used

in efforts to dispose of slash and vegetation with minimum

damage to soil and threat of fire escape. Scheduling burns

after fall rains sufficient to wet the soil or in spring became

common practices. Where slash was lighter, as in harvest 

of young stands, only hand scalping was sometimes used

during planting, and burning was only done at landings.

In coastal clearcuts, where much live residual vegetation may be interspersed with slash, “brown and burn”

methods were found effective. Vegetation was desiccated

with chemicals so slash and brush could be burned when

surrounding vegetation was more fire resistant (Hooven and

Black 1978, Hurley and Taylor 1974). Spraying with herbicides also reduced sprouting (Stein 1995). These methods

provided control of slash hazards, physical access for planting, and control of competition in a single operation.

Major changes in environmental criteria for site preparation have emerged. Smoke management regulations, in

particular, have had great influence on broadcast burning

and development of alternatives. Rules on smoke emissions

and visibility, managed through statewide determination of

“burn-days,” have severely curtailed burning opportunities

and increased costs. Visibility regulations in wilderness

areas are also major limitations on burning upwind from

them. Many units cannot now be burned within the available time windows. Alternative site preparation methods

became necessary even where broadcast burns would have

been feasible, economical, and safe under earlier rules and

would be preferred for a variety of reasons—some of which

are environmental and at odds with environmental regulations that restrict use of fire. Now that most harvests are in

second-growth stands, tree-length yarding and reduced

amounts of large cull material have greatly simplified the

slash disposal problem.

Controlled burning of piled slash is one alternative to

broadcast burning to achieve both hazard reduction and site

preparation (fig. 13). Piling slash to burn later under favorable conditions has long had limited use along roadsides,

near structures, and other places or conditions where broadcast burning was too risky. The high costs of piling slash by

hand generally limited use of piling and burning to situations where it was absolutely necessary.

Developments in mechanical site preparation equipment have made large changes in industrial site preparation.

Recent adaptation of hydraulic excavators with multitined

grapples has led to adoption of slash and brush piling in

tall, narrow piles that can be burned in winter. Trackmounted machines can often pile brush and slash at lower

cost per acre than would be encountered with broadcast

burning under current regulations, even on “burn days.” On

steep slopes of up to 70 percent or more, machines known

as “spiders” can be used; these are mounted on computercontrolled legs and can walk like an insect. Most of these

machines have grapple-mounted booms that can reach 40 to

45 feet (10 to 14 meters). They can clear considerable
Silvicultural Research and the Evolution of Forest Practices in the Douglas-Fir Region

ground without moving, and when moving, they can clear a

broad swath with little soil disturbance. They can maneuver

around down logs left for wildlife habitat, uproot clumps of

herbicide-resistant brush, and can make piles tall and narrow so that piles take up relatively little space and overheat

relatively small patches of soil when burned. When covered

with plastic before fall rains, piles can be burned during wet

weather to minimize smoke hazards and soil damage. If

unburned, planting around piles leaves little ground

unplanted. 

Thus, major advantages of machine piling are improved

choices of planting spots, reduction of fire hazard, selectivity, and the ability to build or maintain certain kinds of

wildlife habitat. 

Disadvantages include safety limitations on use of

tracked machines on steep ground and a relatively narrow

seasonal window when soil does not pack readily. These 

are large, heavy machines. Despite low ground pressure,

track-mounted machines may make several trips over a 

single track as they work, increasing the potential for soil

compaction; the importance of this is currently under investigation (chapter 8). Despite these limitations, this equipment is finding wide use.

Machine piling exposes mineral soil on much of any

unit. Although this is an advantage for natural regeneration

or planting, it also is a favorable seedbed for weed species

and red alder, all of which represent competition for the

plantations that have almost universally replaced natural

regeneration. Control of these competing species is therefore often necessary.

Other site preparation options include complete

mechanical scarification; or mowing, chopping, crushing,

shearing; or scalping slash and vegetation to prepare the

seedbed. These methods have been used more to clear

existing brushfields than to prepare fresh clearcuts. Site

preparation methods have been well described in several

comprehensive summaries (Helgerson and others 1992,

Schubert and Adams 1971, Stewart 1978).

The extensive literature on use of prescribed fire and

its consequences is summarized in the annotated bibliography of Loucks and others (1987) and the compendium

Natural and Prescribed Fire in Pacific Northwest Forests

(Walstad and others 1990).

Control of Competing Vegetation6

Major differences in composition and in species behavior 

exist within the Douglas-fir region, and are associated in a

general way with the gradient from cool moist conditions in

the northern part of the region to warmer and drier conditions in the south. Although Douglas-fir is an important

component and grows reasonably well throughout most of

the region, there are major differences in the associated

species. Thus, the western hemlock, western redcedar, and

red alder that are major components in the north diminish

toward the southern part of the region, where other species

such as ponderosa pine, sugar pine, incense-cedar, and

white fir become important components.

43

Figure 13—Broadcast burning has been greatly reduced in recent

years. Partial disposal by piling and burning is now a common

practice. 

6 This section discusses research involving pesticides. It does not contain

recommendations for their use, nor does it imply that the uses discussed

here have been registered. All uses of pesticides must be registered by

appropriate state or federal agencies, or both, before they can be recommended. CAUTION: Pesticides can be injurious to humans, domestic animals, desirable plants, and fish or other wildlife—if they are not handled

or applied properly. Use all herbicides selectively and carefully. Follow

recommended practices for the disposal of surplus pesticides and pesticide containers.
44

GENERAL TECHNICAL REPORT PNW-GTR-696

There are associated differences in secondary vegetation that are important in silviculture. In the north, major

woody competitors are red alder (which reproduces abundantly from seed) (fig. 14) and bigleaf maple (which

sprouts abundantly). Shrub species important as competitors

include salmonberry, salal, vine maple, Himalayan blackberry, scotch broom, rhododendron, and others. In the

warmer and drier south, tree species important as competitors include madrone, tanoak, canyon liveoak, and

chinkapin. The southern part of the region also has a number of evergreen shrubs (snowbrush, manzanita, etc.) that

are adapted to summer drought and that sprout vigorously,

making them severe competitors with Douglas-fir regeneration (fig. 15). There is a rapidly accumulating literature on

the ecology of competing shrubs and hardwoods and their

effects on conifer development (Halpern 1989, Harrington

and Tappeiner 1991, Loucks and Harrington 1991, Loucks

and others 1996, O’Dea and others 1995; Stein 1995, 1999;

Tappeiner and others 1991, 2001).

The Tillamook Burn stimulated attention on all elements of regeneration, including site preparation and selective release treatments. In 1951, the state of Oregon issued

bonds to pay for rehabilitation of the burned area, which

totaled about 350,000 acres. This project involved a scale of

operation beyond previous experience. Activities included

—in addition to large-scale seeding and planting—removal

of snags to decrease future fire risks, mechanical reduction

of competition, and early testing of herbicides for control 

of competing vegetation arising in the years following the

fires.

The Oregon Department of Forestry was given responsibility for implementing research and operational measures

to reforest the Tillamook Burn. Larry Fick and Carl Smith

led the rehabilitation effort in the field. The Oregon Forest

Research Center was created and staffed with silviculturists,

regeneration specialists, and a mammologist to evaluate

efficacy of large-scale regeneration methods and the site

preparation needed. The combined research and implementation of new forest practices by the Oregon Department of

Forestry and Forest Research Center led to the first verylarge-scale forest rehabilitation program in this country. 

In 1962, the Oregon Forest Research Center became

the nucleus of the Forest Research Laboratory of Oregon

State University (OSU), with continuing emphasis on site

preparation, regeneration, and control of vegetative competition.

Figure 14—Competition by undesired species often overwhelms

desired conifers, as in this stand taken over by red alder.

Figure 15— Broadcast burn on the Umpqua National Forest: (A)

bare soil after the burn and (B) 3 years later showing 90-percent

cover of snowbrush (Ceanothus velutinus). 

A

B
Silvicultural Research and the Evolution of Forest Practices in the Douglas-Fir Region

Simultaneously, the PNW Forest and Range Experiment

Station of the U.S. Forest Service initiated a research program to improve reforestation methods and evaluate chemicals for controlling hardwoods and shrubs. A major effort

was begun in southwest Oregon in the early 1950s, stimulated by the need for rehabilitation of very large more-orless permanent brushfields that had developed after past

fires (Gratkowski 1961a). This effort, first led by Lloyd

Hayes and later by William Hallin, was staffed by scientists

working with both vegetation management and regeneration. 

Several companies, notably Weyerhaeuser, also began

investigations into combinations of thermal, mechanical,

and chemical methods of site preparation and control of

vegetative competition. The combined research and operational experiences from several groups yielded rapid

improvement in reforestation techniques.

Vegetation management, including both site preparation and release, has a long history in Europe. There, inexpensive labor allowed dense planting that minimized

influence of competing shrubs, and summer rains provided

favorable moisture conditions. Vegetation treatments were

generally applied with hand tools. In contrast, the Pacific

Northwest’s fertile residual soils and dry summers combine

to provide excellent conditions for sclerophyll and deciduous shrubs and sprouting hardwoods, many of which support a frequent return of fires, especially in southwestern

Oregon. The dry summers often meant that depletion of soil

water by transpiration could threaten survival of natural and

planted regeneration. Early studies that demonstrated the

negative effect of competing vegetation include those of

Dahms (1950) for manzanita and snowbrush, Ruth (1956)

for salmonberry and alder, and Newton (1964) for herbaceous species. Developing vegetative competition was both

a threat to regeneration and an increased fire hazard.

Safe chemical tools for managing species composition

in forests are a development of the last half century, with

the most rapid development between 1970 and 1990. After

World War II (WWII), there was limited use of sodium

arsenite for debarking pulpwood and controlling cull hardwoods in the Eastern United States. Arsenite was hazardous

to wildlife and domestic animals, and never found wide use.

The beginning of effective large-scale chemical weed

control followed the discovery of the phenoxyacetic acid

herbicides 2,4-D and 2,4,5-T during WWII. Geoffrey

Blackman in the United Kingdom discovered that these

materials could remove broadleaf weeds from grain crops,

and then discovered their selectivity in any grass-related

crop such as corn. Within a few years, 2,4,5-T was shown

to have great efficacy in controlling woody species, and to

be selective in releasing certain conifers at dormant seasons. The phenoxy herbicides became the standard treatment for maintaining low cover along power line, rail,

pipeline, and highway rights of way. The market was large,

and these products soon became economical and well

adapted in a range of products. Bovey and Young (1980)

wrote a comprehensive history of this development, which

had profound effects on management of forest vegetation.

Research to control brush competition on federal lands

began in the 1950s, when Walter Dahms began work on

controlling brush in ponderosa pine, and Robert Ruth 

and associates studied coastal types (Krygier and Ruth 1961

Ruth and Berntsen 1956). Dahms and James (1955) provided an early summary of existing information on chemical

controls in forestry. The first aerial spraying of phenoxy

herbicides in the Pacific Northwest was done in 1951 on the

Waldport District of the Siuslaw National Forest (Hawkes

1953); red alder and several brush species were suppressed

and conifers were relatively undamaged. Henry Gratkowski

(1959, 1961b) began a long sustained research effort, primarily in southwestern Oregon (fig. 16), on brush control

and methods for rehabilitation of the extensive brushfields

that were a major problem.

At OSU, William Furtick did the first significant

research on weeding in woody plant communities, in cooperation with G.H. Barnes. Shortly after, Virgil Freed of

OSU explored modes of action, analytical techniques, and

many other features, not only of phenoxy herbicides but

45
46

GENERAL TECHNICAL REPORT PNW-GTR-696

also of many pesticides. The first symposium on herbicides

and their uses in forestry was held in 1961 by the College

of Forestry (Kallander 1961).

By the end of the 1950s, a solid foundation had been

established for this technology, relying mostly on 2,4,5-T.

Bramble and Byrnes (1972) at Purdue University demonstrated that many similar treatments enhanced browse and

cover for a variety of wildlife, and the application of selective synthetic chemicals was identified as a potential opportunity for large-scale habitat management while promoting

commercial conifer crops. Scientists doing considerable

field research in the Northwest on vegetation management

included Gratkowski (1968, 1975, 1976, 1977, 1978),

Newton (1969), Stewart (1974), Stewart and others (1978),

and Dimock (1981). These and others evaluated both chemical and nonchemical control methods.

In the early 1960s, OSU research (Newton 1964) established that transpirational withdrawal of soil water from 

the surface layers by herbaceous cover could be substantially reduced by application of triazine herbicides. This

speeded the registration of simazine and atrazine for herbaceous weed control in conifer plantations. By the late

1960s, chemical brush control methods were well enough

established so there was seldom any excuse for failure of

plantations because of vegetative competition. A national

symposium, Herbicides and Vegetation Management in

Forests, Ranges and Noncrop Lands, was held at OSU

(Newton 1967). Walstad and Kuch (1987) provided a 

synthesis of information on forest vegetation management

across the commercial forests of North America.

As practices developed, the scope of research broadened to include new chemicals, water quality, and the 

physiology and environmental chemistry for vegetation

management chemicals. In the early 1960s, OSU’s

Department of Agricultural Chemistry developed a significant program to evaluate environmental aspects of vegetation management with chemicals and analytic methods for

their investigation. By the late 1970s, this became a joint

effort with Logan A. Norris and associates of the PNW

Research Station. Oregon became a center of research

activity dealing with forest chemicals. This cooperative

effort contributed greatly to the efficacy and safety of site

preparation and release programs. In the early 1970s, concern for public safety aspects of herbicides led to establishment of an extension toxicologist position in the

Department of Agricultural Chemistry that remains active

today. Newton and Dost7 and Walstad and Dost (1984)

made comprehensive summaries of available safety information for both herbicides and nonchemical methods of

accomplishing the same objectives. McEwen and

Stephenson (1979) compiled a comprehensive summary 

of the environmental consequences of such uses.

In 1981, the FIR Program and CRAFTS (now the

Vegetation Management Research Cooperative, VMRC)

were formed at OSU. These and other programs provided

comprehensive field and laboratory investigations of vegetation management options in the Douglas-fir region (figs.

17, 18, 19). The synthesis by Hobbs and others (1992) gave

detailed summaries of their findings for improving stand

establishment following fires or harvesting in southwest

Figure 16—Henry Gratkowski pioneered vegetation management research in southwestern Oregon. 

7 Newton, M.; Dost, F.N. 1984. Biological and physical effects of forest

vegetation management. Final report to Washington Department of 

Natural Resources. 423 p. Unpublished report. On file with: M. Newton,

Department of Forest Science, Oregon State University, Corvallis, OR, 

and with Washington Department of Natural Resources, Olympia, WA. 
Silvicultural Research and the Evolution of Forest Practices in the Douglas-Fir Region

Oregon and northern California. The VMRC has been the

primary entity for cooperative vegetation management studies by private and government agencies, including evaluation of competition and growth concepts (Newton and

Preest 1988, Rose and Rosner 2005, Rosner and Rose

2006). 

The forest industry also made large advances in forest

rehabilitation methods. The Weyerhauser Company began

investigations of coordinated use of chemical, mechanical,

and thermal methods of site preparation in the early 1960s.

Their research program near the Washington coast undertook studies of manual methods and herbicides to facilitate

fuel desiccation so that slash and brush could be burned

when surrounding vegetation was fire resistant. The brownand-burn approach provided control of slash hazards, physical access for planting, and control of competition in a

single operation. It also reduced smoke. This proved an

effective approach, which was later expanded and refined 

at OSU (Hooven and Black 1978, Hurley and Taylor 1974,

Roberts 1975).

In the mid-1970s, the chemical industry developed 

several herbicide products that substantially improved vegetation management in forests. Whereas the phenoxy herbicides and atrazine had been used for selective control of

shrubs, alder, and grasses since the early 1960s, these tools

were neither broad enough in spectrum of activity nor free

of controversy because of the use of herbicides for military

purposes in the Vietnam war and the discovery of a dioxin

contaminant in the military formulation. The advent of

glyphosate, triclopyr, and hexazinone greatly increased

managers’ choices for selective control of plant species. 

A decade later, imazapyr, clopyralid, fluroxypyr, sulfometuron, and metsulfuron became available for forestry use

47

Figure 17—Aerial spraying of appropriate herbicides can often

provide cost-effective control of unwanted vegetation on large

areas. 

Figure 18—Small problem areas can be effectively treated by hand

application of herbicides. 

Figure 19—Growth acceleration of Douglas-fir after

release from tanoak-Pacific madrone-manzanita

competition. 
48

GENERAL TECHNICAL REPORT PNW-GTR-696

and provided a highly effective set of vegetation management tools for both site preparation and release (Newton

2005). 

By 1990, herbicides and technology were available for

selective removal of all the major weed species in forest

plantations. Perennial competitors could be controlled in

advance of planting. Large, vigorous seedlings grown without significant competition had demonstrated the ability to

reach 2 meters (6.6 feet) height within 2 years of planting,

thus becoming more competitive and evading animal damage. This offered opportunities for shortened rotations for

fiber production, and the same capability also offered

opportunity to provide large trees in programs aimed at rapidly developing conditions approximating late stand development stages, and for establishment of mixed species. The

International Forest Vegetation Management Conferences

since 1992 have led to numerous publications outlining

many options for yield enhancement, wildlife management,

and other purposes that were not economically achievable 

a decade ago.

Research on vegetation management has increasingly

become a cooperative, multiagency endeavor, with products presented in various publications. On a national basis,

Stewart and others (1984) compiled an annotated bibliography on effects of competing vegetation on forest trees. A

symposium in Vancouver, British Columbia, focused on

several aspects of vegetation competition and responses

(Hamilton and Watts 1988).

Today, among the many options for controlling vegetation, site preparation with broadcast ground applications of

herbicides in understories is possible before logging, to 

prevent delay in replanting and the heavy use of postharvest

chemical treatments.8 The sophistication, selectivity, and

safety of these tools is such that managers can favor many

different arrays of vegetation concurrently with reforestation, ranging from zero competition to moderately productive populations of high-quality forage species for large

ungulates, while leaving vertical structure of dead or

injured shrubs and hardwoods intact for habitat purposes.

The ability to control demands on site resources has

also provided opportunities for determining absolute site

productivity for tree growth. Hanson (1997) and Newton

and Hanson (1998) reported that juvenile-tree growth habits

change markedly when plantations are established with

negligible competition from herbs and shrubs. Sites identified by soil characteristics as having average productivity

approach site class 1 capability or greater in their first 30

years if competition is controlled in the first few years and

commercial thinning is done before live crown ratios are

reduced below 45 percent.

Uses of chemicals in forests have encountered severe

political obstacles that currently prevent use of herbicides

on federal lands. These obstacles stem in part from attitudes

engendered by opposition to the use of “Agent Orange” (a

mixture of 2,4-D and 2,4,5-T) in the Vietnam war, and from

demonstrated and well-publicized risks associated with certain specific insecticides (DDT, parathion), which have led

to a public perception that any “chemical” is necessarily

dangerous. These obstacles are exacerbated by conflicting

federal laws and in-house regulations within federal agencies that give rise to procedural lawsuits that delay or 

prevent use of these tools (chapter 12).

Opposition of segments of the public to any use of herbicides—even where unsupported by scientific evidence—

has caused most public owners to restrict or eliminate 

their use. Some private owners may also prefer to do so.

Alternative means exist, although they are generally more

expensive and often ineffective (Harrington and Parendes

1993, McDonald and Fiddler 1993). Other than prescribed

burning and mechanical site preparation—discussed previously—these include controlled grazing, hand removal of

brush clumps, mulching, and manual cutting. 

Of these, manual cutting is the only method that has

had much use. It is applicable to competing tree species

8 Newton, M.; Cole, E.C.; Barry, J. “Waving wand” broadcast hand application of herbicides: technical basis and an example of usage. Manuscript

in preparation. Department of Forest Science, Oregon State University.
Silvicultural Research and the Evolution of Forest Practices in the Douglas-Fir Region

such as red alder and other hardwoods. Manual removal of

tops of sprouting species has generally been ineffective in

very young plantations (fig. 20), but is useful in stands at

the precommercial thinning stage. Success is strongly influenced by time of cutting and physiological condition of the

vegetation treated. Thus, best success with red alder was

found by cutting in early summer, when food reserves were

low (Belz 2003, DeBell and Turpin 1989). 

Need for vegetation control can be reduced by use of

large planting stock (Newton and others 1993); very large

container stock preloaded with fertilizer is very competitive. Rapid early growth can enable planted trees to overtop

competing vegetation, whereas broadcast fertilization

increases vigor of the competition as well as that of desired

conifers. Regimes that provide high stand density after

crown closure and near the end of the rotation may reduce

the vigor of understory shrub species (Tappeiner and others

2001). 

49

Figure 20—Regrowth of brush competition (mostly Ceanothus

velutinus) 3 years after manual cutting. 
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Silvicultural Research and the Evolution of Forest Practices in the Douglas-Fir Region

It has long been recognized in Europe that stand density 

has a marked effect on growth rate of individual trees, on

stem quality, and at least some effect on yield per unit area.

Common European practice was to establish a very large

number of trees (either by natural seeding or planting), followed by early and frequent thinning to maximize volume

production and stem quality while maintaining stand vigor

and aiding in control of competing vegetation. Although

this regime was appropriate under conditions of abundant

labor and favorable markets for small material, in the

United States labor was expensive and markets for small

material were poor or nonexistent. These constraints raised

questions about desirable stand density and feasible means

of attaining it. 

There are basically three possible means of controlling

stand density: (1) in plantations, planting of some optimum

number of seedlings (sometimes combined with treatments

to control volunteer conifers); (2) early “precommercial”

thinning, which removes excess small stems without generating immediate revenue; and (3) “commercial” thinning of

older stands in which the stems removed are salable.

Plantation Spacing

Early Douglas-fir plantations were commonly established 

at close spacings, often 6 by 6 feet (1.8 by 1.8 m), still a

relatively wide spacing compared to the then prevailing

European practice. It was quickly realized that immediate

costs could be reduced by planting fewer trees, and that this

could be advantageous where early thinning would not be

feasible. The uncertainties involved led to a number of

experimental trials of alternative plantation spacing.

Wind River Spacing Trial

In 1925, a Douglas-fir plantation spacing test was established on the Wind River Experimental Forest. This was on

a poor site (IV) that had been severely burned in two successive fires (fig. 21). Square spacings were 4, 5, 6, 8, 10,

and 12 feet (1.2, 1.5, 1.8, 2.4, 3.0, and 3.7 meters). Results

have been reported at intervals over the years, first by

Eversole (1955) and more recently by Reukema (1979) and

by Miller and others (2004). Although inferences are somewhat clouded by the lack of true randomization and replication, by soil variation that suggests that the 10- and 12-foot

(3- and 3.7-meter) spacings may be on a slightly better site

than others, and by planting stock of an unknown seed

source, differences among spacings were and are striking

and show generally consistent trends.

The closest spacings showed a slight advantage in

height growth and much greater basal area and volume

increment in the initial years. This changed markedly over

time. Beginning about age 20, the wider spacings developed a marked superiority in height growth (contrary to a

widely accepted expectation), and volume increment soon

overtook that of the close spacings. Merchantable volume

increment in the wide spacings soon far surpassed that in

the close spacings, and it appears that mean annual increment in wide spacings will culminate later and at much

higher levels than has already occurred in close spacings.

Mortality (mostly weather-related) was severe in close

spacings (fig. 22). 

51

Chapter 6: Stand Density Control1

1 By R.O. Curtis.

Figure 21—Wind River spacing test site at time of planting,

1925. 
52

GENERAL TECHNICAL REPORT PNW-GTR-696

These results led most owners to abandon the close

spacings once commonly used in planting programs, in

favor of 10-foot (3-meter) spacing if thinning was anticipated or even 12-foot (3.7-meter) spacing if thinning was

not anticipated. There were correspondingly great savings

in planting costs.

University of British Columbia Spacing Trials

The University of British Columbia established a series 

of spacing experiments in 1957 and following years on an

excellent site (site I) on its research forest near Haney,

British Columbia (Reukema and Smith 1987). These trials

included Douglas-fir, western redcedar, and western hemlock. Unlike the Wind River trial, spacing had little effect

on height growth of dominant trees on this excellent site.

Spacing recommendations were generally similar, namely:

3.7 or 6.4 meters (12 or 15 feet) for lumber production, and

2.7-meter (8.9-foot) spacing to produce high yields where

early thinning is economically feasible.

Other Spacing Trials

In the 1960s, additional spacing trials were established by 

ITT Rayonier Corp. and Pope and Talbot Corp., with generally similar results (Oliver and others 1986). There are 

also a number of spacing trials established by the British

Columbia Ministry of Forests that date from the 1960s (for

example, Omule 1988a). In the early 1980s, a much more

extensive spacing trial (Bishaw and others 2003) was established on the Wind River Experimental Forest, with six

replicates of six spacings for five conifer species, including

Douglas-fir.

The Nelder design (Nelder 1962) is highly effective for

demonstrating changes in tree growth and form over a wide

array of spacings. Several industrial and public organizations have established Nelder plots with spacings ranging

from 100 to 10,000 trees per acre (247 to 24,700 trees per

hectare). Some have since been abandoned because of difficulties in maintenance and in statistical analysis of results,

even though they provide striking visual demonstrations 

of spacing effects. Nevertheless, several sets exist today

with some continuity of measurement. The first of these

was installed by J.H.G. Smith of the University of British

Columbia in 1965–66. Cole and Newton (1987) have 

several series of Nelder plots dating from 1978 to 1986

with both mixed species and pure stands. Hibbs and

Radosevitch of Oregon State University established Nelder

plots in red alder and mixed Douglas-fir–red alder at the

H.J. Andrews and Cascade Head Experimental Forests. The

Washington Department of Natural Resources has Nelder

plots of several species in pure stands up to about 20 years

of age, but most are not being maintained. In general, the

Nelder experiments demonstrate clearly defined curves of

diameter and crown response to crowding and identify

Figure 22—Wind River spacing test in 1997: (A) 12-foot (3.7-

meter) spacing, (B) 4-foot (1.2-meter) spacing. Extensive windfall

and snow breakage has occurred at close spacing, whereas the

wide spacings have been unaffected. 

B

A
Silvicultural Research and the Evolution of Forest Practices in the Douglas-Fir Region

thresholds of competitive interaction (Newton and Cole, in

press). Unfortunately, the data for many of these studies are

incomplete and confined to unpublished progress reports.

The Stand Management Cooperative established a new

and extensive series of initial spacing trials in the 1990s,

discussed later in connection with thinning.

All these trials have shown markedly greater diameter

growth at wide spacings. The sharp reduction in height

growth at close spacings observed in the 1925 Wind River

trial has not generally been found in Douglas-fir trials on

better sites. Similar effects have, however, been found with

red alder (Bluhm and Hibbs 2006).

Scott and others (1998) reported on early growth of

Douglas-fir plantations having a wide range of planting

densities. These plantations showed a tendency for closely

spaced stands to reach larger sizes (not only in height but

also in diameter) in the first few years than more widely

spaced plantings (Woodruff and others 2002). These observations have given rise to speculation that if early gains

might be made by close spacing and preserved by a precommercial thinning program that would avoid severe competition, the practice might increase effective site index and

productivity. 

Aside from the effects on diameter growth, height

growth, and volume growth that have been the primary

objects of attention, initial spacing also affects wood quality

and value (chapter 10) and development of understory vegetation.

Early Thinning Research: Pre-World War II

European experience dating from about 1800 had shown 

that thinning of young stands could be a beneficial practice,

and thinning has been a common practice in Europe for the

past two centuries. The possible benefits of thinning were

recognized from the earliest days of American forestry. But

thinning was long regarded as impractical under Northwest

conditions because of the low or negative value of small

material and the abundant supply of large high-quality

mature timber. A number of pioneering and—at the time—

visionary thinning studies were established in the period

1920–40. These were limited in scale and poorly designed

by modern standards, and therefore are not amenable to 

statistical analysis. They have nonetheless provided valuable experience and insights into the effects of thinning in

Douglas-fir, and the quantitative data have since been useful in construction of simulation models.

Wind River: Martha Creek and Lookout 

Mountain Road

Three plots established in 1920 in a 9-year-old stand at 

Martha Creek included a check and two thinning treatments. In 1933, three additional plots were established consisting of one check and two plots first thinned at age 22

and rethinned at age 42. Lookout Mountain contained two

check plots and two plots thinned twice, in 1934 and 1953,

at ages 31 and 50. Sites ranged from high IV to low III.

There was considerable variation in initial stocking.

Three early reports were prepared by Meyer (1931),

and by Steele (1955a, 1955b). Data summaries through age

81 are contained in an office report.2 Lack of replication,

variability in site, and stand damage prevented any clear

conclusions about treatment differences, other than that

thinning increased diameter increment. 

Mount Walker (Olympic National Forest)

Four thinned plots and two check plots were established in 

1934 and 1937 in a 60-year-old site IV Douglas-fir stand

(Worthington and Isaac 1952) (fig. 23). The study was

dropped after published results (Worthington 1966) indicated that response had been very slow and that thinned

plots had greater diameters but less volume production than

unthinned. However, the plots were remeasured in 1991

(Curtis 1995). At that time (age 117), the thinned plots

appeared in good condition, with volume production not

obviously different from the checks but with greater tree

diameters. The most heavily thinned plot—which according

53

2 Reukema, D.L. 1987. Final progress report on Wind River P.S.P.’s [permanent sample plots] 13, 14, 15, 16, 17, 18 (Martha Creek Flat) and 10,

11, 19, and 20 (Lookout Mountain Road). 60 p. On file with: Silviculture

and Forest Models Team, Forestry Sciences Laboratory, 3625 93rd Ave.

SW, Olympia, WA 98512.
54

GENERAL TECHNICAL REPORT PNW-GTR-696

to the establishment report had been thinned “far too heavily”—was in excellent condition and developing a layered

structure with considerable redcedar and hemlock.

Schenstrom Thinning (Cowichan Lake, British 

Columbia)

This study consists of a check plot and five thinned plots, 

established in 1929 in an 18-year-old stand on an excellent

site (Warrack 1979). Thinnings have been made repeatedly,

although the originally planned differences in thinning

treatments were more or less lost. Comparisons are clouded

by lack of replication and minor site differences. There

were no clear differences in volume production to age 67,

although thinned plots had considerably great tree diameters than the check.

Kugel Creek (Olympic National Forest)

Four plots, three thinned and pruned, and one unthinned, 

were established in a 38-year-old stand in 1937. They 

were destroyed in the 1951 Forks Fire. Fire mortality was

Figure 23—Mount Walker thinning plots on a poor site (class IV),

1937: (A) unthinned stand; (B) plot 9, light thinning; (C) plot 7,

heavy thinning. In 1991, plot 7 was in excellent condition with

vigorous overstory trees and an understory of redcedar and hemlock. This was one of the earliest commercial thinning trials in 

the region. 

A

C

B
Silvicultural Research and the Evolution of Forest Practices in the Douglas-Fir Region

considerably less in thinned than in unthinned plots

(Staebler 1955b). Initial growth response to thinning

appeared favorable.

Summary of Early Trials

Results from these early thinning trials can be summarized 

as:

• Early (precommercial) thinning produced substantial

increases in diameter growth.

• Thinning in older stands also increased diameter

growth.

• Thinning effects on total volume production could 

not be well evaluated because of lack of replication 

and other defects, but it appears that such effects 

were small.

• An analysis using later data from these plots (Curtis

1995) indicates that none of the stands had reached 

culmination (maximum mean annual volume increment) at ages 73 and 81 (Wind River), 117 (Mount

Walker), or 76 (Schenstrom). 

Thinning Research: Post-World War II 

to the Present

Precommercial Thinning

Results from the spacing trials cited earlier, together with 

observations on existing young stands that were established

either by natural seeding or by early planting at close spacings, made it apparent that many young stands were too

dense for optimum growth. A few trials of very early thinning in dense young stands (Steele 1955a, 1955b) had

shown that precommercial thinning could produce major

increases in diameter growth and concentrate growth on

future merchantable trees. Expected results were larger

trees, merchantable volumes greater than in unthinned

stands, and enhanced resistance to wind- and snow-breakage. In the pre-war period, however, such early thinning

was not considered economically feasible. Views rapidly

changed after WWII. Precommercial thinning became 

common by the 1970s. 

In general, thinning was clearly beneficial, particularly

in view of the prevalence of overstocked young stands.

There were occasional instances of so-called “thinning

shock”—temporarily reduced height growth accompanied 

by chlorosis—usually after heavy thinning of overstocked

stands on poor sites (Harrington and Reukema 1983,

Staebler 1956).

Reukema (1975) published guidelines for precommercial thinning, including procedures for estimating the desirable number of leave trees corresponding to the stand

average diameter judged necessary for later commercial

thinning to be feasible. He also gave estimates of the reduction in number of years to reach commercial thinning size

that could be attained through precommercial thinning.

Reukema and Bruce (1977) elaborated on the rationale of

precommercial thinning and its expected results, concluding

among other things that (1) ideally, thinning should be done

when a stand is 10 to 15 feet (3.0 to 4.6 meters) tall, (2)

number of trees left should be determined by average diameter at which commercial thinning is expected to be feasible

and by a corresponding target basal area or relative density

(Reukema 1975, Curtis 1982) that will avoid unacceptable

reduction in crown development and diameter growth, and

(3) the relative gain from precommercial thinning would be

greatest on poor sites because of the more limited natural

differentiation expected on such sites.

Commercial Thinning

The revival of economic activity after WWII, combined 

with the large and increasing acreage of second-growth

stands and the foreseeable end of old-growth timber, stimulated interest in commercial thinning.

Soon after the war, the Pacific Northwest (PNW)

Research Station undertook a number of operational-scale

thinning experiments. These were conducted on industrial

lands under cooperative agreements with the landowners.

Three experimental forests were established for the primary

purpose of thinning research:

The Hemlock Experimental Forest was established 

in 1949 near Hoquiam, Washington, on a tract belonging to

55
56

GENERAL TECHNICAL REPORT PNW-GTR-696

St. Regis Paper Company. Commercial thinning in 50-yearold western hemlock began in 1952 and ended in 1969.

Treatments were high vs. low thinning on 3- and 6-year

cycles. Thinning had little effect on gross volume production (change in live stand voume plus trees that died or

were cut during the period of observation) but did increase

diameter growth and allow salvage of mortality. 

The McCleary Experimental Forest was established in 1948 on lands of the Simpson Timber Co., near

McCleary, Washington. Thinning vs. no-thinning treatments

were compared in a high-site 57-year-old stand. Four thinnings were made on a 5-year cycle. Results from the first

three thinning periods (Reukema and Pienaar 1973) showed

some gain in diameter growth, a reduction in gross growth,

but a slight gain in net production because of salvage and

forestalling of mortality.

The Voight Creek Experimental Forest was established in 1947 near Orting, Washington, in a stand of natural origin on a medium site, on land of St. Paul and Tacoma

Lumber Co. (later St. Regis Paper Co.). Beginning at stand

age 38, commercial thinnings were made on 3-, 6-, and 9-

year cycles, designed to remove comparable volumes over

an 18-year period. Unlike others, this followed a statistically valid randomized block design. The 21-year results

(Reukema 1972) showed no effect of thinning cycle, small

increases in diameter, some increase in growth percentage

(annual net growth as a percentage of live volume), reduction in gross growth, and a slight increase in usable yield

for thinning compared to no thinning. Three replicates were

not enough to overcome the effect of within-stand variability, resulting in insensitive analyses.

Results of these studies markedly dampened interest in

commercial thinning. They showed little or no short-term

volume gain from commercial thinning in mid-age previously unthinned natural stands. This result, combined with

financial considerations that impelled owners toward shortened rotations, led to abandonment of the experimental

forests at the end of the lease period. In retrospect, this was

unfortunate. Information on long-term effects of repeated

thinning of older stands over extended periods would be

extremely useful today in the present context of controversy

and ecosystem management.

A number of other thinning studies were established in

the 1950s by industrial owners. A number of firms established forestry research organizations and undertook extensive plot establishment programs. Most data remain

proprietary and some have apparently been lost as a result

of reorganizations and ownership changes.

Worthington and Staebler (1961) published an extensive review of information then available on commercial

thinning, much of which remains pertinent.

Williamson and Price (1971) examined nine sets of

thinned and unthinned plots established in 70- to 150-yearold stands over the years from 1928 through 1954.

Although detailed analyses were hampered by the lack of a

consistent overall study design, results appeared to show

that (1) thinning reduced mortality from all causes; in particular, bark beetle mortality on thinned plots was only 40

percent of that on unthinned plots, and (2) these older

stands were still making vigorous growth, although growth

rates were slowly declining. Williamson (1982) reported

further on one of these studies (Boundary Creek), established in a 110-year-old stand in 1952. He found little difference in gross volume growth for thinned vs. unthinned

plots, but a large reduction in mortality on the thinned plots.

Allan Berg of Oregon State University established an

extensive series of thinning trials in the 1950s on the Black

Rock Forest near Corvallis. Although these show some

striking contrasts and have had considerable use as demonstration areas, no formal report on the results has ever been

published.

Reukema and Bruce (1977) synthesized knowledge of

commercial thinning of Douglas-fir and hypothesized

development of stands under repeated thinning regimes.

They recommended that the interval between successive

commercial thinnings should vary with site quality and age,

and should not exceed 24 feet (7.3 meters) of height growth

on site I to about 15 feet (4.6 meters) on site V. They made

recommendations on residual stocking and other matters

that are essentially the same as those adopted for the default
Silvicultural Research and the Evolution of Forest Practices in the Douglas-Fir Region

regime incorporated in the DFSIM simulator (Curtis and

others 1981) (chapter 9). They also concluded that relative

gains in yield from commercial thinning would be greater

on good sites, whereas those from precommercial thinning

would be greater on poor sites.

Overall, the conclusions drawn from these trials of

commercial thinning in mid-age, previously unthinned

stands were that thinning such stands provided little gain in

volume production, some gain in diameter growth of residual trees, and marked reductions in mortality. However, it

was also apparent that most of these studies suffered from

design defects and inherent variability that made comparisons quite insensitive. Most people concluded that the principal justification for thinning in such stands was reduction

in mortality losses, which could be important in stands that

would have to be carried for an extended period of years

before final harvest. It was also realized that most of the

above trials were begun in mid-rotation-age natural stands

without early density control, and that these results did not

necessarily represent the effects of thinning stands that had

had density control from an early age.

There has been renewed interest in thinning in recent

years. Reasons include improved markets for small material; emphasis on reducing the visual effects of harvests; the

fact that some owners have unbalanced stand age distributions that necessitate holding some stands for considerable

periods; wildlife habitat considerations; and the suspicion

that results of thinnings begun comparatively late, after

crown reduction has taken place, probably do not represent

the potential of density management regimes begun at an

early age. It was recognized that appropriate thinning could

salvage or forestall most mortality losses while enhancing

resistance of stands to damaging agents such as wind and

snow and bark beetles. Another consideration is that maximum yield enhancement involves a commitment to relatively long rotations, with a sufficient period after the last

thinning to allow stands to approach maximum density.

The marked differences between stands initially greatly

overstocked compared to stands established with early

spacing control, and with and without nonconiferous 

competition, showed the need for plantation-based thinning

experiments. There are now several large-scale studies in

the region that attempt to address these and related concerns.

The cooperative Levels-of-Growing Stock (LOGS)

study in Douglas-fir is a joint study involving PNW

Research Station, Washington Department of Natural

Resources, Oregon State University, Weyerhaueser Co.,

Canadian Forest Service, and British Columbia Ministry 

of Forests. This was begun in 1962 in 18- to 33-year-old

stands with a wide range in site classes. Nine field installations are located in Oregon, Washington, and British

Columbia. All follow a common design originated by

George Staebler (fig. 24) and Richard Williamson, consisting of 27 plots containing 3 replicates of 8 thinning treatments plus a control, established at stand heights of 20 to

56 feet (fig. 25). Principal results to date are summarized 

by Curtis (2006) and Curtis and others (1997).

• Gross volume increment per unit area is related to

growing-stock level, being highest in the densest

stands. This is contrary to a belief widely held at 

the time the study was initiated.

• Volume increment per unit area is much more 

closely related to growing-stock level than is basal 

area increment, reflecting the effect of the rapid and

continuing height growth—characteristic of Douglasfir—on volume increment.

57

Figure 24—George R.

Staebler joined the newly

established Puget Sound

Research Center after

WWII. He later moved 

to Weyerhauser Co.,

where he was Director 

of Forestry Research,

1966–79, and had a large

influence on silvicultural

research and industrial

W

forestry. eyerhaeuser Archives
58

GENERAL TECHNICAL REPORT PNW-GTR-696

• Net volume increment per unit area of the unthinned control exceeded thinned stand net increment 

in early years, but there are indications that the 

relationship is reversing with advancing age and 

onset of competition-related mortality in the unthinned control, and that some thinning treatments 

will surpass the control.

• All thinning treatments markedly increased 

diameter increment.

• Thinning has had striking effects on understory 

composition and development.

The Stand Management Cooperative (SMC) studies

include several series of spacing and thinning plots, some

with superimposed pruning and fertilization, that extend

over the full range of geographic and site conditions in the

region. This is a large-scale cooperative effort established 

in 1985 and headquartered at the University of Washington

(Chappell and others 1987). Its formation stemmed from

the realization that existing data (1) did not provide adequate coverage of young stands with early density control,

(2) did not provide coverage of a range of initial plantation

spacings, and (3) were often of poor quality and inconsistent in standards. The effort required to develop a database 

adequate to support comprehensive modeling efforts was

clearly beyond the capabilities of any one organization. The

SMC involves most of the larger landowners in the region

and uses standardized design and measurement procedures.

Results to date are necessarily limited because of the short

period of observation, but SMC data are rapidly becoming

the major source of information on young stand development of Douglas-fir and western hemlock. Treatments

include very early thinning to a wide range of initial densities, with later thinning to specified relative density targets;

planting to a very wide range of initial densities; and superimposed fertilization and pruning treatments on subsets of

the plots.

A number of recently established studies are concerned primarily with habitat development or integrated

management for multiple objectives. In the 1990s, the U.S.

Figure 25—Iron Creek Levels-of-Growing-Stock (LOGS) installation in 1995, 46 years after planting. (A) untreated control; 

(B) treatment 7, repeated light thinning maintaining high level of

growing stock; (C) treatment 2, repeated thinning to a low level 

of growing stock. 

A

B

C
Silvicultural Research and the Evolution of Forest Practices in the Douglas-Fir Region

Forest Service and the Bureau of Land Management deemphasized timber production in favor of efforts to promote

development of stands with characteristics and structure

thought to be favorable for wildlife and fisheries, including

specifically endangered species such as the northern spotted

owl (Strix occidentalis caurina). Research was also undertaken by PNW Research Station and the universities on

regimes to develop old-growth-like structures, on alternatives to clearcutting that might be used to reduce conflicts

and make timber production forestry more acceptable to the

public, and on biodiversity and management of previously

neglected species. These efforts do not fall readily into the

conventional categories of regeneration systems and intermediate operations such as thinning and fertilization.

Therefore we discuss them in a later section (chapter 12)

under the heading “Silviculture for Multiple Objectives.”

59
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Silvicultural Research and the Evolution of Forest Practices in the Douglas-Fir Region

Selection for traits useful to man has been practiced for 

millennia in domestic animals and agricultural crops.

Modern urbanized society would not be possible without

the increased agricultural production provided by such

improvements. Yet, the application of similar techniques 

to forest trees is relatively recent.

The first areas of investigation (based on European

experience) were the possibility that exotic species might

be superior to native species, and the probability that seed

collected in one portion of the range of a species might 

not be suitable for other parts of the range. Later research

focused on selection, testing, breeding, and seed production

in tree improvement programs begun in the 1950s and

1960s.

Exotic Species

A number of exotic forest tree species had been introduced 

to Europe in the 19th century, with outstanding results in

some cases. Exotics were and are valuable supplements 

to the relatively few native species available to European

foresters. It was therefore natural for the early foresters to

ask whether exotics might have potential in this country.

A worldwide search for fast-growing exotic trees

appropriate for the Northwest began in 1912 at the Wind

River Nursery and became known as the Wind River

Arboretum. This work was begun and supervised for many

years by T.T. Munger, and directed onsite in the early years

by J.V. Hofmann, E.L. Kolbe, Leo Isaac, R.W. Steele, and

in recent decades by R.R. Silen. A number of progress

reports were issued over this period, and a comprehensive

and probably final report was published by Silen and Olson

(1992). Results demonstrated the superiority of native

species over exotics. Introduced broadleaved species failed.

Among conifers, there was a general similarity of growth

among species from a given forest region. Although some

introduced conifers appeared promising in the early years,

over the 70-year period of observation, they gradually

declined or succumbed to climatic and disease factors.

None of the introduced conifers equaled either the growth

or survival of native species. The study strikingly illustrated

how inferences from early short-term results can be widely

different from long-term forest research findings. The slow

failure of initially promising exotics is the best example.

Provenance Trials, Geographic Variation, 

and Seed Zones

One of the first major long-term studies undertaken in 

the Northwest was a comparison of geographical races of

Douglas-fir and its hereditary characteristics begun in 1912

and referred to as the Douglas-fir Heredity Study. The initial impetus was provided by Raphael Zon as a result of his

knowledge of earlier European provenance investigations.

Seed was collected from 120 parent trees of various ages

and descriptions, at 13 widely scattered locations in western

Oregon and Washington. Elevations ranged from 100 to

3,850 feet (30 to 1170 meters). Seedlings were grown in the

Wind River nursery and then planted in six widely separated localities at elevations ranging from 1,000 to 4,600

feet (300 to 1400 meters). Survival and growth were

recorded over many years. Physical characteristics of the

parent tree (age, size, rot, competition) had little or no relation to performance of progeny (Hofmann 1921, Morris

1934, Munger and Morris 1936). Major differences among

seed sources were found in survival, growth rate, and sensitivity to differences in local climate. Trees of several

sources did not do well at sites differing markedly in climate from their source, indicating the importance of using

seed adapted to local growing conditions. Some sources, 

on the other hand, made good growth over a wide range of

elevations, showing inherently superior growth to other

sources of similar climate and site. Collections from the

Darrington and Granite Falls areas in Washington and

Palmer in Oregon consistently out-performed others and

showed a wide climatic tolerance. A widespread freeze in

61

Chapter 7: Genetics and Tree Improvement1

1 By J.B. St. Clair.
62

GENERAL TECHNICAL REPORT PNW-GTR-696

November 1955, however, damaged many of the larger

trees from these and other provenances, illustrating the

importance rare climatic events have to adaptation (Silen

1963).

While researchers were learning from the early

Douglas-fir provenance trial, foresters were also gaining

experience from operational plantations established in the

first half of the 20th century. Stock of unknown seed origin

was often used in early plantations. Many plantations failed

or grew poorly, which was attributed to the use of seed

sources not adapted to the conditions of the planting site.

Isaac (1949) reviewed several examples of poor growth and

survival of Douglas-fir plantations of known seed sources

in which seed sources from lower elevations had poor

growth and survival at higher elevations. Experiences with

plantation failures as well as the results from the early

Douglas-fir provenance trial led to the first delineation of

seed collection zones (Kummel and others 1944) and seed

collection guidelines (Isaac 1949). A system to certify the

stand origin of forest tree seed was established by the mid

1960s, and in 1966, seed zone maps for Washington and

Oregon were published (slightly revised in 1973).

Revised tree seed zone maps and guidelines were published in 1996 for western Oregon (Randall 1996) and in

2002 for Washington (Randall and Berrang 2002). The 

earlier seed zone maps were based on climatic, vegetative,

and topographic information, and a single map was used for

all species. Research over the past three decades, however,

showed that tree species differ greatly in their distribution

and patterns of genetic variation. Thus, the revised maps 

are specific for each species, and are less restrictive, particularly for latitudinal transfers within elevation bands.

Dissatisfaction with the sampling design of the early

provenance trial and concern that seed movement guidelines were too restrictive led to the establishment of a second provenance trial of Douglas-fir in 1959 (Ching and

Bever 1960). Seed was collected from 16 provenances

across a wide latitudinal range from southern Oregon to

northern Vancouver Island. Seedlings from all 16 provenances were planted at 16 sites in the same area of the seed

collections plus a site near the northern California coast.

Various problems reduced the number of study sites available for analysis to 10. Results for 10 sites at age 20 and the

5 fastest growing sites at age 25 showed that tree growth

did not differ greatly among provinces, except that trees

from the southern Oregon provenance were much smaller

(Ching and Hinz 1978, White and Ching 1985). The provenance x site interaction was nonsignificant; trees from local

provenances did not appear to grow best. White and Ching

(1985), however, questioned the experimental precision of

the study. Furthermore, the study sites presented in the 1985

publication represented a limited range of environments,

and not enough detail is presented in the 1978 publication

to determine the effect of moving seeds from low-elevation

sources to the more challenging, high-elevation sites.

Provenance trials are expensive and long term by their

nature. Because of practical and economic limitations on

the size of tests, only a limited number of seed sources can

be evaluated. Thus, provenance trial results have tended to

be largely descriptive of geographic variation, rather than

predictive. In the 1970s, Robert Campbell pioneered the

development and use of predictive models of geographic

variation to provide seed transfer guidelines and evaluate

seed and breeding zones. In 1974, he published two papers

(Campbell 1974a, 1974b) that predicted the seedling adaptive traits (bud burst or survival) in response to moving

provenances between locations, from information on the

environment of the seed source and the environment of 

the plantation site. Environments were characterized by 

surrogates such as elevation, latitude, or distance to the

ocean. Later, he developed a methodology to estimate transfer risks as a function of the differences between sites and

the genetic variation within sites (Campbell 1979, 1986).

Short-term nursery tests facilitated the development of predictive models by allowing the evaluation of many seed

sources from a large range of environments. Over the next

couple of decades, Campbell and Frank Sorensen used this

methodology to explore geographic variation and provide

seed transfer guidelines for a number of conifer species 

in the Northwest (for example, Campbell 1986, 1991;
Silvicultural Research and the Evolution of Forest Practices in the Douglas-Fir Region

Campbell and Sorenson 1978; Campbell and Sugano 1987,

1989, 1993; Sorensen 1992, 1994).

Tree Improvement Programs in 

Douglas-Fir

Tree breeding work in the United States began with the 

establishment of the Institute of Forest Genetics in 1925 in

Placerville, California (which emphasized work on pines),

and the work of E.J. Schreiner, A.B. Stout, and R.H. McKee

with poplars in the Northeast, begun in 1924. However,

active tree-improvement work in Douglas-fir—beyond

early efforts to determine appropriate seed sources—did not

get underway until the 1950s.

In 1949, Leo Isaac made a strong case for an active

tree-improvement program for Douglas-fir in his book

Better Douglas-fir Forests From Better Seed (Isaac 1949).

Two meetings were held in 1953 to review existing work 

in forest genetics and consider proposals to develop formal

programs in basic biology and forest tree improvement.

Participation included public agencies, the universities, the

Industrial Forestry Association, and a number of the major

industrial firms. This was a period when the major landowners were shifting from natural regeneration to planting,

and they had a keen interest in securing well-adapted seed

and in possible improvements through applied genetics.

Consequently, there was wide support in both public and

industrial organizations for tree improvement programs. 

In 1954, the Industrial Forestry Association initiated 

a program of Douglas-fir tree improvement. John Duffield

was hired to oversee the program. Superior parents were

selected in wild stands, and the first clonal seed orchards

were established by grafting. Also in 1954, a formal

research project in forest genetics and tree improvement

was founded at the Pacific Northwest (PNW) Research

Station, directed by Roy Silen. In February 1955, a meeting, chaired by Leo Isaac, discussed the need for an organization of research workers in tree improvement, to be called

the Northwest Forest Genetics Association (later renamed

the Western Forest Genetics Association). This association

was formally established in June of 1955, with Duffield as

the first chairman. Over the next several decades, extensive

research was carried out on the genetics of Douglas-fir and

the practical problems of producing improved seed. This

involved the PNW Research Station, universities in Oregon,

Washington, and British Columbia, the British Columbia

Forest Service, the Industrial Forestry Association, and

major industrial landowners (Silen 1978). 

As seed orchards became common in the early 1960s, 

a serious problem developed—many seed orchard trees

died because of graft incompatibility. The result was a gradual disenchantment with Douglas-fir tree improvement. In

1966, Roy Silen proposed an alternative strategy to get

around the problem of graft incompatibility. Silen advocated progeny testing of a large number of wind-pollinated

families from less intensively selected roadside trees, followed by the establishment of seedling seed orchards using

full-sib crosses of the parents in the field (Silen 1966, Silen

and Wanek 1986, Silen and Wheat 1979). As information

on the parents became available from progeny tests, the

seedling seed orchards were incrementally rogued (culled)

to provide greater genetic gains. Another feature of the program was small breeding zones to ensure that all planting

stock would be locally adapted. This approach came to be

called the “progressive” tree improvement program. Under

the leadership of Roy Silen and Joe Wheat (of the Industrial

Forestry Association), many local forest landowners, public

and private, adopted the progressive approach as they came

together to cooperate in tree improvement activities across

their interlocking ownerships. The Douglas-Fir Heredity

Study was often used by Silen to show the potential of tree

improvement by pointing out the large differences among

family row plots.

Grafted seed orchards, however, offer advantages over

seedling seed orchards. Grafting mature branches from

select trees onto rootstock provides seed production at

younger ages and with greater certainty of the genetic worth

of the parents. Don Copes of the PNW Research Station

addressed problems in Douglas-fir seed orchards, in particular the problem of graft incompatibility. Copes developed a system to test for graft incompatibility and began a

63
64

GENERAL TECHNICAL REPORT PNW-GTR-696

breeding program to produce graft-compatible rootstock

(Copes 1999, Silen and Copes 1972). As a result, the problem of graft incompatibility has mostly been solved, and

most seed orchards today are clonal seed orchards from

grafted parents (figs. 26, 27).

From 1967 to 1985, cooperative tree improvement programs using the progressive tree improvement approach

were jointly guided by the PNW Research Station and the

Industrial Forestry Association. After the retirement of Roy

Silen and Joe Wheat, the leadership of the cooperative 

programs was passed in 1985 to an umbrella organization

called the Northwest Tree Improvement Cooperative directed by Jess Daniels, hired as a contractor. In April 2000, the

organization moved to Oregon State University and Keith

Jayawickrama was hired as director.

By the 1980s, 125 Douglas-fir breeding programs involving over 30,000 parents tested in nearly 1,000 test plantations were in existence in western Oregon, Washington,

and British Columbia (Johnson 2000b, Lipow and others

2003). Most of these programs are part of the Northwest

Tree Improvement Cooperative, but several organizations

have separate programs with their own approaches and 

history. Second-generation programs were initiated by

Weyerhaeuser and the British Columbia Ministry of Forests

in the 1980s and by the Northwest Tree Improvement

Cooperative in the 1990s. Research at the PNW Research

Station influenced breeding zone size, seed orchard layout,

mating designs, and field-testing procedures (Johnson

1998). As a result, the second-generation breeding plan for

the Northwest Tree Improvement Cooperative is very different from the first-generation strategy (Johnson 1998).

As reforestation relied less on natural regeneration and

tree improvement programs began to advance, forest geneticists and forest managers recognized a responsibility to

conserve the rich genetic heritage within our native forests

(Ledig 1986, Namkoong 1984, Silen and Doig 1976).

Efforts to evaluate and ensure the conservation of forest

genetic resources were begun in the 1990s in western

Oregon and Washington (Wheeler and others 1995) and in

British Columbia (Yanchuk and Lester 1996). Conservation

of genetic resources may be achieved by perpetuating

native stands and processes at their original location, called

in situ conservation, or by collecting and preserving the

genetic material at some other location, called ex situ 

Figure 26—Research to overcome graft incompatibility made

high-genetic-gain seed orchards possible. Most Douglas-fir seed

now comes from seed orchards, such as the Oregon Department of

Forestry’s J.E. Schroeder Seed Orchard, near St. Paul, Oregon. 

Figure 27—Controlled pollination of Douglas-fir in a seed

orchard. Tree breeding for wood production has become an important component of modern forest management.

Oregon Department of

Forestry

Oregon Department of

Forestry
Silvicultural Research and the Evolution of Forest Practices in the Douglas-Fir Region

conservation. Yanchuk and Lester (1996) and Lipow and

others (2004) considered population sizes of conifer species

in in situ protected areas such as wilderness areas, national

parks, and other reserves, and determined that genetic

diversity is well represented. 

Tree improvement populations may be considered a

form of ex situ conservation. Yanchuk (2001) and Johnson

and others (2001) reviewed the role of applied tree breeding

programs in genetic conservation, including discussions of

numbers of parents needed. They concluded that breeding

populations are appropriately structured and populations are

sufficiently large to ensure conservation of genetic diversity. The large number of first-generation Douglas-fir selections in the Northwest represents an important ex situ

genetic resource (Lipow and others, 2003). 

Today most Douglas-fir seed used in planting programs

is produced in seed orchards from selected parents. This has

clearly increased productivity in early stand development.

There is uncertainty as to the magnitude of the increase in

stand productivity over a rotation, because of the limited

period of observation of operationally planted stands. Also,

most genetic tests use mixed-family plantings, which

involve uncertainties in genotype interactions and do not

lend themselves to expansion to a stand basis (St. Clair

1993). Genetic gain trials are being established to compare

realized gains in stand productivity under operational conditions with gains predicted from mixed-family genetic

tests (St. Clair and others 2004).

Tree Improvement Programs in Other 

Species

Although Douglas-fir has received the most attention, 

a substantial amount of similar work has been done in 

western hemlock under the Northwest Tree Improvement

Cooperative and the British Columbia Ministry of Forests

(Daniels 1995). The USDA Forest Service and Bureau of

Land Management have long had special breeding programs for western white pine and sugar pine, aimed at producing blister-rust-resistant planting stock (Johnson 2000a).

The British Columbia Ministry of Forests has breeding programs for western white pine, western redcedar, Alaskan

yellow-cedar, and Sitka spruce. Public agencies have tree

improvement programs for ponderosa pine on the east side

of the Cascades.

The University of Washington (Reinhard Stettler) and

Washington State University (Paul Heilman) were active 

in developing hybrid poplars (usually crosses of the native

black cottonwood with various other Populus species), and

in recent years a number of industrial owners have undertaken extensive poplar planting programs.

65
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Silvicultural Research and the Evolution of Forest Practices in the Douglas-Fir Region

Forest Fertilization

Forest soils in the Douglas-fir region have developed on 

a wide range of rock type, topography, and local climate.

These soils differ greatly in their moisture-holding capacity,

nutrient content, and physical environment for tree roots.

Growth of forests can be limited when one or more nutrient

elements are lacking or in low supply. Nutrient deficiencies

can arise from deficiencies in the native soil and from losses caused by natural events (wildfire, erosion, landslides)

and human activities (timber harvest, site preparation, prescribed fire).

Research on forest nutrition and use of commercial 

fertilizers to correct nutrient deficiencies in the forests of

the Pacific Northwest began at the University of Washington

in the late 1940s. The early research was conducted by

Professors Stanley Gessel (fig. 28) and Richard Walker.

Using field trials and greenhouse studies with potted

seedlings, they demonstrated that tree growth on soils

derived from glacial deposits was strongly stimulated by

adding nitrogen (N) fertilizers (Gessel and Walker 1956,

Gessel and others 1965). Subsequently, other organizations

undertook research on tree nutrition and forest fertilization;

these included Weyerhaueser Company (Steinbrenner

1968), Crown Zellerbach Corporation (Strand and Austin

1966), the Pacific Northwest (PNW) Research Station

(Robert Tarrant and Richard Miller), and Oregon State

University (Chester Youngberg and Denis Lavender). By

the mid-1960s, research results encouraged commercial

application of fertilizers to industrial forests.

Recognizing the need for a wider geographical sampling and further quantification of stand response to fertilization, industry representatives to the Northwest Forest

Soils Council (an informal organization that promotes use

of soils information) proposed council sponsorship of a forest fertilization cooperative. A technical committee drafted

a research design and plan of action that was accepted 

by the council. In 1969, the College of Forestry of the

University of Washington agreed to administer this cooperative, which became the Regional Forest Nutrition Research

Program (RFNRP). Stanley Gessel was the first director,

and Kenneth Turnbull (also of University of Washington)

provided much technical guidance. The initial technical

advisory committee to RFNRP included Gene Steinbrenner

(Weyerhaueser Co.), Robert Strand (Crown Zellerbach

Corp.), Denis Lavender (Oregon State University), and

Richard Miller (PNW Research Station). 

The primary goal of the RFNRP was comprehensive

testing and quantification of stand-level response to urea

fertilizer in both Douglas-fir and western hemlock stands 

in western Washington and Oregon. The initial series of

field trials in 1969–70 (Phase I) tested fertilization in fully

stocked, unthinned stands, 10 to 50 years of age, usually of

natural origin. Douglas-fir stands were stratified into six

“provinces” or physiographic-climatic areas; western hemlock stands were located in three of these provinces. Within

each province, stands were selected to represent four age

classes and four site quality classes (I through IV). Six 0.1-

acre (0.04-hectare) plots were installed in each stand, and

three fertilizer treatments, (0, 200, or 400 pounds of N per

acre (0, 224, 448 kilograms of N per hectare), were randomly assigned. A new series (phase II) was installed in

67

Chapter 8: Forest Fertilization and Long-Term Productivity1

Figure 28—Stanley P. Gessel

pioneered research on fertilization of Northwestern forests.

He was largely responsible for

establishment of the Regional

Forest Nutrition Research

Program, now part of the Stand

Management Cooperative. 

1 By R.E. Miller. 

University of

Washington College of

Forest Resources
68

GENERAL TECHNICAL REPORT PNW-GTR-696

1971–72 with the same treatments, except that fertilization

was preceded by thinning that removed about 40 percent 

of the initial basal area. 

Similar field trials were installed by the British

Columbia Forest Service. Results from the U.S. and B.C.

trials were reported by Miller and others (1986) and

Chappell and others (1992). Practical experience in forest

fertilization was shared at workshops (Anderson and others

1970, British Columbia Ministry of Forests 1991, Chappell

and others 1992, Gessel 1965, Gessel and others 1979, and

Miller and others 1986). About 70 percent of Douglas-fir

stands in the U.S. and B.C. trials increased growth after 

fertilization. The average volume increase was about 300

cubic feet per acre (21 cubic meters per hectare) in the first

6 years after fertilization.

Trial results provided direct evidence on the average

and range of response of Douglas-fir and western hemlock

stands in western Oregon, Washington, and British

Columbia (figs. 29, 30), and stimulated a marked increase

in the area of operational fertilization of forest lands

(Peterson and Hazard 1990, Turnbull and Peterson 1976).

Operational fertilization has been primarily of Douglasfir stands with urea applied by helicopter at rates of about

200 pounds of N per acre (225 kilograms of N per hectare).

Because response of hemlock stands in field trials has been

erratic (especially in coastal areas), operational fertilization

of hemlock has been much more limited. Both naturally

regenerated and planted stands have been operationally fertilized. Decisions to fertilize plantations as well as naturally

regenerated stands are largely based on results of RFNRP’s

phase III (1975) and phase IV (1980) installations in plantations of both species.

In 1991 the RFNRP was merged with the Stand

Management Cooperative (SMC), which is also administered by the University of Washington. The SMC continues

to install and maintain field trials involving density control,

fertilization, and other stand management activities such as

pruning.

Fertilization of established stands within a decade 

of harvest has usually been considered most attractive,

because costs of fertilization can soon be recovered (Miller

and Fight 1979). Potential financial gains from fertilization

of Douglas-fir appear especially favorable when N is

applied to thinned stands, because response is captured by

trees that are expected to reach merchantable size and be

harvested.

Research on effects of other forms of N fertilizer has

been minor. Largely because of its higher concentration,

Figure 29—Relatively small and infrequent applications of nitrogen fertilizer often produce striking responses in tree vigor and

stand development, particularly on poor sites: (A) typical diameter

growth response, and (B) an extreme example of response shown

by paired stem sections from trees on adjacent fertilized and

unfertilized plots on a very poor site. 

A

B
Silvicultural Research and the Evolution of Forest Practices in the Douglas-Fir Region

urea (46 percent N) is preferred to other sources of N, such

as ammonium nitrate (Miller and Harrington 1979, Miller

and Tarrant 1983, Radwan and others 1984). Use of biuret

(Miller and others 1988, 1996a) and concentrated N solutions applied as a foliar spray were also investigated (Miller

1981; Miller and others 1991, 1996a).

Some research has been conducted with elements such

as phosphorus (P), potassium (K), and sulfur (S) as reported

by Gessel and others (1981), Radwan and Shumway (1985),

and Chappell and Miller (1988). Periodically, the effectiveness of combined or balanced fertilizers (N, P, K, S) has

been investigated for improving survival and growth of

recently planted seedlings or established stands. More

recently, application of these other nutrients is being tested

as a possible means for reducing damage from Swiss needle

cast. There has also been some use of controlled-release

fertilizers in containerized seedlings.

To optimize financial returns from operational fertilization, however, reliable site- or stand-specific prescriptions

are needed. Which sites or stands should be targeted for 

fertilization? How can nutrient deficiencies be diagnosed to

predict response to fertilization? Some answers have been

reported (Carter and others 1992, Miller and others 1989a,

Peterson and others 1984, Radwan and Shumway 1984,

Shumway and Olson 1992).

With diagnostic techniques commonly used in agriculture, both foliar and soil analyses have been investigated as

means for predicting nutrient inadequacies for optimum 

tree growth at individual sites. Except for identifying sites

where one or more nutrients are in extreme shortage for 

tree growth, neither diagnostic tool has yet proved practical

for operational use in the Pacific Northwest. Practicality 

has been limited by (1) costs of sampling soil or foliage of

established stands (beyond the seedling stage), (2) great

spatial and temporal variation in soil and tree foliage that

necessitates careful and extensive sampling to obtain representative samples for analysis, (3) unreliable analytical

results, and (4) the time and effort required to establish the

biological linkage between observed growth and soil or

foliar nutrient analyses. 

There has also been considerable work on biological N

fixation, mainly by red alder, in an effort to develop alternatives to commercial fertilizers for correcting N deficiencies,

as discussed in chapter 11 in connection with alder silviculture. A number of other species also fix limited amounts of

N (Gordon and others 1979).

Long-Term Site Productivity

An important and frequently raised concern is whether 

intensive management of forests—especially the shortrotation plantation management now common on industrial

lands—may eventually degrade productivity of the land.

Potential causes of site degradation include frequent losses

of nutrients and organic matter in harvested wood or slash

disposal, and cumulative effects of soil compaction and displacement by heavy logging equipment. This is a difficult

concern to address, because of the need for controlled

experimentation and long-term comparisons, and for sampling the wide range of soils and climates that exist in

forested areas. We assume a priori that nutrient-poor sites,

generally those of low site index, are most likely to be

degraded by nutrient withdrawals and topsoil displacement.

69

Figure 30—Research in forest fertilization led to extensive operational fertilization, usually with urea applied by helicopter.
70

GENERAL TECHNICAL REPORT PNW-GTR-696

Maintaining site productivity is a fundamental objective for all actively managed forest land, regardless of 

rotation length. For federal forests, the National Forest

Management Act of 1976 directed the Forest Service to

monitor its activities and to prevent “significant and permanent loss of land productivity.” Subsequently, “land productivity” was defined as a soil’s capacity to support plant

growth as indicated by some index of biomass accumulation, and a “significant change” in productivity was defined

as the minimal level of reduced growth detectable by current technology. Based on science available at the time,

standards were set that defined “detrimental” soil disturbance (USDA Forest Service 1987). Hundreds of harvested

sites have been monitored to determine if the areal extent 

of detrimental soil disturbance exceed standards.

Early research on aspects of long-term productivity

(soil compaction and displacement) in the Northwest was

reviewed in several symposia (Froehlich and McNabb

1984, Miller and others 1989b, Powers and others 2005).

Some studies have been inconclusive because of short

observation periods and existence of uncontrollable factors.

Other studies have shown impacts ranging from no effect 

to some loss of productivity. There is little or no direct evidence of a general decline in productivity; on the contrary,

because of improved silvicultural practices, many new

stands are more productive than the stands they replaced.

Yet, the period of observation is relatively short and comparisons may be confounded with climatic changes, site differences, changes in site preparation and planting practices,

control of competition, and changes in genetic composition

of the forest.

Nutrients and potential soil organic matter can also be

lost or redistributed by prescribed burning or slash piling.

Minore (1986) reported average 5-year height of several

thousand Douglas-fir seedlings at each of 57 progeny test

plantations in southwest Oregon. Slash was treated by

broadcast burning at 23 plantations, and by piling and burning at 34 plantations. He concluded that site quality probably is reduced by piling and burning.

In 1986, Miller and Bigley (1990) reestablished paired

plots at 44 of the original locations established by Morris

(1970) in 1946–53. The paired plots at each location in the

Cascade Range in western Washington and Oregon were

adjacent and similar in size, slope, aspect, and logging 

disturbance. One plot in each pair was in that portion of 

the unit that could be protected from fire when slash was

burned. The plots were not planted. No consistent difference in site index was found between burned vs. nonburned

plots. Average volume on burned plots was similar to nonburned, although total numbers and volumes of Douglas-fir

and hardwoods were greater on burned plots. At seven 

locations, a third plot was established in planted areas

immediately adjacent to the broadcast burned and naturally

regenerated plots (Miller and others 1993). At stand age 40

years, the planted plots on slash-burned areas averaged

about 40 percent greater volume than naturally regenerated

plots on slash-burned areas. Thus, differences among plots

could be attributed to differences in species composition

associated with fire and in type of regeneration rather than

to changes in soil productivity.

Heavy equipment used to harvest trees or prepare sites

for regeneration physically impacts soil, causing some

degree of both displacement and compaction. Several studies evaluated the effects of skid trails on soil characteristics

and tree growth in the Pacific Northwest. Steinbrenner and

Gessel (1955) reported poor survival and growth of artificially seeded Douglas-fir on compacted and displaced soil

of skid trails at nine clearcuts in western Washington.

Froehlich (1979) also reported reduced height of Douglasfir seedlings several years after planting on skid trails in

western Oregon. In general, soil characteristics are altered

by machine traffic, but tree growth may be decreased, unaffected, or increased depending on soil properties, degree of

disturbance, and climatic stress (Heninger and others 2002;

Miller and others 1996b, 2004). 

In the early to mid 1990s, several long-term studies 

on soil productivity were initiated. These included the U.S.-

Canadian Long-Term Soil Productivity (LTSP) study led by
Silvicultural Research and the Evolution of Forest Practices in the Douglas-Fir Region

Robert Powers of the Pacific Southwest Research Station

(Powers and others 2005). Emphasis in that study is on the

effects of changes in soil porosity, organic matter, and vegetative growth under controlled levels of organic matter

retention and soil compaction (Holcomb 1996, Powers

2002). For example, in northern California, variability in

tree growth responses to soil compaction was attributed to

differences in soil texture and soil water retention after

compaction (Gomez and others 2002). First results from

this very large nationwide study (Powers 2002, Powers and

others 2005) show that response to compaction differed

widely among soils; effects on tree and total vegetative 

productivity could be positive or negative. 

Pacific Northwest Research Station researchers initially

declined to participate in the LTSP study because their limited resources were already committed to the Long-Term

Ecosystem Productivity Program (LTEP). The LTEP is a

long-term cooperative effort led by PNW Research Station

and involves three national forests and the Washington

Department of Natural Resources. The primary objectives

are to determine the long-term effects of species composition and removal of organic matter on net primary production, although there are a variety of subsidiary objectives

(Amaranthus and others 1995).

In 1999, the Fall River Long-Term Site Productivity

study was started on a very productive site in western

Washington (Terry and others 2001). This is a large study

that was jointly designed and conducted by Weyerhaeuser

Company, PNW Research Station, and the University of

Washington. Objectives include evaluation of effects of

organic matter removal, vegetation control, fertilization,

compaction, and tillage on nutrient budgets, soil physical

properties, microenvironment, vegetation development, soil

and plant processes, and tree growth. Because some of the

12 treatments at Fall River are similar to those of the LTSP

study (Powers and others 2005), Fall River is considered an

affiliate installation. Early results indicate that soil moisture

(and associated N availability) is the factor most closely

tied to tree growth at this location, and that vegetation control has the greatest influence on soil moisture (Roberts and

others 2005). Compaction of the silt loam soil increased

available soil moisture and tree size at age 3 (Ares and 

others 2005). Amounts of logging debris retained on site

influenced soil microclimate; the effects on tree growth

were positive or negative depending on growing season

precipitation. Although retention of large amounts of 

organic materials (and N) resulted in greater leaching of N,

the amount lost was small relative to the total N pool

(Strahm and others 2005).

The Fall River productivity research was expanded in

2002 with the establishment of two additional installations

with different soils and climate. Although fewer organic

matter removal and mitigative treatments are being tested 

at the Shelton and Mollala installations than at Fall River,

vegetation control is also a main experimental factor. Each

treatment combination is replicated four times. The expanded study involves the PNW Northwest Research Station,

Port Blakely Tree Farms LP, Green Diamond Resource

Company (formerly Simpson Resources), Oregon State

University, and the University of Washington. Both the Fall

River study and the expanded studies include research on

soil and plant processes to understand and evaluate the

mechanisms of tree response on large, replicated plots. 

Although numerous studies have evaluated the effects

of disturbance on soil properties, relatively few have evaluated tree growth response or the mechanisms of response to

disturbance. It is incorrect to assume that if soil characteristics are altered or degraded, tree growth will necessarily

also be reduced (Miller and Anderson 2002). Additional

research is needed to identify situations where native or

previously impacted soil is more or less at risk, and to prescribe appropriate stand and soil management practices for

specific sites.

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Silvicultural Research and the Evolution of Forest Practices in the Douglas-Fir Region

Site index curves are the most widely used basis for productivity classifications. Volume tables and yield tables are

not usually thought of as part of silviculture. But, volume

tables and yield tables are essential tools in any quantitative

silvicultural work. Yield tables (which evolved into the tree

and stand simulators of today) portray the expected development of trees and stands over time. In their modern form

of tree and stand simulators, they provide an important

management planning tool, a quantitative summary of existing knowledge of average stand performance expected

under specific silvicultural treatment regimes, and a means

of exploring possible silvicultural alternatives.

The following discussion is far from a complete treatment of the subject, but lists several of the more important

publications. Much more complete lists are given in Hann

and Ritters (1982), Hann (1994, 1995), and Ritchie (1999).

Volume Tables and Equations

Munger (1911) produced a Douglas-fir volume table, which

may well have been the first volume table published in the

Pacific Northwest. In subsequent years, various authors

developed a large number of similar tables for most of the

economically important species. These tables were not

always consistent in sampling and measurement standard or

in methodology. Most of the earlier tables were developed

by graphical methods, although regression methods were

coming into use and eventually replaced the graphical

methods. Prior to the electronic computer, relationships

were generally expressed in tabular form.

With the advent of the electronic computer, a number

of more elaborate, more flexible and more consistent systems of volume equations and taper equations were developed by regression methods, and soon replaced the older

tabular formats. Hann (1994) provided an extensive bibliography.

Site Index Estimates 

Site productivity is commonly expressed in terms of site 

index, the mean height attained by a specified stand component, such as dominant and codominant trees or a fixed

number of largest trees per unit area, at a specified reference age. For many years, the height curves used to classify

site quality were derived from tree measurements on temporary plots, by using the guide curve procedure or variations thereof. This procedure consisted of fitting an average

curve of heights over ages and then drawing in a family of

proportional curves, indexed by height at the reference age. 

In the 1960s, stem analyses were widely adopted as a

basis for height growth and site index curves, and largely

replaced the older guide curve method. King (1966) provided the most widely used curves for Douglas-fir, although

others later developed slightly different curves for specific

subregions (Curtis and others 1974, Hann and Scrivani

1987). There has been some use of directly measured periodic height growth as a basis for such curves (Bruce 1981),

a procedure that will probably become more common with

the accumulation of high-quality repeated measurements

from long-term plots.

It is often observed that site index estimates in plantations are higher than those from the prior stand or from

adjacent stands, which presumably reflects some combination of effects of site preparation, vegetation control, genetic selection, and density differences. Flewelling and

others (2001) prepared height-age curves specifically for

planted stands, with adjustments for density. Newton and

Hanson (1998) showed that early weed competition has

considerable effects on early height growth and hence on

site index estimates.

Normal Yield Tables

Methodology

A yield table portrays the expected development of a forest 

stand on land of specified site quality (usually expressed by

73

Chapter 9: Growth and Yield/Mensuration1

1 By R.O. Curtis.
74

GENERAL TECHNICAL REPORT PNW-GTR-696

site index) under a specified form of management. In the

early years of North American forestry, plot data showing

actual growth rates of stands observed over time did not

exist. Therefore, normal yield tables derived from temporary plots were adopted as an interim expedient. These

tables were constructed from one-time plot measurements

in subjectively selected stands judged to be well-stocked

and representing a range of sites and ages. 

Normal yield tables provided much useful information,

but had major limitations: (1) they could be used only for

even-aged stands, (2) their use to project development of

stands of other than those of “normal” stocking was

dependent on questionable assumptions about the

“approach to normality” over time of initially over- or

understocked stands, (3) they were not well suited to

mixed-species stands, (4) they rested on the untestable

assumption that the means of subjectively selected “wellstocked” plots at successive ages represented points on a

true growth curve, and (5) they could not provide estimates

of the response of stands to silvicultural treatments such as

thinning. Despite these limitations, there was no viable predictive alternative under the conditions of the period.

Early yield tables and associated volume tables had

been prepared for various species around the country, and a

need quickly became apparent for some degree of standardization in data collection and analysis procedures. A committee including representatives of the Forest Service,

Society of American Foresters, and Association of State

Foresters was established for the purpose, under the chairmanship of E.N. Munns. Their report (Munns 1926) established the general procedures that were followed throughout

the normal-yield-table era, which extended into the 1960s. 

Douglas-Fir Yield

Beginning in 1909, some temporary tree and plot measurements had been collected and a few permanent growth plots

established. The data formed the basis for yield estimates

by Munger (1911) and Hanzlik (1914). This work was continued by Richard McArdle (fig. 31) beginning in 1925,

who was joined by Walter H. Meyer in 1926. An extensive

field program provided measurements from 2,052 temporary plots on 261 tracts, extending over a wide range of

ages and site qualities. These provided the basis for USDA

Technical Bulletin 201 (McArdle and Meyer 1930), which

was reissued in 1949 and again in 1961 with minor changes

and a supplement by Donald Bruce based on stand average

diameters. 

Bulletin 201 was a landmark publication (Curtis and

Marshall 2004), which had a huge influence on Douglas-fir

forestry and development of the Douglas-fir region. It documented beyond question the enormous productivity of

Douglas-fir forests, and provided a basis for quantitative

management planning. It was a major factor in convincing

landowners to shift from forest liquidation to long-term

management. Despite the limitations common to all normal

yield tables, it was the bible of Douglas-fir managers until

the advent of computer simulation models. The authors

went on to distinguished careers; McArdle eventually

became Chief of the Forest Service, and Meyer was for

many years Professor of Forest Management at Yale.

An offshoot of the Douglas-fir yield table work was a

set of average height-diameter curves classified by site and

age, derived from the same data (Meyer 1936). The original

intent was that these could be used for stand volume calculations in the absence of adequate direct measurements of

height. In retrospect, their primary importance was that they

Figure 31—Richard E.

McArdle (with Walter 

H. Meyer) developed 

the widely used Bulletin

201, The Yield of

Douglas-Fir in the

Pacific Northwest

(1930). This publication

and subsequent 1949 and

1961 revisions had a

large influence on development of Douglas-fir

forestry.
Silvicultural Research and the Evolution of Forest Practices in the Douglas-Fir Region

clearly showed the progressive shift in position of

height/diameter curves over time, which arises from agerelated differences in the trends of diameter growth and

height growth. (Similar shifts can arise from stand treatments such as thinning.) This is a point which even today is

often ignored, although its neglect introduces substantial

biases in volume growth computations.

Sitka Spruce and Western Hemlock Yields

Meyer (1937) carried out a similar study in spruce-hemlock 

stands in coastal Oregon and Washington and southeast

Alaska. 

In later use, some discrepancies appeared, attributed to

differences in the Alaska data versus those from Washington

and Oregon, associated difficulties with the site index

curves, and to inclusion of some stands with a high proportion of spruce. Barnes (1962) subsequently produced

revised tables from the same data, which provided separate

estimates for Alaska and for Washington-Oregon, and

excluded stands with less than 40 percent basal area in

hemlock.

Red Alder Yield

Prior to the 1960s, red alder was generally regarded as a 

weed species and was the subject of little research. It had

some limited commercial value (Johnson and others 1926)

but was of interest mostly as an undesired competitor in

conifer stands.

Worthington and others (1960) developed the first 

reasonably complete normal yield tables for red alder, in

response to expanding markets and increased interest in the

species. Subsequent developments in site evaluation and

yield estimation were reviewed by Hibbs and others (1994)

and Bluhm and Hibbs (2006).

Adjustment of Normal Yield Tables

Many existing natural stands differed from the “normal” 

stocking shown in normal yield tables, and there were a

number of attempts at adjusting the yield tables to predict

development of nonnormal stands.

Meyer (1928) described the permanent plots established in Douglas-fir up to that date, and discussed their

relationships to the new normal yield tables then in preparation (McArdle and Meyer 1930) and the observed

“approach to normality” in stocking over time. He (Meyer

1933) made a further analysis of “approach to normality” in

various measures on permanent plots and found consistent

though weak relationships, apparently tending toward values somewhat higher than those in the normal yield table. 

Johnson (1955) subsequently examined the question

with a subset of the same plots, and concluded that the 

simplest assumption for predicting future yields from the

normal yield table was that understocked stands would

make approximately the same volume growth as that 

indicated by the normal yield table.

Meyer (1930) compared various measures of stocking

in an extensive sample of typical Douglas-fir forests. He

concluded that basal area was preferable to number of trees

as a measure of stocking, and that typical forest stocking

was about 80 percent of normal yield table values. For

comparable site index, highest volumes were found on

approximately 40-percent slopes and on north and east

aspects.

In the period 1972-80, Charles Chambers and Franklin

Wilson of the Washington Department of Natural Resources

produced a series of empirical yield tables for secondgrowth stands of Douglas-fir, western hemlock, and red

alder. These were derived directly from the Department’s

inventory data (for example, Chambers 1980), without 

reference to normal yield tables.

Managed-Stand Yield Estimates

After World War II (WWII), markets for relatively small 

material developed and interest increased in active management of the large areas of second-growth stands that had

developed on previously logged lands. Some means was

needed to estimate yields to be expected under alternative

treatment regimes, not only in volume but also in size and

value of trees produced. The old normal yield tables were

clearly too inflexible to describe stand development for

75
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GENERAL TECHNICAL REPORT PNW-GTR-696

such stands or to provide a basis for selection of thinning

regimes.

Permanent-Plot Data

The earliest permanent (that is, remeasured) plot data in the 

region date from 1910. The early data were primarily from

unmanaged young-growth stands, plus some from a very

few experiments with early density control or later thinning.

After WWII, there was a great expansion in permanent-plot

work in thinning and—somewhat later—in fertilization trials and other aspects of forestry research. To facilitate consistency and comparability in such studies, Staebler and

others (1954) provided a guide to recommended computational procedures for summarizing permanent-plot data.

Early Managed-Stand Yield Estimates

Heiberg and Haddock (1955) and Warrack (1959) developed yield forecasts for managed stands based on very

small amounts of Pacific Northwest data combined with

European data and experience.

Staebler (1955a) combined McArdle and others’ (1949)

net yield estimates with mortality estimates (Staebler 1953)

derived from the permanent plots established earlier, to 

produce estimates of gross production for well-stocked

Douglas-fir stands. Staebler (1960) then used these grossyield estimates to produce estimates of yields of thinned

stands, on the basis of the then-current belief that gross

increment was independent of stocking over a considerable

range of stocking and that moderate thinning would merely

redistribute a constant increment. Although soon superseded

by subsequent work, the procedure is of interest as the first

attempt in the region at a quantitative model of development of thinned stands based on actual Pacific Northwest

data. It was a precursor of the computerized growth and

yield models that soon followed. 

Simulation Models

There was a revolution in growth and yield research in 

the period 1960–2000, and the distinction between such

research and quantitative silvicultural research became

increasingly blurred. Two factors were primarily responsible: (1) the advent of the electronic computer and its evolution into the desktop personal computer, which placed

computing power at the immediate disposal of all scientists;

and (2) the gradual accumulation of massive quantities of

growth data from remeasured plots, including data from

designed silvicultural experiments that included a range of

stand treatments. Another more recent advance has been the

introduction of electronic devices that greatly improve the

accuracy and lower the cost of height measurements.

The electronic computer made it possible to address 

the massive problems of record keeping, data storage and

retrieval, editing, summarization, and analysis involved in

working with very large data sets. By the early 1960s, these

problems had exceeded the capabilities of traditional methods of computation. The computer also made possible the

construction of simulation models representing the growth

of trees and stands and their responses to treatment. Yields

were now often estimated by numerical integration of

growth functions, providing consistent estimates of growth

rates and yields. Such models provide estimates of stand

development and physical and economic yield under a 

variety of possible management regimes. 

Simulation models have commonly been classified as

stand-average models, individual-tree distance-independent

models (which predict stand growth as the summation of

individual tree predictions without reference to tree position), and individual-tree distance-dependent models (which

make predictions for individual trees based on spatial position relative to other trees). Another common classification

is empirical vs. process models, where the first is derived

from fitting functions to observed tree or stand growth data

and the second purports to represent underlying biological

growth processes. In actuality, most existing models of

practical usefulness are “mixed” models, which incorporate

some features of both “empirical” and “process” models

(Bruce 1990). 

There is also a class of so-called “gap” models, popular

with some ecologists interested in long-term successional

trends. In general, these have not so far produced the
Silvicultural Research and the Evolution of Forest Practices in the Douglas-Fir Region

detailed stand information needed by forest managers, and

they are not discussed here.

There is an extensive literature on stand simulation

models, which we necessarily skip over very lightly. Ritchie

(1999) provided a good overall discussion of available simulators.

Possibly the first computer growth-and-yield simulation model in the Pacific Northwest was that of Newnham

and Smith (1964), although this never had wide use. The

first publicly available simulator to have any substantial use

in the U.S. portion of the Douglas-fir region was DFIT

(Bruce and others 1977), although there was some proprietary simulator development at about the same time by Jim

Lin of Crown Zellerbach Corp. and possibly by others.

In the mid-1970s, Pacific Northwest (PNW) Research

Station and Weyerhaeuser Co. undertook a joint effort to

develop yield estimates for managed stands. This was a

cooperative effort using data contributed by a number of

public and private organizations. The result was DFSIM

(Curtis and others 1981), a stand-average type simulator

that had wide use in the Douglas-fir region.

The DFSIM development effort had a number of

important offshoots. Massive quality control and consistency problems were found in much existing data. Also,

despite their quantity, the existing data were extremely

weak for young stands with early density control, and for

stands with both fertilization and thinning, repeated thinning, or extreme thinning treatments. These concerns led to

recommendations by a committee of Western Forestry and

Conservation Association for standardization of plot measurements and record formats, and to a widely used publication on research plot procedures (Curtis 1983, Curtis and

Marshall 2005). These concerns also provided motivation

for establishment of the Stand Management Cooperative in

1985 (chapter 6).

Although stand-average models are relatively simple

and work well for reasonably uniform stands predominantly

of a single species, they are not capable of representing

highly irregular stands or complex species mixtures. Therefore, most recent work has been directed at individualtree-based simulators. Currently, the most important of

these are TASS in Canada, and ORGANON and PROGNOSIS (and its FVS [Forest Vegetation Simulator] descendants) in the United States.

The PROGNOSIS model is an individual-tree 

distance-independent simulator originally developed by

Stage and his associates (Stage 1973) for the northern

Rocky Mountains. It has since been modified into many

regional variants under the name of FVS. These are now

the simulators most widely used by the Forest Service in

the West. TASS (Goudie and others 2005, Mitchell 1975)

has likewise gone through an extensive and continuing evolution, and is now the principal simulator used in British

Columbia. ORGANON (another individual-tree distanceindependent model), originally developed by Hann and his

associates for southwest Oregon, has since been modified

(Hann and others 1997) to extend its range of applicability

by including data from other parts of the region. A number

of proprietary models have also been developed. Monserud

(2003) provided an up-to-date summary.

Recent supplementary developments include LMS

(Landscape Management System) (McCarter and others

1998), which applies stand simulation projections based on

FVS or ORGANON to landscape scales, and visualization

software (McGaughey 1998).

These tree and stand simulators are not merely a means

of updating existing inventories. They also represent the

best available syntheses of existing silvicultural and biological data on stand development and response to silvicultural

treatments. 

Many current young stands differ markedly in origin

and early history from the unmanaged stands and early

plantations that supplied the data for presently available

simulators. More intensive site preparation practices,

improved nursery and planting practices, early control of

competing vegetation, and use of selected genetic stock

have produced young stands that commonly show early

growth considerably exceeding past experience on similar

sites. Thus, stand simulation is tracking a moving target as

forest practices change.

77
78

GENERAL TECHNICAL REPORT PNW-GTR-696

Model Limitations

Current models have a number of shortcomings:

• Basic data are lacking for managed Douglas-fir 

stands grown to advanced ages (more than about 

80 years), for a number of important secondary 

species, and for unconventional management 

regimes (for example, green tree retention or 

repeated thinning over extended periods). There are

few stands available older than 30 to 40 years that

developed under regimes with early and continued 

density control.

• They have very limited ability to predict early 

stages of stand development, or the development 

and effects of associated weed-tree or nontree competition (which involve measurements not customarily taken in the past).

• They do not satisfactorily incorporate the effects of

genetic improvement programs. 

• Flexibility and basic data needed to address new

questions are limited. There is much current 

interest in wildlife habitat, visual effects, and the 

role of forests in carbon fixation, which require estimates of crown cover, layered crown structure, 

understory development, and total biomass. Existing

simulators were originally developed to address 

timber management concerns, although some have

been modified to produce at least some of the 

desired information.

• They do not satisfactorily incorporate the effects of

vegetation control on juvenile growth. Recent data

show that use of large seedlings and weed control

reduce the time for trees to reach breast height by 

several years, and produce more rapid early height

growth than indicated by the widely used height 

curves of King (1966) and McArdle and others 

(1961). Changes in growth trajectories lead to productivity predictions that increase well into merchantable size ranges (Hanson 1997, Newton and

Hanson 1998).

• Changes continue in forest management objectives,

management regimes, genetic composition, underlying biological knowledge, and perhaps in climate.

Thus, no growth-and-yield prediction system can ever

be complete. Continuing evolution and modification is

to be expected.

Stand-Density Measures

Both thinning practice and construction of stand simulators 

necessarily involve some measure of stand density (“stocking” or “competition”). In ecological usage, “density” refers

to number of individuals per unit area. This definition has

limited usefulness in forestry, because trees increase in size

and area occupied over time, within wide limits. A given

number of stems has widely different meanings as an

expression of competition, depending on the stage of stand

development. Therefore, a number of other measures of

stand density have come into use.

Basal area per unit of land area has been and is a widely used measure, primarily because it is easily determined.

Considered alone, it has drawbacks similar to number,

although perhaps to a lesser degree. However, basal area (or

number) becomes meaningful in combination with site and

age, or with other measures of stage of stand development

such as average diameter or height. These are basic components of several measures that express density relative to

some standard condition, thereby more or less eliminating

the direct effect of tree size on area totals.

For many years, it was a common procedure to express

stand density as a “normality percentage,” the ratio of basal

area (or number, or volume) to the corresponding value

given by the normal yield table for the given site and age.

This required the laborious and often inaccurate determination of site index and age for the particular stand. Therefore

a number of relative density measures have been developed

that do not require site index and age. In general, these are

similar in nature and uses although differing in the particular form of expression (Curtis 1970, 1971).

The earliest of these was Reineke’s (1933) stand density index (SDI), which is based on number of trees per unit
Silvicultural Research and the Evolution of Forest Practices in the Douglas-Fir Region

area relative to quadratic mean diameter (QMD) adjusted to

a value corresponding to a QMD of 10 inches (25.4 centimeters). 

Another is Curtis RD (Curtis 1982), the ratio of basal

area to the square root of QMD. This is basically merely a

rearrangement of SDI, with a slightly different exponent of

QMD. Reineke SDI is the measure of stand density used in

the ORGANON and FVS simulators. Curtis RD is used in

DFSIM.

A third common measure is Drew and Flewelling’s

(1979) relative density, which differs from the above in that

it relates number per unit area to mean volume per tree

rather than to QMD. They prepared a rather elaborate stand

management diagram for Douglas-fir, which included a

maximum density line and one representing the onset of

mortality, as well as a lower density limit representing the

point of crown closure. The addition of curves representing

site height allowed estimation of corresponding stand 

volumes.

Long and others (1988) published a similar diagram

using QMD rather than mean tree volume as the predictor.

It is unclear whether QMD or mean volume is inherently

more meaningful, but QMD is easier to use because it does

not involve height measurements. Similar diagrams can be

and have been prepared based on any of the common stand

density measures. These are generally some combination of

QMD or mean volume, number, and basal area. There is no

great difference in practical results.

The various stand management diagrams or their

numerical equivalents provide the silviculturist with convenient guides indicating the approximate limits within

which stands should be maintained to avoid either substantial competition-related mortality or incomplete utilization

of growing space.

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CONTINUE
Silvicultural Research and the Evolution of Forest Practices in the Douglas-Fir Region

Background

General Overview

For many years, old-growth timber of the Pacific Northwest 

had great marketing advantages relative to its competitors:

large stems, narrow rings, a high proportion of clear wood

and—in the case of Douglas-fir—superior strength properties. Some of the region’s advantages in the timber trade

have been reduced, however, as the major source of wood

supply shifted from old-growth timber to young natural

stands and plantations grown on relatively short rotations.

In young-growth stands, stems (and thus logs) are smaller

in diameter, growth rings are generally wider, knots are

more abundant, and strength properties are reduced. A larger proportion of the stem is composed of juvenile wood;

this wood occupies the core of a tree (from the pith outward

for various numbers of rings) and differs from mature wood

in several basic traits—wood density (lower or higher,

depending on the species), shorter fiber length, and greater

microfibril angle. Juvenile wood generally has lower

mechanical strength, greater tendency to shrink and warp,

and lower pulp yield. Although manufacturing changes

allow utilization of smaller, younger trees for many products, the traits previously associated with old-growth trees

are still very important for other products and may command premium prices so long as mills capable of handling

logs more than 30 inches (75 centimeters) in diameter 

continue operation. The number of such large-log mills has

been declining rapidly.

Brief History of Wood Quality Research

Differences in wood properties (hence, quality) of Douglasfir were noted in an early unpublished monograph (see

footnote 3 in chapter 4) on the species by Allen in 1899.

Allen commented that lumbermen recognized two varieties

of Douglas-fir based on color of heartwood: yellow fir was

somewhat lighter, softer and easier to work than red fir.

Yellow fir trees were older (>75 years) than red fir trees

(<70 years) and generally were growing on poorer sites and

drier soils; at the time, some people believed the differences

were caused primarily by age, but Allen considered the theory inconclusive because the oldest trees tended to occur on

poorer sites. 

One of the first activities after transfer of the Bureau 

of Forestry from the U.S. Department of the Interior to the

U.S. Department of Agriculture involved the establishment

of timber-testing laboratories in the Pacific Northwest at 

the University of Oregon (Eugene) and at the University of

Washington (Seattle) about 1905–06 (Munger 1955; see 

also footnote 4 in chapter 4). Studies at the University of

Oregon ended in 1907 (see footnote 4 in chapter 4), but

work was continued for some time and eventually expanded

at the University of Washington (Munger 1955). When the

U.S. Forest Service established its Regional (then called

District Forester’s) Office in 1908 in Portland, Oregon, it

included two small sections devoted to research—Forest

Products and Silvics (Munger 1955). Wood properties of

native species, including Douglas-fir, western hemlock,

Sitka spruce, and western redcedar, were evaluated for

structural and other purposes (for example, Cline and

Knapp 1911). The Forest Products Laboratory at Madison,

Wisconsin, was founded in 1910. Despite early recognition

of the importance of both fields of scientific inquiry, it

appears that little or no overlap or collaboration occurred

between silviculture and forest products research; at the

time, forest products and wood research was concerned 

primarily with the properties and use of the older, naturallygrown timber then being harvested. And during the first

quarter of the 20th century, forest owners and managers

were concerned primarily with reestablishment or regeneration of stands after harvest, and protection from fire.

Munger’s (1911) monograph on growth and management 

of Douglas-fir, however, did point out the significance 

of markets for small material (such as mining props and

81

Chapter 10: Silvicultural Influences on Wood Quality1

1 By D.S. DeBell and R.O. Curtis.
82

GENERAL TECHNICAL REPORT PNW-GTR-696

railroad ties) to yield and value obtainable from young

stands, 30 to 70 years old. Management of young stands

was limited and generally focused on high volume (quantity) production.

Although high volume production remained the primary management consideration for many years, quality as

well as quantity of production gradually began to receive

some attention. Paul (1932), a silviculturist at the Forest

Products Laboratory in Madison, Wisconsin, published 

a thoughtful article in the Journal of Forestry titled

“Improving the Quality of Second-Growth Douglas-Fir.” 

He suggested that management of second-growth stands be

focused on three objectives: freedom from large and loose

knots, uniformity of growth rate, and production of both

dense wood for special uses and nondense wood for other

uses. To achieve these goals, Paul proposed silvicultural

practices to influence stand stocking—interplanting in poorly stocked stands to reduce knot size and enhance natural

pruning, thinnings in well-stocked stands to maintain uniformity of growth rate, and dense stocking plus longer rotations to produce dense wood. It is surprising that Paul did

not mention pruning. Pruning studies established in 1930 in

British Columbia (Schenstrom 1931) and in the mid to late

1930s in the United States (Stein 1955a, Meyer 2) appear 

to be the first attempts to study the effect of silvicultural

manipulations on wood quality. It was another 20 years

before research foresters attempted to quantify relationships

between branch or knot size and spacing or stand density in

plantations (Eversole 1955) and natural stands (Grah 1961). 

Except for a few reports from Canada (for example,

Warrack 1948), research interest in the influence of silviculture on wood quality of Douglas-fir and other Northwestern

species seems to have waned from the mid 1960s until the

early 1980s. Several factors contributed to such decline in

interest—a large portion of the wood supply continued to

come from older forests, most economic analyses done

between 1950 and 1980 indicated that there was little to be

gained by pruning most species (Fahey and Willits 1995),

and a general belief that in the future most wood-based

products would be made from reconstituted fiber (for 

example, Zivnuska 1972).

The situation began to change rapidly in the last 

quarter of the 20th century. Forest area in young managed

stands and the proportion of timber harvest from such

stands increased, and it became apparent that very wide

early spacing and very short rotations have undesirable

effects on stem characteristics and wood properties, and

therefore on timber or log values. Consumers encountered

poorer quality lumber in lumberyards and home improvement stores, and experienced the negative performance of

such wood in service. As a result, research concerning the

effects of stand management on the quality and value of

wood produced has greatly increased during the past 20

years. Considerable effort has gone into quantifying the

basic relationships (Briggs 1989, Maguire and others 1991),

estimating log and lumber values from tree characteristics

(Briggs and Fight 1992; Fight and others 1987a, 1987b,

1988), and using recently developed stand models coupled

with assumptions regarding stem and wood traits to estimate timber values produced under a variety of management regimes (Barbour and others 2003).

General Influences of Silvicultural Practices

Today it is well-accepted that the application and timing of 

several silvicultural practices can exert strong influence (of

considerable economic importance) on stem characteristics

and properties of wood produced in young managed forests:

Stand density management through initial spacing

(plantations) and thinning (natural stands and plantations)

can influence growth rates (ring widths), branch size and

persistence (hence, number, size, and quality of knots), and

the amounts and proportions of juvenile wood. Thus, wide

spacings can produce large green branches and knots,

2 Meyer, W.H. 1935. First report on Columbia thinning plots 4, 5, 6, 7, 8.

Office report. On file with: Silviculture and Forest Models Team,

Forestry Sciences Laboratory, Olympia, WA.
Silvicultural Research and the Evolution of Forest Practices in the Douglas-Fir Region

whereas breakage of dead branches during thinning can

reduce the number of knots.

Pruning (sometimes called “artificial pruning” to 

contrast it with “natural pruning” or “self-pruning”) can

increase the production of clear wood, reduce the number

and size of knots, possibly improve the form factor of the

lower log(s), and accelerate the transition from juvenile to

mature wood.

Fertilization or nutrient applications can influence

growth rate (ring width) and basic wood properties, including density of and the transition between earlywood and

latewood, and probably the size and persistence of branches

(knots).

Genetic improvement (tree breeding) can affect

many stem characteristics and growth traits such as early

growth rate, stem form, branching patterns, and basic wood

properties such as density.

Rotation length will strongly influence stem size (log

diameters), amount of clear wood, heartwood/sapwood

ratios, and the proportion of juvenile wood.

Essentially all of these practices or decisions can influence the uniformity of wood properties in logs harvested.

Uniformity in raw material supply is extremely valuable in

all manufacturing processes (Haygreen and Bowyer 1996);

this is fortunate because this opportunity to affect wood

uniformity is the major wood quality advantage that managed young-growth timber has over the old-growth resource

that fueled the timber industry and economy of the Pacific

Northwest for many years. Wood properties of the latter

were already in place and, although the outer rings had

excellent properties, substantial and abrupt changes in

growth patterns from the pith to the outer rings were 

common. 

The history of research on each of these practices as

related to wood quality is summarized in the sections that

follow.

Pruning

Old-growth Douglas-fir was highly valued for its large proportion of fine-grained clear wood, much in demand for the

plywood industry as well as for a variety of other specialized uses. Paul (1932) pointed out the influence of stocking

and stand density on size and looseness of knots in younggrowth trees. It was early recognized that, even in wellstocked stands, natural pruning in unmanaged younggrowth stands was a very slow process. Bransford and

Munger (1939), Kachin (1940), and Paul (1947) conducted

independent assessments on formation of knots, limb death,

and production of clear wood; their reports estimated that

production of substantial amounts of clear wood would

require 100 to 150 years. It was therefore natural to consider pruning as one component of future management of

young stands (fig. 32).

83

Figure 32—Early experimental pruning at Wind

River.
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GENERAL TECHNICAL REPORT PNW-GTR-696

Some small-scale trials date from the early 1930s (for

example, Schenstrom 1931). A small amount of operational

pruning was done by Civilian Conservation Corps crews on

national forest land during the 1930s, although records are

largely lacking. Pruning was one of the treatments in the

Kugel Creek thinning study (established 1937, destroyed 

by fire in 1951). There was also some small-scale pruning

done about 1940 on the Pack Experimental Forest of the

University of Washington. A pruning study was established

in 1937 (Stein 1955a) in a 28-year-old site IV stand on 

the Wind River Experimental Forest, comparing growth

effects of different degrees of crown removal. The British

Columbia Forest Service installed a combined thinning and

pruning study in stands aged 14 to 20 years (Warrack

1948), and a pruning treatment was also superimposed on

the Pacific Northwest Station’s Voight Creek thinning study

established in 1949.3

Early reports provided time and cost data (Welch

1939), healing times, and effects on stem growth. Anderson

(1951) used material from the Kugel Creek and Wind River

studies to show that healing time for pruned Douglas-fir

was strongly influenced by diameter growth rate, bark

thickness, and pruning technique as it related to stub length.

Stein (1955a) evaluated stem growth in the Wind River

study. He found that in this previously unmanaged naturally

seeded 28-year-old stand, removal of 25 percent of live

crown (length basis) produced a small increase in diameter

and height growth, but that removal of 50 percent and 75

percent of live crown substantially reduced growth. Stein

concluded that one could remove the lower third of live

crown in previously unpruned stands without reducing

growth. Staebler (1963) showed that early pruning removing one-third or more of the live crown altered bole form,

producing more nearly cylindrical stems and reduced ring

width in the lower bole.

Shaw and Staebler (1950, 1952) analyzed the effects of

different factors on profitability of pruning, and concluded

that diameter growth rate of pruned trees is crucial. Other

important factors are price premium for clear wood, cost of

pruning, and interest rate.

A general shortcoming of most early pruning research,

aside from matters of experimental design and documentation, was that most trials were established beyond the optimal age and without the stocking control needed to ensure

rapid diameter growth after pruning. Hence the potential

gains in clear wood were generally underestimated.

Research and operational interest in pruning revived 

in the 1980s based largely on product recovery evaluations

using Douglas-fir trees from a thinning/pruning study 

established in the early years (Cahill and others 1988) and

development of simulation programs that allowed estimation of expected clear material and economic returns (Fight

and others 1987a, 1987b; Mitchell 1995). The Stand

Management Cooperative has installed an extensive series

of new pruning studies in the last decade. The Mount Hood

National Forest established an elaborate replicated trial in

the early 1990s, and several other trials have been established by private owners.

The current state of knowledge about pruning Douglasfir has been summarized by Oliver and others (1986), by

O’Hara (1991), and in a later comprehensive symposium on

pruning and wood quality in northwestern conifers (Hanley

and others 1995). In sum:

• There is a large amount of published research on 

pruning Douglas-fir (and other species worldwide). 

The available information is adequate as a basis for

operational applications.

• Simulations indicate pruning should be profitable on

good sites under reasonable projections of current 

costs and price differentials.

• Pruning should be done at an early age and in conjunction with stand density control (or density 

control plus fertilization) to maintain rapid diameter

growth, provided that the species is not susceptible 

to epicormic branching as a result of the combined

3 Shaw, E.W. 1949. Pruning at the Voight Creek Experimental Forest. 6 p.

Office report. On file with: Silviculture and and Forest Models Team,

Forestry Sciences Laboratory, Olympia, WA.
Silvicultural Research and the Evolution of Forest Practices in the Douglas-Fir Region

treatments (Berntsen 1961b, DeBell and others 

2006.)

• Pruning is best done on a limited number of trees 

that are expected to reach rotation age. Greatest benefits will be obtained on moderately long rotations.

• Some information is available on results of pruning

Sitka spruce, western white pine, and red alder, but

there is virtually no information available on results 

of pruning other major Northwestern coastal conifer

species such as western hemlock and redcedar. 

Operational application of this knowledge has so far 

been relatively minor, limited mainly to integrated companies in which owners and managers of the forest also

control their own mills. A major obstacle to widespread

application appears to be uncertainty as to whether a seller

of pruned logs or stumpage will be able to command a 

premium commensurate with the increased value of the

manufactured products, in the absence of any mechanism

by which a buyer can be sure of pruning history and 

standards.

Initial Spacing and Thinning

Although Paul (1932) had identified opportunities to 

influence three aspects of wood quality (knots, growth rate,

and wood density) by regulating stocking or stand density

throughout the rotation, for the next two decades, research

on relations between wood quality and stand management

was limited primarily to the studies of branch mortality,

natural pruning, and artificial pruning as discussed in the

previous section. No one seems to have measured and

reported the effects of stocking on branch (or knot) size 

or branch mortality in Douglas-fir until Eversole (1955)

reported results from 27-year-old trees in a research plantation of various spacings. He showed that mean size of the

largest limbs in whorls below breast height increased from

0.36 to 0.73 inches (0.91 to 1.85 centimeters) and height to

live crown decreased from 19.5 to 6.7 feet (5.9 to 2.0

meters) as square spacing increased from 4 to 12 feet (1.2

to 3.7 meters). A few years later, Grah (1961) conducted

work in natural, 20- to 40-year-old Douglas-fir stands on

the relation of average spacing to knot diameter. Grah’s 

linear regression may represent the first attempt to quantify

and develop a predictive relationship between a silvicultural

attribute (stand density) and a wood quality trait in

Douglas-fir.

During the past two decades, effects of spacing on stem

form, branch persistence and height to live crown as well as

knot size have been investigated for Douglas-fir (Robbins

2000, Smith and Reukema 1986) and other species such as

western hemlock and redcedar (DeBell and Gartner 1997,

DeBell and others 1994a). Wider spacings increased stem

taper, branch persistence, and knot size, but height to live

crown was reduced. Studies in intermediate-aged stands

specific to effects of thinning on wood quality are limited.

Given that thinning generally tends to maintain or increase

radial growth rate in the remaining trees, it appears to have

little or mixed effects on average wood density of some

species (for example, Douglas-fir, Briggs and Smith 1986)

and reduce it somewhat in others (for example, western

hemlock, DeBell and others 1994b, 2004). Regardless of

the specific effects of maintained radial growth rate on 

density of subsequent wood, the more uniform growth rate

and wood density from pith to bark is probably beneficial

for most applications.

Fertilizer Application

The primary objective in fertilizing Douglas-fir stands is to 

enhance tree and stand volume growth. Soon after research

trials demonstrated good growth response of Douglas-fir

stands to added nitrogen, researchers at University of

Washington (Erickson and Lambert 1958) began to assess

effects of fertilizer on some wood properties. 

As fertilization became operational in the late 1960s

and 1970s, basic wood properties were assessed in some

fertilized young Douglas-fir trees (for example, Megraw

and Nearn 1972, Siddiqui and others 1972). Results indicated that whole ring density was slightly reduced, more so

in the latewood than earlywood component, thus increasing

uniformity throughout the ring. Work on fertilizer-wood

quality relationships has not been extensive, and most

85
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GENERAL TECHNICAL REPORT PNW-GTR-696

hypotheses about the effects of fertilizer on other aspects 

of wood quality have been based on how increased growth

rate, increased foliar retention, and longer branch persistence might increase size of the juvenile core and number

and size of knots. Cahill and Briggs (1992) provided a comprehensive review of fertilization effects on wood properties and tree value, including an analysis of potential effects

on specific wood and fiber products.

Genetic Improvement

Perhaps the earliest work related to wood quality and forest 

genetics of Douglas-fir occurred when Munger and others

collected seed from mother trees for the 1912 heritability

study (chapter 7) and diagrammed the form of each tree

stem (Munger and Morris 1936). Although the outplanting

trial established from this collection represents one of the

oldest forest genetic trials in the world, there was little followup on wood quality traits, probably because Douglas-fir

inherently has superior stem and wood characteristics. But

as tree improvement or tree breeding programs developed

in other regions, particularly in areas where pulp and paper

dominated the industry, wood quality became an important

consideration (Zobel 1961a, 1961b). Soon thereafter

McKimmy (1966) collected increment cores from trees in

the above-mentioned 1912 Douglas-fir heritability study

and evaluated their specific gravity, presumably the first

attempt in the Pacific Northwest to examine the tie between

genetics and a specific wood property. McKimmy found

that trees from different sources differed significantly in

specific gravity, but differences were even greater among

the four outplanting locations.

During the 1960s, interest developed in abnormal stem

forms (forking, sinuosity, and ramicorn branching) sometimes observed in rapidly growing Douglas-fir plantations

(Campbell 1965), but it received little attention in genetics

research until the 1980s (Adams and Howe 1985). Recent

work demonstrated that forking, sinuosity, and ramicorn

branching are subject to genetic improvement (Schermann

and others 1997). Also in the 1980s and continuing to the

present, research increased on the genetic influences on

wood density (specific gravity) and its components, including correlations of juvenile wood properties with those 

at later ages (McKimmy and Campbell 1982, VargasHernandez and Adams 1992). Although the stem form traits

and wood density are heritable, they are considered of secondary importance to volume and adaptability in current

Douglas-fir breeding programs (Howe and others 2005). 

Rotation Age

Tree and stand age have direct and indirect influences on 

wood quality: stem size and the length of branch-free bole

increase, whereas the proportion of juvenile core wood, 

sapwood/heartwood ratio, and ring width decrease as stands

become older.

The first scientific report related to age effects on wood

quality is probably Allen’s report on yellow vs. red fir in

1899 (footnote 3 in chapter 4). The amount of heartwood

was recognized as important in western redcedar, where its

resistance to decay was highly valued for outdoor applications. Various notes on self-pruning followed Paul’s (1932)

paper, which revealed that little clear wood is formed during the first 100 years of tree life. As the concept and properties of juvenile (or core) wood became more widely

recognized (Wellwood and Smith 1962, Zobel 1961b), the

negative properties associated with young rapidly-grown

trees became apparent (Jozsa and others 1989). Juvenile

wood usually comprises the first 10 to 20 rings outward

from the pith (Di Lucca 1989). Compared to later “mature”

wood, juvenile wood tends to have lower specific gravity,

greater tendency to shrink and warp, lower mechanical

strength, and lower pulp yield (Senft and others 1985). It is

therefore less desirable for many uses. The amount of heartwood is important in some species, such as western redcedar where its resistance to decay is highly valued for

outdoor applications.

Until recently, large trees were desirable for reasons

beyond specific wood characteristics; harvest and hauling

costs were lower for large trees than for small ones and

manufacturing costs were reduced for many wood products,

in part because recovery was higher. Recent changes in mill
Silvicultural Research and the Evolution of Forest Practices in the Douglas-Fir Region

technology to handle small logs more efficiently and trends

toward use of engineered wood products, however, have

reduced or eliminated such advantages. At present, large

trees may be difficult to market (Barbour and others 2002)

and may actually incur a penalty of 25 percent or more

(Mason 2002).

Simulation Estimates of the Effects of 

Silviculture on Wood Quality 

In recent years, simulation techniques have been used to 

estimate the effects of management on the various factors

of wood quality and value. In general, these techniques

“grow” trees with individual tree simulation programs such

as ORGANON and TASS that can predict quality-related

values such as taper, crown dimensions, branch size, and

juvenile wood core. These predictions can be combined

with bucking and sawing simulators to generate estimates

of product out-turn and value. Examples are TREEVAL

(Briggs 1989, Briggs and Fight 1992), SYLVER (Mitchell

and others 1989), and ORGANON + TREEVAL (Maguire

and others 1991). Simulations have shown that regimes that

produce the largest trees or the highest volumes are not necessarily those that produce highest value. Value criteria can

lead to management decisions considerably different (higher planting density, longer rotation) from those made with

volume as the primary criterion.

87
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Silvicultural Research and the Evolution of Forest Practices in the Douglas-Fir Region

The preceding discussions have been concerned primarily

with Douglas-fir research. In this section we summarize the

considerably shorter history of silvicultural research on the

principal associated species.

Western Hemlock

After Douglas-fir, western hemlock is the most important 

species in terms of volume and area occupied. It occurs

throughout most of the Douglas-fir region and is the climax

species in most of the region—hence the designation of

much of the region as the western hemlock zone. The

species is most abundant and reaches its best development

in the high rainfall areas along the Pacific coast (where it is

associated with Sitka spruce) and at mid elevations in the

western Cascades.

In the early years, hemlock was regarded as a lowvalue species with limited markets, influenced in part by

the poor reputation of eastern hemlock and by the high

defect common in old-growth western hemlock. Attitudes

changed rapidly after World War II (WWII) as the combined result of depletion of timber supplies, expansion of

the pulp and paper industry, increased use of hemlock in

construction, and an expanding Asian market. However,

prices for hemlock have historically been substantially

lower than for Douglas-fir. 

Prior to WWII, relatively little research was devoted 

to hemlock. Allen (1902) published a monograph on the

species, summarizing available knowledge on the silvical

characteristics of the species, its wood properties, and its

potential for management. Watson and Billingslea (1914)

published observational data on hemlock seed production,

seed dispersal by wind, and the relationships between

seedbed conditions, shading, and early growth of seedlings.

It was early realized that hemlock can become established

and can survive for long periods in dense shade, but good

growth requires at least partial overhead light. Isaac (1930)

measured wind dispersal of hemlock seed, along with that

of Douglas-fir. Meyer (1937) prepared normal yield tables

for mixed spruce-hemlock stands in Washington, Oregon,

and Alaska. These were later reworked by Barnes (1962).

In 1935, twelve 0.4-hectare (1.0-acre) permanent plots

were established in 83-year-old even-aged spruce-hemlock

at the Cascade Head Experimental Forest. Briegleb (1940)

reported results of the first six growing seasons. Fujimori

(1971) examined biomass production on these plots and

concluded that the values obtained were among the highest

in the world. Smith and others (1984) gave a much more

complete summary of 33 years of development. Results

showed extremely high volumes and growth rates, with

average net mean annual increment (MAI) of 17.6 cubic

meters per hectare per year (252 cubic feet per acre per

year) at age 83 and 16.5 cubic meters per hectare per year

(236 cubic feet per acre per year) at age 116.

After WWII, there was a marked expansion of research

on hemlock, both in the United States and in British

Columbia. A commercial thinning trial established in 1952

in a 50-year-old stand at the Hemlock Experimental Forest

showed a slight gain in volume production (mostly because

of salvage of mortality) and increased diameter growth

(Hilt and others 1977). Variation in initial stand conditions,

departures from the original design, and 1962 storm damage precluded sensitive comparisons, and the experiment

was abandoned. Graham and others (1985) reported results

of light thinning in a 100-year-old stand at Cascade Head,

and a number of other more-or-less similar hemlock thinning trials were established by other organizations in the

1950s and 1960s (for example, Omule 1988b). Results were

generally similar, with some reduction in windfall and other

mortality but little gain in overall production. 

Several studies of plantation spacing or precommercial

thinning were established in the same period. Thus, the

University of British Columbia spacing trials established in

the 1950s at Haney, British Columbia (Reukema and Smith

1987), included hemlock. Precommercial thinning trials

established at Cascade Head in 1963 and at Clallam Bay in

89

Chapter 11: Silviculture of Associated Species1

1 By R.O. Curtis and D.S. DeBell.
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GENERAL TECHNICAL REPORT PNW-GTR-696

1971 showed striking response and very high growth rates

(Hoyer and Swanzey 1986). 

Shelterwood cuts have resulted in good natural regeneration (Williamson and Ruth 1976) and are a viable alternative to the prevailing practice of clearcutting, although

growth of regeneration in the trials cited was inversely

related to amount of overstory retained (Jaeck and others

1984).

Recent problems with Swiss needle cast on Douglas-fir

in the Oregon coastal zone have reduced the formerly common practice of planting pure Douglas-fir after clearcutting,

in favor of hemlock or mixed-species plantings.

Comprehensive summaries of past research and the

state of knowledge as of the date of publication include

Ruth and Harris (1979), Atkinson and Zasoski (1976), and

Burns and Honkala (1990). We will not attempt to list here

the many contributors, but only the major points that have

been established by research as discussed in the above references.

• On suitable sites, hemlock volume production can

exceed that of Douglas-fir.

• Hemlock is often abundant in the understory of 

older stands and advance regeneration frequently 

provides a hemlock component in areas planted 

to Douglas-fir.

• Artificial regeneration techniques are available. 

• Hemlock often reproduces abundantly from natural

seeding, but reproduction is often patchy and sometimes excessively dense, so precommercial thinning 

is often needed. 

• Shelterwood regeneration has been successful but 

has not been widely used. The most common regeneration method in the past has been clearcutting, 

with or without slash burning, and either natural or 

artificial regeneration. 

• As in other species, commercial thinning increases

diameter growth but has no great effect on total 

volume production. 

• A number of health problems affect management 

of hemlock: (1) hemlock is very susceptible to butt 

rots that enter through logging injuries; (2) it is 

susceptible to root rots, particularly laminated root 

rot (Phellinus root disease), similarly to Douglasfir; (3) cut surfaces of stumps are often infected by

spores of annosus root disease, and treatment of 

stumps has been recommended although not widely

practiced; (4) dwarf mistletoe is common in older 

hemlock stands; (5) and hemlock is less windfirm 

than Douglas-fir. 

• Dwarf mistletoe and susceptibility to butt rots and 

to windfall make selection systems—which would 

otherwise be well suited to this shade-tolerant 

species— questionable. The butt rot threat has 

caused some to question the merits of commercial 

thinning in hemlock stands.

• Hemlock has not shown consistent response to 

nitrogen fertilization.

Western Redcedar

Western redcedar is a high-value species with unique 

wood properties. Although it occurs throughout most of the

Douglas-fir region, it is most abundant and reaches its best

development in the high-rainfall areas along the northern

Pacific coast and on the lower slopes of the western

Cascades. Its abundance has decreased considerably since

initial Euro-American settlement, primarily because of

wildfire and the management regime of clearcut, burn, and

plant Douglas-fir that prevailed until recently.

Despite its high value, there has been relatively little

silvicultural experimentation with redcedar. This lack of

interest probably arose from the common perception that

redcedar is a relatively slow-growing species, compared to

Douglas-fir and hemlock. This perception may stem from

the fact that redcedar, as a shade-tolerant species and one

that often has slower height growth in early life than its

associates, commonly develops in a subordinate position.

Most available information has been derived from observation of existing trees and stands (beginning with 

Jackson and Knapp 1914), plus empirical trials of seeding and planting techniques analogous to those used with

other species. Manipulative experiments are few. The
Silvicultural Research and the Evolution of Forest Practices in the Douglas-Fir Region

species has received less attention in the United States than

in Canada, where it makes up a considerably larger proportion of the resource. 

Pure redcedar stands of natural origin are rare. Nystrom

and others (1984) located four fully stocked stands that had

originated by natural seeding on areas cut about 1920. They

examined patterns of height, diameter, and volume growth

among crown classes and found stand volume production

comparable to that of Douglas-fir on similar sites. Trees in

these uniform well-stocked stands had excellent form, small

limbs, and were free of the basal fluting common in redcedar grown in the open or in sparsely stocked stands.

Oliver and others (1994) reviewed the available information and suggested that redcedar grown in fairly dense

pure stands (or possibly mixed redcedar-hemlock stands)

could be expected to have good stem form, high yields, and

reduced incidence of the large lower branches and basal

fluting common in trees developing in an understory position. Kurucz (1978) developed site index curves from stem

analyses of selected trees growing in mixed-species stands.

There are no North American yield tables for the species.

Several plantation spacing trials have been established

in recent years:

• The University of British Columbia spacing trials 

previously referred to (Reukema and Smith 1987)

included fixed-area plots of redcedar and one 

Nelder plot with redcedar in addition to hemlock 

and Douglas-fir. At age 25 on this very good site, 

average trees of Douglas-fir were larger than the 

hemlock, which in turn were larger than the redcedar. Comparisons were somewhat obscured by 

damage, particularly browsing of the redcedar.

• A large spacing trial established at the Wind River

Experimental Forest in 1982 included one block 

planted to redcedar. Results have not been reported

to date, but the plantation is known to have suffered

heavily from elk browsing.

• The Washington Department of Natural Resources

established a redcedar spacing trial on the western

Olympia Peninsula in 1984. Spacings were 4, 8, 

and 16 feet (1.2, 2.4, and 4.9 meters). In 2001, there

were large differences in tree diameters among spacings, but the large trees in the wide-spacing plots 

had been severely damaged by bears.

A well-replicated study installed in 1980 in a 15- to 

20-year-old dense poor-site stand on the Olympic Peninsula

compared various combinations of precommercial thinning

and fertilization (Harrington and Wierman 1990). Five-year

results showed very strong response to fertilization and to

fertilization combined with thinning, but limited response 

to thinning only.

Planting of redcedar has increased in recent years. It 

is a preferred species for use on areas heavily impacted by

Phellinus root rot, because of its tolerance of root disease.

There is also a considerable amount of planting as a secondary component of Douglas-fir-redcedar mixtures, motivated in part by a desire to ensure against root disease, and

in part by biodiversity and wildlife concerns. Browsing by

deer and elk remain serious problems, and mixed-species

plantations are not easily established (Stein 1997).

The principal summary publications are Minore (1983,

1990) and Smith (1987). We will simply list the main points

that have been established in reference to silviculture:

• Redcedar is better adapted to imperfectly drained 

soils than its coniferous associates. 

• Redcedar foliage has high concentrations of calcium

and may be important in nutrient cycling.

• Redcedar is very susceptible to fire and logging 

injury.

• Redcedar height growth trends differ from Douglasfir and hemlock; Douglas-fir commonly overtops 

redcedar established at the same time.

• European plantation data indicate high potential 

yields compared to other species; high basal areas 

tend to offset somewhat lesser height growth.

• Seed production is usually abundant.

• Effective nursery and planting techniques are 

available.

• Redcedar is resistant to or tolerant of the coastal 

strain of Phellinus root disease.

• Redcedar is a preferred browse species for deer 

and elk.

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GENERAL TECHNICAL REPORT PNW-GTR-696

High-Elevation True Fir–Hemlock

The forests above about 2,500 feet (800 meters) in the 

northern Cascades and Olympics and above about 3,500

feet (1100 meters) in the southern Cascades are composed

of various mixtures of Pacific silver fir, noble fir, western

hemlock, mountain hemlock (upper elevations), Douglas-fir

(lower elevations), and various minor species, collectively

referred to as true fir-hemlock. There was little active management of these forests until about 1960. Research has

been limited and largely observational in nature; there have

been few manipulative experiments.

Much of the silver fir zone and some lower portions of

the mountain hemlock zone are quite productive (Franklin

and Dyrness 1973). Although we have no U.S. yield tables,

it is clear from observation and from European yield information that true fir stands can develop very high volumes.

Noble fir in particular is a very impressive species

(Franklin 1964a, 1964b) and is widely planted. Pacific 

silver fir often develops abundant advance regeneration; 

its behavior resembles that of the silver fir important in

Europe. The true firs characteristically have slow early

height development followed by a period of acceleration,

with rapid growth continuing to advanced ages. 

Hanzlik (1925) carried out a study that is probably the

first study of noble fir growth, on Larch Mountain east of

Portland, Oregon. This study brought out two points that

have been confirmed by later work: (1) compared to both

Douglas-fir and western hemlock, noble fir makes relatively

slow growth in the early years; but (2) in later years it

maintains rapid growth to advanced ages, exceeding (on

this site) both Douglas-fir and western hemlock in growth

rate. 

Franklin’s (1962) literature review showed that up to

about 1960, the existing information on true firs was concerned principally with species distribution, botanical characteristics, and seeding habits. There was little information

on applicable silvicultural methods.

Herman and others (1978) and Hoyer and Herman

(1989) developed site curves from stem analyses of selected

dominant noble fir and silver fir trees in old natural stands.

Murray and others (1991) found that noble fir and silver fir

established on clearcuts were making substantially faster

height growth than indicated by stem analyses of old trees.

Preliminary site curves exist for mountain hemlock.

Managers have usually assumed that western hemlock 

will behave much as it does on the poorer sites at lower 

elevations. 

The extensive ecology program of the Pacific

Northwest Region of the USDA Forest Service developed

an elaborate plant association classification that is useful in

matching species and management practices to site (for

example, Brockway and others 1983).

Early management attempts using the clearcut, burn,

and plant (often Douglas-fir) practices used in the lowlands

frequently failed (Franklin 1964a). The slow development

and frequent failure of regeneration (often because of late

spring frosts) on harvested areas was a major concern in the

1960 and 1970s, but with improved nursery and planting

practices, less burning, better matching of species to site,

and consequent higher survival, this was replaced with concern about the overstocking that frequently developed. In

the 1980s, the Forest Service undertook an extensive precommercial thinning program in true fir-hemlock. Practices

were based on experience with Douglas-fir because there

were no quantitative stocking standards based specifically

on experience with young true fir-hemlock stands.

Over the years 1987–94, an extensive series of spacing

trials was established on national forest lands (fig. 33). In

time, these trials should produce a basis for estimating

yields of young true fir-hemlock stands under a range of

stocking levels (Curtis and others 2000). The high values of

true fir boughs for Christmas decorations can often cover

the costs of precommercial thinning.

The principal available summaries of existing silvicultural information are Oliver and Kenady (1981) and Burns

and Honkala 1990.

Prior to Euro-American settlement there were extensive

areas of open land in the northern Cascades, maintained in

part by burning by Natives. These lands were highly valued

by the Natives for huckleberry production, and are now an
Silvicultural Research and the Evolution of Forest Practices in the Douglas-Fir Region

important recreational resource. Concern over encroachment of forest on these open areas led to a small amount of

work on huckleberry management (Minore 1972, Minore

and Dubrasich 1978). 

Currently, there is only limited formal research on true

fir-hemlock in progress in the region. There is more emphasis on silver fir and mountain hemlock research and management in British Columbia, where the species occur at

lower elevations and make up a greater proportion of the

commercial forest land base.

Red Alder

Interest in silviculture of northwestern hardwoods is a fairly

recent development. Examples are red alder, Oregon white

oak, and poplars.

Red Alder as a Timber Species

Red alder is the most abundant and economically most 

important northwestern hardwood. It grows best on moist

sites at low elevations, although it occurs on other sites.

Alder is an intolerant and relatively short-lived pioneer

species that reproduces abundantly on bare mineral soil

exposed to direct sunlight. The large clearcuts and fires

common prior to WWII are thought to have considerably

increased the amount of alder, compared to presettlement

conditions. Conversely, fire protection, the widespread

planting of conifers on clearcuts, and conscious efforts in

recent decades to convert alder and mixed-species stands to

conifers have considerably reduced the area in alder and

produced a shortage of young stands. 

Prior to WWII, alder was regarded as a low-value weed

species. Attitudes began to change after WWII. Causes

were (1) increased use of alder for pulp and particle board,

(2) increased use of alder for furniture and similar uses with

correspondingly higher log prices, (3) recognition that

alder’s nitrogen-fixing ability had an important role in soil

fertility, (4) recognition that rapid juvenile growth and early

maturity made alder suitable for management on much

shorter rotations than those appropriate for conifers, and (5)

interest in the 1980s in short-rotation woody crops as a possible energy source. These factors partially offset the higher

volume and value production obtainable with conifers.

Interest in the possibilities of alder led to the establishment

of the Hardwood Silviculture Cooperative at Oregon State

University in 1987.

Two early publications on alder were Johnson (1917)

and Johnson and others (1926). The latter was concerned

mainly with utilization, but also included some discussion

of silvical characteristics, yields, and management possibilities.

Little further work was done with the species until the

1950s. Beginning around 1960, an increasing number of

publications appeared, and today there is a growing literature on alder biology and management, a considerable part

of which is based on formal experimentation. Major summary publications are Worthington and others 1962, Trappe

and others 1968, Briggs and others 1978, Heebner and

Bergener 1983, Hibbs and others 1994, and Deal and

Harrington 2006. DeBell (2006) gave an overall review of

the history of red alder research and changing attitudes. The

various papers included in Deal and Harrington (2006)

showed that production in managed alder plantations considerably exceeds that in natural stands, and suggested that

93

Figure 33—A precommercially thinned plot in a noble fir spacing

experiment. Noble fir has been widely planted at higher elevations. Concern over some early establishment failures was later

replaced with concern about overstocking in many areas. 
94

GENERAL TECHNICAL REPORT PNW-GTR-696

financial returns can be competitive with those from

conifers.

To summarize the main points established by research:

• Compared to its conifer associates, alder makes 

much more rapid juvenile height growth but falls

behind in later years. Consequently, it offers severe 

and often lethal competition to intermingled 

conifers in early life.

• Volume production per year on appropriate rotations is greater for conifers than for alder on most 

sites, but the rapid juvenile growth and correspondingly shorter rotations for alder reduce the financial

advantage of conifers. The current weakness of 

volume and value yield estimates and of volume 

and taper functions specifically applicable to intensively managed young alder stands makes financial

comparisons somewhat uncertain.

• Alder may have an important role in management 

of nitrogen (N)-deficient soils because of its Nfixing capability, albeit with recognition of its 

competitive potential.

• Early thinning trials were unsatisfactory, probably

because they were not begun until after the period 

of rapid height growth. Thinning should be done 

early.

• Plantations with suitable density control can provide

considerable increases over natural stands in volume,

height growth, and stem quality. The regular spacing

achievable by planting or thinning minimizes the

lean and sweep common in unmanaged stands.

• Normal yield tables have been developed for unmanaged stands but are probably not applicable to stands

with early density control, and may overestimate 

yields of older unmanaged stands.

• Site curves and alternative methods of evaluating 

site quality have been developed.

• Stocking guides for plantations and pure natural 

stands have been suggested.

• Suitable nursery and planting practices are available.

• Several plantation spacing trials exist, including 

both pure and mixed species.

• Alder’s immunity to Phellinus root disease makes 

it suitable for planting on root-disease-infested 

areas. 

Interest in alder management has been markedly stimulated by recent development of export markets and increasing log prices.

Red Alder as a SoiI Improver

Johnson (1917) produced the first published reference on 

the role of red alder in the Northwest as a soil-improving

species that actively fixes N. He observed apparent relationships between presence of red alder and increased soil fertility, which he interpreted as caused by alder, and referred

to an analysis by the Forest Products Laboratory showing

that the root nodules on alder contain N-fixing bacteria

analogous to those in legumes.

Tarrant and others (1951) compared litter fall and 

nutrient composition of foliage of the major Northwestern

species. They found that alder litter had much higher N

content than other species, and suggested that it had value

as a soil conditioner.

A severely burned site on the Wind River Experimental Forest was operationally planted to Douglas-fir in

1929. A strip within the plantation was interplanted with red

alder in 1933. Tarrant (1961) and Tarrant and Miller (1963)

found striking differences in stand growth and soil conditions between the Douglas-fir-alder mixture and the adjacent pure Douglas-fir plantation. The mixed planting had

greater total yield, markedly better development of the

Douglas-fir, greater soil organic matter content, lower bulk

density, and greater N content. Miller and Murray (1978)

reported subsequent development of this plantation and

findings in other mixed stands, and suggested possible

regimes to take advantage of alder N-fixation. The Wind

River study had some unique features: (1) the alder was

planted 4 years after the Douglas-fir, (2) there was some

freeze damage to the alder, and (3) the site was very deficient in N because of previous severe burns. These findings

stimulated research interest in alder.
Silvicultural Research and the Evolution of Forest Practices in the Douglas-Fir Region

Franklin and others (1968) and Cole and others (1978)

compared mineral cycling and N accumulation in young red

alder, Douglas-fir, and mixed stands. Soil organic matter

and N accumulation were much greater in the alder, and

greater in the mixed, compared to the pure Douglas-fir

stands. Binkley and others (1994) reviewed the existing

information and concluded that average N accumulation

rates in pure red alder were generally in the range of 100 

to 200 kilograms per hectare per year (88 to 178 pounds per

acre per year). Newton and others (1968) measured N accumulations in scarified soils approaching 300 kilograms per

hectare per year (267 pounds per acre per year), some of

the highest accretion rates reported. They also warned of

differences in growth habits of alder vs. conifers that lead

to incompatibility in mixed stands.

A number of studies have attempted to evaluate mixtures of alder and conifers, as an alternative to chemical fertilizers. The primary problem encountered is that of keeping

early alder competition with the conifers at an acceptable

level while maintaining sufficient vigorous alder to provide

meaningful amounts of N. Experiments are still ongoing,

but it appears that the most feasible approach is either crop

rotation (facilitated by the early maturity of alder) or groupwise plantings.

Research has made clear that alder substantially benefits soil productivity where N is deficient, and that Nfixation by an alder component can be an asset in stand

management. However, similar benefits can also be

obtained by direct application of N fertilizer, and the comparative costs are uncertain. Alder necessarily occupies

growing space that could otherwise be used for higher

yielding conifers. Potential soil benefits from alder have not

generally been a primary consideration by managers who

have direct fertilization available as an alternative.

Additional work on the basic biology of N fixation by

red alder and on alder’s effects on soils and on ecosystem

productivity is discussed in symposium volumes edited by

Trappe and others (1968), Briggs and others (1978), Hibbs

and others (1994), and Deal and Harrington (2006).

Oregon White Oak

Oregon white oak (Quercus garryana Dougl. ex Hook), 

also known as Garry oak, is the only oak native to British

Columbia, Washington, and northern Oregon. Other oaks

are present in southern Oregon and northern California and

may be associated. On most sites, Oregon white oak does

not have the growth rates or maximum height potential of

associated conifers and is thus overtopped and then succeeded by conifers. It is only considered to be climax on

very dry sites. 

At the time of initial Euro-American settlement, there

were extensive areas of oak woodland and oak savannah

and prairie in the Puget Sound region and in the Willamette

Valley. These were maintained primarily by frequent burning by Natives, although natural fires were also important.

Native Americans set fires to facilitate hunting, to favor

food plants associated with the open environments (especially camas (Camassia quamash (Pursh) Greene), whose

bulbs were an important food source), and to facilitate 

collection of other foods such as acorns and hazelnuts

(Boyd 1999).

The areas of oak woodlands, oak savannas, and associated prairies have drastically declined. Reasons for this

decline are (1) conversion to agriculture or urban development, (2) intentional conversion to conifers, and (3) invasion by conifers (primarily Douglas-fir) following fire

exclusion. In recent years, interest has developed in the 

cultural and biological legacies associated with these areas.

Although white oak is of negligible importance as a timber

species, there are many plant and animal communities associated with these open habitats that are not found in conifer

forests and several species considered to be threatened or at

risk, including the western gray squirrel, several birds, the

Mazama gopher, and various invertebrates. Current interests

are in managing oak stands for wildlife habitat, biodiversity,

or to keep or create open areas in the landscape.

Stein (1990b) summarized the then-available information on biology and management of Oregon white oak.

Harrington and Kallas (2002) provided a more recent 

95
96

GENERAL TECHNICAL REPORT PNW-GTR-696

bibliography. Larsen and Morgan (1998) summarized information on the wildlife habitat values of oak and made management recommendations for maintenance and restoration

of oak stands, as did Vesely and Tucker (2005) and

Campbell (2003).

Most oak habitats are on private land, but some public

agencies such as Department of Defense (Fort Lewis

Military Reservation near Tacoma, Washington), Bureau of

Land Management, U.S. Fish and Wildlife Service Refuges,

Natural Resource Conservation Service, Washington

Department of Fish and Wildlife, Washington Department

of Natural Resources, and Oregon Department of Forestry

have programs to preserve, restore, manage, or protect areas

of oak and prairie. Nongovernmental agencies such as The

Nature Conservancy, the American Bird Conservancy, the

Oregon Oak Communities Working Group, and the Garry

Oak Ecosystems Recovery Team are also promoting conservation activities. Researchers associated with the USDA

Forest Service Pacific Northwest Research Station,

University of Washington, and Oregon State University 

are studying various aspects of oak and prairie biology and

management (Peter and Harrington 2002, Regan and Agee

2004, Thysell and Carey 2001, Tveten and Fonda 1999). 

There are three key aspects to managing these systems:

(1) releasing oaks from the overtopping conifers (and preventing future overtopping), (2) managing the understory 

to control species composition and development, and (3)

establishing oaks and related species in areas where they

are currently not present. 

Many oak savannas or low-density woodlands have

been invaded by conifers (fig. 34). Action to remove the

conifers is time critical because the overtopped oaks and

other vegetation are often of poor vigor and will not survive

much longer. Because conifers will grow well on many of

these sites, followup treatments will be needed to prevent

future overtopping. Deciding to manage for oaks or open

areas is a long-term commitment. 

Currently, there are a number of research studies, management trials, and regular forest management activities

aimed at improving the condition of the oak and prairie 

systems. Prescribed burning is an important tool in managing oak (Agee 1996) and is being used by some agencies to

control understory conifers (as well as exotic weeds such 

as Scotch broom and Himalayan blackberry). However, the

danger, cost, and smoke nuisance associated with burning

make this a treatment that can only be used in limited areas.

Where burning is not feasible, mechanical removal or herbicide treatment can be substituted.

Black Cottonwood and Hybrid Poplars

Several small-scale but successful industrial cottonwood 

plantings were made along the Willamette and Skagit

Rivers by paper companies (fig. 35), the earliest being a 

60-acre plantation established in 1893 by Crown Willamette

Pulp and Paper Co., the forerunner of Crown Zellerbach

Corp. (Brandstrom 1957). However, these remained very

small-scale efforts. Major interest in Populus is a recent

development in the region.

Development of fast-growing Populus hybrids had

been underway for many years in Europe and the Eastern

United States. In 1939, two 1.0-acre (0.4-hectare) hybrid

poplar plantations were established at the Cascade Head

Figure 34—Fire exclusion has led to widespread conifer encroachment and overtopping of remaining Oregon white oaks. 
Silvicultural Research and the Evolution of Forest Practices in the Douglas-Fir Region

Experimental Forest and on Lady Island, near Camas,

Washington (Silen 1947).

The energy crisis of the 1970s produced an interest in

short-rotation plantations as a possible source of biomass for

energy production. Department of Energy funding stimulated work with red alder and hybrid poplars in the Northwest,

with projects at University of Washington, Washington

State University, Seattle City Light, and the Olympia

Forestry Sciences Laboratory. Clones and cultural information developed in these projects led to industrial investments in growing Populus for wood fiber.

With the passing of the immediate energy crisis, interest shifted from biomass energy to fiber production and—

recently—to solid wood products. In the 1990s,

considerable acreages of Populus plantations were established by industrial owners, much of it on former agricultural land (Hibbs and others 2004). Their economic

viability is unclear at present.

Recent comprehensive summaries of the subject are

Stettler and others (1996) and Dickmann and others (2001).

97

Figure 35—T.T. Munger in 1914, in an early cottonwood plantation.
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Silvicultural Research and the Evolution of Forest Practices in the Douglas-Fir Region

Over much of the history of northwestern forestry research,

the primary, though not exclusive, interest was in timber

production. This has changed markedly in recent decades.

In this chapter, we briefly discuss some of the social

changes and accompanying changes in public attitudes that

have taken place in the Pacific Northwest and that have led

to major changes in forest management objectives. We then

discuss changes in research direction aimed at supporting

current management goals.

Social Change and Silviculture 

Many concerns that are today referred to as “environmental” influenced policy from the earliest days of North

American forestry. Thus, the writings of Marsh (1864) and

Hough (1873) and others warned of the need to do something about the state of the Nation’s forests, and provided

the stimulus for early legislation and establishment of the

forest reserves (which became the national forests). The

Organic Act of 1897 stated as objectives the preservation of

the forests, improvement of water flows, and provision of a

perpetual supply of timber. Activities and emphasis changed

over time with changes in economic and political conditions and the development of transportation. Early efforts

included rehabilitation of burns, fire protection, and exploration of regeneration methods after wildfire or harvest.

Establishment of wilderness areas and research natural

areas in the national forests began in the 1920s. 

The selective timber management episode (Kirkland

and Brandstrom 1936, Curtis 1998) (chapter 5) was an

early—though unsuccessful—effort at a silvicultural alternative to large-scale clearcutting. The subsequent adoption

of staggered settings (dispersed moderate-size clearcuts

with intervening timber retained as a seed source) was an

improvement over previous practices from the environmental as well as the timber standpoint, beneficial to populations of deer and elk and some other species. Efforts were

directed toward control of insects and diseases, enhancement of tree and stand growth, and improvement of wildlife

habitat.

Although timber production had been one of several

public land management objectives from the beginning, 

its importance increased greatly during the economic boom

following World War II (WWII). Improved transportation

and research in logging engineering helped to reduce the

impacts of harvest operations on soils and streams, and provided greater flexibility in application of silviculture. With

improved access and increased disposable income and

leisure time, public concerns about recreation and wildlife

assumed increased importance and influence on management of public lands. Many, though not all, of the environmental concerns we hear today were addressed under the

name of multiple use (Fedkiw, n.d.). Thus, the emphasis

given to the various uses of forest land has been and is 

continually changing. 

Great changes took place in the social and economic

structure of the Douglas-fir region over the last half of the

20th century. Prior to the 1950s, much of the population

lived in rural or small-town settings. Much of it was

employed in natural-resource-based industries—agriculture,

forestry, and fishing—and had direct contact with practical

resource management. Many people were generally supportive of efforts to place timber production on a permanent

basis as a mainstay of the economy, and realized that

planned management with timber production as a major,

though not exclusive, objective was a vast improvement

over the forest liquidation and widespread fires of the not

very distant past. There was little or no opposition to efforts

in this direction. Many people were also keenly interested

in management of game fish and wildlife species, although

problems with salmon had not yet been generally recognized and nongame wildlife received little attention.

In the post-WWII period, there was a great and continuing influx of people from other parts of the country. Many

99

Chapter 12: Changes in Society, Forest Management

Objectives, and Supporting Silvicultural Research1

1 By R.O. Curtis, D.S. DeBell, and M. Newton.
100

GENERAL TECHNICAL REPORT PNW-GTR-696

of the new immigrants came from urban backgrounds and

had little direct contact with and little understanding of 

natural resource management or of regional history. Most

settled in the expanding cities and found employment in

urban-based industries such as aircraft, computers, and supporting services. Many saw little connection between their

own well-being and the use of forests for commodity production. With increasing affluence and mobility, many came

to value forests primarily for scenery and recreational use

and as wildlife habitat. Many did not understand that forests

are dynamic entities that are perpetually changing, with or

without human intervention, and that it is not possible to

perpetuate a given condition indefinitely. A substantial

number regarded timber harvests as forest destruction and

exerted increasing political pressure for withdrawal of public lands from commodity production and for restrictions on

commercial forest operations. To some, large trees and old

forests had unique spiritual values. A fringe element found

in these attitudes a convenient excuse for disruption and

vandalism, including criminal actions such as the arson

fires that destroyed the Department of Natural Resources

Land Management Center and Animal and Plant Inspection

Service facilities in Olympia, Washington, in 2000 and the

University of Washington Center for Urban Horticulture in

2001 and caused extensive damage to various facilities

elsewhere.

Several developments in Douglas-fir silviculture 

exacerbated the conflicts among groups interested in the

regions’s forests. The shift to planting (primarily of

Douglas-fir) as the primary regeneration method meant that

it was no longer necessary to limit the size of clearcuts and

retain seed blocks. Many owners used larger clearcuts to

save on road and logging costs. Concurrently, there was a

progressive reduction in rotations by many industrial and

other private owners, motivated primarily by the desire to

maximize net discounted timber values. The combined

effect was creation of landscapes with extensive areas of

unsightly recently cut land, with the rest of the landscape

largely occupied by uniform young stands of a single

species that are the least productive condition for many

species of wildlife and that are regarded as unattractive by

many people. Public reaction to these visual effects was an

important factor in the developing opposition to clearcutting as a silvicultural system and to forestry operations

in general. 

The rise of the environmental movement in recent

decades as a factor in Northwestern forestry is associated

with these social and management changes. It has exerted

an increasing influence on public policies, and has had

major effects on both forest land management and silvicultural research. It has stimulated silviculturists and land

managers to adopt broader perspectives, including increased

consideration of social and ecological values. It has been a

significant factor in directing more research toward management for multiple objectives including wildlife habitat,

scenic values, biodiversity, and long-term sustainability, in

addition to traditional commodity production goals. On the

other hand, increased pressures and considerable sensational and often misleading propaganda from activist groups

and individuals have at times overshadowed the efforts of

more moderate groups. Conflicts and extreme positions

often receive more attention in the news media than do constructive accomplishments. Contributing factors include (1)

the difficulty that many people have in grasping the range

of management options that exist and the timescales

involved in forest development, (2) the increasing and

sometimes exclusive public emphasis on wildlife, often

directed at single species—as exemplified by the spotted

owl recovery effort (mandated by court decisions); and (3)

a romanticized and unrealistic view of “untouched nature”

as an ideal condition, necessarily degraded by any human

intervention. To some degree, the differences in viewpoints,

values, and underlying philosophy extend into the scientific

community, (for example, Salwasser and others 1997 vs.

Noss 1995) and have been accentuated by lack of communication and mutual understanding between specialized disciplines.

Namkoong (2005) provided a wide-ranging discussion

of the historical and cultural origins of the different conceptions of the nature and role of forests and the differing
Silvicultural Research and the Evolution of Forest Practices in the Douglas-Fir Region

objectives, which range from short-rotation plantation

forestry aimed exclusively at wood production at one

extreme, to restoration of a mythical untouched nature at

the other.

The tunnel vision evident in many land management

disputes is not limited to the usual pressure groups and 

segments of the public. We like to think that “science” is

unbiased, and no doubt it is, in the long run. But individual

scientists have their own biases, whether they be silviculturists, ecologists, wildlife biologists, or whatever. They also

can become preoccupied with pet topics, and are often

unaware of existing knowledge and historical experience

outside their immediate and sometimes narrow range of

expertise. Also, the behavior of forests is influenced by the

wide variations that exist within the region in soil and local

climate, and by short-term weather fluctuations. Therefore,

generalizations derived from individual studies that are not

replicated in space and time can easily be misleading.

Answers to many forestry questions are dependent on welldesigned and well-replicated long-term experiments, which

are expensive (and therefore few in number), dependent on

continuity in funding and personnel, subject to disruption

by pests and climatic events, and likely to be lost to the

pressures for quick answers to the question of the moment.

There is therefore, at best, considerable uncertainty in interpretation of existing science. 

Incomplete knowledge and conflicting viewpoints and

objectives have resulted in land management policies that

are increasingly driven by political considerations and judicial decisions, some of which have had considerable effects

on research.

Several factors affecting research on federal lands are

associated with the Northwest Forest Plan (FEMAT1993),

Record of Decision (ROD) (USDA FS 1994) These include:

• Inadequate funding and other limitations to conducting large-scale manipulative research over a 

sufficient range of conditions and practices. 

• The near-failure of the adaptive management areas

(AMAs) of the Northwest Forest Plan. The AMAs 

were intended to encourage federal land managers 

to try new and bold approaches, but have not generally been effective. Obstacles have resulted from 

lack of organizational support and from an institutional and regulatory environment that stymies innovation and makes managers unwilling to accept risks

of failure and unwilling to try nonstandard practices 

that may provoke conflicts with segments of the 

public (Haynes and Perez 2001; Stankey and others

2003, 2006). 

• Single-purpose set-asides or constraints that have 

curtailed or shut down ongoing research and negated

the very purposes for which long-time research areas

were dedicated. For example, inclusion of the Wind

River and Cascade Head Experimental Forests in 

late-successional reserves.

Allied to these problems is the difficulty and frequent 

inability to conduct experiments on federal lands because 

of delays and disruptions associated with the regulatory 

and appeals processes (which can destroy the validity of an

experiment), exclusion of large areas from any manipulation, and reluctance of managers to allow treatments that

might provoke opposition or that conflict with existing

guidelines. These difficulties are manifestations of what has

been variously termed the “process predicament” and

“analysis paralysis,” in which the multitude of overlapping

and sometimes conflicting laws, regulations, and court decisions render timely and effective action on anything almost

impossible (Thomas 2000, USDA Forest Service 2002).

One result is that some researchers in the Pacific

Northwest, have abandoned attempts to work with the

national forests in favor of state agencies and industrial

owners.

Contributing factors include the general tendency of

regulations, guidelines, and policies—necessarily based on

incomplete knowledge and often influenced by political

factors and judicial decisions—to become fixed dogma.

Likewise, the tendency under the Endangered Species Act

to direct effort toward individual species to the exclusion of

other considerations, including the habitat needs of many

other species.

101
102

GENERAL TECHNICAL REPORT PNW-GTR-696

The current prohibition on most uses of herbicides on

most federal lands in the Pacific Northwest is an example

of a policy driven by public attitudes that has had serious

effects on land management and considerable impacts on

silvicultural research. Segments of the public are opposed

to any use of “chemicals,” an attitude that initially stemmed

from harmful effects on wildlife of widespread use of the

persistent insecticide DDT and was reinforced by the military use of “Agent Orange” as a defoliant and crop destruction tool in the Vietnam War. Negative perceptions have

been reinforced by the tendency of the public and the media

to lump all such materials under the generic term “pesticide,” without recognizing that there are a wide variety of

such materials, and that these differ in persistence, mode of

action, environmental effects, and uses. 

Alleged human health effects from use of 2,4,5-T on

the Siuslaw National Forest (Newton and Young 2004, US

EPA 1979, Wagner and others 1979) led to suspension 

of use of herbicides on most federal lands in the Pacific

Northwest in 1983. Subsequent development of herbicide

technology and herbicide use continued elsewhere. Despite

convincing evidence that currently used herbicides are often

less expensive and more effective, safer, and more benign

in their effects on the environment than alternative methods

of controlling unwanted vegetation, that amounts used in

forestry are very small compared to those routinely used 

in agricultural and other applications (Kimmins 1999:

129–138), and that currently used herbicides have not been

shown to have harmful effects, advocacy groups opposed to

any herbicide use have been successful in preventing nearly

all use of herbicides on federal lands. This is a major limitation in cost-effective restoration of forests on burns and

other nonstocked areas and in the control of invasive

species and vegetative competition.

Dogmas do not all originate outside the forestry community. Historically, one may cite the clearcut-burn-plantDouglas-fir regime that was nearly universal from about

1950 to the 1990s, as an example of silvicultural dogma.

This regime was highly successful as a means of establishing prompt regeneration, and came to be accepted by a 

generation of foresters as the regime for management of

Douglas-fir. But, its near-universal application in combination with progressively shortened rotations has had undesirable effects on public attitudes, scenic values, and many

species of nongame wildlife. And, because of its very success in the context of the timber-oriented needs of the time,

very little research was done on possible alternative

regimes until quite recently.

Another forestry dogma was the goal of total elimination of wildfire, almost universally accepted until quite

recently. This had only limited effects in the northern portion of the Douglas-fir region, but considerable effects 

in the drier climate of southwest Oregon and northern

California.

There are older examples of historical interest. Thus,

Fernow’s 1903 attempted application of practices widely

accepted at the time in his native Germany was halted, and

the Cornell forestry program terminated, because of public

reaction to visual effects (Dana 1953, Rodgers 1991).

Lesson: public attitudes can and often do override science

and economics and must be considered in silvicultural 

decisions.

Ernst (1998) recounts the conflicts over early introduction of block clearcutting and regeneration in Germany,

which was prohibited by a court decision in one jurisdiction

in 1764. Despite conflicts, it was widely adopted and was

highly successful in rehabilitating extensively degraded

forests, though considerably modified in more recent times.

Lesson: the clearcutting furor of the recent past is nothing

new! 

The environmental historian Radkau (1996), reviewing

the changes in German attitudes to forestry over the past

several centuries, concluded with the statement:

. . .even those foresters who have the good will to 

think ecologically do not find a common basis with

environmental fundamentalists who want to ban 

economic considerations from the woods. . . If 

environmental history is able to produce any 

practical benefit, it could do so by overcoming the
Silvicultural Research and the Evolution of Forest Practices in the Douglas-Fir Region

estrangement between forestry and the environmental movement. . .by criticizing dogmatic tendencies on both sides and arguing against the trend 

of playing off ecology against economy. 

Lesson: North American problems are not unique.

Sustained Yield, Multiple Use, Ecosystem 

Management, and Sustainable Forestry

By the 1990s, differences in attitudes and understanding 

had created a degree of polarization that drastically impacted forest management and the economy of many small 

timber-based communities. It also produced marked changes

in direction of research by public agencies. These changes

included a great expansion in wildlife- and wildlife-habitatrelated research, and initiation of research—most of it necessarily long-term—on silvicultural practices and regimes

designed to promote scenic and wildlife values. Particularly,

on those characteristics commonly associated with lateseral conditions and old-growth-dependent wildlife. There

was also renewed interest in selection systems, natural

regeneration, and species other than Douglas-fir.

Traditional commodity-oriented areas of research such

as regeneration, pruning, fertilization, and tree improvement

continued, but were now carried out primarily by the various landowner-supported research cooperatives at the universities. There was also considerable research by major

industrial owners, some of it in cooperation with the universities and public agencies.

In this period, a number of new terms were added to

traditional forestry terminology, ostensibly to describe

changing management objectives.

Sustained yield is a long-established term for a management objective that dates from the early 19th century 

or earlier in Europe, and was increasingly adopted in the

United States from the 1930s on. Originally, it denoted

organization and management of a forest property for continuous timber production with the aim of achieving—at the

earliest practicable time—an approximate balance between

growth and harvest. By the late 20th century, the larger

ownerships in the region were far along in conversion to

continued production, although attainment of a balance

between growth and harvest was often delayed by unbalanced stand age distributions and by disruptions associated

with ownership changes in the private sector and land use

allocation changes in the public sector. 

The historical definition of sustained yield was broadened in its application to the national forests by the

Multiple Use-Sustained Yield Act of 1960, which stated

(Sec. 4):

Multiple use means the management of all the 

various renewable surface resources so that they 

are utilized in the combination that will best meet 

the needs of the American people;. . .and harmonious and coordinated management of the 

various resources. . .without impairment of the 

productivity of the land, with consideration given 

to the relative values of the various resources, and 

not necessarily that combination of resources that 

will give the greatest dollar return or greatest unit 

output.

Sustained yield of the several products and services

means achievement and maintenance in perpetuity 

of a high-level annual or regular periodic output of 

the various renewable resources without impairment 

of the productivity of the land.

Ecosystem management and sustainable forestry are 

terms of recent origin. To us, they appear little different in

meaning from the 1960 definitions given above. These

terms appear to have come into use as an attempt to distinguish between certain past practices (particularly, largescale clearcutting) and current practices and proposals, and

to offset the perceptions of some to whom “sustained yield”

and “multiple use” have connotations of a primary emphasis on timber production. Shifts in emphasis include deemphasis of timber production in favor of a more holistic

view emphasizing—in addition to the traditional multipleuse concerns for game animals and recreation—maintenance of biodiversity and ecosystem function, visual effects,

and avoidance of hypothesized deleterious long-term effects

from some forms of management (Hobbs and others 2002b).

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GENERAL TECHNICAL REPORT PNW-GTR-696

This collection of ideas is also associated with the closely

related term “new forestry,” common in the 1990s.

There remains a wide gulf between those environmental groups philosophically opposed to any form of active

management, and more moderate enviromental groups who

believe that “do nothing” policies are neither biologically

nor economically feasible in the long run. Unfortunately,

concentration for the past half century on a single form 

of management—clearcutting, planting one species, and

steadily decreasing rotation lengths—has provided the 

public with few on-the-ground examples of the long-term

effects of alternative practices.

Over the past 15 years or so, there has been a great

increase in research by ecologists and wildlife biologists 

on the relations between forest conditions and populations

of small mammals, birds, lichens, and other organisms

(Bunnell and others 1997). The main conclusions appear 

to be (1) large woody debris and large snags have a role in

maintaining populations of certain small vertebrates and

birds, (2) large trees and snags have value as refugia for

organisms such as lichens that may have difficulty in recolonizing large open areas, and (3) different species have

different requirements, and no one condition is favorable to

all. Quantitative relationships between amounts of woody

debris, snags, residual trees, and size and distribution of

openings on the one hand, and their effects on the various

wildlife and plant species on the other, are not well defined.

Because species differ in their habitat requirements, maintenance of all species also requires provision of a wide range

of habitat conditions (DeBell and Curtis 1993, Kohm and

Franklin 1997). The current emphasis on “biodiversity”

does not necessarily require diversity within each stand;

biodiversity may be better achieved by a mosaic of diverse

conditions at the landscape level (Boyce 1995, Kimmins

1999). 

The emphasis on development of stands with late-seral

characteristics arose in part because old growth was perceived as in short supply. In turn, this implies that on some

portion of the land base, management should strive to 

create conditions with some of the attributes of late-seral

stages—large trees, large snags, down wood, and layered

structure (McComb and others 1993). Silviculture can

accelerate the rate of development of these characteristics to

a degree that is not generally realized. Much current silvicultural research is directed at accomplishing this acceleration, through changes in thinning regimes, harvest and

regeneration practices, and rotations. This includes both

new work and reinterpretation of work done in the past.

Curtis and others (1998) synthesized existing knowledge related to silviculture for multiple objectives and

showed that the knowledge base is far greater than generally known outside the field of silviculture. Several papers

included in Monserud and others (2003) and in Hobbs and

others (2002b) also reviewed knowledge and ongoing

research in multiple objective management, including

specifically the promotion of biodiversity.

The change in emphasis has increased interest in silviculture of Northwestern hardwoods, associated in part with

the new concerns with biodiversity. There is also more

emphasis on the visual effects on the landscape, on public

perceptions of silvicultural practices, and on the possibilities of using alternative silvicultural systems.

Visual Effects and Public Perceptions

The conflicts that have developed in recent years between 

the perceptions and desires of an urbanized public primarily

interested in scenic, recreational, and wildlife values, and

the economic needs for efficient commodity production and

support of the rural economy, constitute the most serious

problem in Northwestern forestry today. To a considerable

extent, these conflicts arise from the high visibility of

forestry operations on the landscape. There is thus a growing interest in silvicultural measures that may reduce 

conflicts while maintaining some reasonable level of 

commodity production. Such measures include different

sizes, shapes, and arrangements of harvest areas; different

amounts of green-tree retention on harvest areas; and

extended rotations combined with increased emphasis on

thinning. A number of studies over the past two decades

have addressed the questions of (1) visual acceptability of
Silvicultural Research and the Evolution of Forest Practices in the Douglas-Fir Region

alternative practices and (2) the costs involved (Clausen

and Schroeder 2004).

Visual acceptability questions are often addressed by

surveys in which respondents are asked to rate examples of

typical practices, presented either as on-the-ground examples or—more frequently—as photographs or pictorial

images. Typical examples are work by Brunson and Shelby

(1992), Shelby and others (2003), Bradley and others

(2004), and Ribe (2005). An important aid in such studies is

visualization software (McGauhey 1998), which can create

images of anticipated conditions. In general, results indicate

that acceptability decreases with increased size of openings,

with decreased number of retained trees in partial cuts, and

with increased amounts of slash and down wood.

A drawback of many visual acceptability studies is that

they tend to concentrate on conditions shortly after harvest

rather than average condition over the life of the stand, or

the landscapes produced by application of a regime over an

extended period. Unfortunately, we have at present no concrete examples of the landscapes that can be expected from

long-term application of regimes (including “do-nothing”)

other than conventional short-rotation even-age management.

Green-Tree Retention

Retention of scattered overstory trees, either as groups or 

scattered individuals, for presumed, though largely unquantified, wildlife and ecological benefits (Aubry and others

2004, Franklin and others 1997, Mitchell and Beese 2002)

is now a common and in part a legally mandated practice,

superimposed on even-age management (fig. 36). As

amount of growing stock retained increases, there is a transition from more-or-less conventional even-age management to uneven-age management with either two-aged

(reserve shelterwood) or patch- or group-wise uneven-aged

structures.

There have been several attempts to evaluate the effect

on timber production of retention of overstory trees (greentree retention). Lacking permanent-plot data, most studies

have been retrospective in nature (examples: Wampler

1993, Zenner and others 1998) or simulations (example:

Birch and Johnson 1992). These indicate—as would be

expected—that green-tree retention reduces growth of the

understory, with reduction increasing as number of trees

retained increases. It may also increase the difficulty of

controlling competing vegetation.

The recently established DEMO study (Demonstration

of Ecosystem Management Options) is a large regional

study with six replications, designed to examine the ecological effects of several amounts and physical arrangements

of green-tree retention after a single harvest operation

(Aubry and others 2004, Franklin and others 1999). As

originally planned, it made no provision for postharvest

vegetation management or density control and therefore

105

Figure 36—It is now common practice to leave scattered green

trees or groups of trees and snags on harvest areas for wildlife

and other purposes. Although superficially resembling past seedtree cuts, the trees are not retained for regeneration purposes. 
106

GENERAL TECHNICAL REPORT PNW-GTR-696

does not mesh well with other research and applications

aimed toward sustainable management regimes.

Nontraditional Thinning

The LOGS (Levels-of-Growing-Stock) study in Douglas-fir 

(Curtis and others 1997) and a variety of other less elaborate thinning trials have shown that early and repeated uniform thinning can produce dramatic increases in individual

tree growth and understory development. On good sites,

large trees can be produced at relatively young ages.

Retrospective studies of operationally thinned and

unthinned mid-age stands, and of age distributions and

stand structures in old-growth and young-growth forests,

have shown that appropriate thinning of mid-aged stands

hastens the development of multistory stands (Bailey and

Tappeiner 1998, Poage and Tappeiner 2002) and that many

existing old-growth stands were established at much lower

densities and with a much greater range in ages than young

growth established following harvest. The marked differences in developmental trends suggest that in the absence

of active management, many existing young stands will 

not develop into stands similar to existing old growth

(Tappeiner and others 1997). Muir and others (2002) provided a comprehensive review on the potential of thinning

for shaping stand development and suggested general

guidelines for thinnings in young Douglas-fir forests to 

promote biodiversity and development of late-seral 

characteristics.

Most older thinning studies in Douglas-fir have applied

uniform thinning to uniform even-aged stands. Treatments

have usually been either low thinning or crown thinning,

differing only in amount of growing stock retained and 

frequency of thinning. Several thinning studies have been

established recently to examine techniques for promoting

development of diverse stand structures through unconventional irregular thinning. Associated with these trials are

efforts to maintain or establish secondary species.

One such study in young Douglas-fir plantations compares development of unthinned stands with stands treated

with regular thinning, irregular thinning to create gaps, and

with and without supplemental planting of other species in

the gaps (Reutebuch and others 2004) (fig. 37). The first

block was installed in a large area of uniform plantation in

the Mount St. Helens blast zone.2 An additional block was

subsequently installed on the Willamette National Forest,

and a very similar trial was established by Washington

Department of Natural Resources3 in the Forks area. 

A second large-scale study involves irregular thinning

in several mid-aged stands on the Olympic National Forest

(Harrington and others 2005). A third study is in mid-aged

stands on the Fort Lewis military reservation (Carey and

others 1999). A fourth somewhat similar study was established at about the same time by Oregon State University

and the Willamette National Forest. All recent studies 

use much larger treatment areas than the small plots (0.4

hectare or less, 1 acre or less) typically used in early thinning studies. 

A large study at Oregon State University is designed 

to evaluate silvicultural practices to promote understory

structure and diversity combined with overstory maturation,

as stands mature in a two-story system. Several reports have

described overstory effects on understory (Brandeis and 

others 2001a, 2001b, 2002) and damage to understory in

rethinning (Newton and Cole 2006). Several other trials

with broadly similar objectives, recently established by a

number of organizations, are listed in Hunter (2001).

It has been commonly thought that old trees will not

respond to thinning, a belief that probably stems in part

from the unfavorable results of early selective cutting (chapter 5), in which choice of residual trees was largely dictated

by immediate economic rather than silvicultural considerations. Recent work (Latham and Tappeiner 2002) has shown

that, in many cases, removal of understory and less vigorous

2 Lead scientist is Connie Harrington, Forestry Sciences Laboratory,

Olympia, WA.

3 Lead scientist is Richard Bigley, Washington Department of Natural 

Resources, Olympia, WA.
Silvicultural Research and the Evolution of Forest Practices in the Douglas-Fir Region

trees accelerated growth of trees 200 or more years old.

This not only promotes development of larger trees, but can

be expected to reduce susceptibility to bark beetle attack,

and possibly somewhat reduce the risk of stand-replacing

fires.

Forest Health Issues

Sporadic minor damage from weather, insects, and diseases

is a normal part of stand development, and in recent years

the Douglas-fir region has been largely free from catastrophic damage. This is due at least in part to the prevalence of vigorous young stands, in contrast to the overstocked and low-vigor stands that are currently a major

problem in forests east of the Cascade crest. Silviculture is

the principal means of preventing or controlling a variety of

damaging agents (Curtis and others 1998: 67–72). Recent

changes in silvicultural practices and management policies

may have effects on west-side forest health, which have as

not yet been well evaluated. 

The most serious diseases are the endemic root rots.

Control consists in removal of infected trees followed by

planting of resistant species (or removal of infected stumps).

Recent interest in use of resistant species such as redcedar,

red alder, and white pine to increase species diversity is

consistent with control of root rots.

Extensive damage by Swiss needle cast (Phaeocryptopus gaeumanni), an organism formerly considered innocuous, has occurred recently on Douglas-fir plantations within

or near the Sitka spruce zone. Causes are uncertain, but a

plausible hypothesis is that the needle cast problem is associated with extensive planting of pure Douglas-fir (perhaps

from nonlocal seed sources) on sites formerly dominated by

hemlock and spruce.

In the past, the most serious insect problem has been

the Douglas-fir bark beetle (Dendroctonus pseudotsugae).

Losses to bark beetles are usually a minor factor in young

vigorous stands, but large and very damaging outbreaks

have occurred at intervals in the past, usually triggered by

extensive blowdown or fire events (Furniss and Carolin

1977). Control is by prompt salvage of infested trees, and

by appropriate thinning to maintain vigor and windfirmness. This is no longer possible on some public lands

because of conflicts with reserve status and opposition by

segments of the public. Hence the risk of future major outbreaks is increased.

107

Figure 37—Experimental thinning in a plantation in the Mount St.

Helens blast zone, aimed at creating irregular stand structure to

enhance biodiversity: (A) uniform plantation, (B) uniform stand

created by conventional precommercial thinning, and (C) irregular

thinning. 

C

B

A
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GENERAL TECHNICAL REPORT PNW-GTR-696

Dwarf mistletoe (Arceuthobium tsugense) can be seriously damaging in hemlock. The older practices of clearcutting and broadcast slash burning were effective in

controlling the problem. The shift to green-tree retention

and efforts to develop multilayered stands have the potential to increase future infestations through spread from the

retained trees to regeneration.

Understory development, layered stands, and increased

amounts of coarse woody debris—although desirable from

the standpoints of wildlife habitat and visual effects—can

also increase fire risk through increased fuel loads and 

creation of fuel ladders that can carry fire into tree crowns.

This is of particular concern in the southern and drier part

of the region, where the presettlement pattern was one 

of relatively frequent light burns in contrast to the standreplacing fires that occurred at long intervals farther north

(Agee 1993). Appropriate thinning (followed by underburning in some situations) can reduce fuel loads and minimize

the risk of intense fires. 

Stand density control (initial spacing, thinning) can

markedly reduce the risks of wind and snow damage

(Wilson and Oliver 2000) and also enhance resistance to

bark beetle attack, by lowering height/diameter ratios and

increasing tree vigor. 

Animal damage is often serious. With the general shift

to planting rather than natural regeneration, seed consumption is no longer as critical as it once was. But browsing 

of seedlings by deer and elk, mountain beaver damage to

seedlings and saplings, and bark stripping by bear are all

serious problems. Deer and elk browsing is the principal

obstacle to wider use of redcedar, otherwise silviculturally

and ecologically desirable. There has been extensive

research on animal repellents, physical barriers to browsing,

use of large planting stock, and supplemental feeding in

efforts to overcome the problems (for example, Black 1992,

Newton and others 1993, Nolte and Otto 1996). Success

has been limited, and animal damage remains a serious

problem in many areas.

Nontimber Forest Products

Commercial harvest of nontimber forest products, although 

not new (Adams 1960, Isaac 1945), has become an economically important activity in recent years. These products

include Christmas trees, floral greens (swordfern, salal,

Oregon grape, boughs, moss), beargrass, mushrooms, huckleberries, and medicinal plants. To some extent, productivity can be influenced by silviculture, most notably

through stand density control. Christmas tree and bough

production can be a part of precommercial thinning.

Development of understory species is influenced by stand

density and by stand age. 

Research is in progress on management of nontimber

forest products, which necessarily involves silviculture, and

which we do not review here. General discussions and

extensive references are given by Duncan (2003), Kerns

and others (2003), and Molina and others (1997).

Growth Trends, Rotations, and Carbon

Important research and policy questions are involved in 

choice of management regimes and rotations and their possible effects on carbon sequestration and climate change.

Reexamination of permanent-plot data from past experiments has shown that culmination of mean annual increment in Douglas-fir is later than commonly thought, and is

probably delayed by repeated thinning. Considerable extension of commonly used rotations is possible without loss of

volume production (Curtis 1995, Newton and Cole 1987),

and possibly even with some increase in value production.

Moderate extension of rotations combined with greater use

of thinning could markedly reduce visual and environmental effects of harvest operations while increasing employment, long-term timber yields, tax revenues, carbon

sequestration, wildlife values, and flexibility to respond to

future unknown social and economic changes (Curtis and

Carey 1996).

Carey and others (1999) simulated three alternative

management strategies for an area on the Olympic Peninsula

—no management with protection, maximization of net

present value of timber (clearcutting on 40- to 50-year
Silvicultural Research and the Evolution of Forest Practices in the Douglas-Fir Region

rotations, with required riparian buffers), and a “conservation of biodiversity” strategy (Carey and Curtis 1996) using

a mix of treatments including extended rotations. They concluded that the “conservation of biodiversity” strategy

developed a target proportion of late-seral stands much

sooner than did the protection-only alternative; produced

nearly as much timber as the “maximum net present value”

alternative; minimized area in the stem-exclusion stage

(Carey and Curtis 1996), in which development of understory vegetation is prevented and some trees become suppressed and die; and was generally more desirable from the

ecological and wildlife standpoints. Although the cost in

terms of reduced net present value of timber was higher for

the “conservation of biodiversity” strategy than for the

maximum net present value strategy, the differences were

not large. Lippke and others (1996) concluded that the benefits in enhanced employment, tax revenues, and carbon

sequestration were sufficient to justify some form of publicly funded incentives to compensate landowners for the

added financial costs.

In recent years, there has been much public concern

about climatic warming and its possible consequences, the

marked increase in atmospheric CO2 (attributed to use of

fossil fuels), and the possibility that the latter is a major

causal factor in climatic change and is subject to some

degree of human control. Forests store large amounts of

carbon, and both afforestation and modified silvicultural

regimes are potential means of increasing carbon sequestration. There is also a future possibility of plantation-based

biomass energy production, without the net CO2 production

inherent in the use of fossil fuels (Larson and Johanssen

2001). A goal of increasing carbon storage has at least two

aspects that affect silviculture and needs for silvicultural

research:

• Change in growth conditions associated with predicted warmer climate and increased atmospheric 

CO2 could affect species and family adaptation and

susceptibility to insects and disease. It could also

require modification of growth functions and simulation programs used to predict development of

forests.

• The most obvious silvicultural regime changes for 

the purpose of increasing carbon sequestration are 

an increase in rotation length with an associated

increase in growing stock (Harmon and Marks 200,

Haswell 2000, Peterson and others 2004), combined

with minimal slash removal. Longer rotations would

also benefit long-term wood production, wildlife 

habitat, and scenic values. 

The principal difficulties in any extension of rotations 

are (1) temporarily reduced cash flow for those owners 

currently lacking older stands; (2) reduced net present (discounted) value of future timber yields, which in the absence

of other incentives is an overriding consideration for those

owners whose primary objective is maximum percentage

return on their timber investment; and (3) recent conversion

of many mills to processing small logs, with resulting loss

of price premiums and markets for large logs. The potential

benefits of extended rotations are primarily public benefits

that do not accrue to the individual owner. Thus, extended

rotations are at present primarily an option for public ownerships. This situation could change if present and predicted

climatic trends lead to active public programs that encourage carbon sequestration via carbon credit trading or other

forms of direct or indirect subsidy.

Riparian Silviculture 

West-side stream conditions have been markedly changed 

since the first European settlement. Factors involved

include extensive urbanization with attendant changes in

runoff, stream temperatures, and stream pollution; logging;

dams that obstruct the passage of fish; agricultural operations; and clearance of stream channels to facilitate transportation (including early-day log transport and fish

passage). Marked declines in salmonid populations have

occurred in the past several decades. The decline is at least

partially attributable to the off-shore fishery. Nevertheless,

the decline is widely perceived as having its origins in

declining quality of freshwater habitat. Salmon recovery

has been a major public concern for a couple of decades,

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110

GENERAL TECHNICAL REPORT PNW-GTR-696

leading to restrictions on forest operations in riparian zones.

At present, such restrictions not only limit forest operations

in riparian zones for either harvest or stand improvement,

but also complicate efforts intended to enhance spawning

and survival.

Forests are not static, and presettlement conditions

included periodic large-scale disturbances (fire, windfall)

and debris flows that influenced stream productivity

(Reeves and others 2002). Timber harvest has in part

replaced fire as a major influence, analogous to but not the

same as presettlement disturbances. Low-elevation riparian

zones, especially those characterized by significant terraces,

are frequently occupied by red alder, a species with a limited life expectancy leading to shrub-dominated communities

as overstories senesce (Newton and others 1968). The

dilemma today is how to create a level of disturbance that

ensures establishment of coniferous stands as characterized

in the Oregon criteria for desirable future conditions

(Oregon Department of Forestry 2003).

In the 1950s and 1960s, governmental programs

favored removal of wood from streams in the belief that

this would facilitate passage of fish (Reeves and others

2002). It was subsequently recognized that large woody

debris is important in forming pools essential to spawning

and survival, and current policies aim to provide such material together with streamside shading to maintain low water

temperatures. 

Recent research on riparian silviculture includes efforts

to provide cover needed for cool streams and productive

aquatic communities, to ensure production of large, durable

conifer wood to enhance stream habitat (Bilby and Bisson

1998), and to enhance development of late-seral conditions.

Several events, beginning with reports by Brown (1969)

and Brown and Krygier (1970), led to concerns with

streamside cover and water temperature interactions. This

was reinforced by the Forest Ecosystem Management

Assessment Team report (FEMAT 1993). The recent listing

of many strains of salmon as threatened has stimulated

interest in how riparian forests can be managed to ensure

the future of the salmon resource.

Much of this research is concerned with determining

effects of streamside buffers vs. no buffers, and occasionally with buffer characteristics; with techniques for promoting

desired conditions; and with the possibilities of combining

limited timber production from riparian areas with stream

protection. Extremely restrictive buffer requirements have

major economic impacts, and the future of stands without

maintenance is uncertain. Stream-side vegetation changes

over time, and some stream-side conditions present today 

as a result of previous disturbance are unlikely to develop

desirable characteristics in the long run. Producing large

conifer material for stream channel improvement has been

identified as an important value of mature forests adjacent

to streams (FEMAT 1993, Oregon Department of Forestry

2003). Much research in the last 20 years has been devoted

to active management measures aimed at establishment and

maintenance of conifers and multilayered canopies in the

riparian zone. Salo and Cundy (1987) provided a major

work on interaction of aquatic and terrestrial systems that

led to both regulatory activity and research to resolve issues

on influence of streamside forests. Walsh (1996) provided

some of the first insights on how buffers and their arrangements influence aquatic insects that are a major prey base

for fish. Newton and Cole (2005) expanded this to include

concepts of establishing several species of conifers as longterm streamside cover following conversion from red alder.

Several major initiatives have emerged in the past

decade that illustrate the cooperative nature of programs

within Oregon to resolve conflicts and illuminate some

unresolved questions in riparian management. The Coastal

Oregon Productivity Enhancement (COPE) program

brought together federal, state, and private resources in a

major 10-year effort to improve understanding of the roles

of terrestrial and aquatic portions of the stream environment

and how these influence stream biota. Hobbs and others

(2002a) summarized the findings of this program, which

mostly dealt with stream processes and ecological assessment of coastal forests. Very few manipulative experiments

were conducted, and the need for quantitative analysis of

the specific impacts of forest practices remains.
Silvicultural Research and the Evolution of Forest Practices in the Douglas-Fir Region

Concurrently with COPE, several other cooperative

efforts between the university and state and industrial forest

landowners have led to improved understanding of the

effects of harvest practices on water temperatures

(Zwieniecki and Newton 1999) and of opportunities to

improve streamside stand composition while maintaining

stream productivity. Newton and Cole (2005), for example,

discussed rehabilitation of riparian hardwood forests and

the size of overstory openings needed to secure satisfactory

juvenile growth of conifers. They also observed that riparian reforestation depends heavily on protection from ungulate browsing and beavers. Zwieniecki and Newton (1999)

and Newton and Cole (2005) have shown that harvesting

close to streams while leaving narrow buffers or strategically designed residual shade can maintain cool streamwater, while providing opportunity to establish large durable

conifers close to streambanks. Their work and that of

Rutherford and others (1999) also showed that stream productivity can often be increased by allowing diffuse light to

reach the stream. Skaugset4 provided evidence that timber

harvest along non-fish-bearing headwater streams did not

have a warming influence on downstream waters, although

some unbuffered streams warmed appreciably within units.

These reports reinforce the hypothesis that streamside harvests, at least in small headwaters streams, would not lead

to cumulative warming.

Chan and others (2004) reported a current largescale stand management experiment on Bureau of Land

Management lands in western Oregon that includes comparisons of stream-buffer widths and within-buffer silvicultural treatments. Early results suggest that differences in

residual thinning densities and buffer widths result in relatively small changes in the riparian environment, and that

these effects are not associated with detectable changes in

riparian-dependent organisms. Clearcutting is not a factor 

in this study; all streams were buffered by stands thinned 

to various densities. Long-term renewal of the streamside

coniferous cover was not evaluated.

Integration of stream treatments with fish-biology

research is now recognized as crucial. The Watershed

Research Cooperative at Oregon State University and the

Headwaters Research Cooperative, a consortium of

landowners and agencies, has been formed to conduct

research on managed watersheds and to collect and disseminate monitoring data on stream systems. One major company (Roseburg Forest Products) has contributed a 5,000-

acre (2000-hectare) watershed plus considerable infrastructure in support of the Watershed Research Cooperative’s

Paired Watershed Study, which is a long-term initiative to

evaluate the effects of intensive management on fishery

resources. Two more paired watersheds on industry and

state lands are currently under evaluation. Collectively,

results from these studies will likely have a major effect on

policies affecting streamside silviculture.

Good general discussions on riparian silviculture with

extensive references are Hayes and others (1996), Hobbs

and others (2002b), and Cunningham (2002).

Comparisons of Silvicultural Systems 

and Management Regimes

Silvicultural research in the past was typically carried out 

on small plots selected for uniformity and comparability of

initial conditions and with close control of treatments.

Given suitable experimental designs, statistical tests were

easily applied. Although small-plot experiments have provided much valuable information on forest biology and on

development of trees and stands, their results are often not

directly applicable to the larger and more heterogeneous

areas that a manager must deal with. And they cannot provide information on variables that cannot be evaluated on

small areas, such as wildlife and visual effects.

A few recently established long-term studies are

designed to compare results and costs of alternative management regimes that aim to combine timber production

with reduced visual and ecological impacts (Arnott and

Beese 1997; Maguire and Chambers 2005; McComb and

others 1994; Monserud 2002, 2003). As one example, a

111

4 Skaugset, A. Processes that influence the downstream propagation of stream temperatures. Manuscript submitted to Forest

Science.
• They must be continued over a long period if they 

are to answer questions about the long-term results 

of alternative regimes. Consistency over time in 

treatments and procedures is necessary and difficult 

to obtain.

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GENERAL TECHNICAL REPORT PNW-GTR-696

large replicated study involving the Pacific Northwest

Research Station, Washington Department of Natural

Resources, and the British Columbia Ministry of Forests

compares costs and yields for conventional clearcutting,

two-age management, repeated small-patch cutting with

repeated thinning of the matrix, group selection with repeated entries, and continued thinning on an extended rotation

(Curtis and others 2004, DeBell and others 1997, De

Montigny 2004) (figs. 38 through 44). The treatments are

expected to produce widely different stand structures with

corresponding differences in visual effects, wildlife effects,

and acceptability to the public. This study differs from

DEMO in that it is a comparison of regimes rather than of

results from a single entry. Conversion of the large units

used will extend over the next half century, and a variety of

intermediate growth-enhancing treatments will be applied.

Several other long-term operational-scale experimental trials of alternatives to conventional clearcutting 

are in progress in the United States and western Canada

(Monserud 2002, Peterson and Maguire 2005). Large treatment areas are required to provide realistic evaluations of

operational timber yields, costs, stand structural changes,

and scenic and wildlife effects. These cannot be provided

by the small-plot experiments common in the past.

Large-scale long-term experiments involve some major

challenges:

• It is difficult to find large treatment areas that can 

be considered comparable. At best, there is much

uncontrolled variation that reduces the power of 

statistical tests.

• Variation in soils and local climate make replication 

in time and space important for valid generalizations of results.

• The variety of questions and likelihood of future

unforeseen questions make an interdisciplinary structure highly desirable.

• They require close cooperation and coordination

between the research and land managing organizations.

Figure 38—The Blue Ridge replication of the Silvicultural

Alternatives for Young-Growth Douglas-Fir Forests study, established in 1998 in a stand of 1929 natural origin after cutting and

fire. Several other experiments of similar nature are in progress 

in the region.

Figure 39—Control unit at Blue Ridge, with abundant understory

of suppressed hemlock. It was thinned about 1970 prior to study,

with no subsequent treatment. 
Silvicultural Research and the Evolution of Forest Practices in the Douglas-Fir Region

• They are expensive to establish and maintain, and 

are therefore in competition with activities aimed at

quick answers to the question of the moment.

• They are heavily dependent on continuity in personnel and on support by both the research and administrative organizations.

113

Figure 40—Clearcut treatment at Blue Ridge at year 6 after

planting: (A) planted Douglas-fir with some naturally seeded

hemlock, and (B) leader growth of Douglas-fir in full light. 

Figure 41—Two-age treatment at Blue Ridge, intended to develop

a two-storied stand, 6 years after underplanting with Douglas-fir.

Considerable natural hemlock regeneration is present. Overstory

left after cut was 16 trees per acre (39 trees per hectare) with a

stand basal area of 46 square feet per acre (11 square meters per

hectare).

Figure 42—Patch cut treatment at Blue Ridge, six seasons after

planting.

A

B
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GENERAL TECHNICAL REPORT PNW-GTR-696

• Like all long-term experiments, they are liable to 

disruption by unplanned events (fire, pests, political

changes, interrupted funding).

Nonetheless, such experiments are sorely needed to 

address many important questions. Lacking long-term

experimental data, present estimates of long-term results 

of alternative silvicultural regimes are necessarily based 

on extrapolations and simulations that become increasingly

suspect as they are extended to ages, treatment regimes, and

stand conditions outside the range of existing data. And, 

on-the-ground demonstrations showing the feasibility of

alternative regimes may be more important in a practical

sense than statistical significance of small differences.

Figure 43—Group selection treatment at Blue Ridge after six Figure 44—Continued thinning treatment at Blue Ridge. 

growing seasons.
Silvicultural Research and the Evolution of Forest Practices in the Douglas-Fir Region

Forest management practices have been and are continually

evolving. Formal forestry research has been an important

factor in the process, but it is only one of the factors

involved. Progress in applied silviculture comes from the

interaction of research results, observation and experience

of managers and silviculturists, changes in harvesting and

manufacturing technology, and a continually changing 

economic and social environment. Flora (2003) provided a

good account of these changes from an economist’s viewpoint.

In the following sections we briefly review the historical changes in forest management that parallel and were

influenced by the development of silvicultural research.

Forest Management Changes: 

1900–1925

Establishment of the U.S. Forest Service in the Department 

of Agriculture, by merger of the former Bureau of Forestry

with the forest reserves, provided an effective organization

for management of federal forest lands (Steen 1977) and for

forestry research (Steen 1998). The U.S. Forest Service also

played a very important role in promoting forest protection

and management activities by the states and by nongovernmental organizations.

The greatest advance in this period was the introduction of effective efforts for fire control and fire prevention,

stimulated by the disastrous fire years of 1902 and 1910.

The states passed legislation requiring burning of slash on

freshly cut areas, fire patrol of such areas, provision of

spark arresters on equipment, and firefighting tools. The

Washington Forest Fire Association was formed in 1908,

and the Oregon Forest Fire Protective Association in 1910.

The Weeks Act of 1911 included authorization for federal

participation in the organization and maintenance of cooperative fire control organizations. The newly formed

Western Forestry and Conservation Association, established

in 1909 under leadership of E.T. Allen and George Long,

became an active and effective organization promoting fire

control legislation, public education, and the formation of

cooperative fire control associations among landowners

(Allen 1926, Martin 1945). (In later years, it also became

an effective advocate of improved silviculture and of sustained yield management.) Concurrently, the national

forests developed their own fire control capabilities.

The Clarke-McNary Act of 1924 expanded Forest

Service authority to cooperate with and provide financial

aid to states for fire protection. It also provided similar

authority for aid to states in providing seed and planting

stock for reforestation of denuded lands.

The great Yacolt Fire of 1902 (Felt 1977) and others of

that period had left large areas of land unstocked. A large

and continuing effort was mounted to replant the national

forest lands involved. This necessarily included the establishment and operation of forest nurseries, beginning with

the Silverton Nursery in 1909 and the Wind River Nursery

in 1910 (Cameron 1979). 

Timber harvesting on national forest lands was generally on a small scale, because industry controlled huge

amounts of timber and had little immediate need for purchases of federal timber. Most commonly, national forest

harvests used the scattered seed tree method for regeneration, with a rough standard of at least 2 seed trees per acre

(5 per hectare), in line with recommendations of Munger

and others. A beginning was made on working plans providing for sustained yield management.

In this period, private owners rarely made any specific

provision for regeneration other than the fire protection and

slash disposal required by law. However, defective trees

and inaccessible groups of trees were often left and frequently approximated the seed tree method. On most areas,

115

Chapter 13: Evolution of Applied Forest Management

Practices1

1 By R.O. Curtis and M. Newton.
116

GENERAL TECHNICAL REPORT PNW-GTR-696

the only feasible logging method available at the time was

the logging railroad and steam donkey, and there was therefore no feasible alternative to large clearcuts or at best leaving a few scattered seed trees (fig. 45).

Several of the more far-sighted industrial landowners

acquired large timber holdings beyond their immediate

needs as insurance for future supplies for long-term operation. By the 1920s, a number of large owners undertook

survey and classification of their cutover lands. The largest

of these efforts was that by Weyerhaeuser Timber Co.,

which in 1924 established a new corporation—the

Weyerhaeuser Logged-Off Land Co.—to take over management of the parent company’s cutover lands, with lands

suitable only for timber-growing to be managed for that

purpose (Brandstrom 1957).

This period also saw the beginning of a long-running

controversy over proposals for federal regulation of forest

practices on private lands. Legislation to this end was 

proposed in Congress, and supported by Pinchot (after his

departure as Chief Forester) and by Graves. Graves’ successor, William B. Greeley, took the position (strongly supported by E.T. Allen) that more progress could be made

through cooperation between government and industry. 

The controversy continued and was not laid to rest until

about 1950, by which time a number of states (including

Washington and Oregon) had passed legislation regulating

forest practices.

Forest Management Changes: 1925–1950

During this period there was a continuing increase in the 

effectiveness of fire prevention and control, aided by partial

federal funding under the Clarke-McNary Act (1924). 

The Knutson-Vandenberg Act of 1930 provided additional federal funding for nurseries and planting programs

on national forest timber sale areas. The contribution of the

national forests to regional timber supply was still relatively

small, although steadily increasing (except for the

Depression period). 

During the 1920s, a number of companies (notably

Crown Zellerbach and Long-Bell) undertook forest planting

and seeding on a limited scale (Brandstrom 1957). LongBell Lumber Co. established a nursery near Ryderwood,

Washington, in 1926. The company planted 13,330 acres to

conifers until the Depression halted work in 1931, although

about half of the planted area was subsequently lost to fire.

These private reforestation efforts came to an abrupt end

with the onset of the Great Depression.

The introduction of the motor truck and crawler tractor

opened new possibilities for more flexible logging methods.

Much of the silvicultural knowledge needed for long-term

management was now available (Munger 1927). McArdle

and Meyer (1930) had shown the enormous productivity of

Douglas-fir and had provided a quantitative basis for management planning. It seemed that the stage was set for conversion from an industry engaged in liquidating a wasting

asset to one engaged in growing timber on a permanent

basis.

Then came the Great Depression. Mill capacity, which

had greatly expanded in the boom years of the 1920s, was

now far in excess of plummeting demand. The forest industries descended into chaos, as did many others.

Figure 45—Railroad logging operation some time in the 1930s.

Such areas frequently reseeded naturally, but it was often a slow

process and sometimes led to conversion to brush species or alder. 

Brubaker Aerial Surveys
Silvicultural Research and the Evolution of Forest Practices in the Douglas-Fir Region

One result was the rise of “selective cutting” (chapter

5). This was a silviculturally destructive practice, driven 

by the short-term economics of survival under conditions

where only the biggest and best trees could be handled at 

a profit.

Congress passed the National Industrial Recovery Act

(NRA) in 1933. This act provided for formation of industry

associations with power to set minimum wages and prices

and control production levels (Robbins 1981). The Code 

of Fair Competition for the Lumber and Timber Products

Industries (Dana 1953: 254–257) also included a provision,

Article X, requiring the industry to formulate a Forest

Conservation Code, including enforceable rules of forest

practice. Such a code was formulated by industry leaders in

association with state and federal officials, and adopted in

1934. Then, in 1935, the Supreme Court struck down the

entire NRA program.

Although no longer operative, the NRA Conservation

Code had a considerable educational effect (Recknagel

1938). The West Coast Lumberman’s Association and

Pacific Northwest Loggers Association subsequently (1937)

issued a forest practice handbook, based on the NRA Forest

Conservation Code. This publication summarized existing

knowledge and recommendations on fire prevention and

control, called for natural reseeding of cut areas, and advocated transition to sustained yield as the eventual industry

goal. It reflected changing attitudes in the industry and

formed a part of the groundwork for the shift in direction of

the industry during and following World War II (WWII).

In the late 1930s, a number of large timber holdings

were placed under sustained yield programs, including 

the St. Helens Sustained Yield Unit of Weyerhaeuser Co.

and the Oregon and California Railroad (O&C) land 

grant lands under the General Land Office of the Interior

Department (which later became the Bureau of Land

Management).

With the recognition that the seed tree method was frequently ineffective and that “selective cutting” had been a

silvicultural fiasco, there was a general shift to the use of

so-called “staggered settings”—block clearcutting in units

of moderate size interspersed with blocks of uncut timber

that served as a seed source (fig. 46).

By 1940, the economic upturn associated with the war

in Europe and rearmament in the United States was being

felt. Markets and prices improved, and the outlook for 

timber and other manufacturing industries brightened.

Emphasis shifted to increased production to meet wartime

needs. There was a corresponding shift in industry attitudes

from gloom to optimism.

Nineteen-forty-one brought the birth of the industrysponsored tree farm movement, with dedication of the

Clemons Tree Farm of Weyerhaeuser Co. as the first such

unit. Over subsequent years, this movement became an

important vehicle for encouraging improved forest management. An industry-wide forest tree nursery was established

in 1941 at Nisqually, Washington, to supply seedlings for

tree farm planting, an activity that expanded rapidly. 

The Oregon Forest Conservation Act of 1941 was the

first in the Nation requiring regulation of cutting practices

by the state. Washington passed a similar act in 1945.

Although the Washington act was contested by a group of

timberland owners as an infringement on private property

rights, it was upheld by a 1949 Supreme Court decision.

The great Tillamook Fire of 1933, and subsequent

reburns (1938, 1944, 1951) created a huge area of

unstocked land in northwestern Oregon. The State of

Oregon eventually acquired most of the land involved, and

undertook a massive program of timber salvage followed

117

Figure 46—Unsatisfactory regeneration from the seed-tree method

and from “selective cutting” led to adoption of “staggered settings” in the 1940s—moderate size clearcuts interspersed with

uncut timber that served as a seed source. 
118

GENERAL TECHNICAL REPORT PNW-GTR-696

by seeding and planting, extending through the 1950s. This

effort created the present Tillamook State Forest. The reforestation problems involved provided a strong stimulus to

research in artificial regeneration.

World War II was followed by a strong and continuing

expansion of the general economy, and by a steady rise in

demand and prices for the timber industries. Improved markets and improved transportation meant much more complete utilization of harvested timber, with reduced slash

accumulations. The end of old-growth timber was visible

on the horizon. Second-growth stands took on a new value.

Operations such as thinning, that had previously been considered uneconomic, now seemed feasible. 

In the changed economic climate and the new optimistic view of the future, most of the stronger companies

undertook the transition to permanent sustained-yield management. Concurrently, there was a sharp increase in the cut

from federal lands. This served both to help meet the soaring demand for timber, and to facilitate the transition to 

sustained yield of companies that had badly unbalanced age

distributions or insufficient land base to make sustainedyield operation feasible without supplemental supplies of

federal timber.

Brandstrom (1957) provided an excellent historical

account of industry developments in this period.

Forest Management Changes: 1950–1985

Over the years from about 1950 to 1985, change continued 

in the directions foreshadowed in the immediate postwar

period. Demand for timber products was high. Timber supplies, although not yet seriously limiting, clearly required

foresight and planning. Old-growth timber on private lands

was largely replaced by young stands. Harvests on national

forest lands greatly increased and became a major supply

source, and planning envisioned the gradual conversion of

much of the large amount of old growth remaining on federal lands to managed young growth.

There were major and continuing improvements in

wood utilization. Markets developed for much material that

had previously been unusable. Harvesting equipment

became more efficient and more flexible. With steadily

increasing timber prices and the prospect of future supply

problems, owners were ready to invest in cultural measures

that promised to increase growth rates and value of young

stands. 

The standard regeneration practice over most of the

region was now to clearcut, burn, and plant, usually to

Douglas-fir. The shift to planting as the preferred regeneration method was driven by (1) the frequently unsatisfactory

results of natural regeneration methods, (2) the availability

of Knutson-Vandenberg funds for planting on Forest

Service lands, and (3) the increasingly stringent restocking

requirements under the Washington and Oregon forest practices acts. Improved nursery and planting procedures and

improved vegetation control provided a steady increase in

survival. With planting rather than natural seeding as the

primary regeneration method, it was no longer necessary 

to retain seed blocks. Some owners therefore chose to use

very large clearcuts to reduce logging costs.

With more complete utilization and the gradual shift 

to young growth—which had much less defect than old

growth—less slash was left on the ground. Less slash, better fire control, and public objections to smoke led to a

gradual decrease in the formerly nearly universal practice 

of broadcast burning.

Precommercial thinning became common practice in

naturally seeded stands and in plantations, especially those

with substantial additions from natural seeding.

Commercial thinning was now feasible, although there

were differing opinions as to its desirability. Early trials in

mid-aged stands had not shown the growth response that

many people had anticipated, and some questioned the benefits of thinning on the short rotations that many owners

were adopting. Others—particularly the public agencies

with their somewhat longer rotations—did a considerable

amount of thinning.

Nitrogen fertilization of young stands was widely

adopted by industrial and state owners.
Silvicultural Research and the Evolution of Forest Practices in the Douglas-Fir Region

Both public agencies and the larger companies established tree improvement programs, and operational plantings used selected seed as this became available. The

combination of genetic improvement with improved nursery and planting practices produced plantations that—at

least in their early years—clearly outperformed natural

stands.

These changes were accompanied by a general shortening of rotations used by industrial and some private owners,

in some cases to as short as 40 years. Shortening of rotations was sometimes motivated by need to compensate for

unbalanced age distributions, but primarily by financial

considerations without much attention to other biological,

social, or political effects.

Forest management on federal lands (and to a considerable extent on industrial and state lands) became more centrally planned and controlled. Forest planning became a

major activity on national forests, and forest practice regulations began to affect private operations.

This was also a period of burgeoning population

growth—centered in the urbanized areas around Puget

Sound and the Willamette Valley—and growing affluence

and mobility. The expanding road system made much formerly remote forest land readily accessible. Recreational

use exploded, particularly on the national forests. Increasing areas were designated as wilderness. Conflicts between

user groups intensified. It became increasingly difficult to

reconcile the desires and demands of the various interest

groups. The problems and policy responses on the national

forests, which had a great impact on silviculture from about

1985 on, are well presented in Fedkiw (n.d.), which is also

one of the best available histories of the Forest Service.

Forest Management Changes: 1985 to 

the Present

Several major trends are apparent in this period:

• Controversy and conflicts associated with the

Endangered Species Act (and its emphasis on 

individual species) and the opposition of segments 

of the public and some influential environmental

groups to any form of active management nearly 

halted management activities on the national forests.

There was a drastic decline in harvests and associated economic damage to forest-dependent industries and communities. Federal lands ceased to be 

a major factor in the regional timber supply.

Management emphasis shifted to recreation and 

perceived biodiversity issues.

• Other public ownerships were affected by the same

factors although, so far, to a much lesser degree. 

Legal requirements that state lands be managed to 

provide income for educational and other institutions provided continued incentives for timber production. There was a marked increase in thinning 

and a willingness to consider somewhat longer rotations in management planning.

• Another result of environmental concerns was the

increasing complexity of state forest practice regulations. Although these regulations have undoubtedly

been beneficial on the whole, they sometimes 

impose considerable burdens on landowners and 

can have unintended negative consequences.

Substantial amounts of private land were withdrawn from production to protect riparian and other

areas thought to be important to wildlife and fish 

or other environmental considerations. Restrictions

were imposed on clearcut size, leaving of “green 

trees” was mandated, etc. Although probably justified from the larger environmental standpoint, many 

of these requirements were viewed as a burden by 

the landowner.

• Although the adaptive management area component 

of the Northwest Forest Plan has been a near failure 

on federal lands, collaborative approaches to management of state and private forest lands have been

considerably more successful. Beginning with the

Timber-Fish-Wildlife Agreement of the mid-1980s 

and continuing through the current Forest and Fish

Policy, forest practices in Washington State have been

guided by consensus-building processes. Although

119
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GENERAL TECHNICAL REPORT PNW-GTR-696

there has been some litigation on some aspects of the

Timber-Fish-Wildlife Agreement, this has been minor

compared with that associated with federal land management. Adaptive management projects are undertaken along with cooperative monitoring and evaluation.

Participants include the state, tribes, large and small

forest landowners, local governments, and the environmental community. Such efforts receive peer review

and are used in decisionmaking and regulation by the

Forest Practices Board. 

Faced with a reduced and uncertain public timber 

supply, increasing regulatory restrictions on portions of an

ownership, and increased global competition, industrial

owners managed their remaining lands for maximum shortterm timber production. This often included intensive site

preparation, improved planting stock, control of competing

vegetation, stand density control, fertilization, and short

rotations. It also included extensive corporate mergers,

transfer of operations to lower cost regions both within and

outside the United States, sale of some lands to financial

institutions (insurance firms, retirement funds, etc.), or real

estate development with attendant forest fragmentation.

Thus, the current picture is a division into three broad

management classes by ownership:

• On most federal lands, timber production has 

become a secondary objective, subordinate to recreation, wildlife, and amenity values.

• On state lands timber production remains a major

objective although management practices are 

modified to reduce conflicts.

• On industrial and many other private lands, the 

primary objective is usually maximum return on the

timber investment. Other objectives are likely to be

pursued only in response to regulatory or public 

relations pressures, prospective land use changes, or

possible public provision of incentives.
Silvicultural Research and the Evolution of Forest Practices in the Douglas-Fir Region

The preceding pages have traced the history of silvicultural

research in the Douglas-fir region and its applications in

forest land management. We have made no attempt to discuss the burgeoning literature on forest ecology and tree

physiology, extensive topics that form the foundation of 

silviculture. We have touched only lightly on the important

role of silviculture in prevention and control of insect and

disease problems and in reducing the risks of catastrophic

windfall and fire. We have briefly sketched the concurrent

evolution of management practices, which reflect the combined influence of research, operational experience and

observation, and changing economic and social factors. 

We have confined ourselves largely to the means of

manipulating stand establishment and stand development,

many of which have been developed in a somewhat empirical manner although guided by considerable knowledge 

of the underlying biology. Our lengthy list of citations

includes most of the important research before 1950, but

only a fraction of the large literature that has developed

since then. Although incomplete, these citations should suffice to indicate the scope of the subject and to provide entry

points to the literature for readers without detailed prior

knowledge.

It should be apparent that a large part of our present

knowledge has come from long-term silvicultural experiments. These are expensive; difficult to maintain through

changes in personnel, budgets, and short-term political priorities; and are often unattractive to researchers because of

long lead times between establishment and the publishable

results that are the main criterion for advancement in the

research community. But, long-term experiments provide

information obtainable in no other way. Their results are far

more convincing to field foresters, landowners, and managers than any amount of extrapolation from theory and

short-term observations.

Looking back over the history of silviculture-related

research in the coastal Pacific Northwest, one can see a

number of long-term trends:

• Prior to the 1950s, forestry research was almost 

exclusively carried out by the U.S. Forest Service. 

In the early years, silvicultural research was done 

by a very small number of people of outstanding 

ability and motivation. In general, they were keen

observers and far-seeing individuals with a broad 

outlook, who operated with a high degree of independence on very low but fairly stable funding. A

number of them devoted their working lives to one 

area of primary interest, and developed an unparalleled knowledge of their subject. Much of their work

remains valuable. Despite limited resources, these 

few established and maintained a number of longterm studies that have had major influences on 

management.

• As the Forest Service research organization 

expanded, it necessarily became more highly structured. The Research Station Director became primarily an administrator (although usually with a 

scientific background). With increased numbers of 

people and increased specialization, team efforts 

and formal research organization became more 

important. There was more emphasis on interdisciplinary research.

• There was a great expansion in university research

after World War II (WWII). Most of this was funded 

by grants from various sources, including the 

McIntire-Stennis Act, National Science Foundation,

other organizations (including the Forest Service), 

and (in Oregon) a harvest tax. In general, dependence on short-term grants and graduate student

research assistants, conflicts with staff teaching 

duties, and university reward systems did not 

encourage continuity of effort or long-term studies

(although some were undertaken, usually as cooperative efforts supported in part by federal agencies 

and industry).

121

Chapter 14: In Conclusion1

1 By R.O. Curtis and D.S. DeBell.
122

GENERAL TECHNICAL REPORT PNW-GTR-696

• Considerable industrial research was undertaken 

after WWII. Much of this was aimed at solving 

short-term management questions, but there were 

also some long-term studies. Some of these were disrupted or destroyed in the course of various reorganizations and ownership changes. Most data are not

publicly available. 

• From around 1970 onward, the Forest Service also 

had difficulties in maintaining long-term silvicultural

research. Long-term research was in competition for

funds with short-term studies, which were often

prompted by politically “hot” questions of the 

moment.

• Overall, efforts and funding devoted to silvicultural

research increased rapidly after WWII, peaked sometime in the 1970s, and steadily declined thereafter.

Some of the decline resulted from a mistaken perception in some quarters that we already knew everything we needed to know about silviculture. More

of it resulted from diversion of public agency effort

and funding into the politically more popular though

related fields of forest ecology, wildlife, and associated environmental questions. The decline also

reflected the relatively low priority given natural

resource management compared to other national 

concerns.

• The need for continuity combined with the limited 

personnel and funding resources available in individual organizations has led in the last several 

decades to an increased emphasis on cooperative

efforts, which combine the resources of several 

organizations.

• There has been a revival of long-term silvicultural

studies in the last few years, stimulated by the 

evident need for management regimes that can 

maintain commodity production from forest lands

while simultaneously providing aesthetic, recreational, and wildlife values. Many of the questions

involved can only be answered by long-term 

multidisciplinary studies.

It should be apparent that silviculture and silvicultural

research have a much longer history than most people—

both the general public and natural resource specialists in

other fields—realize. There is a great amount of existing

information available for those with the time, inclination,

and expertise to seek it out. Because of the long-term nature

of forestry and the timescales involved in forest development, public attitudes and desires may change faster than

the forest can respond to changes in management, and

faster than research can provide definitive answers. 

Knowledge can never be complete, and information

needs will continue to change with changes in the biological, economic, and social environment. There is a continuing need for silvicultural research in both traditional areas

such as intensive wood production, and in alternative silvicultural systems and management regimes directed at integrated management for multiple objectives (National

Research Council 1990, 2002). The latter includes the 

relatively new and potentially important goal of carbon

sequestration.

One has only to read the media coverage of various

forestry issues to realize that much of the public and the

media that shape public opinion have little understanding 

of the long history of Northwestern forestry, the nature of

forests, possible management options, or the existence of 

a large body of research-based information. Unfortunately,

much of the existing information is only available in specialized publications that are not ordinarily seen by workers

in other fields, and that are often both inaccessible and

unintelligible to the general public. There is a great need 

for synthesis of existing information and its presentation 

in forms understandable by nonspecialists and by people 

in other natural resource-related disciplines.

We hope that this publication will contribute toward

that end.
Silvicultural Research and the Evolution of Forest Practices in the Douglas-Fir Region

Acknowledgments

We acknowledge many helpful suggestions from reviewers, 

namely: Philip Aune, formerly PSW Research Station

(retired); Robert Buckman, Oregon State University (OSU),

former Deputy Chief for Research, U.S. Forest Service;

Sarah Greene, PNW Research Station; Denis Lavender, 

formerly OSU (retired); John Tappeiner, OSU. Connie

Harrington and David Marshall (PNW Research Station)

provided additional information and assistance. Joe Kraft

assisted in preparation of illustrations. Grace Douglass

assisted in preparation of text in proper format for 

publication.

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Allen, E.T. 1926. Men, trees, and an idea: the genesis of a 

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Silvicultural Research and the Evolution of Forest Practices in the Douglas-Fir Region

Appendix

Table 1—Common and scientific names of European species 

referred to in text

Common name Scientific name

Beech Fagus sylvatica L.

Birch Betula pendula Roth., and

B. pubescens Ehrh.

Maritime pine Pinus pinaster Ait.

Oak Quercus petraea (Mattuschka) Liebl., and

Q. robur L.

Scots pine Pinus sylvestris L.

Silver fir Abies alba Mill.

Spruce Picea abies (L.) Karst.

Table 2—Common and scientific names of North American trees referred 

to in text

Common name Scientific name

Alaska yellow-cedar Chamaecyparis nootkatensis (D. Don) Spach

Bigleaf maple Acer macrophyllum Pursh

Black cottonwood Populus trichocarpa Torr. & Gray

Canyon live oak Quercus chrysolepis Liebm.

Chinkapin Castanopsis chrysophylla (Dougl.) A. DC.

Douglas-fir Pseudotsuga menziesii (Mirb.) Franco var. menziesii

Engelmann spruce Picea engelmannii Parry ex Engelm.

Grand fir Abies grandis (Dougl. ex D. Don) Lindl.

Incense-cedar Libocedrus decurrens Torr.

Jeffrey pine Pinus jeffreyi Grev. & Balf.

Lodgepole pine Pinus contorta Dougl. ex Loud.

Madrone Arbutus menziesii Pursh

Mountain hemlock Tsuga mertensiana (Bong.) Carr.

Noble fir Abies procera Rehd.

Oak, Oregon white Quercus garryana Dougl. ex Hook.

Pacific silver fir Abies amabilis Dougl. ex Forbes

Ponderosa pine Pinus ponderosa Dougl. ex Laws.

Red alder Alnus rubra Bong.

Sitka spruce Picea sitchensis (Bong.) Carr.

Sugar pine Pinus lambertiana Dougl.

Tanoak Lithocarpus densiflorus (Hook & Arn.) Rehd.

Western hemlock Tsuga heterophylla (Raf.) Sarg.

Western redcedar Thuja plicata Donn ex D. Don

Western white pine Pinus monticola Dougl. ex D. Don

White fir Abies concolor (Gord. & Glend.) Lindl. ex Hildebr.

171
172

GENERAL TECHNICAL REPORT PNW-GTR-696

Table 3—Common and scientific names of non-tree plants mentioned in text

Common name Scientific name

Beargrass Xerophyllum tenax (Pursh) Nutt.

Bitterbrush Purshia tridentata (Pursh) DC.

Camas Camassia quamash (Pursh) Greene

Hazelnut Corylus cornuta var. californica (A. DC.) Sharp

Himalayan blackberry Rubus armeniacus Focke

Huckleberries Vaccinium (various species)

India mustard Brassica juncea (L.) Czern

Oregon grape Berberis aquifolium Pursh

Manzanita Arctostaphylos columbiana Piper

Rhododendron Rhododendron macrophyllum D. Don ex G. Don

Salal Gaultheria shallon Pursh

Salmonberry Rubus spectabilis Pursh

Scotch broom Cytisus scoparius (L.) Link

Snowbrush Ceanothus velutinus Dougl. ex Hook.

Swordfern Polystichum munitum (Kaulfuss) K. Presl

Vine maple Acer circinatum Pursh

Table 4—Common and scientific names of insects and diseases mentioned in text

Common name Scientific name

Annosus root disease Heterobasidium annosum (Fr.) Bref (formerly Fomes annosus)

Douglas-fir bark beetle Dendroctonus pseudotsugae Hopkins

Dwarf mistletoe Arceuthobium tsugense (Rosendahl) G.N. Jones

Laminated root rot Phellinus weirii (Murr.) Gilb.

Seed chalcid Megastigmus spermotrophus Wachtl

Swiss needle cast Phaeocryptopus gaumanni (Rohde) Petrak

White pine blister rust Cronartium ribicola Fischer

Table 5—Common and scientific names of wildlife species 

referred to in text

Common name Scientific name

Bear Ursus americanus Pallas, 1780

Beaver Castor canadensis Kuhl, 1820

Deer Odocoileus hemionus Rafinesque, 1817

Deer mouse Peromyscus maniculatus Wagner, 1845

Elk Cervus elaphus Linnaeus, 1758

Mountain beaver Aplodontia rufa Rafinesque, 1817

Mazama gopher Thomomys mazama Merriam, 1897

Northern spotted owl Strix occidentalis caurina Merriam, 1898

Western gray squirrel Sciurus griseus Ord 1818
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