Authors

I

i

ROBERT O. CURTIS is an emeritus scientist and DEAN S. DEBELL and

CONSTANCE A. HARRINGTON are research foresters, U.S. Department of

Agriculture, Forest Service, Pacific Northwest Research Station, Forestry Sciences

Laboratory, 3625-93d Avenue SW, Olympia, WA 98512-9193; J. BRADLEY ST. CLAIR

is a research geneticist, Pacific Northwest Research Station, Forestry Sciences Laboratory, 3200 SW Jefferson Way, Corvallis, OR 97331; DENIS P. LAVENDER is an

emeritus professor of forest sciences, Oregon State University and University of British

Columbia, mail address Department of Forest Sciences, College of Forestry, Oregon

State University, Corvallis, OR 97331; and JOHN C. TAPPEINE and JOHN D.

WALSTAD are professors, Department of Forest Resources, College of Forestry,

Oregon State University, Corvallis, OR 97331.
Errata 

This figure 3 replaces the figure on page 7 

I In I 

1940 1990 1950 2000 

Year 

This figure 21 replaces the figure on page 35 

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We apologize for any inconvenience this may have caused you. 

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Abstract Curtis, Robert 0.; DeBelI, Dean S.; Harrington, Constance A.; Lavender, Denis P.;

St. Clair, J. Bradley; Tappeiner, John C.; Walstad, John D. 1998. Silviculture for

multiple objectives in the Douglas-fir region. Gen. Tech. Rep. PNW-GTR-435.

Portland, OR: U.S. Department of Agriculture, Forest Service, Pacific Northwest

Research Station. 123 p.

Silvicultural knowledge and practice have been evolving in the Pacific Northwest for

nearly a century. Most research and management activities to date have focused on

two major topics: (1) methods to regenerate older, naturally established forests after fire

or timber harvest; and (2) growth and management of young stands. Today forest

managers can reliably regenerate the major conifer and hardwood species under most

conditions by using combinations of natural and artificial regeneration. They also can

control stand density and species composition and growth of individual trees, thereby

influencing stand structure. Available growth models can reasonably predict the outcome of growing conifer stands under a range of densities, species composition, and

management scenarios, providing tree numbers by size class as well as crown characteristics and wood yields.

Most silvicultural efforts have been financed through and directed toward production of

wood. Although some other values have been produced or improved in conjunction with

such activities, public interest and emphasis on nontimber values have increased. It

has become apparent that some values are not benefitted by silvicultural practices

aimed solely at wood production. In most situations, however, desired nontimber values

can be enhanced by silvicultural measures implemented for their direct benefit or by

some modifications of practices applied primarily to produce wood. We discuss the

historical development of silviculture in the Pacific Northwest and review the silvicultural

practices currently available to forest managers. We then point out how these practices

can be modified and used to maintain and produce wildlife habitat, diverse stand

structures (including those usually associated with old forests) and pleasing scenery,

while also producing wood products. Most of the silvicultural knowledge needed to

design and implement regimes for integrated production of these multiple values

already exists.

Keywords: Ecosystem management, multiple use, silvicultural systems, wildlife habitat,

thinning, landscape management, forest ecology, Douglas-fir.
Contents

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Introduction

Foundations

Some Definitions

Historical Development of Silviculture in the Douglas-Fir Region

Forest Conditions, Stand Development, and Management Goals

Forest Conditions

Stand Development

Changing Goals in Forest Management

Regeneration Methods

Natural Regeneration

Direct Seeding and Planting

Shaping Development of Young Natural Stands and Plantations

Social Expectations and Silvicultural Opportunities

Early Density Control

Thinning in Older Stands

Nutrient Management

Pruning

Summary, Shaping Development

Harvesting Considerations

Regeneration Harvests

Rotations

Wood Supply, Cash Flows, and Distribution of Stand Ages and Conditions

Special Forest Products

Summary, Harvesting Considerations

Providing Diverse Structures and Habitats

Species Mixtures

Stand Management for Structural Diversity

Use of Advance Reproduction

Shrub and Hardwood Management

Providing Cavities, Snags, and Coarse Woody Debris

Other Considerations

Summary, Diverse Structures

Maintaining Site Productivity
67 Summary, Site Productivity

67 Damaging Agents and Forest Health

68 Fire

68 Weather

69 Bark Beetles

70 Mammals

71 Diseases

72 Dwarf Mistletoes

72 Summary, Forest Health

73 In Conclusion

73 Management Choices

75 Information Needs

76 Some Policy Questions

79 Acknowledgments

79 Metric Equivalents

79 References

109 Appendix: Some Possible Management Scenarios

120 Glossary
Introduction When biologists took their investigations of the relation

of plants to the environment from the laboratory to the

field, they found the silviculturist already there with the

accumulated facts of a century of field work.

James W. Tourney of Yale University, 1928

The above quotation, from the preface to the first edition of Foundations of Silviculture

Upon an Ecological Basis (Tourney 1928), emphasizes the fact that silvicultural practice

and the research in silviculture and the ecological relations that underpin it antedate the

settlement of much of North America. The early foresters in the Pacific Northwest (and

elsewhere in the United States) began with forest management concepts imported from

Europe. These concepts were in part unsuited to the economic and social conditions

existing in the United States at that time (ca. 1900), and to species and climatic conditions that differed somewhat from those of Europe. But this introduction of forestry

concepts began a continuing process of adaptation and evolution. In reading the early

reports and research publications on forestry in the Pacific Northwest, one is struck by

the keen observations and foresight and the tremendous accomplishments of a small

group of pioneer workers.

Changing social and economic conditions have led to many changes in forest management practices and policies since the early 1900s. In recent years, the interested

general public and specialists trained in disciplines other than traditional forestry have

played increasing roles. New ideas have been introduced and outlook has broadened.

But differences in background and experience often give rise to communication difficulties, misconceptions, and misunderstandings that are not always recognized. New

concepts can be conceived, evaluated, and implemented most effectively when all

participants have a shared knowledge about how current practices were developed and

why they were adopted. Such understanding also will help to retain past gains, prevent

old problems from reappearing, and avoid new problems as new ideas and practices

are incorporated in forest management regimes.

Several years ago, the authors prepared a number of short papers for the symposium

Creating a Forestry for the 21st Century, held in Portland, Oregon, August 24-26, 1993.

These were subsequently published as chapters 8 to 10 in a book of the same title

(Kohm and Franklin 1997). The symposium framework necessarily imposed constraints

on length and scope of discussion, and we subsequently felt that an expanded discussion of the entire subject of silviculture for multiple objectives in the Douglas-fir region

was needed. This publication is the result.

Historically, silviculture developed in response to society’s need to grow wood to

replace declining supplies from unmanaged natural forests, a need that arises sooner

or later in all parts of the world. Much of the existing silvicultural literature and silvicultural terminology is therefore phrased in terms of wood production. But the utility of

silviculture extends far beyond this. Silviculture consists of a body of knowledge and

techniques that can be applied to shape development of forests to meet whatever

objectives are selected-whether the emphasis be on watershed protection, scenic

values, ecological restoration, development of wildlife habitat, or wood production. Most

of our Northwestern forest lands have wood production as a major objective, and some
Foundations

lands have been dedicated to specific nontimber uses. It is now apparent that needs for

wood and for other values can never be adequately met by setting aside major portions

of the forest land base for single uses of any kind. Rather, there is a great need for

management regimes that can produce multiple values. Such multipurpose management does not mean that all values must receive equal emphasis on all lands. We

believe that a variety of regimes must be developed and applied in harmony with land

capabilities and management objectives. These regimes may range from intensive

wood production on a semiagricultural basis with some incidental production of other

values, through management for joint production of wood and nontimber values, to

management primarily for wildlife, aesthetic, and recreational uses with some associated production of wood (Curtis and Carey 1996).

In this report, we review the history of silviculture in the Douglas-fir region and the

available silvicultural options and techniques. We provide some literature references

for those interested in further information. We do not seek to duplicate the excellent

discussion of regional silviculture given by Tesch (1995). Rather, our aim is to point out

the wide range of possibilities for controlling stand establishment and development to

meet a variety of possible objectives, with a focus primarily on the multiple objectives

commonly involved in management of forest ecosystems on both public and private

lands. And, we will point out some related policy questions and offer some opinions.

The science and practice of silviculture provide the means for managing vegetation in

forests and thereby influencing forest health, soil and stand productivity, habitats of

diverse plant and animal populations, and the welfare of forest-dependent communities

and of society in general. In this initial section, we provide general background and

trace the development of silviculture in the Douglas-fir region of the Pacific Northwest

as it has evolved in the 20th century with changes in knowledge, economics, and

philosophies of forest land management. The next section discusses forest and stand

development, changing social expectations and management goals, and opportunities

to meet them through silvicultural practices. Subsequent sections discuss (1) regeneration systems, (2) silvicultural practices as means of shaping development of young

stands to meet desired objectives, (3) harvesting options and rotations, (4) providing

diverse structures and habitats, (5) maintenance of site productivity, (6) damaging

agents and forest health, and (7) some conclusions and implications. Discussion is

primarily in terms of coast Douglas-fir (Pseudotsuga menziesii (Mirb.) Franco var.

menziesil) in the Pacific Northwest west of the Cascade summit, although the associated western hemlock (Tsuga heterophylla (Raf.) Sarg.), red alder (Alms rubra Bong.),

western redcedar (Thuja phcata Donn ex. D. Don.), and true firs (Abies spp.) also are

considered. Many of the concepts involved have much wider applicability.

Some Definitions Some silvicultural terms used in this report may not be familiar to or completely understood by all readers. Although most terms will be explained when first used, there is

also a glossary at the back for easy reference. A few terms that are fundamental to

the discussion are defined below.

Silviculture consists of the techniques used to manipulate vegetation and direct stand

and tree development to create or maintain desired conditions. Silviculture substitutes

small-scale controlled disturbances for large-scale haphazard natural events, such as

wildfires and windstorms. It applies ecological knowledge to attainment of human ends.

Silvicultural practices influence rates of tree growth and stand development, stand

composition, stand structure, and biodiversity.
An ecosystem is a complex of plants and animals and the associated physical factors

of their environment that functions as a unit. It has the attributes of structure, function

(exchange of matter and energy), complexity, interaction and interdependency among

its components, and dynamic change in structure and function over time. Spatial

dimensions are not an inherent attribute. Ecosystem is therefore best regarded as a

concept rather than a specific physical entity (Kimmins 1987, p. 26). Silviculture is (or

should be) based on ecological knowledge, and the ecosystem concept is important

in that it emphasizes the need to evaluate the many environmental and biotic factors

influencing the choice and outcome of silvicultural treatments and their sequence over

time, and the long-term consequences and sustainability of management regimes.

Ecosystem is often loosely used as a synonym for such terms as stand, forest, and

landscape. In this report, however, we elect to use the older, long-established, and

more specific terminology.

Ecosystem management is a currently popular term that, again, represents a useful

concept but lacks specificity. It is useful in that it emphasizes the need to take a holistic

view-on a scale larger than the individual stand-of management possibilities and

consequences of management actions on productivity and sustainability of the many

values that humans obtain from forests. But it is loosely defined and is often given

somewhat different interpretations by different people. And, it seems to be acquiring

ideological and political connotations (e.g., Chase 1995). We have consciously avoided

the term in this report, in favor of the more specific terms of stand, forest, and landscape management.

The words tree, stand, and forest are often used to describe various portions of the

forest environment. A stand is a group of trees and associated vegetation sufficiently

similar in composition, structure, and condition to be distinguished from other groups of

trees within a forest, and large enough to be considered an entity for management

purposes. A forest is composed of stands.

A regeneration system consists of the procedures by which a new stand or group of

trees is intentionally established, after removal of the former stand or part thereof by

harvest, fire, or other disturbance. It includes the harvest method used and subsequent

operations to establish a new age class or classes.

Thinning is the removal of a portion of the trees from a stand to promote development

of the remaining trees (and sometimes understory vegetation) and often to secure

intermediate income prior to final harvest. A thinning is precommercial if the cut trees

are too small for economic use. A thinning is commercial if trees are removed and

sold.

A silvicultural system is a planned program of silvicultural treatments covering the

entire life of a stand (in even-aged management), extending from regeneration through

any intermediate operations to final removal and regeneration. In uneven-aged management, the silvicultural system encompasses methods of tending and removal and

replacement of individual trees or small groups of trees within the stand in perpetuity.

Although unforeseen events such as fire or blowdown often require modification of a

previously planned system, this does not negate the need for a long-term plan of

silvicultural activities.

3

*
Figure 1-Return of the forest in the Wind River Valley. The Wind River

nursery and surrounding area in (A) 1914, after extensive early logging and

wildfire; (B) 1935; and (C) 1954.

4

l
Silvicultural systems are conventionally discussed under a few broad class designations, but there is, in fact, an almost infinite variety of possible systems. Most of the

possible systems have been tried, somewhere, sometime. Silviculture and silvicultural

systems are far from new. Their origins in western society extend back to the late

Middle Ages; some simple systems were in use in parts of western Europe by the 17th

century, and by the mid-19th century silviculture had become an organized and scientifically based discipline with more or less its present terminology (Fernow 1911).

European silvicultural concepts and methods were introduced to North America around

1900 and have subsequently gone through a continuing process of modification and

adaptation to North American species and changing North American social and economic conditions.

Harvest cuts consciously designed to secure regeneration and provide continued

production of timber and other forest values are referred to by the name of the associated silvicultural systems. The wide variety of these are conveniently grouped for

discussion purposes into the conventional categories of (1) clearcutting, (2) seed-tree,

(3) shelterwood, (4) selection, and (5) accessory systems (Matthews 1989). Excellent

discussions are also given by Daniel and others (1979), Nyland (1996), Smith (1986), ant

Smith and others (1997). In any of these systems, regeneration may be by natural seeding, planting, or a combination of the two. Direct seeding has been used occasionally.

Historical Development

of Silviculture in the

Douglas-Fir Region

Forest management practices in the Pacific Northwest evolved from beginnings in the

mid-19th century. Until the early 19OOs, the forests were viewed as a static resource to

be mined, and the usual objective was to harvest high-value timber at minimum direct

cost, with little consideration given to reforestation, protection of soil or water, or provision for wildlife habitat. Because of the physical and economic limitations of railroad

logging, cutting frequently began at the bottom of a watershed and continued to the

uplands until an entire basin was logged. Unmerchantable trees were left standing, and

logged areas often were accidentally or intentionally burned. Wildfires were frequent and

largely uncontrolled. Some, such as the Yacolt fire of 1902 in southwest Washington,

burned huge areas and caused major losses of property and sometimes of human life.

This pattern of large cut areas frequently followed by fire may have more closely

mimicked natural disturbance by large fires than the staggered setting, dispersed

clearcutting approach that followed. Natural regeneration of trees and shrubs often

occurred following early logging or intense fire because mineral soil was exposed and

seed was often available from residual trees or from adjoining stands. The results

ranged from well-stocked, vigorous young conifer stands (fig. 1), to stands of red alder

or sprouting hardwoods, to covers of shrubs or nonwoody plants of various densities

with only occasional conifer or hardwood trees.

Change began with the establishment of the National Forests at the end of the 19th

century. Establishment of the Wind River nursery in southern Washington (1909) and

planting programs for rehabilitation of extensive burns followed. Forest research in the

region began ca. 1910. Organized fire suppression was introduced after the disastrous

turn-of-the-century fires and became increasingly effective through the 1920s and

1930s. Research leading to early yield tables showed the enormous growth capacity of

Northwestern forests (McArdle and Meyer 1930). Methods for consistently regenerating
forests after fire or timber harvest became a high priority for early research. Experimentation with harvest cutting and regeneration techniques began early and continues to

the present.

The first permanent research plots (still extant) to study growth and yield of young

stands were established in 1910 (fig. 2). Seed crops and seed dispersal were studied.

Experiments with plantation spacing and thinning followed. Two pioneering studies

begun in 1912 by the United States Forest Service, Wind River Experiment Station

(later to become the Pacific Northwest Research Station), compared seed sources and

species for plantations. One of the earliest forest genetics studies in the United States

(and in the world) compared results of using Douglas-fir seed from different locations

and from different parent trees within stands (Munger and Morris 1936). A second study

compared 152 forest tree species planted at the Wind River Aboretum over a quarter

century (Munger and Kolbe 1932, Silen and Olson 1992); this showed that Pacific

Northwest species were inherently superior to any of the exotics tried. Both studies

demonstrated the importance of long-term research and the facts that (1) a long time

span may be required to evaluate suitability of a species or seed source to the local

environment, (2) occasional or rare extreme weather events or seasons may be

particularly important in determining adaptation, and (3) maladaptation may be expressed quickly or may occur as a slow decline over many years.

The combination of effective fire control, high productive potential of Northwestern

forests, and development of successful regeneration methods made forest management on a permanent basis possible. Very early, Allen (1911) stated the policy and

information needs for planned forest management and permanence of the timber

industries and forest-dependent communities. The basic silvicultural knowledge needed

to regenerate stands after harvest was available by the late 1920s (Munger 1927),

although many refinements remained to be worked out. Industrial and private owners

and public agencies made substantial forestry investments (Greeley 1948, Hagenstein

Figure 2-Willamette

no. 1 in 1997: this and

two adjacent study plots,

established in 1910,

were probably the first

long-term research plots

in the Northwest and

provide an 87-year

record of the development of a naturally

established untreated

Douglas-fir stand.
1986), and these accelerated rapidly in the changed economic climate that followed the

end of the Great Depression and World War II. The marked and generally consistent

trend of rising timber prices that began shortly after World War II (fig. 3; Haynes and

Sohngen 1994) provided a powerful incentive to industrial and other owners to undertake long-term programs of active forest management, including both forest protection

and large investments in stand regeneration and management. Along with increased

emphasis on planting, tree improvement efforts began in the 1950s with selection of

“plus trees” in native stands and establishment of the first seed orchards (Duffield 1955,

Isaac 1955a). Tree improvement programs greatly expanded in the 1960s and 1970s

(Campbell 1964, Silen 1966, Silen and Wheat 1979, Stonecypher and others 1996), as

did the application of cultural treatments such as early respacing and fertilization. The

Pacific Northwest became the first region in North America, and perhaps the world,

where the people and organizations that came to harvest the original forests stayed

and invested in succeeding ones-and made those investments while much of the

original old-growth forest remained.

Early efforts to adapt silvicultural systems to the Pacific Northwest included the seed

tree method and “selective” cutting, as well as clearcutting.

Though widely applied, the seed tree system did not consistently provide uniform and

timely regeneration. Many seed trees were soon lost to wind and other causes (Isaac

1940a, 1943) and seed supply was often insufficient, although for some areas and

circumstances it was adequate (Garman 1951).

The advent of the tractor and motor truck about 1930 as alternatives to the donkey

engine and railroad logging introduced a new flexibility that made alternative harvest

methods possible. On gentle terrain, tractors could skid logs around obstacles and

residual trees, and expanding road systems allowed truck access to timberlands. A

form of partial cutting popularly called selective logging developed on private lands as a

250

8 250

0

Tii

2

E 250

250

1940 1960 1980 2000

Year

Figure 3-Price trend

for National Forest

timber sales, 1910 to

present, in constant

1982 dollars. The

steady rise since World

War II provided a

powerful incentive for

owners to adopt

management measures

to enhance future wood

production.
8

Figure 4-The

“staggered

setting” pattern

of dispersed

clearcuts was

the most

common

harvesting

practice on

National Forests

in the period

1950-90.

Figure 5-

Clearcut unit

with natural

seeding from

adjacent uncut

timber, 1954.

Figure 6-It has

been common

practice of many

owners to use

large clearcut

harvest units,

which are then

planted with

genetically

selected stock.

f
response to the economic pressures of the depression. Only the more valuable trees

were cut and removed. Selective logging might better have been called high-grading or

“logger’s choice.”

Kirkland and Brandstrom (1936) proposed an elaborate scheme for “selective timber

management” in Douglas-fir and hemlock stands in the National Forests. This proposal

was likewise stimulated by the economic problems of the depression era and was

implemented on the public lands on a fairly extensive scale from the mid-1930s to the

late 1940s. The proposed system called for detailed economic and stand analyses and

frequent entries. It was thought that a number of light partial cuts, each removing

mostly large overmature trees, could pay for roading and show favorable financial

returns under the existing economic conditions. They envisioned eventual regeneration

in group or small patch cuts on the order of 1 to 10 acres, to be introduced gradually

over several cutting cycles after the initial entry.

Debate over selective cutting in Douglas-fir was quite lively (Munger 1950, Smith

1970), and its use apparently ended in the late 1940s. Munger (1950) reported that all

new Bureau of Land Management and Forest Service sales called for clearcutting,

except for some uneven-aged stands of mixed species in southwestern Oregon and

certain other thrifty mature stands. Isaac’s evaluation of partial cutting (Isaac 1956)

and his studies of natural regeneration (Isaac 1943) discredited “selective cutting.”

Five to ten years of observation by Isaac on permanent plots within selectively cut

areas of old-growth forest showed extensive residual tree damage and mortality,

substantial windthrow, bark beetle attack, change in species composition from shade

intolerant to shade tolerant species, and a lack of Douglas-fir regeneration. Isaac

recommended abandoning general use of the system. He did suggest that some form

of partial cutting or uneven-aged management might be appropriate for drier sites in

southwest Oregon, gravel soils of the Puget Sound region, and severe southerly

exposures elsewhere in the region where moisture and shade were critical factors.

In retrospect, Kirkland and Brandstrom’s ideas were never thoroughly evaluated,

because the unsatisfactory early results caused their abandonment before the stands

reached the point of planned group or patch regeneration (Curtis 1998). The primary

reasons for failure (Smith 1970) were that (1) the system was applied in old, previously

unmanaged, and highly defective stands that were unstable when opened up; and (2)

only the largest and best trees could be removed at a profit under the economic

conditions of the period. Contributing factors were (1) limitations of existing logging

technology, (2) inadequate attention to creating suitable openings for regeneration and

to site preparation, (3) total reliance on natural regeneration, and (4) attempted implementation of a single policy despite differences in local site and stand conditions.

The poor results from “selective cutting” in these old stands, the observation that many

of the old liquidation cuts had regenerated well when seed was available from nearby

uncut timber and fire protection was provided, and accumulating information on reproductive requirements of Douglas-fir led to general adoption of the clearcutting system

throughout the region. The clearcutting system evolved over the next half century from

one of dispersed small (i.e., 40 acres or less; fig. 4) harvest units with natural seeding

(fig. 5) from surrounding uncut timber (“staggered settings”), to large harvest units

that commonly receive some form of site preparation and are planted with genetically

selected stock (fig. 6). Clearcutting had biological, operational, and economic

9
advantages. It favored Douglas-fir over its more tolerant and less valuable associates

and enabled Douglas-fir to grow rapidly after establishment. It simplified slash disposal

and brush control measures. It was well adapted to cable logging in steep terrain where

other methods were inefficient or inapplicable. Because harvest was concentrated on

limited areas, it required less road construction than partial cutting systems. But, it was

also highly visible and it became controversial with many segments of the public.

Although clearcutting became the dominant system throughout the Douglas-fir region,

there was some limited use of uniform shelterwood on severe sites (Williamson 1973)

and some work on shelterwood in western hemlock (Williamson and Ruth 1976). Longcontinued experimental trials of other forms of partial cutting and attempts at unevenaged management do not exist in the region, although there are a few trials in early

stages. This lack is unfortunate, for such trials could have provided information useful

in designing and evaluating a range of silvicultural systems to meet current needs.

Reviews of the underlying science and experience related to application of the various

silvicultural systems in the Pacific Northwest are available in Burns (1983, 1989), Fiske

and DeBell (1989) Franklin and others (1983), Harris and Johnson (1983), Tesch

(1995), and Williamson and Twombly (1983).

The early foresters in the Pacific Northwest recognized that thinning was a beneficial

practice that would someday become important. But with huge amounts of large timber

available and a rudimentary transportation system, thinning did not become economically feasible until after World War II. In the 1950s many foresters saw commercial

thinning as the wave of the future (Worthington and Staebler 1961a), and thinning

experiments and some operational thinnings were begun. Subsequent decades saw a

shift to shortened rotations-to as little as 40 to 50 years in some ownerships. A concomitant shift took place in attitudes toward thinning. As rotations became shorter,

many owners invested heavily in precommercial thinning but most private and industrial

owners lost interest in commercial thinning in favor of early harvest of the entire stand.

Until the mid-1970s, there was general agreement that timber production was the

primary objective in management of most forest land. Basic assumptions, accepted by

nearly all at the time, were that wood production in old-growth stands was essentially

static (no net growth), and that insects and disease were diminishing the amount of

usable wood in such stands. It therefore seemed desirable to replace old-growth

forests with young, rapidly growing stands. The biological, political, and economic

environments combined to favor investments in management of young-growth forests

by both public and private owners. Much of the forest land in the Douglas-fir region,

particularly that in non-Federal ownership, was converted from slow-growing natural

mature and old-growth stands to rapidly growing younger managed stands. Although

standing timber volume in Pacific Coast forests declined (about 19 percent) from 1952

to 1986 as old-growth forests were harvested, annual net growth in the region increased and came to exceed harvest (MacLean and others 1992, Waddell and others

1989); this is true for the United States as a whole, although differences exist among

regions and ownership classes (MacCleery 1992, Powell and others 1993).

Many changes have occurred in the Douglas-fir region since the mid-197Os, and

management issues on both public and private land have become much more complex.

Human populations have increased and spread into rural, forested areas. Laws and

10
regulations-some of which conflict with each other and with older legislation-have

been enacted in response to concerns about environmental quality. Forest products

markets have changed; they have expanded in size and location, and tree species that

previously had limited value are in demand. And, nontimber values as well as wood

production have become prominent management considerations.

Forest Conditions, Although the early settlers of the region encountered many large tracts of old-growth

Stand Development, forests with trees of impressive size, the common conception of the presettlement

and Management Northwestern forest as an unbroken sea of giant old-growth trees existing in perpetuity

Goals

Forest Conditions

is false. The proportion of forest that was what we now term “old growth” cannot be

determined with any precision, but several estimates suggest it was no more than 40 to

50 percent (Ripple 1994) and perhaps less, and that it fluctuated markedly over time.

Old-growth forests currently occupy about 18 percent of the productive forest land in

California, Oregon, and Washington (Bolsinger and Waddell 1993), of which more than

80 percent is on Federal land, primarily National Forests. Many sites in the region are,

however, incapable of producing “cathedral-like” old-growth stands. Considerable

lowland areas now in conifer forest were open prairie and oak woodland prior to

settlement (Franklin and Dyrness 1973); at higher elevations extensive grass balds,

shrub fields, and huckleberry fields were common. All were maintained by natural fires

and by native burning. Presettlement forests were dynamic and were periodically

disrupted or destroyed by fire (both lightning and human caused) and windstorms,

which created a patchwork of ages and developmental stages over areas both large

and small (Agee 1991, 1993; Henderson and others 1989; Kay 1995; Walstad and

others 1990).

Most of our present Northwestern forests owe their origin to catastrophic events,

principally fire, logging, or a combination of the two. Although all trees may not have

been killed or removed and regeneration often took place over an extended period

(Spies and Franklin 1991, Tappeiner and others 1997), most stands were more or less

even-aged in youth. As they grow older, they gradually develop a more irregular age

composition and canopy structure as tolerant understory species capture openings

arising from death of individual overstory trees or groups of trees or small-scale disturbance. Because of their fire (or logging plus fire) origin, the forests over much of the

region were and are dominated by the relatively intolerant and fire-adapted Douglas-fir,

even without conscious human effort to maintain the species.

Plantations dominate the forest landscape on industrial lands, and scattered plantations

of smaller extent are a major feature of public lands. Most were planted as pure Douglas-fir, but there are some plantations of other species, including mixed species

plantings. Many plantations have acquired a considerable admixture of other conifers,

hardwoods, and shrubs through natural seeding, sprouting, or advance reproduction

carried over from the previous stand. These plantations do, however, differ considerably from naturally established old forests, as will be discussed in subsequent sections.

Stand Development Stands and their boundaries are influenced by both natural processes and management activities. Stands are dynamic, changing with time and progressing through

successive developmental stages as trees are established, grow, and die. Resource

values provided by or occurring within stands change similarly. Changes occur rapidly

11
Figure 7-Development stages of natural stands can be characterized as (A) stand initiation, (B) stem exclusion, (C) understory reinitiation,

and (D) old growth. Similar stages occur in managed stands but their duration is markedly modified.

12
and are readily apparent in young stands, but may be nearly imperceptible to casual

observation in older stands. Conditions in unmanaged stands may sometimes correspond to the needs and desires of human society or some part thereof; in such cases,

natural disturbance events, seed crops, and stand development processes have

coincided to provide desired features at the time and place they are wanted. In other

cases, natural events and processes have produced forest stands much less suited to

human needs and desires.

Development stages of natural stands can be usefully characterized (Oliver and Larson

1996) as (1) stand initiation, (2) stem exclusion, (3) understory reinitiation, and (4)

old growth (fig. 7). The stand initiation stage follows a major disturbance (e.g., fire,

windstorm, logging) when new individuals and many species become established. The

stem exclusion stage occurs after canopy closure, as the stand begins to differentiate

into size classes and shading and competition for nutrients and water by larger trees

lead to death of smaller trees and much or all of the understory vegetation. The understory reinitiation stage follows as crowns recede and scattered overstory trees begin to

die, and herbs, shrubs, and tree regeneration (usually of tolerant species such as

western hemlock, western redcedar, and true firs) appear on the forest floor. The oldgrowth stage occurs when overstory trees die sporadically and understory trees begin

growing into the overstory, creating multiple canopy layers and a gradual shift toward a

stand dominated by tolerant species. Subdivisions of these stages also may be recognized. Thus, Carey and others (1996a) add four additional stages between understory

reinitiation and old-growth in their description of stages of forest ecosystem development.

The developmental stages described for natural stands also may occur in managed

stands (including planted stands). The transition from stand initiation to stem exclusion,

however, is generally accelerated, and the progression is often truncated by harvest

near the end of the stem exclusion stage. Silvicultural practices strongly influence the

rate of progression from stage to stage, the proportions of the forest in different stages,

and the specific stand characteristics and values provided. //’

Observations on the ecology and development of forest stands, and in particular those

of the Coast Range of Oregon, lead to the hypothesis that many young stands in these

forests may not develop naturally into stands with traits considered typical of old-growth.

This suspicion arises from the fact that forest conditions and other environmental

factors differ from those prevailing during the formative years of existing old-growth

stands, and these are likely to produce different patterns of stand development. These

conditions and factors include:

1. Dense initial stocking. Stands established after logging are often more heavily and

uniformly stocked with Douglas-fir than were preceding stands. The rapid diameter

growth seen in increment cores and stump cross-sections of old-growth trees and

differences in tree ages within some old-growth stands provide evidence of long

regeneration periods and low stand densities during the first century of life of these

old-growth stands (Tappeiner and others 1997).

2. Large populations of browsing ungulates. Current deer and elk populations are far

larger than those in the late 19th and early 20th centuries, and possibly larger than

those of the presettlement period (Kay 1995). Further, the large wildfires that resulted in

13
establishment of existing older stands undoubtedly caused a temporary reduction in

browsing pressure, because an initially reduced animal population was spread over a

very large area of regeneration. Today, selective browsing by deer and elk often retard

or eliminate preferred forage species (such as western redcedar and bigleaf maple

[Acer macrophyllum Pursh]) in the absence of special protective measures. An extreme

example of this effect is the massive impact in the Queen Charlotte Islands of an

introduced deer population with no predators.

3. Changing climate and weather patterns. Quite aside from the current concern over

human-caused global warming, it is well established that there have been substantial

variations in climate over periods of decades to several centuries (Layser 1980). Many

of our present older stands were established under considerably different and more

severe conditions than those prevailing in recent years (Henderson and Brubaker

1986).

4. Existing dense shrub understories. Stands in some areas and sites, particularly in

southern and coastal Oregon, have well-developed understories of shrubs (salal

[Gaultheria shallon] and vine maple [A. circinatum Pursh], as examples) and little

conifer regeneration in the understory. In some situations-particularly in southern

Oregon-this condition can be attributed to fire exclusion over the past 75 or more

years. A similar situation exists on northern Vancouver Island. Work on natural regeneration suggests that these shrub layers often will continue to prevent establishment of

conifers. Similarly, alder stands that were established in many areas after logging often

have well-developed understories of salmonberry (Rubus spectabilis), swordfern

(Polysfichum munitum), and elderberry (Sambucus racemosa) (Carlton 1988). As the

short-lived alder dies, it is likely that many of these stands will be dominated by a dense

cover of salmonberry and swordfern that may persist and prevent establishment of

conifers for many years (Henderson 1978, Tappeiner and others 1991).

5. In some areas, exotic competing species have become established that have a

considerable effect on regeneration, at least locally (e.g., scats broom [Cytisus scoparius], gorse [Eulex europaeus], Himalayan blackberry [Rubus discolor], certain

introduced grasses).

Consequently, we believe that on many sites some management or treatment to obtain

understory conifer establishment, to reduce shrub density, and to reduce overstory

density in heavily stocked conifer stands will be needed if we wish to promote development of characteristics commonly associated with mature and old-growth forests.

Desired characteristics are more likely to be attained by deliberate action than by

neglect or passive management.

Changing Goals in Forest Recent years have seen the steadily rising influence of an increasingly urbanized

Management public, concerned about environmental issues and with greater interest in recreational

and aesthetic features than in utilitarian forest values. Many people have raised questions about possible effects of current forest management regimes on wildlife, fisheries,

and watershed values; on long-term productivity; and on biodiversity in general. There

is great interest in and need for silvicultural practices and management regimes that

will reduce conflicts among user groups while providing concurrent production of the

many values associated with forest lands, on a biologically and economically sustainable basis.

14
These concerns are not confined to the Pacific Northwest or to the United States.

Foresters and interested publics elsewhere also are giving increased attention to

multiple values and are departing from past timber management regimes on significant

amounts of forest land. Silvicultural systems other than clearcutting that have been

applied on some ownerships in Great Britain are described in a recent Forestry

Commission Bulletin (Hart 1995). The Swedish National Board of Forestry produced a

well-illustrated book of practical advice to owners on how to manage forests to produce

high-quality timber while maintaining their beauty and their value as habitat for plants

and animals (National Board of Forestry 1990). Similar interests and major changes in

management practices have occurred in Germany (Plochman 1992).

Many approaches have been or are being developed to meet these needs in the United

States; they range from short-rotation fiber plantations involving intensive culture of

genetically selected hardwood clones, to late-successional reserves, to habitat conservation areas and wilderness areas with little or no active management. Although many

of these approaches may play significant roles in future forest management, we will

focus in this report on silvicultural practices that may be appropriate for forests managed for multiple objectives, including both wood production and those values commonly associated with natural mature and old-growth forests. Many of these practices

or modifications in practices have been suggested in recent years under several

banners: “restoration forestry” (Maser 1988 ); “ecological forestry” (Minckler 1989);

“new forestry” (Franklin 1989); “new perspectives” (Brooks and Grant 1992a, 1992b);

“high quality forestry” (Kuehne 1993); “ecosystem management” (Galindo-Leal and

Bunnell 1995, Loftus and Aune 1995, Overbay 1992, Stewart 1995); “landscape

forestry” (Boyce 1995); and “biodiversity pathways” (Carey and others 1996a; Carey

and Curtis 1996).

The ideas represented by these terms differ in many respects; goals of some practices

or systems may not be clearly defined; and some measures advocated in connection

with these ideas seem based on undemonstrated hypotheses rather than on concrete

knowledge and experience. But they all advocate some change in conventional practices on portions of the forest land base to provide one or more of the features generally associated with older natural forests; they all recognize the desirability of intentionally managing forests for more than wood production; and thus all involve some degree

of multipurpose management.

To sustain diverse, multiple values in specific forest landscapes, we need to systematically foster a balanced distribution in time and space of many stand conditions and

stages of stand development (DeBelI and Curtis 1993). Forests are dynamic entities,

and no condition can be maintained indefinitely. If we wish to have stands with mature

and old-growth (late-seral) characteristics in the future, we must provide for development of some stands with these characteristics as future replacements for existing

stands. Some ideas on how a desirable balance might be attained are discussed by

Carey and others (1996a), McComb and others (1993), and Oliver (1992). Unfortunately, the past history and ownership patterns of the region have created an unbalanced distribution of age classes, both in the region as a whole and within subregions

and watersheds. Private ownerships consist predominantly of young age classes, (<65

years) with little mature and negligible old-growth forest; whereas Federal ownership

15
consists predominantly of much older stands (including considerable amounts of oldgrowth forest) and young stands (<40 years), with more limited areas (differing considerably among individual National Forests) in intermediate age classes (Adams and

others 1992, Sessions and others 1990). Many real and perceived forest management

problems are direct consequences of this imbalance, which has grown more striking in

recent years with the combination of drastic harvest reductions on Federal lands and

accelerated cutting of immature stands on private lands. The latter is in part a consequence of reduction in public timber supplies, current business management practices,

and landowner fears of possible future regulations and constraints on management and

harvests.

Complete knowledge and absolute certainty are unattainable, and the limitations of

existing knowledge often are emphasized by those seeking research funding and by

those questioning or advocating some specific action or policy. But in fact, the research

and experience of nearly a century in the Northwest (and longer in some other countries) have produced a huge body of information on tree biology, stand development,

and forest ecology (Burns and Honkala 1990, Kimmins 1987, Perry 1994, Tourney and

Korstian 1947) and on the application of this knowledge through silviculture. Given

agreement on objectives for which forests are to be managed (which are primarily

determined by social and economic forces) and the conditions needed to achieve them,

much of the silvicultural information needed for designing feasible pathways and

management techniques is currently available.

Regeneration Methods In this section, we briefly review the research and experience that underpin current

methods for establishing stands of forest trees. We consider natural regeneration

(including advance reproduction), direct seeding, and planting. Additional modifications

in harvest cutting used at the time that regeneration is desired are discussed in a later

chapter.

Natural Regeneration Although some of the earliest work on reproduction of western conifers was with

planted seedlings (Munger 1911), most early work focused on natural regeneration, in

both undisturbed forests and clearcuts. Because conifer regeneration was often found

far from any existing seed source, it was hypothesized that Douglas-fir seed was stored

in the forest floor (Hofmann 1917, 1924). However, Isaac (1935) showed experimentally that nearly all Douglas-fir seed germinate by the spring following seedfall. He also

found that conifer seed could be dispersed over great distances (Isaac 1930). Although

most seed falls within 100 to 200 feet of its source, thousands of seeds per acre were

found at distances of 500 to 1,000 feet from seed trees. Thus Douglas-fir regeneration

can occur at considerable distances from the seed source, without seed storage in the

forest floor. This is also true of western hemlock.

Cone and seed crops are highly irregular, with an average of one heavy and one

medium crop in seven years (Hermann and Lavender 1990). Extensive damage by

cone and seed insects in some years contributes to this variability.

The two seed trees per acre specified in many early National Forest harvests were

often quite inadequate to secure satisfactory natural regeneration (Isaac 1943), although results were satisfactory in some instances (Garman 1951). Williamson (1973)

showed that good natural regeneration could be obtained in the Oregon Cascades in

16
shelterwoods that retained 20 to 50 percent of the original basal area. Satisfactory

natural regeneration of Douglas-fir was obtained with 10 to 12 large trees per acre in a

recent study at Oregon State University’s (OSU) McDonald Research Forest (Ketchum

1994), with the combination of a good seed year and some soil disturbance from

logging. Some site preparation and supplemental planting usually would be needed,

however, to ensure satisfactory regeneration.

Natural seedlings are small and susceptible to mortality from a number of factors during

their first several years. Lavender (1958) as well as Garman (1955) and Hermann and

Chilcote (1965) found that natural Douglas-fir seedling establishment is enhanced by

partial shade that reduces soil temperature and soil moisture evaporation. Disturbance

of the forest floor that provides a mineral soil seedbed-and consequently less herbaceous competition, reduced effects of root and stem pathogens, and pests-is also a

key to successful natural regeneration (Haig 1936; Haig and others 1941; Isaac 1938,

1940b, 1943, 1955b). Gashwiler (1967, 1970) and Hooven (1958) studied the effects of

rodents and other predators on seed supply. Seed predation rates of both conifers and

hardwoods are often high both on the tree and on the forest floor (Schubert and Adams

1971, West 1992).

Studies on hardwood regeneration show that protection from high temperatures and

_ frost are also important for small-seeded hardwoods like red alder (Haeusler and

Tappeiner 1993, Haeusler and others 1995) and Pacific madrone (Arbutus menziesii

Pursh) (Tappeiner and others 1986). Species with large seed such as bigleaf maple,

tanoak (Lithocarpus densiflorus (Hook. & Arn.) Rehd.), and vine maple have less

particular requirements for mineral soil seedbeds and shade, although they certainly

are susceptible to predation by rodents and birds (Fried and others 1988, O’Dea and

others 1995, Tappeiner and Zasada 1993, Tappeiner and others 1986).

Similar studies were carried out elsewhere in the West (e.g., Haig [1936] and Haig and

others [1941] in western white pine [Pinus monticola Dougl. ex D. Don]; Dunning [1923]

and Pearson [1923] in ponderosa pine [P. ponderosa Dougl. ex Laws.]; and McDonald

. [1976a] in Sierra Nevada mixed conifers).

Regeneration of shrubs and conifers in the understory of conifer stands is a relatively

new area of investigation. Establishment of salal (Huffman and others 1994) and other

shrubs, as well as western hemlock and western redcedar seedlings (Christie and

Mack 1984, Harmon and Franklin 1989), is favored by decomposing stumps, snags,

and logs on the forest floor although their establishment is not restricted to these

substrates. Shrub and hardwood seedling establishment is greater in thinned stands

than in unthinned stands (O’Dea and others 1995, Tappeiner and Zasada 1993), as is

the vegetative spread by rhizomes and the density of aerial stems produced by developing clones. Clonal shrubs such as salal and salmonberry can apparently persist in

the understory for many years, because they can replace dead aerial stems with new

sprouts from the bud bank on the rhizomes (Huffman and others 1994, Tappeiner and

others 1991).

These and similar studies provide information on biology, ecology, and regeneration of

forest plants, define species regeneration niches (Grubb 1977, Haeussler and others

1990), and provide a basis for understanding responses to silvicultural processes.

17
Site preparation-Conditions on the specific area to be regenerated strongly influence

establishment and early development of regeneration. These include surface soil

conditions; slash accumulations; overhead shade, if any; aspect, slope, and geographical location as they affect moisture relations and surface temperatures; and existing

and prospective vegetative competition and propensity to harbor animals, such as

rabbits and mountain beaver (Aplodontia rufa), that damage regeneration. Failure to

secure prompt and adequate regeneration may result in capture of the site by undesired vegetation, leading to prolonged delays in regeneration, animal damage to

seedlings, and inadequate stocking when regeneration of tree species ultimately does

occur (figs. 8, 9, and 10).

Figure 8-A 6-year-old Douglas-fir plantation developing without significant

brush problems.

Figure 9--Conifer regeneration overwhelmed by unwanted red alder.

Treatment is needed if conifers are to be a major stand component.

18
Figure IO-Dense salmonberry thicket developed after failed conifer

regeneration. Treatment will be necessary if tree species are to be restored

within a reasonable time.

Site preparation is a collective term for various measures that can be taken to alleviate conditions unfavorable to prompt and adequate regeneration, given an adequate

seed supply. These conditions differ widely among physical locations, and the manager

must select types and intensities of site preparation appropriate to the local conditions

and the requirements of the desired species.

Douglas-fir, and many other tree species, regenerate best on exposed mineral soil.

Therefore, some removal or at least some disturbance of the surface organic matter is

indicated. This may be partially accomplished through the mechanical action of machinery used in harvesting operations, but additional measures may be needed.

Removal or temporary suppression of competing vegetation is commonly also necessary, and additional competing vegetation control may be needed after initial establishment of tree species. This is particularly true for sites where soil moisture and sunlight

may be limiting. On sites characterized by highly aggressive shrub, grass and forb

competition, as in much of coastal Oregon and southwest Oregon, thorough treatment

to accomplish this is essential to successful regeneration.

Several site preparation methods, including fire, machine scarification, herbicides, hand

slashing, and combinations of these methods, are employed in Northwest forests. Each

method is effective when it solves the problem and does not conflict with other objectives, and ineffective where it fails to solve the set of problems that are preventing

satisfactory regeneration or where it generates major conflicts with societal values. The

choice of method depends on evaluation of local conditions and problems and the

relative costs and effectiveness of alternatives.

In general terms the attributes of each method may be summarized as follows:

1. Fire exposes mineral soil and may control many species of competing vegetation for

several years. Soil temperature, chemistry, and physical structure may be adversely

affected, however, and certain competing vegetation, such as members of the Ericaceae, may be favored. In the past, fire has been widely used for the dual purposes of

19
site preparation and reduction of fire hazards posed by large slash accumulations (fig.

11). In recent years, air pollution concerns have increasingly restricted its use, while

closer utilization and changes in harvesting practices have reduced slash accumulations and the need to burn slash for hazard reduction.

2. Mechanical site preparation with tractor-mounted equipment can prepare mineral

soil seedbeds and remove some of the existing vegetation (fig. 12). However, this

method also can stimulate establishment of a range of competing vegetation. Excessive removal of the nutrient-rich litter and upper soil horizons can be damaging, as can

compaction by heavy machinery on some soils and in some seasons.

3. Herbicides combine the potential to selectively eliminate unwanted competing

vegetation with minimal effects on soil productivity and low cost (figs. 13 and 14). They

are not appropriate where the main obstacles to seedling establishment are slash or

other materials that physically impede seedling establishment. Herbicides are viewed

by segments of the public as health hazards, and therefore often cannot be used on

sensitive areas (streams or wetlands) or near population centers. Great care must be

taken in their use to adhere to regulatory constraints and label precautions.

4. Hand-slashing provides extreme selectivity and is the method least likely to arouse

objections from the general public. It is, however, generally slow and expensive, must

in many cases be repeated after 2 or 3 years, and is a hazardous activity for workers.

Figure 11-Broadcast burning of slash (A)

was usual in the past, but with reduced

slash accumulations resulting from closer

utilization and other changes in harvest

practices, partial disposal (B) or even no

disposal often suffices.

20
Figure 12-Mechanical site preparation can be used to

crush and pile slash, reduce existing vegetative competition, and expose mineral soil in preparation for either

natural regeneration or planting.

Figure 13-Broadcast spraying of herbicides

provides inexpensive control of undesired

vegetation that competes with tree regeneration on extensive areas.

Figure 14-Hand application of

herbicides provides selective

control of scattered clumps of

undesired vegetation.

Evaluation of natural regeneration systems-Designed experiments on natural

regeneration have been integrated with evaluation of reforestation projects. These

evaluations have identified problem sites, determined success of applied regeneration

practices, and identified alternatives.

Lavender and others (1956) examined natural regeneration on staggered settings, and

Franklin (1963) assessed natural regeneration on strip cuts, small patch cuts (l/4 to 4

acres), and staggered cuttings. These and other studies have shown that partial shade,

aspect, reduction of competing plant cover, intensity of burn used to prepare a seed

bed, and proximity to seed source all contribute to seedling establishment.

Considerable work has been done on regeneration by using the shelterwood method

(Gordon 1970, 1979; Laacke and Fiddler 1986; Laacke and Tomascheski 1986;

McDonald 1976b, 1983; Seidel 1983; Tesch and Mann 1991; Williamson 1973;

Williamson and Ruth 1976). This work has shown that seedling density is generally

satisfactory if sufficient seed producing and windfirm trees are left in the overwood and

if there is adequate site preparation to prepare a seed bed and reduce competition.

21
Minore (1978) and Stein (1981, 1986) examined regeneration results following harvesting on sites considered difficult to regenerate in southwestern Oregon. Minore (1978)

found that shelter prevented frost damage to seedlings and saplings on the Dead

Indian Plateau in southwestern Oregon. Holbo and Childs (1987), Minore (1978) Stein

(1981), and Williamson and Minore (1978) point out the value of advance regeneration,

and of natural regeneration among planted seedlings, on sites with extreme variation in

temperatures and on rocky soils that are difficult to plant.

Advance regeneration-Use of advance regeneration, established naturally before

logging in some stands and after thinning in many others, can be a very effective way

to regenerate forest stands. It should be a common practice on sites difficult to regenerate and in unevenaged systems (Minore 1978, Stein 1981) and may be especially

desirable for preferred browse species, such as western redcedar. In dense stands,

advance reproduction will be comprised almost entirely of shade tolerant species such

as western hemlock, western redcedar, and some true firs; but in open stands and

stands subjected to heavy thinning regimes (particularly on dry and warm sites), less

tolerant species such as Douglas-fir may become established (fig. 15). Gordon (1973),

Helms and Sandiford (1985) Oliver (1986), and Tesch and Korpela (1993) developed

methods for assessing potential vigor of advance regeneration following logging.

Logging damage to advance regeneration increases with seedling size. Tesch and

others (1993) found that damaged seedlings often recovered within 3 to 6 years.

Growth of advance regeneration was similar to that of planted seedlings (Korpela and

Tesch 1992).

Genetic considerations in natural regeneration-Opportunities for genetic improvement are available through choice of seed trees for natural regeneration, and through

selection among trees within a stand during intermediate treatments (Zobel and Talbert

1984). Genetic degradation can occur from dysgenic selection when the best trees are

taken, leaving poor-quality, slow-growing trees to produce the next generation. Traits

under strong genetic control, such as stem form and disease resistance, are the most

responsive to genetic manipulation. Rate of stem growth is only moderately heritable

Figure 15-When advance regeneration of desirable

species is present, naturally established before harvest or

after thinning, this can often effectively supplement

postharvest regeneration: (A) advance regeneration of

Douglas-fir established in a windfall gap, southwest

Oregon; (B) advance regeneration of western hemlock

established under a thinned Douglas-fir stand, Vancouver

Island, British Columbia.

22

f
and thus less responsive to selection. Nevertheless, comparisons between select and

nonselect Douglas-fir in genetic tests in Oregon and Washington indicate that phenotypic selection in natural stands gives an average 5-percent improvement in juvenile

height growth (Stonecypher and others 1996). Although selection may be less effective

with typical silvicultural manipulations, these results indicate that over several generations selection for stem size and other traits will likely lead to large genetic gains.

Conversely, removal of the better trees will produce losses from dysgenic selection.

Natural regeneration can be important for genetic conservation. Genetic conservation

efforts usually involve both ex situ germ plasm collections and in situ habitat preservation. The objective of in situ management is to protect and perpetuate both samples of

genes and genotypes representative of a species and the evolutionary processes and

relationships between a species and its biotic and abiotic environment. Lands that

specifically include this management objective have been termed gene resource

management units (GRMUs) (Krugman 1984, Ledig 1988, Millar and Libby 1991).

These may include both lands excluded from timber harvest and lands in which wood

production is a major objective. In either case, natural regeneration can both perpetuate existing gene pools and allow evolutionary processes to proceed.

Summary-The following generalizations emerge from studies of seedling establishment and natural regeneration methods:

l Seed production is variable, with 6- to 8-year intervals between adequate seed crops

frequent for some species, especially Douglas-fir. Cone and seed insects can cause

partial failure of seed crops and accentuate this variability.

l Most seed falls within 100 to 200 feet of the source, although windborne conifer

seeds can spread up to 1,000 feet.

l Seed predation rates of Douglas-fir, ponderosa pine, and large-seeded hardwoods,

such as bigleaf maple and tanoak, are high both on the tree and on the forest floor.

l Mortality rates during the first 2 to 3 years after germination are high. Causes are

high soil temperatures, pathogens and insects in the forest floor, competition for light

and soil water, litter-fall, and frost.

l Seedling survival of Douglas-fir, red alder, ponderosa pine, and true firs is usually

highest on bare mineral soil; Sitka spruce (Picea sitchensis (Bong.) Carr.), western

hemlock, and large-seeded hardwoods survive well on both mineral soil and organic

seed beds.

l Partial canopy cover often aids initial seedling survival-even for intolerant speciesbecause it reduces soil temperature, air temperature, and evaporative capacity of air

near the ground in summer. It also reduces the chance of frost damage in winter and

early spring.

l Shade conditions that foster early seedling survival in the understory of forest stands

generally do not favor subsequent growth. Seedlings of most species tend to be

shade tolerant when very young but become less so after the initial establishment

stage.

23
Direct Seeding

and Planting

l Intense competition from established grasses, forbs, shrubs, and trees may cause

high seedling mortality.

l Advance regeneration, when present, can provide successful regeneration after

logging and may be especially useful on hard-to-regenerate sites. It often will be of

different species than the former overstory. Augmentation by seeding or planting may

be needed to attain desired species composition and stocking.

l The small openings created by group selection and single-tree selection methods

generally favor shade-tolerant species such as true firs, western hemlock, western

redcedar, tanoak, and bigleaf maple over the less tolerant Douglas-fir in most of the

region. Small openings do, however, favor Douglas-fir and Pacific madrone, chinkapin (Castonopsis chrysophylla (Dougl.) A. DC.), and other sclerophyllous species

over the less tolerant pines on dry, warm sites in southern Oregon and northern

California.

l Shelterwood methods and small openings or small clearcuts (< 10 acres) appear to

be most suitable for the regeneration of true firs at higher elevations (Gordon 1970,

1973, 1979; Gratkowski 1958), although they will work for other species, including

Douglas-fir (Williamson 1973, Worthington 1953).

l Choice of leave trees during silvicultural manipulations may provide opportunities to

achieve genetic gain, or conversely, may lead to dysgenic selection and genetic

degradation. Response to selection may be minimal in one or two generations but

could be significant after several generations.

l Natural regeneration can be a valuable tool on forest lands for which genetic conservation is an important objective.

l Natural reproduction may maintain a forest cover, but does not ensure desired

species composition, stocking and distribution, or timely stand reestablishment

(Lavender and others 1990).

Good overviews of the subject are the series of articles in Hobbs and others (1992) and

Lavender and others (1990).

Conifers-Studies on planting western conifers began in the early 1900s (Munger

1911, Show 1930). The need for reforestation of the great Yacolt (1902) and other

burns in southwestern Washington led to establishment of the Wind River nursery and

initial planting programs. Also, the decision to use clearcutting on Federal lands

(Munger 1950) and the Tillamook burns (a series of fires in 1933, 1939, 1945, and 1951

that burned over 360,000 acres in northwestern Oregon and created the area once

known as the Tillamook Burn and now known as the Tillamook Forest) further stimulated both direct seeding and planting in the Pacific Northwest. The major blowdown

and subsequent salvage operation resulting from the Columbus Day storm of 1962 was

an additional catalyst for large-scale planting.

Prior to the Yacolt, Cispus, and Tillamook fires, most cutover lands were reforested by

natural regeneration. Although seed trees were frequently retained, insufficient numbers of well-distributed seed-producing trees following intense fire and seed predation

by small mammals (Hooven 1958, 1970; Schubert and Adams 1971) strongly limited

24
the usefulness of the method. Direct seeding was used in early reforestation of the

Tillamook Burn. Annual projects of 10,000 to 15,000 acres were seeded with Douglasfir seed treated with rodenticides. Seed treatments were only partially successful in

preventing seed predation. Also, direct seeding was limited by inadequate seed supplies and the fact that large, contiguous areas were needed for efficient application of

aerial seeding. Although direct seeding accounted for reforestation of about 50 percent

of the Burn, emphasis on planting increased as reforestation progressed.

State forest practices acts also affected reforestation practices. Thus, the Oregon State

Forest Practices Act (1941), which required either leaving seed trees or planting, was

changed in 1971 and subsequent years to require that reforestation efforts on clearcuts

begin within 12 months, planting must be completed within two planting seasons, and

at least 200 trees per acre must be “free-to-grow” within five growing seasons of

planting. Current Forest Practices Board regulations for western Washington require

at least 190 established and well-distributed seedlings per acre within 3 years after

clearcut harvest.

Tree spacing in early plantations was often close (6 feet or so) but was later increased

substantially on most lands (to 10 or 15 feet or more) in the hope that planting costs

could be reduced and the need for precommercial thinning avoided. Early plantation

spacing trials also showed poor development at close spacings. At the opposite extreme, most owners concluded that problems with very wide spacing, such as large

branches, lack of opportunity to select trees during juvenile respacing, and unstacked

areas resulting from early mortality, more than offset the decreased costs of planting

stock and labor. And, there is some recent evidence indicating that early tree development is slower at very wide spacings than at intermediate spacings (Scott and others

1998). The most commonly used spacings at present are 10 to 12 feet, differing

somewhat with species and ownership.

Most spacings have been nominally square, but with hand planting on areas that

typically have numerous large stumps, down logs, and slash accumulations, there is

usually considerable irregularity in spacing and geometrical arrangement, although less

than exists in most natural stands.

Tree mortality was often high in the early plantations, and research sought to increase

seedling survival and growth. This research had two major facets: (1) studies of seedling size and morphology (Hermann 1967, lverson 1984, Jenkinson 1980, Newton and

others 1993); and (2) studies of seedling physiology with particular emphasis upon the

effects on seedling vigor of nursery practices such as lifting date, storage, and fertilization (Hermann 1967; Hermann and others 1972; Lavender 1964, 1984, 1985, 1988,

1990a, 1990b; Lavender and Hermann 1970; Lavender and Waring 1972; Lavender

and others 1968; Ritchie 1984; van den Driessche 1984; Winjum 1963).

This research produced methods for growing high-quality seedlings of the major

commercial conifer species (Duryea and Dougherty 1991, Margolis and Brand 1990).

This work also provided a physiological basis for understanding seedling growth

potential and stress from planting or planting site conditions. Foresters have developed

guidelines to select stock types best suited to various microsites on harvested areas

and improved methods for handling and planting of seedlings (Rose and others 1990).

As a consequence, average survival of seedlings has increased to 85 percent or better.

25
Competition from other vegetation also affects regeneration success. Consequently,

extensive research (Stein 1995, Stewart 1978, Stewart and others 1984, Walstad and

Kuch 1987) has addressed effects of such competition and methods for controlling it

when needed. Control of grasses, forbs, and shrubs often is used to ensure favorable

light conditions and adequate soil moisture for seedling survival and growth. The

degree and nature of competition is strongly related to site and plant association.

Competition for moisture is most severe on dry sites in southwestern Oregon. On good

sites in the high rainfall areas along the Pacific coast, shading by tall shrubs and

hardwoods is generally of more concern.

The small openings created in the group shelterwood or group selection methods

(Smith 1986) are similar to those created by small-scale disturbances by wind, insects,

or root disease. Experience in regenerating small openings (0.5 acre) on OSU’s

McDonald Research Forest indicates that the reforestation methods used in larger

clearcuts can be applied. After 4 years, growth and survival of planted seedlings in the

openings were not different from that in clearcuts (Ketchum 1994). This similarity in

seedling development will probably not continue unless openings are widened. As with

clearcuts, animal browsing and shrub competition affect seedling survival and growth in

these small openings. There is a great deal of variability among openings: some with

high light intensity developed covers of grass or low shrubs; others with low light levels

became dominated by tall shrubs. Grand fir (Abies amabilis Dougl. ex Forbes) appears

better suited to regeneration in small openings than Douglas-fir, because the former is

browsed much less and is more shade tolerant. Natural Douglas-fir regeneration was

not plentiful in these small openings, although it was abundant in adjoining stands

where 10 to 12 trees per acre have been left.

Although 0.5-acre openings were used in the study described above (McComb and

others 1994), larger openings or a variety of opening sizes might be more appropriate.

Size of opening, aspect, and height of surrounding trees will all affect seedling development. Thinning the stand between the openings or widening openings may be needed

to increase light and growing space for the young conifers in openings, especially when

on north aspects or surrounded by tall trees. Twenty-seven years of observation of

openings of similar size in the Challenge Experimental Forest in northern California

showed substantially reduced establishment and growth of natural regeneration,

compared to larger openings (Aune 1996, McDonald 1976a). Isaac (1943) recommended openings of 1 acre or larger. Openings of 2 to 5 acres should both facilitate

stand treatments and assure satisfactory development of regeneration (Curtis and

Carey 1996).

Hardwoods-The ecological and economic roles of hardwoods, particularly red alder

and black cottonwood (Populus trichocarpa Torr. & Gray) and Populus hybrids, have

received increasing recognition during the past 20 years (Comeau and others 1996,

Heilman and others 1991, Hibbs and others 1994). Both genera are rapid-growing,

shade-intolerant pioneer trees that require bare or new soil to regenerate naturally.

Thus, natural stands commonly occur along streams and other areas where soil has

been exposed and moisture conditions are favorable.

26
Several industrial firms have recently begun to plant and intensively manage both alder

and cottonwood. The primary objective of pure red alder plantings is raw material for

solid wood products or fine papers. Mixed species plantings of hardwoods and conifers

are less common and occur primarily on public lands; they are established mostly to

enhance site productivity (through nitrogen fixation by alder), riparian habitat, and forest

biodiversity. Plantations in the Wind River Experimental Forest (Miller and Murray 1978,

1979) and the OSU McDonald Forest demonstrate the gains possible with mixtures of

alder and Douglas-fir. Also, red alder is immune to the common root rots that affect

conifers and is thus a suitable species for planting in areas severely infected with

Phellinus weiri (Thies and Sturrock 1995). Although competing vegetation may need to

be controlled, trees can be planted successfully without the extensive exposure of bare

soil needed for natural seeding.

Hybrid cottonwood plantations for fiber production have been established on marginal

agricultural land along the lower Columbia River, in northwest Washington and British

Columbia, and on irrigated sagebrush-steppe land in the Columbia basin of eastern

Washington and Oregon. Rectangular spacings are sometimes used to facilitate

cultivation between rows. These plantations are grown as agricultural crops and are

harvested 6 to 8 years after planting (fig. 16). Such very intensive short-rotation regimes imply a likely future need for agricultural type soil amendments if they are to be

sustainable.

With superior hybrid clones, optimal spacing, suitable soils, effective weed control, and

in some cases irrigation and fertilization, poplars planted in the Pacific Northwest may

average 60 feet in height and 6 to 7 inches in diameter at 6 years. Stemwood production rates may reach three times average production of Douglas-fir under conventional

management regimes (Curtis and others 1981, DeBell and others 1996). One acre

devoted to such management can produce as much wood as 3 acres under conventional forest management or even more devoted to extensive multipurpose management. Thus, in a mix of approaches, clonal poplar culture can reduce pressures on other

lands and create additional opportunities to emphasize other uses on these other lands.

Figure 16--Hybrid cottonwood

plantation, 4 years after planting.

On suitable soils, such plantations can be grown as agricultural crops giving high fiber yields

on very short rotations.

27
Zones 1.23 Zones 5 Zones 8 Zones 4,6,7,5,9-W

o-2oo0, 0-6w singlsc3fevahzone PW

2ool-27w >50(Y=Wbands >1Mw-=3OCrbWldS

>2755’=EQCfbands

Figure 17-Seed collection zones have been established to ensure that planting stock is adapted to local

climatic conditions.

28
Genetic considerations in planting-Basic and applied research in forest tree genetics

has contributed to planting programs for several decades. Proper seed source selection and deployment is important to ensure high productivity and long-term stability of

planted forests. Two general sources of seed are (1) seed collected from parents in

commercial forests or forest reserves, and (2) seed from tree improvement programs,

usually produced in seed orchards. Both assume that seed originating from parents

near the planting site is best adapted to that site. Seed zones and seed transfer rules

are used to ensure adapted seed sources from commercial forests or reserves. Restrictions in mating of parents from different locations (“breeding zones”) are used to ensure

adapted progeny from tree improvement programs.

The degree of local adaptation depends on the genetic structure of the species; that is,

whether genetic variation is predominately among individuals or among populations of

different geographic origin. Thus, western white pine has considerable genetic variation

within stands but little variation among populations (Campbell and Sugano 1989,

Rehfeldt 1979). Western white pine seed therefore may be safely moved over large

geographic and elevational distances, and breeding populations in tree improvement

programs may encompass parents from a large area. Douglas-fir typifies species with

considerable genetic differences among populations and strong geographic patterning

(Campbell 1979, 1986; Campbell and Sugano 1993; Hermann and Lavender 1968;

Rehfeldt 1989; Silen, 1982; Sorensen 1983). Thus, a considerable number of seed

zones and breeding zones are recognized for Douglas-fir.

Seed zones and seed transfer rules were first developed in the Pacific Northwest in the

1960s as a consequence of early observations of poor growth and survival of plantations established with seed from distant, apparently poorly adapted sources. Seed zone

maps (first published in 1966, revised in 1973) were based on local knowledge of

topography, climate, and tree growth. These maps have since been extensively used to

certify origin of forest tree seed. Later, knowledge of geographic genetic variation for

individual species led to the development of mathematical models to more effectively

determine safe limits for seed movement (Campbell 1979,1986; Campbell and Sugano

1987, 1989, 1993). In general, the greater the environmental difference between the

planting location and the seed origin, the greater the risk of maladaptation. Recently,

new seed transfer guidelines and maps have been developed for individual species in

western Oregon based on current knowledge of geographic genetic variation (Randall

1996; fig. 17). The new guidelines are less restrictive, particularly for north-south

movements.

Seed orchards in the Pacific Northwest are beginning to produce a considerable

amount of seed, and genetically improved planting stock is being used increasingly for

reforestation. Tree improvement programs in the region constitute a considerable

investment in enhancing productivity on commercial forest lands. Progeny from more

than 42,000 parent trees are being tested in over 1,300 test plantations covering over

10,000 acres with an investment estimated at approximately a quarter-billion dollars

(Adams and others 1990). Data from these tests are used to rogue (see “Glossary”)

seed orchards and select parents for the next generation of improvement. More than 10

species are included in tree improvement programs, but most effort is focused on

29
Douglas-fir. The primary trait of interest is increased stem volume growth. Wood quality,

tree form, disease resistance, and adaptation to environmental extremes are given

varying emphases in different programs and species.

Adaptation is maintained in improved populations by working with many small, localized

breeding populations, particularly for programs in western Oregon and Washington

(Adams and others 1992, Silen and Wheat 1979). The small breeding zones may be

overly conservative, and opportunities exist in future generations to extend the geographic range of parents in a breeding program (Lester 1986, Stonecypher and others

1996). Genetic sources should be tested over a large geographic area to define the

limits of adaptation, and these tests also should include screening for important adaptive traits such as drought tolerance and cold hardiness (Aitken and Adams 1996,

Zhang and others 1994). Compared to agricultural crops, trees are long-lived and

subject to greater risk from weather extremes. Early results should be interpreted

cautiously, in view of failures of some seed sources in long-term studies and plantations after many years of previously good growth (Silen and Olson 1992). Risk of

maladaptation is minimized by including many parent trees in a program, both within

the initial base population (usually more than 200 selections originating from throughout

the breeding zone) and within the population that is deployed (seed orchards usually

include more than 50 unrelated clones or families). Deployment of mixtures of seed of

parents from different environments may provide another opportunity to create stands

with a broad base of genetic diversity, particularly given the uncertainty of future

climates.

Figure 18-Western white pine (A) is a fine species that has been nearly eliminated from

Northwestern forests by blister rust, a disease accidentally introduced in the early 1900s. (B)

Selection for blister rust resistance has provided resistant planting stock that promises

restoration of this species in Northwestern forests. Pruning provides additional protection

against infection (spores are most abundant near the ground) as well as improved wood

quality.

30
Results from genetic tests indicate heritable differences that support tree improvement

investments, although empirical evidence of realized genetic gains in stand (as opposed to individual tree) productivity is lacking. The gains to be achieved from tree

improvement appear substantial, particularly because even small gains add up quickly

when spread over a large land base. Estimates of genetic gains, however, depend on

many factors. Some factors differ among programs and landowners (e.g., selection

intensities in seed orchards), some are difficult to measure annually (e.g., unequal

contributions of parents and pollen contamination in seed orchards), and some involve

untested assumptions (e.g., the effects of selection at young ages and before appreciable competition). Much forest genetics research is aimed at addressing these

factors, and stand-level plots are being established in the region with the goal of

providing estimates of realized genetic gains to be incorporated into growth and yield

models (St. Clair 1993).

Multipurpose silviculture and ecosystem restoration stand to benefit greatly from

regional tree improvement programs. The rapid juvenile growth of improved planting

stock may help alleviate stand establishment problems associated with reduced site

preparation, increased competition from grass and shrubs, and animal browsing. Rapid

growth also may promote stand development, allowing us to achieve desired tree sizes

and stand structures more quickly. Restoration efforts may benefit from an assured

supply of seed from seed orchards, particularly from species and populations with

infrequent seed years. The development of disease-resistant planting stock allows

continued planting of species such as western white pine and sugar pine (Pinus

lambertiana Dougl.) that might otherwise be extirpated from large areas (fig. 18).

Genetic diversity is a key component of biodiversity, and continued care in the management of genetic diversity is essential to long-term ecosystem health. Components of

genetic resource management include adherence to guidelines for the movement of

seed, avoidance of disgenic selection practices, proper design of advanced generation

breeding programs to maintain adapted and diverse populations, proper deployment of

genetically improved planting stock, and an active genetic conservation program.

Resource managers and restoration specialists are beginning to plant and transfer

seed of many species for which we have no guidelines for seed movement. Development of seed transfer guidelines is badly needed for these noncommercial tree, herbaceous, and grass species. Until guidelines are established, seed from local populations

should be used as much as possible. Genecological studies are critical to the development of seed transfer guidelines, as well as to the design of genetic conservation and

breeding programs.

Site preparation-Considerations and methods similar to those previously discussed

under natural regeneration also apply to establishment of stands through planting.

There are some differences, however. Normally, planting immediately follows (or should

follow) harvest, and planted seedlings commonly make more rapid early height growth

than do natural seedlings. Consequently, the period during which control of competing

vegetation must be continued is often considerably shorter with planting than with

natural regeneration. Exposure of mineral soil often may be unnecessary or can be

limited to the actual planting spot. But, an additional objective of removing or reducing

heavy slash and shrubs or undesired tree species is to remove physical obstacles to

planting crews.

31
Summary-Successful planting requires careful attention to the details of seed source

and nursery and planting practices, as well as a thorough evaluation of environmental

conditions (Hobbs and others 1992) and control of competing vegetation, where

needed. Microclimate, competition from herbs, shrubs, and hardwoods, and animal

browsing (discussed in a later section) often affect seedling survival and growth. The

effects on early growth also carry over into later stand development.

Cafferata (1986), Cleary and others (1978), Hobbs and others (1992), and Lavender

and others (1990) provide excellent overviews of the application of current reforestation

practices. Guidelines for conifers (DeYoe 1986, Schubert and Adams 1971, Strothman

and Roy 1984) and hardwoods (Ahrens and others 1992) are available. In summary,

measures must be taken at all stages to ensure careful attention to the following:

l Proper selection of seed source and proper seed handling

l Nursery procedures that optimize seedling vigor, and storage and handling procedures in nursery and field that minimize seedling dehydration, respiration, and

damage

l Careful planting, including onsite inspection of planting procedures

l Site-specific prescriptions for site preparation and weed control

l Monitoring for 3 or more years to ensure seedling survival and growth

l Early thinning to control stocking and species composition

The ability to consistently regenerate forests with present technology is demonstrated

in the annual reforestation report of the Oregon State Board of Forestry for 1992. This

shows that of 85,689 acres of private land requiring reforestation by the end of 1992,

82,034 acres or 96 percent were in compliance with the standards of the Oregon State

Forest Practices-Act.

Shaping

Development of

Young Natural

Stands and

Plantations

The choice of regeneration system and decisions about patterns of cutting, including

retention of live and dead trees, influence the nature of a regenerating forest after

harvest and affect later growth. Subsequent silvicultural treatments are the tools for

shaping development of established stands to meet specific or multiple objectives,

which may change over time and over the life of the stand.

During the past half century, silvicultural practices (harvest systems, spacing control,

vegetation management, and-to a lesser extent-fertilization and pruning) have been

applied throughout the world, wherever soils and climate, social policies, and markets

combine to favor long-term forestry enterprises. Research, development, and implementation of these practices were justified primarily by the quantity or quality of wood

that could be grown or harvested, although other goals also were served. The basic

knowledge and experience acquired, however, can be applied to meet additional

objectives. Appropriate further silvicultural investments may be justified to meet expanded social desires and concerns for other forest values and products, provided that

goals are specified in terms of desired forest conditions and mechanisms exist for

equitable (or acceptable) distribution of associated costs and benefits.

32
In this section, we first provide some background on changing societal expectations

and their influence on silvicultural opportunities. Then, we describe several silvicultural

practices, how conventional application influences stand development, and how they

might be applied or modified to meet other or additional objectives.

Social Expectations and

Silvicultural Opportunities

It has long been recognized that forests provide the multiple benefits of timber production, watershed protection, wildlife habitat, recreational and aesthetic values. Increased

attention to nontimber values is now demanded by various segments of society and

required by public law. As these values and the stand conditions required to produce

them become more clearly defined, their provision and enhancement over time will

require silvicultural manipulation of stands, integrated at the landscape level.

Although managed forest landscapes may appear more natural and more diverse than

landscapes associated with most human endeavors, extensive areas of young managed plantations do contrast markedly with natural mature and old-growth forests.

Many of the features associated with older natural forests (Franklin and others 1981,

Ruggiero and others 1991) are reduced or absent in young stands, whether managed

or unmanaged (Carey and Johnson 1995); and many are minimized with conventional

short-rotation plantation management. Such features may include large trees, snags,

down woody debris, “ragged” edges, within-stand structural complexity, and diversity in

age, size, shape, and distribution patterns of stands across the landscape (Hansen and

others 1991, 1993). Many of these features contribute to habitat for wildlife (Brown

1985, Hunter 1990, Thomas 1979) or are otherwise thought by some groups or individuals to be related to or essential to other forest values and general forest health.

Existing young natural stands (or plantations) will not necessarily develop into stands

comparable to present old-growth in the absence of human intervention. The desire to

retain such features or to produce similar features in managed forests has stimulated

interest in various modifications of conventional silvicultural practice (Carey and Curtis

1996, DeBell 1989, DeBell and Curtis 1993, Franklin and others 1986, Kohm and

Franklin 1997).

The general nature of silvicultural practices needed to foster structural features similar

to those of natural mature and old-growth forests is fairly apparent, but the specifics of

implementation are not. It may be obvious, for example, that a given feature (such as a

shrub species in the understory) provides important habitat for one or more species.

But little is known about the response of the forest ecosystem or of other species to

various levels or distribution patterns of that feature. Even less is known about other

biological or economic costs and benefits associated with such management. Appropriate practices undoubtedly will differ with forest types, landscapes, specific stand and

site conditions, and public preferences. These uncertainties should not be used to

justify reluctance or failure to modify conventional practices. But they should foster a

skepticism of widespread implementation or legislative requirement of untested, highly

specific modifications, particularly in the absence of effective monitoring efforts. And

such uncertainties also should stimulate soundly designed experiments to test and

compare a range of approaches or options.

33
Figure 19-(A) An exceptionally uniform plantation in the Mount St. Helens blast area. Aerial photography (B) shows that the unthinned

stand is actually much less uniform than it appears from the road. Conventional thinning (C) increases uniformity, but heterogeneity can

be enhanced by irregular thinning (D).

Figure 20-The Wind River plantation spacing trial is a striking example of the effects of differences in initial

spacing on a relatively poor site, without subsequent thinning: (A) 4-foot spacing, and (B) 12-foot spacing, 71 years

after planting.

34
The greatest near-term opportunity to develop such management knowledge and

experience and to provide more diverse habitat lies in the millions of acres of existing

plantations, which range in age from 1 year to 40 or 50 years. Plantations are sometimes disparaged as uniform monocultures of minimal or even negative value for

purposes other than wood production. This view arises in part from the fact that many

plantations in the Pacific Northwest are now in the early stem exclusion stage, in which

relatively uniform and dense canopies have eliminated most understory vegetation.

Moreover, plantations usually appear much more uniform when viewed from a highway

or forest road than they are in fact (fig. 19). Even without further management, this

uniformity is gradually modified by natural processes of stand development and by

such agents as root diseases and snow breakage, in a manner similar to that occurring

in natural stands (Silviculture Interpretations Working Group 1992). Many plantations

established 40 or more years ago are now barely recognizable as plantations. With

appropriate management, stand differentiation can be accelerated (Curtis and others

1997). Most of these plantations are now in a highly plastic stage of development, and

there are major opportunities to mold them-individually and in a landscape contexttoward a variety of objectives.

Objectives will differ by ownership, geographic location, condition of surrounding

stands and landscapes, and public desires. Rapidly growing uniform stands focused

primarily on wood production will be a major or sole management objective for some

plantations. Accelerated development of habitat for threatened or endangered species

may be the primary objective in some others. Many owners and managers will have

multiple objectives, which can be met through use of a variety of silvicultural practices.

A number of modifications of conventional silvicultural practices merit consideration

and some are now being applied by several landowners and organizations.

Early Density Control Initial density has a strong influence on subsequent stand development (Dilworth 1980,

Omule 1988, Reukema 1979, Reukema and Smith 1987, Smith and Reukema 1986).

The effects of initial plantation spacing in the absence of subsequent stand treatment

are well illustrated in the Wind River spacing test (figs. 20 and 21). In dense naturally

seeded stands and in plantations established at close spacings or having a substantial

component of naturally seeded stems (fig. 22), early thinning (=precommercial thinning

=respacing) is often needed to keep stand density within acceptable limits.

Figure 21-Differences

in initial spacing have

produced widely different

diameter distributions in

the Wind River spacing

test. Numbers of trees per

acre by diameter classes

in the 6- and lo-foot

spacings in 1991, 66

years after planting.

DBH, by 1 inch classes

35
Figure 22-Excessive tree numbers without subsequent thinning produce stands with small

diameters, slender boles, and small crowns, with little understory vegetation (A). Such stands

become very susceptible to breakage from wind, ice, and snow (B).

Figure 23-Precommercial thinning of dense young stands accelerates tree growth, promotes understory

development and browse production, and allows selection of the better individual trees. Young noble fir stand (A)

before and (B) after precommercial thinning.

Precommercial thinning is commonly applied near the end of the stand initiation stage

(10 to 15 years) to enhance survival, growth, and value of future crop trees (fig. 23).

Thinnings usually are aimed at leaving the most valuable larger trees at relatively even

spacing (Reukema 1975). This treatment increases stand uniformity; but the reduced

stand density also accelerates tree growth (Hoyer and Swanzy 1986, Omule 1985) and

may promote development of a shrub and herbaceous understory and browse production. It frequently also leads to early establishment of natural regeneration of tolerant

tree species, such as western hemlock and western redcedar (Curtis and others 1997).

Past prescriptions sometimes overemphasized current market values or current tree

size. Thus, western redcedar often was discriminated against in early respacing of

stands on the Washington coast, where long-term growth potential of the species is

high and the species has considerable value for wildlife and possibly in nutrient cycling.

Hardwoods such as red alder (useful in nitrogen fixation) and bigleaf maple likewise

have been singled out for removal.

36
A number of modifications to promote biodiversity are possible and have been applied

to a limited extent on some public lands. These modifications involve selection criteria

for residual trees, spacing distances, and intentional creation of small openings. Trees

left after thinning can be selected to increase diversity in size and species, thus accelerating stand differentiation and increasing structural complexity. Many spacing prescriptions on public lands now specify that occasional hardwoods, western redcedar,

Pacific yew (Taxus brevifolia Nutt.), and western white pine shall not be cut during

thinning, although they are not actively favored. Wide spacing, either initial or in early

thinning, will enhance development of understories and large live crowns and

branches. Spacing can be varied in patches throughout the plantations, and some

patches may be retained in an undisturbed condition. Small openings or gaps can be

created to retain some components of the early stem initiation stage and later develop

patches of young trees. Park and McCulloch (1993) give some guidelines for such

operations.

Thinning in Older Stands Thinning in older stands (=commercial thinning) has long been a generally accepted

practice in European countries and rests on over a century of experience and research

embodied in an enormous literature (Braathe 1957). Commercial thinning was not

widely applied in the Pacific Northwest until very recently, because large volumes of old

timber were available, markets for smaller and poorer quality material were limited, and

equipment then available was not well suited to thinning operations. But the economic,

technical, and social context has changed, and thinning is rapidly increasing in importance. It provides opportunities to both produce wood and enhance nontimber objectives. Thinning combined with extended rotations can maintain visually attractive forest

cover for long periods while still producing wood products and current income.

A considerable body of thinning research exists in the Pacific Northwest, dating from

about 1950 (Curtis and Clendenen 1994; Curtis and Marshall 1986; Hilt and others

1977; King 1986; Marshall and others 1992; O’Hara 1990; Oliver and Murray 1983;

Oliver and others 1986; Omule 1985; Reukema 1972; Reukema and Bruce 1977;

Reukema and Pienaar 1973; Worthington and Staebler 1961a, 1961b). A number of

more or less equivalent density control guides and density measures are available for

planning and administering thinning activities (Curtis 1982, Drew and Flewelling 1979,

Long and others 1988, Reineke 1933). Several publicly available simulation models

and a number of proprietary models exist that provide useful guidance in developing

stand management regimes; for example DFSIM (Curtis and others 1981, Fight and

others 1984), ORGANON (Hann and others 1995), WinTIPSY (Mitchell and others

1995), STIM (Bonnor and others 1995), SPS (Arney 1988), and FPS (Arney 1995).

The traditional purposes of thinning are to harvest potential mortality, maintain or

increase growth rates of remaining trees of desired species, and promote stem quality

and tree vigor while producing intermediate income. Thinned stands produce larger

trees at any given age than do unthinned stands; thinned stands are more open and

sometimes more diverse. One recent study in the Pacific Northwest (Marshall and

others 1992) showed that over a 20-year period repeated thinning in a young stand on

a good site produced increases of 33 to 56 percent in diameter growth of the largest 40

stems per acre, compared to the unthinned condition (fig. 24). Thinning also provides

income and timber flow during the intermediate stages of stand development.

37
T l T 3 T 5 T7 Control

Treatment

Figure 24-Thirty-year increment (ages 20 to 50) in average

diameter of the largest 40 trees per acre, for four treatments

involving early and repeated thinning and a control. Thinning

treatments range from one with low growing stock retention (Tl) to

one with high growing stock retention (T7). Data are from Hoskins

LOGS study (Marshall and others 1992).

Most past thinning studies were oriented to timber production, but thinning also strongly

influences other stand attributes. Thinning, depending on how it is done, may or may

not promote vertical stratification (figs. 25 and 26). It usually accelerates understory

development and succession and movement of the stand into the understory reinitiation

stage. If begun early, changes can be striking over comparatively short periods (fig.

27). Operationally, there can be considerable loss of understory from damage during

thinning. If understory reduction is considered undesirable, such effects can be minimized by training, use of designated skid trails and corridors, proper equipment, and

heavy initial thinning that allows relatively long intervals between subsequent thinnings.

Most thinning research has been done in young and intermediate-aged stands (<60

years). Opportunities to influence tree and stand development through thinning are

greatest if thinning is begun early. A first thinning that is delayed until after stands have

developed high relative densities and shortened crowns involves an increased risk of

windthrow and snowbreakage as well as delayed growth response and therefore must

be lighter (usually) than an early initial thinning. Crown expansion potential slows with

age, and therefore thinnings should generally become lighter and entries less frequent

as stands age; however, even late thinning in vigorous, relatively old stands (>lOO

years) can be effective in capturing some mortality, maintaining stand vigor, and

reducing losses from insects and disease (Williamson 1982, Williamson and Price

1971). The maximum age at which thinning is justified in relatively vigorous stands is

more a matter of owner objectives than biological limitations. Financial returns and

development of specific habitat characteristics may be important considerations.

A less obvious but important effect of repeated thinning is that trees and stands maintain rapid growth to older ages than without thinning. Culmination age (age that maximizes wood production) has yet to be determined for repeatedly thinned Douglas-fir in

the Pacific Northwest, but it is greater than for dense unthinned stands (Curtis 1994,

38
Figure 25-Thinning on good sites can produce large trees and considerable vertical structure

within relatively short periods: (A) Delezenne thinning study ( Curtis 1995, O’Hara 1990) at

age 73, first thinned at age 36, natural origin; and (B) developing hemlock understory in a

thinned stand, Soleduck Ranger District, Olympic National Forest, Washington.

Figure 26-Late thinning in a poor site stand of natural origin, first thinned at age 60, and now

117. Mount Walker thinning study: (A) heavy thinning, and (B) unthinned control.

Figure 27-On good sites, early thinning can greatly accelerate diameter growth and markedly alter stand structures. These photographs from

the Iron Creek LOGS study at age 45 (Curtis and Clendenen 1994) show (A) untreated control plot containing planted trees plus much natural

regeneration, (B) plot with repeated light thinning, and (C) plot with repeated heavy thinning, showing understory western hemlock, western

redcedar, and shrubs and vertical structure developing in response to thinning.

39
Nutrient Management

1995; Curtis and Marshall 1993; Worthington and Staebler 196la). Where terrain and

harvesting methods permit thinning, large trees can be grown on longer rotations, with

no loss and perhaps even an increase in annual wood production per unit area. Stem

quality and value per unit of volume may be increased. Repeated thinnings on extended rotations can maintain forest cover for long periods while providing current

income and employment (Curtis and Carey 1996, Lippke and others 1996), maintaining

tree and stand vigor, promoting stand health and stability, and developing stand structures favorable to certain wildlife species associated with late successional stages

(Carey and others 1996a). It also may provide additional opportunities and flexibility to

capture benefits from stands composed of mixed species with differing tolerance and

growth patterns.

Thinning encourages seedling establishment of shade-tolerant conifers (Del Rio and

Berg 1979), hardwoods (Fried and others 1988) and shrubs (Huffman and others

1994, O’Dea and others 1995, Tappeiner and Zasada 1993), but it also results in

vegetative expansion of shrubs by rhizomes (Tappeiner and others 1991) and layering.

By reducing overstory density and providing a seedbed, thinning results in invasion by

new plants not previously in the stand (Carey and others 1996b) and the spread of

those already established. This generally produces a dense, diverse understory of

shrubs, herbs, and tree seedlings and saplings that may provide enhanced wildlife

habitat.

Regeneration of understory conifers after thinning often will enhance the development

of stands with structures similar to mature and old-growth stands. On some sites,

however, thinning may produce dense shrub layers that inhibit later establishment of

desired conifers. Dense understories of salal, Oregon grape (Berberis nervosa Pursh),

salmonberry, vine maple and other shrubs may develop and prevent establishment of a

second layer of conifers. Conifer seed will germinate under such shrub layers but few

seedlings survive. These shrub layers often are quite persistent. They produce new

aerial stems annually that replace older stems as they die, thereby maintaining a dense

cover for decades (Huffman and others 1994). On some sites (particularly at low

elevations and in the Oregon Coast Range), some disturbance of these brush layers

and possibly underplanting of conifers may be necessary to establish multilayer conifer

stands.

Nutrient management is an important consideration, particularly in the Douglas-fir

region where soils are young and considerable nitrogen is immobilized in organic

matter. Inadequate supplies of available nitrogen limit natural productivity and rates

of stand development on many sites. Relatively small and infrequent applications of

nitrogen fertilizers have been used to increase wood production in conventionally

managed forests, and often produce striking responses in tree growth and stand

development (fig. 28) (Chappell and others 1992b, Gessel and others 1979). The

largest and most long-lasting responses occur when nutrient deficiencies are severe

(Miller and Pienaar 1973, Miller and Tarrant 1983, Miller and others 1986) and when

fertilizer application is combined with thinning (Brix 1993, Chappell and others 1992a).

40
Figure 28--Relatively small and infrequent applications of nitrogen fertilizer often produce striking

response in tree vigor and stand development, particularly on poor sites. Typical response in diameter

growth (A), shown by wide growth rings commencing in the year following fertilization; and an extreme

example of response (B) shown by paired stem sections, cut from trees on adjacent fertilized and

unfertilized plots on a very poor site.

In newly established and very young plantations, broadcast applications of fertilizer

produce earlier canopy closure and greater stand uniformity (DeBelI and others 1986);

in older stands where trees have begun to differentiate into crown classes, fertilizer

application accelerates the stand development processes of crown differentiation and

competition-related mortality (Miller and Pienaar 1973, Miller and Tarrant 1983). Other

site resources, such as amount and nutritional quality of wildlife forage (Sullivan and

Rochelle 1992), may be increased.

One modification of the conventional practice of broadcast application of fertilizer that

could be considered is small-scale individual tree or group application. This could be

used to promote development of a layered canopy and differences in understory

vegetation, in contrast to broadcast applications that simply increase the overall rate of

stand development. It also could be used to enhance growth and nutritional value of

forage in openings created for that purpose. Individual tree application was deemed

feasible and profitable nearly 20 years ago by scientists of the Washington Department

of Natural Resources (Anderson and Hyatt 1979). Coupled with selective thinning and

pruning, individual tree applications also could increase production of high-quality

wood.

Introduction or favoring of nitrogen-fixing plants also merits consideration. These can

provide benefits similar to those of fertilization on some nitrogen-deficient sites (Miller

and Murray 1978, Tarrant and others 1983, Trappe and others 1968) and may have

additional benefits in economic and ecological diversity. Natural red alder regeneration

often is abundant in conifer plantations. Mixed stands could be established by retaining

selected alder stems during precommercial thinning. Individual, scattered red alder

trees have been favored in early thinnings of young conifer plantations on nitrogendeficient soils of the Siuslaw National Forest (Turpin 1981). Early height growth is much

more rapid in alder than in conifers, so wide spacing of the alder would be necessary to

maintain the conifers. Unlike shade tolerant species, alder will not survive beneath a

41
conifer overstory. After 25 to 30 years on good sites, conifers that have not been

suppressed will dominate the alder (Newton and others 1968). Stemwise (tree-by-tree)

mixtures thus are difficult to maintain. Planting or retention of naturally established red

alder in groups or small blocks within conifer regeneration should reduce the crown

competition problems encountered in stemwise mixtures, while still providing nutrient

benefits. A pure alder crop grown prior to establishment of a new Douglas-fir stand

would have nutritional benefits for the latter and may be particularly appropriate on land

heavily infected with Phellinus weirii (a serious root disease of conifers) because of

alder’s immunity (Harrington and others 1994). Other nonleguminous nitrogen-fixing

species, such as Sitka alder (Alnus sinuata (Regel) Rydb.) (Binkley and others 1984,

Harrington and Deal 1982) ceanothus (Ceanothus ssp.) (Binkley and Husted 1983),

and leguminous species (Miller and Zalunardo 1979) may offer fewer competition

problems and add some soil nitrogen and organic matter.

Mixed stands of red alder and conifers are more productive than pure conifer stands

on soils with low nitrogen levels (Miller and Murray 1979), provided the conifers are not

overtopped by the alder. An interplanting of red alder with Douglas-fir at Wind River

Experimental Forest in southern Washington is a classic example of potential opportunities; nearly one-half century after planting, heights of dominant Douglas-fir grown with

interplanted red alder were taller than those in an adjoining pure Douglas-fir stand by

the equivalent of one full site class (Miller and Murray 1978). Volume of Douglas-fir in

the mixed plantation equaled that in the pure stand, but it occurred on fewer and larger

stems and hence had greater value. Total volume of Douglas-fir and alder in the mixed

stand was double that of the surrounding pure Douglas-fir stand. Soil under the mixed

stand contained about 1,000 pounds of nitrogen per acre more than soil under the

adjoining pure Douglas-fir stand (Tarrant 1961, Tarrant and Miller 1963).

Such mixed species stands might also benefit some wildlife species (McComb 1994).

Mixed plantations of red alder and Douglas-fir also have been established by William

Emmingham and Denis Lavender at OSU’s McDonald Forest. The purpose was to use

alder’s nitrogen-fixing ability to increase growth of Douglas-fir while producing greater

diversity in both the tree and herbaceous layers than might occur in a pure Douglas-fir

stand. Because of alder’s rapid juvenile height growth rate, alder in this instance was

planted when the Douglas-fir was over 15 feet tall. Early data demonstrate that competition with Douglas-fir improves the form of alder and that the Douglas-fir are 30 percent

larger than saplings in pure stands, although spacing also may be a factor in the

observed size differences.

Planting different species in small groups rather than as stemwise mixtures should

avoid many of the problems in maintaining stemwise mixtures, although some of the

possible benefits may be delayed or foregone. Harrington and Deal (1982) examined

comparative height growth patterns of Sitka alder and Douglas-fir and provide recommendations for planting mixtures of this less competitive species with Douglas-fir to

avoid overtopping the Douglas-fir while providing a source of nitrogen.

42
Pruning Pruning (removal of branches from the lower bole) has been advocated primarily to

increase the amount of clear wood produced in young stands (Hanley and others

1995). Pruning has been little used until very recently because of uncertainties about

economic returns and future markets, but there is now increased interest and operational application by some owners. It has also been recommended as part of a program

to control blister rust in western white and sugar pines (Russell 1988). Most pruning for

improved wood quality has been in stands in the stem exclusion stage. Current practice

is to begin pruning much earlier than was common in the past. Pruning may be done on

all trees, but-to reduce costs-often is confined to a subset of trees corresponding to

the number expected to be retained after future thinning.

Summary, Shaping

Development

Pruning gives stands an open appearance, which may make them more attractive

aesthetically. If begun before stand closure, removal of lower branches could increase

the amount of light reaching the forest floor and favor development of the woody and

herbaceous understory (which also may somewhat reduce overstory growth). Because

some wildlife species use branches as hunting perches or use some trees with long

continuous crowns, there may be benefits, in addition to cost savings, to retaining

some unpruned trees within pruned stands. In regimes with repeated thinning on

relatively long rotations, removal of some pruned trees during thinning might increase

financial returns and perhaps offset some costs of other silvicultural activities.

There are many opportunities for directing development of young naturally established

or planted stands toward desired future conditions. Well-established techniques are

presented in standard texts such as Smith and others (1997). Although many were

originally developed to promote wood production, these techniques are equally applicable to production of multiple forest benefits. These techniques include:

l Initial planting spacing or early thinning, or both, can be used to control spacing and

species composition.

l Thinning can be applied in older stands to:

-control species composition and stand structure

-shorten the duration of the stem exclusion stage and enhance understory

development

-produce larger, more valuable, and visually more attractive trees at any given age

-produce current income while maintaining visually acceptable forest cover for long

periods

-promote forage production

-promote tree and stand health

-forestall or harvest mortality

l Nutrient management can improve stand vigor and growth rates through application

of fertilizer on nutrient deficient sites, or through use of nitrogen-fixing species (such

as red alder) as alternatives to artificial fertilizers.

l Pruning can improve quality and value of wood produced, help control blister rust in

white and sugar pines, and give stands a more open appearance.

43
Harvesting

Considerations

Timber harvest and the subsequent site preparation and regeneration are probably the

most influential of all operations that can be carried out in multipurpose forests. The

methods used and the manner in which they are applied have dramatic and longlasting effects on forest characteristics. Harvesting is the operation that generates the

most conflict between objectives, between people, and between institutions. It also

generates most of the revenue that directly or indirectly supports management of

forests for multiple objectives.

In this section, we discuss primarily harvests that may occur at the end of a rotation

(even-aged management) or harvest cycle (uneven-aged management) as part of a

planned management regime. Similar considerations apply to harvests that take place

as a response to unplanned, perhaps large-scale, natural disturbances such as windstorms, fire, severe insect outbreaks, and volcanic eruptions; or as a component of

efforts to restore forests that have been drastically altered or degraded by past natural

or human-caused events. We also discuss the question of harvest ages, and conclude

with brief discussion of some considerations related to harvest of special forest products.

Regeneration Harvests A silvicultural system or management regime consists of a regeneration method,

intermediate stand treatments (if any), and a harvest method. The choice of harvest

method is influenced by both desired future conditions and comparative costs. A

method that is perfectly feasible and highly desirable on gentle terrain may be quite

impractical on steep topography. Details of application are influenced by present and

desired future species composition and by differences in site and expected vegetative

competition.

In the appendix, we illustrate a number of possible regimes that appear feasible for

lands having both wood production and nontimber values as objectives, and that are

included in trials now being established on Washington Department of Natural Resources (DNR) lands (Curtis and others 1996). These regimes are expected to produce

widely different stand conditions with differing visual effects and habitat values, while

retaining wood production as a major objective. Many variations are possible.

Planned regeneration harvests are conventionally classified into several broad categories or associated silvicultural systems (Matthews 1989, Nyland 1996, Smith 1986,

Smith and others 1997). These represent segments of a continuum of possible practices classified by site exposure and sequence of operations, rather than rigid and

clearly demarcated alternatives.

The clearcutting method removes all trees from relatively large areas at one time,

followed by regeneration by either planting or natural seeding from adjacent uncut trees

or stands (see figs. 4, 5, and 6). It is highly cost-efficient for wood production with

species and sites where large open areas are readily regenerated. It minimizes road

costs and direct harvesting costs (especially on steep terrain) and markedly simplifies

planning and future administration and management. It is commonly thought, though

not fully demonstrated, to give greater wood production per unit area than alternative

systems. It was the dominant system throughout the Douglas-fir region for many years

and remains important on non-Federal lands. In recent years, it has come under public

attack and its use has been greatly diminished on Federal lands. A clearcut is a highly

visible treatment that is aesthetically displeasing to many people. There also are

perceived or actual unfavorable effects on some wildlife and other environmental

values. These problems are exacerbated by short-rotation management on many

44
ownerships and by unbalanced stand age distributions. Some of the problems in part

reflect changes in societal attitudes and effects of past forest planning, harvest scheduling, and other management practices, rather than inherent characteristics of the

clearcutting method. But such distinctions are commonly lost in public debate.

The seed-tree method leaves widely scattered individual trees or clumps of trees as a

seed source. This has long been abandoned as a regeneration method over most of

the region because it is usually less effective and less reliable than other methods in

regenerating Douglas-fir, though not invariably so (e.g., Garman 1951).

The shelterwood method consists of removal of a sufficient portion of the old stand to

provide the environmental conditions needed for establishment of Douglas-fir seedlings

(either planted or natural), while the remaining overstory (= overwood) provides protection from excessive insolation, temperature, and frost (fig. 29). Once regeneration is

established, the remainder of the old stand is removed to allow free growth of the new

stand. The shelterwood method can be applied uniformly over large areas, or as a socalled irregular or group shelterwood in which openings are gradually enlarged as

regeneration becomes established.

The above methods produce even-aged stands; i.e., stands in which the trees are of

similar age. If applied over contiguous stands within a short period, a large forest area

may consist of stands with little variation in ages; however, such large-scale uniformity

is a result of harvest patterns and scheduling and is not inherent in even-aged methods.

In contrast, selection methods aim to develop unevenaged stands, which contain a

wide range of tree ages within the individual stand. Differences in age structure and

general appearance between adjacent stands will tend to disappear over time. In

single-tree selection, different age classes are developed in a stemwise mixture

through removal of individual trees. This method strongly favors shade-tolerant species

because of the small size of openings. It is difficult and expensive to carry out, and

damage to remaining trees can be extensive. Single-tree selection is therefore rarely

used in the Douglas-fir region. In group selection, the aim is to develop a mosaic of

small even-aged groups or patches of differing ages within a stand (fig. 30). As the area

Figure 29-Regeneration established under a

shelterwood. The overwood is usually removed after

a few years, to produce a new even-aged stand.

Alternatively, the overwood can be retained for further

growth, as a reserve shelterwood or two-aged stand.

Figure 30-

Group selection

in Douglas-fir,

McDonald

Forest, Oregon

State University.

45

5
of the group or patch is increased, conditions within the patch approach those under

clearcutting and become suitable for intolerant species and amenable to the same

regeneration practices.

Accessory systems (Matthews 1989) include conscious establishment of layered and

two-aged stands, potentially important in the Pacific Northwest. These include twoaged systems such as clearcutting with reserves (retention of scattered trees or

groups of trees from the former stand) and reserve shelterwoods (Nyland 1996), in

which a more or less uniformly distributed overwood is retained for much or all of the

next rotation. Both two-aged and layered but essentially even-aged stands often arise

naturally because of differences in species tolerance and growth rates, and often are

thought favorable to wildlife and biodiversity values. Such conditions can be created by

planting appropriate species mixtures or by cultural practices designed to favor development of such species mixtures in either natural or planted stands.

It has become common practice, mandated by state regulations and by management

guidelines on Federal lands, to leave scattered green trees or groups of trees on

harvest units for wildlife and other ecological purposes. Although this may initially

produce stand conditions that appear similar to those created by the seed tree method,

the retained trees are not left primarily for seed production and are not intended or

expected to provide adequate regeneration (fig. 31). Harvest cuts including such

features are sometimes referred to as “retention harvests” or “retention harvest systems” (Franklin and others 1997). This is inconsistent with long-established terminology

used worldwide. Depending on number, arrangement, and planned retention of leave

trees, such harvests are more accurately characterized as “clearcut with reserves,”

“irregular shelterwood” (Smith 1986), or “reserve shelter-wood” (Nyland 1996). Questions of terminology aside, Franklin and others (1997) provide a good discussion of

some of the variations on the basic ideas involved and of the hypothesized value of

these measures in promoting wildlife habitat and rapid recolonization of harvested

areas by a variety of plants and animals.

Figure 31-It is now common

practice to leave scattered

green trees or groups of

trees and snags on harvest

units for wildlife and other

purposes. Although such

“new forestry” harvest units

have a superficial resemblance to the seed tree cuts

of the past, the trees are not

retained for regeneration

purposes.

46
Rotations

Timber harvesting after large-scale catastrophic events often does not easily lend itself

to overall classification, because many of the critical harvesting considerations are

landscape rather than stand-level ones. The scale of disturbance can be orders of

magnitude greater than the mean stand size (many thousands of acres vs. less than

100 acres). Thus, recent management plans in Oregon (e.g., following the Silver and

Longwood fires in the Siskiyou National Forest and the Warner Creek fire in the

Willamette National Forest) have redefined stand boundaries in ways that attempt to

mimic natural patterns on the landscape and have reduced the amount of salvage or

cutting of green trees in some units in an attempt to recreate natural patterns and

accelerate the development of a range of stand structures within the landscape.

The progressive reduction in harvest ages (rotations) in recent decades has contributed

to current problems. The net result of past harvest practices, reduced harvest ages,

and historical harvest patterns is that many landscapes are dominated by recent

clearcuts and by stands in the stand initiation and stem exclusion stages (fig. 6). Many

people find this aesthetically distasteful and regard it as irresponsible destruction of

“nature,” creating horrendous public relations and political problems with huge indirect

costs to the landowner and the public. The possible effects of frequent drastic disturbance on wildlife, hydrology, biodiversity, site productivity, timber quality, and long-term

sustainability also have been questioned. Similarly, people have raised concerns about

regimes in which most of the landscape is occupied by relatively uniform young stands.

A shift to extended rotations on some part of the land base (combined with increased

commercial thinning and-where feasible-regeneration systems other than extensive

clearcuts) can help to reduce the visual impacts of forestry operations. Longer rotations

also would help maintain species diversity, wildlife, and other environmental values on

lands where continued and sustainable timber production is a major objective.

Douglas-fir, because of the past history of the forests and the relatively intolerant nature

of the species, is usually grown in even-aged stands and will probably continue to be

so managed for the foreseeable future. This does not necessarily imply the large units

of a single age class that are common today. Below, we define and discuss some terms

and relations related to even-aged management. Although these are defined in terms of

wood production, they remain important in management and policy decisions involving

any form of integrated management for production of multiple benefits, including wood

production.

Definitions-Rotation is the planned number of years between stand regeneration (or

removal of the previous stand) and final harvest. Yield is the sum of standing volume +

cumulative amount removed in thinnings since stand establishment, at a specified age.

Mean annual increment (MAI) is volume produced (standing volume + volume removed in thinnings), divided by stand age (i.e., average annual production rate from

establishment to the age in question). Current annual increment (CAI) is growth rate

in volume per year at specified age (which is not directly measurable). Periodic annual

increment (PAI) is an approximation to CAI, calculated as the difference in stand

volume at two successive measurements, divided by the number of years between

measurements.

47
300

7. 200

I

x

Tll

$

It: 100

0

2 0 4 0 60 8 0 100 120

Age (years)

Figure 32-The curves for mean

annual increment (solid line) and

periodic annual increment (dashed

line) intersect at culmination of mean

annual increment, at the age which

gives maximum average volume

production. Values are as shown for

site Ill in McArdle and others (1961)

adjusted to volumes to a 6-inch top.

The MAI and PAI trends over time are important expressions of stand and species

development patterns. The MAI and PAI curves for a given stand have characteristic

patterns, (shown schematically in fig. 32) and intersect at the maximum point (“culmination”) of the MAI curve.

Historically, there are three basic theoretical concepts of “optimum” rotation. In traditional presentations, these are based on timber volume or timber value only (Chang

1984, Newman 1988, Pearse 1967):

l The first maximizes value of timber produced per year and corresponds to age of

culmination of mean annual value increment.

l The second maximizes timber volume produced per year and corresponds to age of

culmination of mean annual volume increment.

l The third or financial rotation maximizes the net value of all costs and returns,

discounted either to the present or to the year of stand establishment, at some

specified interest rate. The value discounted to year zero is known as soil expectation value and represents the amount that an investor could pay for bare land to be

used for timber production and still earn the specified interest rate, given full knowledge of future costs and returns.

In general, the first is longer than the second; the financial rotation is the shortest of

the three-much shorter if the assumed interest rate is high. Foresters have argued

about these for a century and a half. Forest economists usually advocate the third, or

variations thereof, as the theoretically “correct” answer. In real life, many other considerations enter into the rotation decision. A major factor today is the existence of multiple

management goals, not restricted to or necessarily emphasizing timber production or

economic return, and often not readily expressible in monetary terms.

Extended rotations-Extended rotations can be a major component of any strategy to

reduce conflicts and promote joint production of commodity and ecological values

(Curtis and Carey 1996, Curtis and Marshall 1993, Kuehne 1993, Lippke and Fretwell

1997, Newton and Cole 1987, Voelker 1973).

48
As rotations have become shorter, a greater percentage of forest land is cut annually,

and more of the stands and total forest area are in the visually least attractive and least

diverse stand initiation and stem exclusion stages. Although short rotations may maximize the discounted present net value of timber, trees are smaller, wood quality and

value at harvest are lower, and productivity of both wood and other forest values are

reduced in comparison with biological potentials.

Long rotations are biologically feasible in the Pacific Northwest because Douglas-fir

and its conifer associates are very long-lived and can maintain rapid growth to advanced ages. The widespread perception in the United States that high yields and

intensive management imply short rotations is not necessarily true. On the contrary,

long rotations have long been associated with very intensive management regimes in

some European countries.

Possible advantages of extended rotations include:

l Reduced land area in regeneration and early development stages, hence:

-reduced visual impacts

- reduced frequency of major site disturbance

- less need for herbicides, slash disposal, etc.

-lower (less frequent) regeneration and respacing costs

l Larger trees and higher value wood

l Opportunity to adjust present age distributions for better balance and a greater range

in ages across landscapes, and to develop multistoried stand structures

l Higher quality wildlife habitat for some species and enhancement of biodiversity

l Hydrological and possible long-term site productivity benefits

l Increased carbon storage associated with larger growing stock

0

l Preservation of options for future management changes

Maximum long-term volume production is attained when stands are grown to the age

of culmination of MAI. The MAI curve is relatively flat in the vicinity of culmination age,

systematic thinning will probably delay culmination, and there is a considerable range

of possible rotation ages that will produce approximately the same MAI (fig. 33).

Moderate extension of rotations over those common at present would not decrease

long-term volume production (Curtis 1992, 1994, 1995; Curtis and Marshall 1993),

might well increase value production, and would certainly increase aesthetic and some

wildlife and biodiversity values.

Age of culmination of MAI is the minimum harvest age specified for National Forest

lands under the National Forest Management Act of 1976. (In application, the age

corresponding to 95 percent of estimated maximum MAI is usually taken as a minimum.) Subject to this constraint, actual harvest ages are determined by a combination

of even-flow constraints on harvests; age class distribution constraints; existing stocking and growth rates; and economic, environmental, and political considerations. One

49
“. . . - . . .

3 0 4 0 50 6 0 7 0 8 0

Age (years)

Figure 33-Systematically thinned

stands often maintain rapid growth well

beyond the culmination age indicated in

old normal yield tables, as shown by

mean values from four repeatedly

thinned plots at Cowichan Lake, British

Columbia. Culmination of mean annual

increment (solid line) has not been

reached at age 76 (Curtis 1995).

difficulty is that culmination age is not a fixed known quantity. It is influenced by management regime, and within regimes, there are substantial differences among available

estimates.

The conventional economic argument based on maximizing the discounted monetary

value of all future costs and returns gives great weight to near-term income and negligible weight to long-term societal values (Overton and Hunt 1974). The most common

and simplistic analyses have major shortcomings. Employment, wildlife, water, fish,

biodiversity and amenity values, which usually do not provide revenue to the landowner, often are ignored. Expression of many of these values in monetary terms is

imprecise at best, and impossible for some. Yet, public policy considerations demand

maintaining productivity of all values and avoiding actions with unacceptable effects on

social values. Public desires for nontimber values have become dominant influences on

management of Forest Service and some other public lands. And, public perceptions

are strongly influenced by the visual impact of management regimes and are a major

driving force behind costly and increasing regulatory constraints and pressures for land

withdrawals for special uses.

Rotations are strongly influenced by financial and supply considerations and owner

objectives as well as by biology, and rotations of maximum MAI in volume or in value

are probably not appropriate for many private owners. Unpredictable damage by wind,

fire, insects, disease, or current stand conditions will always make early harvest of

some stands advisable (Harrington and Knapp 1994). Continuation of the recent trend

toward very short rotations on many non-Federal lands, however, likely will lead to

sharply reduced productivity compared to potential, restricted future management

options, reduced nontimber benefits, and exacerbation of antiforestry attitudes among

major segments of the public.

Wood Supply, Cash Flows, A “desirable” or “optimum” rotation represents a long-term goal, rather than a measure

and Distribution of Stand

Ages and Conditions

that can be immediately implemented everywhere. Change must be gradual because of

constraints of existing age class distributions, economic demand and supply, and public

and political pressures. Extending rotations could ultimately increase wood supplies as

well as the associated nontimber forest values. Unfortunately, both extension of rotations and some recent changes in harvest practices also imply temporary reductions in

50
harvest volumes and (probably) increased operating costs. An immediate practical

problem is the need to maintain some acceptable level of wood supplies and cash

flows (which are generated primarily from timber) during any transition period.

This need is critical for private and industrial ownerships, and should not be ignored by

public agencies. Legislative bodies may be reluctant to fund large-scale land management programs over extended periods to promote intangible benefits, in the absence

of concurrent revenues. Programs based on silvicultural regimes that truly integrate

production of timber and nontimber values and produce substantial current revenues

along with nonmonetary values seem much more likely to survive and prosper.

Increased thinning can help to maintain wood supply and cash flow during any transition period. Silvicultural regimes might be selected to maximize yields from thinnings

even though they may result in some reduction in yields at final harvest. A number of

examples (Curtis 1995) suggest that thinning regimes can be designed that combine

high intermediate yields and relatively infrequent entries with development of stands

acceptable for both timber and nontimber objectives.

Balanced age distributions (i.e., a “regulated forest”) have traditionally been a long-term

goal of forest management, motivated primarily by the desire for stable wood supplies

and cash flows. Balanced stand condition distributions also have an important role in

promoting nontimber values (Oliver 1992). Distributions of stand ages and of stand

conditions are not the same thing, although obviously related; stand conditions are

jointly determined by age, management regime, and site. Stands cannot be maintained

in any given condition indefinitely. Given a mix of different silvicultural regimes and

differences in objectives among owners, we do not necessarily need equal areas in all

age classes. But if we wish to have a given stand condition represented in the future,

we must provide for future replacement of the stands now in that condition. Stand

condition or stand age distributions that are in some sense balanced on local or landscape scales provide a range of seral stages and stand conditions and a variety of

wildlife habitats and are an essential part of long-term sustainability of both commodity

and noncommodity values. Landscapes dominated by a single developmental stage

(sometimes visually monotonous or unattractive or otherwise undesirable for some

values) thereby would be avoided and some impacts related to human and natural

disturbances would be lessened.

Existing stand age distributions are quite unbalanced, on both regional and local scales

(Adams and others 1992, Sessions and others 1990). Figure 34 shows the regional

distribution of age classes for (1) all ownerships combined; and for (2) National Forests

and (3) industrial ownerships, which are the two ownership categories with the greatest

differences in age distributions. Overall age distributions of nonindustrial private owners

and other public agencies (primarily states) appear fairly well balanced to about age 80

but contain few older stands.

On a regional scale, age distributions within National Forest lands appear reasonably

well balanced for production of multiple values and preservation of future management

flexibility. In contrast, that for industry lands is quite narrow and severely limits options

available to owners (Haynes and others 1995). Regional totals such as those for

National Forests, however, mask major differences among Forests and among watersheds or other localized areas within Forests, which reflect differences in fire history

51
3 

$1000 

z 

:: 800 

5 

Y 

0 

@. 

600 

I al 

z 

400 

1 O-year age class midpoints 

5 25 45 65 85 105 125 145 165 165 2OOt 

IO-year age class midpoints 

1400 

1200 

Q 

5 1000 

75 

:: 800 

5 

Y 

0 

E 

600 

3 

a, 400 

a 

200 

'85 io5’ i25’ i4< i65’ 

lo-year age class midpoints 

Figure 34-Overall distribution of ages class in western Washington and 

Oregon for (A) all ownerships, (B) National Forests, and (C) industrial 

ownerships. 

52 

* 
and harvesting history. And, because of the delays involved in the inventory process,

the figures shown (derived from Bolsinger and others 1997 and unpublished data’) do

not include changes arising from accelerated harvesting on industrial lands (and other

private, not shown) following the near-cessation of harvests from National Forest lands

in 1992. The narrow range in ages on industrial lands and the continuing reduction in

harvest ages imply that large blocks of land are and will continue to be devoid of stands

older than about 45 to 50 years. Development of stand age or stand condition distributions that are more nearly balanced on watershed or other local scales will require that

some stands be carried to advanced ages and some others be harvested at ages

substantially less than might otherwise be desirable (which also aids in meeting the

short-term timber supply problem). Spatial distributions and total areas involved are

both important.

Special Forest Products

Summary, Harvesting

Considerations

Efforts to create a wider range in ages and stand conditions and more balanced age

and spatial distributions are likely to be severely hampered by the current near-elimination of timber harvests from Federal lands. Indeed, current policies are having an effect

directly counter to that intended. The scramble for timber supplies following the nearcessation of harvests from Federal lands has produced sharply accelerated and

excessive cutting of immature stands on private lands. This cannot be continued for

long and will result in decreased future production and degradation of environmental

values that will last for decades. Conversely, stable supplies of Federal timber at some

reasonable and predictable level would reduce pressures for immediate harvest on

private lands and thereby could help in achieving improved management of the region’s

forests for both commodity and noncommodity values. There is precedent for some

form of cooperative harvest planning-though in a different context-in the Sustained

Yield Forest Management Act of 1944 (Dana 1956, p. 284).

Harvesting of special forest products (floral greens, Christmas trees and boughs,

berries, mushrooms, bark for medicinal purposes, moss, shrubs, plants for landscaping) is becoming a substantial revenue source and involves a number of scientific and

management questions (Molina and others 1997). Management practices can either

promote or degrade productivity of these values. Information on the effects of repeated

harvesting of these products and specific measures to promote their production is quite

limited, but common sense indicates that harvesting of some of these must be controlled to be sustainable. It has been shown, for example, that repeated harvesting of

swordfern fronds reduces frond length and plant survival considerably (Isaac 1945).

Anecdotal information suggests that repeated harvesting of mushrooms and some

harvesting practices may reduce future crops; studies are underway on this topic

(Amaranthus and Pilz 1996). Stand density control has obvious effects on productivity

of species such as salal and huckleberry (Vaccinium ssp.). Production of Christmas

trees and boughs from young true fir stands often enables managers to turn needed

spacing and pruning into revenue-producing operations (Murray and Crawford 1981).

Harvest operations that take place at the time of removal and regeneration in evenaged management (or in each cutting cycle in uneven-aged management) are the

major source of both user conflicts and revenues that support management of most

‘Data for western Oregon provided by Tim Swedberg, Pacific

Northwest Research Station, Portland, OR, April 25, 1997; and by

John Teply, USDA Forest Service, Pacific Northwest Region,

Portland, OR, May 7, 1997. On file with: Forestry Sciences

Laboratory, 3625-93d Avenue SW, Olympia, WA 98512.

53
forest benefits. They have a profound effect on the nature and development of stands

and forests. Appropriate methods must be used to attain desired objectives.

l Regeneration harvests are conventionally classified into a number of silvicultural

systems or methods, discussed at length in standard texts. These are not rigid

procedures, but segments of a continuum of possible actions. Selection and application of harvest methods depend primarily on characteristics of the specific stand and

site, tempered with public relations and environmental considerations. No one

system should be applied everywhere.

l Rotation length affects forest productivity for all values. Extension of rotations

beyond ages now in common use would have important benefits for some values.

Reduced frequency and extent of regeneration harvests would benefit aesthetic,

fish, and watershed values. The older stands would include stand structures more

favorable to some wildlife. Extended rotations would provide more flexibility to

respond to future changes. They might also give greater long-term wood production

and employment.

l Rotation choices involve important economic and policy considerations. Choices will

be different for different owners and owner objectives. The need to maintain some

stability in wood supply and cash flows is an important limitation on the rate and

magnitude of changes in rotations and management regimes.

l Stand age and stand condition distributions are important in long-term sustainability.

No stand condition can be maintained indefinitely. Provision must be made for

continuous replacement of stands over whatever range of stand ages, stand conditions, and spatial distribution is considered desirable for owner and societal

objectives.

l Special forest products (commodities such as floral greens, boughs, berries, Christmas trees, mushrooms) have become important and in some cases provide substantial revenues. Special forest products create additional opportunities but may require

some management modifications.

Providing Diverse

Structures and

Habitats

Forest management goals are commonly expressed as desired forest conditions. The

characteristics of individual stands as well as broad landscapes strongly influence

attainment of management goals and the choice of appropriate silvicultural measures.

Stands can be described in terms of structure, species composition, and site quality.

Stand structure includes the dimensions and vertical and horizontal arrangement of

trees, shrubs, herbs, grasses, nonvascular plants, and also snags, down logs, forest

floor depth, etc. Species composition describes the variety or relative species richness

of plants present within a given stand. Site quality integrates a combination of factors

(soil physical characteristics, soil fertility, climatic conditions) that affect potential stand

growth. Recent work suggests that increased diversity in structure and composition,

within and between stands, will enhance some wildlife habitat, biodiversity and aesthetic goals (Carey and Curtis 1996; Carey and Johnson 1995; Carey and others

1996a, 1996b).

Biological diversity has several aspects. These include the number (richness) and

relative abundance (evenness) of species present in a given stand; the variation in

54
species and their abundance among stands and across landscapes; the variation in

presence and structure of canopy layers, within and between stands and across

landscapes; and the genetic variation among individuals within a species. Stand

structure and composition change over time as stands develop. Different wildlife

species tend to be associated with different stand conditions. Thus, landscapes that

include substantial areas in early successional stages favor deer, elk, and berries;

those with substantial areas in late successional stages favor spotted owls (Strix

occidentalis). It follows that to provide and maintain habitat for a wide variety of species, a balanced distribution of stand structures and developmental stages needs to be

developed across landscapes (Oliver 1992).

Because forests are dynamic entities, this implies active management to produce

desired structures and regenerate stands as needed to maintain the desired age and

stand condition distributions. The biggest current imbalance is the general lack of

mature and old-growth stands on non-Federal lands. The recent establishment of large

late-successional reserves will, if long continued, produce a similar shortage of early

successional stages on Federal lands in the future. These imbalances will not be

mutually compensating because of wide geographic separation.

Much recent discussion of biodiversity has focused on old-growth stands and on efforts

to shape younger stands toward similar conditions, although this represents only one

segment of the needed range in stand conditions. This emphasis on old growth probably arises from the perception that this is the condition in most limited supply and most

difficult to replace if lost.

Forest characteristics important for some wildlife and aesthetic values do include some

characteristics commonly associated with mature and old-growth stands: (1) large trees;

(2) layered structure including some understory trees and shrubs; (3) mixed species

composition; (4) presence of large snags and live trees with cavities or other attributes

needed for nesting, roosting, and foraging; (5) presence of large woody debris on the

forest floor; and (6) within-stand variation in overstory density and corresponding variation in density of the understory. Although these characteristics commonly develop at

advanced ages in unmanaged stands, there is abundant evidence that their development can be markedly accelerated in much younger stands by appropriate silvicultural

measures (e.g., table 1; Curtis and Carey 1996). Currently heavily stocked young stands

may not develop these characteristics without silvicultural treatment (Tappeiner and

others 1997). Many of these measures also can produce direct economic benefits

through the concomitant production of wood.

Composition and structure of forest stands can be markedly altered by silvicultural

practices applied at appropriate stages in stand development. Some examples of such

practices have been mentioned previously. Below, we further discuss (at risk of some

repetition) practices that can be used to increase the range and diversity of stand

structures and to promote wildlife and other nontimber values. Practices must be

evaluated for each site, in relation to management objectives, stand characteristics,

cost, and safety considerations. If practices are properly applied, inherent site quality

can be maintained indefinitely.

55
Species Mixtures

Table l-Measures for producing diverse structures and habitats

At harvest At stand establishment

Young to

mid-age stands

Use long rotations

Use advance regeneration,

group selection, group

shelterwood, strip

shelterwood small

patch cuts (1-10 acres)

Thin to variable densities

within same stand

Save advance Encourage natural seedlings

regeneration within plantations

Retain snags and

down logs

Save patches of hardwoods

and shrubs to increase future

stand variability

Retain green trees,

groups or singly

Work toward balanced

age distribution on

landscape level

Plant with mixed species,

irregular spacing

Leave portions of stand

undisturbed by site

preparation or slash disposal

Thin to produce large

trees with deep crowns

and to promote understory development

Thin to variable densities

within stand

Release advance tree

and shrub regeneration

Retain existing snags and

down logs when thinning

Make additional snags and

down logs where needed

Underplant where natural

understory regeneration

is lacking

Mixed species planting with suitable density control can produce multilayered stands

because of differential species growth patterns and differential browsing by herbivores.

For example, Douglas-fir and western redcedar planted together may form stands with

multiple layers, because the redcedar generally grows slower than Douglas-fir, is more

susceptible to browsing, and its shade tolerance allows survival in the understory.

Subsequent thinning may be needed to maintain the slower growing species in the

understory. Natural regeneration of hemlock and other tolerant species often is abundant in young Douglas-fir plantations, and retention of some stems of these species

during precommercial thinning will favor development of mixed stands and layered

structures. Differences in species susceptibility also may make such mixed species

stands less susceptible to damage from root rots.

Douglas-fir plantations often quickly develop a considerable component of other conifers

and hardwoods. Good stems of species such as western hemlock and western redcedar,

and occasional hardwoods such as bigleaf maple, can be retained in precommercial and

later thinnings to enhance species and structural diversity of the future stand.

56
Stand Management for

Structural Diversity

Modifications of conventional thinning practice (table 1) might include favoring trees

of diverse species and sizes to foster crown stratification and understory development

for improved wildlife habitat (Hagar and others 1996). Small openings or gaps can be

created, which ultimately will be occupied by younger trees. Root rots, bark beetles,

and windthrow often do this independent of human intervention. As stands grow older,

dead trees can be retained to provide snags needed for some wildlife species; if needed,

additional snags can be created. Tolerant tree species such as western redcedar,

grand fir, Pacific yew, western hemlock, and bigleaf maple can be introduced through

underplanting, if seed sources of these species are lacking. Most species are more

tolerant when young, and conditions suitable at establishment may have to be altered

as plants age. Regeneration in riparian areas can be especially challenging; these

sites often have substantial existing understory vegetation, and animal damage to

young trees may be severe.

Modifications such as irregular thinning and underplanting are being evaluated in the

forest ecosystem study recently installed at Fort Lewis, WA (Carey 1993, Carey and

others 1996b), the Olympic habitat development study (Harrington and Carey 1994),

and the COPE (Coastal Oregon Productivity Enhancement) program (Emmingham

1996). Thinning prescriptions in these studies are designed to increase within-stand

variation in crown lengths, tree size, species composition, and understory distribution.

Although large-diameter trees are a desired component of these stands, the thinnings

are designed to promote increases in spatial heterogeneity and in the other structural

attributes found in natural stands. This contrasts with conventional uniform thinning

prescriptions, which produce more evenly spaced, large-diameter trees with more even

understory distribution. As stands grow older, some trees will die and provide snags

needed for some wildlife species. Other cavity trees will form as a result of damage

from wind, snow and ice breakage, and thinning injuries. If needed, managers can

provide additional cavity trees by killing, wounding, or topping some trees.

There are many well-stocked young stands (10 to 50+ years) in the Douglas-fir region

that have been established after fire or timber harvest. About 30 to 60 percent of many

watersheds on Federal land, and a majority of private lands, are stocked with these

young stands. For the most part, they have been regenerated and managed at high

densities to produce high yields of wood, and not to develop diverse structure. In

contrast, old-growth stands often have only 10 to 30 trees per acre in the upper canopy

(Spies and Franklin 1991). Thus, if we wish to develop future old-growth-like characteristics in some portion of these young stands, considerable reduction in stocking over

time is needed to produce large trees with deep crowns and provide a more open

environment for understory development. Seedlings of tolerant species can be established after thinning in young conifer stands, but subsequent reduction in canopy

density will be needed to ensure their future development.

Thinning and regulation of overstory density can be used to produce large trees quickly,

develop stand structure, and generally aid the development of mature forest and oldgrowth-like characteristics (Curtis and Marshall 1993, Newton and Cole 1987, Hayes et

al. 1997). Advance regeneration can be released to produce multiple layers. There

often are numerous hardwood seedlings and conifers (Fried and others 1988,

Tappeiner and McDonald 1984) in the understory that will respond to a reduction in .

57
overstory density. In dense stands with no tree understory, the increased light and

limited soil disturbance from thinning favor establishment of both conifer seedlings

(Del Rio and Berg 1979) and hardwood seedlings (Fried and others 1988, Tappeiner

and others 1986). In a western Oregon study that compared understory characteristics

in thinned and unthinned Douglas-fir stands, one of the most striking differences

between the stands was the stocking of natural conifer seedlings in the understory of

the thinned stand (Bailey 1996). Additional thinning to mimic natural stand development

could release conifers and hardwoods and leave the overstory at variable densities to

encourage “patchy” understory development, but this also would cause considerable

damage to the existing understory.

Shade-tolerant conifers can be planted in the understory after thinning to develop

multilayered stands, with some of the characteristics that are found in naturally developed stands of much greater age and that are considered favorable to some wildlife

species. Thus, Alan Berg of Oregon State University thinned a 40-year-old Douglas-fir

stand to 50 trees per acre and planted western hemlock in the understory. About 40

years later, this is a well-developed two-storied stand (Curtis and Marshall 1993). At

80 years of age, the overstory of 50 trees per acre is probably too dense for continued

understory growth, although the overstory trees are still growing rapidly. Average

diameter of the Douglas-fir overstory is about 30 inches. In the nearby unthinned stand,

average diameter is only 15 inches with practically no understory.

Pure red alder stands are common in riparian areas, especially in coastal forests.

But, some conifer component is often desirable in these areas to provide large logs

for stream channnel structure and to produce a more diverse forest for wildlife.

Emmingham and others (1989) successfully planted western hemlock under thinned

red alder stands. Both overstory density reduction and long-term salmonberry control

were needed to establish hemlock. Elk (Cervus elaphus) and beaver (Castor canadensis) have caused major damage to planted seedlings on similar sites. Chance of

seedling establishment is increased by using large planting stock and planting large

areas at a time, to reduce animal damage (discussed in a later section). Where advance conifer regeneration is present under red alder, it can be released to grow large

conifers. Newton and others (1996) discuss problems and applicable techniques.

Use of Advance

Reproduction

Current methods of planting and tending young stands can be altered to produce stands

of diverse structures and species composition after fire, clearcutting, or other disturbance. Retaining poles, saplings, and seedlings of acceptable vigor and form from the

previous stand will accelerate the regeneration of the next stand and tend to encourage

development of more “patchy” stands and a variety of tree sizes and species (Tesch

and Korpela 1993). Such use of advance reproduction is most promising on the drier

sites and in the mixed species stands common in southwestern Oregon. On the better

sites and in the northern part of the region, advance regeneration is likely to be of

tolerant species (hemlock, true firs) that are highly susceptible to rot entering through

logging wounds, and early removal of damaged trees may be needed.

Shrub and Hardwood

Management

Managing competition of shrubs, herbs and hardwoods at the time of regeneration will

affect species composition, structure, and subsequent development of the future stand.

The models developed by Harrington and others (1991 a, 1991 b) for tanoak and Pacific

58
madrone and by Knowe and others (1995) for bigleaf maple estimate the amount of

cover produced by sprouting hardwoods, the effects on conifer survival and growth

rates, and effects on stocking of understory shrubs and herbs. Use of such models will

help forest managers forecast the development and influence of hardwoods during

early stages of stand establishment.

Shade-tolerant hardwoods such as bigleaf maple and tanoak will provide a layered

stand as they are overtopped by conifers at about 40 to 50 years of age. Large overtopped hardwoods provide cavities as large branches die and decay. California black

oak (Quercus kelloggii Newb.) and Pacific madrone are more likely to be shaded out by

overtopping conifers. They can be maintained in well-stocked older conifer stands by

growing them in groups and thinning adjacent conifers. Hardwoods provide important

structural diversity and diverse food sources (seeds and nuts) for wildlife.

Thinning favors regeneration of shrub understories under established stands. These

understories can be beneficial from a wildlife standpoint but also can be a major

obstacle to future regeneration of tree species. Salal (Huffman and others 1994) and

salmonberry (Tappeiner and others 1991) commonly increase with reduction of overstory density through rhizome extension and other means of vegetative expansion.

Vine maple clones are spread by “layering” as a result of thinning. Slash from natural

disturbance of the overstory or from commercial thinning may pin the vine maple

crowns to the forest floor where the branches often root and form a dense understory of

new sprouts (O’Dea and others 1995). Establishment of salal, vine maple, and salmonberry seedlings is also favored by thinning, but their expansion and development of a

dense cover is mainly by vegetative clonal expansion. (Huffman and others 1994,

Tappeiner and Zasada 1993, Tappeiner and others 1991). Thus, dense, continuous

understories of these and other shrub species can develop after heavy thinning or

partial removal of the overstory. Because of the potential for rapid vegetative expansion

of shrubs, there may be a relatively “narrow” window for establishment of new conifer

plants by natural seeding or by planting, and vegetation control measures also may be

necessary. Composition and severity of shrub competition are strongly influenced by

differences in site and canopy density (Klinka and others 1996) and by stand history.

Providing Cavities, Snags, In stands managed for wood production, decadent, dying, and dead trees have been

and Coarse Woody Debris viewed as problems to be avoided or at least minimized by harvesting before they

deteriorate or contribute to spread of insect pests and disease. Thus, spacing guidelines are based on the number of trees that can be grown to some desired size before

significant competition-induced mortality occurs. Trees killed by insects, diseases, and

fire usually have been salvaged immediately where economics and accessibility permit.

Until recently, existing snags were commonly felled for fire hazard reduction and worker

safety. Debris from harvesting operations often was burned to reduce fire hazard,

facilitate planting, and control shrub competition. Yet dying, dead, and down trees are

important components of forest ecosystems, and a variety of organisms are associated

with them. These organisms range from cavity-dwellers like squirrels and other small

mammals and many birds, to amphibians and invertebrates, to diverse vascular and

nonvascular plants and microorganisms. Provision therefore should be made for dead

wood management in multipurpose forests, particularly those where conservation of

biodiversity is a primary management objective. Low-value tops, defective logs, and

59
coarse slash can be left onsite. Stumps (and the attached root systems) represent a

substantial fraction of the biomass. We know of no quantitative evaluation of the role of

stumps after harvest of young-growth Douglas-fir; but it is obvious that, if trees are

grown to large sizes, stumps will serve some of the same functions attributed to large

down logs.

Retaining large trees, snags, and down logs in some ways mimics the results of natural

disturbance by fire or wind (Spies and Franklin 1991). Natural disturbances often do

not kill all trees, and trees that die contribute large pieces of wood to the forest floor.

Retention of some large trees after harvest-especially those with large limbs and

cavities-as well as large snags and logs will help ensure later development of a stand

with diverse structure (fig. 35). Leaving undisturbed groups of trees may aid carryover

of some plants and other organisms, so-called biological legacies, from one stand to

the next. Leaving groups of large trees (small patches) rather than scattered individuals

also may facilitate logging and reforestation. Although partial overhead shade is often

beneficial to initial establishment of tree seedlings, even a few retained overstory trees

markedly reduce subsequent growth of established regeneration (Acker 1995, Hoyer

1993, Wampler 1993, Zenner 1995); a cost that may or may not be partially offset by

growth of the reserve trees.

Surveys of plant communities in clearcut and burned areas indicate that most herbaceous plants growing in old forests are adapted to disturbance (Dyrness 1973, Franklin

and Dyrness 1971, Halpern 1988, Halpern and Spies 1995), and that changes in

understory diversity after disturbance are usually fairly short-lived. Therefore, use of

different silvicultural systems or thinning regimes is not likely to have a great long-term

effect on the herbaceous component of forest stands.

B

Figure 35-Presence of (A) large trees and (B) large woody

debris and snags and cavities are wildlife-related characteristics of old-growth forests that are often lacking or present

to a lesser degree in young forests, especially in plantations.

Protection or creation of snags is important to maintaining

populations of cavity-using birds and small mammals.

60
Plans for management of snags, live trees with cavities, and down wood must consider

numbers, sizes, species, spatial distribution, and dynamics of decay and persistence.

Many questions on desirable amount, distribution, condition and expected longevity

of dead and down material are currently unanswered. Because of the importance of

snags to wildlife (Carey and Johnson 1995, Carey and others 1996b) and the high

economic cost of protecting or creating them, it is critical that uncertainties be resolved

and methods for snag creation be developed that are both biologically effective and

economically acceptable. In the absence of definitive information, forest managers

and wildlife biologists from nearly every region have recommended snag densities

that are remarkably consistent, with an average of 2 to 4 snags per acre suggested as

a reasonable target (Hunter 1990). Snag dynamics have been studied in the Pacific

Northwest (Neitro and others 1985), and computer programs exist that estimate

desirable numbers for various bird species and snag persistence over decades (Marcot

1992). A minimum size (diameter and height) usually is suitable for each species, and

in general large snags are better than small snags because they will last longer and

more species will be able to use the snag. Carey and others (1991) report that all

species of cavity-using birds in natural forests preferentially selected moderately

decayed snags over 30 inches in diameter at breast height. Similar results were

reported by Lundquist and Mariani (1991). In managed forests where residual snags

may be rare (and cavity-using bird populations low), birds will use well-decayed hardwood snags. A range of sizes may be needed, however, because some cavity users

“defend” the snag from use by other species (Gibbons and Lindenmayer 1996). Slowly

decaying species are usually most desirable because they will persist longer, but both

“hard” and “soft” snags are needed. New snags of suitable characteristics must be

recruited periodically to replace those that have fallen and are providing values

associated with down wood.

Five matters specific to management of cavities and dead wood should be considered

in silvicultural efforts to shape stand development and vegetative habitat:

1. Protection or retention of standing dead (snags) and down trees. Some and perhaps

all of the largest of these should be retained during silvicultural operations, where

feasible. Unfortunately, retention of existing snags often conflicts with fire prevention

needs and current logging safety requirements, which differ among states and

regions. Operational and safety considerations may make it preferable to create and

preserve snags within small uncut groups of trees, rather than distributed over an

area. Existing snags, however, are good sources of coarse woody debris for the

forest floor.

2. Protection of live trees with cavities. Although snags are a recognized element of

wildlife habitat for many animals, the importance of live trees with cavities is sometimes overlooked or underrated. Thus, Carey and others (1997) report that over 50

percent of flying squirrel (Glaucomys sabrinus) nests are in live trees. Cavity trees

can be equally or more important than snags for several reasons: living trees with

cavities may persist much longer than dead trees, and the presence of live foliage

can increase cavity security and modify microclimate in ways beneficial to cavity

dwellers.

61
3. Creation of snags and down trees in stands where they are scarce or absent due to

past stand history. Trees in existing stands can be killed by girdling or injection with

herbicides, but there is uncertainty about the biological effectiveness of such methods because of differing decay development patterns. Some biologists and managers have tried other techniques, including blowing off tops with explosives, cutting off

tops with saws, inoculating with fungi, and attracting beetles with sex pheromones

(Baker and others 1996, Bull and Partridge 1986, Conner and others 1983). The

existence of some low-quality trees in most stands (that otherwise would be removed

in thinning) provides a low-cost opportunity to create snags. In some instances in

British Columbia, snags have been “planted” in clearcuts by using material of little

merchantable value, although their long-term value has not been demonstrated.

4. Creation of cavities. In general, retention of existing snags, perhaps supplemented

with snag creation, will provide cavities sufficient to meet wildlife objectives. In

specific instances, however, installation of nest boxes or creation of cavities by denrouting (Carey and Sanderson 1981) or by cutting a hole with a chainsaw and

covering it with a faceplate (Carey and Gill 1983) may be appropriate. These approaches are being evaluated for effects on flying squirrel populations in younggrowth Douglas-fir forests (Carey 1993); 2 years after installation, nestboxes were

used more heavily than artificial cavities, and both nestboxers and cavities had

greater usage in previously thinned than in unthinned stands (Carey and others

1996b).

5. It may be possible to accelerate development of snags and cavities in live trees by

indirect and less costly treatments. Thinning and fertilization could be applied in

ways that increase variation in tree growth (e.g., release or fertilization of individual

trees). Favored trees would become superdominants, with crowns extending above

the general canopy. Such superdominant trees would be expected to have large

branches in the upper canopy, and some would develop the crook or umbrella tops

that favor nesting or roosting by animals using such structures. The types of stands

(age, stocking) and site conditions most responsive to such activities can be identified, but the details of such treatment have not been worked out or their effectiveness evaluated.

In summary, many standard silvicultural practices (such as thinning, fertilizing, and

pruning) can be applied to favor the growth and development of trees of desired

characteristics (size, species, form, age) in specific locations. With appropriate rotation

lengths and better understanding of the dynamics of snag populations, it should be

relatively easy to provide standing dead and down wood in amounts and locations

consistent with forest management objectives and without major effects on other

objectives and costs. The possible benefits of clumping versus scattering of coarse

woody debris in conjunction with thinning operations is being evaluated in a long-term

study in the Olympic National Forest (Harrington and Carey 1994).

62
Other Considerations Several aspects of extended rotations and associated thinning and regeneration

options will generally favor biodiversity and production of wildlife (Curtis and Carey

1996) and will help maintain plant species diversity (Halpern and Spies 1995):

l Extended rotations allow development of a wide range of age classes, tree sizes,

and structures and provide the opportunity to develop late successional characteristics within stand management programs.

l Thinning and alternative regeneration systems, combined with extended rotations,

will minimize the influence of the stem exclusion stage and of harvests on dispersal

and colonization processes. They will promote development of structural diversity

and, with suitable placement and sizes of harvest units, should reduce or eliminate

the unfavorable effects often thought to be associated with forest fragmentation into

spatially disconnected units of radically different characteristics.

l Thinning entries usually will be infrequent during the latter part of a rotation, and

there will therefore be some unsalvaged mortality that will provide snags and coarse

woody debris, additional to stumps and tops, from thinning. If these are insufficient,

additional trees can be killed or treated to provide snags, cavities, and coarse woody

debris.

l Thinning provides flexibility in control of stand density and structure that can be

consciously used to promote habitat for late-successional species through development of understory and creation of small openings and within-stand density variation.

Systematic thinning begun at a relatively early age can produce large trees and

markedly alter stand structures within relatively short periods.

Summary, Diverse

Structures

The emphasis given to these options obviously will be strongly influenced by existing

land ownership and owner objectives.

Stand characteristics favorable to some biodiversity, wildlife, and aesthetic goals can

be actively enhanced by a number of modifications to conventional silvicultural practices and additional measures. These include:

l Modified thinning practices to develop mixed species stands, muliple canopy layers,

and more diverse understories. Irregular thinning and underplanting of openings with

tolerant species can be used to promote vertical and horizontal heterogeneity.

l Thinning, especially if begun early, to produce large trees with deep crowns (more

nearly comparable to those in existing older stands) and a more open environment

for understory development. Early thinning minimizes the duration of the least

diverse and least productive (for wildlife) stem exclusion stage of stand development.

l Retention of some hardwoods and minor species in thinning can enhance species

and structural diversity.

9 Release of existing conifers and underplanting of tolerant species in riparian hardwood stands can provide a more diverse riparian forest and eventually produce the

large conifer logs needed to enhance stream channel structure.

l Protection or retention of standing dead and down trees, where feasible, for nest

sites and coarse woody debris.

63
Maintaining Site

Productivity

l Protection of live trees with cavities as nest sites.

l Creation of snags, cavity trees, and down trees in stands where they are scarce or

absent.

l Retention of scattered trees or (probably preferable) groups of trees at harvest, for

future production of snags and coarse woody debris.

l Use of extended rotations (in combination with thinning) and alternative regeneration

systems to develop a wide range of stand ages, tree sizes, and structures.

Productivity as a general concept, as opposed to productivity for a specific product, is

not easily defined or measured. Forest or ecosystem productivity can be discussed or

quantified in various ways. One could seek to determine the productivity of forest

landscapes for spotted owls, for deer, for harvestable crops of mushrooms, or for cubic

feet of wood. Or, overall productivity can be expressed as the rate of production of

organic matter in a system that is in some more or less stable (if such exists) or average condition. Forest ecosystems can be described in terms of basic functions (biomass accumulation and nutrient cycling) and structure (species diversity and complexity) (see Bradshaw 1987; Harrington, in press; Magnuson and others 1980). In

ecological terminology, forest ecosystems that exhibit increases in biomass accumulation and nutrient cycling rates or in complexity of species composition are considered to

be aggrading, and systems that exhibit losses in these factors are degrading. Thus,

ecosystem degradation can occur through simplification of the system (reduction in

species or structural complexity) without necessarily reducing the inherent productivity

potential of a site or its potential to aggrade in the future.

In a forestry context, productivity is commonly defined in terms of biomass production

per unit of time, net primary productivity (Grier and others 1989). But measurement of

biomass production rates is difficult and imprecise, and they are markedly influenced by

stand age and condition. Forest productivity and soil productivity are related but somewhat different concepts. Forest productivity refers to the entire forest system composed

of soil, climate, and the associated vegetation and other organisms. Forest productivity

is influenced by species composition, genetic composition, stand structure, and age

structure, all of which can be readily modified by management over relatively short

periods.

In contrast, soil productive capacity (or site productivity) refers specifically to inherent

potential as determined by local climate and soil conditions. Gross climate is not

subject to human control, but some management actions can influence soil characteristics and hence soil productivity. Some actions can improve soil productivity, whereas

others can be harmful. Sustainable forestry obviously requires that soil productivity

shall not be materially reduced and, if possible, increased by management activities.

Soil or site productivity is usually discussed in terms of the basic ability of the site to

produce biomass, or more commonly, surrogates such as bolewood volume or site

index (height at a specified reference age), which are much more easily measured and

for which considerable data are available. Much information is available about soil

characteristics that are related to fertility (Heilman and others 1979). The general

direction of effects that specific management practices may have on these is known,

64
whether or not these effects are large enough to produce measurable or important

effects on soil productivity. The magnitude of effects will be markedly affected by

conditions existing on the specific site.

The effect of plant species composition on site productivity is not well known, with

some exceptions. If a site is nitrogen limited, then nitrogen-fixing plants can enhance

productivity. There are substantial differences in nutrient cycling among plant species,

related to nutrient uptake, leaching, or chemical composition of leaf and other plant part

litter. For example, western redcedar takes up calcium from deep soil layers and transports it to the surface via litter fall; this may be an important mechanism to maintain

productivity on some sites (Weetman and others 1987). Many deciduous tree and

shrub species also serve specialized roles in cation cycling. Presence of some species

has been associated with acidification (e.g., red alder and spruce-hemlock; see

Bormann and others 1994). Most of these effects have been documented but their

effects on long-term productivity are unclear.

Soil porosity and soil organic matter are generally recognized as important factors in

fertility. Porosity is reduced by compaction by heavy machinery. Porosity (and nitrogen

content) also is strongly related to organic matter content. Organic matter in the surface

layers (and ultimately, in the lower horizons) is reduced by very close utilization and by

severe or repeated burning.

Nutrient content is important. Nitrogen is the only nutrient currently recognized as

widely growth limiting in the Douglas-fir region, a deficiency probably resulting from the

relatively young age of soils developed on glacial or volcanic parent materials as well

as more recent fire history. Other nutrients, however, are also necessary. Long-term

nutrient status depends on both the initial supply and the balance between nutrient

withdrawals and nutrient inputs-which are usually from natural sources, although

fertilizer applications also can supply them. Nutrient withdrawals occur through removal

of biomass from the site, through leaching and erosion, and through volatilization

during burning (principally nitrogen). Nutrient inputs occur through decomposition of

minerals; nitrogen and sulphur deposition in rainfall; biological nitrogen fixation; and

(sometimes) fertilizer application. Rainfall deposition is in part human-caused, and

biological nitrogen fixation can be promoted through management and control of

species composition.

1. Concerns sometimes are raised about the possible effects of forest management

practices on long-term soil productivity. Possible changes attributable to management

are not clearly separable from changes attributable to factors such as climatic variations, air pollution, pathogens, and changes in stand composition and structure that

may be associated with either natural events or management practices. Thus, the

widely cited spruce decline in Germany in the early 1900s was the result of misguided

attempts to convert sites that formerly supported hardwood or mixed species stands to

pure spruce (Aune and others 1990, Lutz and Chandler 1946, Stone 1973, Troup

1952); more recent problems are associated primarily with air pollution rather than

stand management. Similar problems can arise from use of unsuitable seed sources.

Although excessive soil disturbance in harvesting and site preparation can cause

reductions in growth of unknown duration (Lavender and Newton 1985, Miller and

65
others 1989), there is little or no concrete evidence in the Douglas-fir region that forest

management practices similar to those now in use have caused substantial long-term

site degradation (Morris and Miller 1994), and few instances in moist temperate climates elsewhere in the world (Worrell and Hampson 1997). They can have the opposite effect, as shown by superior growth observed in some second and third generation

stands. Thus, recent European data (IUFRO 1995) seem to show a general increase in

site index and growth rates in managed stands over the last half of the 20th century. A

rare instance of accurate yield records extending over three successive rotations is

given by Evans (1996), who found no evidence of decline in productivity in Pinus pafula

plantations in Swaziland.

Nutrient budget calculations seem to indicate that on most sites there is little likelihood

of substantial degradation through loss of nutrients in stands conservatively managed

for conventional saw-log and pulpwood material. Substantial reduction in nutrient

capital and site productivity does appear possible with very short rotations and complete tree utilization (Kimmins 1987, Morris and Miller 1994, Proe and others 1996).

Continued production under very intensive short-rotation agricultural-type regimes, as

with Populus hybrids, implies a need for intensive nutrient management similar to that

in agriculture.

In general, the nutrient content per unit of weight or volume of tree crowns is greater

than that of sapwood, which in turn is greater than that of heartwood. Consequently,

nutrient removals are greater with complete tree utilization vs. bolewood utilization only;

greater with complete bole utilization vs. utilization to a diameter limit; and greater for

vigorous small trees vs. large mature trees. Hot slash burns and frequently repeated

burns cause substantial losses of organic matter and nutrients, particularly nitrogen.

Soil disturbance in logging, road building, and site preparation can cause measurable

erosion losses and soil compaction.

Because sites differ in initial nutrient capital, in erodibility, in susceptibility to compaction, and in rates of biological soil development processes (including nitrogen fixation),

positive and negative effects of specific practices differ among sites. In general, any

detrimental effects that may exist will be more serious on poor sites than on good sites.

Thus, current data from the generally good sites of the Tillamook Forest seem to

indicate greater productivity of young stands established after severe fire and intense

salvage logging than was exhibited by the previous stands. One would not expect such

results from stands on adverse sites and shallow rocky soils.

One can easily imagine a worst case regime that could not fail to cause site degradation. But this would be far outside the range of regimes currently in use. We do not

know whether or not current practices may have long-term negative (or positive) effects

on soil productivity. We can indicate, however, some choices associated with greater

or less likelihood of such effects. Likelihood of site degradation will generally be less if

(see the series of articles in Perry and others 1989):

l Harvest is with cable systems; or if by ground systems, skidding is confined to

designated skid trails.

l Slash burning is avoided or limited to the minimum necessary for acceptable hazard

reduction and regeneration establishment.

66
Branchwood and tops are left on site; very intensive utilization is avoided.

Provision is made for restoring nitrogen on nitrogen-deficient sites, through use of

either nitrogen-fixing vegetation or artificial fertilization.

Mechanical soil disturbance during site preparation is minimal.

Intervals between thinning entries are relatively long.

Rotations are relatively long, hence

-a high proportion of wood removed is heartwood.

-need for site preparation and regeneration (i.e., site disturbance) arises only at

long intervals.

Beuter and Johnson (1989) point out that conventional economic analyses, based on

discounted timber values, provide little justification for expenditures to maintain longterm productivity beyond the current rotation even if declines are real and substantial.

This would seem to conflict with the long-term interests of society and with the widely

accepted goal of sustainability, unless lost productivity can be restored in the future at

reasonable cost; it is perhaps indicative of the limitations of conventional economic

analyses. The question is perhaps moot in the absence of evidence of declining

productivity, but prudence suggests that severe site disturbance, complete tree utilization, unnecessary use of fire, and very short rotations should be avoided.

Summary, Site Productivity There is little or no evidence in the Northwest, or in moist temperate climates elsewhere, that forest management measures similar to those now in use in the Pacific

Northwest have reduced site productivity, and some have increased it. Possible unfavorable effects are difficult to detect over short time spans, however, and are probably

related to characteristics of the individual site. Existing knowledge and prudence

suggest that in general:

l Soil disturbance and slash burning should be restricted to the minimum necessary to

secure adequate regeneration.

l Whole-tree utilization should be avoided.

l Very short rotations should be avoided.

Damaging Agents and Trees and forests are subject to various forms of injury from fire, weather, insects,

Forest Health mammals, and disease. These agents can at times materially alter the development

and composition of stands and forests, prevent attainment of desired goals, place

limitations on the use of otherwise desirable management measures, and reduce

productivity. They may require specific management actions to avoid unacceptable

losses. Thus, they can be important considerations in selection of silvicultural regimes

to meet various objectives.

The major causes of tree damage and death in coastal Douglas-fir and its associates

(aside from normal competition) are fire, weather, bark beetles, mammals, various root

and foliage diseases, and bole rots. With the exception of fire, these are more or less

67
Fire

Weather

endemic factors in stand development and of little concern so long as they involve only

occasional trees. Indeed, death of occasional scattered trees can be beneficial in that it

provides snags and down wood for wildlife and tends to promote development of

diversity in species composition and stand structure. However, these agents also can

cause major economic losses, drastically disrupt stand management, and preclude

attainment of desired forest conditions and management goals. Management practices

can reduce the probability and magnitude of such events.

Most of the Northwest forest found by the early European settlers originated as a result

of wildfire. But uncontrolled fire is incompatible with any form of planned management

or even human occupancy, and establishment of effective fire prevention and control

was one of the great early achievements of forestry. We have not had a really big fire

(on the scale of the Yacolt and Tillamook fires) in the Douglas-fir region since the

1940s. Although modern fire prevention and control measures greatly reduce the

probability of large fires, they do not eliminate the possibility, given sufficiently extreme

weather conditions (fig. 36). Some changes in land use may reduce risks (e.g., highways, agriculture, urbanization), but others, such as residential expansion into forest

areas, increase both the risks and the potential magnitude of damage. Some measures

currently advocated and used to favor wildlife and biodiversity also increase the risks

and difficulty of controlling fire: notably, retention of standing dead trees, large accumulations of dead wood on the ground, and development of layered stand structures that

can readily carry fire from ground to tree crowns.

Wind-Douglas-fir is a relatively windfirm species. But windfirmness differs with soils,

soil moisture content, topography, previous stand history, and location with respect to

adjacent recent harvest areas, and must be taken into account in management. Sporadic windfall must be expected. Heavy thinning in previously unthinned stands can

result in increased windfall in the first few years after treatment. Losses can be high in

shelterwood or other partial cuts in dense stands that have developed without thinning

and along edges of clearcut units, particularly in exposed situations. Extremely high

stand density also can lead to major losses from wind and snow breakage in unthinned

stands. Systematic thinning begun early reduces windfall losses through development

of strong root systems, large bole diameters in relation to height, and increased live

crown ratios, which lower the center of crown mass (Stathers and others 1994).

Catastrophic windfall events occur somewhere in the region at intervals of 10 to 30

years. Examples are the great 1921 blowdown on the western Olympic Peninsula, the

1950-51 blowdown in the Oregon Coast Range, and the 1962 Columbus Day and 1993

Inauguration Day storms that caused widespread blowdown in both Washington and

Oregon.

Minor scattered windfall and breakage from wind and snow are frequent, are a part of

normal stand development, and provide a source of snags and down wood of value for

wildlife. Major windfalls are not only an economic loss and a disruption of stand management but also create serious fire hazards and potential for bark beetle outbreaks

(fig. 37).

68
Bark Beetles

Figure 36-Wildfires can destroy large areas of forest

and drastically alter species composition. This large

burn in the northern Sierra Nevada was salvage

logged and planted, producing a new forest rather

than the unproductive brushfield that otherwise would

occupy the site for many years.

Figure 37-Minor scattered windfalls are a part of

normal stand development and provide snags and

down wood of value to wildlife. Major windfalls can

destroy entire stands, are an economic loss, and

create serious fire and insect hazards.

Ice, snow, and freeze damage-These occur sporadically at fairly long intervals, and

resulting losses can be severe. Thus the 1955 freeze caused extensive defoliation and

top dieback of conifers in western Washington, and the 1996 ice storm caused extensive bole and branch breakage of red alder and top breakage in Douglas-fir. Management can do little to avoid such damage, other than using appropriate seed sources

and avoiding development of very dense stands with high height-to-diameter ratios.

Compared with the interior form of Douglas-fir (and with most other conifers), coast

Douglas-fir is relatively free from serious insect pests. The major pest is the Douglas-fir

bark beetle (Dendroctonus pseudotsugae Hopkins). Sporadic outbreaks of this insect

have caused major losses in the past. A notable example is the large outbreak in

western Oregon and southwestern Washington triggered by the combination of extensive blowdown in 1950 and 1951 and two successive drought years. An estimated 10

billion board feet of timber was blown down and an additional 3 billion board feet was

killed by the Douglas-fir beetle (Greeley and others 1953). Small localized and less

spectacular outbreaks are common in mature and old-growth stands.

Damage by the Douglas-fir bark beetle has declined markedly with the decreasing

acreage in old and highly susceptible stands and improved access for salvaging

windthrown and fire-damaged timber. As with other bark beetles, the primary control is

through silviculture. Practices promoting tree and stand vigor also reduce susceptibility

to bark beetle attack. Major outbreaks are usually triggered by windfall or fire events

(Mitchell and Sartwell 1974). Drought and root disease also predispose trees to attack.

The beetles are attracted to and breed in green damaged or down trees and spread

from these to nearby healthy trees. Maintenance of stand vigor and prompt salvage of

dead, dying, and infested trees after windfall or fire therefore are the best means of

prevention and control (Furniss and Carolin 1977). Failure to conduct prompt salvage

operations when they are appropriate may lead to greatly increased damage.

69
Mammals A considerable number of mammal species cause significant damage and can seriously interfere with and modify stand establishment and development. The extent and

severity of damage are highly variable and often localized. The most important mammal species damaging forests in the coast Douglas-fir region are:

l Mountain beaver, a rodent peculiar to the Pacific Northwest (unrelated to the true

beaver). These rodents cut seedlings up to 1 inch in diameter and strip branches and

bark from considerably larger trees. They can seriously impede establishment of

regeneration. The shrub and herbaceous understory common in low-density stands

and thinned stands provides the food supply for an endemic population. Harvest or

natural disturbance may briefly reduce the food supply and is usually followed by

prolific development of shrub and herbaceous vegetation within the next several

years. A corresponding increase in the mountain beaver population (and associated

damage) reflects in part an increase in the resident population and in part in-migration from immediately surrounding areas.

l Deer (Odocoileus hemeonus) and elk. These species browse the leaders on conifer

seedlings and small saplings, and foliage and twigs on western redcedar and

hardwoods. Severe browsing can cause regeneration failure. Although Douglas-fir

is not a highly preferred browse species, damage often is severe locally (fig. 38).

Preferred browse species such as redcedar and bigleaf maple may be eliminated.

Most hardwoods (other than tanoak) are browsed whenever leaves are present,

although red alder is not commonly browsed until late summer or fall (Dobkowski

and others 1994, McComb 1994).

l Black bear (Ursus americanus). Bear strip bark from pole- and small-sawtimber-size

trees, often killing the tree or creating wounds that are entrance points for bole rots

(fig. 39).

Figure 38-Deer and elk browsing at times causes severe

damage to regeneration and may eliminate species such as

western redcedar. This western redcedar seedling is only a

foot in height after 15 years of repeated browsing.

Figure 39-Bark stripping by black bear

often kills trees or provides entrance points

for rots. Damage can be extensive.
Diseases

Although some damage from these causes is unavoidable and part of natural stand

development, severe damage is incompatible with any form of planned management

and can change the course of stand development. Methods for limiting such damage at

the stand level include:

l Use of vigorous planting stock and vegetation management to promote rapid early

growth, thereby reducing the time during which regeneration is exposed to significant

clipping and browsing damage.

l Use of repellents and plastic tubes to protect seedlings.

l Local reduction in populations through trapping (mountain beaver) or hunting (deer,

elk, bear).

l Removal of individual problem animals or supplemental feeding (bear).

l Fostering alternative and preferred forage (Campbell and Evans 1978).

The severity of animal damage problems and methods for limiting damage differ with

size of animal populations, current stand conditions, and conditions in neighboring

stands. Existing information is summarized in Black (1992), and possible control

measures are further discussed by Nolte and Otto (1996).

Root rots-The major problem diseases in coastal Douglas-fir affect tree roots. These

are (1) laminated root rot, caused by Phellinus weirii, (2) armillaria root disease

(Armillaria obscura); (3) annosus root disease (Heterobasidion annosum); and (4) black

stain root disease (Ceratocystis wageneri) (Hadfield and others 1986). Of these, the

most serious is P. weirii. This is endemic throughout the Douglas-fir region, with impacts ranging from minor to severe. Minor infections can be considered part of the

natural process of stand development and may benefit some objectives. Snags resulting from root rots meet some habitat needs but often fall relatively quickly. The resulting

down wood and openings have a long-term influence on canopy structure and species

diversity. Major infections cause severe economic losses and may seriously interfere

with attainment of other stand management objectives.

Control can be achieved by removal of infected stumps (Thies and Sturrock 1995). This

is economically feasible only in the case of severe infections on highly productive land

and gentle terrain. Losses from light infections can be minimized by salvage of dead

and dying trees during thinning. For more severe infections, the most generally feasible

approach is to cut trees of susceptible species on and adjacent to root rot pockets and

replace them with resistant or nonsusceptible species, such as western redcedar,

hardwoods, or pines. (Red alder is not only immune and fast growing in youth but also

 adds substantial amounts of soil nitrogen.)

Bole rots-In the past the largest economic loss from disease has probably been the

loss of merchantable wood caused by heart rotting fungi in old stands, particularly

Phellinus (formerly Fames) pini (Boyce and others 1953). These are primarily diseases

of old, unmanaged stands and become comparatively minor in second-growth stands,

even when these are managed on long rotations. Stem rots in young stands occur

principally in western hemlock and true fir damaged during harvesting operations. Bear

damage is also a common source of entry. The principal control measure is careful

71
Dwarf Mistletoes

planning and close control to minimize mechanical damage during thinning and partial

harvest operations. Some rot will always be present and, in minor amounts, has value

in that it facilitates cavity excavation by some wildlife species.

Foliage diseases-There is considerable concern over recent damage by Swiss

needle cast (Phaeocryptopus gaeumanni) to Douglas-fir, which in the past was not

regarded as a serious pest (Kanaskie and others 1996). Extent and future importance

of the damage and possible control measures have not been well evaluated, but the

problem seems confined at present to Douglas-fir plantations in the Picea sitchensis

zone along the Oregon coast.

Dwarf mistletoes are parasitic seed plants. Two species occur in the Douglas-fir region,

Arceuthobium douglasii on Douglas-fir and A. tsugense on western hemlock, mountain

hemlock (Tsuga mertensiana (Bong.) Carr.), and Pacific silver fir (Abies amabilis Dougl.

ex Forbes) (Bega 1978). Dwarf mistletoes spread by seed released from dwarf mistletoe plants growing on infested, principally overstory, trees. The released seed falls on

the foliage of other trees below the infested tree and is washed onto young stem tissue,

where it germinates and infects the new host and causes stem and branch deformities

and reductions in vigor and growth rate. The potential radius of spread from the host

tree therefore is limited.

Although Douglas-fir dwarf mistletoe is a serious pest in the interior West, it is absent or

of minor importance on most coast Douglas-fir. It does cause considerable damage in

southwest Oregon and northern California and along the east slope of the Cascade

Range. In contrast, hemlock dwarf mistletoe is present on western hemlock, mountain

hemlock, and Pacific silver fir throughout the region and can cause substantial damage

and considerable reductions in growth (Ruth and Harris 1979).

Control consists of removing all infested trees at time of harvest. The clearcutting

widely practiced in the region is also an effective means of dwarf mistletoe control,

particularly when followed by slash burning, which eradicates infested advance reproduction. Removal of any residual stems and visibly infested advance regeneration in

early precommercial thinning also can be effective (Russell 1976).

A concern that has not been satisfactorily evaluated is that the partial cutting systems

and green tree retention requirements recently adopted by some agencies and organizations may lead to a greatly intensified dwarf mistletoe problem in western hemlock

and true fir forests, through spread from infested residual trees to regeneration. This

problem was totally ignored in the management plan developed for the Clayoquot

Sound area on Vancouver Island, BC.

Summary, Forest Health

A recent comprehensive monograph provides much information on biology, pathology,

and control of dwarf mistletoes (Hawskworth and Wiens 1996).

Sporadic minor damage from various weather events, insects, animals, and diseases is

a normal part of stand development. Severe damage can cause unacceptable losses

and disruption and is to be avoided to the extent feasible. Some applicable management measures include:

l Systematic thinning to develop trees with high vigor and low height-to-diameter ratios

that are resistant to windfall, snow breakage, and insect attack.

72
In Conclusion

l Planting stock and site preparation methods that provide rapid juvenile height

growth, thereby reducing the period of exposure to animal browsing.

l Prompt salvage of major windfalls as a precaution against bark beetle outbreaks.

l Planting or favoring resistant species in and around existing root disease centers.

Silviculture consists of the techniques for manipulating the establishment, composition,

structure, and rates of development of forest stands, including both trees and associated other vegetation. These techniques are the product of a long history of accumulated research and experience. Although many of these techniques were originally

developed to enhance wood production, they can easily be extended to the broader

problems of developing forests, stands, and trees with the characteristics desired for

multiple forest objectives. In young stands particularly, stand characteristics can be

markedly modified and development rates sharply accelerated within relatively short

periods. Details of application must of course be worked out for any specific set of

conditions and objectives.

Future stand management will probably involve a range of silvicultural regimes and

objectives (Curtis and Carey 1996), from (1) some stands managed with the primary

objective of producing high wood yields, through (2) others under multipurpose management designed for joint production of wood and nontimber values, to (3) others

managed primarily to promote wildlife, biodiversity, recreational and mature-forest

values along with some incidental wood production. We believe that considerable

wildlife habitat and other values can be provided while producing relatively high yields

of wood in production forests; and that significant amounts of wood can be produced in

multipurpose forests while meeting the other needs and desires of society. The knowledge and skills are available to pursue diverse objectives effectively in both kinds of

forests. Many owners will likely manage stands within their forests under a combination

of both approaches.

Management Choices The selection and application of appropriate regimes requires well-defined objectives.

Unfortunately, the lack of clear definition and acceptance of objectives today hinders

effective management of many forests, particularly those in public ownership. Objectives also change over time in response to changes in economic and social factors.

Some obstacles to establishment of objectives include:

l Lack of agreement on the desired balance of forest conditions, forest products, uses,

and values

l Inadequate knowledge and understanding of the relations between stand conditions

and nontimber values

l Inadequate knowledge and understanding of the associated costs and benefits

l Lack of agreement on distribution of costs and benefits among segments of our

present and future society

l Uncertain political environments and regulatory controls

73
What is the desired future stand condition for a specific tract or ownership? What

are the relative values to the landowner and to society of the several forest outputs

involved-wood, special forest products (boughs, mushrooms, berries, etc.), wildlife

(what kinds of wildlife?), water, aesthetics? And, what are the associated costs of

producing these? Objectives must be defined in terms allowing measurement of

progress or success.

The wide variety of possible management regimes and of objectives in stand management are in part a landowner’s choice, but major constraints also are imposed by

differences in stand conditions and sites. Management regimes begun at stand establishment or early in the life of the stand offer far more opportunity to shape stand

composition and development than is available when efforts are begun relatively late

in the life of the stand. Responses to specific silvicultural measures differ markedly

among sites. No one management regime can be applied uniformly to a species or

forest type with satisfactory results. (Some of our present problems stem from past

attempts to do just that!) Rather, treatments must be tailored to stand and site conditions as well as to management objectives, and they must be chosen in the context of

the surrounding landscape, rather than stand by stand. Will landscape productivity for

any desired values be markedly influenced by treatment of the stand? Can a particular

treatment regime enhance or provide conditions that are needed and now lacking in the

larger unit? Applicable measures and reasonable objectives will differ among stands.

There is necessarily much uncertainty in objectives, in current judgments of the value

of specific stand characteristics for different objectives, and in the effects of specific

treatments (including no treatment) on those values. Management objectives of a few

years ago were markedly different from those of today, and those of a few years hence

will probably differ from today’s. Thus, it is generally recognized that snags and some

down wood are important, but we do not know how much is necessary or how it should

be distributed to meet selected objectives in different forest landscapes: and we will not

know without long-term experimentation and monitoring. Incomplete knowledge and

uncertainty about the future are facts of life. Yet, a manager must make decisions

involving long-term goals and programs while attempting to retain flexibility to respond

to future goal changes.

We can make reasonably solid predictions (at least qualitatively) of the likely course

of stand development, given a present condition, a specified treatment regime, and

freedom from major stand damage or catastrophe. But it is clear from the known history

and prehistory of Pacific Northwest forests that major stand damage and catastrophes

are abundant on time scales approaching the biological life span of forest trees. And,

management objectives change over time. Attempts to delineate specific physical areas

for preservation or development of a target condition over periods of one to several

centuries are unlikely to succeed. Rather, objectives should be specified in terms of a

desired mix of future stand conditions and rotations, and stand management regimes

adopted that will preserve future flexibility.

Despite the uncertainties, we have a large body of research and experience showing

that stand characteristics and rates of stand development can be markedly altered

within relatively short periods through appropriate silvicultural treatments to meet

whatever future objectives may be selected.

74
Information Needs Additional information and experience needed to successfully implement the regeneration and stand management treatments that have been suggested include:

l Quantitative evaluation of effectiveness and costs of measures such as green tree

retention, snag retention and snag creation, retention of large woody debris. How

much is needed? How should it be distributed? What use is made of different stand

structures and stand components (snags, down wood, understory vegetation layers)

by wildlife species? What are the actual gains in value of wildlife habitat and in biodiversity from different amounts of these structural features? What are the tradeoffs

among these benefits and costs? What are the most cost-effective means of providing these benefits?

l Quantitative comparisons of a range of silvicultural systems and stand treatments

and of their arrangement in space and time. What are the effects on wildlife populations, on timber outputs, and on aesthetic, watershed, and other environmental

values? What are the comparative costs and economic returns of feasible alternatives?

l Development of cost-efficient methods for accelerating development of mature- and

old-forest characteristics in selected young stands.

l Quantitative information on growth and development patterns of mixed species

stands and mature stands (100+ years) and their response to stand treatments.

l Quantitative information on the effects of stand density and harvesting methods on

reproduction and growth of hardwoods, conifers, and shrubs in the understory of

conifer stands, and effects of understory and overstory density on other components

of the ecosystem and on incidence and severity of damage from wind, pathogens,

insects, etc.

l Development of improved simulation models that allow reliable prediction of regeneration and stand and forest development for a wide range of initial stand structures

and silvicultural regimes and to stand ages of 200 years or more.

l Information on the biology and management of previously neglected tree and shrub

species.

l Adequate techniques for evaluating the economic and social consequences of

management actions, in benefits produced and benefits foregone. The techniques

traditionally used in forest economics are clearly inadequate, but we do not have

satisfactory and generally accepted alternatives.

Discussion has been primarily in terms of Douglas-fir, which is the most important

species in the region and the one most extensively studied, as evidenced by numerous

citations above and the summary papers in Oliver and others (1986). However, its

associates-western hemlock, red alder, grand fir, Pacific silver fir, noble fir (Abies

procera Rehd.), and western redcedar-also are ecologically and economically important. There is a considerable body of research and experience on the biology and

management of western hemlock (e.g. Atkinson and Zasoski 1976, Hoyer and Swanzy

1986, Ruth and Harris 1979) and red alder (Briggs and others 1978, Hibbs and others

1994). Existing information on all aspects of the biology and management of the true

75
firs and of western redcedar is much more limited (Franklin and others 1983, Oliver and 

Kenady 1981, Smith 1987) and should be a fertile field for research, particularly with 

the current interest in mixed species management and biodiversity. 

Some Policy Questions Resolution of current conflicts and improvement of future forest land management 

involves some fundamental social, political, and economic questions. United States 

industrial wood use is at an all-time high and is projected to increase by nearly 40 

percent in the next half century (Haynes 1991, Haynes and others 1995; Kaiser 1997) 

(fig. 40). World population is projected to double (Keyfitz 1989), and wood consumption 

is expected to increase worldwide in response to the combination of population growth 

and economic growth (Brooks 1997). The United States is already one of the largest 

importers of wood and wood products in the world and has the largest per capita use of 

wood products. The present primary limitations on U.S. wood production involve 

questions of social objectives, attitudes, and policies rather than of biological or economic productivity or technical knowledge (Beuter 1995, Frederick and Sedjo 1991). 

Will we in the United States produce our own wood supplies? Or will we seek our 

wood supplies elsewhere in the world from much less productive lands where long-term 

sustainable management is less likely (Dekker-Robertson and Libby 1998)? How much 

land can or should we retain in forest? What is the desired balance of products, uses, 

and values for whatever forest land is available? There are many possible combinations and they can be greatly affected by management. 

Some considerations are: 

l The population of the United States has doubled within the lifetime of the authors 

and is still increasing 

l United States industrial wood use is at an all-time high and increasing 

l Wood is one of the most environmentally “friendly” materials used by human 

societies (Koch 1991) 

28 

26 

24 

22 

20 

18 

16 

14 

12 

10 

1940 1960 1980 2000 2020 2040 

Year 

Figure 40-United States historical roundwood consumption 1952-91 and 

projections to 2040. (Haynes and others 1995). 

76 
120+ 85+ 50+ 

Productivity class (ft3*acre-‘*year-‘) 

DF subregion 

m 

All other U.S. 

Figure 41-Productivity of forest land in the Douglas-fir region far 

exceeds that of most other regions of the United States (graph 

derived from Waddell and others 1989). 

l The Pacific Northwest is one of the most productive forest regions of the world (fig. 41) 

l The Pacific Northwest is one of the few places in the developed world where substantial areas of intact, original forest remain, with unique challenges and opportunities for management of forest landscapes and biological diversity 

l Our actions cannot for long be isolated from trends and consequences in the rest of 

the world (Brooks 1993, Schallau and Goetzl 1992, Sedjo 1993) 

It does seem clear that although multipurpose forestry and ecosystem management 

give increased weight to forest values other than timber, timber values will remain 

important on most forest lands. Sustainability of forests and human society requires 

active management (Berlyn and Ashton 1996), although the specifics will necessarily 

differ by sites, with existing stand and forest conditions (Kimmins 1997), with the 

prevailing economic and social climate, and with owner objectives. No one silvicultural 

system or management regime exists that can or should be applied to all areas. And, 

the need to develop a balanced distribution of stand structures and developmental 

stages should not be forgotten in the current preoccupation with old-growth values. 

Most silvicultural activities in the past have been driven by the objective of maximizing 

landowner revenues, which arise primarily from wood production. Most other forest 

values are benefits that accrue to society at large rather than to the landowner. Some 

measures that can be taken to enhance these values involve little or no increase in 

costs or decrease in revenue to the landowner. But others are quite costly. It would 

seem justifiable for society to provide incentives to private landowners to offset increased costs and reduced revenues associated with measures to promote societal 

values on individual ownerships (Bourland and Stroup 1996, Boyce 1995, Lippke and 

Fretwell 1997, Lippke and Oliver 1993, Framstad 1996) and to promote cooperative 

planning across land ownerships (Johnson 1995). Such measures would probably be 

less expensive, less disruptive, and socially more acceptable than attempts to force 

77 
change through regulation (Lippke and others 1996). Indeed, some current regulatory

approaches are counterproductive in that they penalize socially desirable behavior by

the landowner. Thus, uncertainties and fears about future constraints (e.g., of a regulatory “taking” as endangered species habitat) have undoubtedly motivated some owners

to cut stands now rather than holding them for higher yields and improved environmental values in the future.

On public lands, some part of the additional costs and decreased revenues associated

with recent changes and conflicts has been offset from general tax revenues. But

historically, revenues from commodity production have directly or indirectly supported

most other activities on public lands. It seems unlikely that society can or will indefinitely subsidize on a huge scale measures to promote intangible and nonmonetary

values in the absence of concurrent revenues. We therefore believe that regimes that

include commodity production at reasonable and sustainable levels will be a necessary

component of future programs for management of public lands, particularly in the West

where the public lands represent such a large portion of the forest landscape.

A considerable part of our perceived problems stems from the unbalanced distribution

of age classes, both regionally and-even more-within local areas. This arises from

past and recent harvesting history and from reluctance to manage stands for longer

rotations and differing stand structures. Management should strive to reduce the

imbalance. This implies that some lands should be managed under extended rotations

and for a variety of stand and landscape structures and characteristics. Major questions

and opportunities are involved in future management of the huge area of plantations,

and these will become major research and policy questions of the near future.

The art and science of silviculture continues to evolve. There is a huge and often

unappreciated body of silvicultural research and practical experience, both in the

Pacific Northwest and elsewhere, that provides guidance on how to attain chosen

objectives in ways that are both biologically and economically feasible. Successful use

of the various possible silvicultural systems and regeneration methods will depend to a

large extent on public perceptions and acceptance. There is no one universally applicable system or management regime. Management regimes must be tailored to site

characteristics and management objectives.

Increasingly, societal pressures are exerted to influence objectives by constraining the

use of practices that could yield positive results in terms of habitat, biodiversity and

other environmental values along with wood production. Forest managers and researchers therefore need to involve the public in developing clearly defined forest and

stand management objectives and selecting appropriate practices to achieve them.

Given Societal agreement and acceptance, much of the silvicultural knowledge needed

to achieve most objectives (whether single or multiple) is currently available, although

there is a continuing need for both monitoring and designed experiments to work out

the details of application to specific situations and changing objectives.

78
Acknowledgments We acknowledge contributions by a considerable number of people other than the

named authors. Richard Haynes of the Pacific Northwest Research Station provided

partial funding from the Northwest Forest Plan, helpful text suggestions, and overall

review. Reviews and helpful suggestions also were provided by Philip S. Aune,

Pacific Southwest Research Station; Michael Newton, Oregon State University; Lee

Boeckstiegel, former silviculturist (now retired) Mount Baker-Snoqualmie National

Forest; Andrew B. Carey, Pacific Northwest Research Station; and J. Alan Wagar,

University of Washington. Robert McGaughey and Stephen E. Reutebuch, Pacific

Northwest Research Station, and Nancy K. Allison, graduate student at College of Forest

Resources, University of Washington, provided the computer-generated illustrations.

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Metric Equivalents 1 inch = 2.54 centimeters

1 foot = 0.3048 meter

1 square foot = 0.09290 square meter

1 cubic foot = 0.028 cubic meter

1 acre = 0.4047 hectare

1 square foot per acre = 0.2296 square meter per hectare

1 cubic foot per acre = 0.06997 cubic meter per hectare

1 mile = 1.609 kilometers

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108
Appendix: Some The regimes listed below represent some alternatives for combined timber production

Possible Management and habitat development objectives, which we believe to be feasible on the basis of

Scenarios existing knowledge, although they are not equally desirable for all purposes. Examples

of several of these exist in the region, but long-continued designed experiments are

lacking for evaluation of regimes other than clearcutting, and little or no information is

available on comparative costs and outputs. The regimes listed do not by any means

represent all possibilities.

The regimes listed are taken from an ongoing cooperative management experiment.’

Specifications are written in the context of an ownership (Washington Department of

Natural Resources) that has wood production as a major objective but also has major

concerns about wildlife values and aesthetic values in visually sensitive locations. The

starting condition is even-aged stands that are predominantly Douglas-fir and in the

age range of 50 to 70 years. These are preferably, but not necessarily, stands that have

had prior thinning. Sites are quite productive, in an area (Capitol State Forest) where

shrub competition with regeneration is considerably less severe than on many coastal

sites. The species composition desired in future is Douglas-fir with a secondary component of western hemlock, western redcedar, and occasional hardwoods. In those

regimes involving repeated entries, we use a 15-year cycle as the basis for planning,

although either a shorter or a longer cycle may ultimately prove preferable. In all

regimes, residual trees will be left along streams and in small uncut groups elsewhere

within the stand to provide stream protection, wildlife trees, and a future source of

snags and large down logs.

The regimes considered are outlined in figure 42 and described below. The illustrations

of expected stand development are projections made with the west-side variant of the

forest vegetation simulator (FVS, formerly called PROGNOSIS; Wykoff and others

1982), depicted with the stand visualization system (McGaughey, in prep.).

~

1. Clearcut This system is well understood and is included primarily to provide a direct quantitative

comparison of costs and outputs with the other systems discussed.

Initial cut-Cut all merchantable and unmerchantable trees on the area, except for

streamside strips and scattered groups of leave trees to meet Forest Practice Act and

Habitat Conservation Plan requirements. Mark root rot pockets so they can be identified later.

Regeneration-Plant according to current Washington Department of Natural Resources (DNR) practice (400 Douglas-fir per acre), except plant root rot areas with

some combination of western redcedar, white pine, or hardwoods; or (less desirable)

favor hemlock regeneration if present.

Subsequent operationsBrush control-If and when needed, according to current DNR practice.

Precommercial thining (PCT)-Decision at around 10 years, to depend on stocking

achieved and feasibility of very early commercial thinning as an alternative. Retain

some naturally established stems of species other than Douglas-fir, when present.

1

 Curtis, R.O.; Clendenen, G.W.; DeBelI, D.D.; DeBelI, J.;

Shumway, J.; T. Poch, T. 1996. Silvicultural options for harvesting

young-growth production forests. Part I: The stand-level silvicultural

experiment. Unpublished study plan. On file with: Forestry Sciences

Laboratory, 3625-93d Avenue SW, Olympia, WA 98512.
INITIAL 

STAND 

CLEARCUT 

PATCH CUTS UNIFORM 

1.5-5 acres RETENTION 

+ thinning 15 trees/acres 

GROUP 

SELECTION 

o-1 5 acres 

DEFERRED 

REGENERATION 

REPEATED 

THINNING NOTHINNING 

Figure 42-Some alternative management regimes that are expected to produce markedly different stand 

conditions. 

Commercial thinning ((X)--Repeated thinnings, to reduce RD (relative density, Curtis 

1982) to about RD35 in the first thinning and thereafter maintain density in the range of 

RD40 to RD60. 

Harvest-At a rotation age to be determined, probably in the range of 60 to 80 years. 

Characteristics-Well-understood regime, simple management, will probably maximize yield and minimize administrative and harvest costs. Appearance objectionable to 

much of public, may not be politically possible in future. 

Figure 43 illustrates expected stand conditions at 1, 30, and 75 years after initial cut. 

2. Two-Aged Stand 

Management (=Reserve 

Shelterwood) 

This initially resembles a conventional shelterwood but with the overwood or a portion 

of it carried through the second rotation to provide large sizes and high-quality material. 

On many areas, the younger age class will probably contain an increased proportion of 

western hemlock. A hemlock-cedar understory will probably develop reasonably well 

under overstory densities that restrict establishment and growth of Douglas-fir. 

Initial cut-This will remove a high percentage of the initial basal area. Residual basal 

area stocking will be ~20 percent of “full” stocking. Leave trees would be principally 

well-distributed Douglas-fir selected for vigor and stem quality, plus some vigorous and 

well-formed redcedar and hemlock. Redcedar and hemlock will be preferred within or 

immediately adjacent to root rot pockets. 

110 
Figure 43-Projected appearance of the clearcut regime at time from initial cut of (A) 1 year, (B) 30 years,

and (C) 75 years.

111
Regeneration-Supplement existing and prospective natural regeneration by

underplanting Douglas-fir. Aim is a mixed species stand, but including at least 50

percent Douglas-fir.

Subsequent operationsBrush control-If needed.

PCT-This probably will be needed some years after initial cut, to control spacing and

remove advance regeneration damaged in harvesting.

CT-As needed to maintain reasonable growth rates in the younger cohort.

At some point a need will arise to remove additional stems from the overstory, both to

salvage dead and dying trees and to keep density low enough to allow satisfactory

growth of the understory. We have no present basis for estimating timing, but this will

certainly be needed by the time basal area reaches 50 percent of “full” stocking based

on current QMD (quadratic mean diameter) of residuals, and maybe sooner.

Harvest-At a rotation age to be determined, perhaps 60 years after the initial cut. This

would correspond to stand ages of about 60 years for the understory and 120 years for

the Douglas-fir overstory.

Characteristics-Maintains at least partial forest cover over two conventional rotations, sharply reducing the area in the highly visible freshly harvested condition. Potential for high value production in the retained overstory. Layered structure favorable to

some wildlife. Probable increase in hemlock component. Possibility of major windfall

losses.

Figure 44 illustrates expected stand condition at 1, 30, and 75 years after initial cut.

3. Patch-Wise Even-Aged

Management

Small patch cuts on the order of 1.5 to 5 acres can be regenerated either naturally or

by planting and can be treated by conventional even-aged management techniques

emphasizing Douglas-fir. Over time, a unit can be converted to an uneven-aged mosaic

of such even-aged patches that would be predominantly Douglas-fir (with lesser

proportions of western hemlock and western redcedar) while lacking large and visually

obtrusive harvest areas. The visual effects will be strongly influenced by cutting cycle

and rotation age (which determine the proportion of the area in the early regeneration

stage) and by patch size.

A possible sequence of operations follows.

First entry-Cut all stems on patches of 1.5 to 5 acres in size, dispersed over the unit

and amounting to 20 percent of the available area. Patches to be somewhat irregular

and differing in shape, but length-to-width ratio should not exceed 2:l. Concurrently,

do a light thinning in the intervening areas, aimed to reduce RD in the thinned area to

perhaps RD45 (except, do not remove more than one-third of prethinning basal area in

the first cut in previously thinned stands, or one-fourth in unthinned stands). Plant

patches to Douglas-fir or a mix of Douglas-fir and other species, but use western

redcedar, white pine, or hardwoods in and around former root rot pockets where

feasible. Do any brush control needed to obtain reasonable survival and early growth.

112
Figure 44-Projected appearance of the two-aged (reserve shelterwood) regime at time from

initial cut of (A) 1 year, (B) 30 years, and (C) 75 years.

113
Subsequent entries (15-year cycle)-Do patch cuts and secure regeneration on

another 20 percent of area. Precommercially thin previously regenerated areas as

needed. Commercially thin intervening areas as appropriate, to maintain in the range of

RD40 to RD60 in the older cohort and somewhat lower levels (RD35 to RD55) in

younger cohorts established in cut patches. This will in time produce a stand consisting of five age classes with a 75-year rotation; a condition that could be maintained

indefinitely.

The minimum patch size of about 1.5 acres is determined by the needs for (1) direct

light for satisfactory development of Douglas-fir, and (2) avoidance of future need to fell

trees into existing regeneration. The latter requirement leads to a minimum patch size

of about two mature tree heights in diameter. Because of the extended conversion

period involved, the first cut might ideally be made at a somewhat younger age than in

the case of the other systems listed and later cuts will be at ages considerably greater

than 75 years.

Characteristics-This regime avoids large and highly visible harvest areas, provides

near-constant landscapes, and will probably maintain the Douglas-fir component and

provide long-term yields near those under clearcutting. It uses well-known even-aged

management techniques in treatment of patches. It provides higher yields in early years

than regime (5) below, while automatically working toward a balanced age distribution.

Compared with regimes (1) and (2) above, harvest and road costs will be higher, and

there will be increased costs and complexity in maintaining control over operations on

many small areas. The mix of habitat conditions should be favorable for many wildlife

species. The intimate mixture of age classes should obviate the possible problems

associated with fragmentation and species recolonization.

Figure 45 illustrates expected stand conditions at 1, 30, and 75 years after the initial

cut.

4. Group Selection This will resemble regime (3) above, except that removals will cover a range from

individual trees to groups not exceeding 1.5 acre in size.

Because of the small size of groups it will not be feasible to control the cut in terms of

area. But residual basal area over the area as a whole will be comparable to that in

regime 3 of the same replication. In early entries, cuts will not differ much from conventional thinning, except that they will include conscious creation of scattered small

openings intended to secure or release regeneration.

114
Figure 45-Projected appearance of the patchwise even-aged management regime at time from initial cut of

(A) 1 year, (B) 30 years, and (C) 75 years.

115

3
Figure 46-Projected appearance of the group selection regime at time from initial cut of (A) 1 year, (B) 30

years, and (C) 75 years. [Note that this is a considerably larger scale than the patch cut in figure 45.]
Characteristics-Compared to regime (3), the smaller group size would mean (a)

reduced visual impacts, (b) increased difficulty of managing intermediate treatments,

and (c) increased harvesting costs and damage. The small size of openings will likely

mean reduced representation of Douglas-fir in regeneration and possibly reduced

growth of all species.

Figure 46 illustrates expected stand conditions at 1, 30, and 75 years after initial cut.

5. Continued Commercial Available information suggests that systematic thinning of vigorous Douglas-fir stands

Thinning on Extended

Rotation

can maintain high growth rates in volume and value for extended periods, to ages of

100 years or more. Culmination has not been observed within the range of ages

included in existing commercial thinning trials. Continued commercial thinning can

prolong the period of high production and produce current income, while producing

aesthetically desirable large trees and reducing the area of land in the highly visible

regeneration stage at any point in time. This is therefore one of the options to be

considered for reducing visual impacts.

Repeated commercial thinning is expected to produce an understory of tolerant species. The stand would ultimately be reproduced by clearcutting, shelterwood, or patch

cuts, at some rotation age now unspecified but possibly of the order of 120 years. The

regime will produce large and high-value trees.

Figure 47 illustrates expected stand conditions at years 1, 30, and 75 years after the

initial cut.

6. Extended Rotation

Without Commercial

Thinning

This provides a basis for comparison with gains obtainable by commercial thinning

(regime 5) when stands are held on an extended rotation. It also constitutes a management option for reducing the proportion of the forest in highly visible harvest operations

while adjusting currently unbalanced age distributions. Figure 48 illustrates expected

stand conditions at establishment of the experiment and 75 years later.
Figure 47-Projected appearance of the continued thinning regime at age (A) of first thinning, (B)

first thinning +30, and (C) first thinning + 75.

118
Figure 48-Projected appearance of the unthinned stand at (A) year 1, and (B) year 75 after

establishment of the experiment.

119
Glossary’ accessory system-a silvicultural system that does not fit within other conventionally

recognized classifications, usually involving the creation or maintenance of two age

classes.

age class (cohort)-a distinct aggregation of trees of more or less similar age originating from a single natural disturbance or regeneration cutting.

basal area--the cross-sectional area of tree stem(s) at standard height (usually 4.5

feet); the total of such values on a per unit area basis (=stand basal area) is a stand

attribute widely used in stocking and thinning guides.

CAI-abbreviation for current annual increment.

clearcutting method-a method of regenerating an even-aged stand in which a new

age class develops in a fully exposed microclimate after removal, in a single cutting,

of all trees in the previous stand. Regeneration may be from natural seeding, direct

seedling, planted seedlings, or advance reproduction. Harvesting may be done in

groups or patches (group or patch clearcutting) or in strips (strip clearcutting). In the

clearcutting system, the management unit or stand consists of the individual clearcut

stand.

clearcutting with reserves-a clearcutting method in which varying numbers of

reserve trees are left to attain goals other than regeneration.

clone-a group of individuals of identical genotype, usually arising from vegetative

propagation.

commercial thinning-a thinning in which the trees removed have value at least equal

to the cost of harvest. Abbreviated CT.

culmination age-age at which mean annual increment (usually in volume) of a stand

attains its maximum.

current annual increment-growth rate per year at a specified point in time. Abbreviated as CAI.

density-(l) number of individuals per unit area (in ecology); (2) any measure expressing degree of competition (loose usage in forestry).

ecology-the study of relations between plants (and animals) and their environment.

ecosystem-a distinguishable community of plants and animals interacting with the

physical factors of its environment.

even-aged stand-a stand of trees containing a single age class, usually considered

to include a range in tree ages of less that 20 percent of the rotation.

forest-an area supporting trees, ordinarily including multiple ages, species, and

conditions.

forest management--the practical application of scientific, economic, and social

principles to the administration and working of a forest property for specified objectives.

1See also Ford-Robertson 1971, Society of American Foresters

1993.

120
genotype--the genetic composition of an individual organism.

group selection method-a method of regenerating uneven-aged stands in which

trees are removed and new age classes established in small groups. Maximum width

of groups is approximately twice the height of mature trees. The management unit or

stand in which regeneration, growth, and yield are regulated is an aggregation of such

groups.

intolerant-lacking the ability to grow in shade of or in competition with other and taller

plants.

landscape-a view or vista of scenery; hence, an area of considerable size including

multiple stands and (often) multiple uses and ownerships.

MAI-abbreviation for mean annual increment.

mean annual increment-average growth rate of a stand up to a specified point in

time. Calculated as the sum of present volume plus volume of any thinnings, divided by

age. Abbreviated as MAI.

old growth-a stage in stand development characterized by advanced age, large

trees, layered structure, and abundant woody debris. Usually applied to stands that

have had no human intervention.

PAI-abbreviation for periodic annual increment.

periodic annual increment-an approximation to current annual increment (most

commonly in volume), calculated as the difference between measurements at two

points in time, divided by number of years between the two measurements. Abbreviated as PAI.

precommercial thinning-an early thinning removing trees too small to have commercial value, usually done to improve spacing. Synonym, respacing. Abbreviated as PCT.

regeneration-(l) newly established plants, (2) the process by which new plants are

established.

regeneration method-a technique or set of techniques for securing regeneration.

reproduction-synonym for regeneration.

reserve-(l) a tree or group of trees, left unfelled in a stand that is being regenerated,

and kept for part or whole of the next rotation (synonym, standard); (2) an area set

aside for some specific purpose, such as a natural reserve.

respacing-an early thinning done to improve spacing that does not remove trees of

commercial value.

rhizome-a modified belowground stem that grows horizontally and produces roots,

leaves, and suckers at irregular intervals.

roguing-systematic removal of undesirable individuals, as in a seed orchard.

rotation-age of final harvest.

seed-tree method-an even-aged regeneration method in which a new age class

develops from seedlings that germinate in fully exposed microenvironments after

121
removal of all the previous stand except a small number of trees left to provide seed.

Seed trees are removed after regeneration is established.

selection, group-a silvicultural system involving removal of scattered groups of

mature trees at frequent intervals, leading to a groupwise uneven-aged condition.

selection, individual tree-a silvicultural system involving removal of scattered

individual trees at frequent intervals, thereby leading to an unevenaged condition with

regeneration in clumps of size equivalent to the space occupied by a single large tree.

selection method-a collective term for the single tree selection and group selection methods, which create and maintain an uneven-aged structure by removing some

trees in all size classes, either singly, in small groups, or in strips.

selective cutting-a loose term for any form of cutting that removes only part of a

stand. Often incorrectly used as a synonym for selection system. Undesirable because

of confusion introduced by past use of the term for destructive high-grading practices.

shelterwood method-a method of regenerating an even-aged stand in which a new

age class develops beneath the partially shaded microenvironment provided by the

residual trees (overwood). Harvesting may be done uniformly throughout the stand

(uniform shelterwood), in groups or patches (group shelterwood) or in strips (strip

shelterwood). The overwood is removed once the regeneration is established.

shelterwood with reserves-a variant of the shelterwood method in which some or all

of the shelter trees (overwood) are retained, to attain goals other than regeneration.

The resulting stand may be two-aged or may tend toward an uneven-aged condition as

a consequence of both an extended period of regeneration establishment and the

retention of reserve trees that may represent one or more age classes.

silvicultural system-a planned program of silvicultural treatment over the life of a

stand, extending from regeneration through intermediate operations to harvest and

regeneration.

silviculture-the body of techniques used to manipulate stand environments and

direct stand and tree development to create or maintain desired conditions.

simulation model-a mathematical or graphical system that attempts to represent and

predict the development of trees and stands in response to environment, initial stand

condition, and stand treatment.

single-tree selection method-a method of creating new age classes in uneven-aged

stands in which individual trees of all size classes are removed more or less uniformly

thoughout the stand to achieve desired stand structural characteristics. Synonymous

with selection, individual tree, above.

site-(l) a physical location; (2) a class or numerical measure of soil productivity.

site preparation-a collective term for various measures that can be taken to alleviate

conditions unfavorable to prompt and adequate regeneration.

slash-the residue of tops, branches, and other unused material left on the ground

after harvest.

122
stand-a contiguous group of trees sufficiently uniform in age class distribution,

composition, and structure, and growing on a site of sufficiently uniform quality,

to be a distinguishable unit.

stand management--the practical application of scientific and economic knowledge

through silvicultural measures designed to direct development of a stand toward

desired objectives.

thinning-removal of a portion of trees in a stand to promote development of the

remaining trees and vegetation and to secure income prior to final harvest, while

retaining the even-aged character of the stand.

tolerant-having the ability to become established and grow under shade of or in

competition with taller plants.

two-aged stand-a stand composed of two distinct age classes that are separated in

age by more than 20 percent of rotation age (based on the older age class).

123
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Curtis, Robert 0.; DeBelI, Dean S.; Harrington, Constance A.; Lavender,

Denis P.; St. Clair, J. Bradley; Tappeiner, John C.; Walstad, John D.

1998. Silviculture for multiple objectives in the Douglas-fir region. Gen.

Tech. Rep. PNW-GTR-435. Portland, OR: U.S. Department of Agriculture,

Forest Service, Pacific Northwest Research Station. 123 p.

We discuss the historical development of silviculture in the Pacific Northwest

and review the silvicultural practices currently available to forest managers.

We then point out how these practices can be modified and used to maintain

and produce wildlife habitat, diverse stand structures (including those usually

associated with old forests) and pleasing scenery, while also producing wood

products. Most of the silvicultural knowledge needed to design and implement regimes for integrated production of these multiple values already

exists.

Keywords: Ecosystem management, multiple use, silvicultural systems,

wildlife habitat, thinning, landscape management, forest ecology, Douglas-fir.

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.

The United States Department of Agriculture (USDA)

prohibits discrimination in its programs on the basis

of race, color, national origin, sex, religion, age, disability,

political beliefs, and marital or familial status. (Not all

l prohibited bases apply to all programs.) Persons with

disabilities who require alternative means of communication

of program information (Braille, large print, audiotape, etc.)

should contact the USDA TARGET Center at

(202) 720-2600 (voice and TDD).

To file a complaint, write the Secretary of Agriculture,

U.S. Department of Agriculture, Washington, DC 20250,

or call (800) 245-6340 (voice), or (800) 720-1127 (TDD).

USDA is an equal employment opportunity employer.

Pacific Northwest Research Station

333 S.W. First Avenue

PO. Box 3890

Portland, Oregon 97208-3890