\
\
=-‘!% OLYMPIC SALAMANDE
n
k
+,
----____
Olympic
North
j
-_----.__
Dunn’s salamanderoften occurs along creeks and streams.
In seepsand headwater habitats, the speciesmay be found
in the samemicrohabitat with the Olympic salamander
(Nussbaumand others 1983). Dunn’s salamanderdoes not
occur in the CascadeRange of Washington (fig. 3). This
specieslacks larvae; individuals develop directly from egg
to adult.
Material and Methods
We sampled 59 streams(seefrontispiece) in three physiographic provinces: the Southern Washington CascadeRange,
the Oregon CascadeRange, and the Oregon Coast Range
(Franklin and Dymess 1973). A similar study was conducted
in northwestern California and southwesternOregon (Welsh
and Lind, this volume). We sampledsix streamsin each
forest age-class(young, mature, old growth) in the Oregon
and Washington Cascades.In the Oregon Coast Range, we
sampled streamsin 3 young, 10 mature, and 10 old-growth
stands.We sampled an additional 20 streamsflowing
through managedsecond-growthforests to study the
long-term effects of logging (Corn and Bury 1989).
Proximity of streamsto establishedterresbial study-areas
varied. In the Oregon Cascades,all of the streamsflowed
through standsused in the terrestrial community studies (see
Gilbert and Allwine, this volume c). Few of the streams
selectedin the Oregon Coast Rangeor Washington Cascades
were in the terrestrial study areas.Ages of thesestandswere
basedon visual inspection of dominant trees and available
timber maps (USDA Forest Service and U.S. Departmentof
the Interior, Bureau of Land Management).We selected
permanent, l- to 2-m wide, first- or second-orderstreams.
We adaptedthe habitat variables sampled from standard
stream-surveytechniquesof Platts and others (1983). Bury
and Corn (in press) and Corn and Bury (1989) describethese
techniquesin detail. Briefly, sampling consisted of an intensive searchof 10 m of water and bank along a representative
stretch of each stream.We usedstandarizedtechniquesfor
measuringwater depth, stream width, percentagegradient,
pool-to-riffle ratio (100 percent pool = 1.0; 100 percent riffle
= 0). percentageslope of the channel on each side of the
stream,and water temperature.
355
TAILED FROG
DUNN’S SALAMANDER
I-
We estimatedby eye the particle size of the subsaatum that
was most abundant across the stream at ten l-m intervals.
We categorized substrataas silt or sand (~2 mm diameter),
gravel (2-32 mm), pebble (32-64 mm), cobble (64-256 mm),
and boulder (>256 mm). When possible, we recorded where
eachanimal was fast seen (pool, riffle or bank-seep)and
measuredthe depth of water and size of the cover object
over individual animals. All animals were collected by hand.
Representativevouchers of each specieswere retained from
many sites and deposited at the National Museum of Natural
History in Washington, DC, the Burke Museum at the University of Washington, or the Conner Museum at Washington
StateUniversity.
We identified significant differences in streamcharacteristics
among forest age-classesand among provinces with a oneway analysis of variance, which we also used to test for differencesin amphibian densities among age-classes.Densities
were transformed as the natural log of (density + 1). and
percentagevariables (streamgradient, pool-to-riffle ratio)
were arcsine-transformed.
Results and Discussion
Scopeof Comparisons
Considerable variation was found in the biotic communities
both within and among streamsin each province we studied,
yet we sampleda relatively small number of streams(minimum N = 18 in eachprovince). Thus, our results should be
viewed as a first attempt to compare aquatic amphibian
communities in the Pacific Northwest.
Naturally Regenerated Stands
Stream characteristics-The streamswe sampledin young,
mature, and old-growth forests had similar gradients, widths,
depths, side-slopegradients, and water temperatures(table 1).
This finding was somewhatsurprising considering the large
geographic area and different mountain ranges where streams
were examined (seefrontispiece). We purposely selected
headwatersand small streamsthat were about 1 to 2 m wide,
however, and some variables (such as water depth) may
simply reflect or be correlated to streamsize (width). Sizes
of substratawere evenly distributed (P = 0.27) in streamsof
young, mature, and old-growth forests (fig. 4).
Table l-Mean valuesof physicalcharacteristicsof streams
sampledduring streamsurveys
Oldgrowth Mature
Variable
Numberof Streams
22
22
Gadicnt (9%)
Width h)
11.4
1.23
14.4
1.16
Pm1 ratio
Side slope ($0)
water temperature (‘C)
0.38
43.4
to.9
0.40
44.1
10.9
Depth&i)
4.8
4.6
Young
P
15
8.3
1.17
4.5
0.40
46.9
11.4
0.23
0.85
0.81
0.83
0.82
0.73
Table 2-Mean density (IndividualsIm~ of amphibiansin
streamsfor different forest age-classes
Species
Tailedfrog
Old-growth
Mature
22
0.86
22
0.98
1.71
22
0.37
0.73
22
1.39
1.70
1.14
22
0.61
1.09
22
1.21
8
smams
Mean
0.13
0.38
16
0.21
0.26
22
2.89
2.74
SD
streams
Mea”
Young
P
15
0.84
1.03
15
0.15
0.25
15
1.26
1.48
8
0.37
0.49
9
0.10
0.27
15
2.50
1.92
8
0.50
0.61
16
0.36
0.60
22
3.19
2.50
0.98
0.23
0.93
0.28
0.30
0.62
Siltkand Pebble Gravel Cobble Boulder
Substrate
Amphibian abundance and forest age-Abundance (individuals/m’) of each amphibian specieswas highly varied, but
no significant differences in abundancewere found among
any of the forest types (table 2).
Giant salamanderswere the most common amphibians. Pacific giant salamanderswere present in 50 of the 59 (85 percent)
streamswe sampled,and Cope’s giant salamanderoccurred
in 11 of 24 (46 percent) streamswithin their limited geographic range. Together, these specieswere present in 53 of
the 59 (90 percent) streamssampled.Tailed frogs were the
next most frequent species,occurring in 45 of 59 (76 percent)
streams.Olympic salamandersdo not occur in the Mount
0
1
2
3
4
Number of species
357
Table S-Depth of water and size of rocks used for cover for
each specks of stream smphiblsn (adult includes all transformed
juvenlks and sexually mature adults)
cover size (Cm*)
Depth (4
A%
N
Mean
SD
N
Mean
SD
Adult
lava
93
491
4.1
4.9
2.9
4.1
60
302
1.011
415
3,579
668
Adub
Olympic
salamander Larva
36
170
3.9
3.6
8.3
4.1
z
629
467
637
717
Adult
Larva
31
728
5.4
6.8
5.9
6.2
24
347
2.410
712
6,072
2.032
Cope’s giant Larva
salamander
76
8.0
7.5
37
807
699
lhnnk
salamander Adult
-
85
1.003
1,399
Sue&s
Taikd frog
Pkfi~ giant
rakmdcr
Species
-
Rainier area, but we found this speciesin 31 of 55 (56 percent) streamswithin its geographic range. Dunn’s salamander occurred in 23 of 41 (56 percent) possible streamsin the
Oregon Cascadesand Coast Range. Two streamslacked
amphibians, but most (88 percent) had 2 to 4 spies present
(fig. 5). Thus, almost all permanent streamsflowing through
the natural forests of the Pacific Northwest have multispecies
communities of aquatic amphibians.
Microhabitat
association-We
found no significant
relations
between the abundanceof any amphibian speciesand the
physical habitat variables we measured(streamgradient, pool
ratio, mean depth or median subs&atevalues). Significant
differences (P < 0.05) were found among speciesin their use
of microhabitats within streamswe studied (fig. 6). however.
Both tailed frogs and Olympic salamanderswere found most
often in riffles, and about 25 percent of the Olympic salamanderswere taken on streambanks or in shallow seepsat
streammargins. Cope’s giant salamandermostly frequented
pools. but Pacific giant salamanderswere taken about equally
in riffles and pools. Dunn’s salamanderis often semi-aquatic,
and OUTcapturesof this specieswere almost entirely on
stream-bankor seephabitats.
The majority of amphibians were found under rock or log
cover (we were unable to determine the exact undisturbed
position of all animals). Of those capturesthat provided data
on the position of animals, 471 of 722 (65 percent) Pacific
358
-
-
giant salamanders,418 of 564 (74 percent) tailed frogs, 184
of 239 (77 percent) Olympic salamanders,65 of 78 (83 percent) Cope’s giant salamanders,and 94 of 101 (93 percent)
Dunn’s salamanderswere collected from under a cover object. Larval giant salamanderswere often found in open water
in pools, and tailed frog tadpoles were observedattachedto
rocks in riffles by meansof their suctorial mouth.
Differences were found between amphibian age-classes(larvae versus all transformed individuals) and among speciesin
the depth of water and the size of rock cover under which
they were found (table 3). The larvae and neotenesof tbe
Pacific giant salamander(P = 0.056) and tadpoles of the
tailed frog (P = 0.015) were in deeperwater than adults of
each species.No difference was observed between the depth
of occurrencefor larval and adult Olympic salamanders(P =
0.44). We found that the larvae of both the Pacific giant
salamander(P < 0.001) and tailed frog (P = 0.001) were
under smaller rocks than were adults, but no significant
differences were found between the use of rocks by larval
and adult Olympic salamanders(P = 0.11).
Both adults (P = 0.035) and larvae (P = 0.001) of four speties (excluding Dunn’s salamander;table 3) were observed
at different water depths. Differences in the size of rocks
used for cover among five species(table 3) were also significant for both adults (P = 0.029) and larvae (P < 0.001).
Many of thesedifferences in the selection of cover objects
likely reflect the marked variation in speciessize. Large
adults of the Pacific giant salamanderand adult tailed frogs
were mostly found under larger rocks or boulders, whereas
the smaller larvae of Olympic salamandersand tailed frogs
often occurred under small rocks or in beds of gravel,
pebble, and cobble.
Table 4-Physical
characteristics
ot streams in each province
Table 5-Mean densities (inditiduals/m2) of stream amphibians
in each province; subprovinces are listed from northern to south-
ern (seefrontispiece)
18
19.1
1.10
4.2
0.38
48.5
10.9
IS
8.8
1.20
4.6
0.42
38.8
9.7
o.oQ,
0.45
0.42
0.63
0.31
0.002
ongon coast
Range 03)
Coast (4)
Siuslaw (5)
0.76
0.86
0.76
coquille (6)
0.65
Umpqua
(8)
/_ Andrews (6)
$,,Roguem
2.28
1.94
2.41
2.28
2.40
-
0.41
0.18
0.24
0.57
(1.49
: 0.25
0.48
0.88
: 0.38,
/ 0.10
1.40
1.75
0.04
0.07
0.07
0.28 : : 0
0.15
0.15
0.40
0.40
0.31
0.22
0.83
0
0.29
-
0.81
Qt&m Cascade%:;
m
: Mt.Hmd(@
i
50
0.29
0.14
0.16
0.22
0.58
‘_
I
0.01
0.02
so. wasbiigum
Substrate
Fire 7-Distribution
of sizes of substrates in sueatns in the sotiem
Washingtan Cascades (SW). the Oregon Cascades(Oc). and the Oregon
Coast Range (CR).
Regional Patterns
Stream characteristics-Analysis of habitat variables suggestedthat tie s!xams we sampled in eachprovince were
similar. No significant differences were found in width,
depth, or pool ratio among pmvinces (table 4). Streams
sampled in the Oregon Cascadeshad steepergradients than
in the other regions (P < 0X01), mostly becauseof a few
streamswhere very steepreaches(30-45 percent) were
sampled.The mean water temperaturein Coast Range
streamswas wanner, perhapsreflecting differences in
regional climate. Sites in the interior parts of the Coast
Range are in areasthat are subject to higher summer
temperaturesthan are streamsat higher elevations in the
CascadeRange.
Cascades (18)
ML Rainier (4)
Cowlilz River (4)
1.72
0.60
0.42
0.35
1.I 1
-
0.10
Lewis River (5)
0.70
0.45
0.34
0.10
1.20
Wind River (5)
4.32
0.97
0.16
-
For OUTsamples,statistically significant variation was found
among provinces in substrateof streams.More boulders and
fewer pebble or cobble-sized rocks were found in the streams
we studied in the Oregon Cascadesthan in the other two
regions (fig. 7). Someof the.Oregon Cascadestreamsmay
have been underlaid with bedrock, and the reduction in cover
sites may partly explain the generally low abundanceof amphibians in someof these streams.Streamswe examined in
the Washington Cascadeshad more gravel, pebble, and cobble than those in the Oregon Cascades.The Coast Range sites
had more cobble and pebble substratethan either of the Cascadeprovinces, but the differences were minor.
Amphibian abundance-Considerable variation was found
in the abundanceof each speciesamong the streamswe sampled in the three provinces (table 5). Pacific giant salamanders and Dunn’s salamanderswere most abundant in the
streamswe studied in the Oregon Coast Range, and tailed
frogs reached their highest densities in streamswe sampled
in the Washington Cascades.Olympic salamanderswere
more abundant in the streamswe searchedin the Washington
Cascadesthan in those we sampledin the Oregon Cascades
or Coast Range.
Within each of the provinces, someclinal patterns were
found. Abundance of amphibians in the Oregon Cascadesites
varied fmm the southernmoststreamsthat contained only
three speciesin low numbers to streamsin the northernmost
area (Mount Hood) that had up to five speciesin moderateto
359
Table 6-Mean
bfomass (g/m”) and dens&y (inditidualsh~
of streamamphibiansand salmonid tlshes(from Platts and
McHenry 1988)in the Pacillc Northwest
Managed Stands
Timber harvest increasesinsolation on waterways and raises
streamtemperatures(seeBeschta and others 1987, Hartman
and others 1987). Such effects usually last only until the canopy is reestablished.In the Oregon Coast Range, Antis and
Froehlich (1988) reported that shading over streamsmay
reach 50 percent in less than 5 years after clearcutting and
may approachprelogging cover by age 10. Tailed fmgs and
Olympic salamanders,however, have low and narrow temperature tolerances,and these speciesare likely to be negatively affected by the increasedwater temperaturein smeams
in clearcuts (Bury and Corn 1988b, de Vlaming and Bury
1970). Conversely, Pacific giant salamandersmay be more
abundant in streamstraversing clearcuts than in densely
high abundance.Except for Cope’s giant salamander,amphib- forested stands(Hawkins and others 1983, Mtuphy and
ians in Washington streamsshowed a reverse pattern with the Hall 1981, Murphy and others 1981). possibly becauseof
most speciesand highest abundancein streamsto the south.
enhancedpopulations of invertebrate prey for several years
We found few differences from north to south among the
after timber harvest. Invertebrates, salmonids and salamander
streamsin the Oregon Coast Range, except that Olympic
populations decline once shadeis reestablishedover streams
salamanderswere more abundant in the southernmoststreams in western Oregon (Hawkins and others 19X2,1983; Murphy
(Coquille River drainage). The four coastal streamsin the
and others 1981).
Coast Range did not differ from inland streams.
Logging can causesedimentation in streams,which eliminates
Someof thesepatterns may be due to regional variation in
crevices and cover habitat apparently neededby larval salaclimate or streamproductivity. Becauseof relatively small
manders (Bury 1988b, Bury and Corn 1988b. Hall and others
sample sizes,however, observed differences may also reflect
1978). This habitat feature is the most important determinant
variations in the collecting efficiency of field crews, or simof the number of amphibians over the long term (Corn and
ply random variation among the streamssampled.Further
Bury 1989).
work is neededto document possible clinal changesin the
occurrenceand abundanceof species.
Coarsewoody debris in and along streamsreducesdebris
torrents and channelization, functions as a sediment nap,
Comparison to Salmonid Fishes
and provides sourcesof nutrients and cover for animals in
Recently, Platts and McHemy (1988) summarizedthe known
streams(Franklin and others 1981, Harmon and others 1986,
literature on density and biomass of salmonid fshes. For
S&l1 and Swanson 1984). Timber harvest can also reduce
streamsin the Pacific region, our data indicate that aquatic
the introduction of new pieces of down wood into the streamamphibians are 10 times more abundant with 4 times the
bed (Bryant 1985, &dell and Swanson 1984, Swansonand
biomassthan what was reported for salmonids (table 6). We
Lienkaemper 1978), and such material helps maintain the
do not have comparabledata for other fishes (for example,
ecological role of streams(Meehan and others 1977,
sculpins). Even if tailed frogs are excluded becausetheir
Scrivener and Andersen 1984). The juxtaposition and patlarvae are herbivorous and the adults forage above or out of
tern of stand types resulting from forest fragmentation
the water, small streamsstill harbor populations of aquatic
becauseof logging, furthermore, may influence the occuramphibians that exceed any known estimate for coldwater
rence and abundanceof stream amphibians. Corn and Bury
fishes. Several reamns may account for these differences.
(1989). for example, suggestthat the presenceof uncut
timber upstreaminfluences the presenceand persistenceof
Amphibians may reach high densities and biomassbecause
aquatic amphibians in streamsflowing through logged areas
their adults can exploit both aquatic and terrestrial prey (Bury downstream.
and Martin 1973,Nussbaum and others 1983). Salmonid
fishes forage on invertebrates that land on or occur in water.
The responseof aquatic amphibians to clearcutting or other
Fish are attack predators and highly active, but amphibians
disturbancesmay vary regionally. Hawkins and others (1988)
often hide under cover as sit-and-wait predatorsand thus
found that tailed frogs were virtually extinct in drainage
convert more energy to biomass than do fishes. Amphibians
basins deforestedby the eruption of Mount St. Helens,
appearto be the predominant vertebrate predator in many
Washington, whereasfrog densities were high in partially or
headwatersand small streamsin the Pacific Northwest.
completely forested basins. In the Oregon Coast Range, Corn
and Buy (1989) reported that the densities and biomassof
amphibian species in unlogged streams were 2 to 7 times
greater than in logged streams. They suggested that logging
severely reduces microhabitats for larval salamanders because
streams in logged stands had more fine sediments than control
streams. Tailed frogs and Olympic salamanders were especially sensitive to logging, and in some streams these species
may experience local extinction immediately after clearcutting (Corn and Bury 1989, Nussbaum and others 1983).
Tailed frogs and Olympic salamanders are closely tied to the
stream habitats they occupy. These species appear to have
limited dispersal abilities that may prevent them from recolonizing altered streams even after the forest canopy has been
reestablished. The likelihood of recolonization by tailed frogs
is very low in streams surrounded by hot, arid environments
(see Daugherty and Sheldon 1982, Hawkins and others 1988,
Metter 1967).
There are fewer data on the response of aquatic amphibians
to timber harvest in the Cascade Range, on the Olympic
Peninsula, or in British Columbia. Aquatic amphibians in
these regions may have a higher probability of surviving the
effects of clearcutting because northern and higher elevation
montane regions are generally cooler than those at lower
elevations or lower latitudes.
The response of Pacific giant salamander populations to logging is dependent on stream gradient (Corn and Bury 1989,
Hall and others 1978). For several decades after logging, their
population numbers remain small in low gradient streams,
whereas they appear to be little influenced in high-gradient
streams. Logging does not appear to cause local extinction of
this species, and timber harvest may even temporarily enhance some giant salamander populations where there are
increases in stream productivity related to greater insolation.
I
Research Needs and Management
Recommendations
Additional research is needed on:
l
l
l
The effects of timber harvest on the occurrence and
abundance of aquatic amphibians in the Pacific
Northwest;
The habitat preferences and environmental tolerances of
aquatic amphibians, especially the Olympic salamander;
The life histories, ecology (particularly dispersal abilities),
and viable population sizes of tailed frogs and Olympic
salamanders;
l
The effectiveness of different types and sizes of buffer
strips along streams to protect amphibians; and
l
The value of different-sized patches of forested habitat in
watersheds as reservoirs or source areas for aquatic
amphibians.
We recommend that intensive research and improved streammanagement practices be directed at the Olympic salamander
and the tailed frog, which we consider to be the species most
sensitive to the effects of timber harvest. The survival of
aquatic amphibian populations in most forested areas of the
Pacific Northwest ultimately will depend upon their abilities
to persist in streams flowing through managed forests. Comprehensive planning and the protection of small streams
during logging are essential components of management
strategies aimed at protecting aquatic amphibian populations.
Bury and Corn (1988b) suggested that headwaters should be
surveyed for Olympic salamanders and tailed frogs before
timber sales, and if these species are present, then protection
efforts should be made. Buffer strips have been shown to be
effective at protecting stream biota and habitat by maintaining shade and reducing sedimentation (Beschta and others
1987, Hartman and others 1987, Murphy and others 1981,
Newbold and others 1980, Raedeke 1988). Costs of buffer
strips are higher on smaller streams than on larger streams
(Andrus and Froehlich 1988), and it may be difficult to
convince land managers that the benefits of buffer strips,
and riparian zones outweigh the costs (Bury and Corn
1988b). We therefore need to investigate alternatives for
reducing the costs of buffer strips and yet ensure the
protection of amphibians, fishes, and other wildlife along
headwaters.
Retention of deciduous vegetation (bigleaf maple, alder) and
unmerchantable conifers (small or cull trees) may be one
inexpensive way to preserve shade. We strongly recommend
that natural woody debris (large pieces that are partially
buried or decayed) be retained in streams. If merchantable
timber is felled away from the stream, the deciduous trees
within riparian areas would be left mostly intact. Cull or
broken trees that fall across streams or along the streambank
during timber harvest provide needed sources of nutrients,
sediment traps, shade and cover for wildlife. Moderate
amounts of slash and coarse woody debris are best left where
they fall. Retention of streamside trees and woody debris
also reduces the cost of removing logging debris.
361
Aquatic amphibians have small home ranges, and the protection of relatively small patches of streamside habitat might
provide habitat for viable populations. In the Oregon Coast
Range, we found that some species can occur in disturbed
reaches if protected waters are present upstream in the same
drainage (Corn and Bury 1989). The protection of only part
of a drainage (for example, a forest patch containing headwater creeks) or a buffer zone (for example, a 50-m wide
strip) may ensure survival of aquatic amphibian populations.
Headwaters and streams comprise less than 5 percent of the
total surface area of northwestern forests (Bury 1988). Wise
management of this rare and ecologically important resource,
however, is essential for maintaining the health and stability
of wildlife and fisheries populations in the Pacific Northwest.
362
Acknowledgments
We thank Robert M. Storm, and two anonymous reviewers
for their comments on the paper. Andrew B. Carey assisted
with development of the sampling design, and participated
with work in the Oregon Coast Range. We also thank the
many biologists who assisted with the field work and stream
surveys.
This paper is contribution 127 of the Wildlife Habitat
Relationships in Western Washington and Oregon Research
Project, Pacific Northwest Research Station, USDA Forest
Service. q
Continue