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Changes 30 Years After Logging in Large Woody Debris,
and Its Use by Salmon ids 1
Mason D. Bryant2
Abstract.--Changes in large woody debris in fourth and fifth-order
salmon streams with logged, unlogged, and partially logged riparian zones
are documented from maps--for 1949 to 1960--and from field surveys done
in1983 and 1984. Over the 30-year period, most changes in the amount of
large woody debris occurred in the logged systems. During and immediately
after logging large increases were noted, but in 1984 the amount of large
woody debris in the logged systems was less than that observed before
logging in most categories. Amounts of large woody debris in the other
streams remained relatively stable. Thirty years after logging, habitat
formed as a result of large debris provides important rearing areas for
juvenile salmonids. Results from this study emphasize the importance of
managing riparian zones as a source of large organic debris.
Large woody debris is an important component
in the habitat used by juvenile salmonids and the
the riparian zone is the primary source of large
woody debris (Dolloff 1983, Elliott and Hubartt
1978, Sedell and Luchessa 1981). Streams flowing
through old-growth forest systems typically contain numerous accumulations of tree-size material
(Swanson et al. 1976, 1984). This material
enters as a result of floods, bank scour and
blowdown (Heede 1972, Keller and Swanson 1979,
Moore 1977, Toews and Moore 1982). Because
large-scale logging in the riparian zone can
eliminate the sourceof large woody debris, the
amount, type, and rate of entry into streams of
large woody debris may change following logging.
coarse ( > 10-cm diameter) woody debris and
destabilization of the stream channel in
streams flowing through recently logged areas
(Bilby 1984, Bryant 1981, Swanson et al. 1984).
Dolloff (1983) and Elliott and Hubartt (1978)
show that woody debris is an important factor in
maintaining productive salmonid habitat in small
streams in southeast Alaska. Dolloff (1983)
showed a decrease in coho salmon (Qncorhynchus
kisutch) production following debris removal in
second-order tributaries. Bustard and Narver
(1975) demonstrated the use of woody debris as
winter habitat for juvenile coho salmon in
British Columbia streams. Bisson and Sedell (in
press) show similar effects of debris on the
habitat of juvenile coho salmon in small streams
in Washington. The effects of logging in the
riparian zone on the relation of large woody
debris to salmonid habitat has not been studied
in the larger stream systems of southeast Alaska.
Immediately following logging, the density and
number of larg~ woody debris accumulations increased and stability of debris decreased in
Carnation Creek, British Columbia (Toews and
Moore 1982), and in Maybeso Creek in southeast
Alaska (Bryant 1980). In Maybeso Creek an
overall decrease in the number of accumulations
was observed 20 years after logging. Other
studies in first- and second-order streams report
higher densities of both fine (<10-cm diameter)
and coarse (>10-cm diameter woody debris and
destabilization of the stream channel in streams
flowing through recently logged areas was
observed 20 years after logging. Other studies
in first- and second-order streams report higher
densities of both fine ( < 10-cm diameter) and
The objectives of this study are to (1)
document changes in the number of debris accumulations following logging, (2) identify the
effects of changes in the number of large woody
debris accumulations on channel morphology, and
(3) determine the use of accumulations of large
woody debris by juvenile salmonids in fourth- and
fifth-order streams.
METHODS
1 Paper presented at Riparian Ecosystems and
their Management. [Tucson, Arizona, April 16-18,
Study Area
1985~
Research Fishery Biologist, USDA Forest
Service Pacific Northwest Forest and Range
Experiment Station, Forestry Sciences Laboratory,
Juneau, Alaska.
Five fourth- and fifth-order streams on the
east coast of Prince of Wales Island, approximately 100 km northwest of Ketchikan, Alaska,
were selected for study (fig. 1). The streams
flow directly into the salt water.
329
Table 1.-Physical
The riparian zone of each stream has been
affected differently by land management activity
(table 1). The Old Tom Creek drainage has not
been logged; the riparian zones of the Harris
River and Maybeso Creek study sections were
completely logged in the early 1950's; the
Twelve-Mile Creek watershed has been extensively
logged at various times since the late 1950's,
but a fringe of noncommercial timber was left
along the stream. The lower 1000 m of the
Indian Creek study section has been partially
logged.
cha~teristics
of the five study streiiiiS.
25yr
Streaa
Length
Area
Discharge
1
Flood Event
Riparim
(m 3/sec)
Zone
Harris River
11l.O
711.6
1.211
285.9
Logged
to bmk
Maybeso Creek
10.0
39.3
3.86
113.7
Logged
to
Indian Creek
8.5
22.9
2.113
172.5
Logged lower
bank
2 lcm,
old-growth
upper section
Twelve-Mile
11.7
29.6
2.28
91.6
Logged with
fringe mostly
Creek
non c<liiiD!rcial
conifer
Old Tom Creek
3.1l
15.3
1.06
21.7
Old growth
1Average per year
and (3) more than 10 pieces. Although the
categories were arbitrary, they provided a measure
of small, medium, and large accumulations and were
easily identified on the maps and during
on-the-ground surveys in 1984.
Study sites approximately 100 m long were
selected on each stream for remapping and sampling
of salmonid populations. Each stream included
habitat with no debris,• and habitat with accumulations in each of the three categories described
above. Some habitat types were continuous, but
divided by a naturally occurring feature such as
rapids, a riffle, or a gravel bank.
Figure 1.--Location of study streams, Prince of
Wales Island, Alaska.
Sampling and Data Base
The five study streams were selected because
each had been accurately mapped in the 1950's;
most were first mapped in 1949, before logging.
The maps showed the stream course, significant
morphological features--bedrock, gravel bars,
pools--attd accumulations of large woody debris.
The maps began at the intertidal zone and
continued upstream 3 to 5 km. They provided the
data base for changes in channel morphology and
number of debris accumulations from 1949 through
logging during the 1950's. In 1983 and 1984, the
sections of the streams that had been mapped in
1949 were located and debris accumulations were
counted in each section. Because different
lengths of stream were mapped, the debris counts,
by category, are reported as number of accumulations per kilometer of stream.
Salmonid populations were sampled with 3.1~
(1/8-in) mesh wire minnow traps baited with salmon
eggs. Traps were set for at least 1 hour at each
location. Each fish was measured and marked with
a small hole in the caudal fin. Differential marks
were used in contiguous sections to detect fish
movement. Traps were reset the following day to
recapture marked fish. Population size was
estimated with the Bailey modification of the
Peterson estimate (Ricker 1975). Estimates of coho
salmon fry (less than or equal to 55 mm total
length) and of age 1+ coho (> than 55 mm) were
computed separately.
RESULTS
Changes in Debris Loading
Large woody debris was defined as material
The number of accumulations of large woody
debris increased from 1949 to 1952. This may be
attributed to additional accumulations that were
missed during mapping in the previous year. At the
onset of logging, however, obvious changes were
> 2 m in length with one end > 30 em in diameter:
this included most tree-size material and excluded
slash and branches. Sizes of accumulations were
categorized as: (1) 1-4 pieces; (2) 5-10 pieces;
330
detected and all categories of large woody debris
increased in the affected streams.
relatively stable throughout the 30-year period.
The Indian Creek drainage was unlogged in the upper
section but generally contained few large woody
debris accumulations; the decrease in the number of
accumulations of large woody debris from 1960 to
1980 may be attributed to removal of debris and
straightening the stream channel in the lower
section during the 1960's to enhance spawning areas
for pink salmon (Q. gorbuscha).
In 1952 (before logging), Twelve-Mile Creek,
Maybeso Creek, and Old Tom Creek consistently had
more large woody debris in all three categories
(fig. 2). The greatest changes occurred in Harris
River and Maybeso Creek. In 1960, after these two
watersheds had been logged, the number of accumulations of 10 or more pieces more than doubled. A
similar increase occurred in Old Tom Creek--an
undisturbed system--but as a result of blowdown.
The accumulations in the Harris River and
Maybeso Creek were usually composed of logging
residue-- cut rootwads, logs, and snags--that was
trapped by smaller debris accumulations. In
Maybeso Creek, this resulted in a decrease in the
5- to 10-piece category and an increase in the 10+
category. By 1984 the number of accumulations in
all categories of large woody debris in the systems
with logged riparian zones was less than the number
observed before logging except for the 10+ category
in the Harris River. The number of accumulations
of large woody debris in Twelve-Mile Creek, the
system wi~h an unlogged riparian zone, remained
DEBRIS ACCUMULATION BY CLASS
Blowdown and stream braiding appeared to be
responsible for most of the larger accumulations
before logging. Generally once a section of stream
had been exposed to blowdown and braiding, the
effects remained over the 30-year period. Some
important differences appeared between large woody
debris accumulations in streams with logged and
unlogged riparian zones. These differences are
caused by the complete removal of large trees along
the stream bank and to large amounts of unstable,
floatable material, consisting of cut rootwads,
logs, and cut snags left by logging.
Most of the sections of Old Tom Creek with
accumulations of four or more pieces continued to
show the effects of blowdown 30 years later.
Changes in channel morphology occurred, but most
pieces of large woody debris remained in place
(fig. 3). In 1949 a remnant channel was evident,
OLI7 TOM CREEK
.SECTION 1
'1-6-49
N
1~
OLP TOM CREEK
5EGTION 1
7-28-54
N
1
'
(f)
z
50
0
~
[OlD TOM
_J
~... ·~~.:~_
- " f=_
CRff1
/
~~c~~~-/
·--.~~·_,;-·
,£(TION J
:::J
~
1
:::J
N
0
0
!
<(
LS:::J TWELVE-MILE
CSZJ
MAYBESO
1960
~HARRIS
~OLD
-
jf
<f'---,
~ ,i~<~(~:¥"JoTo:;JG-;;
.J~;,
-~~-Q~c'l._j;il)J' \
•. ~y. ), ~<J!.A (_,l[-11../0:
. ~-!a-)___· ~(-::c-
0~
'l.
.f
~
({It~'~&
'<t
I
1952
-tm
1984
/Jt_~,;:;ff" •. . )
~INDIAN
~·
TOM
Figure 2.--Relative densities of the three
categories of LWD for 1953, 1960, and 1984 in
the 5 study streams.
Figure 3.--Ghange in channel morphology of Old Tom
Creek from 1949 through 1984, resulting from
blowdown in the riparian zone.
331
but by 1952 the stream had cut through the remnant
channel and formed two channels, each heavily
influenced by LWD. The same overall morphology was
retained through 1984. Similar long-term effects
were evident elsewhere in Old Tom Creek and in
Twelve-Mile Creek where an accumulation of 10+
pieces formed before 1956 and has remained stable
through 1984 (fig. 4).
Figure 4.--Comparison of the same debris
accumulation (10+ pieces) in Twelve-Mile Creek
in 1956 and 1984.
Similar changes in the morphology of the Harris
River Channel were caused by large woody debris
present before logging (fig. 5). Changes in the
stream channel from 1949 to 1956 resulted from
blowdown and bank erosion, as reflected in the
number of rootwads attached to trees. By 1984,
large woody debris in the study section was
predominantly cut logs, cut rootwads, and snags.
An accumulation of more than 10 logs was lodged in
the middle of the channel and was well embedded in
the gravel, stabilized by the large number and size
of the pieces in the accumulation. What had been
the main channel in 1949 has evolved into a
backwater and overflow channel in 1984. The north
bank is eroding, and although the debris
accumulation is stable, the stream channel is not.
Figure 5, a-d.--Evolution of Harris River channel
morphology from 1949 to 1956 (before logging)
through 1984 (following logging).
Salmonid PQpulations
Coho salmon was the most abundant species
caught in all streams followed by Dolly Varden
(Salyelinus mslma) and steelhead trout (~
gairdneri). Steelhead trout were common in Harris
River, Indian Creek, and Maybeso Creek.
No differences in densities of juvenile coho
salmon appeared among the three categories of
debris accumulations (table 2). Where debris was
absent, densities of coho salmon were consistently
lower. Backwaters and side channels associated
with accumulations of large woody debris had higher
densities of juvenile coho salmon than did many of
the main channel areas with debris.
332
The density of coho salmon fry was less than
that of the age 1+ coho salmon in habitat with
large woody debris accumulations of 10 or more
pieces. The density of fry appeared to decrease as
the size of the accumulation increased. The
relatively higher density of coho fry in habitat
with no debris and in the smaller pools created by
single pieces probably reflects transient
populations that have not established territories
in better habitat.
The densities of both age groups of coho salmon
varied widely among large woody debris categories.
Some of the variation may have been related to the
Although logging debris can provide habitat for
juvenile coho salmon, it is generally less
effective than material entering a stream from
natural causes. When large woody debris enters
streams from natural causes, it is associated with
the bank and frequently includes the rootwad. As a
result it is more stable than either a cut log or a
cut rootwad. Large woody debris mid channel is
subject to higher water velocities, even during low
flow periods, than is large woody debris along the
bank. High water velocities decrease the utility
of large woody debris as habitat for juvenile
salmonids by decreasing the stability of both the
channel and the accumulation of LWD.
location of the debris accumulation. Most mid
channel debris accumulations, regardless of size,
supported lower densities of coho than did
accumulations with large rootwads that occurred
along the bank. For example, the densities of fry
and age 1+ coho in the mid channel accumulat~on
shown in Figure 5d were 0.15 and 0.07 fish/m,
respectively, whereas the densities in the adjacent
side channel (entering at the lower left df fig.
5d) were 1.29 and 0.32 fish/m 2 , respectively.
Table 2. Coho sal1110n density (number/meter) by size debris acc1.1111.1lation
and in off-channel areas for all streams combined.
Habitat
category
Number of
Fry (Age 0)
Age 1+
reaches
x (range)
x (range)
2
------------Number per m ----------
Debris Accumulation
0 pieces
3
0.26 (0-0.79)
0.09 (0-0.10)
1-4 pieces
5
0.82 (0-2.56)
0.60 (.15-1.10)
5-10 pieces
5
0.66 (0-1.51)
0.57 (. 18-1.02)
10+ pieces
5
0.26 (0-.63)
0.65 (.07-1.41)
3
1.01 (0-3.02)
1.00 ( .29-1.83)
1.29
0.32
Off-channel habitat
Backwater
Side Channels
.V 1954 counts, later counts not available until 1984.
DISCUSSION
The interaction between the streambank and
large woody debris creates rearing habitat by
forming backwaters and side channels. These areas
are in many respects similar to the small tributaries that commonly provide productive habitat for
juvenile coho salmon. Off-channel sections of the
study streams were complex, with varying amounts of
woody debris ranging in size from branches and
large stems to whole trees. Few juvenile salmonids
were captured in mid channel habitat--either with
or without debris--in the main stream reaches.
Habitat along the edges consistently supported
higher densities of juvenile coho salmon than did
mid channel habitat. Populations along the edges
were found primarily in the habitat created by LWD.
Changes in the amount of large woody debris in
the five study streams from 1949 to 1984 were
related to changes in streamside vegetation, with
the possible exception of Indian Creek. Both
Harris River and Maybeso Creek are losing LWD.
Although accumulations of large woody debris in
1984 appear to be relatively stable, new material
is not entering the accumulations. The accumulations in Old Tom Creek are continually being
renewed. In Twelve-Mile Creek, accumulations are
relatively stable, but are less active than those
in Old Tom Creek. Indian Creek contains small
amounts of large material even though its riparian
zone is old-growth forest. High peak discharges
control the channel morphology of Indian Creek and
debris is rapidly routed out of the channel. As a
result, the channel is predominantly bedrock.
As large woody debris deteriorates in the
streams with logged riparian zones (Harris River
and Maybeso Creek), the off-channel areas, edge
habitat, and backwaters will gradually disappear,
because the source of new material has been
eliminated. With the loss of these habitat types,
the number of coho salmon in these streams is
likely to decline.
The conditions in Harris River and Maybeso
Creek reflect logging methods that are no longer
practiced on National Forest land in Alaska (U.S.
Department of Agriculture 1983). Forest management
practices in Alaska presently require that trees be
felled away from streams and that material entering
the streams be removed within 48 hours (U.S.
Department of Agriculture 1977). In Harris River
and Maybeso Creek, material introduced by logging
was the major component in most of the
accumulations observed in 1984. Removal of
streamside timber eliminated the source of new
material for the streams. Logging practices that
prevent large woody debris from entering streams
will eliminate or reduce the source of this
material in the future; riparian zones must
therefore be managed for recruitment of large
debris to streams.
LITERATURE CITED
Bilby, R. E. 1984. Removal of woody debris may
affect stream channel stability. Journal of
Forestry. 82(10):609-613.
Bisson, P. A., and J. R. Sedell, (in press).
Salmonid populations in western Washington
streams flowing through old-growth forests and
333
recent clearcuts. ln Proceedings of a
symposium on fish and wildlife relationships in
old-growth forests. [April 12-14, 1982]
American Institute of Fishery Research
Biologists. Juneau, Alaska.
Moore, M. K. 1977. Factors contributing to
blowdown in streamside leave strips on
Vancouver Island. Land management Report 3.
34 p. Victoria, B.C.: Ministry of Forests.
Ricker, W. E. 1975. Computation and interpretation
of biological statistics of fish populations.
Bulletin of the Fisheries Research Board of
Canada. Bulletin 191. 382 p. Ottawa, Ont.
Bryant, M. D. 1980. Evolution of large, organic
debris after timber harvest: Maybeso Creek,
1949 to 1978. USDA Forest Service General
Technical Report PNW-101. 30 p. Pacific
Northwest Forest and Range Experiment Station,
Portland, Oreg.
Bryant, M. D. 1981. Organic debris in salmonid
habitat in southeast Alaska: measurement and
effects. p. 239-265 In N.B. Armantrout [ed]
Acquisition and Utilization of Aquatic Habitat
Inventory Information: Proceedings of a
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Division Amercian Fisheries Society, Portland,
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the winter ecology of juvenile coho salmon
(Qncorhyncbus kisutch) and steelhead trout
(~ gairaneri). Journal of the Fisheries
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·
Swanson, F. J., M.D. Bryant, G. W. Lienkaemper,
and J. R. Sedell. 1984. Organic debris in
small streams, Prince of Wales Island,
southeast Alaska. USDA Forest Service General
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Portland, Oreg.
Swanson, F. J., G. W. Lienkaemper, and J. R.
Sedell. 1976. History, physical effects, and
management implications of large organic debris
in western Oregon streams. USDA Forest Service
General Technical Report PNW-6, 15 p. Pacific
Northwest Forest and Range Experiment Station,
Portland, Oreg.
Dolloff, c. A. 1983. The relationship of wood
debris to juvenile salmonid production and
microhabitat selection in small southeast
Alaska streams. Ph.D. thesis Montana State
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Elliott, s. T. and D. Hubartt. 1978. Study of land
use activities and their relationship to sport
fish resources in Alaska: Ecology of rearing
fish. Annual performance rep. Vol. 19. Study
D-I-B p. 39-52. Alaska Department of Fish and
Game, Juneau.
Toews, D. A., and M. K. Moore. 1982. The effects of
streamside loggiug on large organic debris in
Carnation Creek. Department of Fisheries and
Oceans, Land Management Report 11 29 p.
Vancouver, B. c.
Heede, B. H. 1972. Flow and channel characteristics
of two high mountain streams. USDA Forest
Service Research Paper RM-96. 12 p. Rocky
Mountain Forest and Range Experiment Station
Fort Collins, Colo.
Keller, E. A., and F. J. Swanson. 1979. Effects
of large organic materialon channel form and
fluvial processes. Earth Surface Processes
4:361-380.
334
U.S. Department of Agriculture. 1977. Southeast
Alaska area guide. 280 p. USDA Forest Service,
Alaska Region, Juneau [unnumbered publication].
U.S. Department of Agriculture. 1983. Final
environmental impact statement for the Alaska
Regional Guide. USDA Forest Service, Alaska
Region Report 126 p. 75. Juneau.