Table S-Contribution of landscape variables to squared multiple R (R' change) in stepwise regressions of 

vertebrate richness and log. (abundance) with stand and landscape variables (alpha to enter and remove in 

rerression = 0.15) 

Sd%%Sd 

variables 

Model R2 

Regression P 

Stand buffer composition 

Clewcut 

Old growth 

Late successional forest 

Landscape composition 

Clearcut 

Old growth 

Late successional forest 

Landscape pattern indices 

FrtXtal 

DOminance 

Point diversity 

Disturbance 

Richness Abundance 

Table 6Speannan correlations of bird, small mammal, and amphibian species richness and 

abundance in old-growth stands with landscape variables 

Species richness Abundance 

Sample stand 

Area 

P&II&T 

Edge index 

EkVtXiO” 

Stand buffer composition 

Clearcut 

Old growth 

Late successional 

forest 

Landscape composition 

Clearcut 

Old gmwth 

Late successional forest 

2 

0 

0 

1 

1 

0 

1 

3 

0 

1 

435 
Table 6-continued

Landscape pattern indices

Fractal

Dominance

Point diversity

Disturbance

Species richness Abundance

Birds Mammals Amphibians Birds Mammals Amphibians

-.44*** .41*** -.29* -.03 -.10 -.40***

-03 -.20* .15 -.33** .42*** .19

.08 .16 -.03 .39** -.14 -.14

.29* -.22 -.09 .28* -.37** .OO

* P < 0.10; ** P < 0.05; *** P < 0.01; **** P < 0.001.

Individual bird species-Few strong associations between

the abundance of 22 bird species and landscape variables

were revealed by partial correlation (table 7). Most correlations were < 0.50, indicating a weak association with less

than 25 percent shared variation. Moreover, the number of

significant correlations may not be different than expected by

chance alone (P < 0.10). Dark-eyed juncos were the only

species that showed an association with stand-scale variables:

abundance increased with stand area, perimeter, and edge,

which were all somewhat collinear. Red-breasted nuthatches

and rufous hummingbirds were associated with clearcuts in

the buffer and negatively associated with complex patchshapes measured by the fractal index. Consistent with these

neighborhood relations, red-breasted nuthatches increased

with clearcut area in the landscape. Rufous hummingbirds

however, were positively correlated with old-growth area in

the landscape.

The abundance of winter wrens was associated with undisturbed buffer zones: abundance decreased with clearcut area

and increased with late-successional-forest area in stand

buffers. Their abundance was not associated with the wholelandscape variables. Black-throated gray warbler abundance

showed a very strong negative correlation with late-successional forest in stand buffer-zones. The combined abundance

of hermit and Townsend’s warblers was similarly associated

with young forest: abundance decreased with old-growth area

at the buffer and landscape scales. Hermit and Townsend’s

warblers were grouped into one functional species because

hybridization in southern Washington made them indistinguishable in the field (see Manuwal, this volume).

Cavity-nesting birds-Several abundance relations were

graphically examined for cavity-nesting birds (hairy woodpecker, red-breasted nuthatch, chestnut-backed chickadee,

brown creeper) based on the hypothesis that these birds

would be negatively affected by the loss of vertical structural

diversity from clearcut logging and snag-reduction policies in

remaining forest stands (Manuwal, this volume).

Our questions were:

l Does abundance increase with the size of the sample

stand?

l Is abundance in young stands greater when surrounded

by old growth (may abundance in young stands be subsidized by adjacent old forest)?

l Is abundance less in stands that have a clearcut neighborhood (buffer zone)?

l Is abundance less in stands embedded in a clearcut

landscape?

Cavity-nesting bird abundance showed no significant relation

to stand area (fig. 9A). Abundance increased with clearcut

area in the buffer in a weak (R2

 = 0.102), but significant

(P = 0.033), linear relationship (fig. 9B). The linear relation

between abundance and total clearcut area (fig. 9D) was not

significant (P = 0.127), however. The hypothesis that abundance is higher in young stands surrounded by old growth is

supported (fig. 9C) with a significant linear regression (P =

0.011) and high R = 0.76, if the apparent outlier in the top

left comer is deleted.

Individual small mammal species-Some strong partial

correlations were found between individual small mammal

species’ abundance and stand or landscape variables, but

these correlations could have occurred by chance (P < 0.10)

(table 8). The creeping vole was the only species showing an

association with stand variables: abundance was negatively

correlated with stand perimeter and the edge index. Northern

flying squirrels and marsh shrews both were negatively

associated with late-successional forest in the buffer zones,

but the water shrew was very strongly associated with latesuccessional forest in the buffer. Marsh shrew abundance

also was positively correlated with landscape clearcut area

and the disturbance index, and negatively associated with

late-successional-forest area. Ermine were associated with

high point diversity.

436
Table ‘I--Partial correlation coefficients (stand age and elevation constant) of bird species’ abundance with landscape variables 

(data for 1984 and 1985 were combined) 

RRCR 

CBCH 

DEm 

EVGR= 

GCKI 

GFUA 

HAFL’ 

HAWOc 

HETH’ 

HETO 

PISS 

RDN” 

RUHU’ 

.27 -.13 .16 

-.16 -.18 39 

-.,6 -.14 .w 

.,I .06 .2O 

.m .36 -.28 

-.21 .I7 -.,I 

.24 -03 .19 

-0.34 15 

-.04 8 

43 88 

-.lS 91 

33 83 

-3l 12 

.Ol 92 

.O4 64 

-.I6 23 

.O7 26 

.I6 39 

.10 78 

30 31 

.19 72 

.I6 31 

-.04 22 

.2O 17 

.rn 87 

-.a7 84 

.02 9 

.2O 24 

46 91 

N 

Individual amphibian species-A few significant partialcorrelations were strong enough to be unlikely due to chance 

(table 8). Amphibians responded more strongly to stand-scale 

variables and more weakly to neighborhood- and landscapescale variables than birds or small mammals. Abundance of 

the western redback salamander was associated with more 

variables than other species: abundance was positively COTrelated with stand arca and the associated variables of perimeter and edge, and negatively associated with old growth in 

the buffer. The abundance of western redback salamanders 

was also correlated with habitat dominance. The abundance 

of tailed frogs was negatively correlated with stand edge and 

complex patch-shapes represented by the fractal index. 

Pond-breeding amphibians-We hypothesized that the 

abundance of pond-breeding amphibians (northwestern salamander, roughskin newt, red-legged frog, Cascades frog) 

would decline with fragmentation as a result of the increased 

isolation of subpopulations and postbrceding dispersal mortal. 

ity in clearcut barriers. The abundance-area. relationship was 

not significantly different from zero (fig. 10A). Abundance 

appeared to increase with clearcut area in the buffer zone, 

but the linear relation was not significant. Abundance also 

was not associated with clearcut area in the landscape in a 

significant linear fashion. Abundance in young stands, however, showed a strong negative relation to buffer-zone oldgrowth, with a significant linear regression model (P S 0.05; 

R2 = 0.55). 

Discussion 

Limitations of the Data Set 

The stand-scale vertebrate data set is limited in several ways 

for a landscape-scale analysis. The criterion that study stands 

be larger than 40 ha restricted the examination of speciesarea relations to relatively large stands, where the effects of 

size may be less important. Rosenberg and Raphael (1986) 

found that forest stands ~20 ha in northern California had 

less than the full complement of species. The minimum-size 

criterion also may have resulted in the selection of landscapes 

with less fragmentation than might have occurred had selection been unconstrained. 

431 
Area (hectare) Clearcut (proportion) 

L 

00 

Old-growth (proportion) Clearcut (proportion) 

Sampling bias for relatively large stands may have excluded 

highly fragmented areas from the analysis, resulting in conservative estimates of fragmentation. Study landscapes on 

National Forest land ranged from 0 to 48 percent clearcut, 

with most landscapes less than 30 percent cutover. The mean 

cutover percentage was 16 percent. The mean percentage 

cutover for the entire Forest, based on data from the TRI 

database (G. Gmelich, unpubl. data), was also 16 percent, 

with a range of 14 to 19 percent cutover by Ranger District. 

The similarity of the means may be misleading, however, 

because Forest-wide estimates are averages made for a larger 

Disbict scale of measurement. Proper comparison requires 

estimates from a random sample of 2025ha landscapes 

across the Forest, which is a project beyond the scope of 

our study. 

The vertebmte sampling design also had limitations for detecting uncommon and medium- to large-bodied species that 

may be most influenced by fragmentation (Diamond 1984; 

Lehmkuhl and Ruggiem, this volume: Pimm and others 1988; 

Terborgh and Winter 1980). The nine species suggested by 

Rosenberg and Raphael (1986) as most sensitive to fragmentation are all uncommon with medium-to-large body-size for 

their taxa: we examined data for only three of these species. 

Also, sampling area for vertebrates was constant in all stands 

so that large stands had relatively less area sampled than 

small stands. An attempt was made to distribute the sampling 

effort throughout the stand, but our sampling in large stands 

with high habitat-heterogeneity and associated heterogeneous 

species distributions may not have detected all of the species 

present (Robbins and others 1989). Thus, species-area relations may be more underestimated by the relatively smaller 

sampling areas in large stands than in small stands (Wilcox 

Table &Partial correlation coefficients (stand age and elevation constant) of small mammal and amphibian species’ abundance with 

landxape variables (data for 1984 and 1985 were combined) 

COLMOC 

MASHC 

Maw 

WASH= 

TRSH 

VASHS 

N 

56 

.03 -18 -.ll -.18 83 

-.14 .47 -3 -.a 6 

.oo 20 -.I” -..I5 87 

~06 .,I -28 -.03 21 

438 
Table &--(continued) 

Amphibian/ 

hWSA 

TLFR 

ENS.4 

RBSA” 

RLF’R’ 

CAFF 

RASP= 

RSNE= 

.n .,3 -.08 -.,2 43 

-.2@’ 49 .*o .0367 

-.03 2, .02 .07 69 

.26 .st** -.04 -.23 20 

.09 .m .,6 .,4 33 

.22 47 3, .I6 9 

.w .32 -.02 -.24 2s 

-.23 .32* -45 -.29’ 34 

1980). Finally, interpretations of abundance in young or 

mature stands was constrained by sample sizes less than half 

(n = 11) the number of old-growth stands (n = 26). 

Despite these limitations, we believe our studies provide 

valuable insight for examining the effects of landscape context on vertebrate richness and abundance in the communitystudy stands. 

Landscape Dynamics 

Habitat-Area Relations 

The reciprocal relation of late-successional forest and clexcut areas in the landscape conformed to the Franklin and 

Forman (1987) checkerboard model: the composition of the 

landscape mat& switched from late-successional forest to 

clearcut at 50 percent cutover (fig. 1). The model did not 

hold for old-growth and clearcut areas, however: clearcut 

area exceeded old-growth area earlier in the harvest regime 

when the landscape was 30 percent cutover. Timber harvest 

apparently was not restricted to old-growth stands, and the 

amount of clearcutting in an area did not indicate the loss of 

old-growth forest, but rather the loss of late-successional forest. The 30.percent cutover threshold means that old-growth 

patches and populations of closely associated species will be 

isolated more rapidly than will late-successional forest 

patches and animals as cutting continues. 

Area (hectare) 

Old-growth (proportion) Clearcut (proportion)