assessed with data from stands in the age gradient, whereas

variation from relative differences in moisture condition

among old-growth stands was assessed with data from stands

in the moisture gradient.

These analyses, and others conducted by Spies and Franklin

(this volume), resulted in the construction of complex

environmental gradients along which each stand could be

assigned a quantitative value. We included these scores in

our analyses to provide a means of identifying amphibian

habitat relationships occurring along broad environmental

gradients.

Amphibian Sampling

We sampled amphibians with pitfall traps in each stand after

the onset of fall rains in 1984 and 1985. We installed 36 pitfall traps in each stand in a 6 x 6 square array with traps

spaced 15 m apart. To prevent bias from the depletion of

individuals in the immediate area of sampling, we moved

each grid at least 50 m within the stand in 1985. We sampled

all stands for 30 to 34 days each fall (with the exception of

one stand that we sampled for only 24 days in 1984), and we

checked the traps about once a week. All salvageable specimens were collected, preserved, and deposited in the University of Washington Burke Museum in Seattle.

Vegetation Sampling

We sampled vegetation at nine points within each grid, such

that each vegetation point was uniquely associated with four

traps. We sampled live vegetation and dead woody debris in

two concentric circles around each vegetation point. We visually estimated the cover of vegetation and woody debris in

the herb and shrub layers within a 5.6-m radius (100 m2

),

and estimated physiographic midstory, and canopy variables

within a 15-m radius (707 m2

). A list and description of the

variables collected on each pitfall grid, the combined variables we constructed, and additional physiographic variables

and environmental gradients that were used are included in

appendix table 4.

Data Analyses

Because samples from 1984 and 1985 are not independent,

we used the mean value for vertebrate and vegetation data

from both years in all analyses. We calculated abundance

indices for amphibian species as captures per 100 trap-nights

for each stand. Data from time-constrained searches conducted in these stands in the spring of 1984 (Aubry and

others 1988) were included only in species richness and

presence/absence data sets.

Community-habitat relationships-Several species did not

occur throughout the geographic range encompassed in our

study; we therefore calculated species richness as the number

of species captured in a stand divided by the number of

species known to occur in the geographic area of the stand.

The Shannon diversity index (H') was used to characterize

species diversity for each stand. Note that, although our

knowledge about the geographic distributions of birds and

mammals in the Pacific Northwest is virtually complete, this

is not true for amphibians. New distribution records have

recently been reported for the Larch Mountain salamander

(Aubry and others 1987), Van Dyke’s salamander (Aubry

and others 1987), Cope’s giant salamander (Jones and Aubry

1984), tailed frog (Welsh 1985), and clouded salamander

(Jones and Raphael 1989), among others.

We examined community patterns of amphibian abundances

with detrended correspondence analysis (DCA) using the

computer program DECORANA (Hill 1979a), and we identified stand clusters with TWINSPAN (Hill 1979b). We identified environmental gradients associated with each DCA

axis with Spearman rank correlations and used direct gradient analysis (Gauch 1982) to further elucidate communityhabitat relationships.

Species-habitat relationships-We used nonparametric

analysis of variance (Kruskal-Wallis test) on log-transformed

abundance values to examine differences in amphibian abundances among age-classes within the age gradient, and

among moisture-classes within the old-growth moisture

gradient. Because the study sites were preferentially selected

to sample the full range of variation occurring within each

age- and moisture-class (Carey and Spies, this volume), the

variances in our data would be expected to exceed those

resulting from random sampling. We therefore used an alpha

level of P < 0.1 for all tests of significance. Because sampled

stands were not selected randomly, we used these analyses to

evaluate ecologically meaningful patterns in the data, rather

than to conduct rigorous hypothesis testing. We identified

significant pairwise differences using the Tukey Studentized

Range test (P < 0.05).

We converted count variables in the vegetation data-set to

densities, and transformed each vegetation variable with log,

square-root, square, reciprocal, and arcsine transformations.

We examined the resulting distributions for normality and

performed all subsequent analyses on the transformed variables that best approximated univariate normality. We examined the relationships between abundances of individual

species and physiographic and vegetative variables with

Spearman rank correlations of transformed variables.

329
We used presence/absence data to further examine specieshabitat relationships. We conducted stepwise and canonical

discriminant function analyses (DFA) of stands in which a

species was present versus those in which it was absent to

identify habitat variables that may determine whether a species occurs in a stand. Because stands were not selected randomly, we used DFA only as an exploratory tool, and not as

a method for deriving a predictive model. We used a subset

of 33 uncorrelated habitat variables in all discriminant

analyses (appendix table 4).

Results

We captured 1516 amphibians of 13 species (table 1). We

selected seven species for inclusion in community- and

species scale analyses of habitat relationships: ensatina,

western redback salamander, northwestern salamander,

roughskin newt, tailed frog, red-legged frog, and Cascades

frog. The last five species have aquatic larval stages.

Because juveniles of these species disperse seasonally from

ponds and creeks, we do not know if such individuals

captured in our pitfall traps were resident or simply moving

through the stand to preferred habitats. For this reason, we

only used data from adult captures of these species for our

analyses (see table 1).

Other species were excluded because their abundances or

percentage occurrence in sampled stands were too low (longtoed salamander and Pacific giant salamander), because they

did not occur in all of the geographic areas sampled (Larch

Mountain salamander and Olympic salamander),, or because

they are not effectively sampled with pitfall traps (western

toad and Pacific treefrog). Data on Pacific giant salamanders

and Olympic salamanders were only used in calculations of

species richness.

Community-Habitat Relationships

We found no significant differences in species richness or

species diversity among stand classes within either the age

gradient or the old-growth moisture-gradient. Our data,

however, do suggest trends of increasing species richness

and diversity with stand age, and with drier conditions in

old-growth stands (fig. 1). Species richness and diversity

were also less variable in old growth than in younger stands,

suggesting that old-growth stands may be more stable in

community composition. Species richness appears to be

influenced more by elevation than by stand age. We found

significant negative correlations (P < 0.05) between species

richness and elevation for both the age gradient (fig. 2) and

the old-growth moisture gradient (fig. 3).

Age gradient-Ordination of abundance data for amphibian

communities occurring in stands within the age gradient resulted in two non-overlapping clusters of stands with distinct

community composition (fig. 4). The first DCA axis (X axis)

330

Table l-Amphibians captured in pitfall traps in the southern

Washington Cascade Range in 1984 and 1985

Species

Total Percentage

capturesa

of stands

Salamanders:

Woodland salamandersEnsatina

Western redback salamander

Larch Mountain salamander

800

162

Mole salamandersNorthwestern salamander

Long-toed salamander

135 52

5 2

NewtsRoughskin newt 87 46

Giant and Olympic Salamanders

Pacific giant salamander

Olympic salamander

12

14

Frogs and toads:

True frogsRed-legged frog

Cascades frog

69 48

11 17

Tailed frogsTailed frog 203 67

TreefrogsPacific treefrog 5

True toadsWestern toad 12

Total captures 1516

85

28

2

11

9

4

13

l00

a

 Only adults are reported for the long-toed salamander (snout-vent length

(SVL) >45 mm); northwestern salamander (SVL >70 mm); roughskin newt

(SVL >40 mm); red-legged, Cascades, and tailed frogs (SVL >35 mm).

represents a gradient of increasing moisture and elevation;

the second DCA axis (Y axis) is negatively associated with

slope and temperature and positively associated with stand

age. Most of the separation of clusters occurs along DCA 2.

Stands in cluster 1 are located near the origin of DCA 1,

whereas stands in cluster 2 occur along the entire length of

this axis.

Ensatinas were abundant in most stands, but all other species

occurred in high numbers in only one of the two clusters.

Cluster 1 consists of stands with abundant pond-breeding

frogs and salamanders (red-legged and Cascades frogs, northwestern salamanders, and roughskin newts) and few tailed

frogs (a stream-breeding species) and western redback salamanders (a woodland salamander that breeds on land).
Cluster 1 primarily consists of mature and old-growth stands 

that are relatively flat and cool; only one young stand occurrcd in this cluster. 

The wettest and highest elevation stands occur in cluster 2, 

which is characterized by low numbers of the pond-breeding 

species and abundant tailed frogs, western redback salamanders, and ensatinas. The stands in this cluster are generally younger than those in cluster 1 and characterized by 

steeper slopes and wanner temperatures. They encompass the 

full range of variation in moisture and elevation that occurs 

in stands within the age gradient. 

Old-growth moisture gradient--Ordination of the abundance data for only old-growth stands also resulted in two 

clusters of stands with distinct community composition 

(fig. 5). DCA 1 (X axis) represents a gradient of increasing 

elevation and moisture, whereas DCA 2 (Y axis) is weakly 

associated with a stand-development gradient that is primarily related to increasing basal area of western hemlock and 

other shade-tolerant species (Spies and Franklin, this volume) 

Most of the stands occur in cluster 1 and all seven species 

are relatively abundant. Stands in cluster 2 were depauperate, 

by comparison, with low abundances of all species except 

tailed frogs and northwestern salamanders. Complete overlap 

c 0 100 200 300 400 500 600 700 

.p Age (years) 

0.0 L300 560 760 960 1 lb0 1: 

Elevation (meters) 

3c 10 

of clusters 1 and 2 occurred along the stand-development 

gradient, but the clusters were fully distinguishable along 

the gradient of increasing elevation and moisture. Stands in 

cluster 2 consist of the wetter, higher elevation, old-growth 

stands. 

Species-Habitat Relationships 

Age gradient-Mean abundance values for the seven 

selected species and for all seven species combined within 

each age-class of the age gradient are shown in figure 6. 

Significant differences among age-classes were found only 

for the tailed frog, which was more abundant in mature 

stands than in young stands. 

Although differences among age-classes for other species 

were not significant, patterns of association with age were 

evident. The ensatina and western redback salamander were 

most abundant in young stands. Western redback s&manda, in particular, occurred in very low numbers in mature 

331 
0.0 300 900 1100 

Elevation (meters) 

and old-growth stands. The northwestern salamander, roughskin newt, and Cascades frog all reached their highest abundances in old gowth. Tailed frogs and red-legged frogs were 

most abundant in mature stands and least abundant in young 

stands. Total combined abundances of all seven species was 

highest in young stands, although variation among stands in 

this age-class was high. Variation in total abundance among 

mature and old-growth stands, by contrast, was relatively 

low, which again suggests that older forests may provide 

more consistently suitable habitat for amphibians than do 

young forests. 

z 

++ All species 

RBSA RLFR 

z i I 

LOWer Elevation Higher 

Drier Moisture Wetter 

Old-growth moisture gradient-Mean abundance values 

for amphibians among old-growth moisture-classes are de 

pitted in figure. 7. Abundances for the roughskin newt alone 

varied significantly among moisture-classes, but multiplerange tests failed to identify which moisture-classes differed ro”&kin newt. RLFR = red-legged f, og, CAFR = Cascades frog. TLFR = 

significantly. tailed frog. 

332 
Ensatina Western redback salamander Red4egged frog 

Northwestern salamander Roughskin newt $ Tailed frog 

- 

Wet old-growth stands appear to provide low-quality habitat 

for several species. The ensatina and roughskin newt were 

rarely found in wet stands, and mean abundance values for 

northwestern salamanders, and for all seven species combined, increased with drier conditions. Red-legged and Cascades frogs reached their highest abundances in stands with 

moderate moisture, whereas western redback salamanders 

and tailed frogs showed little association with moisture 

condition. 

All stands-Significant correlations between species abundances and physiographic, vegetative, and structural habitat 

variables are listed in table 2. Several of the environmental 

variables associated with community organization (figs. 4, 5) 

and with abundance patterns across the age and moisture 

gradients (figs. 6-9) showed meaningful correlations. These 

included negative correlations with increasing elevation and 

moisture for the ensatina, roughskin newt, and red-legged 

frog; positive correlation with increasing elevation for the 

tailed frog; positive correlation with increasing temperature 

for the western redback salamander, negative correlation 

with increasing age for the ensatina; and negative correlation 

with increasing slope for the red-legged frog (table 2). 

Table ZSignificant correlations (P < 0.05) between physiographic and vegetative variables and abundances of amphibian 

species in the southern Washington Cascade Range (variables 

ace listed in order of decreasing importance, by column) 

Ensatina MDTREE (+) STIJMPC (-) COMFI. (-) 

WDCAl (-) LMSNAGA (-) LITTERD (-I 

F..wRuo (+I WATER (-) AGE (-) 

ELE” (-) LMSNJAGC (+) CONIFVL (-) 

BRODL.EAF (+) LTSNAGC (i) 

MTSNAGB (-) MSHRUR (t) 

westem Aback SNAGSB (-) slTJMPB (-) WPDCAZ (t) 

salamander CBTREE (-) CDWE (-) 

Rrqhskin newi ELI?” (-) Wlxxl (-1 SHRUB (+) 

BRODI.EAF (+) SN*TAGSC (-) MSNAGS (-) 

MDTRIRBE (+) snJMrc (-) 

Cascades frog SSNAGC (+) 

Tailed frog ESHRUB (-1 TALUS (+) SS~CSB (-) 

EL!3 (+) FEW (-) MSHRUB (-) 

MOSS (-) BROADM (-) DLOGSFI (-) 

333 
Western redback salamander 

0.20 

Red4egged frog Cascades frog 

Correlations with vegetative and structural variables were 

difficult to interpret, especially for those variables that 

were positively correlated with abundance. Except for the 

northwestern salamander, which was positively correlated 

with only three different height- and diameter-classes of 

intact snags, most species were positively correlated with 

vegetative features of the shrub and canopy layers. Speculating about the habitat value of such features for amphibians 

occupying the forest floor is difticult. 

Discriminant function analyses of presence/absence data 

revealed sets of variables for each species that diCfered somewhat from those generated with correlation analysis (table 3). 

Variables in the DFA models also generally supported the 

findings of detrended correspondence analysis of the composition of amphibian communities (figs. 4, 5). Ensatinas and 

red-legged frogs were typically absent from relatively wet 

stands. Ensatinas did not occur in stands containing surface 

water, however, whereas red-legged frogs wex found in 

relatively flat stands where surface water was present Tailed 

frogs occurred in relatively steep stands containing surface 

water. Both ensatinas and roughskin news were absent from 

high-elevation stands. Northwestern salamanders occurred in 

stands containing surface water and a relatively deep litter 

layer. ‘Ibe red-legged frog was the only species of amphibian 

associated with high amounts of woody debris. 

Discussion 

Community-Habitat Relationships 

A suite of environmental variables--of which stand age is 

but one minor factor-apparently determines the structure 

and composition of terrestrial amphibian communities in 

unmanaged Douglas-fir forests in the southern Washington 

Cascade Range. Young stands contained a relatively depauperate amphibian community compared to older stands, but 

young stands were also generally steeper and warmer. These 

conditions generally result in a lack of ponds and correspondingly poor habitat Car the pond-breeding salamanders and 

frogs that represent the majority of species studied. Older 

stands with flatter slopes and cooler temperatures, which 

presumably favor formation of ponds, generally contained 

the most species (fig. 5). Species richness and diversity generally increased with stand age (fig. l), but age appeared to 

have less influence on community composition than either 

elevation or moisture condition. 

In OUT study sites, elevation and moisture condition were 

highly correlated; the highest elevation stands were also the 

wettest (see figs. 4,5). Harsher climatic conditions at higher 

elevations in the Cascade Range (Franklin and Dymess 1973) 

may account for lower species richness there, but very wet 

stands also appear to provide low-quality habitat for most 

amphibians. Ensatinas, which prefer moist habitats and are 

not tied to streams or ponds for reproduction, are rarely found 

334 
Table 3-Results of discriminant function analysis between stands in which a species was present versus those in which it was absent

Item

Variablesb

R

2

Percentage correct’

WPDCAl

MCTREE (+)

CDTREE

SSNAGS

ELEV

WATER

CCTREE (+)

DLOGS

0.63

90

Northwestern

alamander

(24:22)

roughskin

newt

(21:25)

ELEV

SNAGSC

ASPECT

Redlegged

frog

(2224)

WPDCAl

CCTREE

SLOPE

WATER (+)

DLOGS (+)

TALUS

Cascades Tailed

frog frog

(9:37) (31:15)

DLOGSA ESHRUB

DLOGS SLOPE (+)

CDTREE (+) CANOPY

FLITTER MCTREE (+)

CCTREE (+) WATER (+)

BRODLEAF (+:

CBTREE (+)

0.47 0.51 0.42 0.57

60 72 68 75

a

 Numbers in parentheses indicate the number of stands in which a species was present in proportion to the number of stands in which a species was absent.

b

 Variables are listed in order of decreasing importance in the model. Variables that are associated with the Occurrence of a species are indicated with a plus

(+).

c

 The percentage correct classification was established through cross-validation.

in wet old-growth stands where soils may be saturated with

water (see also Aubry and others 1988). Northwestern

salamanders and roughskin newts also rarely occurred in

wet old-growth stands (fig. 7), even though these species

were most abundant in old-growth stands in the age gradient

(fig. 6). Among stands in the old-growth moisture gradient,

species richness was lowest in wet stands (figs. 1,5), and

combined abundances for all species were substantially lower

in wet old-growth stands than in either moderate or dry

stands (fig. 7).

The structural and functional complexity that is characteristic

of old-growth Douglas-fir forests has resulted from hundreds

of years of stand development. This ecological complexity

would not be expected to occur in younger forests (Franklin

and others 1981). We consequently expected to find significantly lower amphibian species richness and abundances in

young stands. The reason we did not is probably related to

the pattern of input and loss of coarse woody debris in stands

that have regenerated after catastrophic wildfires. Naturally

regenerated young stands have a large carryover component

of snags and logs (Spies and others 1988). Younger-aged

unmanaged stands therefore have many of the ecological

characteristics of old-growth forests. In unmanaged closedcanopy forests, these features provide habitat for amphibians

that would not be expected to occur in forest stands that

result from current timber-harvesting practices (Aubry and

others 1988; Bury and Corn 1988a, b; Spies and Cline 1988).

Unmanaged closed-canopy forests of similar physiography

apparently support similar terrestrial amphibian communities,

regardless of age. Whether these communities would also

occur in managed forests is not a question that can be adequately addressed with our data.

Species-Habitat Relationships

Ensatina-Ensatinas were most often found in young stands

in the age gradient (fig. 6), and in moderate and dry stands in

the old-growth moisture gradient (fig. 7). Relatively dry to

mesic conditions at low to mid-elevations appear to be the

major environmental influences on abundance for this

species (tables 2,3).

Previous studies of microhabitat use in the Cascade Range

indicate a positive association between ensatina abundances

and amounts of coarse woody debris, especially with moderately and well-decayed logs and snags (Aubry and others

1988, Bury and Corn 1988a). Our pitfall results also support

this hypothesis. Ensatinas were least abundant in mature

stands (fig. 6), which typically contain less coarse woody

debris than do either old-growth or young stands (Spies and

others 1988). This pattern was primarily because of high

inheritance of coarse woody debris in young stands resulting

from catastrophic fires. Lower amounts accumulate in mature

stands as existing debris decays, but inputs remain low. By

comparison, old-growth stands accumulate high amounts of

debris as the large Douglas-firs die and inputs are high.

Ensatina abundances were also positively correlated to the

density of well-decayed stumps and snags >50 cm d.b.h. and

at least 1.5-m tall (table 2). Such features provide favorable

habitat for ensatinas as the bark sloughs to the ground in

piles around the snag and forms multilayered, structurally

complex cover (Aubry and others 1988). Well-decayed

stumps and snags may also provide below-ground habitat

within the decomposing root system.

The ensatina is not associated with old-growth stands, but

some evidence indicates that this species is associated with

the large amounts of coarse woody debris characteristic of

335
old-growth forests (Franklin and others 1981). Our results

suggest that ensatinas may be adversely affected by timber

harvesting because intensive forest management results in

substantially less coarse woody debris than that encountered

in unmanaged forests (Spies and Cline 1988). Provision for

increased amounts of coarse woody debris in managed

forests would be expected to benefit this species.

Western redback salamander-Western redback salamanders were most abundant in young stands. Young stands,

however, were also relatively steep, warm, and dry (fig. 4),

and analyses of habitat variables suggest that these factors

are more important environmental influences for this species

than is stand age. Abundance of western redback salamanders

was positively correlated with a gradient of increasing temperature (table 2), yet neither analysis indicated a negative

association with age.

Previous authors have reported that western redback salamanders are commonly found in talus slopes (Herrington

1988, Nussbaum and others 1983). Although this species

favored steeper slopes, we found no evidence of an association with talus in the southern Washington Cascade

Range. Our observations indicate that talus slopes are

relatively rare in these forests. The drier conditions of steep

slopes apparently are more important for this species than

the presence of talus. Studies of cover-object use showed

that western redback salamanders are most frequently found

under moderately decayed logs >l0 cm in diameter (Aubry

and others 1988). The western redback salamander is also

not strongly associated with old-growth stands, but the

retention of coarse woody debris in managed forests would

probably also create conditions favorable for this species.

Northwestern salamander-Northwestern salamanders were

five times more abundant in old-growth than in younger

stands (fig. 6). The northwestern salamander was also the

only species of salamander present in relatively high numbers in both clusters of the old-growth ordination (fig. 5).

Mean abundance increased with drier conditions in old

growth, but variation in abundances in dry stands was extremely high (fig. 7). The age-gradient ordination indicated

that this species and all other pond-breeding salamanders and

frogs reached their highest abundances in relatively old, cool,

flat stands that were not extremely wet or high in elevation

(fig. 4). We found a strong correlation with all sizes of

relatively intact snags (table 2), but how these structural

features might provide habitat for northwestern salamanders is not clear.

Our results showed the northwestern salamander to be

closely associated with old-growth Douglas-fir forests in the

southern Washington Cascade Range during the late fall.

Bury and Corn (1988a) previously found little evidence that

northwestern salamanders were associated with old-growth

forests in the southern Washington Cascade Range, but

differences in the timing of sampling probably explain our

divergent results. Bury and Corn (1988a) ran their pitfall

traps from May to November, and our traps were open from

late September to November. Northwestern salamanders

migrate seasonally to and from breeding ponds, and captures

during the reproductive season may therefore simply reflect

individual movement through the stand to and from breeding

ponds rather than selection of the habitat in which they were

captured. Suitable breeding ponds are essential habitat

features for this species, but high-quality overwintering

habitat may also be critical for population persistence. Our

results indicate that old-growth forests are important habitats

for northwestern salamanders during the nonbreeding season

in southern Washington.

Regional comparisons by Bury and others (this volume a)

showed that northwestern salamanders were associated with

old-growth forests only in southern Washington, and that

late-fall abundances in both the Oregon Cascade Range and

the Oregon Coast Range were similar across the age gradient. Pitfall captures for northwestern salamanders were much

lower in the Coast Range (38; Corn and Bury, this volume b)

and the Oregon Cascade Range (38; Gilbert and Allwine, this

volume c), than in the southern Washington Cascade Range

(135; this study). Data on this species from the Oregon provinces, therefore, should be interpreted with caution. These

results may, however, indicate a latitude effect whereby

harsher climatic conditions in more northerly forests (Franklin

and Dymess 1973) force north-western salamanders to seek

overwintering sites in old-growth forests where climatic

conditions are less extreme (Spies and Franklin 1988). Results from the Oregon Cascade Range provide additional

support for this hypothesis. The northernmost 16 stands in

the Oregon Cascades (in the vicinity of Mount Hood) accounted for 31 of 38 captures for this species in the Oregon

Cascade Range. For these stands, northwestern salamanders

occurred at significantly higher abundances in old-growth

forests than in either mature or young forests (Gilbert and

Allwine, this volume c).

Roughskin newt-Roughskin newts were four to five times

more abundant in old growth than in younger stands (fig. 6).

Unlike northwestern salamanders, however, this species was

much less abundant in wet old-growth than in either moderate

or dry stands (fig. 7). This difference was also evident in the

old-growth ordination, where roughskin newts were found

at lower abundances than northwestern salamanders in wetter

stands at higher elevations (fig. 5). Ordination of stands in

the age gradient showed that roughskin newts exhibited the

same community associations as northwestern salamanders in

stands where environmental conditions were relatively moderate (fig. 4). Unlike northwestern salamanders, however,

roughskin newts were generally absent from high-elevation

stands (table 3). Consequently, although the roughskin newt

336
is closely associated with old-growth forests during the

nonbreeding season in southern Washington, it does not

occupy wet sites at high elevations.

Just as for northwestern salamanders, marked variation was

found in regional abundance patterns for roughskin newts

(see Bury and others, this volume a). In the Oregon Cascade

Range, roughskin newts were associated with young forests

(Gilbert and Allwine, this volume c). In the Oregon Coast

Range, by contrast, no strong patterns were found in the data

although roughskin newts reached highest abundances in

old-growth stands (Corn and Bury, this volume b). These

results may also reflect a latitude effect where old-growth

forests provide critical overwintering habitat only at northern

latitudes.

Red-legged frog-Red-legged frogs were most abundant in

mature stands within the age gradient (fig. 6) and in moderate

old-growth stands within the old-growth moisture gradient

(fig. 7). In terms of community association, red-legged frogs

exhibited the same patterns as the other pond breeders, with

the exception of the northwestern salamander, which alone

occupies the higher, wetter old-growth stands (figs. 4, 7).

This species was negatively associated with elevation, stand

moisture condition, talus, and steep slopes, and was positively

associated with cover by woody debris and the presence of

water (tables 2, 3). The presence and abundance of this species apparently was largely determined by conditions favoring the formation of ponds in relatively moderate stand conditions. This species showed little association with stand age,

but its presence was correlated with high levels of woody

debris, which suggests that red-legged frogs may require this

habitat feature for hiding cover.

Cascades frog-Captures for Cascades frogs were low, but

their abundance increased with stand age (fig. 6). Of 13 Cascades frogs captured (11 in pitfalls and 2 in time-constrained

searches), 10 (77 percent) were found in old-growth stands.

Community-association patterns for Cascades frogs were the

same as for red-legged frogs (figs. 4,5), as were their apparent preferences for old-growth stands of moderate moisture

condition (fig. 7). Patterns of association with individual

habitat variables revealed little interpretable information,

probably because of low abundance values. Further work is

needed on this species to evaluate its potential preference for

old-growth forests.

Tailed frog-The tailed frog was significantly more abundant in mature stands than in young stands (fig. 6). Its patterns of community association were the same as those for

western redback salamanders within the age gradient (fig. 4)

and for northwestern salamanders within the old-growth

moisture gradient (fig. 5). Habitat analyses indicated that

tailed frogs were associated with steep slopes, high elevations, talus, and the presence of water (tables 2,3).

Western redback salamanders appear to be correlated with

the drier environmental conditions found on steep slopes, but

tailed frogs are more likely associated with the cool, clear

creeks that also occur on steep slopes (Nussbaum and others

1983). Our results do not show the tailed frog to be associated with old-growth forests; however, young stands apparently provide relatively unsuitable habitat for this species in

the southern Washington Cascades.

Recommendations for Further Research

Intensive research is needed on the northwestern salamander and roughskin newt to elucidate the ecological

basis of their association with old-growth forests in

southern Washington. These studies should be conducted

during both the breeding and nonbreeding seasons to

evaluate the potential seasonality of habitat association

patterns.

Research should also be directed at evaluating the importance of coarse woody debris as habitat features for

the ensatina, western redback salamander, and possibly

the red-legged frog, to determine if amounts of coarse

woody debris in managed forests will be sufficient to

maintain viable populations of these species in Douglasfir forests.

Studies of the tailed frog should be undertaken in both

unmanaged and managed young forests to investigate the

low habitat quality of young stands.

Extensive studies of amphibian communities in managed

forests should be initiated immediately.

Long-term research on terrestrial amphibians in unmanaged and managed Douglas-fir forests should be initiated

to determine if patterns of association and habitat relationships vary over time, and to evaluate the extent to

which amphibian populations may be affected by forest

management over the long term.

337
Acknowledgments

We thank Diane Converse, Lynn Dils, Mike Emers, Eric

Hoberg, Janet Kormandy, Richard Pastor, Leslie Propp,

Doreen Schmidt, and Dave Somers for their hard work and

dedication during many long and difficult days of field work.

Robert Storm and two anonymous reviewers provided helpful comments on a previous draft of the manuscript.

This paper is contribution 133 of the Wildlife Habitat Relationships in Western Washington and Oregon Research

Project, Pacific Northwest Research Station, USDA Forest

Service. c]

Appendix

Table 4-Physiographic and vegetative variables examined in the southern Washington Cascade Range (variables used in

discriminant function analyses are indicated with a solid circle)

Variable Description

Physiographic:

. ELEV

* AGE

. ASPECT

* SLOPE

. WPDCAl

. WPDCA2

CDACHRNl

CDACHRN:!

CDAOLDGl

CDAOLDGZ

. TALUS

OUTCROP

INTSTREM

PERSTREM

POOLS

. WATER

Elevation

Age

Aspect

Percentage slope

Moisture gradient

Temperature gradient

Age gradient

Coarse woody debris gradient

Stand-development gradient

Stand-development gradient

Percentage of stations with talus present

Percentage of stations with outcrops present

Percentage of stations with intermittent streams present

Percentage of stations with perennial streams present

Percentage of stations with pools or ponds present

Percentage of stations with a source of water present

Variable Description

Live-tree density:

CONIFS Conifer trees, d.b.h. l-10 cm

CONIFM Conifer trees, d.b.h. lo-50 cm

. CONIFL Conifer trees, d.b.h. 50-100 cm

* CONIFVL Conifer trees d.b.h. >loO cm

. CONIFERS All conifer trees

BROADS Deciduous and broadleaved evergreen trees, d.b.h. l-10 cm

BROADM Deciduous and broadleaved evergreen trees, d.b.h. lo-50 cm

l BROADL Deciduous and broadleaved evergreen trees, d.b.h. 50-100 cm

* BROADVL Deciduous and broadleaved evergreen trees d.b.h. >loO cm

l BRODLEAF All deciduous and broadleaved evergreen trees

Percentage cover:

GRASS

HERB

l ROCK

’ SOIL

MOSS

* LICHEN

. FLITTER

FERN

l ESHRUB

DSHRUB

l BSHRUB

SHRUB

TALLCOVR

MSHRUB

. MCTREE

MDTREE

. MBTREE

MCANOPY

. CDTREE

* CBTREE

* CCTREE

* CANOPY

l DLOGSA

DLOGSB

DLOGSC

* DLOGS

Grass

Herbaceous vegetation

Rocks

soil

Moss

Lichen

Fine litter

Fern

Evergreen shrubs

Deciduous shrubs

Berty-bearing shrubs

All shrubs

AlI shrubs and ferns

Shrubs in the midcanopy

Conifer trees in the midcanopy

Deciduous trees in the midcanopy

Broadleaved evergreen trees in the midcanopy

Midcanopy

Deciduous trees in the canopy

Broadleaved evergreen trees in the canopy

Conifer trees in the canopy

Canopy

Intact woody debris

Moderately decayed woody debris

Well-decayed woody debris

Woody debris

Stump and snag densitx

STUMPA

STUMPB

STUMPC

STUMPS

SSNAGA

SSNAGB

SSNAGC

. SSNAGS

MMSNAGA

MMSNAGB

MMSNAGC

MTSNAGA

MTSNAGB

MTSNAGC

l MSNAGS

LMSNAGA

LMSNAGB

LMSNAGC

LTSNAGA

LTSNAGB

LTSNAGC

. LSNAGS

SNAGSA

SNAGSB

* SNAGSC

In&t to slightly decayed stumps

Moderately decayed stumps

Well-decayed stumps

Other:

SCAN

l LITTERD

TREPIT

stumps

Intact to slightly decayed snags, d.b.h. 40 cm, ht cl.5 m

Moderately decayed snags, d.b.h. ~10 cm, ht cl.5 m

Well-decayed snags, d.b.h. 40 cm, ht cl.5 m

All snags, d.b.h. 40 cm, ht cl.5 m

Intact to slightly decayed snags, d.b.h. lo-50 cm, ht 1.5-15 m

Moderately decayed snags, d.b.h. lo-50 cm, 1.5-15 m

Well-decayed snags, d.b.h. lo-50 cm, ht 1.5-15 m

Intact to slightly decayed snags, d.b.h. lo-50 cm, ht >15 m

Moderately decayed snags, d.b.h. lo-50 cm, ht >15 m

Well-decayed snags, d.b.h. lo-50 cm, ht >15 m

All snags, d.b.h. lo-50 cm, ht >1.5 m

Intact to slightly decayed snags, d.b.h. 250 cm, ht 1.5-15 m

Moderately decayed snags, d.b.h. >50 cm, ht 1.5-15 m

Well-decayed snags, d.b.h. >50 cm, ht 1.5-15 m

Intact to slightly decayed snags, d.b.h. >50 cm, ht >15 m

Moderately decayed snags, d.b.h. >50 cm, ht >I5 m

Well-decayed snags, d.b.h. >50 cm, ht >15 m

All snags, d.b.h. >50 cm, ht >1.5 m

All intact to slightly decayed snags

All moderately decayed snags

All well-decayed snags

Presence of super-canopy trees

Depth of litter layer

Density of tree pits

338
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Regional Patterns of Terrestrial Amphibian

Communities in Oregon and Washington

R. Bruce Bury, Paul Stephen Corn, and Keith B. Aubry

-

Authors

R. BRUCE BURY and PAUL STEPHEN CORN are zoologists, U.S. Department of the Interior, Fish and Wildlife

Service, National Ecology Research Center, Fort Collins,

Colorado 80525-3400. KEITH B. AUBRY is a research

wildlife biologist, USDA Forest Service, Pacific Northwest

Research Station, Olympia, Washington 98502.

Abstract

We examined the occurrence and abundance patterns of terrestrial amphibians in the Pacific Northwest, mostly based

on captures in pitfall traps at 130 study sites. Seven of eight

widespread species showed a marked variation in abundance

between the Oregon Coast Range and the Cascade Range in

Oregon and Washington. Only two species were associated

with an age gradient (young, mature, and old-growth forests):

the northwestern salamander was usually most abundant in

old growth, whereas the western redback salamander occurred

in highest numbers in young stands. Ensatina was most abundant in dry old growth in the Cascade Range and was the

only species with a marked response across a moisture gradient (wet, moderate, and dry forests). Abundance of species

was more often associated with physiographic variables than

with vegetation features. On the basis of multidimensional

scaling of species richness, the amphibian community in the

Coast Range appears distinct from that in the Cascade Range.

The highest species richness was in the Oregon Coast Range,

whereas the lowest species richness was in the Cascade

Range in Washington. The same analysis was unable to discriminate differences in the species richness of amphibians

among young, mature, and old-growth stands. Special habitat

features influenced the abundance of amphibians. Ponds and

streams are required for several aquatic-breeding amphibians,

but these waters were unevenly distributed in the stands we

studied. Large, well-decayed down wood was essential for

several terrestrial salamanders, and these species may eventually be reduced in numbers or extirpated in managed forests

where down wood is scarce. Rocky substrate also appeared

to influence the occurrence and abundance of several salamanders. The Pacific Northwest has several endemic species

with restricted distributions and specialized habitat requirements. Unless management strategies are tailored to these

unique species, they may decline locally or be extirpated.

Introduction

The value of old-growth forests for wildlife habitat and the

effect of timber harvest on this resource is the subject of

current debate (see Fosburg 1986, Harris 1984, Kerrick and

others 1984, Meslow and others 1981, Norse 1990, Salwasser

1987, Wilcove 1987). Old-growth forests dominated by

341
WASHINGTON ! 

‘--- ..-__ -____ 

i 

: 

---I 

,> 

J” 

OREGON l 

/ 

Douglas-fx have a wide range of tree sizes and ages, a deep 

multilayered canopy, large individual trees, and accumulations of large pieces of coarse woody debris (Franklin and 

Spies 1984). These distinctive attributes of old-growth forests 

may be important habitat elements for several species of the 

Pacific Northwest herpetofauna. 

Reptiles are prevalent in open habitats such as oak woodland or grassland (Raphael 1987, Welsh 1987), where different techniques are needed to sample them adequately. 

Results of sampling terrestrial amphibians have been reported 

for four provinces: Southern Washington Cascade Range, 

from Mount Rainier National Park south to the Columbia 

River (Aubry and others 1988; Aubry and Hall, this volume), 

Oregon Cascade Range (Bury and Corn 1988a: Gilbert and 

Allwine, this volume c), Oregon Coast Range (Corn and 

Bury, this volume b), and the Klamath Mountains province 

in southern Oregon and northern California (Raphael 1987b; 

Raphael 1988~; Welsh and Lind 1988, this volume). Aquatic 

amphibians were analyzed separately (Bury and others, this 

volume b; Bury and Corn 1988b; Corn and Bury 1989). 

Here, we attempt to identify which species of the herpetofauna are associated with gradients of forest age and moisture condition in naturally regenerated forests for the three 

provinces north of the Klamath Mountains. Our specific 

objectives are: 

l To compare the species richness and relative abundance 

of terrestrial amphibians among different forest stands; 

l To elucidate regional differences in the structure and 

composition of terrestrial amphibian communities relative to their biogeographical patterns; and 

l To provide guidelines for managing and protecting these 

species. 

Methods 

._. We compared 1patterns patterns of abundance abundance among the three provinces by using several several statistical statistical approaches. approaches. We used twoway analysis of variance variance (ANOVA) (ANOVA) to test for significant significant 

differences differences among provinces provinces in the abundance abundance of species species that 

occur in all three provinces. provinces. Study sites were not selected selected at 

random because of logistical problems (for example, inaccessible wilderness) and land-use patterns (for example, private 

ownership or active logging nearby). Thus, we used statistical tests to identify major patterns in the data rather than to 

test specific hmotheses (see Carey and Spies, this volume). 

Methods of sampling amphibians included time-constrained 

collecting, which is useful for capturing certain terrestrial 

species, and pitfall trapping, which is effective for sampling 

most terrestrial species, especially migratory forms. These 

techniques are based on general herpetological sampling 

(see Bury and Raphael 1983, Campbell and Christman 1982, 

Jones 1986, Raphael and Barrett 1981). and specific methods 

developed for Pacific Northwest forests (Bury and Corn 1987: 

Corn and Bury 1990; Raphael 1988~). 

distribution maps (Nussbaum and others 1983, Stebbins 1985) 

Most areas in the Pacific Northwest support as many as 19 to 

23 species of amphibians and reptiles, based on published 

and our field studies (fig. 1). Further, these herpetological 

communities may be ecologically important because of the 

high numbers and biomass of resident amphibians and 

reptiles (see Bury 1988). 

Recently, the Old-Growth Forest Wildlife Habitat Program 

(see. Ruggiero and Carey 1984) conducted several studies on 

amphibians and reptiles in forested habitats. Few reptiles 

were captured, and they are not discussed in this paper. 

342 
Species included in the ANOVA analyses were the northwestern salamander, Pacificgiant salamander, Olympic salamander, ensatina, western redback salamander, roughskin

newt, tailed frog, and red-legged frog. Only data derived from

pitfall captures were used in these tests because abundance

data from time-constrained collecting may be biased (Corn

and Bury 1990, this volume b). Abundance was expressed as

number captured per 100 trap-nights. We excluded juveniles

of the northwestern salamander (<70 mm snout-vent length

[SVL]), roughskin newt (<40 mm SVL), tailed frog (<35 mm

SVL), and red-legged frog (<35 mm SVL) from the analyses

so as to minimize the effects that seasonal pulses of aquatic

breeders moving through the study sites would have on

estimates of abundance (see Bury and Corn 1987,1988a).

Separate two-way ANOVAs were performed for amphibians

across gradients of age and moisture. Most stands were naturally regenerated after catastrophic fire, and three age-classes

were represented: young (35-79 years old), mature (80-195

years), and old-growth (200-730 years). A moisture gradient

(wet, moderate, and dry) was established for the old-growth

stands (see Spies and Franklin, this volume).

Pitfall trapping was conducted in 147 stands. We compared

pitfall data among 130 stands across the chronosequence and

83 old-growth stands on the moisture gradient. We used a

6 by 6 grid of traps (15 m apart) in each stand, which is

described in detail elsewhere (Corn and Bury 1990).

Some differences in techniques were used for each province.

In the Oregon Cascade Range, trapping was conducted in 56

stands; all stands were sampled in 1984, and the same grids

in the central stands (on or near the H.J. Andrews Experimental Forest) in 1985 (Gilbert and Allwine, this volume c).

Stands in the southern Washington Cascade Range (n = 45)

and the Oregon Coast Range (n = 46) were trapped in both

1984 and 1985, and trap grids were moved between years in

Washington (Aubry and Hall, this volume) but not in the

Coast Range (Corn and Bury, this volume b). Values are

expressed as mean captures to facilitate comparisons between

provinces that have different numbers of stands. We used

1985 data from the Oregon Coast Range and the Cascade

Range in Washington because the analyses of these data

within each province combined the captures from both years

(Aubry and Hall, this volume; Corn and Bury, this volume b).

We used gradient analyses to investigate relations between

the abundance of species and habitat variables (physiographic

and vegetative). Physiographic variables were measured on

each pitfall grid (see Corn and Bury, this volume b) and included stand age, elevation, aspect (cosine-transformed), percentage slope (arcsine-transformed), and the presence or absence of surface water or exposed talus. Individual vegetative

variables were combined into broad stand-scale gradients

using canonical discriminant analysis. Separate analyses

resulted in four variables (Spies and Franklin, this volume):

DF1A and DF2A from an analysis of stands in the chronosequence, and DF1M and DF2M from an analysis of stands

in the moisture gradient. DF1A is positively correlated with

stand development (for example, number of large trees, stand

age, and variation in tree diameter), and DF2A is positively

correlated with coarse woody debris (primarily volume of

snags and down wood). DF1M was negatively correlated

with the basal area of shade-tolerant trees and apparently

represents a temperature gradient (stands from the Coast

Range have high scores, Washington stands have low scores).

DF2M was negatively correlated with the density of subcanopy trees and cover of evergreen shrubs, and it represents

a moisture gradient (wet stands have high scores).

Because the abundances of most amphibian species varied

among provinces, we tested for associations between abundance and continuously distributed habitat variables. We

compared abundance among provinces by using the habitat

variables as covariates. The presence or absence of variables

(water and talus) were tested in a two-way ANOVA with

province.

We compared the structure and composition of amphibian

communities among provinces by determining the presence

or absence of 12 species. Eight species occurred in all provinces, and four others were present in one or two provinces

(the clouded salamander, Oregon slender salamander, Dunn’s

salamander, and the Cascades frog). We combined the results

of time-constrained collecting and pitfall trapping to generate

lists of species in each stand. Such an approach precludes the

use of abundance data, but it provides a more complete list

of species than pitfall data alone (Corn and Bury 1990).

Species richness was based on one time-constrained collection (or survey of down wood) and 2 years of pitfall trapping

in each of 55 stands. Surveys of down wood (equivalent to

time-constrained collection) were done in only 15 of the

study sites in the Oregon Coast Range (Corn and Bury, this

volume b), so we selected subsamples (the central stands)

from both provinces in the Cascade Range. In Oregon, we

used data from 19 stands in or near the H.J. Andrews Experimental Forest (Gilbert and Allwine, this volume c), and in

Washington, we used data from 21 stands in the PackwoodRandle area (Aubry and Hall, this volume).

We used multidimensional scaling (MDS) to represent the

pattern of presence or absence of the 12 species; MDS computes two-dimensional coordinates for a set of stands so that

the distances between pairs of stands fit as closely as possible to their measured similarities (Wilkinson 1988). Similarity between pairs of stands was computed with Jaccard’s

index (Pielou 1984), which is the number of species present

in one stand in proportion to the total number of species

present in the pair of stands.

343
Table I-Mean captures (number per 100 trap-nights) of amphibians across the chronosequence of forest stands (standard 

deviations are in parentheses) 

Table 2-Separate two-way analysis of variance of abundance 

versus province and age-class, and abundance versus province 

and moisture-class 

Using the same set of data on species richness, we performed 

a nonhierarchical clustering of stands using the K-means procedure of SYSTAT (Wilkinson 1988). The K-means procedure produces a specified number of nonoverlapping pools 

(clusters) of stands. We chose three pools because three provinces and three forest age-classes were analyzed. 

Results 

Variation Within the Chronosequence 

Marked variation was found in the abundance of amphibians across the chronosequence of selected stands (table 1). 

Ensatina was usually the most common species captured in 

all stand ages for each province, followed by roughskin 

newts. Western redback salamanders were an exception, 

being more abundant in young and old-growth stands in the 

Oregon Coast Range than either of the other two species. 

We found that seven of eight species showed marked variation in abundance among provinces (table 2). Only the 

northwestern salamander and the western redback salamander were significantly associated with the age gradient when 

variation among provinces was taken into account. The northwestern salamander was more abundant in old growth (this 

pattern was not apparent in the Coast Range) than in mature 

or young stands. They were most abundant in Washington. 

The western redback salamander was most abundant in young 

stands and in samples from the Coast Range; the species was 

rare in the Cascade Range in Oregon. A strong interaction 

was found between province and stand age for roughskin 

newts. This species was most abundant in old-growth forests 

in Washington and in the Coast Range, and in young stands 

in the Oregon Cascade Range. 

Variation Within the Moisture Gradient 

Ensatina was the only species with a significant response to 

the moisture gradient (tables 2 and 3). In both Cascade Range 

provinces, ensatina was most abundant in dry old-growth 

stands. 

344