Ordination of Bird Data 

Geographic and stand-age patterns-DCA ordiiation of 

bird species’ abundances from all 132 stands produced low 

eigenvalues of 0.16 and 0.13 for the first two axes, respectively. Stand scores organized by geographic location separated into relatively distinct groups, but scores organized by 

sand age-classes overlapped extensively (fig. 14B, C). Additional ordinations of each province separately, although not 

shown. produced similar results: distinct clusters of stands 

could be identified easily by geographic location (that is, by 

subprovince) and not by stand age-class. 

Bird communities that separate along DCA axis 1 were in 

two groups: stands from the central and southern Oregon 

Cascades, and stands from the Oregon Coast Ranges, northem Oregon Cascades, and southem Washington Cascades 

(fig. 14B). Along axis 2, bird communities from the southern 

Washington Cascades were distinct from the Oregon Coast 

Ranges and Oregon Cascades. Bird communities within the 

three subprovinces of the Oregon Cascades showed the most 

intra-province variation; however, the geographic area 

sampled in this province was far more extensive than the 

other two provinces (see frontispiece and fig. 1; table 1). 

Bird communities in the north subprovince of the Oregon 

Cascades (fig. 14B; left dashed circle) were more similar in 

species composition and abundance u) those of the southern 

Washington Cascades and Oregon Coast Range than in subprovinces of the central and southern Oregon Cascades. 

191 
All stands 

04 * 

0 50 100 150 20 0 

Provinces 

/a 

..-' 

50 100 150 2 

DCA 1 

Age categories 

CR = orsgon coast Rang* 

OR = Oregon Cascade Range 

SW = Southern Washington Cascade Range 

Table -pearman rank correlations of DECORANA scores of 

axes 1 and 2 with environmental and biological variables 

Variable DCA Axis 1 DCA Axis 2 

Latitude 

Longihlde 

Elevation 

Smd age 

Aspect 

Sl0pe 

Understory vegetation DCA 1 

(wet to dry”) 

Understory vegetation DCA 2 

(cool moist to warm moista) 

Douglas-fir density 

Western hemlock density 

Bark-forager relative density 

Aerial-forager relative density 

Canopy-forager relative density 

Understory-forager relative density 

Resident relative density 

Migrant relative density 

Species richness 

Total abundance 

-0.376 

-0.171 

0.455 

-0.213 

-0.127 

0.034 

0.524 

0.664 

0.568 

0.153 

0.009 

-0.177 

0.310 -0.513 

-0.461 -0.604 

0.426 -0.165 

-0.303 0.344 

-0.051 0.375 

0.068 -0.659 

0.590 0.459 

-0.740 -0.086 

-0.394 0.747 

0.367 -0.734 

0.034 -0.273 

-0.252 -0.389 

’ DCA ordination scores of cwcr of understow vegetation collected by 

T. Spies. Imerpretntion of envimnmentll gradienu far each axis were 

made by T. Spies @em corn.) and (Spies and Franklin. this volume). 

192 

Correlation and interpretation of the DCA axes-Fiftyfive percent of the Spearman rank correlations between DCA 

axis 1 and the environmental and bird abundance variables 

were significant at P < 0.001 (rs >0.283 or ~4.283, n = 130) 

and 67 percent were significantly correlated with DCA axis 2 

(table 6). In general, axis 2 yielded higher correlation coefficients than axis 1; however, no single strong association for 

either axis emerged from the variables measured (table 6). 

The complex patterns seemed to follow a temperature and 

moisture gradient, especially along axis 2, that was related to 

elevation, latitude, longitude, and understory vegetation 

(figs. 15, 16). Also strongly correlated with axis 2 were the 

abundance of resident and migrant species, in positive and 

negative directions, respectively (fig. 16). Abundance patterns along axis 1 were highly correlated with the abundance 

of understory-foraging species (fig. 15). 
Flrat-axls decorana acorea 

based on bird abundance data 

Relationships to Habitat 

All 32 multiple regression equations of relationships to habitat, whether for all provinces combined or each separately, 

were significant at P 5 0.007 (table 7, see appendix table 9). 

Yet, in general, the linear relationships were weak. Only 47 

percent of the regression models had an R2 > 0.40 and only 

13 percent were ~0.50. The linear relationships of all provinces combined and each separately were strongest for t,Je 

understory foragers (range R = 0.36 to 0.63 and mean R2 = 

0.54) (table 7) and weakest for species richness (range R = 

0.18 to 0.35 and mean R2 = 0.26) (table 7). The lowest R2 

was 0.18 for species richness in the Oregon Coast Range 

(table 7) and highest was 0.65 for canopy foragers in the 

Oregon Cascades (table 7). In general, the proportion of 

variance explained by the regression equations tended to be 

lower in the Oregon Coast Ranges than the other provinces 

(table 7). 

Fifty-two vegetation variables were selected for the 32 regression equations (table 7). Tbe variables selected differed mxkedly between each province for each of the eight dependent 

variables. Only three vegetation variables were associated 

with the same dependent variable in more than one province: 

density of live deciduous trees was positively associated with 

abundance of migrant bid species (table 7); evergreen shrub 

cover was negatively associated with resident bid species 

(table 7); and fern cover was positively associated with 

understory foragers (table 7). 

Live deciduous-tree variables-namely, density, basal 

area, and importance value-were selected in at least one 

regression model for every species-richness or abundance 

dependent variable tested, except for the bark foragers (table 

7). The live deciduous-wee variables were selected most 

frequently with the data sets of both the Oregon Coast 

Ranges and all provinces together and were always positively related to species-richness and bird abundance. Other 

variables selected often in the regression models were two 

dead-wood variables-mean snag diameter and density of 

snags 10 to 50 cm in d.b.h. and 5 to 15 cm tal-that were 

positively and negatively associated with the dependent 

variables, respectively. 

193 
70 

*o * l ‘. - 

r = -0.734 

Second-axls deccwana scores 

based on bird abundance data 

47, *- - 

‘II 

1 

* . . . 

. . . . .r -. 

t$! 15 

. 

. . . . *. -* 

i 

-- ,“” ,_” _“I 

Second-axis decorana scores 

based on bird abundance data 
Table ‘I-Multiple regression using all possible subsets of independent vegetation variables with 

dependent variiibles of bird species richness, total abundance, abundance of residents and migrants, 

and abundance of bark, aerial, canopy, and understory foragers 

Regression Two-tailed Contibntion’ 

coefficient T-statistic significance toI? 

‘All provinces 

(dp = 5, 117; R*' = 0.25;Pd= 0.000) 

Intercept 

Basal area of live deciduous trees 

Percentage ground cover of moss 

hnp~rtance value of live western redcedd 

Mean height of live dominant trees 

Density of western hemlock snags >1.5 m tall 

Oregon Coast Ranges 

(df= 2, 40; R2= 0.18; P = 0.007): 

Intempt 

Density of decay-class-2 log< 

Basal area of live deciduous trees 

Oregon Cascades 

(df= 4, 43; R2= 0.25;P = 0.002): 

hltW%pt 

Percentage cover of ferns 

Density of snags >50 m d.bb. and S-15 m tall 

Density of live trees 50.99 cm d.b.h. 

lmpmmce value of live western redcedar 

Southern Washington Cascades 

(df = 4. 34: R2 = 0.35; P = 0.001): 

IntCICEp 

Density of snags lo-50 cm d.b.h. and 5.15 m tall 

Densitv of western hemlock snaes >1.5 m tall 

Imp&c, value of live west&redcedar 

Density of live @es 2549 cm db.h. 

Total abundance: 

All Pmvinces 

(df= 4. 118: R* = 0.41:P = O.OCQ 

lIlt.%Xpt 

Density of snags 10.50 cm d.b.h. and 5-15 m tall 

Basal area of live bigleaf maple 

Percentage CoYa of plants 4.5 m tall 

Basal .wea of live pine trees 

Oregon Coast Ranges 

(df= 4. 38: RZ= 0.25:P = 0.004): 

Intercept 

Basal area of live deciduous trees 

Density of live incense-cedar 

Volume of decay-class-5 snags 

Density of live Douglas-fir 

12.996 13.15 .OOO 

0.359 2.74 .OO7 .046 

4.025 -2.61 ,010 .042 

a010 -2.5 ,014 ,038 

0.047 2.38 ,019 ,035 

-0.017 -2.12 ,036 ,028 

16.846 21.20 

-0.338 -2.43 

0.245 2.01 

.a00 

,019 

.051 

.115 

.079 

15.542 11.98 

-1.492 -2.34 

-0.569 -1.95 

0.148 1.27 

-0.008 -1.20 

.004 

.024 

,057 

0.211 

0.235 

.088 

,061 

,026 

,023 

14.059 6.33 

-1.841 -2.28 

-0.022 -1.95 

-0.010 -1.82 

1.076 0.76 

.mo 

,029 

,059 

,078 

,455 

,089 

,065 

,057 

,010 

6.952 35.61 .om 

-0.659 -5.78 .OMl 

0.303 3.87 .om 

0.008 2.06 ,041 

0.040 1.35 ,179 

.I62 

.073 

,021 

.oQ9 

7.774 20.03 

0.125 2.88 

-0.035 -1.57 

0.285 1.39 

-0.032 -1.31 

,004 

,006 

,125 

,172 

,198 

,148 

,344 

,034 

,030 

195 
Table 7-cootinued 

Dependent variable/independent variables 

Regression Two-tailed Contibution’ 

coefficient T-St&tiC significance tORZ 

Oregon Cascades 

(df= 3,44; R2= 0.24; P = 0.002): 

htEZCf+X 

Mean height of live dominant trees 

Relative do,nina~,ce of Douglas-fir snag volume 

Density of live trees 50.99 cm d.b.h. 

Southern Washington Cascades 

(df= 3, 35; R2= 0.3O;P = 0.001): 

IntffEpt 

Percentage COYeI of plants <OS m tall 

Percentage raya of live deciduous tx.es 18 m tall 

Mean d.b.h. of snags 

Resident swies: 

All pro&es 

(df= 5. 117: Rx= 0.42: P = 0.000): 

Basal area of live deciduous trees 

Density of snags lo-50 cm d.b.h. and 5-15 m tall 

Percentage cover of evergreen shrubs 

Biomass of decayclass- snags 

Basal area of live needle-leaved evergreen trees 

Oregon Coast Ranges 

(df= 4, 38; RZ = 0.45;P = 0.000): 

IntWSpt 

Basal area of live deciduous trees 

Importance value of live western redcedar 

Density of live Douglas-fu 

Oregon Cascades 

(df= 4.43; R2= 0.42; P = 0.000): 

Relative ckninance of Douglas-fr snag volume 

Southern Washington Cascades 

(df= 4.34; R2= 4.47; P = 0.000): 

IntW.Spt 

Percentage cover of plants co.5 In tall 

Density of snags >50 cm d.b.h. and S-15 m tall 

Percentage cover of evergreen shrubs 

Percentage cover of live deciduous trees S8 m tall 

5.251 9.18 .I00 

0.032 2.88 ,006 

4.008 -1.49 ,142 

0.031 0.86 .396 

.134 

,036 

.012 

3.194 2.28 .029 

0.014 2.16 .038 

-0.114 -1.90 ,066 

1.599 1.85 ,073 

,086 

,066 

,063 

3.328 3.36 .JOl 

0.199 4.41 .oOO 

-0.375 A.06 .OW 

-0.089 -2.94 .004 

0,368 2.43 ,016 

1.25 2.33 .022 

.093 

,079 

,042 

,028 

,026 

6.23 17.09 ,000 

4.007 -3.22 ,003 ,134 

0.087 2.21 ,033 ,063 

0.006 2.00 ,053 .052 

-0.033 -1.30 .200 ,022 

4.735 9.65 ,000 

4.136 -3.86 .oOO 

0.005 2.34 ,024 

0.021 2.30 ,027 

a.006 -1.42 .164 

,185 

.068 

.065 

,025 

4.87 14.06 ,000 

0.016 2.97 ,005 

0.244 2.59 ,014 

-0.105 -2.18 ,036 

4.068 -1.34 ,191 

.124 

,094 

,067 

,025 

196 
Table 7-continued 

Dependent vruiable/iidependent variables 

Regession Two-tailed Contribution’ 

coefficient T-Stati& significance toR2 

au pro;inces 

(df = 4, 118; R2= 0.44;P = 0.000): 

Intercept 

Den&v of snaes lo-50 cm d.b.h. and 5-15 m tall 

Importance V.&e of live Pacific silver fu 

Relative frequency of western hemlock snags 

Importance value of live deciduous trees 

Oregon Coast Ranges 

(df= 4, 31; RZ= 0.38;P = 0.001): 

Density of live incense-cedar 

Percentage cover of shrubs 0.5-2.0 m tall 

Percentage ground cover of moss 

Density of live deciduous trees 

Oregon cascades 

(df= 4. 43; R2 = 0.24;P = 0.003): 

Intercept 

Immrtance value of live Pacific silver fir 

Density of live trees 50.99 cm d.b.h. 

Density of decayclass- logs 

Percentage cover of live deciduous trees 58 m tall 

sourhan Wahington Cascades 

(df = 4. 34; ~2 = 0.36; P = 0.001): 

InttXZZpt 

Density of snags 1.549 m tall 

Relative frequency of Douglas-fir snags 

Basal area of live needle-leaved evergreen trees 

Density of live deciduous trees 

Bark foragers: 

AU~provinces 

(df = 5, 124; R* = 0.31; P = 0.000): 

Density of live trees 25-49 cm d.b.h. 

Basal area of live bigleaf maple 

Basal area of live needle-leaved evergreen trees 

Basal area of live grand fir 

Mean height of snags 

Oregon Coast Ranges 

(df=4.38: Rz=0.40:P=0.0W): 

Intercept 

Basal area of live bieleaf ma& 

Basal area of live needle-lea&d evergreen trees 

Density of live !xees 25-49 cm d.b.h. 

Density of live western redcedar 

4.69 26.86 .M)O 

-0.563 -5.15 .oOO 

4.008 -3.87 ,000 

-0.015 -2.73 ,307 

0.004 2.18 .03 1 

4.407 16.86 ,000 

-0.056 -3.39 ,002 

0.091 1.88 ,070 

0.010 1.64 ,111 

0.001 0.73 ,471 

3.95 14.17 ,000 

4.008 -2.56 ,014 

0.066 2.08 ,043 

-0.012 -1.83 ,074 

0.045 1.30 ,200 

5.449 2.79 ,009 

4.009 -2.45 ,020 

0.017 2.36 ,024 

-1.878 -1.88 ,069 

0.011 1.51 ,141 

0.869 1.04 ,300 

-0.539 -3.37 ,001 

0.085 3.14 .I02 

1.033 2.97 .I04 

0.050 2.43 ,017 

0.584 2.01 ,047 

1.114 0.89 ,377 

0.070 2.52 ,016 

1.219 2.23 ,031 

-0.5 12 -2.02 ,051 

0.004 1.98 ,055 

,123 

,070 

,035 

,022 

,205 

,063 

,048 

009 

,107 

,070 

,054 

,027 

,101 

,094 

,059 

,038 

,060 

,052 

a47 

,031 

,021 

,090 

,071 

,058 

,055 

197 
Table 7-continued 

Dependent variable/independent variables 

Regression Two-tailed Connibution~ 

coefficient T-statistic significance toR2 

Oregon Cascades 

(df= 3, 44; R2= 0.38; P = 0.000): 

Intempt 

Percentage cover of shrubs 2.0-4.0 m tall 

Basal area of live needle-leaved evergreen trees 

Relative dominance of Douglas-fir snags 

Southern Washington Cascades 

(df= 2, 36; R2 = 0.40; P = 0.000): 

0.967 

AI.609 

1.175 

-0.006 

Density of live needle-leaved evergreen trees 

Density of snags >50 cm d.b.h. and >15 m tall 

Aerial foragers: 

All provinces 

(df= 4. 118; RZ= 0.40; P = 0.000): 

Intercept 

Density of snags 10.50 cm d.b.h. and 5.15 m tall 

Mean height of snags 

Percentage MVCI of ferns 

Inpxtance value of live broad-leaved evergreen 

- 

Oregon Coast Ranges 

(df= 3. 32; R* = 09o;P = 0.002): 

InterCept 

Density of live incense-cedar 

Mean d.b.h. of live trees 

Percentage cover of live evergreen trees ~8 m 

tall 

Oregon Cascades 

(df=4, 43; R2=0.32;P = O.ooO): 

Intercept 

Vohlme of Douglas-fir snags 

Density of snags 10-50 cm d.b.h. and 5.15 m tall 

Equitability index of tree basal area by heightclassesg 

Importance value of live grand fir 

Southern Washington Cascades 

(df= 3, 35; R* = 0.4o:P = O.OCQ: 

Intercept 

Basal area of live western yew 

Density of live deciduous trees 

Density of live western redcedar 

5.041 

-1.226 

0.194 

1.669 

-0.497 

1.358 

0.355 

0.003 

5.17 

-0.036 

-1.221 

0.123 

1.159 1.68 ,101 

0.645 3.28 .I02 

-0.429 -2.77 ,008 

a.537 1.61 .077 

0.003 1.43 .160 

1.800 15.56 .ooo 

0.280 3.52 .oOl 

0.012 2.45 ,019 

aOQ3 -2.07 ,046 

1.13 ,263 

-3.43 ,001 

2.64 .Oll 

-1.66 ,105 

6.00 .ooQ 

-4.20 ,000 

2.80 ,008 

3.92 .oal 

-5.04 mo 

3.10 .ow. 

2.50 ,014 

1.97 ,051 

5.08 .ooo 

-2.83 .008 

-2.00 ,054 

1.68 ,103 

,155 

,092 

,036 

,278 

,123 

.125 

.047 

,031 

,019 

.160 

.080 

,057 

,157 

,112 

048 

,030 

,197 

,396 

,068 

198 
Table 7-continued 

Dependent variable/independent variables 

Regzssion Two-tailed Contributiona 

coefficient T-Std.& significance tOR2 

canopy foragers: 

All provinces 

(df= 4, 118; R2= 0.34; P = O.OWl): 

Intercept 

Basal area of live deciduous trees 

Percentage ground cover of moss 

Basal area of live pine trees 

Density of snags 1.5-4.9 m tall 

Oregon Coast Ranges 

(df = 3, 32. R* = 0.41; P = 0.000): 

Basal area of live deciduous trees 

Equitability index of tree density by diameter- 

&.%e$ 

Percentage c4wer of berry (vacciniwl spp.) 

shrubs 

Oregon Cascades 

(df= 3. 44; Rz = 0.6S:P = O.OC0): 

Percentage cover of grass, herbs, and fems 

Densitv of live tTees 50.99 cm d.b.h. 

Basal &ea of live pine trees 

southern Was~gton cascades 

(df= 4. 34; R = 0.38;P = O.OCO): 

lllt.%C.Spt 

4.647 35.51 ,000 

0.205 4.93 .wo ,131 

4.011 -3.76 ,000 ,076 

0.072 2.88 .nl5 ,045 

-0.003 -1.76 ,081 ,017 

5.975 11.36 .wo 

0.177 3.43 ,002 ,198 

a.455 -2.56 ,015 ,111 

4.827 -2.29 ,029 ,088 

4.291 22.33 

-0.021 -6.53 

0.129 5.30 

0.043 2.26 

.OoO 

.OOO 

.OOO 

,029 

.319 

,211 

,038 

4.383 18.88 ,000 

-2.50 ,017 

-2.25 ,031 

2.13 ,040 

-1.56 ,127 

,102 

,082 

,074 

.040 

Biomass of decay-class-5 snags -0.982 

Percentwe cover of live deciduous trees <8 m tall -0.101 

Percentage ulver of plants co.5 m tall 0.011 

Basal area of live western yew -0.150 

Understory foragers: 

All provinces 

(df = 5, 117; R* = 0.61; P = O.C+O): 

Intacept 

Pacentage COYa of plants 0.5-2.0 m tall 

Basal area of live deciduous trees 

Mean d.b.h. of snags 

Density of live pine trees 

Mean number of live twe species 

1.388 1.99 .049 

0.175 6.07 .OOO 

0.201 5.26 ,000 

1.784 4.79 .oim 

-0.034 -3.95 .OOQ 

-1.715 -3.67 .OOQ 

&egon Coast Ranges 

(df = 3, 32; R2 = 0.36; P = 0.001): 

Intercept 

Percentage cover of ferns 

lmpmance value of live incense-cedar 

Basal area of live needle-leaved evergreen trees 

6.235 4.21 

0.643 2.50 

-0.012 -2.26 

-0.951 -1.72 

.ooo 

,018 ,115 

,031 ,094 

,095 ,055 

.117 

.088 

.073 

.049 

.043 

199 
Table 7-contloued 

Dependent variablefidependent variables 

Oregon Cascades 

(df = 4, 43; R* = 0.63: P = 0.000): 

Intercept 

PeKxmage cover of ferns 

Impmce value of live pine trees 

Mean height of live dominant trees 

Biomass of logs 

Regression Two-tailed Conbibutionn 

coefficient T-Stati& significance tOR2 

0.738 1.40 .I68 

0.575 3.76 ,001 ,110 

-0.007 -3.69 ,001 ,106 

0.027 3.52 ,001 ,096 

0.607 2.52 ,016 ,049 

southem wahingmn Cascades 

(df = 4,34; Rz = 0.56; P = 0.000): 

Intercept 

Percenta8e cover of Plants <OS m tall 

Percenta8e cover of evergreen shrubs 

Mean d.b.h. of snags 

Percentage cova of live deciduous trees $8 m 

tall 

1.439 1.55 ,130 

0.016 3.65 ,001 ,155 

Al.114 -3.01 .005 ,105 

1.380 2.49 ,018 ,072 

4.067 -1.66 ,107 ,032 

Discussion 

Regional Patterns 

Our results suggested that bird abundance patterns were regionally distinct (fig. 14B) and that abundance was substantially higher in the Oregon Coast Ranges than in the other two 

provinces (figs. 6-13). even though >70 percent of the bird 

species were detected in two or mope. provinces. Location of 

the study stands by latitude, longitude, and elevation; inconsistencies in sample design; and varying degrees of forest 

fragmentation appeared m be partly responsible for the 

differences among regions. 

In the ordination analyses, regional abundance patterns 

(fig. 14B) were best explained by correlations with latitude, 

longitude, and elevation (table 6: figs. 15, 16). They were 

negatively associated with latitude and elevation and positively associated with an east-to-west longitudinal gradient 

(fig. 2). Elevation was essentially overlooked when stands 

were selected and varied substantially within and among provinces. Partial correlation using elevation as a constant was 

impractical for explaining abundance patterns. The southemmost stands in the Oregon Cascade Ranges were among the 

highest in elevation and generally had more birds than stands 

to the north, while stands in the Oregon Coast Ranges were 

generally the lowest in elevation but were higher in abu’ndance than stands in the Cascade Ranges (table 1, fig. 1). 

Although we detected a relatively high correlation between 

longitude and abundance (fig. 2), we assumed longitude per 

se had little effect on bird abundance within one broad vegetation zone (see Hamel and others 1986). The increase in 

abundance from east (Cascade Range) to west (Oregon Coast 

Ranges) was likely more directly related to the moderate 

climate of the Oregon Coast Ranges relative to the colder 

Cascades, or to variation in elevation among the provinces. 

Shortening the interstation distance to 50 m to accommodate 

the smaller stand sizes in the Oregon Coast Ranges may have 

resulted in higher bird counts than in stands with longer interstation distances. Field observers were trained not to count 

individual birds more than once on a given day; however, 

double counting was possible. We attempted to minimize 

these biases by using only detections ~50 m from a counting 

station in all three provinces, except during the analysis 

specifically on individual species. 

High species richness and abundance in Oregon Coast Range 

stands may also be a result of forest fragmentation that has 

increased the diversity of stand ages over the landscape and 

may have in turn increased the packing of individuals within 

200