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Old Growth Forests and the
Distribution of the Terrestrial
Herpetofaunal
Hartwell H. Welsh, JrS2and Amy J. Lind3
The coniferous forests of the Pacific
Northwest are currently the focus of
a national conflict between competing interests. These ancient forests,
previously more species rich and
continuous across the continental
United States, have undergone a
natural decline since the Mesozoic in
conjunction with broad climatic and
geologic changes (Axelrod 1976).
This process eliminated most of the
wooded areas of the Midwest, but
left expansive tracts of forest in the
eastern and western United States. In
the last hundred years, many of these
remaining ancient forests have been
harvested for wood products, changing the species composition, structure, and forest age (Harris 1984).
These natural forest ecosystems have
been altered so rapidly that we are
only now recognizing the loss of
some plant and animal species and
the threat to others [eg., the spotted
owl (Strix occidentalis)] (Simberloff
1987).Recent concern for the health
and well-being of these forest ecosystems, and the need for more knowl'Paper presented at the Symposium on
Management of Amphibians, Reptiles, and
Small Mammals in North America (July 7 92 1, 1988, Flagstaff Arizona).
Wildlife Biologist, Pacific Southwest Forest and Range and Experiment Station,
Forest Service, US. Department of Agriculture, Arcata, California 9552 1.
3BiologicalTechnician,Pacific Southwest
Forest and Range and Experiment Station,
Forest Service, U.S. Department of Agriculture, Arcata, California 9552 1.
Abstract.-Terrestrial herpetofauna were sampled
by pitfall traps and time-constrained searches on 42
stands of Douglas-fir/hardwoodforest in southwestern Oregon and northwestern California. Stands
ranged in age from 40 to 450 years. We found 25
species of herpetofauna. Species diversity was
greater in older forest stands than in young stands.
Amphibians were significantly more abundant in old
than in young stands and significantly less abundant
in dry than in moist stands. Our research indicates
that changes in forest structure due to forest practices results in reduced species diversity and abundance among the herpetofauna.
edge to meet management goals and
the requirements of the National Forest Management Act 1976 and the
~ n d a n ~ e r eSpecies
d
Act 1973 has
prompted research into the structure
and composition of the vertebrate
communities of these forests
(Meslow et al. 1981, Raphael 1984,
Ruggiero and Carey 1984).
From 1981 through 1983, Raphael
(1984,1987, this volume) used a variety of sampling methods to collect
data on the forest age, moisture, and
habitat associations of birds, mammals, reptiles, and amphibians in forests of northwestern California. From
1984 through 1986, researchers from
the Forest Service's Pacific Southwest
Forest and Range Experiment Station
extended these studies to include
southwestern Oregon. By measuring
differences in the species composition and relative abundance of the
herpetofaunal community in altered
versus unaltered habitats it is possible to indicate biologically meaningful differences in habitat quality
(e.g., Bury et al. 1977, Busack and
Bury 1974, Jones 1981, Luckenbach
and Bury 1983, Ortega et al. 1982).
Such information on differences in
the composition of the herpetofauna,
relative to forest age and moisture,
have scientific value as well as practical value, as indicators of habitat
change, useful to natural resource
managers.
This paper reports on a study to
determine the occurrence and abundance of the forest herpetofauna rela-
California
0 Coastal Stand
A Inland Stand
Figure 1.-Study stands in Douglas-fir forests
were located in northwestern California
and southwestern Oregon. Triangles =
stands in the inland area, circles = stands in
the coastal area.
tive to forest age and moisture, and
to compare two methods (time-constrained searches and pit-fall trapping) used to sample this herpetofauna in northwestern California
and southwestern Oregon.
STUDY AREA
This study was conducted in
Douglas-fir (Pseudotsuga menziesii)/
hardwood forests at low to mid-elevations in the Klamath Mountains
and Coast Range. We sampled 54
stands, but we use data from only 42
stands, omitting nine higher elevation, white-fir dominated, stands and
three stands on serpentine soils because they differed so greatly from
our remaining stands. Even-aged
stands in the above forest type were
selected in three areas within the Klamath Mountains and Coast Range
(fig. I ) in accordance with procedures outlined by Spies et al. (in
press). Using stand characteristics
(Franklin et al. 1986) and tree age, we
assigned stands to one of three age
classes: young, mature, and oldgrowth forests. Stands ranged in age
from 40 to 450 years. Stands in oldgrowth were further categorized into
three moisture classes: dry, mesic,
and wet (fig. 2). Stands ranged in size
from 21 to 150 hectares, and in elevation from 53 m to 1205 m. One-half of
the stands occurred within the Coast
Range, an area formed primarily of
Franciscan parent materials and
dominated by the maritime climatic
influences of the Pacific Ocean. These
stands were classified as coastal forest stands (fig. 1). All stands were
dominated by Douglas-fir and conOld Crowlh
Dry:
C
Old CroNth
MCSIC:
Moislure Class
Old Gtowth
Wct:
+
Figure 2.-Distribution of study stands by
forest age and moisture class, and by
coastal and inland area.
tained a significant hardwood element, primarily tanoak (Lithocarpus
densiflora) and madrone (Arbutus
menziesii); about half also contained
coast redwood (Sequoia sempervirens).
The other sites were designated
inland stands (fig. I), occurring
within the Klamath Mountains, primarily on granitic and metamorphic
parent materials. This area is subject
to colder winters and drier, hotter
summers than the Coast Range. The
inlands stands were dominated by
Douglas-fir in association with
tanoak, madrone, and to a lesser extent, canyon live oak (Quercus
chysolepis), black oak (Quercus kelloggii), ponderosa pine (Pinus ponderosa), sugar pine (Pinus lambertiana),
and incense cedar (Calocedrus decurrens). For a more complete description of the vegetations of these two
provinces see Raphael (in press) and
Sawyer and Thornburgh (1977).
METHODS
Herpetofauna Sampling
A herpetofaunal sampling design
was developed for the USDA Forest
Service's old-growth wildlife habitats
project in Oregon and Washington
by Corn and Bury (in prep.). Their
design used two methods to sample
species composition and relative
abundance of the herpetofauna: pitfall traps (PF) and time-constrained
searches (TCS) (Bury and Corn, this
volume; Welsh 1987). The TCS
method employed in our study differed from that described by Corn
and Bury (in prep.) in that headwater
habitats (springs, seeps, and first order streams) were included in the
sampling. Pitfall trap grids consisted
of 36 cans buried at ground level and
spaced 15 m apart. Traps were covered with bark or cedar shakes. We
sampled 40 stands in the fall of 1984
and 1985, for 50 and 30 nights, respectively. Our total pitfall trapping
effort amounted to 115,200 trapnights. Time-constrained searches
consisted of intensively searching all
terrestrial microhabitats in the forest
environment for a fixed amount of
time. Only actual search time was
counted, when an animal was encountered the timer was stopped
while data were collected. A 4-person-hour TCS was conducted on
each of the 42 stands in 1984 and
1985. An additional 4-person-hour
TCS was conducted on 30 stands in
1986. Our total effort for TCS
amounted to 456 person-hours.
Forest Age
Forest age was determined for each
stand by increment borer, or by
counting rings on stumps in adjacent
logged areas. Dominant or co-dominant size class Douglas-fir trees were
selected for aging and trees were
cored at breast height. Two to 10
trees (average 3) were cored on each
stand and the sample mean was used
to estimate forest age for the stand.
On the basis of tree coring, ring
counts, and structural characteristics
(Franklin et al. 19861, we grouped
stands into three age classes: young
forest, <I00 years; mature forest, 100200 years; and old-growth forest,
200+ years (table 1).
Moisture Class
Stands that were classified as oldgrowth were also assigned a moisture classification (dry, mesic, or
wet), depending on plant species
composition and percent cover of the
herb and shrub layers within the
stand. The data were independently
recorded from three to five 0.1 ha
circular plots selected at random
within each stand. Moisture class assignment was based on mean percent
cover values and the absolute constancy of particular shrub and herb
species within each stand.
Faunal Comparisons
We tested the null hypotheses (Ho)
that mean capture frequencies for
herpetofauna did not differ between
either forest age or moisture classes
(1) within the coastal and inland areas, (2) between the coastal and inland areas, and (3) among all stands
(coastal and inland areas combined).
Only the mesic old-growth stands
were used in the age analysis (fig. 2).
One coastal old-grow th dry stand
prevented testing for differences in
means among moisture classes
within the coastal area, and between
the coastal and inland dry stands.
We emphasize that our inferences
are drawn from observations and not
experimental manipulations. Though
our results are described in the context of hypothesis testing, our study
is primarily exploratory. In addition,
the power of our tests was low because our sample sizes were relatively small. Our approach yields
preliminary results about forest age
and moisture relationships among
the herpetofauna, but we caution
against making broad inferences.
Combining Data Across Years
Data from pitfall trapping were totaled, by stand, for each species, divided by 50 (1984 data) or 30 (1985
data) nights x 36 traps and multiplied by 1000 to yield captures per
1000 trap-nights. Data from timeconstrained searches were adjusted
for unequal sampling effort by expressing abundance of each species
in captures per person-hour.
We performed paired t-tests between years (total captures per
stand) for each data set. TCS samples
were not significantly different between years: 1984 vs. 1985, t = 1.16, P
= 0.25; 1984 vs. 1986, t = 1.24, P =
0.22; 1985 vs. 1986, t = 1.85, P = 0.075.
PF samples were also not significantly different between years: 1984
vs. 1985, t = 1.85, P = 0.072. Consequently, we combined years for each
sampling method for all analyses.
Statistical Comparisons
For each method, we tested for statistical differences in mean capture frequencies among age and moisture
classes, across, within, and between
inland and coastal areas. These tests
were performed on the total herpetofauna, taxa at the level of class, order, and sub-order, and on those species captured on at least one third of
our stands in either area.
Mean capture frequencies of each
faunal grouping were tested for statistical differences among three forest
age classes and three moisture
classes. In cases where group variances were equal among classes, we
used one-way analysis of variance
(ANOVA). We used Hartley's F max
test (Milliken and Johnson 1984:18)
with P 5 0.01 to determine the equality of variances for all three-group
tests. We used P 5 0.01 because
ANOVA is robust under moderate
violations of the assumption of equal
variances (Zar 1984:170).If a significant F-statistic resulted from the
ANOVA test, we tested further for
significant differences between pairs
in order to isolate the source of the
differences by using the Tukey test
(TU) for mu1tiple comparisons (Zar
1984:186).Where group variances
were not equal or where one of the
three age or moisture classes had no
captures, we performed all pairwise
tests (mu1tiple comparisons) using
the Games and Howell modification
of the Tukey test (GHMC) (Keselman
and Rogan 1978).
To test for statistical differences in
capture frequencies in age and moisture classes between coastal and inland areas, we used two sample ttests (Zar 1984:131).We followed the
more conservative approach of not
pooling variances. Between-area
comparisons consisted of two families of tests: (1)a single paired comparison based on all stands, and (2)
five pairwise comparisons defined by
the different forest age and moisture
classes. Tests in the first family were
considered statistically significant at
the P 5 0.05 level. A Bonferroni adjustment (Miller 1981:67)was used
for tests done within the second family to maintain an overall significance
level of P 5 0.05.
For the species richness analyses,
stand records from the TCS and PF
data were combined. The means of
the total number of species for each
forest age and moisture class were
tested for differences described.
Also, the similarity of species'
composition among equal numbers
of stands (selected randomly) in each
forest age class were determined by
using Jaccard's similarity coefficient
(Sneath and Sokal 1973:131):
in which, for any two classes, a =
number of species in common, b =
number of species in the first class
only, and c = number of species in
the second class only.
RESULTS AND DISCUSSION
We sampled 25 species. Amphibians
accounted for 97.8% (salamanders,
96.3%)of all captures, and reptiles
2.2%. The TCS method yielded more
than 66% of all captures (table 2),
sampling 22 species (table 3) and accounting for 67% of the amphibians
and 85%of the reptiles. The PF
method sampled 19 species (table 4)
and accounted for slightly less than
1/3 of all captures (table 2).
Species Composition, Richness
Similarity Indices
Based on species presence-absence
data, an analysis of faunal similarities between forest age classes
(coastal and inland areas combined)
indicated that greatest similarity in
species composition occurred between the mature and old-growth
stands (table 5). Jacard's Similarity
Index (TSI)values, for comparisons
between young and old-growth
stands and young and mature
stands, indicated that young stands
were different in species composition
from both classes of older forest
stands. These differences were greatest between young and old-growth
stands (table 5).
Species Richness
The number of species per stand for
all 42 stands ranged from 3 to 13 (fig.
3). The coastal mature stands yielded
the highest mean number of species
overall, while the lowest mean number of species occurred on the inland
mature stands (table 6, fig. 3). The
coastal stands had significantly more
species per stand than the inland
stands (fig. 3, table Al).
With coastal and inland areas
combined, our mean species values
indicated that species richness was
greatest on mature stands (table 61,
but was not statistically different.
In the inland area, the old-growth
dry stands had the greatest mean
number of species (table 6) but no
comparisons yielded significant differences (fig. 3). Within the coastal
area, mean numbers of species were
significantly different between forest
age classes. Multiple comparisons
(TU)indicated that the greatest differences occurred between young
and mature stands (fig. 3).
The significantly higher number of
species in the coastal vs. the inland
area (fig. 3) is attributable to the
salamander Aneides lugubris and four
snakes (Thamnophis couchii, T. sirtalis,
T. elegans, and Charina bottae), which
were all sampled in very low num-
bers and only in the coastal area
(tables 3-4). We believe this is an artifact of the difficulty of sampling for
snakes in forested habitats (Bury and
Corn 1987, Raphael and Marcot 1986,
Welsh 1987). Most snake species exist
in low densities, and available sampling methods only establish presence. All of these snake species occur
in the inland area. The arboreal
salamander, Aneides lugubris, is absent inland at the northern latitudes
we sampled (Stebbins 1985).
The fact that we generally found
more species on older stands and
that we found a greater similarity
between mature and old-growth
stands than betwcen either of these
older classes and young stands (see
also Raphacl, this volume) suggests
that both the mature and old forest
age classes provide more suitable
habitat and a more diverse herpetofauna than young forests.
Relative Abundance Analysis
Differences Between TCS and PF
A notable aspect of our data is the
differences be tween the TCS and PF
methods-both in terms of kinds of
species and numbers of individuals
captured. These differences follow
from the different natures of these
sampling methods. TCS is an active
search method that permits the investigator to seek out animals where
they hide. PF is a passive method
that relies on animal surface movement or the seeking of shelter under
trap covers (Welsh 1987.)
The results of our comparisons of
salamander captures between coastal
and inland areas using TCS and PF
data, which appear contradictory,
serve to illustrate the pronounced
differences between the two methods. With TCS data, in all comparisons except the old-growth wet category, the coastal area had higher
mean captures than the inland area.
This result was due to high captures
(over 900 individuals) of a single species of salamander, Batrachoseps attenuatus, a species that occurred in all
age and moisture classes. This species is absent inland. However, several factors unique to the inland area
acted to counter the effects of the
high captures of B. at tenuatus. Those
factors were the high captures of Plethodon elongatus (more than 250 captures), a species found almost exclusively on the inland stands, and
higher relative captures of Ensatina
eschscholtzii inland (865 inland vs. 580
coastal).
In contrast, results from PF, indicated significantly higher captures on
inland stands than on coastal stands,
for all stands combined (table Al).
PF captured few (n=72) of the highly
sedentary Batrachoseps at tenua tus
relative to TCS (n=972).Captures of
the relatively more vagile salamander species, P. elongatus and E. eschschol tzii, were greater on the inland
stands than the coastal stands, for the
PF data.
TCS provided a more complete
data set, sampled more species (particularly reptiles) and had twice as
many individuals as did PF (tables 24). The active nature of TCS accounts
for the disparities in capture numbers, and in the lack of consistency of
statistically significant differences
among forest age and moisture
classes between these data sets, even
for the same species (table A1 ). Most
significant results from our analyses
derived from the larger TCS data set.
Subsequent discussion of results will
refer to these data unless they are
identified as PF data. Mean captures
(+ one standard deviation) for all
taxa analyzed are found in tables 3
and 4. Results of all tests on both
data sets, and test statistics for those
tests with significant differences, are
found in table Al.
Salamanders
Almost all captures (96.3%)were
salamanders (table 2), consequently,
the results of our analyses were essentially the same for all herpetofauna, amphibia, and salamanders
(species combined) (table Al). Salamanders were not equally distributed among forest age classes. Testing the equality of mean captures
among age classes, with coastal and
inland areas combined, yielded significant differences. Multiple comparisons (TU)indicated these differences were between the young and
old stands, with more captures on
the old stands (fig. 4).
Salamanders were not equally distributed among forest moisture
classes. Multiple comparisons
(GHMC), with areas combined, indicated a significant difference in mean
captures between the old-growth
mesic and old-growth dry stands,
with more captures in the mesic
stands (fig. 4). These differences are
probably a result of the fact that drier
sites offer less equable habitat for
amphibians. We also captured fewer
Figure 3.-Numbers of species of herpetofauna captured in the coastal and inland
areas in three forest age and three forest
moisture classes of Douglas-fir dominated
forests from 1984- 1986. Captures were by
time-constrained search (TCS) and pitfall
traps (PF).
amphibians on old-wet stands than
old-mesic stands, although the difference is not statistically significant.
Within the coastal area, multiple
comparisons (TU) indicated that both
mature and old-growth mesic stands
were significantly different from
young stands, but not from each
other, with the lowest mean captures
occurring on the young stands (fig.
5a). Between-area comparisons for
salamanders indicated a significant
difference in means between coastal
and inland mature stands (fig. 5a).
The PF data yielded no significant
differencesbetween mean captures
in age or moisture classes with
coastal and inland areas combined or
within either area (table Al). However, comparisons between these areas indicated a significant difference
with all stands combined (fig. 5b).
The greatest differences occurred between the old-growth wet stands;
however the results were not significant (fig. 5b).
The greater number of individuals
in older stands parallel our findings
of greater numbers of species in
older forest age classes (table 6). As
with the species richness analysis, the
number of individuals was greater in
older forests of the coastal area than
in the inland area. These differences
suggest that older forests support
both a richer and more abundant
salamander fauna.
The lower capture rates on oldwet s tands compared to old-mesic
was an unexpected result. We offer
two possible explanations for these
lower sample values. One possibility
is that the habitat structure is more
complex on these wet forest stands,
with more and larger downed
woody material, a thicker duff layer,
and denser understory vegetation
requiring more time to search and
making it more difficult to find animals (TCS method) and making them
less likely to be moving about on the
surface and cncoun tering our traps
(PF method). A second possibility is
that the wet stands actually contain
fewer salamanders.
Salamanders play an important
functional role in forest ecosystems
because of several unique aspects of
their ecology. Though they are small,
with 90% of species having.adult
body masses less than those of small
birds and mammals (Pough 1980),
they are often a major portion of the
vertebrate biomass in a forest. At the
Hubbard Brook Experimental Forest
in New Hampshire, a single species
of salamander accounted for a
greater portion of biomass and secondary productivity than any other
vertebrate group (Burton and Likens
1975a,b). Their small size enables
them to exploit prey too small to be
used by birds and mammals and
subsequently to convert these prey
into biomass that is available to
larger vertebrates (Pough 1983).
Pough et al. (1987) cites both direct
observations of predation and the
ubiquity of defensive mechanisms
among salamanders as evidence of
their importance as a food source for
both avian and mammalian predators. Because salamanders are ectotherms and have the lowest metabolic
rates of any terrestrial vertebrates
(Feder 1983), this biomass conversion
process is extremely efficient, with
40-80% of the energy invested being
used to produce new biomass
(Pough et al. 1987).As a consequence
of these characteristics, salamanders
are quantitatively and qualitatively
important components of food webs
STAND TYPE
of many forest ecosystems. The fact
that their numbers appear to be reduced by certain forest practices
could potentially affect energy flow
and biomass production at all biological levels.
Frogs
Testing the equality of mean captures
yielded significant differences in captures of frogs in coastal age and
moisture classes, with significantly
higher mean captures in old vs.
young stands and mesic vs. wet
stands (table Al). These results are
attributable to a single species, the
Pacific treefrog. No other significant
differences were found (table Al).
Figure 4.-Captures of salamanders per
person-hour (TCS) in three forest age and
three moisture classes. Data are from the
coastal and inland a r e a combined, and
sumpling occuned from 1984-1986.
STAWD WE
Figure 5.-Captures of salamanders per person-hour (A:TCS) and per 1000 trap-nights (B:PF)
in the coastal and inland areas. Data are from 1984-1986 (ICS) and 1984-1985 (PF).
Reptiles
The reptile fauna in the forests of the
Pacific Northwest is depauperate
(Nussbaum et al. 1983, Stebbins 1985)
with most species occurring in relatively low abundance (tables 3-4).
Distribution of rep tile species, by age
and moisture class, indicated about
equal numbers of species in the
young, mature, and old-growth age
classes, with lower numbers of species in old-growth wet forests.
Based on TCS and PF data, our
mean captures of reptiles (species
combined) were higher on both drier
and older stands, but the differences
were not statistically significant. Our
sample sizes were not sufficient to
analyze for differences among age
and moisture classes at the species
level, except for the northern alligator lizard for which our data indicated no statistically significant association with a particular forest age or
moisture class (table Al).
We did not sample in any recently
harvested areas, but given their preferences for open areas and their related heliothermic natures, reptiles,
particularly lizards, probably increase following logging, and
through the early sera1 stages of regenerating forests (see Raphael, this
volume). Raphael and Marcot (1986)
indicated that the sagebrush lizard
(Sceloporus graciosus) was four times
Figure 6.-Captures per person-hour (TCS)
of the Pacific treefrog (Hyla regilla), in three
forest age and three moisture classes. Data
are from the coastal area from 1984- 1 986.
as abundant in early vs. late shrub
stages.
Relative Abundance of Common
Species
Common species (captured on at
least one third of our stands in either
area by either sampling method)
were analyzed for differences in
mean captures in age and moisture
classes, across, within and between
coastal and inland areas (table Al).
Besides the northern alligator lizard,
these species consisted of amphibians-2 frogs and 7 salamanders.
Other amphibians whose distributions relative to forest age were considered noteworthy are also discussed.
Yellow-Legged Frog (Rana
boylii).-This species was absent
from all young stands (table 4)) but
they were also captured at such low
frequencies on our inland stands as
to preclude analyses within this area.
Within the coastal area, no significant
differences were found for capture
frequencies of this species in forest
age or moisture classes (table Al).
The yellow-legged frog is a highly
aquatic species (Stebbins 1985)and
therefore our PF captures (table 4)
must be considered incidental. These
captures may have been frogs seeking terrestrial overwintering cover
above high water levels (PF sampling
was done in the fall). However, this
frog was absent from young stands.
Three facts need be considered: (1)
all but a single capture occurred in
the coastal area; (2) in general, the
coastal stands were closer to perennial streams and creeks than were
the inland stands; (3) within the
coastal area, only two out of eight
young stands had PF grids near suitable aquatic habitat, whereas all the
mature and old-growth stands had
PF grids near such habitat. Thus we
can not rule out the possibility that
this frog's absence from young
stands in our samples is an artifact of
our stand locations relative to avail-
able and suitable aquatic habitat
(Bury and Corn, this volume).
Twenty-one records from area-constrained aquatic surveys (H. Welsh,
unpubl. data) were almost equally
divided between creeks in young and
mature forests. On the other hand, it
is possible that older forests provide
some particulars of microhabitat required by overwintering yellowlegged frogs not present in young
forests.
Pacific Treefrog (Hyla regilla).The Pacific treefrog is the only frog
for which our data indicated significant differences in captures between
both forest age and moisture classes
(fig. 6). Within the coastal area, this
frog was captured at significantly
different frequencies in both forest
age and moisture classes. However,
these differences were not observed
within the inland area, probably due
to lower captures and higher variances on these stands (table Al).
Because the Pacific treefrog is not
restricted to forested habitat (Stebbins 1985), we are suspicious of our
data indicating greater abundance in
older forests (fig. 6). Conceivably
older forests provide more cover and
foraging areas for this species than
do young forests and thus support
higher relative abundances. Most of
our captures of treefrogs occurred in
association with large downed
woody material. However, we cannot rule out the possible influence of
proximity of breeding sites on these
results (Bury and Corn, this volume).
The older forest stands were generally closer to standing water than the
young stands (as with Ram boyfii)in
the coastal area.
The difference in captures of
treefrogs between the mesic and wet
moisture classes (fig. 6) may be an
artifact of unequal detectability. Most
treefrogs were captured by TCS and
they are more easily exposed and
seen by investigators in the more
open understory of the mesic stands.
The alternate possibility, that there
are actually more treefrogs on mesic
stands, is consistent with the in-
creased incident radiation in the mesic stands which would promote
higher productivity of invertebrate
prey, and thus possibly support
more treefrogs.
The Tailed Frog (Ascaphus
truei).-This frog was captured only
on mature and old-growth stands
(tables 2-3); however, the total number of captures (5) was too low for
statistical tests. This species is of
interest, nonetheless, because of its
absence from young stands. The
tailed frog, like the yellow-legged
frog, is highly aquatic (Bury 1968,
Stebbins 1985).Therefore these records based on terrestrial sampling
are considered incidental. However,
results from another study employing an area-constrained aquatic Sampling method yielded more than 400
captures of tailed frogs (Welsh, in
prep.). These data were consistent
with the incidental records reported
here; there were significant increases
in tailed frog abundance with increased forest age.
Olympic Salamander (Rhyacotriton olympicus).-This species was
absent from all young stands (tables
3-4). Low captures prompted us to
combine moisture classes for the age
analysis. Multiple comparisons
(GHMC), coastal and inland areas
combined, indicated that older
stands had significantly greater numbers of Olympic salamander than
young stands (fig. 7).
This species is restricted to headwater habitats, such as seeps,
springs, and small creeks in forests
where it prefers cold water flowing
over rocky substrates (Anderson
1968, Nussbaum et al. 1983). Because
of the relative scarcity of this microhabitat in the areas of our study,
Rhyacotriton occurs in a patchy distribution. It can be abundant where
conditions are suitable, but we found
appropriate microhabi ta t islands for
this species to be few, small, and
widely scattered on our stands. This
rcsul ted in relatively few captures
(tables 3-4). We found Rhyacotriton
absent in younger forests (fig. 7),
which is consistent with results from
other studies (Bury 1983; Bury and
Corn 1988; Welsh, in prep.). This species appears to be sensitive to forest
harvest practices because of its particular habitat requirements (Bury
and Corn 1988; Welsh, in prep.). Current harvest practices do not protect
headwater habitats. Such habitats are
often radically altered by harvest
practices, which can change water
flow and temperature, increases sediment loads, and change the structure
and composition of the riparian
vegetation (Bury and Corn 1988). The
result of these changes is often the
extirpation of local populations of
this species.
Clouded Salamander (Aneides ferreus).-Multiple comparisons
(GHMC) indicated significant differences in mean captures of clouded
salamanders between young and old
stands in the inland area but not in
the coastal area (fig. 8a). Testing for
differences with coastal and inland
areas combined revealed significant
differences in mean captures among
moisture classes; multiple comparisons (TU) indicated that the mesic
stands had significantly higher mean
captures than did dry stands (fig.
8b).
This species, a habitat specialist,
occurs most often under exfoliating
bark on downed conifer logs (Stebbins 1985, Nussbaum et a1 1983).At
several coastal redwood localities,
Bury (1983) and Bury and Martin
(1973) found it to be more abundant
in young stands than older stands.
They attributed the differences to an
increase in bark on downed woody
material from logging. Our data from
the coastal area (fig. 8a) indicated
slightly more A. ferreus in younger
than older forests, but the differences
were not significant. However, in the
inland area the clouded salamander
was found in significantly higher
numbers on old vs. young stands
(fig. 8a). We suspect that these differences are due to the differences in
moisture regimes between the two
areas. This idea is supported by our
findings of significant differences in
capture means between mesic and
F O E S 1 ACE CUSS
Figure 7.-Captures per person-hour (TCS)
of the Olympic salamander (Rhyacotrifon
olympicus), in three forest age classes.
Data are from the inland and coastal areas
combined, from 1984-86.
Figure 8.-(A) Captures per person-hour (TCS) of the clouded salamander (Aneides ferreus)
in the coastal and inland areas, in three forest age classes. (B) Captures per person-hour
(TCS) in three forest moisture classes; data are from coastal and inland areas combined
Sampling occurred from 1984-86.
dry old-growth sites (fig. 8b). We
suggest that logs on inland young
stands are subjected to higher
evapotranspiration rates than are
logs on old-growth stands because of
greater incident radiation. Possible
increases in clouded salamanders on
young stands from an increase in
slash and logs after harvesting may
be outweighed by the loss of suitable
microclimatic conditions due to increased exposure.
Black Salamander (Aneides
flnvipuncfatus).-We found significantly greater numbers of this species in the coastal area than in the inland area (fig. 9). Lynch (1981)
pointed out that inland populations
occur in a patchy distribution charac-
STAND N P E
Figure 9.-Captures per person-hour (TCS)
of the black salamander (Aneides flavipunctafus) in coastal and inland areas, in
three forest age and three moisture classes.
Data are from 1984-86.
STAND TYPE
teristic of a species on the decline.
Further, he attributed the inland
patchiness to climatic constraints and
noted that the black salamander is
restricted to low-lying suitable areas
receiving at least 75 cm of annual
precipitation. Its restriction to rocky
habitats and its low relative abundance in northwestern California
preclude drawing any conclusions
from our forest age and moisture
class analysis (table Al).
California Slender Salamander
CBatrachoseps aftmuatus).-The
slender salamander, like the black
salamander, appears to be restricted
to low-lying suitable areas with relatively high annual precipitation
(Maiorana 1976a).This species was
absent from our inland sites, but accounted for the highest captures of
any species within the coastal area.
This was one of the few species we
captured in sufficient numbers with
both sampling methods to test both
data sets for differences between forest age and moisture classes (see
table All. Within the coastal area,
both TCS and PF data indicated significant differencesin mean captures
among forest age classes (figs. IOa-b).
Multiple comparisons (TU) indicated
that these differences were between
both young and mature and young
and old-growth stands (figs. IOa-b).
Our findings here were consistent
with trends found by others (Bury
1983, Bury and Martin 1973).
STAND TYPE
Figure 10.-Captures per person-hour (A:TCS),and captures per 1000 trap-nights (B:PF), of
the California slender salamander (Batrachoseps aftenuatus), in three forest age and three
moisture classes. Data are from the coastal area from 1984-86 (TCS) and 1984-85 (PF).
The PF data showed a significant
difference between captures in moisture classes, with a higher mean captures on mesic than on old-growth
wet stands (fig. lob), but the TCS
data did not (fig. 10a). For a salamander species whose presence and relative abundance is correlated with
relatively high and predictable moisture (Maiorana 1974,1976a1, this result is unexpected and may be an artifact of different sampling efficiencies between forest moisture classes.
The old-growth wet stands appear to
contain habitat with relatively great
structural complexity: a thick and
complex layer of understory, decomposing woody material, and mossy
duff. Such habitat provides abundant
microhabitat for a ground dwelling
and semi-fossorial species like the
slender salamander.
Slender salamanders may not frequent the surface as much to forage
as they would on drier stands. Foraging in more protected areas would
reduce exposure to predation and
thus incur a selective advantage.
Maiorana (1976b) termed this submergent behavior (our concept is a
slight variation of her idea; she hypothesized that a species might actually forage less at times to avoid exposure to predation). As a result of
less surface activity, fewer slender
salamanders are captured in the pitfall traps. The same logic can also be
applied to the TCS method, in which
lower captures would be expected in
the structurally more complex habitat per unit of search time. With TCS,
we did get slightly lower captures on
old-growth wet stands for this species (table 31, but the active nature of
TCS allowed us to detect enough
slender salamanders that the capture
rates between moisture classes were
not significantly different.
Ensatina (Ensatina eschscholtzii).-Ensatina has broad
ecological tolerances, occurring from
relatively dry woodland habitats to
moister forests at high elevations
(Stebbins 1954).This species has the
most extensive geographic distribu-
tion of all the western woodland
salamanders, ranging from British
Columbia to Baja California (Stebbins
1985). Ensatina were captured in the
highest numbers of any species we
sampled (table 3-4). There were significant differences in mean captures
among forest age classes, with
coastal and inland areas combined
(fig. 11). Multiple comparisons (TU)
indicated that old stands had significantly higher captures than young
stands (fig. 11).
Both PF and TCS data indicated
significant differences in mean capture frequencies between the coastal
and inland areas (figs. 12a-b). Greater
numbers were found on the inland
stands. These differences between
areas indicate that this species may
be more abundant in the drier inland
area than along the coast.
Del Norte Salamander (Plethodon
elongatus).-Except for three captures from our most northern coastal
stand, this species was sampled only
on our inland stands. These salamanders are found primarily on or in
rocky substrates (Stebbins 1985,
Nussbaum et al. 19831, and reach
high densities in talus and outcrops
of fractured metamorphic rock. Such
habitats were not present on some of
our stands. Also, our study region
encompassed the geographic range
of this species, and all of our southern and some of our easternmost
stands were beyond its geographic
limits. Despite the patchy distribution of this species due to habitat restrictions, and absence from sites beyond its range, both methods indicated a higher relative abundance on
older forest stands and a lower relative abundance on drier stands (figs.
13a-b, tables 3-4). These differences
were not statistically significant;
something we attribute to high variances within forest age classes resulting from this lack of appropriate microhabitat and the inclusion of stands
beyond the range (table Al). A separate analysis of only stands from
within the geographic range of the
Del Norte salamander indicated that
the abundance of this species is significantly correlated with increased
forest age (Welsh, in prep.).
Rough-Skinned Newt (Taricha
granulosa).-Both TCS and PF
showed a marked increase in captures of this species in older forests
(figs. 14a-b, tables 3-4). Lack of statistically significant differences in captures between forest age classes
(table Al) is probably related to specific habitat requirements of this species. We suspect that the critical habitat component was proximity to
creeks or ponds, a breeding requirement for this species (Stebbins 1985).
Many of our stands, particularly
within the inland area, were a considerable distance from suitable
breeding habitat for this newt. We
had no TCS captures of this species
on old-growth stands in our inland
area, yet the rough-skinned newt is
common there (Stebbins 1985, pers.
observ.).
particularly salamanders, were significantly more abundant in older
forests and significantly less abundant in drier forests.
We found the TCS method, actively searching for animals in their
preferred microhabitats (usually associated with downed woody materials in these forest habitats), yielded
more useful data on herpetofaunal
diversity and abundance relative to
forest age and moisture class than
did PF. The TCS method sampled
more individuals and species in addition to taking less time and expense than PF (see Welsh 1987).
Recent research in forested habitats (Bury and Corn 1988, Pough et
al. 1987, Enge and Marion 1986, Bury
CONCLUSIONS
Our research indicates that salamanders comprise the majority of both
species and individuals among the
herpetofauna of the Douglas-fir /
hardwood forests of northwestern
California and southwestern Oregon.
We found species diversity of the total herpetofauna to be greater in
older forest age classes. Amphibians,
Figure 1 1 .-Captures per person-hour (TCS)
of Ensatina (Ensatino esckhot/tzii), in
three forest age classes. Data are from
coastal and inland areas combined, from
1984-86.
Figure 12.-Captures per person-hour (A:TCS),and captures per 1000 trap-nights (B:PF), of
Ensatina (Ensatina eschxhotltzii) in coastal and inland areas, in three forest age and three
moisture classes. Data are from 1984-86(TCS)and 1984-85 (PF).
1983, Bennett et al. 1980, Bury and
Martin 1973) has indicated a pattern
of fewer species and reduced abundance of herpetofauna after logging.
We also found lower numbers of
both species and individuals on
younger stands.
Greater species diversity and
greater relative abundance, for most
species, on mature and old-growth
stands may be related to greater
structural complexity in older forests
(Franklin and Spies 1984, Franklin et
al. 1981).Older forests also have a
narrower and more stable range of
moisture and temperature than precanopy and young forests (Bury
1983, Harris 1984).Bury (1983)
sampled amphibians on four paired
plots in coastal redwood forest, each
pair consisting of a logged and an
old-growth forest stand. He attributed the lower diversity and relative
abundance of amphibians on the
logged sites to microclimatic differences. Bury (1983) also found higher
numbers of amphibians associated
with a greater volume of downed
woody material, but he considered
these differences in cover habitat to
be of secondary importance. Recently, Bury and Corn (this volume)
found that coarse woody debris is
related to salamander occurrence
and abundance in the Oregon and
Washington Cascades.
We believe that structural complexity or spatial heterogeneity (Pi-
anka 1966) plays an important role in
promoting the addition of species
and numbers of individuals in older
forests. Downed woody material, besides affording cover, creates microclimatic pockets that can act to buffer
the moisture and temperature fluctuations in the forest at large, and it
provides protection from predation
as well. Maiorana (1978) reported
that space (small cavities and burrows) was more important in regulating relative abundance between
two sympa tric salamanders (Aneides
lugubris and Batrachoseps atfenuafus)
than competition for food resources.
Therefore, more salamander species
and individuals should be expected
in more structurally complex habitats. In fact, both microclimate and
cover are probably interrelated, ultimate factors (Baker 1938) determining habitat suitability for temperate
forest herpetofauna. Both are clearly
affected by forest harvest practices
and probably jointly account for
most of the differences in diversity
and abundance observed in the herpetofauna between young, mature,
and old-growth forests in northwestern California and southwestern Oregon.
STAND M E
ACKNOWLEDGMENTS
Figure 13.-Captures per person-hour (A:TCS), and captures per 1000 trap-nights (B:PF), of
the Del Norte salamander (Plethodon elongatus), in three forest age and three moisture
classes. Data are from the inland area, from 1984-86 (TCS) and 1984-85 (PF).
We thank the members of the field
crews of the Pacific Southwest Forest
and Range Experiment Station's Timber/Wildlife Research Unit for their
help in collecting data; James A.
Baldwin and Barry R. Noon for advising on statistical methods; C. John
Ralph, R. B. Bury, and M. G. Raphael
for their reviews of the manuscript;
and Dana L. Waters for his help with
the figures and tables in the manuscript.
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