n= 1 5 1 5 1 5

20

Cave Willow Branscomb

Junction Creek

Figure l-Comparison of the number of bird species by region. The means,

standard errors, and ranges are shown for stands in each region. Sample size

is shown below.

Few species showed other geographical patterns. Only two

species were more abundant at the central Willow Creek

stands: the lazuli bunting and hermit thrush. Only the westem wood-pewee was less abundant in these central stands

than in either the northern or southern stands.

Relation of abundance to stand age-By comparing the

average number of species recorded in a stand by stand age

(fig. 2), we found no difference among mature (33.5), young

(33.7), and old-growth (34.7) forests (Duncan’s Multiple

Range Test). A correlation between stand age and average

number of species also showed no relation (r = 0.13; P =

0.132), in contrast to results of Manuwal and Huff (1987),

who found an increase in richness in their old-growth stands.

Stand age was an important factor in the abundance of many

species in the community. For three species, the California

quail, hairy woodpecker, and pileated woodpecker (fig. 3),

age was selected as the sole significant contributor to our

model (table 2). The quail was found in younger forests, and

the two woodpeckers in greater numbers in older forests.

When we used stand age as a classification variable in a

separate analysis, three species (the hairy woodpecker,

western flycatcher, and brown creeper) were significantly

more abundant in old-growth forests than either the mature

or young stands. Except for their occurrence in modest

numbers in younger stands, these birds could be considered

old-growth species.

20

N.S.

n= 10 16 19

Young Mature Old-growth

Figure 2-Comparison of the number of bird species by age-class. The

means, standard errors, and ranges are shown for stands in each age-class.

Sample size is shown below.

For 17 species, or 24 percent of the 71 species total, both

stand age and region were selected in the linear model as

affecting the numbers of individuals recorded. The abundances of four species (chestnut-backed chickadee, Hammond’s flycatcher, red-breasted nuthatch, and wrentit) were

special in that they showed a consistent, positive relation

with age among all three regions. That is, the interaction

between age and abundance was not significantly different

between regions. These species, along with the two woodpeckers mentioned above, showed the strongest affinity

between abundance and age of forest.

Eight of the 17 species’ abundances were positively related

to stand age, and occurred most commonly in older forests:

Allen’s hummingbird, western flycatcher (fig. 3), gray jay,

brown creeper (fig. 3), winter wren, golden-crowned kinglet,

hermit warbler (fig. 3), and black-headed grosbeak. Only

four species were more common in younger stands and also

had their numbers influenced by region: Townsend’s solitaire, varied thrush, warbling vireo, and black-throated gray

warbler. The red crossbill was influenced by both region and

stand age, but the effect of age was not clear. Although the

abundances of many species were influenced by geography,

these data showed that stand age was an important determinant for a large proportion of the species.

Selection of Forest Types

Comparing the stands as to their recorded number of species

indicated that the richness of bird species was higher in

stands with more conifers (r = 0.28; P < 0.05) and lower in

stands with more hardwoods (r = -0.53; P c 0.001).

387
3P 

West&n flycakhe~ 

q 

AA 

AA -I 

0 100 200 300 400 500 

q Branscomb A Cave Junction l Willow Creek 

The abundance of many species was strongly correlated 

with the number of conifer or hardwood txes in the plots 

(table 3). In many of these species, we expected a positive 

correlation with one type and a negative with the other. 

Fourteen species were positively associated with conifers, 

which was the commonest association: flammulated owl, 

Allen’s hummingbird, olive-sided flycatcher, western woodpewee, Hammond’s flycatcher, gray jay, red-breasted nuthatch, winter wren, golden-crowned kinglet, yellow-romped 

warbler, Townsend’s warbler, hermit warbler, pine siskin, 

and evening grosbeak. Three species apparently had a negative association with conifers, but were not positively assoiated with hardwoods: Steller’s jay, scrub jay, and blacktbroated gray warbler. Only seven species were positively 

associated with hardwoods: band-tailed pigeon, chestnutbacked chickadee, hermit thrush, varied thrush, Hutton’s 

vireo, warbling vireo, and black-headed grosbeak. Finally, 

eight species were negatively correlated with hardwoods, but 

were not positively associated with conifers: blue grouse, 

red-breasted sapsucker, dusky flycatcher, mountain chickadee, 

Townsend’s solitaire, MacGillivray’s warbler, fox sparrow, 

and dark-eyed junco. 

In all of these species, a more detailed, species-by-species 

analysis of habitat association patterns by plant species, as 

well as actual habitat use, is needed to determine the actual 

environmental factors that limit their distribution and 

abundance. 

388 
Table ‘l-Number of mammal captures by species and trapping technique within each study area’ (for each technique, significant 

differences among captures in each study area are indicated by different lettws after the totals) 

Technique 

Tmwbridge’s shrew 

Pacific shrew 

vagrant shrew 

Mash shrew 

Shrew-mole 

Coat mole 

Chipmunks 

Golden-mantled ground squirrel 

Northern flying squirrel 

Bow’s pocket gopher 

Deer mouse 

Pilion mouse 

Dusky-footed woo&at 

Bushy-tailed woodrat 

Western red-backed vole 

Red nee vole 

Califomia vole 

Long-tailed vole 

creeping vole 

Black rat 

Pacific jumping mouse 

EtIlIine 

Number of trap-night? 

Cave J”llCtiOll 

Willow Creek 

Branswmb 

349 296 

14 16 

- 1 

- 1 

11 21 

- 1 

2 

6 - 

5 

51 36 

1 1 

2 

341A 186 - A 

5 9 

1 - 5 

2 2 

1 

1 r 

- 

247 

3 

27 57 17 

: 6 2 3 

:- ,z -: 

1 I - 2 ; ; 

y- - : 

: 171 39 72 

’ 1 

2 T 7 

I- c_ 

; ’ 41 A 204R 159 B 

:113A 16 124B 

: 4 6 I8 I 

5 - - 

1 

‘- - - 

- - 5 

/-.’ 

:’ I T -: 8 /_ - - 

.3 1 r 

3’ 

- 

43,200 7.263 

48,960 8,2R9 

48,960 7.815 

Bird Community Organization 

Using the number of individuals observed for each of the 

29 most-common species as an approximation of the composition of the avian communities in a cluster analysis, we 

found some divisions (fig. 4). The divisions were largely 

geographical and probably depend on major vegetation types 

related to altitude. A secondary division occurred between 

the young stands and the combined group of mature and 

old-growth categories. No clear distinction could be made, 

judging from the bird community, between old-growth and 

mature communities. 

The first division was a separation of the younger Branscomb 

stands, which contained a great deal of chappxal. The second 

division was between the upper elevation Cave Junction 

stands that had a substantial amount of true fu, and the young 

Willow Creek stands. The third major separation was between the Branscomb and Willow Creek stands with mature 

and old-growth being intermixed. The TU stand that Bingham 

(pers. comm.) classed as young did have some remnant oldgrowth trees, and the bird species associated with these trees 

apparently increased the stand’s similarity to the older stands. 

These patterns confirm the information from the individual 

species: that clear geographical separations are present, and 

that, although young forests differ from older forests, mature 

and old-growth forests are much alike. 

Mammal Abundance Comparisons 

Twenty-three species of small mammals were captured during 

the study, though several were represented by only a few 

individuals (table 4). The three techniques differed in their 

effectiveness for capturing different species of mammals. 

Six species or species groups had sufficient captures (X00 

individuals or more, by one or more of the trapping techniques) to permit intensive analyses. These we*e the western 

389 
0.0 

Average distance between clusters 

0.2 0.4 0.6 0.8 1.0 1.2 

CAVE ;:: I.<. :::i;:.:;.:./.:;:./ 

J”NCT. 00 >? $5 ? :.>; a:.: :.< > :.< 

CG .L)/:j: .p*.. 

on 
Table S--Comparison of the correlationa between the abundance of small mammal captures and the age of the stand, amount of 

conifers, amount of hardwoods, and amount of hard and soft logs 

Species 

Snap traps 

Western red-backed vole 

Deer moue 

Pacific shrew 

Tmwbridge’s shrew 

Piiion rnO”X 

As 

0.350’ 

.171 

.236 

-.113 

-.248 

COnifer 

0.302 

-.I25 

,303 

,010 

-.462* 

Hardwood 

-0.163 

,114 

.333* 

-.222 

,369’ 

Hard log 

0.161 

,129 

,242 

,010 

-.048 

sofi log 

0.172 

-.129 

.497* 

.466* 

-.026 

red-backed vole, deer mouse, pilion mouse, Pacific shrew, 

Trowbridge’s shrew, and the combined chipmunk species. In 

addition, two squirrels and the chipmunks were counted 

during the bid counts. 

We captured most species of mammals in all three areas, and 

by all three techniques, with the exception of some of the 

mer species (table 4). We have discussed at length .the strong 

differences among the different capture methods (Taylor and 

others 1988). Among the mammals, the western red-backed 

vole had significantly fewer captures in the more southerly 

Branscomb region than in the central and northern regions. 

We have reported (Taylor and others 1988) that the vole’s 

abundance was significantly correlated with true firs found 

on 11 stands in the north and none in the south. The two 

mice species were significantly more abundant in the south 

than in the north. The shrews were equally common in all 

regions, and the sample sizes of other species, including the 

chipmunks, were perhaps tco small to demonstrate the effect 

of region. 

The western red-backed vole was the only captured species that had a significant positive association with the age of 

the forest stand (P < 0.05; table 5), which confirms previous 

studies (Raphael 1988, Raphael and Barrett 1984) in the 

Willow Creek area. Bird count data indicates that Douglas’ 

squirrel was also positively associated with stand age, and 

this greater abundance in older stands was consistent among 

the regions (table 2). The abundance of the chipmunk species 

and gray squirrel were related to repion. Chipmunks and 

Douglas’ squirrel were more common at Cave Junction, and 

the gray squirrel was more common at Branscomb. 

The phion mouse had the clearest association with hardwood density and clearly lacked association with stands that 

included conifers (table 5), judging from captures in both 

snap and live traps. The Pacific shrew was positively associated with hardwoods and soft logs, and Trowbridge’s 

shrew was also positively associated with soft logs. The 

combined chipmunk species were positively associated with 

hardwoods, and negatively with conifers. 

Discussion 

Total species richness of birds in our stands is much higher 

than for stands discussed elsewhere in this volume that are 

lozated farther north in Oregon and Washington. We suspect 

this results from the much greater diversity of vegetation in 

our stands (Bingham and Sawyer, this volume) that resulted 

from a greater abundance of hardwood. Indeed, a few of our 

bid species showed a close association with hardwoods in 

general. A matter of concern is that present logging practices 

in our region are directed towards eliminating hardwoods as 

an important component of the commercial forests. As 

Raphael (1987) has shown, and our data reaffirm, the numbers of many species would probably be greatly reduced if 

this strategy was successful. Perhaps fortunately for the 

wildlife, silviculture is an imperfect art and many harvested 

conifer stands are regenerating into stands with a high per391 
Number of bird species

Figure 5--Number of breeding forest birds by geographic region, (a) taken

from Blom (National Geographic Society [1987]), and (b) Harris (1984).

centage of hardwoods. We are experiencing a permanent loss

of mature hardwoods, however, which may profoundly

affect some animal species.

Harris (1984) points out that Pacific Northwest forests were

the richest in North America in terms of bird species, based

on MacArthur and Wilson’s data (1967) (reproduced in

fig. 5b). MacArthur and Wilson, however, were discussing

alI breeding birds, not just forest birds. Our recalculation of

the number of breeding forest birds (fig. 5a) showed that the

northeastern United States is the richest area in the North

America, with about 140 species, and the Rocky Mountain

area and the Pacific Northwest are tied at about 110 species

each.

Although the Pacific Northwest is not particularly rich in

forest-bird species, it does have many species endemic to the

area. A comparison (based on the range maps of the National

Geographic Society 1987) of the endemic species largely

confined to the four regions of figure 5a showed a striking

contrast. The Rocky Mountain area has no species confined

to that region’s forests. The northeastern region of the United

States has only the golden-winged warbler. Only the southeast and the northwest have a significant number of endemic

forest birds. The southeast has six (red-cockaded woodpecker,

ivory-billed woodpecker, brown-headed nuthatch, Swainson’s

warbler, Bachman’s warbler, and Bachman’s sparrow) and

the northwest has seven (Vaux’s swift, rufous hummingbird,

white-headed woodpecker, red-breasted sapsucker, hermit

warbler, and chestnut-backed chickadee). That most of the

endemics in the southeast are now extinct, rare, or declining,

may not be irrelevant because that region’s old-growth forest

was essentially eliminated during the last century.

Many species in our study showed affiliations with stand age.

Three birds were significantly more abundant in old-growth

forests than either the young or mature stands: the hairy

woodpecker, western flycatcher, and brown creeper. Many

other birds were more common in the mature and old-growth

stands than in the young stands. For these species, older

forests are probably a preferred, but perhaps not required,

forest configuration. Age was a major factor only when the

difference between the young forests on the one hand, and

the combined mature and old-growth forests on the other is

considered. Between the two older categories, the species

composition was quite similar.

Raphael (1984,1987) and Raphael and Barrett (1984) conducted a study of forest birds and mammals and their standage associations in one of our study regions near Willow

Creek, California. Raphael (1984), compared stand age with

the abundance data from a single year for birds in the Willow

Creek area. He found 25 significant relations (see table 2).

Of the 25 species, our data agreed for 8 species, but disagreed for 7 species. In these seven cases, Raphael (1984)

found a negative relation with stand age, and we found a

positive relation. We found no significant relation for the

remaining 10 species. We are not certain of the reason for

this disparity of results, although methods did vary because

our study covered a wider geographical range over a period

of 2 years, and Raphael’s (1984) study used 136 study plots

from a single year.

Of the mammals we studied, only the abundance of western

red-backed voles and Douglas’ squirrels were positively associated with the age of the forest stand. Raphael (1988) found

both species associated with older stands. He found 10 mammals that were positively correlated with stand age. Voles

had by far the strongest relation to stand age. Perhaps the

techniques we used did not adequately sample the larger

carnivores that he found associated with stand age.

The stands chosen to represent different age-classes occurred

naturally in the Cave Junction and Branscomb regions;.that

is, the young stands originated from fire or other catastrophic

events, rather than as the result of timber harvests, and often

were heterogeneous, with some structural and floristic com392
portents that resembled old-growth stands. Scattered old trees

and abundant dead-and-down material were sometimes present in young stands. These characteristics, which are usually

absent from young stands that originated from clearcut timber harvests, may be important factors that affect patterns of

bird abundance. Results from even-aged stands regenerating

from a clearcut may be very different. The cluster analysis

did, however, group the bird community of the natural,

young Branscomb stands with the young Willow Creek

stands that resulted from timber harvesting.

Our study area was fire-prevalent, and for that reason, it may

have been a poor area for examining species that become dependent on old-growth stands. The stands in this southern

area of Douglas-fir are subject to drier conditions and more

frequent fires than their counterparts to the north. Many species may have developed more flexibility in the southern

portion of the range of their habitat type.

When a species is more common in older forests, we cannot

make a statement about the species’ reliance on older stands

without information on the activities of that species in younger stands. The three bird species of significantly greater abundance in old-growth forests (the hairy woodpecker, western

flycatcher, and brown creeper) are a case in point. Some

evidence (van Home 1983) indicates that a species’ density

is not necessarily correlated with habitat suitability. Thus,

although these three species do attain moderate numbers in

young and mature forests, those stands may include habitat

that is unsuitable for breeding.

By far the most common habitat association pattern we detected was a positive association with conifers. The next most

common, perhaps the converse, was a lack of association

with hardwoods. Only seven bird and no mammal species

were positively correlated with hardwoods. The association

with conifers, both direct and indirect, might not be surprising given the conifer dominance of these forests. As we

have suggested above, however, greater abundance of hardwood could be a factor in the increased species richness of

the southern Douglas-fir forests. Raphael (1987) also found

some species strongly associated with tanoak, an important

hardwood species. This association included six positively

correlated (P < 0.05) species, some of which were in agreement with our data. Raphael found one, the olive-sided flycatcher, positively correlated with tanoak, but our data indicated a negative correlation with all hardwoods. He also

found the western flycatcher and hermit warbler positively

associated with hardwood, but we did not. Our results agreed

with Raphael’s for only three species: the hermit thrush,

varied thrush (only in the winter), and warbling vireo. The

differences quite likely result from our method of combining

all hardwood species, and Raphael’s concentration on tanoak.

They may, however, be related to the much larger geographic

region included in our study.

The strong geographic influence on patterns of species abundance within our study area has important management implications. We found that species abundances often differed

significantly between regions in their relation to age (the ageregion interaction shown in table 2); that is, in one region the

relation might be positive, in another negative, and in the

third, have no pattern. These differences are to be expected

because at the periphery of its range or habitat, a species is

most likely to be constrained to a narrower range of environmental conditions than at the center. Land managers might

find that, to maintain a species in a given region, quite different strategies of land use from those used in other regions

might well be necessary.

Because many species’ abundances are related to stand age

and composition, further alterations of the landscape will

likely result in profound changes in the abundance patterns

of many of the species in the study area. This, however,

will probably not result in any extinctions in the foreseeable

future. For the great majority of the species in this study, the

pervasive influence of stand age and composition on population levels should warn us that close monitoring of some

species may be necessary. At the very least, periodic sampling should be conducted to determine the population status

of species in the area.

Acknowledgments

We thank the members of the field crews of the Redwood

Sciences Laboratory’s Timber-Wildlife Research Unit for

their hard work and dedication in collecting data: C. Barrows,

W. Block, L. Brennan, K. Calabrese, D. Carle, K. Clough,

S. Edwards, S. Goldwasser, P. Hall, M. Hamady, L. LaClaire,

D. Laush, P. Manley, W. McCleod, K. Milne, C. Ogan,

K. Purcell, T. Quinn, M. Rassmussen, R. Reynolds,

A. Schaffer. K. Schmidt, J. Sterling, H. Sakai, D. Taylor,

G. Therien, and R. Wilson. We also thank James A. Baldwin,

Sylvia Mori, and Barry R. Noon for their advice on statistical

methods; Andrew B. Carey, Robert J. Cooper, Sherri Miller,

Michael Morrison, Barry R. Noon, and Carol P. Ralph for

their perceptive reviews of the manuscript; and Sherri Miller

and Susan Sferra for their help with the analysis at various

stages.

c l

393

The Structure of the Herpetofaunal Assemblage

in the Douglas-Fir/Hardwood Forests of

Northwestern California and Southwestern

Oregon

Hartwell H. Welsh, Jr., and Amy J. Lind

Authors

HARTWELL H. WELSH, JR., and AMY J. LIND are wildlife biologists, U.S. Department of Agriculture, Forest Service, Pacific Southwest Forest and Range Experiment Station,

Arcata, California 95521.

Abstract

Terrestrial and aquatic herpetofauna were sampled by three

methods, time-constrained searches, pitfall traps, and areaconstrained searches from 1984 to 1986 in northwestern

California and southwestern Oregon. The 54 terrestrial and

39 aquatic study sites were in Douglas-fir/hardwood forest

stands that ranged in age from 30 to 560 years. Results of

these surveys are presented in terms of species richness,

equitability, relative abundance, relative biomass, and

macrohabitat and microhabitat associations.

Although species richness did not differ among forest ageclasses, the composition of the herpetofauna was notably

different. Old and wet sites had proportionately more amphibian species, and young and dry sites had proportionately

more reptile species. Terrestrial salamanders were more abundant on old-growth than on young sites. We also found that

structural components associated with older forests were the

best predictors of increased numbers of salamanders. Analyses of microhabitat associations indicated that large, welldecayed logs were the most heavily used woody debris,

though use of particular size- and decay-classes varied

among salamander species.

Harvesting forests without immediately affecting herpetofauna is probably not possible; however, strategies can be

developed to minimize long-term adverse effects. We provide a summary of management recommendations designed

to assure long-term viablity of herpetofauna in areas subject

to logging.

Introduction

Old-growth forests are a unique and complex ecosystem

where many life forms occur in numbers disproportionate to

their occurrence in other parts of their range (Thomas and

others 1988), but the nature of the ecological dependencies

(Ruggiero and others 1988) between these species and the

ancient forest ecosystem are only beginning to be understood.

More knowledge about the spatial and temporal distributions

of species in old-growth and in younger natural and managed

395
forests, and an understanding of habitat requirements and

ecological interdependencies are required to make sound

decisions that assure healthy forests in the future.

We describe the species composition and relative abundance

of members of the herpetofaunal assemblage in the southern

portion of the Douglas-fir region, with a focus on how presence and abundance are related to forest age and structural

aspects of the forest habitat.

Heatwole (1982), in a review of available literature on the

structure of temperate and tropical herpetofaunal assemblages,

noted how little is known about them and their relation to the

larger community of organisms that constitute a complete

ecosystem.

Pough (1980, 1983) outlined some of the unique adaptations

of herpetofauna that illuminate their critical role in ecosystem

dynamics and place them in a larger ecological context. Their

small body size and elongate body form, energetically unfeasible for endotherms, permits them to use space and exploit

food resources unavailable to other vertebrates. Their ectothermic nature facilitates a life of low energy demand. They

are better suited than endotherms to periods of limited food,

water, or oxygen. Endotherms are generally viewed in terms

of the energy they consume, but reptiles and amphibians are

more realistically considered in terms of the biomass they

produce and make available to other trophic levels (Pough

1980: 104). These small vertebrates comprise an essential

trophic level in the ecosystem, where invertebrate biomass is

converted to vertebrate biomass far more efficiently than by

endothcrms. Pough, comparing the efficiency of secondary

production of endotherms and ectotherms, noted that the

“...net long-term conversion efficiencies of amphibians and

reptiles are many times greater than those of birds and

mammals. The ecological significance of this efficient

biomass production is enormous” (Pough 1980: 102).

Methods

Study Area

The study was conducted in Douglas-fir/hardwood forests

of the Klamath Mountains and Coast Range of northwestern

California and southwestern Oregon; the southern portion of

the Oregonian Province (Udvardy 1975). Fifty-four terrestrial

study sites, ranging in size from 21 to 150 ha, and 39 aquatic

study sites (15-m lengths of second- or third-order streams)

were sampled (see frontispiece and appendix table 9). For

site selection procedures see Bingharn and Sawyer (this volume). Forests at the terrestrial sites ranged in age from 40 to

450 years; forests at the aquatic sites ranged in age from 30

to 560 years.

Herpetofauna Sampling

Four methods were used to sample the species composition, abundance, and biomass of the herpetofauna; timeconstrained searches (timed searches), pitfall traps (pitfall),

area-constrained searches (area searches), and opportunistic

observations. These methods are described in more detail

elsewhere (Bury and Raphael 1983, Corn and Bury 1990,

Raphael and Rosenberg 1983, Welsh 1987). Timed searches

recorded the search effort of two to three persons while they

moved about the forest at random examining all microhabitats encountered, raking through litter, turning rocks and logs,

tearing open decomposed logs, probing in vegetation, and so

on. The clock was stopped when animals were encountered

and while data were gathered. Our timed searches differed

from those of Corn and Bury (1990) in that we searched

seeps and springs in addition to rocks, logs, bark, and litter.

The pitfall method consisted of trap grids with 36 traps

spaced at 15-m intervals in a 6 x 6 arrangement. Traps were

made of two, number 10 tins taped together and buried with

the lip at the groundline and concealed by a cover of bark or

cedar shake propped above the ground.

Terrestrial sites were sampled with timed searches, pitfalls,

and opportunistic observations. We conducted four personhour timed searches on each of 54 sites from April to June

of 1984 and 1985, and on a subset of 30 sites from April to

May of 1986. Our combined effort for timed searches totaled

552 person-hours. We ran 36-trap pitfall grids on 49 sites in

October and November of 1984 for 50 nights and October of

1985, for 30 nights. The total pitfall effort equaled 141,120

trap-nights. Twenty-six amphibians and reptiles were recorded by opportunistic observation during sampling for

other vertebrate groups or while vegetation data were

collected.

Area searches were only done at aquatic sites. Our sampling

of aquatic habitats consisted of area-constrained searches of

39 second- or third-order streams (Strahler 1952) on or near

the terrestrial sites. We selected three 5-m reaches 1 to 3 m

wide along each stream by walking 50 m upstream from the

nearest trail or road access for the first reach, and 50 m from

the top of the previous reach for subsequent reaches. Stream

searches occurred during the summers of 1984 and 1985.

The method consisted of mapping each reach to scale in

order to plot captures, then methodically and sytematically

searching all substrates, with catch nets placed downstream

to capture dislodged animals.

Measurements of Forest Landscape, Structure, and

Composition

Forest age- and moisture-classes-Sites were grouped into

three forest age-classes: young, mature, and old-growth; and

old-growth sites were classified into three moisture-classes:

wet, mesic, and dry. Forest age was determined by tree

396