United States 

Department of 

Agriculture From the Forest 

Forest Service 

United States 

Department 

of the Interior to the Sea: 

Bureau of 

Land Management 

General Technical 

Report 

PNW-GTR-229 

September 1988 

* Story of 

I-auen I rees 

===- 

_& 

---.- 

--a. 

-_- 

km* 

.-- 

s- 
Maser, Chris; Tarrant, Robert F.; Trappe, James M.; Franklin, Jerry F.,

tech. eds. 1988. From the forest to the sea: a story of fallen trees. Gen.

Tech. Rep. PNW-GTR-229. 153 p.

Large, fallen trees in various stages of decay contribute much-needed

diversity of ecological processes to terrestrial, aquatic, estuarine, coastal

beach, and open ocean habitats in the Pacific Northwest. Intensive

utilization and management can deprive these habitats of large, fallen trees,

This publication presents sound information for managers making resource

management decisions on the impact of this loss on habitat diversity and on

ecological processes that have an impact on long-term ecosystem

productivity.

Keywords: Decomposition, fallen trees, habitat diversity, ecosystem function,

land, water, sea.

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 U.S. Department of Agriculture is an Equal

Opportunity Employer. Applicants for all Department

programs will be given equal consideration without

regard to age, race, color, sex, religion, or national

origin.

Pacific Northwest Research Station

319 S.W. Pine St.

P.O. Box 3890

Portland, Oregon 97208
From the Forest to the Sea: A

Story of Fallen Trees

Chris Maser, Robert F. Tarrant,

James M. Trappe, and Jerry F. Franklin

Technical Editors

Pacific Northwest Research Station

U.S. Department of Agriculture

Forest Service

Portland, Oregon

General Technical Report PNW-GTR-229

1988

Published in cooperation with

Bureau of Land Management

U.S. Department of the Interior
Authors Patricia A. Benner

Department of Fisheries and Wildlife

Oregon State University

Corvallis, Oregon 97331

Peter A. Bisson

Weyerhaeuser Company

Weyerhaeuser Technology Center

WTC 2F19

Tacoma, Washington 98477

Steven P. Cline

Department of Forest Science

Oregon State University

Corvallis, Oregon 97331

Kermit Cromack, Jr.

Department of Forest Science

Oregon State University

Corvallis, Oregon 97331

Jerry F. Franklin

USDA Forest Service

Forestry Sciences Laboratory

3200 S.W. Jefferson Way

Corvallis, Oregon 97331

Jefferson J. Gonor

Department of Oceanography

Oregon State University

Corvallis, Oregon 97331

Stanley V. Gregory

Department of Fisheries and Wildlife

Oregon State University

Corvallis, Oregon 97331

Everett Hansen

Department of Botany

Oregon State University

Corvallis, Oregon 97331
Chris Maser

Sustainable Forestry, Consultant

1462 N.W. Taylor

Corvallis, Oregon 97330

Formerly:

U.S. Department of the Interior

Bureau of Land Management

Forestry Sciences Laboratory

3200 S.W. Jefferson Way

Corvallis, Oregon 97331

James R. Sedell

USDA Forest Service

Forestry Sciences Laboratory

3200 S.W. Jefferson Way

Corvallis, Oregon 97331

Thomas A. Spies

USDA Forest Service

Forestry Sciences Laboratory

3200 S.W. Jefferson Way

Corvallis, Oregon 97331

Frederick J. Swanson

USDA Forest Service

Forestry Sciences Laboratory

3200 S.W. Jefferson Way

Corvallis, Oregon 97331

Robert F. Tarrant

Department of Forest Science

Oregon State University

Corvallis, Oregon 97331

James M. Trappe

USDA Forest Service

Forestry Sciences Laboratory

3200 S.W. Jefferson Way

Corvallis, Oregon 97331
Abstract

Maser, Chris; Tarrant, Robert F.; Trappe, James M.; Franklin, Jerry F., tech.

eds. 1988. From the forest to the sea: a story of fallen trees. Gen. Tech. Rep.

PNW-GTR-229. 153 p.

Large, fallen trees in various stages of decay contribute much-needed diversity of

ecological processes to terrestrial, aquatic, estuarine, coastal beach, and open ocean

habitats in the Pacific Northwest. intensive utilization and management can deprive

these habitats of large, fallen trees. This publication presents sound information for

managers making resource management decisions on the impact of this loss on

habitat diversity and on ecological processes that have an impact on long-term

ecosystem productivity.

Keywords: Decomposition, fallen trees, habitat diversity, ecosystem function, land,

water, sea.
Contents 1 Introduction Robert F. Tarrant and Chris Maser

5 Chapter 1. Coarse Woody Debris in Forests and Plantations of

Coastal Oregon

Thomas A. Spies and Steven P. Cline

25 Chapter 2. What We Know About Large Trees That Fall to the

Forest Floor

Chris Maser, Steven P. Cline, Kermit Cromack, Jr.,

James M. Trappe, and Everett Hansen

47 Chapter 3. What We Know About Large Trees That Fall Into

Streams and Rivers

James R. Sedell, Peter A. Bisson, Frederick J. Swanson,

and Stanley V. Gregory

83 Chapter 4. What We Know About Large Trees in Estuaries,

in the Sea, and on Coastal Beaches

Jefferson J. Gonor, James R. Sedell, and

Patricia A. Benner

113 Chapter 5. Looking Ahead: Some Options for Public Lands

Jerry F. Franklin and Chris Maser

123 References

151 Appendix

Color illustrations appear at the ends of chapters.
This page was intentionally left blank
introduction Robert F. Tarrant and Chris Maser

Forest productivity is declining over large areas of managed forest in central Europe

(Cramer 1984, Schutt and Cowling 1985), China (Zhang and others 1980), and North

America (Bruck and Roberge 1984, Knight 1987, Sheffield and others 1985, Siccama

and others 1982, Zedaker and others 1987). In calling attention to this major problem

several years ago, the Society of American Foresters (1984a) stated its concern: “In

the face of mounting evidence that forest productivity is declining worldwide, researchers know too little about complex ecosystems and the cumulative effect of subtle

stresses from atmospheric pollutants.”

Certainly our knowledge of biological processes and their interactions within forest

ecosystems is incomplete, and we know too little about the cumulative effect of a

wide range of stresses on the ecosystem. But integrative research at the ecosystem

level shows clearly that the many processes operating within forest systems interconnect in important ways (Waring and Schlesinger 1985). Further, diversity of microscopic and macroscopic plant and animal species is a key factor in maintaining these

processes (Blaschke and Baumler 1986, Durrieu and others 1984, Li and others

1986, Plochmann 1968, Franklin 1988, Froidevaux 1981).

The Congress of the United States addressed the matter of species diversity in the

National Forest Management Act of 1976 (U.S. Laws, Statutes, etc. 1976): “...regulations, under the principles of the Multiple-use Sustained Yield Act of 1960...shall

include...guidelines which...provide for diversity of plant and animal communities ...."

Elsewhere in the Act, the Congress offers a philosophical basis for constructive

forestry goals: ”. ..the Forest Service has both a responsibility and an opportunity to

be a leader in assuring that the Nation maintains a natural resource conservation

posture that will meet the requirements of our people in perpetuity....”

An underlying principle of the congressional direction is that people, as a significant

part of the forest ecosystem, have the right and the obligation to manage biological

processes to produce products and amenities afforded by forests. Such management, however, must be consistent with the need to maintain health of the biologically productive machinery over the long run. The 1986 “National Forum on BioDiversity,” sponsored by the National Academy of Sciences and the Smithsonian

Institution, was a needed step toward recognition of the problem. Now, forest

scientists must be strongly challenged to define the relations between biological

processes and forest health.

In this book, we document that a large dead tree is not a wasted resource; indeed,

it continues to function as an important part of a terrestrial or water system, either

while remaining on the site at which it once lived, or by becoming a structural part of

an aquatic or marine habitat. We aim to help anyone interested in perpetual forest

productivity to understand the importance of large, dead woody debris. The book

develops certain principles and ideas in sequence from the forest to the sea. The

dynamics of coarse woody debris (any dead standing or fallen tree stem on land or

in water at least 4 inches in diameter at breast height on snags and at the large end

on fallen trees) in forests and plantations of coastal Oregon are summarized in chapter 1; on the forest floor, chapter 2; in streams and rivers, chapter 3; and in estuaries

1
and the open ocean, chapter 4. Intensive and diversified management and the need 

for future research are examined in chapter 5. Most of the information is specific to 

the Coast Range of Oregon but also applies generally to western Oregon and western Washington, western British Columbia, and southeastern Alaska. 

Oregon’s coastal zone extends from the crest of the Coast Range to the Continental 

Shelf and contains some of the world’s most inherently productive forest systems 

(Franklin and Dyrness 1973, Fujimori 1971, Waring and Franklin 1979) (fig. 1.1; 

fig. 1.2, color). Here, a continuum of terrestrial, stream, estuarine, and coastal ocean 

ZONE : 

OREGON .-.-.-.- .-.-. -.-. - 

CALIFORNIA 

Figure Ll-The Oregon coastal zone. 
sites composes one macrosystem (Vannote and others 1980). The parts of this system are related by water and atmospheric transport of chemicals and organic and

inorganic substances of various sizes along an elevational gradient from 4,000 feet

above sea level to an ocean depth of 1,200 feet (200 fathoms).

Few regions of the world support vegetation that grows faster, more densely, and to

greater heights than that along the Oregon coast. The mix of species and the structure of plant communities vary greatly, even over short distances, because of siteto-site differences in elevation, climate, geology, soils, and nutrient availability.

Drought is not a problem along drainages where the soil is constantly wet and air

humidity is high, but plants may suffer from lack of water on a sun-warmed hillside

in midsummer. Most coastal soils are of medium texture, moderately deep, and

reasonably well supplied with nutrients.

Along Oregon’s northern coast, the vegetation is mainly of the same species seen in

coastal Washington, British Columbia, and Alaska: Sitka spruce, western hemlock,

huckleberry, salmonberry, and salal (see “Appendix” for scientific names). Along the

southern Oregon coast, the species mixture is much richer-the “northern” species

mix with California plants growing at or near their northern limits: redwood, tanoak,

California laurel, western azalea, and blueblossom. The Klamath-Siskiyou Mountain

region of the southern Oregon and northern California coast supports still other localized species such as Port-Orford-cedar.

The Oregon coast landscape was disturbed periodically long before human habitation. Floods and landslides are part of the natural geological aging of coastal mountains. Windstorms and wildfires set by lightning destroy vast tracts of forest. We may

think such events now are unusual and catastrophic, but in fact they are very much

a part of the natural cycle of events. After human settlement, additional massive

changes in vegetation occurred. People frequently cause wildfires or convert large

areas to agriculture and urban uses.

The native forest of the Oregon coast has undergone intensive commercial exploitation only in the past century, so biological stresses are probably less than in much of

the world. Here, forest managers still have time to benefit from the long-term experience of others. And here especially, forest scientists and resource managers have

the opportunity to work in concert in developing sound management systems that

can also be models for achieving the recovery of declining forests elsewhere.

3
Figure ILZ-The cnasta zone of Oregon extends from the 

crest of the Coast Range to the Continental Shelf. 

In the following chapters, we synthesize existing research information and offer some 

hypotheses and conclusions based on current knowledge. We offer this information 

and our interpretations for consideration by forest managers and others interested in 

long-term forest productivity. 
Chapter 1. Coarse Woody Debris in Forests

and Plantations of Coastal

Oregon

Thomas A. Spies and Steven P. Cline

Summary

Introduction

The forest portion of the ecosystem is the sum of three diverse, mutually dependent

components: physical structures, biological entities, and ecological functions. These

components are dynamic, continually developing diversity.

Diversity develops in a forest as a result of changes that occur at different rates at

different places. Disturbances cause relatively rapid changes in ecosystems, whereas

succession slowly returns ecosystems to previous conditions or directs them to new

states. Structural diversity in the current mosaic of forest age classes was created by

a variety of disturbances, such as fire and wind, and this mosaic changes from succession and new disturbances (fig. 1.1, color). Today’s forested coastal landscape

bears the legacy of many landscapes in the form of remnant old-growth trees, snags,

fallen trees, landslides, and patches of young and mature forests.

The forest’s character changes with succession. Net primary productivity is greater in

young forests than in old ones. Old forests conserve nutrients, whereas very young

forests are susceptible to erosion and nutrient loss (Franklin and others 1981). Forests of the Coast Range interior valleys produce less wood than do those on more

moist sites nearer the ocean. And internally, the old unmanaged forest is more diverse than many young and mid-age forests. Old forests have deeper, multilayered

canopies, larger accumulations of coarse woody debris (any dead standing or fallen

tree stem at least 4 inches in diameter at breast height (d.b.h.) on snags and at the

large end on fallen trees), and more specialized plants and animals than young

forests have.

A coastal Oregon forest may change slowly through growth, succession, mortality,

and decay, or it may be altered rapidly by catastrophic disturbance. Whatever the

agent of change, the imprints of previous forests and disturbances persist into succeeding forest generations. Organic material in the form of dead tree stems is one

of the more persistent legacies. This material exerts ecological influences on a site

for hundreds and thousands of years; first, as snags and fallen trees; later, as fine

organic matter in the soil. These organic remains create seed germination sites,

moisture reservoirs during summer drought, sites of nutrient exchange for plant

growth, habitat for forest organisms, and favorable soil structure.

5
The Unmanaged 

Forest 

Forest Disturbances 

The major agents of disturbance are fires, winds, insects, diseases, and accelerated 

mass soil and debris movements. Disturbance, along with forest stand development 

and plant succession, helps create the coarse woody debris that is part of the forest. 

Wildfire of various intensities and sizes has been the most significant catastrophic 

disturbance throughout the Coast Range (Martin and others 1976). Some fires have 

burned more than a million acres, and many areas have reburned within 30 years. 

Two of the many large wildfires in the Coast Range are especially impressive. In 

1849, a fire between the Siletz and Siuslaw Rivers burned more than one-half-million 

acres (Morris 1936). Many fires have burned in a patchy manner, creating a very 

complex mosaic of dead and live trees. Humans have strongly influenced the dynamics of woody debris in the Coast Range through accidental or intentional setting of 

fires. Between 1933 and 1951, for example, the many Tillamook burns covered 

335,000 acres, killing more than 13 billion board feet of timber (Lucia 1983). Large, 

severe fires add massive amounts of coarse woody debris to the ecosystem because 

large branches, stems, and most of the coarse woody debris are not consumed by 

the fire (Harmon and others 1986) (fig. 1.2). 

Figure 1 .P-Amounts of coarse woody debris after 

a fire that killed an old-growth stand. 

6 
Figure 1.3-Blowdown patch in a spruce-hemlock 

stand. 

Windthrow, the next most important catastrophic forest disturbance, is common in 

the Coast Range where hurricane-force gales are recorded several times each year 

(Badura and others 1974). Such events in 1950, 1953, 1957, and 1958 caused extensive damage (Childs and Clark 1953, Lynott and Cramer 1966, Ruth and Yoder 

1953). During the “Columbus Day” storm of October 12, 1962, 11 billion board feet of 

timber was blown down in western Oregon and western Washington (Orr 1963). Tree 

mortality from wind damage adds dead wood directly to the forest floor, in contrast to 

fire damage that usually leaves dead trees standing for many years (fig. 1.3). 

Wind-caused mortality also creates a different successional pathway than does fire 

mortality. Wind increases the proportion of shade-tolerant species, such as western 

hemlock, because understory trees are released after the canopy dominants are 

removed. Thus, when trees in the released stand die, the contribution of dead wood 

is from smaller diameter, more rapidly decomposed western hemlock stems. Western 

hemlock stands lacking massive successional dominants, such as Douglas-fir or Sitka 

spruce, accumulate less coarse woody debris than do stands with these dominants. 

7 
Forest Stand

Development

and Succession

Although insects have occasionally caused catastrophic mortality in Coast Range

forests, they usually inflict only scattered mortality. Outbreaks of the Douglas-fir bark

beetle often follow other events that kill and damage trees (Furniss and Carolin

1977). Such an outbreak, a patchwork of small groups of trees in recently killed

timber, spreads to nearby trees where the insects form galleries in the phloem and

girdle the trees. The beetles also introduce a fungus that plugs the conductive

tissues in the vascular system. Trees killed by bark beetles usually die standing,

although decay has already begun.

Laminated root rot fungus is a primary pathogen of Douglas-fir and western redcedar

in the Coast Range. This fungus is not a direct agent of catastrophic mortality because patches of mortality are relatively small (about 0.25 acre) and spread slowly

(about 1 ft/yr) (Gedney 1981, Nelson and others 1981). It is, however, widespread in

the Coast Range and predisposes many trees and stands to windthrow. Red ring rot

fungus, another important organism that predisposes canopy trees to wind damage,

starts the process of wood decay before the trees die.

Steep slopes are generally unstable as a result of high precipitation, unstable soils,

and deeply weathered bedrock. Debris avalanches, rapid shallow soil movement

(Swanson and others 1982), and floods can suddenly destroy small areas of forest.

Debris avalanches are estimated at more than 2.5 avalanches per square mile every

2 years on part of the Siuslaw National Forest (Swanson and Lienkaemper 1985).

These small events move an average 872 cubic feet of soil and occur most often in

headwall areas of steep drainages. Despite their small size, they have a cumulative

effect on coarse woody debris. Debris avalanches and floods knock down and uproot

trees, tearing them out of streambanks. The coarse woody debris produced is often

moved from the site, however, and redeposited downslope or in streams.

Coastal Oregon’s forest lands occupy three vegetation-type zones: western hemlock

(72 percent), Sitka spruce (17 percent), and mixed-evergreen (11 percent) (Franklin

and Dyrness 1973). After major disturbance, stand recovery rates and successional

pathways vary by location, site, and vegetation type. Most forest stands, however,

follow a similar course of successional development that proceeds through five

stages (based on Oliver 1981):

1. Stand initiation.-- Trees of the new stand occupy recently disturbed sites.

Grasses, forbs, and shrubs may dominate for 20 to 30 years. On some coastal

sites, however, 50- to 60-year domination is possible.

If wildfire destroyed the previous stand, regrowth will be dominated by newly

established seedlings. If wind destroyed the previous stand, the new stand will

develop from newly established seedlings plus newly released, shade-tolerant

understory trees.

2. Stem exclusion.-- Canopy closure prohibits further establishment of new trees.

Vertical stratification develops among individuals and species of the canopy. Intense

competition among densely spaced trees causes natural thinning of suppressed

individuals that may last 10 to 30 years. Input of coarse woody debris begins as tree

competition causes mortality.
3. Understory reinitiation.-- Canopy dominance diminishes, allowing herbs, shrubs,

and small trees to establish. Cavity-nesting birds begin to use dead trees, now 15 to

20 inches in diameter (Neitro and others 1985). Fallen tree stems are of sufficient

size that they persist much longer than the small trees of the previous stage. This

stage may last until shade-tolerant trees reach the canopy-100 to 150 years.

4. Old growth.-- Shade-intolerant overstory dominants (Douglas-fir or Sitka spruce)

die and are replaced by understory trees, such as western hemlock. This stage lasts

500 to 800 years or more. Stand structure includes a wide range of tree sizes, massive individual dominants, great accumulations of coarse woody debris, numerous

foliage layers, and patchy tree distribution. The death of one dominant Douglas-fir

can create more than 22 tons of dead wood, some of which can persist for hundreds

of years (Harmon and others 1986).

5. Climax.-- The forest reaches the climax stage when the shade-intolerant dominants

have died and the stand is composed of only shade-tolerant species. Such stands

are rare, however, because of the great longevity of Sitka spruce and Douglas-fir and

because disturbance usually reinitiates succession. A climax forest contains less

coarse woody debris than does the old-growth forest because it lacks the original

overstory dominants.

Coarse Woody Debris Rates of coarse woody debris inputs and loss by decay.--Coastal Oregon forests

contain some of the world’s largest accumulations of standing dead and fallen trees.

Coarse woody debris may exceed 175 tons per acre (dry weight), more biomass than

the total live and dead biomass of many deciduous forests (Harmon and others

1986). These large accumulations of coarse woody debris result from two processes:

addition of newly dead material and slow loss from decay of older material. The balance between addition from dead trees and subtraction of decaying wood determines

the amount and dynamics of coarse woody debris in a forest.

The amount of coarse woody debris that will accumulate in a stand can be predicted

if rates of input and decay are assumed to be constant (fig. 1.4). Two to four percent

of the dead wood in a stand decays annually, rates similar to those reported for other

forests (Harmon and others 1986). Accumulations of coarse woody debris in the

coniferous forests in western Oregon are much larger than in other forests, however,

probably because of higher rates of input.

New coarse woody debris is not added to young Douglas-fir stands until the stem

exclusion and understory reinitiation stages. Mortality rates for canopy trees in these

stands are relatively high (l-2 percent/year) (Franklin and others 1986), but accumulations of coarse woody debris are low in young stands because many of the trees

that die are below the minimum diameter of coarse woody debris (4 inches) and

because the small stems decay more rapidly than larger ones (Harmon and others

1986). Coarse woody debris from the young stand accumulates slowly during the

first 100 years, then rapidly between 100 and 400 years (fig. 1.5).

9
Input 4 

per year 

(lonslacre) 

3 

Figure 1.4-Relation between input rate of coarse woody 

debris and accumulation of coarse woody debris for different 

rates of decay of coarse woody debris; based on data from 

Harmon and others (1966) and adapted from an unpublished 

figure by M. Harmon. 

coarse 

woody debris 

(Ions per 

ECW) 

00 I 

Stand age (years) 

Figure 1.5-Accumulation of coarse woody debris in relation 

to stand age in Douglas-fir stands in western Oregon and 

Washington; based on data from Spies and others (in press). 

10 
In mature (late understory reinitiation stage) and old-growth stands, windthrow, diseases, and insects more than other agents cause most mortality in canopy trees.

Mortality rates in old-growth stands decline to about 0.5 percent of all trees annually

(Franklin and others 1986). Mortality rates are not constant, however, and windstorms or bark beetle outbreaks can cause sharp increases. Annual mortality in a

180-year-old stand of Douglas-fir near Coos Bay increased from less than 0.2 percent to more than 3 percent over 10 years after a Douglas-fir bark beetle outbreak

(Wright and Lauterbach 1958). Woody debris averaged 7.6 tons per acre per year

(Harmon and others 1986). Despite the relatively low mortality rate of mature and

old-growth stands, coarse woody debris accumulation is high because massive trees

decay more slowly than smaller ones. Input may reach 3 tons per acre per year

(Grier and Logan 1977), several times that found in other temperate forest ecosystems (Harmon and others 1986).

Losses of coarse woody debris from decay result from several processes, such as

organic matter leaching into the soil, physical and biological fragmentation (breaking

off and loss of fine pieces), and respiration by microbes (Harmon and others 1986,

Maser and Trappe 1984b). Loss rates from these and other processes depend on

moisture, temperature, and stem size.

As snags and fallen trees decay, their chemical and physical nature changes.

Douglas-fir wood density decreases by almost half during the first 100 years.

Nitrogen concentration almost doubles during the same time (Franklin and others

1981). The physical appearance of fallen trees and snags also changes in crosssectional shape from round to oval to flattened as the stem settles into the forest

floor.

Amounts of snags and fallen trees.--The greatest amounts of coarse woody debris

actually occur immediately after catastrophic wildfire or windthrow in early succession. Young stands (30 to 80 years) (fig. 7.6, color) in the Pacific Northwest have

more snags and fallen trees and a greater volume and biomass of coarse woody

debris than mature stands (80 to 200 years old) (fig. 7.7, color). Some young stands,

however, contain fewer snags and fallen trees than do mature and old-growth stands

(Spies and others, in press). For closed-canopy stands of the Pacific Northwest, oldgrowth (~200 years) contains the highest volume and biomass of snags and fallen

trees (fig. 1.8, color).

The number of snags per acre differs with their diameter. In Douglas-fir stands in

western Oregon and western Washington, the density of snags of all sizes is about

70/acre in young stands, 50/acre in mature stands, and 24/acre in old-growth stands

(Spies and others, in press). This pattern is different, however, when only large

snags (20 inches in d.b.h. and 16 feet tall) are considered; large snags are most

abundant in old-growth (six/acre), less so in young stands (four/acre) and least

abundant in mature stands (three/acre) (fig. 1.9). Large snags are most commonly

used by cavity-nesting birds (Mannan and others 1980, Neitro and others 1985).

11
Number of 60 

snags per 1 

M) 

so 

40 

so 

20 

10 

^ I 

m Young 

q Mature 

0 Old growth 

<zlMn 

d.b.h. 

rzo-In ,20-in d.b.h. >2C-in d b.h. 

d.b.h. and >16 Illall and >50fllall size 

Figure 1 g--Number of snags per acre by size class in young, 

mature, and old-growth Douglas-fir stands in western Oregon 

and Washington; adapted from Spies and others (in press). 

Number of 190 

fallen trees 

per acre 

100 

n Young 

q Mature 

q Old growth 

Figure l.lO-Numbers of fallen tree stems per acre by size 

class in young (Y), mature (M), and old-growth (0) Douglasfir stands in western Oregon and Washington; adapted from 

Spies and others (in press). 

Numbers of fallen trees in stands are generally similar to those of snags. Young 

stands often have the greatest numbers of fallen trees of all sizes, although oldgrowth stands have the highest numbers of large fallen trees (>24 inches) (fig. 1 .lO). 

Many young stands, probably established after fires in young- rather than old-growth 

forests, do not have large fallen trees and snags carried over from previous stands. 

Therefore, some young stands in the Coast Range do not fit this pattern; they have 

fewer fallen trees than old-growth stands have (Spies and others, in press). 

12 
Elomass so 

(Ions per acre) 

i 

El Snags 

Fallen trees 

Figure 1 .l l-Mean biomass of total coarse woody debris in 

young, mature, and old-growth Douglas-fir stands in western 

Oregon and Washington; Spies and others (in press). 

Volume 9,000 

(cubic feet 

per acre) 

6,OW 

Snags 

Fallen trees 

I 

Figure 1 .lP-Mean volume of total coarse woody debris in 

young, mature, and old-growth Douglas-fir stands in western 

Oregon and Washington; adapted from Spies and others (in 

press). 

In Douglas-fir forests of western Oregon and western Washington, the volume and 

biomass of woody debris in old-growth stands average about 7,175 cubic feet and 

55 tons per acre, more than twice that of mature stands (figs. 1.11 and 1.12) (Spies 

and others, in press). The volume and biomass in many old-growth stands exceed 

10,000 cubic feet and 76 tons per acre, and maximum values approach 24,300 cubic feet and 178 tons per acre. Young stands have intermediate levels of woody 

debris (figs. 1 .l 1 and 1.12), whereas mature stands have the lowest volumes and 

biomasses. 

13 
Distribution of

Coarse Woody

Debris by Decay

Class

Spatial distribution.-- Coarse woody debris is unevenly distributed on the forest. The

amount may vary tenfold between closely adjacent areas, and more than half the

coarse woody debris may fall on less than one-fifth of the total area (Spies, unpublished data). Several factors contribute to such patchy distribution. The large successional overstory trees that contribute heavily to the dead wood supply are irregularly

distributed. Mortality from natural causes is often patchy. Dead wood may be moved

downslope to accumulate at a resting place on concave topography. In many oldgrowth stands, highly decayed wood is more evenly distributed than material of an

intermediate decay level, although the opposite may be true in some young-growth

stands because fires burn unevenly.

Stands on dry sites have less coarse woody debris than those of the same age on

moist sites. In the east-central Coast Range, the amount of coarse woody debris in

stands less than 150 years old is correlated with slope, aspect, and topographic

position (Spies and others, in press). These relations may reflect differences in

productivity between sites and in the frequency and severity of wildfire as it is

affected by topography and dampness of sites.

Many mature stands on the west slope of the Coast Range have much more coarse

woody debris than do mature stands on the east slope. High amounts of coarse

woody debris in young and mature stands may result from cool-burning wildfires that

kill only portions of the original old-growth stands in scattered patches, leaving many

large snags and surviving old-growth trees. Large accumulations of coarse woody

debris in the subsequent stand result from mortality of remnant old-growth trees,

some of which were weakened by the fire.

Physical changes in snags and fallen trees have been arranged into five decay

classes, based on readily observed physical characteristics (Cline and others 1980,

Fogel and others 1973) (table 1 .1). The distribution of total coarse woody debris

biomass in these five decay classes varies with stand age (fig. 1.13). In the average

young stand in the region, the highest biomass occurs in decay class IV. In mature

and old-growth stands, the greatest proportion of woody debris often occurs in decay

class III. The proportion of total biomass in highly decayed material (decay classes IV

and V) generally decreases with stand age. Material from decay classes IV and V

accounts for 57 percent of the total biomass in young stands but only 26 percent of

the total biomass in old-growth stands. Across all age classes, however, differences

in the absolute amounts of highly decayed material are relatively small. The relative

differences among the age classes typically are least for decay class V and greatest

for decay class III; the higher decay classes are a relatively more stable, slowly

changing component of the dead wood in the system.

14
Table 1.1-A 5-class system of decay based on fallen Douglas-fir treeSa 

Decay class 

Characteristics 

of fallen trees I II III 

Bark Intact Intact Trace 

IV V 

Absent Absent 

Twigs, 1.18 inches Present Absent Absent Absent Absent 

Texture Intact Intact to 

partly soft 

Hard, large 

pieces 

Small, soft 

blocky pieces 

Soft and 

powdery 

Shape Round Round Round Round to oval Oval 

Color of wood Original color Original color Original color 

to faded 

Light brown to Red brown to 

reddish brown dark brown 

Portion of tree 

on ground 

Tree elevated 

on support 

points 

Tree elevated on Tree is sagging All of tree on All of tree on 

support points near ground ground ground 

but sagging 

slightly 

Invading roots None 

a Adapted from Maser and others (1979). 

None In sapwood In heartwood In heartwood 

The ratio of woody debris in fallen trees to woody debris in snags increases as decay 

increases. Fallen trees constitute 32 percent of the woody debris in decay classes I 

and II and 71 percent in decay classes IV and V; most dead standing trees decay 

partially before falling. In the Coast Range, fallen trees constitute 42 percent of the 

material in decay classes I and II, a higher value than the regional estimate, perhaps 

because of the greater incidence of wind-related mortality in the Coast Range. 

15 
Young 

z 

P 101 Mature 

Old growth 

-I 

2 20 

s 

15 

10 

5 

0 

Decay class 

Snags 

Fallen 

stems 

Figure 1.13-Distribution of mean total coarse woody debris 

by decay class in young, mature, and old-growth Douglas-fir 

stands in western Oregon and Washington; adapted from 

Spies and others (in press). 

Carryover Woody Debris Carryover woody debris is the coarse woody debris in a current stand that’was laid 

down in the previous stand, often old-growth. Young stands with large amounts of 

coarse woody debris inherited it from the previous stand. Those that have small 

amounts are mostly in the south and east Coast Range where multiple wildfires in 

the past 150 years consumed much of the coarse woody debris. 

16 
Coarse 400 * 

n Carryover 

0 Accumulation from fire mortality 

0 Accumulation from new stand 

200 300 

Stand age (years) 

Figure 1.14-Predicted changes in coarse woody debris after 

a catastrophic fire in a 450-year-old Douglas-fir-western 

hemlock forest; adapted from Spies and others (in press). 

Cycles of Woody 

Debris Accumulation 

Several patterns of accumulation of woody debris occurred in the past. A simple 

scenario would be a major disturbance killing an old-growth Douglas-fir stand and a 

new stand becoming established and growing for hundreds of years before a major 

disturbance (fig. 1.14). At stand age 500 years, about 80 tons/acre of coarse woody 

debris is present. Then a major stand-replacing fire occurs, consuming some woody 

debris, although about 67 tons/acre remains. Large amounts of new coarse woody 

debris are added by the fire, which destroys few large live stems. This sudden injection of dead wood adds 180 to 450 tons/acre. A new Douglas-fir stand is established 

soon after the fire. A period of 30 to 40 years passes before the canopy closes and 

mortality adds more coarse woody debris to the site. Decay reduces coarse woody 

debris by more than 50 percent during this time, but amounts are still high because of 

large input after the fire. By age 100, the accumulation of coarse woody debris is at a 

low point because almost all the coarse woody debris present immediately after the 

disturbance is now gone, and additions of new dead wood from the developing stand 

are less than losses from decomposition. At this point, more than 50 percent of the 

coarse woody debris is inherited from the previous stand. 

After age 100, coarse woody debris increases gradually as a result of mortality of 

the canopy trees. As canopy tree size increases, coarse woody debris also increases 

and probably peaks somewhere between 400 and 600 years. New woody debris 

comes increasingly from the death of western hemlocks at about age 500. The 

standing crop of woody debris decreases gradually toward a lower equilibrium, after 

1,000 years, when Douglas-fir passes from the stand. The last Douglas-fir dies at 

age 1,200 years, and evidence of it can still be found 300 or more years later. 

17 
Coarse 400 

rwdy debris 

(tons 360 

per acre) 

d 

q Carryover 

320 0 Accumulation from fire mortality 

0 Accumulation from 

280 

new stand 

240 

200 

Time since 

0 25 50 100 

first fire 

Ftres 200 300 400 500 (years) 

50 100 200 300 400 Age of Sand 

Wears) 

Figure 1.15-Predicted changes in coarse woody debris after 

a catastrophic fire in a 450-year-old Douglas-fir-western 

hemlock forest and two fires 25 and 50 years later; adapted 

from Spies and others (in press). 

The scenario above is probably not the most common because disturbances, such 

as fire, may recur several times, especially in the first 30 to 50 years of a new stand 

when fine fuel levels are high. Multiple fires would consume more woody debris and 

live biomass over time than a single fire and would reduce the amount of carryover in 

the young stands, so that the site would have relatively low amounts of woody debris 

for 200 to 300 years (fig. 1.15). Multiple fires would delay the addition of new material 

and prolong the period of low accumulation, which would reduce the minimum 

accumulation. 

The Intensively 

Managed Plantation 

Thus far, we have discussed the unmanaged forest, which is rapidly being replaced 

by plantations in which various phases of biological development are controlled to 

produce maximum wood fiber in the shortest time. Plantation establishment decides 

Effect of Plantation 

Management on 

species distribution and initial tree density. Periodic mechanical thinning and removal 

Coarse Woody Debris 

of logs replaces the self-thinning of unmanaged stands that provided coarse woody 

debris from dead stems. In the plantation, production of coarse woody debris is 

minimized, and uniformity-rather than diversity-is fostered. 

Most plantations in the Douglas-fir region are established after an old forest has been 

clearcut. The first step in plantation establishment is to reduce the coarse woody 

debris accumulated before and during logging. Coarse woody debris is reduced most 

often for three reasons: to increase use of woody debris, to clear sites for tree 

planting, and to reduce fire risk. 

18 
Wood utilization standards assume that any piece of dead wood that has sufficient

strength to withstand yarding is usable (Howard 1981). At least 14 variables may

influence the amount of coarse woody debris that remains after logging (Howard

1978):

1. Stand age

2. Gross cruise volume per acre

3. Percentage of stand defect

4. Average slope percent

5. Size of clearcut

6. Average stand diameter

7. Percentage of exportable volume

8. Estimated distance to nearest processing center

9. Estimated hauling distance on secondary roads

10. Percentage of whitewoods in stand

11. Percentage of western redcedar

12. Appraised stumpage value

13. Current utility lumber price index

14. Current general lumber price index

Unusable material is often yarded into piles close to roads. Much of the heavily decayed material is broken into fine organic matter. Most logged areas then are broadcast burned to remove remaining coarse woody debris and finer woody material for

easier tree planting. Such fire consumes fine fuels-limbs, branches, and litter.

To help us understand the effects of intensive removal of coarse woody debris, we

used a model to simulate the dynamics of coarse woody debris in Douglas-fir plantations (fig. 1.16). The model represents a Douglas-fir stand established naturally

on site II land. The stand was precommercially thinned to 300 trees/acre at age

11 years; commercially thinned at ages 31, 40, 53, 68, and 83; and harvested at

age 100 (table 10C in Curtis and others 1982). We assumed that this stand became

naturally established after an old-growth Douglas-fir stand was clearcut. The stand

had a harvest volume of about 100,000 board feet per acre and a coarse woody

debris volume of 10,000-11,400 cubic feet/acre (80-89 tons/acre) (Spies and others,

in press). In this example, the minimum diameter of woody debris is 3 to 4 inches,

depending on data source. The rate of disappearance of coarse wood was assumed to be 3 percent per year (Graham 1982; Sollins 1982; Sollins and Cline 1987;

Spies and others, in press).

The model assumes that 80 tons/acre of coarse woody debris are on the site before

logging. By the end of the first 100 years of the plantation, only 20 tons/acre remain

and only 4 of the original 80 tons are still on the site. New coarse woody debris

would be added as logging slash (62 percent) and dead trees (38 percent) at a rate

of about 0.4 ton/acre between age 30 and final harvest (fig. 1.16).

During a second 100-year rotation of the simulated, manipulated forest, total coarse

woody debris decreased from 24 tons/acre at the beginning of the rotation to only

5 tons at the end of 100 years, before harvest.

19
Figure 1.16-Predicted changes in coarse woody debris in 

three rotations of an intensively managed forest after clearcutting of a 450-year-old Douglas-fir-western hemlock stand. 

The small peaks represent accumulations of coarse woody 

debris after thinnings. The peaks also include natural mortality that occurred between thinnings. 

Coarse 

woody debris 

‘““2~~ 

100 200 300 400 500 

Flreklearcut Yean since fire or clearcuttlng of old-growth stand 

Figure 1.17-Comparison of predicted changes in coarse 

woody debris during 500 years of natural Douglas-fir forest 

development and five rotations of an intensively managed 

Douglas-fir forest. 

We have compared coarse wood loadings during the life of a 500-year-old forest 

with five loo-year plantation rotations (fig. 1 .17). Several major differences between 

coarse woody debris in a forest and in plantations occur over the five centuries. At 

least six times more wood carries over after wildfire in old growth than would have 

carried over after logging in an old-growth stand. The carryover coarse woody debris 

after wildfire is abundant the next 90 to 100 years. On the plantation, more than 

8,500 cubic feet/acre of the large wood that would have carried over is removed as 

20 
n After logging 

q After YUM yarding 

Diameter Class (inches) 

Figure 1.18--Relative change in percentage of volume of 

woody residue by size class after logging and yarding unmerchantable material (YUM) in two Douglas-fir stands in western 

Oregon (after Pong and Henley 1978). 

a product. Coarse woody debris cannot accumulate to levels reached by the 

500-year-old forest if loo-year rotations are the maximum prescribed. Coarse woody 

debris follows a variable pattern during formation of the 500-year-old forest. After 

decreasing from a maximum after wildfire to a minimum at loo-150 years, coarse 

woody debris accumulations begin to increase as large trees die. 

A second difference between the forest and plantations lies in the size of the trees 

and their wood quality. The short-rotation plantation produces smaller diameter trees 

that disappear more rapidly than large trees because they decay faster. 

The size of wood left after disturbances differs greatly between forests and plantations. In the forest, disturbances leave large pieces of coarse woody debris. In the 

plantation, clearcutting leaves relatively small material-branches and small-diameter 

tops (figs. 1.18 and 1.19). Inherited coarse woody debris, especially class IV and V 

material, is broken up during harvest. 

21 
Figure 1 .lg-Clearcut 2 years after harvest showing low 

carryover of coarse woody debris. 

Figure 1.2O-Size and pattern of forest “disturbances” in a 

managed landscape. 

A final difference in coarse wood dynamics between forests and plantations is in the 

input rate during stand development. In the forest, self thinning and other mortality 

proceeds uninhibited and woody debris accumulates. In a plantation, loss of trees is 

substantially slower, and the trees that do die are harvested. 

Short-rotation plantations greatly reduce coarse woody debris, which changes the 

functional characteristics of the ecosystem. Drastically reduced accumulations of 

coarse woody debris could seriously impair the function of plantations as vertebrate 

habitat and might reduce productivity (Bartels and others 1985, Maser and Trappe 

1984b, Neitro and others 1985). In the intensively managed landscape, no more 

periodic large inputs of coarse woody debris is expected; and the size, severity, and 

pattern of the disturbances will vary less (fig. 1.20). Ecological diversity will be greatly 

reduced. 

22 
The intensively managed landscape differs from the unmanaged landscape in how it

changes with time. The levels of coarse woody debris in the managed landscape will

change little. In the unmanaged landscape, irregularity in the frequency of past disturbances ensures that, during a several-hundred-year period, a given site will experience periods of both very high and relatively low accumulations of woody debris.

These periodic large inputs, which help maintain soil organic matter and site productivity, are not planned for plantations in which many rotations may pass without large

inputs of woody debris.

23
Figure 1 J-Young stand with moderate accumulations of coarse 

woody debris. 

Figure 1. l-Mosaic of stands created by wildfire, 

showing patches of snags and trees that survived 

the fire. 

Figure 1 B-Old-growth stand with large accumulations 

of coarse woody debris. 

Figure 1.7-Mature stand with low accumulations 

of coarse woody debris. 
Chapter 2. What We Know About Large

Trees That Fall to the Forest

Floor

Chris Maser, Steven P. Cline, Kermit Cromack, Jr.,

James M. Trappe, and Everett Hansen

Summary

Introduction

This chapter explains how living and dead trees are linked together in the living

machinery of a forest.

Pacific Northwest forests contain an array of fallen trees in various stages of decay,

both in young and old-growth stands, in natural, managed, and recently clearcut

stands. Most trees of Douglas-fir region forests are conifers, of which there are six

major lowland species north of the Siskiyou Mountains (table 2.1). In total, these

temperate forests contain 25 conifer species, many of which are the largest and

longest lived of their genera (Waring and Franklin 1979). Large, fallen trees are

unique, critical components of forest systems (Franklin and Hemstrom 1981, Franklin

and others 1981, Maser and others 1979).

Future forests will contain much less coarse woody debris (CWD), and that debris

will be smaller and of different quality than that seen today. We have the technology

to remove most coarse woody debris from the forest; in fact, current wood utilization

standards encourage such removal (fig. 2.1). Moreover, converting natural forests to

intensively manipulated stands reduces tree lifespans from centuries to decades;

future trees will be much smaller than they are today, and wood quality will

undoubtedly be different from that of today’s forests.

Individual trees have different characteristics that produce diversity within the forest.

Trees can live for hundreds or even thousands of years because they produce new

functional tissues every year, but most die much earlier from injury, disease, or both.

The cause of death (table 2.2) determines diversity of the structural and functional

roles served by the dead tree in its tenure on the forest floor. When a tree dies and

remains standing as a snag, this new, different structural and functional unit adds

diversity to the system, diversity important to many forest organisms (fig. 2.2; tables

2.3, 2.4, 2.5). When a snag or a green tree falls to the forest floor, diversity again is

added (figs. 2.1, 2.3, 2.4; tables 2.6, 2.7).

25
Table 2.1-Typical and maximum ages and diameter at breast height attained 

by 6 species of coniferous trees on fertile soils in forests of the Pacific 

Northwest= 

Species Age 

Typical 

Diameter Height 

Maximum 

Age Diameter 

Overstory trees: 

Douglas-fir 

Grand fir 

Western hemlock 

Sitka spruce 

Western redcedar 

Understory trees: 

Pacific yew 

Years Inches Feet Years Inches 

>750 60 to 88 228 to 260 1,200 174 

>190 36 to 48 163to 195 - 72 

>400 _ 36 to 48 163 to 211 >500 104 

>500 72 to 92 228 to 244 >750 210 

>l,OOO 60 to 120 >195 >1,200 252 

>90 6to12 20 to 40 425 18to30 

a Adapted from Peattie (1953), Sudworth (1967), and Waring and Franklin (1979). 

Figure 2.1-A clearcut on Marys Peak in which most of the large 

woody debris has been removed. Note how small the remaining 

pieces are. 

26 
Table 2.24ome causes of death and the type of dead tree produced 

Cause of death 

Type of dead tree 

Standing Fallen 

Whole Piece(s) Whole Piece(s) 

Physical damage: 

Ice, snow 

Lightning 

WindStem breakage 

Uprooting 

Falling treesStem breakage 

Uprooting 

Injuries to bark, 

by vertebrates 

Fire 

Insects: 

Bark beetles 

Defoliators 

Diseases: 

Rots and cankersOf stem 

Of base and roots 

Mistletoe, 

foliage 

0 

0 0 

0 

Suppression and competition l 

Sources: Aho (1966, 1982); Bull and others (1980); Crouch (1969); Etheridge (1973); Hadfield 

(1985); Hawksworth and Wiens (1972); Houston (1981); Johnson and others (1964); Koonce and 

Roth (1980); Krebill (1968); Leaphart (1959); Maser (1967); Neff (1928); Poelker and Hartwell 

(1973); Roth (1970); Ruth and Yoder (1953); Sanders (1964); Schowalter (1985); Shigo (1973, 

197% Shigo and Marx (1977); Shortle (1979); Wargo (1984); Wright and Harvey (1967). 

Figure 2.2-Snags are important structural components of the 

forested landscape. 

27 
Table 2.3-Physlcal characteristics of Douglas-fir snags by deterioration stage, western Oregona 

Stage of deterioration 

Item 1 2 3 4 5b 

Snag 

characteristic:c 

Limbs and 

branches 

Top 

Diameter, 

broken top 

Height 

Bark remaining 

(percent) 

Sapwood: 

Presence 

Condition 

Heartwood 

condition 

All present 

Pointed 

Few limbs, no 

fine branches 

Broken 

Increases at decreasing rate 

Decreases at decreasing rate 

100 Varies 

Intact 

Sound, incipient 

decay, hard, 

original color 

Sound, hard, 

original color 

Sloughs 

Advanced decay, 

fibrous, firm 

to soft, light 

brown 

Sound at base, 

incipient decay 

in outer edge 

of upper stem, 

hard, light to 

reddish brown 

Only limb stubs 

Sloughs 

Fibrous, 

soft, light 

to reddish 

brown 

Incipient decay 

at base, 

advanced decay 

throughout 

upper stem, 

fibrous, hard to 

firm, reddish 

brown 

Few or no 

stubs 

None 

Varies >20 

Sloughs 

Cubical, 

soft, reddish 

to dark brown 

Gone 

Adanced decay at Sloughing, cubical, 

base, sloughing soft, dark brown, or 

from upper stem, fibrous, very soft, 

fibrous, or dark reddish brown, 

cubical, soft, encased in hardened 

dark reddish brown shell 

Estimated age 

at which snags 

reach a given 

stage of 

deterioration: 

4-18 inches in 

d.b.hd O-4 years 5-8 years 9-l 7 years >17 years Fallen 

8-19 inches in 

d.b.he O-5 years 6-13 years 14-29 years 30-60 years ~60 years 

~19 inches in 

d.b.h’ O-6 years 7-18 years 19-50 years 51-l 25 years >125 years 

a Adapted from Cline and others (1980). 

b Mostly remnant snags. 

’ Characteristics of a snag at each of the 5 stages of deterioration. 

d Characteristic in Douglas-fir forests 40 years old; mean d.b.h. 5 f 1 (SE) inch. 

’ Characteristic in Douglas-fir forests N-200 years old; mean d.b.h. 13 k 3 inches. 

’ Characteristic in Douglas-fir forests ~200 years old; mean d.b.h. 39 f 16 inches. 

28 
Table 2.4-Some uses of snags by selected wildlife specie&’ 

- 

iii Y 2 

25 2 2 

Use Source 

Cavity nest sites 

Nesting platforms 0 0 

Feeding substrate 0 00 

Plucking posts 

Singing or drumming 

(communication) 

Food cache or granary 

Location of courtship 

Over-wintering sites 

Roosting 

Lookout posts 

See footnote at end of table. 

0 0 0 0 0 0 

0 0 0 

0 

0 0 0 

0 Bull 1978, 

Gale 1973, 

Jackman 1974a, 

Maser and others 1981 

Miller and Miller 1980, 

Zarn 1974 

Bull 1978, 

Evans and Conner 1979, 

Raphael and White 1976, 

White and Raphael 1975 

Miller and Miller 1980 

Bull 1975, 

Jackman 1974b, 

Rushmore 1973 

0 Balgooyen 1976, 

Scott and others 1980, 

Swearingen 1977 

Jackman 1974b, 

Jackson 1976, 

Kilham 1979 

0 Bent 1964, 

McClelland 1979 

Maser and others 1981, 

Scott and others 1980 

Miller and Miller 1980 

29 
Table 2.4-Some uses of snags by selected wildlife species (continued)a 

Use 

UY 5 cc Source 

Hunting and 

hawking perch 

Fledging site 

Dwelling or dens 

Loafing sites 

Nesting under bark 

Communal nesting or 

nursery colonies 

Anvil sites 

Thermally regulated 

nests 

l eo 0 

0 0 

0 0 

0 0 0 

0 l 

0 0 

0 0 

0 a 0 0 0 0 

Gale 1973, 

Scott and others 1980, 

White and Raphael 1975 

White and Raphael 1975 

Maser and others 1981, 

Scott and others 1980, 

Thomas and others 1979 

Scott and others 1980 

Harrison 1978, 

Maser and others 1981, 

Miller and Miller 1980, 

Scott and others 1980 

Bull 1978, 

Jackman 1974b, 

Maser and others 1981, 

Scott and others 1980 

Miller and Miller 1980, 

Swearingen 1977 

Beebe 1974, 

Conner 1979, 

Maser and others 1981, 

McComb and Noble 1981 

a Adapted from Neitro and others (1985). 

30 
Table 2.5-Snag diameters and decay stages most often used 

for cavity nesting by woodpeckersa 

Species 

Snag d.b.h., Decay stages’ 

with bark Hard 2-3 Soft 4-!F 

Inches 

Downy woodpecker ll+ 0 

Hairy woodpecker 15+ l d 

Red-breasted sapsucker 15+ 0 

Acorn woodpecker 17+ 0 

Lewis woodpecker 17+ 0 

Northern flicker 17+ 0 

Pileated woodpecker 25+ l e 

’ Adapted from Mannan and others (1980) Neitro and others (1985) Raphael and 

White (1984). 

* From Cline and others (1980). 

’ Stage 5 snags, except those with a hard outer casing, are too decomposed to be 

used for nesting by most primary excavators. 

d May also use decay stages 2-3. 

’ Also use hard snags of decay stage 1. 

Figure 2.3-Fallen trees add a critical 

dimension of diversity to the forest floor, 

The man is 6 feet 7 Inches tall. 
STAGES 

BROKEN 

STAGE 7 

DECOMPOSED 

Figure 2.44Vhen they fall, trees and snags immediately enter one of 

the first four decay classes (modified from Maser and others 1979). 

Table 2.6-A 5class system of decay based on fallen Douglas-fir tree@ 

Characteristics 

of fallen trees I II 

Decay class 

Ill IV v 

Bark Intact 

Twigs, 1 .18 inches Present 

Texture Intact 

Intact Trace Absent 

Absent Absent 

Small, soft 

blocky pieces 

Absent 

Absent 

Soft and 

powdery 

Oval 

Absent 

Intact to 

partly soft 

Hard, large 

pieces 

Shape Round 

Color of wood 

Round 

Original color 

Round Round to oval 

Original color Original color 

to faded 

Light brown to 

reddish brown 

All of tree on 

ground 

Red brown ?o 

dark brown 

All of tree on 

ground 

Portion of tree 

on ground 

Tree elevated 

on support 

points 

Tree elevated on 

support points 

but sagging 

slightly 

None 

Tree sagging 

near ground 

Invading roots None In sapwood In heartwood In heartwood 

a Adapted from Maser and others (1979). 

32 
Table 2.7-Stage and condition of snag by decay 

class of fallen tree,a and fallen trees by decay class 

In an old-growth Douglas-fir standb 

Snag stage Decay class 

and condition of fallen trees 

Number of 

fallen trees 

per acre 

1-3, hard snag 

4-5, hard snag 

5-6, soft snag 

7, soft snag, 70+ percent 

soft sapwood 

Fallen snag 

Total 

I 11 

II 6 

III 13 

IV 16 

v 75 

121 

a Adapted from Maser and others (1979). 

b Adapted from MacMillan and others (1977). 

Forest Floor 

Diversity 

The forest floor is the interface between the belowground and the aboveground 

components of the forest. As a center of intense physical, chemical, and biotic 

activity, it both influences and reflects ecosystem functions. In turn, ecosystem 

functions reflect the array and quality of processes resulting from structural diversity. 

Physical Diversity When a tree falls-be it a wind-uprooted, healthy tree or a decomposing snag-a 

sequence of ecological consequences begins. The fall of understory trees, usually 

western hemlock or western redcedar, is caused by wind being funneled below the 

overstory canopy. Falling of understory trees does not visibly affect the overstory 

canopy, but additional light is admitted to the forest floor. The falling of an overstory 

Douglas-fir, however, creates an evident canopy opening in which shade-tolerant 

understory trees will be released to grow. 

The opening increases considerably if the falling tree causes successive uprooting 

and breaking of neighboring trees. The probability of a tree causing such a domino 

effect when it falls increases with its size and vigor. A large, healthy tree is more 

likely to fell the trees it strikes than is a decayed snag, which is more likely to break 

or shatter. A large snag falling in a young stand is more likely to knock over a 

smaller live tree than is one falling in a mature or old-growth stand. 

The effect on canopy space is less dramatic when a tree dies standing and becomes 

a snag. The snag occupies space and casts shade that affects the understory 

vegetation. Over time, however, the snag deteriorates, its effect changing as 

decomposition advances and pieces slough off. 

Fallen trees create opportunities for new plants to become established. An old-growth 

Douglas-fir may be uprooted or may break off at or above the ground, depending on 

its health (fig. 2.5, color). Trees that break near the ground are infected with butt or 

stem rots. The roots and stump decompose in place, leaving understory vegetation 

intact and creating few new sites for establishment of vegetation. A tree with root rot 

may be uprooted, but the roots break off instead of being pulled from the soil. 

33 
Chemical Diversity

In contrast, when roots of a healthy tree are pulled out of the ground when it falls,

bare soil is exposed as an extensive root-pit and mound (fig. 2.6, color). The

bare mineral soil of a root-pit and mound-and with time the fallen tree itselfpresents habitats readily colonized by tree seedlings and other plants (Christy and

others 1982).

The surface of a forest floor is roughened by fallen tree stems, their uprooted butts,

and the pits and mounds left after the uprooting (fig. 2.7, color). Living trees roughen

the surface of the forest floor by sending roots outward along slopes, often near the

litter layer. Tree stems also affect the surface by sloughing bark, which arrests soil

creep at their bases. Of all the factors affecting surface microtopography, the

pit-and-mound topography produced by uprooting trees is best known (Beatty 1984,

Bratton 1976). Topography is a major influence in creating and maintaining species

richness of the herbaceous understory (Bratton 1976, Thompson 1980) and on the

success of tree regeneration (Henry and Swan 1974). Pit-and-mound topography is

common in all types of forests and is a major cause of soil mixing (Stephens 1956).

Live tree roots increase soil shear strength; as dead roots decompose, soil strength

declines. For this reason, mass soil movement on slopes increases after clearcutting

(Burroughs and Thomas 1977, O'Loughlin 1974, Ziemer 1981).

As tree stumps and roots decompose, they often form interconnected,

surface-to-bedrock channels that rapidly drain excess water (Beasley 1976, de Vries

and Chow 1978, Gaiser 1952) (fig. 2.8, color). The collapse and plugging of these

channels during latter stages of decomposition are believed to foster slope instability

after logging by forcing more runoff to drain through the soil matrix, reducing soil

cohesion and increasing hydraulic pressure (Chamberlin 1972).

Large, stable tree stems lying along slope contours reduce erosion by forming a

barrier to downhill soil movement (fig. 2.9, color). Soil and forest floor materials

deposited along the upslope side of a fallen tree reduce nutrient loss and form an

excellent site for establishment and growth of vegetation.

Fallen trees are a major source of soil organic material in Pacific Northwest forests.

They also contain essential nutrients that are released during decomposition by

micro-organisms and plants, fungi, and animals, such as termites (fig. 2.10), that

derive nutrients from the micro-organisms. The decomposer community is adapted to

the relatively low nutrient concentrations in wood; wood-decomposing fungi can

survive and function at nitrogen concentrations about one-third those usually found in

undecomposed wood (Cowling and Merrill 1966).

The five decay classes (table 2.6) of fallen trees have different concentrations of

nutrients-the higher the decay class, the higher the nutrient concentration (tables

2.8 and 2.9). As carbon compounds in wood decay to carbon dioxide, water, and

residual compounds, their nutrient contents, such as nitrogen, are released from the

wood matrix. Micro-organisms and the larger creatures that decompose the wood for

energy and structure concentrate these nutrients in their tissues as they metabolize

the carbon compounds.

34
Figure 2.10-A Pacific dampwood termite 

worker. A termite can digest the wood it 

eats because of a mutually beneficial, 

three-way relation between the 

tndrvrdua termite, cellulose-drgesting 

protozoa,, and mtrogen-frxmg bacteria 

that live in its gut. The protozoa digest 

the cellulose in the wood and convert it 

to a form that the termite can use as 

food. In turn, the termite’s body 

provides an anaerobic chamber that is 

replete with food for the protozoa. Wood 

particles eaten b the termite 

J 8 

ass into 

the chamber an are enaulfe bv the 

protozoa, which in turn ferment ihe 

cellulose. Major products of fermentation 

are carbon dioxide,, hydrogen, and acetic 

acid. The acetic acid is absorbed throuoh 

the wall of the termite’s hindgut and is - 

oxidized as energy (Breznak 1975). 

Nitrogen concentrations can increase severalfold during progressive stages of decay 

(table 2.8), in part because of biological nitrogen fixation by free-living bacteria in the 

wood (Silvester and others 1982). Absolute gains or losses of nitrogen or other 

elements depend on the balance between nutrient inputs and losses during decay. 

Nutrients that are conserved by plants and animals during decomposition include 

nitrogen, calcium, magnesium, and sodium. Others, such as potassium, usually are 

leached and recycled (Grier 1978, Yavitt and Fahey 1982). 

Fallen trees are a substantial reservoir of soil organic matter in old-growth Douglas-fir 

forests (table 2.10). In two Douglas-fir forests, the organic matter from all decay 

classes of fallen trees older than 500 years represented about 30 percent of the total 

soil organic matter (Means, Cromack, and MacMillan, unpublished data). Nutrients 

are less concentrated in fallen trees in all decay classes than in leaf, twig, and root 

components of the forest floor (table 2.9). Because of the great amount of large 

wood in an old-growth Douglas-fir forest, however, the total amount of nutrients in 

fallen tree stems is still important (table 2.10). The proportion of the total soil organic 

matter contributed by fallen trees can be nearly fourfold greater than that of the other 

forest floor materials (table 2.10). Litter components take 1 O-50 years to decompose 

(Fogel and Cromack 1977), whereas fallen trees take as long as several centuries 

(Means and others 1985). Thus, the nutrient pool of a fallen tree cycles on a much 

longer time scale than that of the rest of the forest floor. 

The forest floor and its decaying wood receive nutrients from throughfall (rain, snow, 

or dew that picks up nutrients as it falls through the canopy) (fig. 2.11). If fallen trees 

occupy, say, 10 percent of the ground surface in an old-growth Douglas-fir forest, 

and if they remain in place for 100 years, they potentially could accumulate nutrients 

equivalent to 10 times the nutrients carried in the average yearly throughfall 

(table 2.11). 

35 
Table 2.8-Representative data for decay classes, nitrogen, carbon, and C:N 

ratios of decaying fallen trees in western coniferous forests 

Ecosystem and tree species 

Decay 

class N C C:N 

H.J. Andrews Experimental Forest,= 

old-growth Douglas-fir 

Sequoia National Park,’ 

mixed conifers: 

White fir 

Jeffrey pine 

Sugar pine 

Olympic National Park:C 

Western hemlock 

Sitka spruce 

I 

II 

III 

IV 

V 

I 

II 

III 

IV 

I 

II 

III 

IV 

I 

II 

III 

IV 

I 

II 

III 

IV 

I 

II 

III 

IV 

Percent 

0.08 52 655 

.09 53 615 

.lO 54 534 

.13 55 411 

.23 56 244 

.lO 49 488 

.13 50 384 

.17 49 287 

.25 53 213 

.09 51 572 

.15 51 338 

.12 50 419 

.36 52 144 

.ll 50 457 

.19 54 282 

.22 52 234 

.20 55 276 

.lO 50 500 

.14 50 357 

.ll 50 454 

.26 50 200 

.08 50 625 

.08 50 625 

.lO 50 500 

.23 52 217 

* Sollins and others (1980). 

b Harmon and others, in press. 

’ Graham and Cromack (1982). 

36 
Table 2.9-Nutrient concentrations in the forest floor and in fallen trees in an 

old-growth Douglas-fir forest on the H.J. Andrews Experimental Forest in the 

western Cascade Range in Oregona 

Component N P K Ca Mg Na 

Percent 

Total forest floor 0.50 0.098 0.11 0.87 

Fallen tree stemsb 

0.26 0.014 

.lO .0031 .Olll .076 .0076 .0024 

* The forest is a site class Ill, and elevation ranges from 1,400 to 2,080 feet. The data are from Sollins 

and others (1980). 

b Weighted average concentration of fallen tree decay classes II-IV. 

Table 2.10-Mass and nutrient content of the forest floor and fallen trees in an 

old-growth Douglas-fir forest on the H.J. Andrews Experimental Forest in the 

western Cascade Range in Oregona 

Component Organic matter N P K Ca Mg Na 

Pounds per acre 

Total forest floor 45,568 228 44.7 50.1 396.4 118.5 6.4 

Fallen tree stems 191,350 191 6.0 21.3 145.4 14.5 4.7 

a The forest is a site class III, and elevation ranges from 1,400 to 2,080 feet. The data are from Sollins 

and others (1980). 

Decomposition of fallen trees is aided by a variety of micro- and meso-organisms 

that live in, on, or near them (Elton 1966, Harmon and others 1986). Potential thus 

exists for considerable uptake, utilization, and export of nutrients from fallen trees 

during decomposition. Substantial cycling of nutrients occurs, for example, in 

decayed, fallen lodgepole pine (Yavitt and Fahey 1985), especially after snowmelt. 

Decomposition of fallen trees releases nutrients for microbial and plant growth 

(Yavitt and Fahey 1985). Fruiting bodies of hypogeous mycorrhizal fungi produced 

in association with tree roots in rotten wood provide nutrients and energy to insects, 

mollusks, and mammals (Maser and others 1979). 

Woody litter, regardless of type or size, takes considerably longer to decompose than 

does needle and leaf litter (table 2.12). Needles, leaves, and small twigs decompose 

faster than larger woody material and nutrients are thereby recycled faster in the 

forest floor. About 140 years are needed for nutrients to cycle in large, fallen trees 

and more than 400 years for such trees to become incorporated into the forest floor; 

they therefore interact with the plants and animals of the forest floor and soil over a 

long period of forest and stand successional history (table 2.12). During this time, a 

variety of shrubs and trees, such as western hemlock and Sitka spruce, have the 

opportunity to develop part or all of their root systems within rotting wood (Harmon 

and others 1986). 

37 
Figure 2.1 l-Large fallen trees decay slowly 

and over time receive nutrients from such 

ecological processes as rain falling through 

a nutrient--¥nch canopy. 

Table 2.11-Nutrient content of fallen trees compared with annual 

throughfall nutrient inputs in an old-growth Douglas-fir forest on 

the H.J. Andrews Experimental Forest in the western Cascade 

Range in Oregon= 

Component N P K Ca Na 

Total annual 

throughfall 4.9 

Pounds per acre 

1.2 12.5 6.7 5.9 

Fallen tree 

nutrient 

content 191 6.0 21.3 145.4 4.7 

Throughfall 

on fallen 

trees in 100 

years 49 12 125 67 59 

a The forest is a site class Ill, and elevation ranges from 1,400 to 2,080 feet. The 

data are from Sollins and others (1980). 

Release of nutrients, especially nitrogen, from forest litter is a function of the decomposition rates and the ability of micro-organisms to retain the nitrogen in their tissues 

(Mahendrappa and others 1986). Work of Bosatta and Staff (1982) suggests that, for 

slower decomposing substrates, such as wood, the rate of nitrogen release per unit 

of carbon mineralized increases as the decomposition rate decreases. Nitrogen 

concentration is an important variable in the regulation of decomposition, especially 

in the earlier stages of decay. Lignin is important in later decomposition because it 

affects the proportions of different residues that may be incorporated into humic 

materials (Berg 1986) (table 2.13). 

38 
Table 2.12-Annual rate of decomposition and time estimated for 

95percent decay of forest litter in the Pacific Northwesta 

Species 

and 

litter component Location 

Annual Time for 

decomposition 95-percent 

rate decay 

Douglas-fir: 

Needles 

Small branches 

Cones 

Bark 

Fallen trees 

Oregon, Cascade Range 

Oregon, Cascade Range 

Oregon, Cascade Range 

Oregon, Cascade Range 

Oregon, Cascade Range 

Percent 

23.0 

a.5 

6.5 

3.4 

.7 

Years 

11 

34 

45 

86 

429 

Western hemlock, 

fallen trees Coastal Washington 1.0 273 

Sitka spruce, 

fallen trees Coastal Washington 1.0 273 

a Decomposition data for needles, leaves, and small woody litter are taken from Fogel and Cromack 

(1977) and Edmonds (1980); decomposition data for fallen trees are from Graham and Cromack 

(1982) and Means and others (1985). The time for 95percent decay is calculated from Olson (1963). 

Table 2.13-Quality of Pacific Northwest forest litter 

components for carbon and nitrogena 

Species 

and 

litter component C N C:N Lignin Lignin:N 

Douglas-fir: 

Needles 

Small branches 

Cones 

Bark 

Fallen trees 

Western hemlock, 

fallen trees 

Sitka spruce, 

fallen trees 

Percent 

5 0.820 61 22 27 

49 .150 333 43 289 

49 .240 208 44 184 

56 .190 289 59 308 

50 .lOO 500 27 270 

50 .076 658 29 381 

50 .098 510 27 275 

Percent 

a Data on nitrogen and carbon are from Cromack and Monk (1975) Fogel and 

Cromack (1977) Graham and Cromack (1982) and Petersen (1984). 

39 
Woody litter components are generally higher in initial lignin than are nonwoody

components (table 2.13); high lignin content results in formation of large quantities

of humus in the latter stages of decay (Berg 1986; Berg and McClaugherty, in press;

de Hann 1977). High concentrations of initial lignin and higher lignin-to-nitrogen ratios

in woody substrates mean they decompose slowly (Melillo and others 1982).

Humus formation is important in regulating the incorporation of nitrogen into humic

materials (Allison 1973, Broadbent 1970, Mahendrappa and others 1986, Russell

1973). Because of its high cation exchange capacity and slow decomposition, rotten

wood can retain available mineral nitrogen from throughfall and decomposition as

well as organic nitrogen compounds mineralized within the wood chemical matrix.

Roots and mycorrhizae of plant species that colonize decaying wood use its available

nitrogen.

Animals facilitate the process of microbial colonization of fallen trees by such

activities as boring and tunneling (Elton 1966, Maser and Trappe 1984a). Ants and

termites excavate 10-18 percent of the fallen trees, such as Jeffrey pine and sugar

pine, in Sequoia National Park, California (Harmon and others, in press). Ants also

extensively excavate decaying mountain hemlock near Waldo Lake, west-central

Oregon Cascades (Cromack, unpubl. data). In addition to excavating, termites have

internal nitrogen-fixing micro-organisms in their intestines (Breznak 1975, Elton 1966).

Nitrogen limits forest productivity in the Pacific Northwest, so it is important that

decaying, fallen trees are sites of nitrogen fixation by free-living bacteria (Cornaby

and Waide 1973, Silvester and others 1982). The rates of nitrogen fixation in

decaying wood are relatively low compared with those of symbiotic nitrogen-fixing

plants, such as red alder and snowbush (Binkley and others 1984, McNabb and

Cromack 1983, Tarrant and Miller 1963, Youngberg and Wollum 1976). About 1

pound per acre per year of nitrogen is fixed in decaying wood (Sollins and others

1986). About half the volume of the annual input of nitrogen is in rainfall (Sollins and

others 1980).

The long-term input by nitrogen fixation in decaying fallen trees and by canopyinhabiting lichens maintains a positive balance of nitrogen in the ecosystem.

Little nitrogen is lost through soil erosion and leaching in undisturbed forests, so

additions through relatively small rates of nitrogen fixation and input from precipitation

gradually accumulate to significant amounts. This positive balance permits periodic,

large losses of nitrogen by fire and accelerated erosion to be more than recovered

when added to large inputs of belowground nitrogen fixation from early successional,

nodulated species, such as red alder and snowbush.

The net gains of nitrogen through time have led to substantial accretion of nitrogen

and associated soil organic matter in many undisturbed forests of the Pacific

Northwest. Nitrogen in these forests has accumulated from about 17,800 pounds/

acre on highly productive sites to 2,670-4,450 pounds/acre on poor sites. Even

forests low in nitrogen, such as a mountain hemlock forest growing on tephra

deposited by the eruption of Mount Mazama about 6,700 years ago, has gained

1,335-l ,602 pounds/acre of nitrogen in the absence of major nitrogen-fixing plants

(Boone 1983). This gain may be due in part to the presence of coarse woody debris

and some nitrogen-fixing lichens.

40
Biotic Diversity

Classical agricultural soil theory suggests that nitrogen is available to plants only

when the C:N ratio is less than about 25:1 (Russell 1973). Even in advanced decay,

the C:N ratio in fallen trees remains consistently much higher than that of the forest

floor. An important new hypothesis, however, suggests that nitrogen availability is

controlled as much by the availability of easily decayed carbon substrates as by

nitrogen concentration per se (McClaugherty and Berg, in press). Wood-rotting fungi

can extract nitrogen from substrates with a C:N ratio of 18OO:1 (table 2.8), nearly

three times as much as sound wood of typical western conifer species. Mycorrhizal

fungi, the major organs of nutrient uptake by the roots, also have decomposing

capability (Durall, Todd, and Trappe, unpubl. data). Thus, decaying wood has

long-term potential for contributing nitrogen for tree growth as residual lignin and

humus are decomposed.

The new theory regarding nitrogen availability suggests that decomposing wood

loses easily biodegradable carbon substrates faster than do other litter components,

such as leaves (Berg 1986; McClaugherty and Berg, in press). Consequently, nitrogen from decaying wood becomes available for plant growth at the higher C:N ratios.

Wood appears to facilitate colonization by long-lived decomposer and mycorrhizal

fungi that capture nutrients, such as nitrogen, within a chemical matrix that promotes

nitrogen retention. A slow-release nitrogen system operates in coarse woody debris

because nitrogen has the potential for becoming available for plant growth at higher

C:N ratios than in typical agricultural residues (Berg 1986; McClaugherty and Berg, in

press). Other beneficial properties of large, fallen trees in forests include high waterholding capacity and cation-exchange capacity (Means and others 1985, Sollins and

others 1986), and habitat for micro-organisms, invertebrates, vertebrates, and higher

plants (Maser and Trappe 1984a) (fig. 2.9).

The manner in which a fallen tree comes to rest on the forest floor greatly influences

subsequent diversity of both external and internal plant and animal habitats. The

decomposing fallen tree provides a changing spectrum of habitats over many

decades-even centuries. It provides diversity within a given successional stage and

forms a physical-chemical link through the many successional stages of a forest.

Placement of fallen trees-how they lie on the landscape-determines the chain of

events leading to diversity. The cause of tree death and characteristics of the site

and its forest stand mainly determine the initial placement of a fallen tree (fig. 2.12).

In the absence of human interference, the ultimate placement is determined by how it

decomposes and becomes incorporated into the soil (Franklin and others 1981,

Maser and Trappe 1984a).

A fallen tree performs various ecological functions between the time it falls and the

time it is finally incorporated into the soil. If it lies up-and-down slope or falls across

other downed trees, most of its volume is initially suspended above the ground. Such

elevated relief adds complexity to the forest floor by creating cover and shade.

41
Figure 2.12-Diversity on the forest floor is created 

b 

Y Y 

the wa trees fall; here a Douglas-fir tree, decay 

c ass I, fe I before the Douglas-fir snag, which 

entered decay class III. 

When a fallen tree decomposes, unique new habitats are created within its body as 

the outer and inner bark, sapwood, and heartwood decompose at different rates. The 

quality of the habitat depends on its physical and chemical properties (fig. 2.13). 

A fallen tree interacts with its environment through internal surface areas. A newly 

fallen tree is not yet a habitat for plants or most animals. But once organisms gain 

entrance to the interior, they consume and break down wood cells and fibers. Larger 

organisms-mites, collembolans, spiders, millipeds, centipedes, amphibians, and 

small mammals-must await the creation of internal spaces before they can enter. 

The flow of plant and animal populations, air, water, and nutrients between a fallen 

tree and its surroundings increases as decomposition continues (fig. 2.14). 

Internal space develops in a fallen tree through physical and biological processes. A 

tree cracks and splits when it falls and dries. Microbial decomposition breaks down 

the cell wall and further weakens the wood. Wood-boring beetle larvae and termites 

tunnel through the bark and wood, not only inoculating the substrates with microbes 

but also opening the tree to colonization by other microbes and small invertebrates. 

Wood-rotting fungi produce zones of weakness, especially between annual rings, 

by decaying spring wood faster than summer wood. Plant roots that penetrate the 

decayed wood split and compress it as the roots elongate and grow in diameter. 

Because of all this internal activity, the longer a fallen tree rests on the forest 

floor, the greater the development of the surface area of its internal cavities. Most 

internal surface area results from biological activity, the cumulative effects of which 

not only increase through time but also act synergistically-insect activity promotes 

decomposition through microbial activity that encourages establishment and rooting 

of plants. 

42 
Decay rate 

Soluble carbohydrates 

Taxifolin content 

Nitrogen content 

Mineral content 

Water content 

Lignin content 

Total extractives 

Cetlulose content 

C:N ratios 

Density 

IB > 

IB > 

IB < 

IB > 

IB > 

SW > 

06 > 

OB > 

HW > 

HW 2 

OB 2 

SW 

SW 

SW 

08 

OB 

IB 

IB 

IB 

SW 

SW 

IB 

> 

> 

< 

> 

> 

> 

> 

> 

> 

> 

> 

HW 

HW 

HW 

SW 

SW 

06 

SW 

HW 

IB 

IB 

HW 

> OB 

> OB 

< OB 

> HW 

> HW 

> HW 

2 HW 

> SW 

> 06 

> 06 

> SW 

Figure 2.13~-Relative decay rates and composition of different substrates of fallen trees: Of3 = outer bark; IB = inner bark; SW = sapwood; HW = heartwood (adapted from various sources). 

EXTERNALSUCCESSION 

GRASS-FORS, 

SHRUB-SEEDLING 

‘OLE.SAPL,NG YOUNG FOREST 

RNALSUCCESSION 

4ATURE FOREST OLD GROWTH 

DECAY CLASS” 

Figure 2.14-Fallen trees progress through two simultaneous successional processes-internal and external (modified from Maser and 

others 1979). 

43 
Conclusions 

Numerous physical and chemical changes occur as fallen trees decay: (1) density 

decreases; (2) water content increases until decay classes III and IV are reached, at 

which time the water content stabilizes (fig. 2.15); (3) mineral and nitrogen contents 

increase; (4) cellulose content decreases; (5) relative lignin content increases; (6) 

C:N ratio decreases (Fogel and Cromack 1977, Foster and Lang 1982, Graham and 

Cromack 1982, Grier 1978, Lambert and others 1980, Sollins 1982); and (7) internal 

temperature fluctuations are buffered as the fallen tree comes in contact with the 

ground (Sollins and Cline, unpubl. data). 

Habitats, both external and internal, are influenced by tree size. An uninterrupted 

supply of new, immature wood in young forests decomposes and recycles nutrients 

and energy rapidly. Habitats provided by the death of young trees are short lived 

and rapidly changing. In contrast, the less frequent, more irregular mortality of large 

trees in old forests is analogous to slow-release fertilization. The lasting quality of 

large fallen trees creates stable habitats in which large woody debris accumulates 

(fig. 2.76, co/or). Scattered accumulations of large woody debris are associated with 

openings in the forest canopy (Stewart 1984). Large fallen trees in such an area 

often contact each other physically, creating external habitats of intense biological 

activity (Maser and others 1979, Neitro and others 1985, Stewart 1984, Thornburgh 

1967). 

Decaying, fallen trees contribute to long-term accumulation of soil organic matter, 

partly because the carbon constituents of well-decayed wood are 80-90 percent 

residual lignin and humus (Means and others 1985). Decaying wood in the soil and 

establishment of conifer seedlings and mycorrhizal fungi on dry sites are positively 

correlated (Harvey and others 1987). Fallen trees also create and maintain diversity 

in forest communities. Soil properties of pits and mounds differ from those of surrounding soil (Beatty and Stone 1985); such chemical and topographic diversity 

in turn affects forest regeneration processes (Lyford and MacLean 1966). All this, 

especially large fallen trees that reside on the forest floor for long periods, adds to 

spatial, chemical, and biotic diversity of forest soils, and to the processes that 

maintain long-term forest productivity. 

350 WINTER 

SUMMER 

Figure 2.15-Water content of fallen Douglas-fir trees in winter 

and summer; each point represents a decay class from I (newly 

fallen trees) to V (fallen trees decomposed to a mound of brown 

cubical rotted wood). 

44 
Figure 2.SWind may break unhealthy trees above the ground. Figure 2.6Wind blows over healthy trees and 

pulls their roots from the soil. 

Figure 2.7-Forest floor diversity is partly 

maintained by windthrown trees that create a 

pit-and-mound topography as they are uprooted. 

Figure 2.6-Large stumps from old-growth trees are a finite resource, 

and their loss from the forest affects both soil shear strength and 

watershed hydrology. 

Figure 2.4-A fallen tree oriented along the contour of a slope. The 

upslope side is filled with humus and inorganic material that allows invertebrates and small vertebrates to tunnel alongside. The downslope 

side provides protective cover for larger vertebrates. When under a 

closed canopy, such trees are also saturated with water and act as a 

reservoir during the dry part of the year. 

Figure 2.16-Large fallen trees are a finite resource that create a 

myriad of changing habitats through time as they decompose and 

recycle into the forest soil and new, living trees. 
This page was intentionally left blank
Chapter 3. What We Know About Large

Trees That Fall Into Streams and

Rivers

James R. Sedell, Peter A. Bisson, Frederick J. Swanson,

and Stanley V. Gregory

Summary

Introduction

History of Wood

in Northwest

Streams and Rivers

The most productive habitats for salmonid fish are small streams associated with

mature and old-growth coniferous forests where large organic debris and fallen trees

greatly influence the physical and biological characteristics of such streams.

In western Oregon, most of the 17,000 miles of fish-bearing waterways are small

streams averaging less than 10 feet wide; shown below is the mileage by ownership:

Owner Miles Source

Private

Bureau of Land

Management

USDA Forest Service

9,144

2,025

5,800

Oregon Department of Fish and Wildlife;

Oregon Department of Forestry

U.S. Department of the Interior

Everest and Summers

(1982)

Total 16,969

Dense vegetative canopies help keep waters cool, and falling tree litter delivers

nutrients to the stream portion of the ecosystem. Large organic debris and fallen

trees greatly influence the physical and biological characteristics of small streams

that may contain as much as 200-700 tons/acre of such material (Anderson and

others 1978, Bisson and others 1987, Franklin and others 1981, Harmon and others

1986, Keller and Swanson 1979, Swanson and Lienkaemper 1978).

Most early descriptions of streams and rivers in the Northwest were recorded in

British and United States army journals. Valleys were so wet that early travel was

confined to edges of the hills (Dicken and Dicken 1979). Oregon’s Tualatin Valley

was “mostly water connected by swamps” (Ogden 1961, p. 122). Much of this

flooding resulted from beaver dams, accumulated sediment, fallen trees, and living

vegetation in the channels. The valley bottoms had long accumulated alluvial silt and

organic material, so the land was drained for agriculture early in the time of

settlement.

47
The condition of Willamette Valley streams in 1910 was described by Williams (1914,

p. 13):

Many of the smaller streams...through these flat sections of the

valley flow sluggishly and frequently overflow their banks during

periods of heavy winter rainfall.... Most of these have sufficient

grade to carry even more water than ordinarily comes to them;

seldom less than 3, and usually more, feet of fall per mile. The

annual overflow is caused from the obstructing of the channel by

the growth of trees and the extension of their roots, the dams

thrown across the channels by beavers and the consequent accumulation of sediment and other debris.... It is common condition,

however, and usually all that is necessary is a clearing out and

opening up of the clogged channel of the stream to afford entire

relief...to the farmer....

Streams of the Puget Sound lowland in Washington State were also a network of

sloughs, islands, beaver ponds, and driftwood dams with no main channel. The

Skagit River lowlands encompass about 198 square miles, of which more than

50 square miles were once marsh, sloughs, and wet grass meadows. Maps of the

lower Nooksack and Snohomish Rivers show large areas of sloughs, swamps, and

grass marshes before 1900 (Reports of the Secretary of War 18751921).

The channels of both high- and low-gradient rivers contained large amounts of woody

debris, regardless of the bed material. The lower Siuslaw River and North Fork

Siuslaw River were so filled with fallen trees that trappers could not explore much of

these systems in 1826 (Ogden 1961).

In 1870, the Willamette River flowed in five separate channels between Eugene and

Corvallis. Reports of the Secretary of War (18751921) describe many obstacles to

navigation of the Willamette River above Corvallis and say that the riverbanks were

heavily timbered for half a mile on either side. More than 5,500 drifted, dead trees

were pulled from a 50-mile stretch of river in a lo-year period. These trees ranged

from 5 to 9 feet in diameter and from 90 to 120 feet in length. The river was also

confined to one channel by engineering activities.

Many other rivers in Oregon and Washington were completely blocked by driftwood

in the lower, main channels; the Skagit River had a driftwood jam three-fourths of a

mile long and one-fourth of a mile wide. The Stillaguamish River was closed by six

driftwood jams from the head of tidewater to river mile 17. Drifted, dead trees were

so numerous, so large, and so deeply imbedded in the bottom that a steam “snag

boat” operated for 6 months to open a channel only 100 feet wide.

48
Driftwood in high-gradient river systems often jams where the channel gradient is

abruptly decreased. A section of the South Fork Nooksack River was described by

Morse (1883, p. 9):

...we came to a place where the river, during freshets had ground

sluiced all the earth away from the roots of the trees, and down

some 6 feet to the gravel. This covered a region of country a mile

in width by five in length. Overgrown yellow fir timber had once

covered most of that section. If the river below there was only

clear of jams that place would be paradise of hand loggers. On

the gravel lay many million feet of sound fir timber, which only

needed to be junked up during the summer and the winter freshets would float the logs down to the sea. Immediately below this

place, the jams first extend clear across the river, and for the next

20 miles there is a jam across the river nearly every mile.

Large, woody debris was obviously an important part of early river systems of the

Pacific Northwest; however, human objectives dictated that debris be cleared from

river channels. Throughout North America, people have systematically cleaned

downed trees and woody debris from streams for more than 150 years (Sedell and

Luchessa 1982, Sedell and others 1982b). From the mid-1800’s to about 1920, large

and intermediate-size rivers in North America were cleaned so steamboats and rafts

could navigate. From the 1880’s to about 1915, small rivers and streams were

cleaned so logs could be transported from the woods to the mills (fig. 3.1). Splash

dams were built on many streams to temporarily augment the flow so logs could be

floated (Sedell and Duval 1985, Sedell and Luchessa 1982) (fig. 3.2). Such channel

clearance and splash damming removed large quantities of woody debris from

medium to large streams, which significantly changed the physical and biological

conditions of the streams (Harmon and others 1986).

During the 1950’s and 1960's, west coast fishery managers feared that woody debris

in streams restricted fish passage, supplied material for log jams, and caused channel scouring during floods (Hall and Baker 1982, Narver 1971). The great ecological

value of organic debris was not yet known, and during times of extreme water-flow, all

the managers’ fears might be realized (Gharrett and Hodges 1950, McKernan and

others 1950). The result of these fears was that fishery biologists were forced into

the role of river engineers, a part for which they were not trained.

Debris is not now removed on the same scale as in the 1950’s and 1960's, but

removal is still a large part of salmon enhancement programs in several Western

States and is mandated by virtually every State Forest Practices Act in the western

United States and Canada. The combination of removal of debris in watershed

headwaters so that fish could pass, splash damming, and removal of drifting wood

and log jams from large rivers has left entire drainage systems almost devoid of large

wood (Sedell and Swanson 1984).

49
Figure 3.1-Logs in a small stream awaiting enough water to 

be floated to the mill (photo from USDA Forest Service historical files). 

Figure 3.2-A splash dam at Austin Place, Hamilton Creek, 

Oregon, August 16, 1907. Such dams were used to regulate 

the flow of water to float logs down a stream to the mill (historical photo, courtesy of the Horner Museum, Oregon State 

University). 

50 
Figure 3.3-Stream order (after Strahler 1957) in a typical 

watershed. The majority of stream mileage is in first- and 

second-order tributaries in all watersheds of western Oregon 

and Washington. 

Stream Categorization Streams are characterized by their “order” (Strahler 1957) (fig. 3.3). Headwater 

stream channels are designated first-order; two first-order streams combine to form a 

second-order stream. Two second-order streams combine to form a third-order, and 

so forth. 

In western Oregon, first- and second-order streams constitute 79 percent of the total 

stream mileage (Boehne and House 1983) (table 3.1). Such streams rise in very 

small watersheds with limited water storage capacity. These streams may have only 

scanty or intermittent flow during the dry season, but during high flows they may 

move large amounts of sediment and woody debris. Headwater streams mainly 

determine the type and quality of downstream fish habitat. 

First- and second-order streams are influenced by the geomorphology, soils, and 

vegetation of their channels. Large woody debris is common, covering as much as 

50 percent of the channel (Anderson and Sedell 1979, Swanson and Lienkaemper 

1978, Triska and others 1982). The stream is continuously shaded by vegetation. 

Flow energy in the channel is continually dissipated by woody material and vegetation that slow erosion and foster deposition of organic and inorganic materials. The 

average gradient of these streams often exceeds 10 percent, but the channels usually have a stairstep configuration of flat reaches connected by riffles and low falls. 

Salmonid reproduction may be sufficient, even in some ephemeral streams, to furnish 

fry to larger waters downstream (Everest 1973, Everest and others 1985). 

51 
Table 3.1-Stream order analysisa 

Number Total 

of order streams Length 

Average 

Average watershed 

length area Density 

Coastal 

watersheds:b 

1 

2 

3 

4 

5 

Cascade Ran 

watersheds: B e 

Number Acres Miles/acre 

20 5.0 0.25 25 0.010 

20 24.0 1.20 146 .008 

20 94.9 4.70 410 .012 

19 303.4 16.00 1,823 .OlO 

9 393.3 43.70 4,635 .OlO 

20 5.0 .25 35 .007 

20 27.9 1.40 222 .008 

19 101.9 5.00 876 .008 

20 407.9 20.40 2,761 .009 

7 249.9 35.70 4,649 .008 

a Adapted from Boehne and House (1983). 

b Ordered on 17 2,000 scale. 

Third- and fourth-order streams usually flow continuously. Average gradient is less 

than 5 percent, but there may be intermittent stretches of rapids or falls. Woody 

debris usually covers less than 25 percent of the channel. High flows may flush 

woody material from the system or deposit it in jams. The vegetative canopy over 

third- and fourth-order streams varies in density. These streams can transport large 

amounts of sediments, which are often deposited around channel obstructions, in 

narrow, winding areas, or in other areas of low velocity-accretion bars, estuaries, 

and the flood plain. 

The direct influence of riparian areas is moderated in fifth-order and larger streams 

but remains important. Canopies of large, old-growth trees provide some shade, 

vegetated riparian zones keep the main channel confined, and the largest stems of 

down trees that remain in the stream provide important summer and winter salmonid 

habitat. Flood plains of the larger streams contain complex arrays of side channels, 

overflow channels, and isolated pools. Side channels are often created and maintained by large woody debris (Bisson and others 1987, Sedell and others 1984). The 

gradient in large streams is usually less than 1 percent, but rapids and falls may 

occur. Alluvial material and woody debris may be deposited in quiet areas, but 

accumulations are flushed and rearranged during high flows. 

52 
Table 3.2-Physical variables in relation to stream order in 2 Oregon 

watersheds= 

Watershed type Stream order 

and physical variable Unit 2 3 4 5 

Coastal watersheds: 

Gradient 

Width 

Depth 

Pool 

Riffle 

Spawning gravel 

Bottom substrateBedrock 

Boulder 

Cobble 

Rubble 

Gravel 

Fines 

Cascade watersheds: 

Gradient 

Width 

Depth 

Pool 

Riffle 

Spawning gravel 

Bottom substrateBedrock 

Boulder 

Cobble 

Rubble 

Gravel 

Fines 

Percent 18 6 

Feet 2 5 

Inches 8 16 

Percent 22 27 

Percent 78 73 

Square yards per mile 121 455 

Percent 2 16 

Percent 11 15 

Percent 26 15 

Percent 9 10 

Percent 36 29 

Percent 16 16 

Percent 

Feet 

Inches 

Percent 

Percent 

Square yards per mile 

Percent 

Percent 

Percent 

Percent 

Percent 

Percent 

11 

4 

2 

55 

45 

73 

- 

- 

- 

- 

13 

3 

4 3 

10 11 

16 33 

31 37 

69 63 

1,176 63 

14 9 

15 14 

17 19 

15 11 

27 27 

12 20 

9 6 3 

7 9 24 

4 8 12 

56 58 49 

44 42 51 

125 376 1,321 

- 

- 

- 

- 

16 

4 

- - 

- - 

- - 

- - 

18 20 

5 3 

- = not available. 

a Adapted from Boehne and House (1983). 

Most salmonids spawn in fourth-order coastal streams and fifth-order watersheds in 

the Cascade Range (table 3.2). Resident salmonids use some second-order coastal 

streams but are nearly always found in third-order or larger streams. Fourth- and 

fifth-order streams in western Oregon can support rearing of anadromous salmonids 

unless barriers or gradients of more than 12 percent stop upstream movement of 

adults. 

53 
FEET 

Y&7( 

MICROBES-, 4 JE;, 

_ ._ 

,/w MACK CREEK 

79s’ 

LOOKOUT CREEK 

Figure 3.4-Diagram of first- to eighth-order streams showing 

width, dominant predators, producer groups, P:R (production:respiration) ratios, importance of wood, and proportion of 

invertebrate functional groups (adapted from Vannote and 

others 1930); CPOM = coarse particulate organic matter, 

FPOM = fine particulate organic matter. 

Ecosystem Structure 

and Function in 

Unmanaged Streams 

The stream network is a spectrum of physical environments and associated biotic 

communities (Vannote and others 1980). Streams form a longitudinally linked system 

in which downstream processes (cycling of organic matter and nutrients, ecosystem 

metabolism, new metabolism) are linked to upstream processes, The spectrum concept is a good framework for studying and managing streams as heterogeneous 

systems (O’Neil and Reichle 1980). Useful generalizations can be developed about 

magnitude and variation of organic matter through time and space, the structure of 

invertebrate and fish communities, and resource partitioning along the entire river. 

First- and second-order streams feed third- and fourth-order streams with partially 

used food, the amount of which becomes progressively smaller as stream order 

increases. Small streams derive much food for invertebrates from wood or leaf litter 

under old-growth forests. The forest influence diminishes as streams become progressively larger and the stream energy base comes more from algae and less from 

forest litter (fig. 3.4). The forest influence is greatest in very small streams, but most 

diverse organic input mechanisms and habitats are in third- to fifth-order streams. 

Invertebrates reflect these downstream shifts with fewer shredders (leaf eaters) and 

more grazers (algal feeders) in small rivers (fig. 3.4). Dominant organisms change as 

the size of a forested stream changes, as does the role of each functional group of 

organisms in using organic materials (fig. 3.4). 

54 
Figure 3.5-Woody debris in a small pristine stream. 

Consider a first-order woodland stream and a sixth-order stream (intermediate-size 

river) in the context of continuums of communities with associated abiotic factors 

(fig. 3.4). Both systems include the same organic processing components, but they 

vary in relative magnitude of the components, rates and amounts of organic transfer 

between components, and species engaged in the transfers. The two systems are 

essentially modifications of the same trophic scheme, so the entire stream-to-river 

complex can be considered a single system composed of a series of communities 

along a continuum. 

The continuum example deals primarily with food resources for organisms ranging 

from invertebrates to fish. More important to resource management, however, is the 

ecological rationale for a protective vegetation zone along streams and rivers of all 

sizes. Streamside vegetation zones are justified on the grounds of stream temperature control, bank stabilization, and food resources. Streamside vegetation is also the 

primary supplier of large organic debris-snags or tree stems 8 inches in diameter 

with the rootwads attached, or tree branches more than 8 inches in diameter. 

Forests adjacent to streams supply large debris (stems, rootwads, large limbs) 

(fig. 3.5). Erosion may contribute debris to streams and account for water transporting pieces of debris. Organic debris in streams increases aquatic habitat diversity by 

forming pools and protected backwater areas, provides nutrients and substrate for 

biological activity, dissipates energy of flowing water, and traps sediment. 

Aquatic ecologists, hydrologists, and geomorphologists only recently have recognized 

that large organic debris has always been an important part of forested streams. For 

western streams, such recognition developed from the following viewpoints: manipulation by humans (Bisson and others 1987, Froehlich 1973, Heede 1972, Marzolf 

19781, functions of the ecosystem (Bilby 1981, Bilby and Likens 1980, Harmon and 

others 1986, Meehan and others 1977, Sedell and Swanson 1984, Swanson and 

others 1976, Triska and others 1982), and the historical aspect (Sedell and Froggatt 

1984, Sedell and Luchessa 1982, Sedell and others 1982a, Triska 1984). 

55 
processes ’ Snow avalanche slldlng down adiacent hillslope 

alowdown C 

’ Bank cutting -) 

tTra”spon from upstream + 

Debris torrent fro tributary 

Debris avalanches, Streamside slides 

Eanhflows Into maln channel 

OUtpUt Debris torrent 

processes ’ Leaching ’ 

’ Biological breakdown 

- Physical breakdown (abrasion...) 

Flolatlo” 

1 I I I I I I I f 

0.03 0.1 0.3 1 3 10 30 100 366 

Distance from headwater (miles) 

I I 1 I I I 

1 2 3 45 6 7 

Stream order 

Figure 3X-Debris input and transport processes by stream 

order in the McKenzie River system of western Oregon. 

Arrows indicate direction of increasing importance (adapted 

from Keller and Swanson 1979). 

Several mechanisms transfer large woody debris to stream channels: bank undercutting and collapse, tree blowdown, tree collapse from snow or ice, snow avalanches, and mass soil movements (Keller and Swanson 1979). Each of these 

mechanisms contributes in some way to channel, slope, forest stand processes, 

watershed geology, and stream size. 

The processes of transferring large pieces of wood from forests to stream channels 

are: chronic-frequent inputs irregular in time and space; and episodic-infrequently 

spaced, often very large inputs (fig. 3.6). Chronic input processes include tree mortality from disease and insects combined with windthrow or gradual stream undercutting of root systems. Episodic input processes include large-scale epidemics of 

insects or diseases, extensive blowdown (fig. 3.7), logging, debris avalanches, and 

massive erosion of banks during major floods. 

Forest succession alters the composition of woody material entering streams through 

mortality and bank undercutting, causing trees to fall after logging. In young-growth 

plantations of the Pacific Northwest, low- to mid-elevation riparian zones are dominated by deciduous species, such as red alder, if no mature conifers remain along 

the stream after logging. Most trees that enter stream channels in young-growth sites 

are red alder (fig. 3.8, color), which has a shallow root system, and therefore, low 

resistance to undercutting. The rate of input of young-growth conifer debris is slow 

and does not increase until about 60 years after logging (Grette 1985) (fig. 3.9). 
Figure 3.7-Blowdown is a major cause of large woody debris 

in streams. 

714 

r 

Alder 0 

s 

P 

f ” 536 

: 5 

F 357 179 E

Conifer 

0 

5 10 15 20 25 30 35 40 45 JO 55 60 65 

Years me, loggtng 

Figure 3.9-Red alder and conifer debris in small 

streams in second-growth forests in western 

Washington (adapted from Grette 1985). 

Chronic inputs of woody debris larger than 20 inches in diameter are more common 

in mature and old-growth forests because of tree mortality than in young-growth 

stands where most or all of the trees are small. Inputs of smaller debris (less than 

4-inch diameter) from young stands may, however, equal or exceed the rate of input 

of small debris from old-growth forests (Long 1987). 

57 
Distribution of

Fallen Trees

The location, stability, and longevity of debris influence the quality of habitat in all

fish-bearing streams, although the arrangement of woody debris varies according to

stream size and valley morphology (Swanson and others 1976). Spacing of individual

pieces of debris or clumps of pieces can be strongly influenced by input processes. If

the dominant input is from bank undercutting of living trees or direct falling of dead

trees, debris is spaced at random intervals along very small channels where discharge is insufficient to carry the debris pieces downstream. In most fish-bearing

streams, however, there is some degree of debris clumping, the magnitude and

spacing of which generally increases downstream. In streams wider than 5 to 7 feet

(usually third- to fourth-order), woody debris enters the stream after bank undercutting. Trees that fall directly into the stream are moved during storms and deposited on channel obstructions and on the outsides of river bends near the high water

line. Deposited debris may greatly increase width of the channel, produce midchannel bars, and facilitate the formation of meander cutoffs (Keller and Swanson 1979).

Short, braided stream reaches and secondary channel systems formed in this manner are especially productive sites for rearing salmon and trout in Pacific Northwest

rivers (Sedell and others 1984).

A major flood moves live trees to the stream, but downed trees and stumps can

enter or leave streams annually with smaller floods. Large streams that flow through

steep, narrow valley walls (for example, ravines) often cannot develop deposition

zones, so they become dominated by boulders rather than by large woody debris.

Clumps caused by debris avalanches, extensive blowdown, or movement of large

amounts of material from the flood plain in a major flood tend to be more widely

spaced and of greater volume than those in streams where the foregoing input

processes do not occur frequently.

Yet another input process is the debris torrent, a slurry of debris, soil, and water

that can occur when a landslide enters a steep headwater channel (Swanston and

Swanson 1976). Large logs jam at the terminus of a debris torrent, along with much

sediment and debris, but the torrent itself scours the channel as it travels downstream. The result is a track that may be nearly devoid of debris and sediment-very

poor fish habitat (Swanson and others 1976). A study of channels scoured by debris

torrents in the Queen Charlotte Islands, British Columbia, revealed that debris remaining in torrent tracks usually lie parallel to the streamflow direction, in contrast to the

more common diagonal orientation found in streams of unlogged areas or of channels with no torrents. This shift in orientation reduces channel width, depth variability,

cut banks, pool areas, and channel stability, and thus reduces fish habitat diversity

and quality. The debris dam formed by a torrent can be so extensive that it forms a

major barrier to fish passage. Such dams are commonly found near tributary junctions where small first- and second-order channels that have suffered a debris torrent

empty into larger, low-gradient streams.

58
Debris torrents usually travel short distances and may not affect large rivers unless a

headwater channel discharges directly into a mainstream, as is the case in many glacial valleys. Large woody debris, however, can still be clumped along intermediate

and large rivers as a result of infrequent events, such as major floods (Swanson and

Lienkaemper 1978). Movement of floatable debris from headwaters or flood plains

may form massive accumulations of driftwood wherever the channel narrows or low

gradient depositional zones occur. Extensive driftwood dams, common in coastal

streams before river clearance, are now rare (Sedell and Luchessa 1982). More common now are sporadic large accumulations of debris deposited on upper streambanks and flood plain terraces inundated only during floods. Such debris is normally

above the water line, so its use by fish is limited to high flows. The temporary refuge

provided by inundated debris accumulations along the upper banks of streams with

well-established flood plains, however, may be very important to survival of fish when

main channel velocity is high (Tschaplinski and Hartman 1983).

Forest type and successional stage, disturbance history, and channel size all influence the amount of wood in streams. Woody biomass ranges widely-from 2 to 400

pounds per square yard (table 3.3)--as does woody volume, from 0.08 to 144 cubic

feet per yard (Harmon and others 1986).

Stream biomass is also strongly influenced by geomorphic processes. Loss or deposition of sediment in channels may change the measurable biomass in streams

(Harmon and others 1986).

Numbers of downed trees and large pieces of woody debris vary among streams

in mature and old-growth forests, young-growth forests, and blowdown vegetation

(table 3.4). Streams flowing through young-growth forests and recently harvested

areas contain from one-fifth to one-twentieth the number of large woody pieces

found in streams in mature forests.

Average length and frequency of large pieces of wood in pristine forested streams

are greater than those of wood in manipulated streams or salvage-logged areas

(fig. 3.10). Total pieces of wood and their average diameter and length were determined in two small Coast Range streams (fig. 3.11; Sedell, unpublished data). One

stream drains a wilderness area; the other stream drained an area of which about

95 percent had been harvested over the past 30 years. The wilderness stream has

more than one hundred times more pieces of wood and downed trees per unit length

of channel. The average diameter class of wood for both streams was about 20 inches, but the average length of wood in the logged watershed was about 16 feet compared with 33 feet in the pristine stream. The role of wood in shaping and stabilizing

habitats has been greatly diminished in the harvested watershed.

59
Table 3.3-Biomass of large woody debris in streams flowing through 

unmanaged old-growth forests along the Pacific Northwest coast 

Large woody debris 

biomass 

Location and dominant Sample Mean channel 

riparian tree species sizea width Mean Range 

Number Feet Pounds/square yard 

Prince of Wales Island, 

Alaska: 

Sitka spruce and 

western hemlock 4 0.00 - 16.40 15.43 4.41 - 19.84 

1 32.81 - 49.21 26.46 - 

Coastal British Columbia, 

Canada: 

Sitka spruce and 

western hemlock 1 

3 

West slope Cascade Range, 

Oregon: 

Douglas-fir 19 

5 

1 

2 

2 

Northwest coast, 

California: 

Coast redwood 

Klamath Mountains, 

California: 

Douglas-fir 8 0.00 - 16.40 

2 16.40 - 32.81 

1 32.81 - 49.21 

32.81 - 49.21 39.68 

49.21 - 65.62 48.50 

0.00 - 16.40 55.12 4.41 -121.25 

16.40 - 32.81 57.32 28.66 - 74.96 

32.81 - 49.21 50.71 - 

49.21 - 65.62 22.05 13.23 - 30.86 

>65.62 13.23 4.41 19.84 

0.00 - 16.40 295.42 

16.40 - 32.81 141.09 

32.81 - 49.21 149.91 

49.21 - 65.62 35.27 

33.07 

55.12 

2.20 

- 

46.30 - 50.71 

22.05 - 396.83 

39.68 - 242.51 

- 

4.41 - 101.41 

2.20 - 110.23 

- 

- = not available. 

’ The number of stream reaches surveyed (from Harmon and others 1986). 

60 
Table 3.4-Number of large pieces of woody debris per 100 yards of stream 

length in streams with drainage areas less than 6 square miles, by forest 

conditiona 

Forest 

condition 

Old-growth or 

mature forest: 

Mack Creek 

Lookout Creek 

Lobster Creek 

Sheehan Creek 

Cummins Creek 

South Fork Hoh 

River tributaries 

Stream 

location 

Oregon, Cascade Range 

Oregon, Cascade Range 

Oregon coast 

Southeast Alaska 

Oregon coast 

Washington, 

Olympic Peninsula 

Pieces of woody debris per 

100 yards of stream reach 

22 - 28 

18 - 20 

18 

33 - 45 

20 - 23 

18 - 20 

Young growth: 

Knowles Creek Oregon coast 

Lobster Creek Oregon coast 

Fish Creek 

(repeatedly salvaged) Oregon, Cascade 

Blowdown buffer strip: 

Sheehan Creek Southeast Alaska 

Range 

l-3 

l-2 

4-5 

135 

a Adapted from Sedell and others (1984). 

Figure 3.10-The average length of large pieces of downed 

wood in pristine forested streams, such as those shown, is 

greater than those in streams in managed forests. 

61 
Figure 3.11~lnstream frequency trends for an old-growth 

forested watershed (Cummins Creek) and a second-growth 

(less than 30 years) watershed (Knowles Creek) in the central 

Oregon Coast Range: A. Diameter of woody debris. 8. Length 

of woody debris. 

The North Fork Breitenbush, a high gradient, sixth-order stream in the central Cascades of Oregon, at bank-full stage is often wider than 98 feet, large enough to move 

even the largest and longest, downed trees. The river is divided by a wilderness 

boundary. Salvage logging had been carried out several times since 1965 on the 

lower 60 percent of the fish-bearing channels of the river. The average length of 

wood pieces in the managed stream was about 26 feet compared with 48 feet in the 

wilderness stream (fig. 3.12). Between 49 and 64 percent of the total large pieces of 

wood were less than 15 feet long in the managed stream compared with less than 

18 percent in the wilderness stream. Pieces of wood longer than 50 feet accounted 

for more than 41 percent of the total wood in the wilderness stream compared with 

8 to 17 percent in the managed stream (fig. 3.13). About 67 percent of the pieces of 

wood with a rootwad attached were longer than 49 feet in the wilderness stream 

compared with 14 to 23 percent in the logged stream. Stumps made up more than 

60 percent of the wood in the managed stream compared with less than 6 percent in 

the wilderness stream. Total volume of wood had not changed for the wilderness or 

the managed streams, but the pieces were much less stable in the salvage-logged 

stream where the channel had widened by 40 percent. Clearly, the trend is toward 

smaller and fewer pieces of wood in stream channels of all sizes in the logged areas 

(fig. 3.14; compare with fig. 3.10). In addition, stream channels in the logged area are 

wider and less stable. The volume of wood may be the same in the managed and 

the unmanaged streams, but it is more clumped in the managed forest and volume 

per unit of stream area is less. 

B 

500 

406 

300 

- Cummins Creek 

5.41 square miles 

1,726 pieces 

- Knowles Creek-upper basin 

7.34 square miles 

165 pieces 

Length 

ShotI-> Long 

62 
65 - 

59 - 

3 52 - 

&6- 

g 

ii 

39 - 

P 33 - 

z 26 - 

5 

E 

20 - 

-I 13 - 

7- 

0 1 I 

I I I I I I 

1.1 2.4 3.7 5.0 6.3 7.6 

Distance from mouth (miles) 

Figure 3.12-Length of pieces of wood in the North Fork 

Breitenbush River. 

North Fork Breitenbush River 

Length frequency of total wood pieces 

77 

10.4 

49.3 

63.9 

Below bridge 

0.6 mile 

Bridge to wilderness boundary 

0.65.0 miles 

41.2 

19.6 

Wilderness 

5-7.5 miles 

q >50fea 

F! 

30-50 feet 

ls30feet 

IF@ 

cl5 feet 

Figure 3.13-Frequency of wood pieces with rootwads, North 

Fork Breitenbush River. 

63 
Figure 3.14-The trend is toward smaller and fewer pieces of 

wood in channels of streams running through managed 

forests. 

Residence Time 

and Stability of 

Fallen Trees 

Longevity 

The residence time of woody debris in stream channels is affected by transport 

processes, chemical constituents of the wood that affect decomposition rates, and 

resistance to breaking and abrasion. Dendrochronologic dating of instream debris in 

coniferous forests of the Pacific Northwest has identified pieces that have been in 

channels for 200 years or more (Keller and Tally 1979, Swanson and others 1976). 

Old-growth conifer debris is estimated to decay at a rate of 1 percent per year, although the rate may vary among tree species (Grette 1985). Western redcedar 

resists decomposition in streams better than does Douglas-fir or western hemlock, 

but all three conifer species far outlast red alder (Anderson and others 1978). 

Logging alters the composition of riparian vegetation by reestablishing early successional stages. Debris from young-growth stands has a shorter residence time in 

stream channels than debris from preharvest forests. The frequency of red alder 

debris in young-growth forested streams is about twice that of alder in old-growth 

streams (Grette 1985). Red alder disappears from streams in young-growth forests 

more rapidly, however, than does conifer debris (primarily hemlock and spruce) 

because the alder debris is shorter, of smaller diameter, more easily broken, and less 

well anchored than conifer debris from the preharvest forest. The rate of input of 

alder debris from young-growth stands exceeds the input rate of conifer debris, but 

the reduced longevity of alder debris results in streams with less cover and fewer 

pools than streams in unlogged forests. Loss of cover in streams in young-growth 

forests has the most significant impact on salmonid populations in winter, when fish 

are strongly attracted to debris (Grette 1985) (fig. 3.15). 

64 
Figure 3.15-Loss of cover in streams in young-growth 

forests has the most significant impact on salmonid 

populations in winter. 

Stability of Fallen Trees Stable debris accumulations are assumed to be important for maintaining good fish 

habitat. If debris does not move frequently, its functions of pool anchoring, cover, and 

substrate storage are increased over those of unstable accumulations (Bryant 1983). 

Size, including length and diameter (fig. 3.16), is a major factor contributing to debris 

stability (Bilby 1984, 1985; Bryant 1983; Grette 1985; Toews and Moore 1982). Other 

dimensions, such as the presence of a rootwad or branches, also influence when or 

where a piece of debris will move. Debris length appears to be most important to its 

stability where stream discharge is sufficient to float large diameter stems (Bilby 

1985, Swanson and others 1984). Branches and rootwads add to the stability of 

debris pieces by increasing the mass and surface area available for snagging on 

instream obstructions; whole trees are thus potentially more stable than tree fragments. Tree fragments, about half the width of a bank-full channel, were floated 

downstream during winter storms, but large stems with intact rootwads remained in 

place for at least 70 years in small, low gradient streams in southeast Alaska (Bilby 

1981, Swanson and others 1984). Relatively short pieces of debris can be stable in 

narrow channels, but longer pieces are necessary for stability in wider channels. 

Trees whose length exceeds that of a bank-full channel may have much of their 

weight supported by ground outside the channel where they lodge against standing 

trees during high streamflow (Swanson and others 1984). 

Other aspects of debris that influence stability include orientation, degree of burial, 

and the proportion of the piece that lies in water. Whether a piece is buried depends 

in part on the rate of sediment input to the channel and the longevity of the piece. 

Pieces are stable if their angle of orientation relative to the axis of flow is less than 

30 degrees; they are likely to move, however, if their angle of orientation is greater 

than 60 degrees (Bryant 1983). The degree of burial strongly influences debris movement; pieces with both ends anchored to the streambed or bank move less than 

pieces with only one or neither end buried. The degree of burial also influences 

potential movement (Bilby 1984). Partial burial is less effective than complete or 

nearly complete burial in preventing downstream transport during storms (Grette 

1985, Toews and Moore 1982). 

65 
30 

26 

26 

p 24 

e “- 22 

ki 

iE 20 

E 

c 16 

.= 

I I I I I I I I I 

10 16 23 29 36 42 49 55 62 66 

Channel width (feet) 

Figure 3.16--Relation between the length and diameter of 

stable debris and channel width. Each point represents the 

geometric mean length or diameter of logs not held in place 

by other debris at each of the western Washington study 

streams (adapted from Bilby (1985) and Bisson and others 

(1987)). 

Even the largest fallen trees cannot span the bank-full channel width in large rivers. 

In such cases, the amount of wood and the number of fallen trees on exposed gravel 

bars provide constancy to wood in the river channel even though position of the material may change annually. The likelihood of fallen trees being transported back to 

the main channel is greatly reduced once they have formed jams at bends or outer 

margins of the flood plain, unless the river changes course. 

66 
Processes of

Wood Removal

Much relatively small debris enters streams after logging and is therefore more apt to

move than would naturally occurring debris (Bryant 1980, Grette 1985, Lammel 1972,

Swanson and Lienkaemper 1978, Toews and Moore 1982). Removing all newly

added debris after logging, a requirement of many forest practices regulations, may

involve bucking large debris into smaller pieces that are removed to the high water

line. Such mandatory debris cleaning, however, usually takes place during low flow

periods, and some of the material deposited on the upper bank may subsequently

re-enter the stream at high flows. This increases the amount of shorter, less stable

pieces in the channel (Bisson and Sedell 1984, Hogan 1985, Lestelle 1978, Osborn

1981).

High quality fish habitat declines as debris is exported (Bryant 1985, Scrivenerr and

Andersen 1984). Downstream transport of small, unstable debris can lead to accumulations in debris dams that may remain in place for only a few years before moving on. Although debris dams may temporarily block fish migration, a greater longterm consequence for fish populations is the lack of large structure in the channel

after debris is removed. Debris loading increases immediately after logging, then

declines as accumulations gradually wash away (Bryant 1982, 1985; Toews and

Moore 1982).

Large floods move great quantities of wood onto the upper flood plain and downstream. Low frequency, high magnitude floods add much material to streams. The

wood becomes more clumped through either flood or debris torrent forces. On small

coastal streams, debris torrents may temporarily dam sections of streams draining

basins larger than 6-9 square miles. When these dams fail, the resulting debris flood

scours wood from the channel and deposits it high on banks or in estuaries.

Physical abrasion is the most powerful mechanism for removing stable pieces of

wood from streams and rivers. Sand and gravel carried at flood velocities abrade

large pieces of wood. Abrasion is greater in high gradient or sediment-rich streams

than in gentle, spring-fed or low-gradient streams and rivers.

Biological decomposition is only a minor process in removing wood from streams.

Water-logged wood decays slowly, but wood at the stream-terrestrial interface hosts

very active microbial and invertebrate activity. Here, the biotic components respond

to a gradient of temperature, moisture, and oxygen. Wetting and drying at the streamterrestrial interface allows rapid biological decomposition of wood (Triska and

Cromack 1980).

Forest management has greatly influenced the sequence of events in watersheds.

The impact of natural processes that increase the rate at which woody debris disappears from stream systems is minimal compared with the impact of human activity on

disappearance of wood over the last few decades.

Streams may be cleaned either immediately after logging to remove slash, or later

to remove a specific blockage of fish passage (fig. 3.17, color). Postlogging stream

cleaning is usually done by a professional crew with small equipment. Debris barriers

to fish are usually removed under the supervision of a fishery biologist, who may

need to use heavy equipment and explosives. Stream cleaning may damage fish

habitat (Sedell and others 1985).

67
The State of Washington has required thorough removal of logging slash from

streams for about the last 10 years. During this time, the effect of stream cleaning

has been evaluated in several Pacific Northwest areas. In almost every such study,

debris removal has resulted in loss of important habitat features and reduced fish

populations (Bryant 1980, Dolloff 1983, Elliott and Hubartt 1978, House and Boehne

1985, Lestelle 1978, Lestelle and Cederholm 1984, Osborn 1981, Toews and Moore

1982).

Removing large, stable wood along with smaller material reduces channel stability

and the quality of pools and cover. Small, easily floated wood has sometimes become temporarily abundant after stream cleaning (Meehan and others 1969, Toews

and Moore 1982). Any such increases have come from new slash entering the water

from debris stacked near the high water line during cleaning, or the breakup of wood

in the stream before logging. In most cases, unstable debris is flushed from the

cleaned reach within a few years, and channels are thus degraded.

The proportion of riffles increases and the number of pools decreases in cleaned

stream channels (Bisson and Sedell 1984). The increased frequency of riffles increases the abundance of underyearling steelhead and cutthroat trout, which prefer riffle

habitats; however, the abundance of coho salmon and older age classes of steelhead and cutthroat, which prefer pools, is correspondingly reduced.

State and Federal agencies annually spend more than $6 million to remove debris

jams, but the impact on habitat has had little study. In one study, fish populations in

the vicinity of log jams were reduced immediately after complete removal of debris,

but abundance did not decline significantly where part of the jam was allowed to

remain (Baker 1979). Downstream spawning and rearing areas were damaged by

large flows of sediment released when the log jams were removed. Partial removal

appears to be biologically preferable to complete removal and is less expensive.

Most salvage logging in streams has been done since the great Pacific Northwest

storm of 1964. Since then, Federal funds have been provided for cleaning and salvaging wood from streams after every major storm. Major timber sales on public land

focus on streams of fifth-order or larger because access to established main roads is

easy. A major reason for removing woody material from streams has been protection

of downstream bridges and culverts to reduce property liability court cases. Even

some sports clubs remove tree debris from rivers where such obstacles might impede travel (Oregonian 1986).

Use of wood-burning stoves has increased tremendously in the last 10 years

(fig. 3.18). Most of the wood cut for fuel does not come from streams, but the

demand for high quality wood that might otherwise reach a stream is great.

In the last 100 years, millions of trees have been cleared from rivers. County sheriffs,

port commissions, and recreational boaters routinely clear fallen trees from rivers for

safety and convenience. As a result, most Pacific Northwest rivers bear little resemblance to their pristine condition.

68
Trends in Wood 

Inputs 

Number 

of permlts 

Issued 

(thousands) 

3w 

290 

260 

240 

220 

2w 

160 

190 

140 

120 

100 

80 

w 

40 

20 

O!.,.,.,.,.,.,.,., 

1974 197s 1976 1977 1979 1979 1980 1981 1992 

Figure 3.18-Forest Service, Pacific Northwest Region, free 

use wood permits. 

Riparian zones in the past have supplied large trees to the stream, but most streambanks now have smaller trees of fewer species. Most big cedars and Douglas-firs 

along streams in the Cascades and along most coastal streams greater than thirdorder have been removed or are about to be. On private land, 60-70 percent of 

conifer trees larger than 14 inches in d.b.h. have been harvested within 100 feet of 

a fish-bearing stream (table 3.5) in both the Oregon Coast Range and the Cascade 

Range. Fewer conifers than might be expected, larger than 12 inches in d.b.h., are 

growing along coastal streams (Sedell, unpublished data). 

Table 3.~Conifers larger than 14 inches in diameter harvested from 

loo-foot-wide leave strip 

Distance from stream (feet) 

Location O-50 50-l 00 l-100 

Percent 

Coast Range: 

Drift Creek 

Yaquina River 

Siuslaw River at Pugh CreekBelow North Creek 

Above North Creek 

Wolf Creek 

0 0 0 

50 100 86 

44 74 65 

83 82 82 

0 13 9 

53 90 68 

Cascade Range: 

Santiam River 

Thomas Creek 

Unnamed order 1 stream 

- = not available. 

- >57 57 

57 92 76 

100 100 100 

69 
Wood as Habitat 

in Freshwater 

Systems 

Influences of Wood 

on Stream 

Characteristics 

Table 3.6-Stocking levels of large conifer trees (larger than 14 inches) 

in streamside areas after successive harvests 

Streamside area 

Pristine 

forest Recently Leave 

more than harvested strip 

70 years ago stand stand 

Trees per acre 

Cascade Range, 

both sides of unnamed order 1 stream, 

within 50 feet 43 24 

Coast Range, 

1 side of Yaquina River: 

Within 50 feet 

Within 100 feet 

16 6 3 

36 22 3 

The number of streamside conifers larger than 14 inches in d.b.h. has been drastically reduced from the number present 70 years ago at the first harvest (table 3.6). 

Conifers larger than 14 inches in d.b.h. ranged from only 0 to 19 percent of the 

pristine stocking level after recent logging. 

Woody debris influences stream channel flow and creates and maintains rearing 

habitat for salmonid fishes (Lisle 1982, Sullivan and others 1987). Free-swimming 

species, such as salmon and trout, require rearing sites where food is plentiful and 

little effort is needed to hold a feeding position against the current (Dill and others 

1981, Fausch 1984). Such small, quiet areas are usually located behind boulders 

and are occupied by large, aggressive fish (Bachman 1984). Stream riffles have few 

such sites. 

Some species, notably coho salmon, avoid riffle habitats almost entirely when competitors are present (Bisson and others 1982, Dolloff 1983, Hartman 1965); instead, 

they rely on pools with ample cover provided by large woody debris (Bisson and 

others 1985, Stein and others 1972). 

Most stream fishes inhabit pools in which the current velocity is lower and the water 

usually deeper than in riffles. Deep pools offer fish a better chance of escaping from 

terrestrial predators, and also allow fish of different species or age classes to coexist 

in layers within the water column (Allee 1982, Fraser 1969). 

Woody debris creates many of the pools in Pacific Northwest streams (Keller and 

Swanson 1979, Swanson and others 1976) (fig. 3.79, color). In small streams (up 

to about 3d order), single large pieces of debris or accumulations of smaller pieces 

anchored by a large piece often create a stepped longitudinal profile (fig. 3.20; 

fig. 3.27, color) that consists of an upstream sediment deposit, the debris structure, 

70 
I Debris jam from 

PI”“& pool Stored sedimeniFigure 3.20-Role of woody debris in storing 

sediment and creating pools in streams: The 

“stepped profile” is characteristic of stored 

sediments and plunge pools created by woody 

debris. Removing a debris dam destroys and 

reduces these habitat features (adapted from 

Bisson and others 1987). 

and a downstream plunge pool (Heede 1972, 1985). Numerous debris accumulations 

generally increase pool frequency (Lisle and Kelsey 1982). Numbers of pools are 

positively correlated with numbers of debris pieces in low-gradient streams (Grette 

1985). Eighty percent of the pools in small streams of the panhandle of Idaho are 

caused by fallen trees larger than 10 inches in diameter (Rainville and others 1985). 

The frequency and volume of pools decrease in stream channels from which slash 

and naturally occurring debris were removed after logging (Bilby 1984, Bisson and 

Sedell 1984, Toews and Moore 1982). 

The position of debris also influences the size and location of pools. The size of a 

single stem or the accumulation of stems spanning the channel affects the size of 

the associated pool. In an experimental flume, larger logs created longer and deeper 

pools, provided they were suspended above the streambed (Beschta 1983). In other 

studies, pool area was positively correlated with the volume of debris that anchored 

the pool, and the correlation improved as channel width increased in streams up to 

7 feet wide (Bilby 1985, Bisson and others 1987) (fig. 3.22). Many pools, however, 

are created by eddies behind debris and other structures located at the channel margin rather than by the scouring action of channel flow. These backwater or eddy 

pools, common in all streams, are used by salmonids throughout the year for rearing 

(Bisson and others 1982; Bryant 1985; Bustard and Narver 1975a, 1975b; Dolloff 

1983; Gibson 1981; Lister and Genoe 1979; Mundie 1969; Murphy and others 1984; 

Sedell and others 1982a, 1984; Stein and others 1972; Tschaplinski and Hanman 

1983). 

71 
1075 , 

Channel wid!h 41 feet 

2150 Channel width ~33 feet. 

-1075 

f 

. 

t? =33 . 

. It..., . 

0. 

Channel width 21-33 feet 11 ( , , , , , , , 

4 7 15 36 71 173357714 

Deb& volume lmlcx 

(cubic Ieel) 

1 , , , , , , , , , , 

1 2 4 7 10 36 71 179357714 

Debris volume Index 

(cubic test) 

L 

Figure 3.22--Relation between size of woody debris and pool 

area created for different-size streams in the Pacific Northwest. One 12-inch Douglas-fir tree contains about 72 cubic 

feet of wood; adapted from Bilby (1985). 

Woody debris increases the complexity of stream habitats by physically obstructing 

waterflow. Trees extending partially across the channel deflect the current laterally, 

causing it to widen the streambed (Zimmerman and others 1967). Sediment stored 

by debris also adds to hydraulic complexity, especially in organically rich channels 

that are often wide and shallow and possess a high diversity of riffles and pools in 

low gradient streams of alluvial valley floors (Keller and Swanson 1979, Keller and 

Tally 1979). Even if the stream becomes so large that trees cannot span the main 

channel, debris accumulations along the banks cause meander cutoffs and create 

well-developed secondary channel systems (Keller and Swanson 1979, Swanson 

and Lienkaemper 1982). Debris also creates variation in channel depth by producing 

scour pools downstream from obstructions (Hogan 1985, Keller and Tally 1979). 

Wood therefore maintains a diverse physical habitat by (1) anchoring the position of 

pools along the direction of the stream, (2) creating backwaters along the stream 

margin, (3) causing lateral migration of the channel and forming secondary channel 

systems in alluvial valley floors, and (4) increasing depth variability. 

Large, fallen trees affect live vegetation along watercourses. Trees carried by 

floodwaters can severely batter live plants on a flood plain, but normally only in a 

narrow belt along the immediate channel. Large, stabilized pieces of wood, on the 

other hand, protect riparian sites where alder and other species of plants can 

become established. 

72 
Figure 3.23-Note the large pieces of wood on the flood 

plain, especially in the lower right corner where stable wood 

has formed a protected site that has allowed the alder to 

grow. 

Live vegetation eventually stabilizes a stream channel. Features, such as gravel 

bars, also become stabilized and enriched with fine sediments and organic materials 

as plant root systems develop and the stems resist the flow of water and reduce its 

velocity. 

Fallen trees protect thickets of vegetation on exposed channel bars. Alders growing 

in channel bar areas not protected by down trees are repeatedly pruned heavily by 

floating woody debris and moving bedloads (Swanson and Lienkaemper 1982) 

(fig. 3.23). The down trees that protect the outer edge of a thicket and those in the 

thicket itself create local environments of quiet water where fine sediments and organic debris are deposited during high flows. This debris, coupled with leaf and 

woody litter from the stand, boosts soil development and vegetative growth. The 

large, fallen trees thus help a stand to reach a stage of structural development that 

allows it to better withstand floods. Fallen trees on gravel bars also provide sites 

where some stream-transported species of hardwoods and shrubs can reroot and 

grow. 

Stream restabilization after major floods, debris torrents, or massive landslides is 

accelerated by large, woody debris along and within the channel. After wildfire, 

while the postfire forest is developing, an aquatic habitat may be maintained by 

large, woody debris supplied to the stream by the prefire forests (Swanson and 

Lienkaemper 1978). In many instances, however, streamside salvage logging 

destabilizes channel structure and, thereby, the quality of the habitat. 

73 
Wood as Habitat 

Sites of high biological activity and maximum habitat diversity are preferred spawning 

and rearing areas for salmonids. In the Pacific Northwest, many such zones of sediment and debris are located where a first-order channel debris torrent has entered a 

third- to fifth-order stream. 

Animal associations on woody debris in aquatic systems vary from those restricted to 

living on the wood to those using it only opportunistically. The sequence of colonists 

parallels the stage of wood decay. New wood entering a stream is used primarily as 

habitat, colonized by a community of algae and microbes that in turn provides food 

for a group of insects called grazers or collectors. This type of feeding does not significantly affect the structure of the wood, but colonization of the superficial layer by 

fungi softens wood enough that it may be abraded and ingested by invertebrates that 

scrape their food off surfaces. Most important, however, the wood becomes suitable 

for obligate wood grazers and the more generalized wood shredders, such as caddisflies and stoneflies, which eat fungal-infested wood. These activities result in a sculptured surface texture that provides habitat for many organisms. Decades of fungal 

colonization and growth soften the wood and allow oxygen to penetrate. Invertebrates that bore into the internal matrix of a fallen tree speed the decomposition 

process by consuming the wood and by transporting microbes into the tree. In the 

final phase of decay, detritivores, such as earthworms, penetrate the material; continued decomposition then resembles organic matter in soil and damp, terrestrial 

habitats (Anderson and others 1978, 1984; Dudley and Anderson 1982) (fig. 3.24). 

Some wood that enters a small stream is already altered by fungi and other terrestrial organisms. Such preconditioning allows more rapid internal colonization by aquatic microbes and invertebrates and thereby shortens the aquatic decomposition 

process. Decomposition is also faster in large streams during periods of high water 

because physical abrasion removes softened tissue as the wood is transported or 

deposited in the stream. Rotting wood cannot retain enough structural integrity to 

provide a substrate for aquatic invertebrates during the final stages of decomposition 

except in small headwater streams or in backwaters of large streams. 

Figure 3.24-A model of wood-aquatic insect interactions in a 

small stream (redrawn from Anderson and others 1984, with 

permission). 

74 
Wood quality and texture help determine the kinds of organisms that will colonize a

piece of wood. The species of wood, degree to which it is waterlogged, and decay

class all affect the quality. The extent of colonization by terrestrial fungi and woodboring insects also influences the attractiveness of the wood once it enters the water

because such activity is closely associated with decay class.

The ecological role of wood-eating aquatic invertebrates is limited compared with

that of terrestrial systems and marine environments. The three most important woodprocessing invertebrates in Oregon streams consume about 2 percent of the available woody debris per year in small streams (Anderson and others 1978, Steedman

and Anderson 1985). Wood processors are more abundant on hardwoods than on

conifer wood. Microbial activity and nitrogen content are greater in decaying alder

than in decaying conifer wood, a nutritional difference that helps explain the higher

abundance of processors in hardwoods.

Summer populations of salmonids in western Washington streams flowing through

old-growth forests have been compared with those in recently clearcut areas (Bisson

and Sedell 1984). Total salmonid biomass increased after logging, but species richness declined to a population of only steelhead trout, most less than 1 year old.

Coho salmon and cutthroat trout, between 1 and 3 years old, were proportionately

less abundant in logged areas (Bisson and Sedell 1984). The shifts in species composition and age groups are related to habitat changes after logging of old growth

and removal of large, stable, woody debris from the stream channel. Stable debris

declined and unstable debris increased in the years after the 1976 Washington Forest Practices Act that mandated immediate removal of debris after logging (fig. 3.25).

Pool size decreased and riffle size increased after old growth was clearcut and the

stream channel cleared. Numbers of pools and riffles per unit of stream length declined after logging, which suggests that normal stairstep stream profiles had been

reduced to a more even gradient (fig. 3.26).

Coho biomass in coastal Oregon streams is directly related to pool volume. Large,

stable, woody debris is preferred as protective cover by young coho salmon, yearling

steelhead, and older cutthroat trout, particularly in high-gradient river systems (Bisson

and others 1987; Bustard and Narver 1975a, 1975b; Everest and Meehan 1981;

Lister and Genoe 1979; Nickelson and others 1979; Osborn 1981; Sedell and others

1982a, 1982b, 1985).

Most salmonid species use different habitat in winter than in summer. Large, stable,

woody debris is important winter habitat for coho salmon, steelhead trout, and cutthroat trout because it enhances the use of other habitats within pools. All species

prefer pools during base streamflows in winter, but the level of preference is determined by pool quality and abundance of woody debris; the more woody debris, the

more fish use the pool. Large, stable debris also attracts fish to pools along the

stream edge rather than to those in midchannel.

During winter floods, the pool-riffle sequence or stairstep stream profile becomes a

continuous, high-velocity torrent, in which there is little protection for salmonids from

moving bedload sediment or swift, turbulent waters. During these brief flood periods,

slack water refuges are associated almost exclusively with debris as fallen trees and

standing vegetation in riparian flood plains. All three species of salmonids enter these

75
Pieces greater than 

10 feet long 

(mostly stable) 

Pieces less than 

IO feet long 

(many unstable) 

50 

Valley wall streams 

Valley floor streams Ii 25 

Number 2. 

per110 

20 

yards 

I5 15 

10 10 

5 5 

Figure X25-Effects of stream cleaning on the relative abundance of stable and unstable debris in steep valley wall 

streams and low-gradient valley floor streams in southwestern 

Washington; after implementation of the Washington Forest 

Practices Act; adapted from Bisson and Sedell (1984). Number of sample sizes is indicated on each bar. 

Old growth q 

Clearcut q 

Volume 52 

(cubic (number/O.&? 

“artId ,_.__, 1 Frequency mile1 '7 

39 120 

26 80 

13 40 

0 0 

I 

fll 33 *a *s *,tl f23 *xl f27 

“&3”.202 nrnn.23, n.12 n=r3 “.I2 “=I3 

Pools Riffles Pools Riffles 

Figure 3.26-Comparison of volumes and frequencies of 

pools and riffles in streams in old-growth forests with streams 

in recently clearcut areas; 95percent confidence limits and 

sample sizes are indicated on each bar. 

debris-enhanced refuges until streamflows subside. Large, woody debris may also 

expand the feeding space by creating or enhancing areas of slow-moving or standing 

water in organic-rich flood plains, even along the smallest streams (Bustard and 

Narver 1975a, 1975b; Koski and others 1985; Murphy and others 1984). 

76 
Table 3.7-Juvenile chinook and coho salmon densities from different 

woody habitat types in the main channels of the Chickamin River, 

southeast Alaska, March-April 1984 

Average number 

of salmon 

Woody habitat Number of 

type sample sites Chinook Coho 

No woody habitat, 

slack water along edges 3 5 8 

Rootwads without boles, 

stumps 12 56 50 

Single downed trees, 

rootwad and stem 14 87 90 

Log jam, 

several downed trees 7 292 195 

i 

iis 0.53f0.13 

1 i =0.07*0.05 

ii = 0.50f0.32 

Plugged Unplugged Other 

Il.9 kl 1 n=s 

Figure 3.27-Densities of coho salmon in Upper Queets River 

side-channels, which are capped or plugged at the head by 

cobble and organic debris. Plugged side-channel areas represent 58 percent of total side-channel habitat; unplugged sidechannels, 31 percent; and intermediate side-channels, 11 percent. Bars represent 95percent confidence intervals. 

Almost all juvenile anadromous fish in large rivers are reared on stream edges in a 

wood-rich environment (table 3.7 and fig. 3.27). Whole fallen trees or debris jams 

offer more productive, more diverse habitat than that around rootwad or stump habitats (Canadian Fisheries and Marine Service and The International Pacific Salmon 

Fisheries Commission 1979; Cornelius and Siedelman 1984; Sedell and others 

77 
tb I 3 

62-/-{ Hypothetlcal channel value based on 

flow in single channel 

I I I I 1 

0 

900 

600 

200 

00 

2000 4000 6000 EOO( 

Discharge (cubic feet per second) 

Figure 3.28~-Relation between discharge and selected rearing indices in the Morice River. 

1982a, 1984). Essentially, the hydraulic forces around any rough element such as 

fallen trees or stumps mainly determine the quality of fish habitat. Relations between 

discharge and wet debris jams can be quickly constructed to determine changes in 

fish habitat quality caused by salvage operations or water diversions (fig. 3.28). 

78 
Decomposition and Trees falling in streams decompose at different rates and in different patterns than

Nutrient Cycling those that fall to the ground. Wood decomposes more slowly in water than on land;

waterlogging prevents deep penetration of oxygen into the wood. The fungi and invertebrates that cause the most rapid decomposition of fallen trees on land are also

strongly aerobic (Triska and Cromack 1980). Waterlogged parts of fallen trees decompose in thin (0.25 inch) surface layers. As the decomposed surface is grazed or

abraded, oxygen penetrates farther into the wood, and that area becomes food for

the decomposers. If only part of a fallen tree is constantly in contact with water, that

part decomposes slowly, but the exposed part may decompose rapidly because neither low oxygen nor extremes of moisture limit decomposer activity. Trees that fall in

very small streams may contact water only during the rainy season when streamflow

is highest. Low stream level and air drying the rest of the year may speed wood

decomposition.

The concentration of essential nutrient elements increases as large pieces of wood

decompose. Nitrogen increases primarily through biotic use of the carbon and

through nitrogen-fixing micro-organisms. Nitrogen fixation on fallen trees in streams

accounts for 5 to 10 percent of the annual nitrogen supply to the stream (Triska and

others 1982). Although bark decays more slowly than wood, the tannins in Douglas

fir bark do not affect nitrogen fixation (Baker and others 1983).

Although rates of biotic wood processing differ in stream systems from headwaters

to mouth (terrestrial to marine) (table 3.8), the slow decomposition of wood in freshwater streams maximizes the influence of wood on stream stability and as habitat.

As we understand better the critical function of large organic material in streams and

rivers, we realize that productivity of aquatic habitats depends on the biological diversity provided by a continuous supply of coarse woody debris.

79
Table 3.8-Processing rate of large woody debris in the forest floor, in 

streams, and in estuarine habitatsa b 

Organism 

Microbes 

Forest floor (fast) 

Rot fungi diverse 

and abundant 

Stream (slow) 

Aquatic 

hyphomycetes 

(rot fungi, 

virtually absent) 

Estuary (fast) 

Fungi minor 

or absent 

Invertebrates: 

Insects Diverse and abundant, Few species Absent 

including gallery- (for example, Lara, 

forming social Brilla (Tipulidae), 

insects no social insects) 

Others Oligochaeta important 

in later forms 

Absent Annelida, 

Mollusca, and 

Crustacea 

diverse (some) 

boring forms 

with cellulase) 

Vertebrates Gallery or destroy 

wood in search of 

invertebrate food 

Absent Absent 

Environmental 

controls 

Temperature, moisture, 

and oxygenC 

Temperature 

and oxygenC 

Temperature 

and oxygenC 

a Adapted from Cummins and others (1984). 

b Hardwoods decompose faster than conifers. 

’ Lignin little decomposed anaerobically. 

80 
nds in young-growth sites are red alder, which 

has a shallow root system and low resistance to 

undercutting. 

would have been a candidate for stream cleanup 

in the 1960’s and 1970’s because of the slash. 

Figure 3.1 g--Woody debris creates many of the 

pools in Pacific Northwest streams. 

Figure 3.21-Accumulattons of small debris behind one large piece of debris often create a 

longitudinal, stepped profile. 
This page was intentionally left blank
Chapter 4. What We Know About Large

Trees in Estuaries, in the Sea,

and on Coastal Beaches

Jefferson J. Gonor, James R. Sedell, and Patricia A. Benner

Summary

Introduction

Coarse woody debris is an important part of estuarine and oceanic habitats, from

upper tidewater of coastal rivers to the open ocean surface and the deep sea floor.

An estuary is a body of water at the coastal end of a river system, in which freshwater mixes with saltwater before it enters the ocean. An appreciably wider shallow

basin or embayment with extensive tidelands is in the estuarine section of most

Pacific Northwest river systems. In some systems with large flows and narrow, deep

channels, such as the Rogue River in Oregon, the truly estuarine region is confined

to a short reach upstream of the river mouth. Fallen trees in streams or within reach

of flood or tidal waters move downstream to enter estuarine and marine systems.

The estuarine portion of the ecosystem supports important environments and habitats

including those of people, most of whom live around the lower ends of river systems.

The ecologic and economic role of woody debris in these ecologically complex,

productive systems is not well known.

Origin and History During the late Pleistocene, eustatic sea level was about 325 feet lower than it is

of Pacific Northwest today. Pacific Northwest coasts were not glaciated, and rivers excavated deep

Estuaries valleys in the flat, exposed coastal plain. Sea levels rose after the close of the

Pleistocene, and the coastal plain was submerged to form the present Continental

Shelf. The seaward ends of many of these river valleys became flooded, and

sediments accumulated in former meanders in the rivers’ old flood plains. The main

channels of these drowned rivers remain as the central, deeper channels of modern

estuaries that retain the elongate, sinuous topography of a river in its flood plain

valley. Channels are relatively shallow for most of their length.

The position and configuration of estuaries, no older than 10,000 to 15,000 years,

remain dynamic, but the physiography has changed. Estuaries have long existed on

the continental border of the Pacific Northwest, and they have moved across the

Continental Shelf and present coastal plain in response to fluctuations in sea level

changes.

Today’s estuary continues to accumulate sediments in the former channels and on

the flood plains, usually river-derived silts and muds in the upper reaches and

increasingly sandy material near the mouth. Estuarine tidal flats and marshes occupy

the former flood plain areas along the drowned river valleys that are now estuarine

embayments (fig. 4.1).

83
Figure 4.1--An Oregon estuary: Coquille River marsh at Bandon, 

1985 (photo, courtesy of Tony Howell). 

Figure 4.2-Lower estuary, Tillamook, Oregon, 1871 (photo, courtesy 

of the Oregon Historical Society, negative ORH 52608). 

History of Wood in U.S. Government reports and early visitors’ journals of the Pacific Northwest 

Northwest Estuaries documented great amounts of large wood in the estuaries and on the beaches at 

and Coastal river mouths. These mid-1800 accounts describe the quantities and size of the drift 

Beaches trees, also called “snags,” that significantly exceeded present amounts of woody 

debris in the lower portions of river systems and beaches (fig. 4.2). 

Coast survey reports in the 1850’s recorded that many of the drift trees in the lower 

Columbia River were as large as 150 feet long by 13 to 18 feet in circumference; the 

largest was 267 feet long (Secretary of the Treasury 1859). Swan (1971) also 

reported drift trees as large as 250 feet long by 8 feet at the base, with a root span 

of some 20 feet, on the beach near the mouth of the Quillayute River in the 

Washington territory. 

84 
EXAMLNATION OF JUNE lSS4, 

JettyConslrucllon. Shoretillre-~hdChn~ulcL 

Figure 4.3-Driftwood at the mouth of the Coquille River; adapted 

from U.S. Army Corps of Engineers historical map (Report of the 

Secretary of War 1884). 

The U.S. Army Corps of Engineers reported that Northwest estuarine shorelines and 

river-mouth beaches had often been covered with driftwood in the 1870’s, as was the 

mouth of the Coquille River in the 1880’s (fig. 4.3). 

For several years after the coastal areas were settled in the 1850’s and 1860’s, 

roads were limited and land travel was impractical, especially in the winter. The 

coastal rivers were under the influence of tides for 12 to 40 miles from their mouths 

and had a low-gradient, deep channel along which commercial boats and log rafts 

could travel. Slowing currents and stormwind patterns, however, created zones of 

wood deposition in the estuaries. Many snags and sunken driftwood presented major 

obstacles for river traffic. The Corps’ responsibility on many rivers during the late 

1800’s was to improve and maintain the navigability of the portions of the rivers 

deemed to be economically important (table 4.1). 

85 
Table 4.1-Snags removed from rivers by the U.S. Army

Corps of Engineers, 1891-1917a

River

Number of

snags removed Related activities

Tillamook River,

12 river miles

Coos River,

22 river miles

Coquille River,

40 river miles

9,829+

8,591+

6,407+

86+ overhanging trees cut

1,751 boulders blasted

81 scow loads of drift

(1891-93)

a Reports of the Secretary of War (1891-1921).

The wood-removal operations by the Corps represented only a portion of the total

wood pulled from the lower river systems. Gill-net fishers formed teams to remove

wood that threatened to tear fishing nets. Local landowners and later, port

authorities, also worked to maintain channel navigability.

Sources of Wood

For Estuaries and

Beaches

Driftwood is found throughout an estuary, both in the channel and on mudflats and

higher vegetated areas. Currently, the greatest concentration of woody debris is

found along the shoreline of an estuary out of reach of tidal water. The most

stationary wood is in the marshes, or at least partly buried in the channel.

Driftwood deposited in marshy areas between the main channel and the shoreline

in the lower Nehalem estuary is estimated to have 50 percent fewer pieces and

60 percent less volume than in 1939. Stranded wood in the marsh in 1939 probably

included many escaped lumber company logs that had been floated downriver or

held in booms.

Another human-related source of wood is the many pilings and associated wood

structures. Port authorities estimated that nine estuaries in Oregon in 1986 had at

least 15,000 maintained pilings and thousands more wood structures-old stubs from

abandoned log pens and channel projects, old mill pilings, and remnant docks. This

wood can be considered a partial substitute for the snags that naturally occurred

before the late 1800’s.

Streams and rivers have long supplied estuaries and beaches with wood, and most

of the material was transported downstream during higher flows. A captain in the

U.S. Army Corps of Engineers in 1897 noted of the Coquille estuary, “It has always

been difficult to keep this portion of the river open. The drainage area is densely

wooded, and every freshet brings down many stumps, logs and trees; these lodge

and arrest sediment, forming shoals.” (Report of the Secretary of War 1894-95).

86
Watersheds annually replenished wood in the lower portions of the river basin and

often floated wood into the ocean, from which it washed up onto the beaches. The

lower river and estuary banks (riparian corridor) probably were the most common

sources of the largest driftwood in the bays. In the 1960's, the banks of the upper

half of the Coquille estuary were lined with mature hardwoods that made travel on

the Coquille like walking “dim aisles in ancient cathedrals” (Dodge 1898). In the

Tillamook River system in 1904, the U.S. Army Corps of Engineers cut down all

overhanging trees along the banks of the estuary in an attempt to alleviate the woody

debris problem (Report of the Secretary of War 1904-5).

The woody vegetation along many river corridors was cut in the 1800’s to clear land

and for a local source of wood. Upstream, the riverside forests were among the first

to be commercially harvested because the logs could be floated down the river to the

ports at a time when no other transportation was available (Sedell and Duval 1985).

Major sources of large wood for estuaries and beaches along the Northwest coast

were exhausted by 1920.

The ocean is another source of driftwood in estuaries and on beaches. Winter storms

blow ocean-transported wood into river mouths and onto coastal beaches, generally

north of the debris’ origin. Some of the woody debris may be buried for long periods

by river-bottom sediments in the estuaries or in sandy spits on the coast, but much of

the wood probably remains fairly mobile. Other driftwood is deposited on the

marshes and along the higher ground of the estuary boundaries, where it remains

until it decomposes.

Flow Regimes in

Pacific Northwest

Coastal Estuaries

Estuarine tidal exchange and streamflow features govern the transport and retention

time of woody debris and create salinity gradients. This physical regime in turn

affects the distribution of marine wood-boring animals and their degradation of wood

in these estuaries.

Tide affects river level much farther upstream than the penetration of even the most

dilute seawater at the highest tides. This hydraulic effect causes river levels to rise

and fall and can even reverse the direction of flow in the reach referred to as the

“tidal river.” Its farthest upstream extent is the “head of tide.” This effect, present

throughout the year, increases the rate of transport of floating woody debris faster

than might be expected and increases the chance that wood stranded on the

shoreline by freshets will be reached by subsequently higher tides and be returned to

the downstream flow. Tidal reaches for Oregon rivers vary; the two longest tidally

influenced river sections are those of the Columbia (140 miles) and the Coquille

(40 miles) (table 4.2).

The most distinctive environmental features of estuaries along their length are the

horizontally created gradients of salinity and temperature caused by the mixing of

fresh river water with ocean saltwater; such gradients are vertical at times, going

from fresh to saline conditions as depth increases. The salinity gradient along the

length of an estuary varies greatly over time because of the twice-daily ebb and flow

of the tides and the seasonal changes, such as winter floods’ moving the freshwater

seaward. These variations are greatest in the middle of the estuary where salinity

conditions are intermediate between the upper freshwater and lower saltwater.

87
Table 4.2-Tidally influenced reaches of major coastal Oregon riversa

Head of tide

River and estuary (river mile)

Alsea 16

Columbia 140

coos 27 (both Millicoma and South Fork Coos Rivers)

Coquille 40

Necanicu m 3 (Necanicum River) and 4 (Neawanna Creek)

Nehalem 9

Nestucca 7

Rogue 5

Siletz 22

Siuslaw 25 (Siuslaw River); and 7 (North Fork Siuslaw River)

Tillamook 7 (Tillamook River); 4 (Trask River); 2 (Wilson River);

1 (Kilchis River)

Umpqua 27

Yaquina 26

a

 Adapted from Percy and others (1974)

Seasonal

Stratification and

Flushing

The density differences between freshwater from streamflow entering an estuary and

seawater entering from the mouth can result in vertical stratification of the estuatine

water mass. In a density-stratified estuary, a low salinity, low density, mixed surface

layer flows toward the sea, and the denser, more saline, seawater originating at the

mouth flows upstream near the bottom. This bottom flow replaces the seawater that

is entrained and mixed upward, along the length of the estuary, into the surface

outflow. This upward mixing continually increases both the volume and salinity of the

upper layer as it flows down the estuary.

The presence and extent of vertical-density stratification vary seasonally in Pacific

Northwest estuaries, mainly during the rainy winter season when streamflow dominates estuarine hydrography. Winter floods may produce vertical stratification even

in the lower segment of the estuary near the mouth; at this season, the upstream

flow of saline, ocean water is strong near the bottom and the downstream flow of

dilute, mostly riverine water is strong at the surface. The near-bottom flow of marine

water weakens gradually in the upstream direction and finally ceases at some point

upstream. Flows in the upper estuary above this point are downstream near both the

bottom and the surface.

The “null point” in the system in short-term subsurface transport of water and

suspended materials, including woody debris, is in the midestuarine region where

near-bottom flow is not appreciable either upstream or downstream. Its exact position

varies with the volume of river discharge. Below this null point, water and sediment

may be transported upstream along the estuary bottom. At and above it is a region of

increased turbidity and sedimentation as suspended riverine sediments enter a

region of decreased velocity and flocculation. Woody debris may be incorporated into

sediments in the estuarine channels of this zone, to be periodically remobilized and

flushed farther down the estuary during periodic winter floods when increased

88
rivet-flow moves the null point downstream. In summer, floating wood might be

retained in the upper estuary, moving downstream only during tidal cycles with the

greatest vertical range. In winter, the hydrographic regime favors downstream

transport along the entire estuary.

Water in Pacific Northwest estuaries is not strongly density stratified in summer when

seasonal rainfall and resulting streamflow are at a minimum and tidal exchange

dominates the estuarine hydrographic regime. The relatively great tidal range of the

region results in enough volumes and energy to mix the estuary vertically through

most of its length. In summer, difference between surface and bottom water at any

point is much less than in winter.

Pacific Northwest estuaries typically have a large proportion of tidelands-to-subtidal

area that results in a high exchange ratio (Johnson and Gonor 1982). This is the

ratio of the tidal prism (intertidal volume) to the total high tide volume of the estuary

and is proportional to flushing time if flow is not restricted. Many of the known

flushing times are fewer than 10 days in summer. Because of the length of the

estuaries compared with the cross section of the mouth, however, these estuaries

are “choked.” The lower well-mixed sections flush rapidly in the larger estuaries, but

the upper regions may take two to four times as long to flush. Successive upstream

segments of the estuary take longer to flush, and at one point in the upper estuary

the water present at high tide cannot reach the estuary mouth and exit during a

single ebbing tide. Most of this water from the upper reaches is returned on the

succeeding floodtide to the region of its previous position. This is a seasonal null

point. Above this point, the water mass is only gradually replaced by streamflow and

tidal mixing, so that it attains a characteristically high salinity in summer and an

elevated temperature in shallow areas from warming by the sun.

Both floating and suspended woody debris are retained longer in upper estuarine

regions with the longest flushing times, whereas floating wood in the lower segments

exits more rapidly. Marine wood borers adapted to the annual salinity and temperature regime of the upper reaches grow and reproduce rapidly at the warm temperatures reached above the summer null point. Decreased flushing also increases

the chance that the dispersion stages of wood borers will be retained longer in the

upper estuary and thus increases their chance of encountering new wood that is also

retained longer in the upper estuary.

Velocity of ebb tide current may be high at the mouth of Northwest estuaries (Bourke

and others 1971). Maximum ebb currents may be 6 knots per hour at the mouth of

the Columbia River, as much as 7 knots at Coos Bay, and 5 knots at the entrance to

Grays Harbor-sufficient to move floating wood rapidly away from the immediate

coast and into the coastal current system.

A tidally related, clockwise rotating eddy has been identified just off the mouth of the

Columbia River (Barnes and others 1971). The eddy is strongest at ebb tide and

brings floating material onshore just north of the river mouth. Large rafts of drift trees

off the mouth of the Columbia River, noted in the historic record of early explorations,

may have been related to this eddy. Such an eddy would have collected trees

washed out of the Columbia and retained them in the near-shore ocean.

89
Marine,

Wood-Degrading

Organisms

lsopods

Much of the water leaving the lower estuary on the ebb tide mixes with outside

ocean water and is moved away from the mouth by the longshore current (Johnson

and Gonor 1982). The water re-entering the lower estuary on the incoming tide is

thus mostly oceanic in temperature and salinity. Outside ocean water is thoroughly

mixed with water within the estuary during every tidal cycle below the summer null

point. The summer and, to a lesser degree, the winter environmental regime of the

lower parts of Pacific Northwest estuaries closely resembles that of the cold nearshore ocean. The marine wood borers of this lower estuarine region cannot tolerate

upstream conditions in summer, where the water is warmer, less saline, and more

characteristic of southern waters. Because of longer water retention times in the

upper estuary, the colonization and survival of warm-temperate wood-boring species

are favored once they are introduced.

The fate of trees entering estuarine and marine portions of the ecosystem is mainly

determined by organisms that degrade the wood and recycle its nutrients and

energy. The kinds of organisms involved and their relative roles in marine and

terrestrial environments vary widely. Marine organisms known to degrade wood

entering the sea belong to taxonomic groups different than those dominating this

process in terrestrial and freshwater environments. They are not as diverse as those

in terrestrial environments, and the relative roles of micro-organisms and animals in

initial attack on cellulosic materials differ. Marine fungi and bacteria appear to play

minor roles in the initial invasion and degradation of wood in the sea. The major roles

in degradation of marine wood are played by a few genera of wood-boring crustacea

and a larger number of bivalve mollusks (table 4.3). In contrast to the fate of fallen

trees in terrestrial environments, wood in estuarine and marine environments is

rapidly attacked by animals, long before significant soft rot takes place; the animals

disperse it before, not after, microbial decomposition of its constituents.

Wood-boring isopod crustacea (gribbles) of the genus Limnoria are major reducers of

wood in estuarine and marine waters of the Pacific Northwest. Only two species are

involved, L. lignorum, the endemic northern species, and L. tripunctata, the

introduced species that is predominantly southern in distribution but is also found in

the upper reaches of Pacific Northwest embayments and estuaries. Limnoria

lignorum is a coldwater species that occurs in embayments and the lower reaches of

estuaries. It can reproduce in the cold outer coastal waters where L. tripunctata can

survive as adults but can rarely reproduce or establish new colonies.

Both species are typical isopods in appearance, resembling small, elongate pill bugs

of terrestrial environments. Limnoria lignorum is large; individuals average 0.012 to

0.016 inch long and 0.004 inch wide. Adult L. tripunctata are smaller, typically about

0.012 inch long and 0.004 inch wide. Although both gribble species are small

animals, they are major wood-deteriorating organisms in the sea because (1) they

live in dense colonies in interconnecting burrows in the surface layers of sound

submerged wood, and (2) they are abundant and widely distributed. They do not

attack rotted wood, but bore actively and continuously by removing small pieces of

fresh wood from the blind ends of their burrows and consuming them. All wood

removed by gribbles during burrowing is ingested. About 45 percent by weight is

used and the rest is voided as fecal pellets (Ray 1959a, 1959b). These small,

flattened, cylindrical pellets are composed of finely ground wood fibers lightly bound

together by a thin membrane of chitin secreted by the hind gut. Fecal pellets are

continually washed from the gribble burrow systems by respiratory ventilating

90
Table 4.3-Wood degraders in estuaries

Classification Organism Relation with wood Life History

Arthropoda; class, lsopods (gribbles,

Crustacea: or wood borers)

Limnoria lignorum

Limnoria tripunctata

(introduced)

Mollusca; class,

Bivalvia: Family,

Teredinidea

Bankia setacea

Teredo navalis

(introduced)

Shipworms (wood--

boring mollusks)

Family PholadidaeXylophaga species

Xylophaga

washingtona

Xylophagid borers

Burrow and live in wood

in inland marine waters

Ingest all wood excavated

during borrowing

65 percent by weight of

wood is voided as fecal

pellets

Bore and live in wood

located in coastal and

saline estuary waters

Line burrows with calcium

carbonate walls

Consume some of the

wood that is bored

Deeper, oceanic wood

borers:

Burrow and live in sunken

wood on ocean floor

Ingest wood as food

source and process it for

other marine benthic

organisms

Live in dense colonies in wood; as

many as 30 organisms per 0.4

square inch of wood surface

1- to 2-year lifespan

Burrow 0.4-0.8 inch per year in the

Pacific Northwest

Weak swimmers as adults; no

free-swimming larval stage;

juveniles or recently matured

individuals swarm from colony and

are dispersed by currents to other

wood; long-distance dispersal may

be by floating wood containing

colonies

Live in dense colonies in wood in

shallow marine waters

Bankia: lays eggs in water; pelagic

larval stage lasts 3-4 weeks at

12-15 oC and is dispersed by

currents; 7-month lifespan

Teredo: 1 O-week lifespan broods

developing eggs

Long-lived larval stage; high

reproductive rate; early maturity and

rapid growth; characteristics

suitable for effective use of an

unpredictable and transient food

source

currents created by the animals. The nonbuoyant pellets sink rapidly in still water.

They are light enough, however, to be easily dispersed by the typical wind-driven

turbulence and currents of estuarine and coastal shallow waters. Gribbles convert

wood in one step from the original massive, intact form to microscopic, nonbuoyant

particles freely dispersed in the environment and deposited in surficial sediments. As

individuals of a colony burrow deeper, the outer, riddled region of the wood with the

older galleries becomes waterlogged and softened by micro-organisms. Consequently, it is fragile and easily broken into small pieces by abrasion and wave action

that gradually removes the outer layers no longer occupied by the gribble colony.

Gribble population density in wood is high, as many as 30 animals per 0.4 square

inch of wood surface. Long-distance dispersion along the coast or between

embayments is mainly by colonies in wood that floats from one location to another.

91
Chemical reduction of wood by isopods.--Although gribbles remove a significant

fraction of the total weight of wood by passing it through the digestive tract, they do

not use all the major polysaccharide components with equal efficiency; and there is

no evidence that they can alter lignin (Ray 1959a, 1959b).

Both species of gribbles in waters of the Pacific Northwest are predominantly

intertidal or subtidal animals that principally attack wood located in the lower, saline

intertidal zone or the portions of large upright pieces, such as pilings, below midtide

depth. Gribbles are intolerant of sediment in their burrow system. When colonized

logs are rolled by waves across mudflats or sand beaches, the burrow systems

become clogged and the colony is reduced or killed. Such wood is readily reinvaded

if it is refloated by subsequent tides.

Wood-Boring Mollusks Other than gribbles, the only shallow-water, wood-boring animals in the Pacific

Northwest are two species of shipworms. These are the most important reducers

of wood in estuarine and shallow marine waters of the region. The most common

species of shipworm is Bankia setacea, a coldwater native to the North Pacific

found in the open coastal ocean as well as in embayments and the lower parts of

estuaries. Because of its abundance, large size, and rapid growth, B. setacea is the

major marine, wood-destroying animal in these waters. The other species is Teredo

navalis, a smaller, introduced warmwater species of restricted distribution in the

Pacific Northwest.

Shipworms are specialized bivalved mollusks that inhabit shallow water (maximum

650 feet) and coastal areas. They have elongated bodies and use toothed ridges on

their specialized shell valves for mechanically rasping their way into wood. As ship

worms bore into wood, they secrete a calcium carbonate lining to their burrows.

Bankia larvae first attach to wood by a byssal thread and penetrate the wood

within 48 hours. Cutting teeth develop on the larval shell after attachment, and the

metamorphosed larva begins to bore into the wood, burying itself completely within

24 hours.

These infestations, often so dense that their burrows nearly touch, can rapidly attack

and convert the interior of large, solid trees into finely divided wood powder that is

dispersed into the estuarine environment. The role of shipworms as agents of wood

conversion and dispersion in the carbon and energy cycles of Pacific Northwest

coastal waters has not been studied. Bankia sefacea is a highly opportunistic species

with rapid growth, a relatively short adult lifespan, a high reproductive output, and

widely dispersed, long-lived pelagic larvae capable of rapidly colonizing new wood as

it arrives in the coastal waters. In Pacific Northwest coastal waters, infestations of

wood by Bankia are intense.

Bankia uses the cellulose fraction of the wood with about the same efficiency as

gribbles. Lignins and the remaining cellulosic material are not digested but are voided

as finely divided detrital particles in fecal pellets. Shipworms must bore to grow, so

much of the bored wood is not ingested but is flushed directly out of the burrow as it

is ground into a fine powder. Shipworm fecal pellets are lightly bound with mucus

and easily break apart. The fine wood particles they contain are not buoyant but are

easily suspended. Shipworm wood borings thus become microdetritus, like those

from gribbles, and directly enter the detritus web.

92
Xylophagld Borers

Fungi

Bacteria

Deep-sea wood-boring bivalves (xylophagid borers) are found off the Pacific

Northwest coast. These borers quickly invade wood in the deep sea and grow

rapidly. Their boring activity converts the wood into fecal pellets that settle to the

sediment surface and attract other deep-sea benthic animals. Their conversion of

wood into a readily available detritus source supports the development of a complex

benthic community.

Like the shipworms of shallow water, the deep-sea xylophagids are opportunistic

species. They quickly colonize wood that, having been carried offshore, becomes

waterlogged and sinks to the deep-sea floor. In the North Atlantic, test boards on the

floor of the sea (5,948 feet) became infested with a dense population of two species

of xylophagids within 104 days (Turner 1977). These deep-sea wood borers have a

high reproductive rate, an early maturity, a high population density, and rapid

growth-characteristics suitable for effectively using wood that is an unpredictable

and transient habitat and food resource in the deep sea. Because adults die as the

wood is consumed and disintegrates, dispersion must be through an abundantly

produced, efficient, and long-lived larval stage that searches for wood at the

sediment-water interface.

Like shipworms, xylophagids use wood for both habitat and food. They are probably

the most important deep-sea organisms for converting wood into a finely divided

detrital source of food for other deep-sea benthic organisms. They also provide

locally abundant prey to deep-sea benthic predators.

Marine fungi degrade cellulosic materials, but their ability to rapidly or extensively

degrade large pieces of wood appears to be much less than that of terrestrial fungi.

Cellulolytic activity has been demonstrated, however, in some taxonomically diverse

marine species of Fungi Imperfecti and Ascomycetes. These same organisms have

been associated with soft rot attack and weight loss in experimental blocks of wood

placed in the sea (Jones and others 1976). Virtually nothing seems to be known

about their ecological roles in wood degradation and energy or nitrogen flow in

marine detrital systems. Marine fungi are not requisite for the initial attack on wood

by the primary marine wood-deteriorating organisms in Pacific Northwest waters.

Most of the fungi that break down lignin attack only the wood surface, no deeper

than one-eighth inch. Species of the fungal genus Luworthia, however, penetrate

deeply into wood and are more like terrestial wood-decaying fungi.

The role of cellulose-degrading bacteria in the sea is obscure, but many species of

marine bacteria have been identified as active degraders of cellulose (Kodata 1958).

Cellulose-decomposing aerobic bacteria are abundant in seawater and bottom

sediments and are widely distributed in the sea and estuaries. These organisms play

an important role as remineralizers of cellulose-containing organic matter, but their

exact role in marine and estuarine carbon cycles is not known. Some cause rapid

deterioration of cotton nets in the sea, and some colonize and attack submerged

wood. Cellulolytic bacteria in the digestive tract of the shipworm Teredo navalis are

probably responsible for the breakdown of ingested cellulose. Previous or concurrent

direct attack on wood by bacteria, however, is not a prerequisite to marine borer

activity. Bacteria seem to be important in the breakdown of finely divided wood

particles, but the intermediate ecological roles of cellulolytic bacteria in the

degradation of cellulosic detritus produced by marine wood borers have not been

evaluated.

93
Fallen Trees in the 

Tidally Influenced 

River 

High water, especially winter storm floods, brings large trees into the tidally 

influenced region of coastal stream systems. Tides influence water level even in the 

extreme upper region of the estuary where the salinity is too low for marine 

wood-boring animals to survive. Surface salinity is virtually zero, but bottom water 

may contain some salt in summer. The ecological functions of fallen trees in the tidal 

river water are much the same as those upstream, but many of the fish and other 

animals are different from those upstream. Fallen trees and logs are present in 

channels and on intertidal banks, including any freshwater marshes in the reach 

under tidal but not salt influence (Secretary of the Treasury 1859) (fig. 4.4). 

A large drift tree whose roots embrace a mass of hard clay or 

stones...may very readily be carried outward by the strong effluent 

current of the Columbia, and especially in the season of freshets; but 

when the current slacked the root of the tree would remain upon the 

bottom, sink into the sands, and continue stationary whilst the 

remaining movement of the current would be able to shift the loose 

sand and deposit it around the roots. 

Fallen trees influence the estuarine portion of the ecosystem, mainly through their 

physical properties as large masses; they form heavy, solid objects and firm 

substrates in an environment where the bottom consists mainly of fine sediment. 

Fallen trees in the tidal river segment of coastal stream systems create riffles and 

provide shelter from predators for upper reach fishes. Examples of common fishes in 

this section of Pacific Northwest estuaries are stickelback, sturgeon, starry flounder, 

and juvenile and adult salmonids. Fallen trees can also affect local waterflow patterns 

by creating turbulence and thereby affecting the sedimentation pattern and the 

formation of bars or mudbanks. Emergent parts of fallen trees stranded in the 

channel or partly or wholly on tidally exposed banks are used by water birds as 

refuge perches during daily rest cycles, or by predatory birds, such as herons and 

eagles, as hunting perches. 

i 

Figure 4.4-Rootwads help anchor driftwood (photo, courtesy of the 

Oregon Historical Society, negative ORH 45285). 

94 
Fallen Trees in the

Tidal River

Biological decay in the uppermost estuary (freshwater, but tidally influenced river

section) is slow, on the order of many decades, especially for trees partly embedded

or buried in typically anaerobic upper estuarine muddy sediments where attack would

be only from cellulolytic fungi. Unlike the saline lower estuary, there are no animal

groups to act as rapid degraders. Battering by trees rafted downstream on floods or

uplifted and carried by tides is probably the major force breaking trees into smaller

components. Rolling breaks branches, and trees are typically caught on tideflats by

stubs of broken branches.

Fallen Trees in the

Upper Estuary

Fallen trees are further transported by floods and tides from the tidal river into the

upper estuary system, that brackish, tidally influenced region above the summer null

point. Salinity in summer at both surface and bottom can be appreciable but less

than in the more marine lower reaches. Salinity in winter is very low, and most

marine animals not adapted to prolonged lower salinity cannot survive. Because of

lower streamflow and limited tidal flushing in summer, water temperatures in the

upper estuary are significantly higher than those in the lower reaches, so marine

wood borers are not present.

The gribble Liminoria tripunctata is found in marine waters from inland British

Columbia through the Puget Sound region and in all the major estuaries of the

Douglas-fir biome. The introduced shipworm Teredo navalis is established on the

Pacific coast in San Francisco Bay and in the inner parts of a few embayments on

outer Vancouver Island. It is more resistant to periods of lower salinity and higher

temperature than the native shipworm Bankia setacea and consequently can

establish populations in upper estuarine areas where Bankia cannot colonize. Trees

and logs caught in the channels, or stranded, or embedded in the banks and tideflats

of the upper estuary are soon attacked by the gribble L. tripunctata.

Attack by gribbles provides continuous and rapid physical breakdown of the wood

surface that reduces the radius as much as an inch a year and produces large

quantities of fecal pellets. The easily suspended fecal pellets are a carbon source of

the sediment surface and the midwater pelagic system. Gribbles transfer fine wood

particles to the carbon pool of the benthic sediment system by enormously increasing

the surface area of wood and effectively converting trees directly into nonbuoyant

wood powder. Further microbial degradation of gribble fecal pellets by cellulolytic

bacteria in the surface sediments may channel this carbon source into the benthic

detrital food web. The role of wood transferred to benthic and pelagic detrital systems

in the form of fecal pellets from marine wood borers has not been examined. Organic

detritus is the principal energy source for food webs in estuarine and shallow marine

benthic portions of the ecosystem; the principal source of this detrital carbon is debris

from macrophytes in the system. Some of the pelagic food web is also based on

detritus, and fecal pellets from gribbles are an appropriate size for direct ingestion by

zooplankton. Attack by marine borers dramatically increases the rate at which the

wood becomes waterlogged and sinks. The role of such wood as large, solid, inplace

objects is similar to its role already described for the upper estuary.

Sediment lodges in the extensive spaces of abandoned outer burrow systems of

gribble colonies, and some sediment fauna are found in the old, riddled wood. As the

surface area of the hardened wood increases, the older portions are invaded by

bacteria and marine lignicolus fungi that attack the remaining wood.

95
Recently arrived, buoyant trees and logs in the upper estuary are transported by river

floods and winter high tides to the extreme edge of the highest reach of winter high

waters, the highest of the year. This usually results in a dramatic strandline of large

trees and logs, sometimes in continuous rafts, in the upper or high salt marsh that is

the community type characteristically present at this tide level within the upper

estuary. Trees and logs function here as agents of disturbance in an otherwise very

dense, productive, and uniform plant community, the consequences of which we

discuss later (fig. 4.5, color).

Fallen Trees in the

Lower Estuary

The lower estuary, from below the null point to the mouth, is dominated by marine

influence. Its salinity and temperature range are nearer to those of the open coast

than to those of the upper estuary. Trees and logs here are degraded to smaller

detritus but have the same physical role as in the upper reaches of the estuary.

Trees and logs transported into the lower region of Pacific Northwest estuaries enter

a habitat too cold in summer for reproduction by L. tripunctata. Lower estuarine

salinity regimes, however, are sufficient for occupation and survival by the two

indigenous species of marine wood borers, L. lignorum and B. setacea. Both can

colonize wood for most of the year, and Bankia, in particular, has a high growth rate

and can significantly degrade large pieces of wood within 1 year. Between the two,

any stationary wood in the lower estuary is rapidly destroyed. The result, again, is

reduction of large masses of wood to a fine, nonbuoyant wood powder, most of

which is introduced into detritus-based food webs of the estuary. Both the mass and

the physical properties of trees are altered; waterlogging increases, and the surface

of the trees is converted into a friable mass of riddled wood rapidly abraded into

macrodetritus by waves and battering. Shipworm wood borings and fecal pellets

become microdetritus and directly enter the detritus web.

Fallen Trees in

Salt Marshes

Salt marshes are densely vegetated, low coastal wetlands at elevations within the

annual vertical range of regular tidal fluctuations. Plants of the salt marsh community

are capable of growing in saturated estuarine sediments and withstanding stresses

from salinity and tidal inundation. The requisite conditions of lower salinity, extensive

areas of soft sediments at high tide levels, and low wave energy are virtually

restricted to estuaries in the Pacific Northwest.

There are no true open coast salt marshes in the Pacific Northwest. Estuarine

marshlands have built relatively rapidly toward the sea by deposition of sediments

influenced mainly by modern economic activities. Extensive areas have been

removed from estuarine systems through diking for agriculture, pastures,

roadbuilding, and construction. Logging, road construction, and cultivation-all of

which disrupt watershed stability-increase sediment loads in rivers and streams and

result in increased sediment accumulation rates in estuaries.

Salt marshes are important parts of estuarine systems in the Pacific Northwest. Salt

marshes have very high annual plant production rates, a significant fraction of which

is exported to the rest of the estuarine portion of the ecosystem as plant detritus.

They also function as hydraulic buffers to flood and storm surges because of their

extensive area. Migratory waterfowl and juvenile fishes, especially salmonids, use

tidal drainage creeks in the marsh at high tide.

96
Eilers (1975) examined the role of trees in salt marshes of the Nehalem estuary in

Oregon through the use of historic charts and aerial photographs and by direct

observation. Information indicated that trees have long been important in salt

marshes. The upper margins of the high salt marsh were clearly delimited in 1939

aerial photographs by extensive and continuous piles of large drifted trees. Trees,

many of them large, were abundant enough to obstruct the channel in the period

around 1900. An island, which first appeared in the Nehalem estuary between 1875

and 1914, was covered with live trees and fallen trees associated with other changes

in topography. The island today stands 6 feet above tide level, illustrating the

sediment trapping ability of piles of down trees and associated vegetation.

Eilers (1975) found that circular-to-oblong depressions, 1.8 to 6.8 feet in diameter

and 0.8 to 1.6 feet deep, common in the high marsh at tidal elevations between 9

and 10 feet above mean low water were former resting places of large drifted trees

that had been moved about by extreme high tides. When drift trees remain in place

in marshes for long periods, the general elevation around them increases from

siltation and accumulation of organic matter. When these trees refloat during

unusually high tides, floods, or storm surges, the shallow depressions that remain in

the marsh increase habitat diversity; at low tide, these depressions are filled with

juvenile fishes. Refloated trees are an important source of disturbance that also

influences the distribution of marsh plant communities and plant succession

(fig. 4.6, color).

The relative mobility of large drift trees and logs in different parts of the high marsh

influence successional processes in opposite ways. A spruce/alder/willow wetland

forest community dominates the highest portions (9.4 to 9.8 feet mean lower low

water) of the salt marsh, slowly invading it as the progradation characteristic of

marshes in this region proceeds (Eilers 1975, Johannessen 1964). This forest

advances in some places by active colonization of stable piles of drift trees and logs

left on the high marsh by past storms. Large drifted trees embedded in the marsh are

colonized by terrestrial plant species unable to grow directly on the marsh soil

because of salinity. Most of the spruce in the high marsh were growing on nurse

trees, and few of the spruce roots extended into the marsh soil (fig. 4.7). In other

parts of the marsh exposed to winter storm waves, the forest edge was in retreat,

mainly because accumulations of drifted trees battered against the trees and upper

marsh shore at abnormally high tides (Eilers 1975).

Drifted trees in the upper marsh are exposed to a wet, predominantly freshwater

environment and resemble decaying fallen trees in terrestrial environments rather

than trees elsewhere in the estuary. If these trees remain in place, they are attacked

by wood-decaying fungi and show the typical sequence of internal rotting. Their

relation to nitrogen cycles in the upper marsh and to small mammals inhabiting this

environment is not known.

97
Figure 4.7-SItka spruce grow on nurse logs in Oregon coastal 

marshes. 

Use of Drift Trees in Much of the following information about birds’ use of emergent portions of drifted 

Estuaries by Birds trees and logs in estuaries is from Bayer’s (1978, 1983) extensive studies of birds’ 

and Seals use of estuarine resources in Yaquina Bay, Oregon. 

Bald eagles use trees and logs away from shore on tideflats and on sides of estuary 

channels; they avoid perching directly on soft mud surfaces. Because eagles forage 

from a central place, use of perches near shore rather than more distant, taller trees 

conserves the birds’ energy. They perch in places that provide good visibility of open 

channel water and of tideflats where they watch for opportunities to capture aquatic 

birds or steal prey caught by gulls and herons in the shallows on the tideflats 

(Stalmaster and others 1985). Drift trees on flats are more centrally placed in relation 

to potential food resources for eagles, so flight time to and from a foraging area is 

less (fig. 4.8). 

Green herons, great blue herons, and great egrets are predators that prefer to stand 

and wait for prey, principally fish, to pass by. They can wade in the intertidal flats 

only when the water is no more than 8 inches deep. Herons and egrets use drifted 

trees that remain partly out of water at times of high tide, as well as floating logs, log 

rafts, and booms as perches for resting and foraging. Great blue herons defend 

feeding territories on log rafts when they are available, virtually confining their feeding 

activity to these territories. They conserve energy by using emergent wood near or 

surrounded by water to combine two necessary daily activities-perching and 

foraging. Herons thus have more time for foraging than they would hunting for fish 

when the tide is low enough for them to wade in the shallows. When perches on 

tideflats or in the channels are not available, herons must alternate between perching 

in distant trees to rest and wading at low tide to forage, with flights necessary 

between perching and foraging locations. Herons in upper Yaquina Bay have 

established territories on log rafts floating along channel margins. These herons can 

avoid long foraging flights and require smaller feeding territories because the rafts 

are over deeper water than they could wade in; thus they can also catch larger fish 

found in deeper water than they could by wading on the flats where smaller fish 

usually occur. 

98 
Figure 4.&-Bald eagles choose to perch on mudflat objects, such as 

d&wood, rather than on the tidal substrate (photo, courtesy of Range 

Bayer). 

Cormorants and brown pelicans also require perches for rest between periods of 

foraging, and they prefer perches surrounded by water and away from the 

shoreline-wooden structures, such as piling, and stranded logs and trees. Small 

shorebirds that feed on tideflats at low tide and require perches for resting at high 

tide use any available emergent wood. 

Natural, old, drifted trees are more abundant in Siletz and Nestucca Bays than in 

some of the other Oregon estuaries; birds can nest in young trees growing on drifted 

trees and logs stranded in the intertidal area. Purple martins, which require rotting 

wood for cavity nesting, use tree butts sticking out of the flats at Siletz Bay. Because 

rotting trees on land near water have become scarce, suitable stranded trees 

become important resources for these birds. 

Gull-nesting areas within estuaries are uncommon today because of limited suitable 

nesting habitat. Pilings, humanmade structures that resemble formerly more 

abundant stranded trees, are used by gulls for nesting (Bayer 1983). 

Natural drifted trees in estuaries and the use of herring spawn by marine birds in 

Oregon estuaries are indirectly related. Herring that enter estuaries to spawn require 

solid substrates in the intertidal area for egg (spawn) attachment. In estuaries where 

the intertidal area and shore are predominantly soft muddy sediments, solid surfaces 

are limited. Masses of herring spawn are attached to red algae, rockweed (Focus), 

eelgrass, rock, shells, and pebbles on the flats and on any available wood, such as 

logs and drift trees, especially branches of trees stranded in estuaries. Using 

herrings’ preference for finely divided spawning substrate, Pacific Northwest Indians 

once placed brush and cut branches in the estuaries during the herring spawning 

season to collect spawn to eat. At present, suitable intertidal spawning substrate is 

limited in Oregon estuaries, and herring spawn becomes overlaid and crowded on 

the substrate. Crowding greatly reduces hatching success by creating oxygen 

deficiencies in the mass of spawn. Masses of excess spawn break free and are 

99 
rolled across the tideflats by waves to accumulate on beaches. Both this beached

spawn and the spawn remaining attached in place are eaten by birds, including

nonaquatic species, such as crows. Gulls feeding alone can consume most of the

spawn on a beach at low tide. During the herring spawning period in Yaquina Bay,

the total resident bird population increases from about 1,000 to 2,000 birds of each

species to a total of about 10,000 birds (Bayer 1980). To the extent that suitable

intertidal substrate, such as stranded tree branches, limits herrings’ spawning in

estuaries, the availability of herring spawn as food to birds associated with estuaries

is limited.

Rafted and stranded trees and logs away from the shoreline and undisturbed by

people are potentially important to harbor seals, which require haul-out areas for

resting out of the water. These seals now haul out on log booms and log rafts in the

channels of estuaries. The availability of log booms during the day increases the time

that suitable haul-out space is available to harbor seals. Without this type of

resource, seals can haul out on shore only at night when people are not present.

Natural rafts and drifted trees stranded on tideflats very likely were once also used

for haul-out by harbor seals and may have been one of the limiting resource for seal

populations in Pacific Northwest estuaries (Bayer 1981, 1985; Calambokidis and

others 1978).

Fallen Trees Rafted Aboard a seagoing vessel off the Northwest coast in heavy seas during a storm in

Out of Estuaries November 1852, James Swan (1857) reported:

The next morning we found ourselves about thirty miles to the

westward of the Columbia River, from which a huge volume of water

was running, carrying in its course great quantities of drift logs,

boards, chips, and saw dust, with which the whole water around us

was covered.

How much wood was historically transported to the ocean is not known, though it

must have been substantial at a time when most of the riparian zones along the river

corridors and in the watersheds were dominated by large conifers. Hundreds of

millions of board feet of logs and downed trees have come down into Puget Sound in

Washington and Georgia Strait in British Columbia from the rivers that drain the

Washington Cascade Range and the British Columbia coastal mountains. These

large quantities were joined by significant numbers of logs that were separated from

rafts in estuarine log storage areas or from towed rafts (fig. 4.9). More than 10 billion

board feet of logs are annually stored or travel in estuaries and lower rivers of the

Pacific Northwest from Alaska to California, including British Columbia (Sedell and

Duval 1985). A 1 -percent-escape rate would allow more than 100 million board feet

to enter the ocean from this source alone.

More than 2 billion board feet of wood is estimated to be annually transported to the

North Pacific ocean, an estimate believed to be conservative because large regional

storms were excluded from the calculation, and pieces of wood less than 10 feet long

were not considered (Sedell and Hansen, unpubl. data). Two billion board feet per

year is a small amount for the entire northeastern Pacific from San Francisco Bay to

Nome, Alaska. This is testimony to the retentive nature of rivers and estuaries, as

well as to the substantial reduction in volume and size of wood now entering western

streams.

100
Figure 4.9-Logs and other escaped wood added to driftwood in estuaries and on beaches (photo, courtesy of Jack’s Photo Service, 

Coos Bay, Oregon). 

Amounts of wood in rivers and estuaries in the past were high compared with today’s 

supply. In the past, sources of large, long trees were abundant; a large amount of 

wood was stored on beaches, in estuaries, and in rivers; and there were no dams on 

the rivers (fig. 4.10). A vast array of organisms have adapted to the use of this 

material. Some may find substitute habitats, but others-obligate feeders of wood in 

the ocean environment<annot. 

Today, only 7 of the 17 coastal port authorities in Oregon are directly involved in 

snag, stump, and debris removal in their estuaries. The sources of drift have been 

greatly reduced since the 1850’s, and the opportunities for wood to be retained in the 

lower estuary have also been reduced through diking, marsh filling, and 

channelization. Pilings create retention sites, but these sites are likely to be cleared 

of debris. 

Ocean Transport of 

Woody Debris 

The transport and fate of floating or sunken woody debris discharged from estuaries 

into the ocean is determined by regimes of coastal wind and current. Along the 

Oregon and Washington coasts, these regimes differ in direction and intensity with 

season, so that the direction of wood transported from the same estuary varies 

greatly. The California current flows south along the coast all year, a broad and slow, 

surface flow of about 0.2 knot per hour. During the winter, a second coastal flow 

known as the Davidson current forms and flows northward over the Continental 

Shelf, pushing the California current somewhat offshore. Its mean velocity is 0.35 

knot per hour and results from strong northerly atmospheric circulation. 

Prevailing coastal winds shift north-south direction seasonally, with short transitional 

periods of weak winds. Strong winds blow predominantly out of the southwest from 

October through April (Barnes and others 1971) (fig. 4.llA). Occasional periods of 

onshore winds during the summer move a shallow layer of surface water northward 

along the coast and toward the shore. Storm winds often beach large trees floated 

out of estuaries and northward along the coast. Redwood stumps from northern 

California are stranded on Oregon beaches when high tides and storm surges 

combine to cause unusually high water. 

101 
Figure 4.10-Beached wood in the late 1800’s often included cut logs 

as well as drifted trees (photo, 

Society, negative ORH 26616). 

courtesy of the Oregon Historical 

Figure 4.11-Nearshore currents transport wood north along Oregon 

coastal beaches (after Parmenter and others 1985): A. Summer 

circulation off Oregon. The California current, a broad,, shallow 

surface current, drifts slowly southward over the ContInental Shelf 

and slope during the summer. The California undercurrent is a 

narrow, fast-moving current flowing northward at depths greater than 

650 feet over the Continental Slope. B. Winter circulatron off Oregon. 

The fast-moving, relatively narrow Davidson current flows northward 

at all depths over the Continental Shelf. The California current, flowing slowly southward on the surface, is pushed offshore by the 

Davidson current. 

102 
Weaker coastal winds that are more constant in direction blow from the

north-northwest from May to September and create a nearshore current that flows

south and offshore (fig. 4.11 B). In contrast, when floods bring large quantities of

wood downstream into the coastal system, wind and currents keep floating wood

inshore and do not allow it to circulate in the open ocean. In summer, offshore

movement of water from the nearshore zone is balanced by upwelling of deep water

in a zone 5 to 10 miles from the shore. Complex shoreward movements associated

with these upwelling fronts may also entrain wood and retain it in the coastal region.

Fallen Trees Along

the Shore

Driftwood deposits of the Pacific Northwest differ in both kind and quantity from those

observed along other coasts. More important even than the great size of individual

trees or logs is the massiveness of the overall deposits, each of which may cover

many acres of beach to a depth exceeding 10 feet (fig. 4.72, color). The total

accumulation of driftwood between Cape Mendocino in California and Puget Sound

in Washington is estimated to be several million cubic yards or a few billion board

feet (Stembridge 1979).

Trees are driven ashore on sand beaches by wind and waves along most of the

Pacific Northwest coast. These trees form large piles of driftwood, once characteristic

of Pacific Northwest shores, until removed by extremely high water. They act as

barriers to wind-transported sand and can form the nucleus for at least a temporary

accumulation of sand. Drifted trees are often found deep in the base of large dunes

and spits when another cycle of waves erodes the sands.

Drifted trees play an important role in natural cycles of erosion and deposition of

beaches and foredunes along the Oregon coast. These cycles were examined by

use of a series of aerial photographs beginning in 1939 to study long-term changes

in the Siletz spit (Komar 1983, Komar and Rea 1976). There, erosional and

accretional episodes occur along segments of the shore 325 to 1,950 feet long. The

following sequence of events was identified:

1. Rip-currents begin to erode embayments in the foreshore. During periods of high

tides and high waves, the deepened embayments permit waves to reach the backshore area and the seaward edge of the foredunes, eroding a vertical scarp into

them.

2. Subsequent high tides deposit drifted trees and logs in the embayment at the base

of the scarp.

3. Lower energy waves build a broad, high “summer” berm in the embayment.

4. The criss-crossed mass of trees and logs behind the berm effectively trap sand

washed in by waves or blown onto the upper beach at low tide by the predominantly onshore winds.

5. Windblown sand continues to accumulate around the trees and logs, reestablishing the foredune, which becomes colonized by dune grass. The foredune often becomes reestablished in 10 to 15 years.

6. Dune reformation is eventually followed by another episode of erosion, repeating

the cycle and exposing trees and logs previously embedded in the dunes.

103
More evidence of the influence of driftwood on shoreline stability and accretion

comes from a study of the Alsea spit in Oregon (Stembridge 1974, 1979) and from

studies of the beaches of northern Puget Sound in Washington (Terich and Milne

1977). Recent changes were charted along Oregon’s 300-mile ocean shoreline, and

110 miles of stable sandy shore and 40 miles of prograding sandy shore were

identified (Stembridge 1976). Much of the stability and accretion was attributed to

changes in land-use during the 20th century that resulted in an increase in the

coastal sediment supply, in the deposition of saw-log driftwood, and in the

introduction of European beach grass.

Drifted trees may thus act as passive, stabilizing objects along coastal dune fronts.

Because trees shelter or shade some sand, colonizing plants often grow in the

moister sand at the base of stranded trees. Other plants, such as Sitka spruce, grow

on drifted nurse logs on the backshore. Driftwood not only provides beach stability

but contributes moisture and nutrients that appear to be necessary for the

establishment of woody vegetation (Stembridge 1979). The role of driftwood in the

maritime dune fringe community has not been well studied. Burrows of mice and

insects can be found around the highest, oldest, driftwood trees embedded in dunes

behind sandy beaches, particularly on shores in a prograding phase.

Trees beached on rocky shores undergo quite different processes. Winter storm

waves batter and pile up large quantities of driftwood against the sides of rocky

points and headlands. Such trees are highly abraded and roughly splintered, and

winter shores abound in the freshly broken fragments of these trees. Most of this

splintered and shattered material is partly waterlogged, and much of it is not buoyant.

It appears to undergo further direct grinding on rocks into coarse woody debris, some

of which lodges among and below rocks, whereas the greater part is washed into

deeper water by the waves. Rocky shores are thus another site of direct and rapid

degradation of large trees into small fragments capable of entering a detritus-based

system through physical rather than biological agents.

Trees have an important ecological role in rocky shore intertidal community structure.

Sessile plants and animals in this community compete for the major limiting

resource-attachment space. In the absence of other influences, the more successful

or dominant competitors gradually exclude others and occupy all surface space,

which results in decreased community diversity. Battering by trees at high tide during

winter storms is a significant force in opening up patches of unoccupied space, which

thereby contributes to the maintenance of a mosaic community of higher diversity

(Dayton 1971). Patches of attached organisms or those cleared by tree abrasion

produce a mosaic of different phases of colonization and thus prevent complete

occupation of all space by the competitive dominants, with concomitant reduction in

community species diversity. Disturbances of both physical (waves and trees) and

biological (grazing and predation) origin were the major forces that produced

structure and order in the space-limited intertidal community of rocky shores (Dayton

1971).

104
Figure 4.13-DrIftwood Beach State Park, San Juan Island, shows 

that some beaches are still (1986) covered with wood. 

As much as 50 percent of the trees along the rocky shores of San Juan Island 

showed saw-cut ends and were obviously from logging operations (fig. 4.13). About 

15 percent of the trees had intact root systems, indicating they originated from 

erosion of shores and streambanks. The remaining 35 percent of trees on these 

rocky shores were too worn to determine their origin. By contrast, at an open coast 

site on the Olympic Peninsula, less than 1 percent of drift trees were saw cut, 

indicating that most of the large accumulations of such wood in this relatively remote 

location were of natural origin (Dayton 1971). Even today, naturally derived trees play 

an important role in community processes on some rocky shores. This role is 

obviously proportional to their abundance and size, which once were greater than 

they are now. 

Present-Day Look Wood volume on coastal beaches varies between locations and fluctuates between 

at Wood on Coastal seasons. In winter, storms transport wood downriver into the ocean, then deposit it 

Beaches and in on the beaches. In other seasons, there may be a net loss of wood from the beaches 

Estuaries back to the ocean. 

Seventy percent of the volume of woody debris longer than 1.6 feet was lost from 

river-mouth beaches from 1970 to 1984 (Benner and Sedell, in press). 

Gone are the mature stands of trees that were the source of large driftwood before 

the late 1800’s. Wood is being used for fuel in home wood stoves, and the number of 

Forest Service free-use wood permits (fig. 4.74, co/or) issued by the Pacific 

Northwest Region for cutting cords of firewood have increased by more than 800 

percent from 1970 to the present (fig. 4.15). Forest practices regulations that directed 

the cleaning of wood from stream channels during logging operations in the 1970’s in 

the Northwest also reduced the source of woody material for estuaries and beaches. 

Fewer logs now escape from lumber operations and other human-related sources 

(fig. 4.16). 

105 
Number 

Of permlls 

Issued 

(Ihousands) 

Figure 4.15~Increase in Forest Service free-use permits for firewood, 

1974-82, 

Figure 4.16-Log boom stores logs in an Oregon slough in the late 

1800’s. Some logs escaped to the beaches (photo, courtesy of the 

Oregon Historical Society). 

Drifted Trees in the Floating trees can travel long distances and are quickly colonized by shipworms, 

Open Sea gribbles, and barnacles. When this moving wood sinks to the bottom of the ocean, it 

forms the primary energy base in a diverse community of invertebrates and functions 

as an island of productivity in an othervvise stable, low diversity, low productivity 

environment. Schools of small fish are also attracted to floating objects, including 

drifting trees and slow-traveling boats. The schools in turn can attract predator fish, 

such as tuna, and an ecological community becomes associated with the floating 

forms. 

106 
Transport and Fates Drifting trees that escape the inshore tidal currents enter the open sea. In winter,

nearshore currents along the Pacific Northwest coast transport trees northward.

Unless these trees are moved farther offshore, they will eventually be beached by

stormwinds. The direction of transport in the California current system is southerly

inshore in summer and offshore all year. If trees escape onshore transport and enter

the current, they are carried into the open sea where they may enter the westward

transport of the North Pacific gyre.

An inventory of driftwood along some beaches on the Hawaiian Islands showed that

most of the trees were from the west coast of North America (Strong and Skolmen

1963). The other trees were native to the Philippines, Japan, or Malaya. Even if

attacked by marine borers, large trees remain afloat for long times and, if they are

carried into the central gyre system of the North Pacific, may be transported for long

distances across the Pacific, to beach in such places as the Hawaiian Islands.

Ancient Hawaiian civilizations prized and preferred the huge Douglas-fir trees that

washed up on their shores. Local chiefs made double canoes from the large stems,

which were described by explorers and missionaries in the early 1800’s (Heyerdahl

1952, Strong and Skolmen 1963). The anthropological records show an integrating of

large, floated Douglas-fir and redwood trees into the customs and rituals of Oceania

cultures.

Biological Role of

Floating Trees

Large trees capable of remaining afloat for long periods of time are natural agents in

the dispersion of marine wood borers and attached, sessile plants and animals, as

well as of nonswimming mobile animals associated with these encrusting or “fouling”

species. Trees at sea are usually heavily laden with growths of such epifauna and

flora, including both attached species from the open sea and nearshore species

acquired in transit to the open sea. In addition, the water strider, the only insect to

have invaded the open sea and become pelagic, lives and lays eggs on driftwood.

Many pelagic fish species of commercial and recreational importance associate with

floating objects in the open ocean. Tunas in particular aggregate around trees and

logs and other flotsam. Both Japanese and American fishers routinely seek such

objects while fishing for skipjack tuna and yellowfin tuna in the eastern and western

Pacific (Inone and others 1963, 1968; Kimura 1954; McNeely 1961; Uda 1952), and

their success rate for tuna was well over 4:1 in favor of seines set around drifting

trees and logs (Pacific Tuna Development Foundation 1979).

Several hypotheses have been suggested to explain this association. One is that

shadows cast by floating objects make zooplankton more visible to predators

(Damant 1921) or that pelagic fish simply seek shade from the floating material

(Suyehiro 1952). Floating trees and logs serve as egg and algal attachment sites, as

invertebrate food and habitat, and as cleaning sites where external parasites on

pelagic fish are removed (Gooding and Magnuson 1967). Communities of organisms

may form food webs in association with drift logs (Brock 1985). Small fish initially

accompany a drift tree, feeding on small planktonic organisms in its vicinity. With

time, larger predators arrive, taking advantage of accumulated prey. Prey respond by

using the floating tree as a shelter. Within 5 weeks from the time of initial object or

tree placement, the forms of predators (tunas and dolphin-fish) in the vicinity of the

object may vary as much as 100 tons. Predators rapidly deplete the available prey,

albeit prey continuously recruit to the object. In their search for food, predators move

away from the object to return later, apparently using it as a focal or reference point.

107
Based on underwater and surface observations, dolphin-fish may range from 0.3 to

2.5 miles from a floating tree and return 15 minutes to 1 hour later. Yellowfin and

bigeye tuna have been ultrasonically tagged and tracked in Hawaiian waters and

found to travel 6 to 12 miles from a floating tree, then to return 10 to 20 hours later

(Brill and others 1984).

Size of floating debris has an effect on the attraction of fish to it. Objects with greater

dimensions have experimentally been found to attract larger numbers of fish (Hunter

and Mitchell 1968). A lower size limit of effectiveness of an object appears to be

about 1 square foot. Drifting trees with limbs and roots vertically oriented in the water

attract fish better than do trees or logs with horizontal orientation (Yabe and Mori

1950).

Wood in the deep sea not only serves as a source of energy in an energy-scarce

environment but also contributes to environmental diversity and associated

community complexity in the deep sea. Wood, along with other remnants of land

plants, was often present in dredges from the deep-sea floor, even from deep-sea

trenches (Bruun 1957). A sunken tree is a focus of abundant deep-sea life for a long

time (Bruun 1957, Turner 1977). Wood is more common on the deep-sea floor off the

mouths of rivers and wooded coastlines, and deep-sea hauls rich in land-plant debris

had a large number and high diversity of deep-sea animals (Bruun 1959; Knudsen

1961, 1970).

Trees escaping into the nearshore system are usually infested with gribbles and

shipworms or become invaded while near shore. Such trees gradually become

waterlogged and sink slowly if they are not driven ashore by winds. Trees that are

attacked by marine borers and sink over the Continental Shelf or in the deep sea

represent a direct entry of terrestrially fixed carbon into the oceanic benthic system.

The sources, forms, and routes of supply of organic material to the energy-poor deep

sea are little known. Woody debris containing deep-sea species of molluscous wood

borers of the genus Xylophaga have also been recovered from deep ocean areas. It

has been experimentally demonstrated that these deep-sea molluscous wood borers

quickly attack wood samples placed on the floor of the sea.

These pelagic teridas have large populations, high reproductive rates, rapid growth,

and short lifespans, making them the first known case of an opportunistic species in

the deep sea. Like their shallow-water shipworm relatives, they produce large

amounts of finely ground wood fragments. Piles of fecal pellets produced by borers

may attract more than 40 species of epibenthic, deep-sea invertebrates known to use

detrital sources (Turner 1981). The enrichment of the bottom, a result of the

disintegration of the wood and the accumulation of fecal pellets, contributes to the

development of a rich fauna.

108
Wood also appears to be the normal habitat of some species of small deep-sea

mytelid bivalves that attach themselves to crevices in burrows of wood borers.

Terrestially derived plant material in the deep sea contributes to niche specialization

in groups other than mollusca. Deep-sea species known to be associated with

terrestrial plant material include echinoderms that feed on this material, bilaterally

symmetrical hermit crabs that live in hollowed plant stems, and gammared

amphipods that live in or feed on wood. Chiton, small putilliform gastropods, and

sepunculids as well as nematodes and polychete worms are often found on wood or

in old burrows of wood borers (Turner 1981). How this wood-dependent deep-sea

community finds new wood is still unknown.

Woody debris from decomposition of large pieces of wood on land enters the

bedload of streams and is transported downstream to join similar nonbuoyant debris

produced in coastal waters and estuaries. This material enters the ocean in large

quantities (Hedges and others 1982), to be transported by bottom currents. Near

the shore, as far as 1.25 miles from the beach, bottom currents in water less than

130 feet deep result from wave motion and are predominantly a shoreward flow that

returns material to the wave zone. Offshore, where water is deeper than 130 feet and

thus below the effect of waves, bottom and near-bottom currents on the Continental

Shelf flow northward, parallel to the coast.

Vascular plant debris is one-third of the total organic matter in bottom sediments in

the Columbia River system (Hedges and others 1982). The major types of plant

debris are derived from nonwoody angiosperm tissue and gymnosperm (conifer)

wood. The transport of woody plant debris to the sea introduces it into marine food

webs as a terrestrially derived organic carbon energy source. The proportions and

fluxes of terrestrial plant material into sediments on the Washington continental shelf

have been described (Hedges and Mann 1979). The fine sand sediment on the inner

continental shelf has a low organic carbon content, mostly derived from marine

phytoplankton. On the midshelf, between 12.5 and 25 miles offshore, the sediment is

a finer organically enriched silt, as is nearshore sediment around the Columbia River

mouth, where the sediment content of terrestrial plant debris would be expected to

be high. Ninety-five percent of the organic matter in the sediment off the Columbia

mouth is of terrestrial origin, that of nearshore sand is about 20 percent, and the

midshelf silts 22 to 25 miles offshore contain 46 to 61 percent terrestrial organic

carbon (Hedges and Mann 1979).

Thus, an appreciable quantity of lignin-containing panicles derived from coniferous

wood is transported across the Pacific Northwest continental shelf, at least 49 miles

offshore, and is deposited in the midshelf sediments where it constitutes at least

half the total sediment organic carbon content. The role of intact wood in marine

pelagic and benthic food webs remains unknown, as does the potential role of offshore marine wood borers in initial reduction of this wood. The significant amount of

coniferous wood products on the floor of the midshelf, however, suggests a potentially valuable research area that could shed light on the interactive link between the

forests of the Pacific Northwest and the ocean portion of the ecosystem.

109
Current

Management of

Wood on Beaches

and Estuaries

When logs do reach the shore or beach, should they be removed or allowed to

remain (fig. 4.17)? The thinking developed in this chapter argues that abundant drift

logs help stabilize beaches by capturing land and shielding the shore from wave

action. The States of Oregon and Washington differ in their policy about removing

logs. Oregon has the following policy for removal of logs from its beaches:

To assure continuation of scenic and recreational values for public

enjoyment at the ocean shore and to protect marine life and intertidal

resources, beach logging, as a general practice, shall be prohibited

unless such removal can be shown a significant public benefit.

Washington State’s policy on log removal appears to contrast markedly with

Oregon's. The Department of Natural Resources (DNR) has an established

procedure for licensing individuals who wish to retrieve drift logs, either from the

Puget Sound or the Columbia River below Grand Coulee Dam. Certain restrictions

are imposed on the license holders, but the department cooperates by administering

the sale of unbranded drift or salvage logs retrieved by the licensee. If the log is just

floating in the Sound, there is little question about a permit holder’s being able to

latch onto it. But if the log is lying on a beach in front of a house, who does it belong

to? The DNR's answer is as follows:

Log patrolmen, brand owners, and their agents all have the right to

enter peaceably any tideland, marsh, beach, etc., for the purpose of

salvaging logs. Likewise, beach owners have rights also; where one

right ends and the other begins is hard to define. Generally speaking,

the removing of logs from the water side by boat does not infringe

upon the rights of the beach owner. A beach owner does not have

any legitimate claim to a log that washes upon his beach, and to

exercise any appreciable claim over this log could result in criminal

action.

But if the beach-front owner believes the logs should be left to protect the beach

from wave erosion, the stage is set for argument. The matter is not trivial as more

than 9 million board feet were salvaged in 1974 by log patrolmen. The policies of

Oregon and Washington apply only to coastal beaches and tidal portions of rivers;

neither policy applies to estuaries. The difference is that the beaches in Oregon are

public, whereas those in Washington are private.

110
Volume 

mf wood 

Human sources 

Figure 4.17-Estimates of wood inputs to beaches and estuaries in 

Oregon from 1840 through 1985. 

The other major regulatory arena in estuaries centers on wetlands and mitigation 

policy and involves the provisions in section 404 of the Clean Water Act of 1972. 

When wetland or marshes are removed, filled, or dredged, wetlands in another area 

within the estuary must be created, restored, or enhanced. In Oregon, large woody 

debris is not currently an issue in the mitigation process. The Division of State Lands 

and the Department of Environmental Quality, which administer wetland and marsh 

alteration permits, do not consider woody debris to be an issue in Oregon tidal 

marshes. They do not encourage removal of wood. There is no mitigation credit 

for removing wood. Also, in the enhancement and restoration process, wood is 

not considered. In effect, the Division of State Lands and the Department of 

Environmental Quality take a neutral stand about wood. They do not encourage 

removal, and wood is not considered in wetland management. The hope is that 

the management of the estuary linked to the forest through large woody debris can 

become a part of the creative mitigation process and can become consistent with the 

way nature has linked the two. 

111 
se? 

od deposited by storms in the high marsh can 

ve as nurms to the forest surrounding the estuary. 

Figure 4.&Sitka spruce and huckleberry on nurse log in Nehalem 

Bay, Oregon. 

Figure 4.12-Beachwood along the Washington coast. 

112 

Figure 4.14-Collecting firewood reduces the amount of driftwood in 

Oregon estuaries and on beaches 
Chapter 5. Looking Ahead: Some Options

for Public Lands

Jerry F. Franklin and Chris Maser

Summary Intensive and diversified forest management are compared. These approaches

represent opposing ends of a continuum of philosophies and of techniques available

to the forest manager.

Introduction Most public forest lands in the Pacific Northwest are and will be used to produce

commodities and amenities. We must maintain biological diversity on these lands if

we are to achieve multiple-use management objectives that require a healthy

ecosystem. The key to a healthy ecosystem is structural and functional diversity

across forested landscapes (Franklin and Forman 1987).

We use coarse woody debris as a good example of biological diversity that may be

either retained or lost by management decision; each decision will affect forests,

streams, rivers, estuaries, and oceans.

We know too little about complex ecosystems (Society of American Foresters

1984b), so we need constantly to re-evaluate management philosophy in light of new

information. We conclude this chapter with recommendations for research needed to

better understand and maintain biological diversity.

Intensive Forest

Management

Intensive forest management is the use of artificial means to produce wood fiber in

the shortest time possible. The economic advantage of such management is the

continuation of industrial production after the old-growth forest is removed. But

biological disadvantages cause concern about the long-term economics of intensive

management.

The current approach to intensive forest management maximizes timber output

by simplifying forest biology and subsidizing it with energy inputs. This approach

homogenizes the forest, thus reducing ecological diversity.

Biological simplification is a serious issue, both ecologically and economically (OldGrowth Definition Task Group 1986). Simplification occurs at many levels, such as

genetic, structural, and so forth. Simplification is often carried out when it is not

essential to management objectives or is even economically disadvantageous.

113
Genetic simplification takes many forms, including eliminating or excluding some

species and reducing variability in others. Local elimination and subsequent exclusio

of a species usually results from accident rather than by design. Exclusion of a species from a significant amount of the landscape can result in extinction, as has been

hypothesized for the northern spotted owl (Gutierrez and Carey 1985). Local extinctions in the aggregate cause global simplification through loss of species. Intraspecific genetic variability is often reduced by design in genetic manipulation of

Douglas-fir or, even more drastically, in cloning it. Other forest activities, such as

artificial regeneration of trees from wild seed, can also result in substantial,

unplanned modification of the natural genetic variability.

Structural simplification of stands includes eliminating snags and fallen trees, reducing the range of tree sizes and growth forms, and geometrically spacing trees. Long

before intensive forest management was applied, foresters removed deadwood because of concerns about wildfire. Intensive forest management seeks uniformity in

tree size and form by concentrating on one or two species. Trees are regularly

spaced to optimize stand growth and to provide access for mechanical equipment.

Unmanaged landscapes in the Douglas-fir region are dominated by a wide mix in

size of patches, from small to very large, and with a high degree of heterogeneity or

structural variability within patches. Patch boundaries often merge gradually or are

feathered at their edges. Wildfire and windstorms created most of these patches.

Management has increased the number of patches in forested landscapes, particularly with the dispersed clearcutting system used on Federal lands. The patches are

much more uniform in size, however, and very homogeneous. The boundaries or

edges between patches have also been drastically increased, sharpened, and

straightened under intensive management. Management may have increased the

number of patches in forested landscapes, but numerous small patches of Douglasfir less than 100 years of age may not be desirable ecologically or economically

(Franklin and Forman 1987, Thomas and others 1979).

The temporal or successional simplification from intensive management affects both

early and late successional stages. Rapid establishment of a fully stocked, closedcanopy conifer forest is a major economic objective; planting and elimination of competing vegetation contribute to this objective. Intensive timber management aims to

eliminate three successional stages: grass-forb, mature, and old-growth. In coastal

Douglas-fir forests of the Pacific Northwest, grass-forb is the earliest stage; the

mature stage usually begins at 80 to 100 years of age (culmination of mean annual

increment) and persists for about 100 years, during which time substantial growth

continues and biomass accumulates. Old-growth conditions develop gradually and

begin when the trees are 175 to 200 years old (Old-Growth Definition Task Group

1986). The concept of successional simplification becomes clear when rotations

under intensive management are compared with those under unmanaged conditions

(fig. 5.1).

114
Figure Bl-Contrast in duration of successional stages under 

natural and human disturbance regimes. Typical frequency for 

fire return under natural conditions is 350 to 450 years in 

northern Oregon and Washington. Normal rotation for 

managed stands is 70 to 90 years. Managed rotations 

eliminate the mature and old-growth stages of stand development and abbreviate the open, preforest canopy stage. 

Diversified Forest 

Management 

Diversified forest management emphasizes maintaining long-term site productivity 

through ecological diversity in the forest portion of the ecosystem. This method 

includes rotations longer than 80 years, reinvesting organic matter and nutrients in 

the site in the form of large snags and down stems, and producing diversified forest 

products. 

The biological advantage of diversified forest management is that forest health is 

maintained indefinitely. But the social and economic disadvantage is disruption of 

industrial and community stability during the transition period to diversified management. Essentially, the choice is between short-term or long-term effects. 

Maintalnlng Options Maintaining options is the basis of diversified forest management. A manager retains 

the ability to respond to changes in product needs, in environmental conditions, and 

in knowledge about how forests function. Economic conditions and markets have 

changed drastically in the last two decades. Is there any reason to expect greater 

stability in the future? Climatic changes and increasing pollutant loads can be expected. Do our tree-breeding programs take these changes into account? 

Diversified management accommodates change and recognizes our limited knowledge of how forests function. The amount of fundamental information, such as that 

concerning the dynamics of the belowground forest component, is growing rapidly. 

Only about 20 percent of the biomass is belowground, but turnover of fine roots and 

mycorrhizae may be so high that most of the photosynthate is needed for their maintenance. Other examples of recent scientific findings are: (1) the importance of photosynthesis that occurs outside the normal growing season-including such sites as the 

productive coastal Sitka spruce-western hemlock forests (Franklin and Waring 1980); 

(2) the significance of tree canopies as sites for condensing and precipitating water, 

115 
Maintaining Forest

Productivity

Accommodating

Early and Late

Successional

Species

nutrients, and pollutants-producing, on some sites, 25 percent or more of the water

input (Harr 1982); and (3) the many locations at which nitrogen fixation occurs in

forests-in canopy lichens (Carroll 1980), in fine litter (Silvester and others 1982),

in rotting wood (Harmon and others 1986), through small mammals (Li and others

1986), and in the rhizosphere (Li and Castellano 1987). The importance of coarse

woody debris has been recognized only since the late 1970’s.

Compared with an intensively managed forest, a diversified forest provides a greater

array of timber products and biological organisms and much greater inputs of soil

organic matter and nutrients. Safeguarding the genetic diversity of a forest contributes to sustained productivity because the potential for loss of trees to pathogens,

climatic change, or pollutants is less.

A diversified forest contributes significantly to the stability of streams, rivers, and

estuaries; it provides coarse woody debris, essential to the stability, diversity, and

productivity of the tributary aquatic portion of the ecosystem. Intact riparian zones

help maintain high water quality and provide large pieces of organic material.

Intensive forest management shortens the early stage in succession that precedes

tree canopy closure and eliminates the late successional stages. In contrast, diversified management accommodates all successional stages.

Many organisms use early successional stages. The herb and shrub stage has the

highest diversity (number of species) of any stage in forest succession. This is also

the stage of succession during which nitrogen-fixing plants, such as alder, ceanothus,

and lupine, carry on most of their activity; the largest single input of nitrogen occurs

during this successional stage.

The young, closed-canopy forest, by contrast, is the least diverse stage of succession; here also, the trees mobilize all resources of the site. The relation between

species diversity and successional stage is exemplified by mammals (fig. 5.2). Other

groups of organisms, including higher plants and terrestrial and aquatic invertebrates,

show similar relations.

The time of full canopy closure can be delayed by using wide spacings, which also

might reduce planting and thinning costs (Oliver 1986). Results of spacing trials

suggest that such stands produce lower total yields but produce trees with much

larger diameters (Reukema 1970).

Maintaining mature and old-growth stands can be facilitated by reserving existing

stands and creating new stands with long rotations. Management regimes can be

designed to generate old-growth characteristics earlier than would occur under natural conditions (Old-Growth Definition Task Group 1986). Harris (1984) suggests a

scheme that combines old-growth islands with much larger, long-rotation buffer areas.

116
Figure 5.2-Relation between successional stage and number of mammal species using each stage as primary habitat 

(data based on Harris 1984). 

Reservation and creation approaches are both needed because some reserved 

mature and old-growth stands will be lost to catastrophe as reserved forest patches 

in highly fragmented landscapes are lost now (Franklin and Forman 1987, Ruediger 

1985). Loss of old-growth stands to natural successional processes does not appear 

to be a serious problem because changes are slow and stands appear stable for 

many centuries. 

Natural old growth is a finite resource from which we must learn to simulate the oldgrowth condition in the managed forest. Our ability to successfully implement long 

rotations is unproved, even with the current knowledge of old-growth forest characteristics. Ecological theory suggests that reserved old-growth islands will have greater 

diversity than old-growth islands created from managed forests (Harris 1984). 

Mixed Stands Soil improvement is a major objective of growing mixed-species stands. The classic 

example is using alders in mixture with conifers because of alder’s nitrogen-fixing 

capabilities; other species also have favorable nutrient benefits. Cedars and related 

species (Cupressaceae and Taxodiaceae) are calcium accumulators (Kiilsgaard and 

others, in press; Zinke and Cracker 1962). Cedar litter contributes to development of 

soils comparatively rich in bases, low in acidity, and more favorable to biological 

productivity (Alban 1967, Turner and Franz 1985). Many hardwoods also produce a 

base-rich litter. 

Hardwoods mixed into coniferous stands may be appropriate for a variety of nontimber objectives besides their effects on soil nutrients. Deciduous hardwoods result 

in an open canopy for part of the year and thus influence conditions on and in the 

forest floor. Some invertebrate and vertebrate populations respond favorably to 

increased sunlight. Hardwood trees themselves provide a very different habitat for 

epiphytes, invertebrates, and some kinds of predators. Bigleaf maple, for example, 

is an outstanding substrate for epiphytic plants. 

117 
Mixed-structure stands could be created to provide truly uneven-aged stands with

the classic, inverted-J, size-class distribution, which means that the large number of

small trees decreases as the size of individual trees increases. This is often interpreted as indicative of a stable population. A single-tree selection system could be

used to manage such a stand for continuous yields. Consequences of such a harvest

system on specific species will vary from site to site and will depend on the mix of

shade-tolerant and shade-intolerant species. A much simpler and broadly relevant

example of a mixed-structure stand is the development of a two-layered forest, consisting of two distinct age classes. One approach being tested is the creation of

shelterwoods in which the leave trees are left through the entire next rotation. This

could create greater canopy diversity (perhaps for wildlife habitat or moisture condensation), provide a source of large deadwood structures, or produce higher quality

wood.

Protecting Riparlan

and Wetland Habitats

Healthy riparian habitat is an important goal of diversified management. Coarse

woody debris provides much of the basic structure for the smaller streams. Litter

from streamside vegetation provides the primary energy base of the aquatic

community.

Riparian management should conserve as much structural and compositional diversity as possible. A mixture of herb, shrub, and tree species is desirable for perpetuating litter and wood inputs that vary in timing and quality. Maintaining multiplecanopy layers contributes significantly to structure and composition, as well as to a

more varied physical environment in which canopies include both deciduous and

evergreen components.

Streamsides may be protected by maintaining vegetated corridors, especially along

large streams. Prescriptions for managing riparian zones must include methods for

maintaining needed structure, composition, and windfirmness over a long period in

harmony with treatments on adjacent lands.

Maintaining Coarse

Woody Debris In the

Ecosystem

Providing coarse woody debris to the terrestrial and aquatic portions of the ecosystem is a major challenge in land management because of the linkages involved.

These include a continuous flow from (1) producing large trees to (2) creating and

maintaining large snags to (3) creating and maintaining downed stems and, finally, to

(4) producing and transferring wood from the terrestrial to the aquatic environment.

Snags and downed stems are transitory structures, so they must be produced

continuously. Snags are especially short lived in the Douglas-fir region, rarely

persisting (in forms useful to cavity dwellers) beyond 60 or 70 years. To fulfill all

functions, snags must also be renewed in sizes greater than 24 inches in d.b.h.

The practice of removing unmerchantable material is ecologically undesirable when

all large woody material is removed from a site. Such practices need to be modified

or eliminated.

118
Some live trees can be retained as sources of future snags. Saving trees with crown

and upper stem defects, such as top rot, broken top, or fork, is desirable because

they are likely to contain some decay that produces desirable snags for cavity dwellers. Lower stem, butt, or root defects should be avoided because they may be susceptible to windthrow that would reduce their longevity as snags. Live trees may also

be converted to snags by fire or girdling. One strategy may be to kill trees at intervals

to provide a continuing source of snags through the next rotation.

Need for a Landscape

Perspective

The size, shape, and location of individual forest patches or stands have profound

effects on landscape stability and productivity (Franklin and Forman 1987). The spatial arrangement in the landscape of management activities, stand types, stream

habitats, and so forth is also critical to diversified management. In some cases, the

importance of spatial arrangement is well known, such as the juxtaposition of feeding

and hiding habitat for wildlife. But many other relations, such as those between forests and streams, are poorly understood. One of the most difficult spatial issues is

the movement and changing roles of wood in a river drainage, from headwater to

estuary. Aggregates of wood in aquatic ecosystems have great significance for

productivity and biological diversity.

Size, shape, distribution, and context (degree of contrast with the surrounding landscape) of diverse patches are important landscape considerations. Shape and location of clearcuts have dramatic effects on windthrow in adjacent forest stands

(Gratkowski 1956, Ruth and Yoder 1953) and the amount of recently cutover forest

can significantly influence hydrologic regimes (Christner and Harr 1982, Geppert and

others 1984).

The staggered-setting system of clearcutting, used widely on Federal lands in the

Douglas-fir region, intersperses 25 to 40-acre clearcuttings with live timber and

results in a patchwork that maximizes the amount of high-contrast edge within a

landscape. Such landscapes are particularly vulnerable to catastrophic windthrow

or other disturbances once 20 to 30 percent of the landscape is cut over. Forest

patches large enough to provide an environment suitable for species that inhabit the

forest interior generally disappear by the time half the landscape is cut over. Furthermore, creating small management areas and dispersing management operations

over the landscape is economically inefficient. Many effects of management could be

reduced by aggregating rather than dispersing cuttings, although cumulative effects

on hydrologic regimes would need to be carefully considered. Evaluating specific

ecologic, economic, and social implications of staggered-setting clearcutting and

alternative approaches of managed landscapes is badly needed (Franklin and

Forman 1987); however, the general importance of a landscape perspective in

management decisions is already clear.

Information Needed Little biological research was done in Pacific Northwest forests before about 1950.

for Developing Then research facilities were expanded to allow some scientific focus on the more

Improved obvious and practical issues of that time, such as growth and yield of forest stands,

Management methods for tree regeneration, and control of various tree-damaging agents. We have

Regimes only recently begun to identify critical ecological questions. Quantifying many of the

relations, such as those between levels of coarse woody debris or habitat for specific

119
Long-Term Site

Productivity

organisms, is demanding and expensive. Much research is still needed to convert the

qualitative information to management prescriptions and to confirm hypotheses about

the role of woody structures in the world ecosystem.

Needed research appears to fall into three major categories: (1) long-term site

productivity, (2) roles of coarse woody debris, and (3) dynamics of coarse woody

debris.

No more important forestry issue exists than that of the sustainability of commercial

forest-land productivity. This requires more than simply insuring that soils are not

compacted or eroded or that some critical level of soil nitrogen is maintained. But,

unfortunately, our knowledge does not go much beyond this simple perspective. We

must have more insightful information; at the least, we need to determine what is

required for sustaining forest production.

One major component of needed research is quantifying the effects of coarse woody

debris on site productivity, including the contribution of coarse woody debris to the

physical, chemical, and microbiological properties of the soil. What role do decayresistant components of wood play in soil structure? How important are pockets of

woody material in a soil matrix in the functioning of specific belowground components, such as mycorrhizae, at specific times of year and in different forest types?

What role do dead roots play in maintaining soil structure and providing belowground

energy and nutrient sources?

The relation between woody debris and long-term productivity is critical for freshwater, estuarine, and marine portions of the ecosystem just as it is for the terrestrial

portion. Developing information for aquatic communities may be more difficult

because the supply and dynamics of wood in rivers must be considered over an

entire drainage.

We must synthesize existing and new information. Computer models can now address some questions of long-term site productivity (Kimmins and Scoullar 1979,

Shugart 1984). Such models are valuable tools in synthesizing and identifying

information needs. Models are also the only way we can explore the effects of

various management activities as they might develop over decades or even centuries; thus, refining old models and developing new ones are high priority. Such

models are as much management tools as research tools.

Quantifying the Roles We know that snags and downed stems are important in terrestrial and aquatic

of Coarse Woody Debris environments, but we do not know how much of this material is needed in what

sizes, decay states, or spatial arrangements. These questions must be primary

research objectives because management costs associated with creating and

maintaining coarse woody debris are considerable.

120
Quantifying needs for coarse woody debris to achieve both game and nongame wildlife objectives is a pressing management issue. We know that coarse woody debris is

an essential resource for animals, but we do not have detailed information on how

much is needed. Important variables include snag and down stem densities, tree

species, decay state, and size. The spatial arrangement of downed stems on cutover

areas is also important. How much continuity is required from the standpoint of

animal movement into and across cutover areas?

A long-term experiment at the H.J. Andrews Experimental Forest in western Oregon

will examine the effects of several management treatments on site productivity.

Coarse woody debris is one major variable in the experimental design that has the

specific objective of quantifying the effects of downed stem density and spatial arrangement on mammals’ movements into and across clearcuts. Studies of this type

are expensive but essential for getting quantitative information needed for long-term

management decisions.

Research also needs to be conducted on the roles of coarse woody debris in geomorphic processes and in aquatic environments from headwater streams to deep ocean

habitats. How do stem size, density, and spatial arrangement (parallel or at right

angles to the slope) affect surface erosion? How are the quantitative relations between stem or log-jam numbers related to aquatic productivity? What densities and

sizes of stems are necessary for essential structural diversity and substrate in

estuarine environments?

Dynamics of Coarse

Woody Debris

Snags and downed stems are transient structures, so knowledge of their dynamics is

essential. Much useful information has already been generated from various ecosystem and wildlife-oriented research programs. Among other things, this information

has created an understanding of the highly variable nature of coarse woody debris

and its decomposition.

The factors that affect patterns and rates of disappearance of snags and downed

stems are important variables for which information is inadequate. These variables

include tree species, cause of death, size of piece, wood quality as reflected in

growth rate and proportions of heart and sapwood, and patterns of decomposition

along major environmental gradients. Some contrasts are already apparent between

mixed-conifer and ponderosa pine forests east of the Cascade crest and the Douglasfir-western hemlock forests to the west, but information is fragmentary. Patterns of

decomposition relative to moisture and temperature need to be learned. Other variables that need to be investigated are comparisons of wood decay in clearcuts and

forests and comparisons of decay of burned (charred) vs. unburned material of comparable type.

Similar wood decay variables require investigation in aquatic environments. There

are additional important dimensions, such as how does mechanical battering affect

fragmentation of large wood in streams and the ocean? How does transport and

aggregation of woody debris in aquatic environments differ from that on land?

121
Conclusion 

A long-term study of wood-decay processes at the H.J. Andrews Experimental Forest 

(f@. 5.3, color) is designed to examine the effects of tree species (Douglas-fir, western hemlock, western redcedar, and Pacific silver fir), wood size, and early insect 

colonizers on pattern and rate of decay. Nearly 500 logs about 24 inches in diameter 

and 19.5 feet long have been placed in a replicated design that should allow sampling to continue for about two centuries. This study has already provided some surprising results, especially on the effects of invertebrate populations. A related study 

of decomposition in aquatic environments has been established in a third-order 

stream with smaller logs of Douglas-fir, red alder, and western hemlock. 

Synthesis of information on the dynamics of snags and downed stems should take 

the form of simulation models. Only one model deals with the dynamics of woody 

debris over long periods (Graham 1982); such models need much greater emphasis. 

Simulators are needed that can provide managers with information on the yield of 

coarse woody debris for different environments and under different management 

regimes-yield models for dead material instead of live trees! 

The challenge to managers of public forest lands is to maintain ecological diversity in 

perpetuity. We must understand and accept biological complexity. We must follow the 

basic principle of maintaining or restoring genetic, structural, and spatial complexity. 

planned to span a 200-year period has been installed at the 

H.J. Andrews Experimental Forest in the central Oregon 

Cascade Range; major variables include species, size, and 

presence or absence (log enclosed in insect-proof tent) of 

invertebrates during early stages of decomposition. 

122 
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150
Appendix Common name Scientific name

Nomenclature

Fungi:1

Red ring rot

Yellow laminated rot

Plants:2

Alder

Bigleaf maple

Blueblossom

California laurel

Coast redwood

Douglas-fir

Eelgrass

European beachgrass

Grand fir

Huckleberry

Jeffrey pine

Lodgepole pine

Mountain hemlock

Pacific silver fir

Port-Or-ford-cedar

Red alder

Red algae

Red oak

Rockweed

Salal

Salmonberry

Sitka spruce

Snowbush

Sugar pine

Tanoak

Western azalea

Western hemlock

Phellinus pini (Thore ex Fr.) A. Ames

Phellinus weirii (Murr.) Gilbn.

Alnus sp.

Acer macrophylum Pursh

Ceanothus thyrsiflorus Esch.

Umbellularia claifornica (Hook. & Am.) Nutt.

Sequoia sempervirens (D. Don) Endl.

Pseudotsuga menziesii (Mirb.) Franco

Ammophila arenaria (L.) Link

Abies grandis (Dougl.) Lindl.

Vaccinium spp.

Pinus jeffreyi Grev. & Balf.

Pinus contorta Dougl. ex Loud.

Tsuga mertensiana (Bong.) Carr.

Abies amabilis (Dougl.) Forbes

Chamaecyparis lawsoniana (A. Murr.) Parl.

Alnus ruba Bong.

Fucus spp.

Quercus borealis ( L .)

Fucus spp.

Gaultheria shallon Pursh

Rubus spectabilis Pursh

Picea sitchensis (Bong.) Carr.

Ceanothus velutinus Dougl. ex Hook.

Pinus lambertiana Dougl.

Lithocarpus densiflorus (Hook. & Am.) Rehd.

Rhododendron occidentale (T.& G.) Gray

Tsuga heterophylla (Raf.) Sarg.

’ After Aho (1982).

‘After Franklin and Dyrness (1973), Simon and Schuster (1978).

151
Western redcedar

Western yew

White fir

Willow

Insects:3

Douglas-fir bark beetle

Net-spinning caddisfly

Water strider

Fish:4

Bigeye tuna

Chinook salmon

Coho salmon

Cutthroat trout

Dolphin fish (mahimahi)

Herring

Skipjack tuna

Starry flounder

Steelhead trout

Stickelback

Sturgeon

Yellowfin tuna

Birds:5

Acorn woodpecker

Bald eagle

Brown creeper

Brown pelican

Cormorant

Crow

Downy woodpecker

Great blue heron

Great egret

Thuja plicata Donn

Taxus brevifolia Nutt.

Abies concolor (Gord. & Glend.) Lindl.

Salix spp.

Dendroctonus pseudotsugae Hopkins

Hydroptila spp.

Gerris spp.

Thunnus obesus (L.)

Oncorhynchus tshawytscha (Walbaum)

Oncorhynchus kisutch (Walbaum)

Salmo clarki Richardson

Coryphaena hippurus (L.)

clupea spp.

Katuwouvs pelamis (L.)

Platichthys stellatus (L.)

Salmo gairdneri Richardson

Gasterosteus aculeatus L.

Acipenser spp.

Thunnus albacares (Bonnaterre)

Melanerpes formicivorus (Swainson)

Haliaeetus leucocephalus (L.)

Certhia americana Bonaparte

Pelecanus occidentalis L.

Phalacrocorax spp.

corvusspp.

Picoides pubescens L.)

Ardea herodias L.

Casmerodius albus

3 After Borror and DeLong).

4After Bown (1985) Gooding and Magnuson (1967).

5 After Robbins andothers (1983).

152
Green heron

Gull

Hairy woodpecker

Lewis woodpecker

Northern flicker

Osprey

Pileated woodpecker

Purple martin

Red-breasted sapsucker

Turkey vulture

Mammals: 6

Black bear

Harbor seal

Raccon

Butorides striatus (L.)

Larus spp.

Picoides villosus (L.)

Melanerpes lewis (Gray)

Colaptes auratus (L.)

Pandion haliaetus (L.)

Dryocopus pileatus ( L .)

Progne subis (L .)

Sphyrapicus ruber (Gmelin)

Cathartes aura (L.)

Ursus americanus Pallas

Phoca vitulina L.

Procyon lotor (L .)

“After Hall (1981).

153
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Maser, Chris; Tarrant, Robert F.; Trappe, James M.; Franklin, Jerry F.,

tech. eds. 1988. From the forest to the sea: a story of fallen trees. Gen.

Tech. Rep. PNW-GTR-229. 153 p.

Large, fallen trees in various stages of decay contribute much-needed

diversity of ecological processes to terrestrial, aquatic, estuarine, coastal

beach, and open ocean habitats in the Pacific Northwest. Intensive

utilization and management can deprive these habitats of large, fallen trees,

This publication presents sound information for managers making resource

management decisions on the impact of this loss on habitat diversity and on

ecological processes that have an impact on long-term ecosystem

productivity.

Keywords: Decomposition, fallen trees, habitat diversity, ecosystem function,

land, water, sea.

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 U.S. Department of Agriculture is an Equal

Opportunity Employer. Applicants for all Department

programs will be given equal consideration without

regard to age, race, color, sex, religion, or national

origin.

Pacific Northwest Research Station

319 S.W. Pine St.

P.O. Box 3890

Portland, Oregon 97208
U.S. Department of Agriculture

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