This Page Was Intentionally Left Blank

This page was intentionally left blank

Small Mammal Communities in the Oregon Cascade Range

Frederick F. Gilbert and Rochelle Allwine

Authors regenerated (usually after fire) and thus did not represent conditions that might be expected in stands managed for FREDERICK F. GILBERT is a professor and wildlife biolo- timber production. gist and ROCHELLE ALLWJNE is an agriculture research technician, Department of Natural Resource Sciences, Wash- ington State University, Pullman, Washington 991646410. Introduction The effects of forest fragmentation or general loss of habitat Abstract are seldom immediately visible in small mammal communities. Studies in the western National Parks, though, support Pitfall and snap-trapping of small mammals in the western the contention that declines in species richness are likely Oregon Cascade Range in 1984-85 revealed no significant over time with insularization of habitat (Weisbrod 1976). differences in species richness among young, mature, and old- Harris and others (1982), Raphael (1988c), and Rosenberg growth Douglas-fir stands. Trowbridge’s shrew was the most and Raphael (1986) suggest that the long-term reduction of abundant small mammal captured, accounting for about half old-growth forests will negatively affect small mammal popu- of all captures. Species showing some association with older lations. Comparisons of species occurrence and abundance in stands included Trowbridge’s shrew, the shrew-mole, the different-aged stands may provide insight into the effects of deer mouse, and the red tree vole. The coast mole was found truncation of seral development on existing faunal communi- only in mature and old-growth stands in 1985. These species’ ties. The objectives of the current study were to assess the associations with vegetational and physical characteristics small mammal communities of young, mature, and old- indicated temporal and spatial differences in habitat use. The growth Douglas-fir stands in the Oregon Cascade Range and tree squirrels (Douglas’ squirrel and northern flying squirrel) and determine which environmental factors might be showed strong positive correlations with snags. The Soricidae responsible for any differences observed. segregated themselves on latitudinal, elevational, and moisture gradients. Materials and Methods Results from this study need to be treated with some caution: Three locations on the western slopes of the Oregon Cascades the young and mature stands contained many characteristics were studied in 1984. Twenty stands were selected in the of old-growth stands because they had been naturally Rogue River and Umpqua National Forests (Rogue-Umpqua), 20 near the H.J. Andrews Experimental Forest (Andrews) and 16 in the Mount Hood region (Mt. Hood). These stands

257 were selected to represent young, mature, and old-growth visually estimated. The species capture rates (corrected for Douglas-fir forests and a moisture gradient (wet, mesic and actual trap nights of operation) were compared to these dry) in the old-growth stands (Gilbert and Allwine, this vol- environmental variables. ume b: see appendix table 15). In addition, a few stands were selected to represent either a mature-age moisture gra- Statistical Analysis dient or managed stands. Final analyses were done for fewer Data analysis was based on two major statistical goals: test- than 56 stands to assure comparison between mesic, un- ing the hypotheses that animal abundance did not differ managed stands of the three age-classes (22 old-growth, among age-classes, moisture-classes, and locations, and num- 17 mature, and 9 young); 28 old-growth stands were in the ber of species (species richness) did not differ among these moisture-gradient analysis (7 dry, 9 mesic, 12 wet). classes; and using exploratory statistics to associate individual species with individual habitat components and with Trapping Methods either age-classes or moisture-classes. Pitfall grids (6 x 6) were established in each stand and checked during September and October 1984. One pitfall We used nonparametric analysis of variance (ANOVA) to trap consisting of 2 number 10 cans taped together and lined test the hypothesis that abundance (number of captures per with plastic margarine tubs was buried within 2 m of each 1000 trap-nights) of animals and species richness did not grid station. A cedar shake was placed above the opening to differ among the age- and moisture-classes or locations. We minimize rain and snow accumulation in the cans. Water used detrended correspondence analysis (DCA) (Hill 1979a) was removed at each check. The traps were opened in early to explore the relations between animal abundances and September and checked every 5 to 7 days for at least 50 habitat-classes or environmental variables. Detrended days. In 1985, 15 stands at the Andrews were studied; the correspondence analysis is an ordination technique that old pitfall grids were used in all stands, and new grids were arranges a matrix of species’ abundances (communities) by established in 8 of them (Gilbert and Allwine, this volume b: samples (stands) in low-dimensional space so that the com- see appendix table 15). Results from the old and new pitfall munities occurring in each stand are represented in space grids were compared to determine whether the previous along several axes. Thus, many components are reduced to a year’s trapping had affected the resident populations. Chi- few important ones and variability is reduced. Communities square testing was used to examine species captured and with similar species composition and relative abundances number of individuals of each species in the eight stands. occupy positions near each other within the space described Because the new grids showed no difference in species com- by the first and second DCA axes. In this way, it functions position and abundance, the old grids were used for analysis. as a principal components analysis. To determine whether stands grouped themselves according to a physiographic In 1984, snap trap grids (12 x 12) with 15-m spacing be- gradient, a plot of the detrended correspondence analysis tween grid locations also were used to sample the small- axes scores was examined to detect clustering. mammal fauna. Trapping took place in July and August, and each stand was trapped for 4 consecutive nights. Two Mu- To classify sites into community phases, two-way indicator seum Special traps (Woodstream Corp., Lititz, PA) baited species analysis (TWINSPAN) (Hill 1979b) was used. This with a mixture of peanut butter and rolled oats were placed method, based on a multi-level two-way partitioning of the within a 1.5-m radius of each grid location. correspondence analysis scores, was used to classify species into categories related to location or to age- or moisture- Mammals caught in the pitfall traps usually had drowned or classes. Species found to be associated with old-growth otherwise died by the time of collection. All animals were forests, from TWINSPAN analysis or from Spearman rank identified to species, sexed, measured, and preserved in the correlations of animal abundances with stand age, were then Conner Museum at Washington State University as skulls, correlated (Spearman rank correlations) with individual envi- skeletons, or skins and skulls. Identifications were verified ronmental and vegetative variables to examine the relation by museum staff. Even with the examination by museum per- between animal species and individual habitat features. sonnel, many Soricidae could not be identified to species. Statistical significance was determined as P < 0.05. Means Vegetative Measurements are given + SE. The physical and vegetative characteristics of the trapping grids were sampled at 9 points within the pitfall grid and Results 16 points within the snap trap grids, with the center of each Pitfall Trap Results sampling point equidistant from four stations. Measurements were made using a nested-plot design, with 5.6-m and 15-m A total of 18 species of small mammals were caught in the radius circles (appendix table 12). Percentage cover was pitfall traps in 1984. Species richness was greatest at Mt. Hood (16) and lower at Andrews (11) and Rogue-Umpqua

258 (13). Species’ abundances (number of captures per 1000 trap- Table 1-Signiflcant ANQVA values for small mammal abund- nights) varied by subprovince, with five species having sig- ance based on pitfall captures corrected for effort (number of captures per 1000 trap-nights) related to subprovince location, nificantly more captures at Mt. Hood and two more at Rogue- Oregon Cascades 1984 Umpqua (table 1). Trowbridge’s shrew, by far the most common species at all three locations, accounted for 62.6 percent Species Locationa F-Value P of all captures and ranged from 53.0 percent at Mt. Hood to 59.2 percent at Rogue-Umpqua and 75.8 percent at Andrews Western red-backed vole RRU > HJA,MTH 25.59 <0.0001 (table 2). The Soricidae represented 76.9 percent of the total Pacific shrew RRU > HJA, MTH 11.33 <0.0001 captures. The western red-backed vole was the only nonshrew Deer mouse RRU > HJA 4.81 0.01 species to represent more than 10 percent of the captures sorex spp. HJA > MTH, RRU <0.05 (14.6 percent) mainly because of a relative abundance of Pacific jumping mouse MTH > HJA, RRU 45.37 <0.0001 Northern flying squirrel MTH > HJA, RRU 35.64 <0.0001 26.5 percent at Rogue-Umpqua. Montane shrew MTH > HJA, RRU 16.40 <0.0001 Ermine MTH > HJA, RRU 8.10 <0.0009 Old-growth stands had 17 species, mature 15, and young 12. Townsend’s chipmunk MTH > HJA, RRU 3.91 <0.03 The average number of individuals captured by age-class Heather vole captured only at MTH 2.91 0.06 was old-growth (49.5 + 5.0), mature (46.5 + 5.7), and young (49.1 + 12.9). The deer mouse (R = 0.35, P = 0.01) and the a RRU = Rogue River-Umpqua; HJA = H.J. Andrews; MTH = Mt. Hood. red tree vole (R = 0.37, P = 0.005) were significantly positively associated with stand age. No species were significant- Table 2-Small mammal relative abundance (captures per 1000 ly associated with any age category in the chronosequence trap-nights) from pitfall trapping by location, Oregon Cascades, 1984 (values in brackets are percentage of capture at that (ANOVA, P < 0.05) (table 3). The average number of cap- location) tures per stand was not different along the moisture gradient (wet 47.3 + 5.7, mesic 50.8 + 7.5, dry 53.0 + 12.1), and no Species Rogue-Umpqua Andrews Mt. Hood species were significantly associated with the moisture gradient (ANOVA, P < 0.05) (table 3). DECORANA analysis Trowbridge’s shrew 331.1 (59.2) 316.9 (75.8) 244.2 (53.0) Western red-backed vole 148.3 (26.5) 21.2 (5.1) 39.9 (8.7) confirmed that age and moisture conditions did not influence sorex spp. 8.3 (1.5) 42.2 (10.1) 2.7 (<1.0) the mammal distribution (figs. 1,2). A location effect was Montane shrew 0.6 (<1.0) 1.7 (<1.0) 76.0 (16.5) related to the pitfall captures (fig. 3), however. TWINSPAN Pacific shrew 39.0 (7.0) 12.8 (3.1) 0.0 (0.0) analysis showed no indicator species for age or moisture Vagrant shrew 2.8 (<1.0) 2.2 (<1.0) 12.3 (<1.0) conditions, but the Pacific jumping mouse, the montane Marsh shrew 2.7 (<1.0) 4.4 (1.1) 5.1 (1.1) Water shrew 0.0 (0.0) 0.0 (0.0) 0.5 (0.0) shrew, the heather vole, Townsend’s chipmunk, the northern Pacific jumping mouse 1.2 (<1.0) 1.7 (<1.0) 35.1 (7.6) flying squirrel, and the ermine separated out as Mt. Hood Shrew-mole 6.1 (1.1) 8.8 (2.1) 11.2 (2.4) indicators; Townsend’s vole and the northern pocket gopher Deer mouse 12.9 (2.3) 1.1 (<1.0) 7.3 (1.6) were indicator species for Rogue-Umpqua. Northern flying squirrel 0.0 (1.0) 0.0 (0.0) 11.9 (2.6) Coast mole 3.8 (<1.0) 4.5 (1.1) 6.2 (1.3) Townsend’s chipmunk 0.0 (0.0) 0.0 (0.0) 3.4 (<0.0) No significant differences were found between the old and Creeping vole 1.7 (<1.0) 0.6 (<1.0) 0.5 (<1.0) new grids in species abundances or richness (P < 0.05). Sig- Townsend’s vole 0.5 (<1.0) 0.0 (0.0) 0.0 (0.0) nificantly more small mammals were caught in young stands Heather vole 0.0 (0.0) 0.0 (0.0) 0.6 (<1.0) (average 59.0 + 4.6) than in old-growth stands (29.8 + 4.2) in Northern pocket gopher 0.6 (<1.0) 0.0 (0.0) 0.0 (0.0) Douglas’ squirrel 0.0 (0.0) 0.0 (0.0) 1.1 (0.0) 1985. The mature-stand average (46.7 + 6.8) was not differ- Ermine 0.0 (0.0) 0.0 (0.0) 2.9 (<1.0) ent from the other two age-categories. Fourteen species were captured in 1985 compared to 10 in the same stands in 1984. The four additional species (red tree vole, Pacific shrew, Snap Trap Results Townsend’s chipmunk, and the montane vole) were represented only by 1 to 3 specimens each. Eighteen species and 1493 individuals were captured in the snap traps (table 5). Trowbridge’s shrew was the dominant None of the small mammals captured in 1985 were sig- species at all locations (44.8-55.4 percent of all captures). nificantly related to old growth in the chronosequence, The Pacific shrew was the second most captured species although five species showed an association with mature (24.1 percent) at Andrews, the montane shrew (14.2 percent) or young stands (table 4). The coast mole and red tree vole at Mt. Hood, and the western red-backed vole (29.4 percent) were only captured in mature and old-growth stands. The at Rogue-Umpqua. Species richness was not significantly only significant difference in age- or moisture-classes for different between locations. The western red-backed vole, the any species between 1984 and 1985 was the increased pro- deer mouse, and the marsh, montane, and Pacific shrews portion of Trowbridge’s shrew caught in young stands in were significantly associated with location (table 6). This 1985 (x2 = 56.6, P < 0.0001).

259 Table 3-Caphwes of individual mammals in pitfall traps (mean number captured per stand, corrected for effort in parentheses) for age- and moisture-classes, Oregon Cascades1984

’ Westernred-backed vole 95 (10.7) 866 (0.7)(9.6) 553 (0.3)(4.4) : Townsend’s chipmunk - Northern flying squirrel 6 (0.7) 7 (0.6) creeping vole l(O.1) l(O.1) Townsend’s vole l(O.1) 2 (0.2) Ermine 2 (0.2) Shrew-mole T(l.0) -G (0.8) Deer mouse 4 (0.6) 12 (1.4) ‘i $ii Coast mole 2 (0.3) 4 (0.4) 7 (0.6) Marsh shrew l(O.1) 4 (0.4) 7 (0.6) Montane shrew l(O.1) 6 (0.8) 47 (3.8) Sorer spp. 10 (1.6) 13 (1.4) 19 (1.7) Heather vole ’ _I l(O.1) Pacific shrew 17 (2.9) 24 (2.8) 17 (1.4) 54 (34.4) 264 (29.6) 334 (27.7) 4 (1.3) 2 (0.2) 12 (1.1) 2 (0.1)

G(1.4) 24 (2.2)

young values were significantly different, but the values for location effect was verified by the DCA scores, which old-growth did not differ significantly from the other two showed definite clustering (fig. 4). No similar moisture or age-classes. Captures of the Pacific shrew were significantly age effects were found (table 7; figs. 5,6). associated with mature stands (ANOVA, F = 3.62, P < 0.04). Spearman rank correlations showed the shrew-mole and The mean captures per stand were highest in mature (29.2 ? Trowbridge’s shrew to have a positive association with stand 3.6) and lower in old-growth (26.3 * 2.5) and young stands age that neared significance (P = 0.06). The mean capture (15.5 * 3.5) (ANOVA, F = 3.24, P < 0.05). The mature and rates of all species did not differ along the moisture gradient (wet 26.4 k 3.7, mesic 30.3 * 3.9, dry 21.0 f 3.5). Only the

260 Table SSmaU mammal captureson the snap-trapgrids, 140 = Mount Hood Oregon Cascades 1984 q Rogue-Umpqua Location

247 262 217 126 tJ *O 165 54 41 2.56 60 52 12, 2 175 46 15 1, 72 40 8 6n 3 7, 0 50 52 20 11 1: 17 39 1 14 13 3 30 0 4 11 15 0 3 11 14 0 20 40 60 80 100 120 140 1.40 3 3 4 10 7 1 1 9 DCA 1 3 3 2 7 0 1 1 * 0 I 0 1 1 0 0 I 1 0 0 I 1 0 0 1 Table 4-SmaU mammals significantly awxlated 0 1 0 1 (ANOVA) with age of stand for pitfall captures, Oregon Cascades 198.5 559 555 379 1493 Species Standage associatiw, Table 6-Small mammalspecies-abundance values corrected Westernred-backed vole Mature > old-gmwth for effort (number of capturesper 1000trap-nights) snap- Coast mole M&UIe trapped In the Oregon Cascades, 1984, showing significant Momme shrew Young > old-growth (ASOVA) associationswith location Tmwbridge’s shrew Young > old-growth vagrant shrew Mature > old-growth capturelocationn Species association F-value P

western red-backed vole showed a relation to moisture con- Western red-baEk.4 ditions that was near significance, with averagecaptures in V& RRU>HJA.RRU>h%TH 9.67 o.ooo3 Deer mouse RRU>HlA 4.35 RRU 3.51 HJA.MTH>RRU 20.03 RRU,HJA>MTH 13.23

Table ‘I-Captures of individual mammals In snap traps (mean number captured per stand corrected for effort in parentheses) for age- and moisture-classes, Oregon Cascades, 1984 Moisture

Westernred-backed vole Townsend’schipmunk Montmevole creepingvole Shrew-mole Deermouse Coastmole Townsend’smole Marshshrew Montme shrew Pacificshrew Tmwbridge’sshrew Vagrantshrew sorer spp. Westernpocket gopher Pacificjumping mouse Dusky-footedwoodrat also was captured at sites with deciduous shrubs and trees The northern flying squirrel was positively associatedwith (table 9). The western red-backed vole was positively asso- large and medium sized (lo-50 f cm d.b.h.), tall (15-m) ciated with needleleaf evergreen trees in all height-classes. snagsof decay-classes3 and 4, as well as medium snagsof decay class 5. The Douglas’ squirrel was found in stands The montane shrew was the most widely distributed shrew with various-sized snagsof decay-class5. basedon shrubs and understory trees. It was positively associated (R = 0.51-0.59; P < 0.0001) with berry-producing Pitfall resultsIn 1985, the red tree vole was captured at shrubs of all three height-classesand deciduous shrubs in sites with small bigleaf maple, (R = 0.53, P = 0.04) large the first two height-classes(R = 0.42-0.46; P < 0.001). The golden chinkapin, and very large grand fr. Also, it was montane shrew was the only speciesassociated with ever- highly correlated with sites with medium Pacific dogwood green shrubs (0.5-2 m; R = 0.36; P = 0.007). (R = 0.995; P < 0.0001). In 1984, it was associatedonly with

262 Table S-Qniflcant Spa-man rank correlations (P 5 0.05) for forest floor charscterlstics at the pitfall grids and selected small mammals captured, Oregon Cawades, 1984

DCA 1

Table 9-SignUicaot Spesrmao rank correlations (P S 0.05) for understory and ground-cover characteristics at the pitfall grids and selected small mammals captured, Oregon Cascades, 1984

Grasses(c-O.5 In) 0.45 q Old Fern (O-0.5 m) a47 km (0.5-Z m) -0.44

N Mduoussblubs(O4Sm) 0.27 Decid”O”S trees (O-0.5 m) 0.50 Deciduous trees (0.5-Z m) 0.47 Needle-leaf evergreen (2 m-midstory) 0.34

Deer mowe Bellyproducing shrubs (00.5m) 0.29 Dezidws *@.lbs(&O.5m) 0.29 Deciduous Wee6 (O-O.5 m) 0.42 Dezidwus trees (0.5-Z m) 0.32 Deciduous sb~bs (2 m- midstay) 0.32

Grass (oa.5 m) -0.43 Fem(Oa5m, 0.31 Berry-p-ducingshrubs (0.0.5 m) 0.50 Evergrrmskmbs(O.O.5m) -0.42 medium canyon live oak (R = 0.29; P < 0.03). Limited con- Deciduous shbs (CKxSm) 0.35 sistency was found in vegetative and physical characteristics D,%id”O”S shrub (0.5~2m) 0.43 with which the small mammal species were positively or neg- Benypmhcing shrubs atively associated between years. The red-backed vole was (2 m-midJtor/) 0.54 negatively associated with moss ground cover (R = 4.55, P = 0.04) in 1985 as was Trowbridge’s shrew (R = -0.58, P = 0.02). Both showed similar results in 1985. Most species varied behveen years in the characteristics of the sites at which they were caught, but few significant changes (Spearman rank correlations) occurred from positive to negative or from negative to positive. The more common result was that some characteristics were significantly assc- ciated one year and not the other.

263 The montane shrew was positively associated with berry- Table M-Significant Spearman rank correlations for vegetative characteristics at snap-trap capture locations for producing shrubs up to the midstory level (R = 0.26-0.50; small mammals, Oregon Cascades, 1984 P < 0.05) and all deciduous shrubs (R = 0.34; P = 0.001) up to 2.0 m high (table 10). The montane shrew, the marsh Species Vegetative characteristics R-value P shrew, and Trowbridge’s shrew were caught at sites where ferns were a dominant ground cover. The Pacific shrew was Western red-backed associated with broadleaf evergreen trees in the 0.5- to 2.0-m vole Grass (0-0.5 m) 0.54 <0.00 Fern (0-0.5 m) -0.36 0.007 zone (R = 0.50, P c 0.0001); it was negatively associated Evergreen shrub (0-0.5 m) 0.26 0.05 with berry-producing and deciduous shrubs (R = 0.32) and Fern (0-5.-2 m) -0.28 0.04 was caught at sites with evergreen shrubs (R = 0.47) up to Berry-producing shrub 0.5 m tall (table 10). Forest floor characteristics associated (2 m-midstoty) -0.28 0.04 Deciduous shrubs (2 m- with the marsh shrew were logs of decay-class 1 (R = 0.26) midstory) 0.29 0.03 and 3 (R = 0.26), and with the montane shrew were lichen Needleleaf evergreen trees and aspect (R = 0.30; P = 0.02); the vagrant shrew was (super canopy) 0.39 0.003 negatively associated (R = -0.38) with lichen (table 11). Townsend’s mole was caught in traps with logs of decay- Trowbridge’s shrew Fern (0-0.5 m) 0.40 0.002 Fern (0.5-2 m) 0.40 0.002 classes 2 to 5 (R = 0.27-0.32) nearby. Marsh shrew Grass (0-0.5 m) -0.31 0.02 Discussion Fern (0-0.5 m) 0.35 0.007 Fern (0.5-2 m) 0.28 0.04 The red tree vole, deer mouse, Trowbridge’s shrew and the Berry-producing shrubs shrew-mole were the only small mammals positively associ- (0.5-2 m) 0.29 0.03 ated with older stands in our study, and none seemed depend- Needleleaf evergreen tree -0.37 ent on the availability of old growth. Corn and others (1988) (super canopy) 0.005 generally concur with this and found that only the red tree Pacific shrew Berry-producing shrubs vole was significantly associated with old-growth Douglas-fir (0-0.5 m) -0.41 0.002 stands in their study of the Oregon Cascades. Raphael (1984, Evergreen shrubs (0-0.5 m) 0.47 0.0003 Deciduous shrubs (0-0.5 m) -0.32 0.02 1988c) and Raphael and Barrett (1984) listed 10 small mam- Broadleaf evergreen trees mals significantly associated with old-growth Douglas-fir for- (0-0.5 m) 0.50 <0.0001 ests in northern California, an area not dissimilar to Rogue- Broadleaf evergreen trees Umpqua. Trowbridge’s shrew can be discounted as an (0-0.5 m) 0.61 <0.000l old-growth associate because it is a very common species Needle-leaf evergreen trees (0-0.5 m) -0.28 0.04 that occurs in all ages of stands. Needleleaf evergreen trees (2 m-midstory) -0.28 0.03 The mean species richness observed in this study was higher and more variable on the chronosequence than that observed Grass (0-0.5 m) -0.27 0.04 Fern (0-0.5 m) 0.29 0.03 by Corn and others (1988) or Raphael (1984). Species diver- Berry-producing shrubs sity studies are limited usually by the short temporal span of (0-0.5 m) 0.49 <0.000l sampling the environment, and, because studies such as ours Evergreen shrubs (0-0.5 m) -0.38 0.003 tend to rely on data gathered from many single sample sur- Broadleaf evergreen trees veys, erroneous correlations can be drawn (Wiens 1981b). (0-0.5 m) -0.55 <0.0001 Berry-producing shrubs Greater replication, especially between years, would have (0.5-2m) 0.50

264 Table 11-Significant Spearman rank correlations for forest- burrower (Dalquest and Orcutt 1942). What associations did floor characteristics at snap-trap capture sites for small exist in our study suggested an ubiquitous use of the environ- mammals, Oregon Cascades, 1984 ment, similar to the findings of Corn and others (1988). Species Variable R-value P Red-backed voles were negatively associated with sites with Trowbridge’s shrew Logs, decayclass 2 0.31 0.02 fern as a dominant ground cover. Ferns were often found with shrub or other understory cover, which suggests avoid- Marsh shrew Fine litter -0.30 0.03 Logs, decay-class 1 0.26 0.05 ance of such areas. As a mycophagist (Maser and others Logs, decay-class 3 0.26 0.05 1978, Ure and Maser 1982), the red-backed vole would be expected to occur in conifer-dominated locations, at least at Pacific shrew Lichen -0.37 0.006 the time of foraging for fungi. Negative associations with Pacific dogwood and golden chinkapin support this. Lichens Montane shrew Bare soil -0.33 0.01 Lichen 0.35 0.008 are preferred food for red-backed voles in the Pacific North- west (Vre and Maser 1982), and these voles were highly asso- Townsend’s mole Bare rock -0.29 0.03 ciated with areas of lichen ground cover in our study. Maser Coarse litter 0.28 0.04 and others (198 1) say that the distribution of red-backed Logs, decay-class 2 0.39 0.02 Logs. decay-class 3 0.30 0.03 voles is influenced by the presence of rotting, punky logs. Logs, decay-class 4 0.27 0.04 Hayes and Cross (1987) found capture of the species to be Logs, decay-class 5 0.32 0.02 positively correlated with mean log diameter and size of the log overhang, suggesting they use this space as travel corri- Coast mole Bare rock -0.26 -0.05 dors. Our captures were positively associated with logs of decay-class 5, and many of our captures (Gilbert, pers. obs.) were in the space under log overhangs. This supports the speculation that temporal variation of habitat use occurred, which reduced the predictability of results The Soricidae were segregated somewhat in the western based on physiognomy. Oregon Cascades. The vagrant shrew was found primarily in higher elevation stands in the northern Oregon Cascades. Al- We captured too few red tree voles for meaningful statistical though the montane shrew was also associated with Mt. analysis or to conclude that they are related to older stands Hood, it selected young stands and thus was significantly of Douglas-fir. Such a relation has been suggested for this associated with shrubby areas. The Pacific shrew was species by other authors, and old-growth Douglas-fir is con- restricted to the central and southern subprovince locations, sidered to be optimum habitat (Corn and Bury 1986, Franklin and it was a generalist in its use of the habitat. A lot of the and others 1981, Meslow and others 1981). We, and the shrews from Andrews could not be identified to species other authors, found the red tree vole primarily in mesic to (other than that they definitely were not Trowbridge’s shrew) wet old-growth stands but the strong associations with medi- because of mixed characters. Hennings and Hoffman (1977) um Pacific dogwood, berry-producing shrubs, and deciduous and Findley (1955) have discussed the taxonomic difficulties trees of smaller diameter may be a function of the small with the montane, Pacific, and vagrant shrews, and, until the sample size. They may have been selecting such vegetation taxonomic issue is resolved we decided to identify these for food, however. Some of the animals we captured may individuals only to genus. Terry (1981) could not correlate have been dispersing; most of the males were juveniles, and the montane shrew with any vegetational factors and found the species is supposed to be arboreal and thus seldom found the vagrant shrew may have been excluded competitively by on the ground (Maser and others 1981). The females were Trowbridge’s shrew. Dalquest (1941) considered the vagrant mainly adult, and the sex ratio was almost equal. Although shrew to be dominant over Trowbridge’s shrew. Our findings we cannot draw any conclusion as to the function of terres- did not reject competitive exclusion by either species. trial activity in the species, it obviously occurs. Terrestrial nesting has been suggested for males (see Corn and Bury Although this study provided data on habitat usage by small 1986). but we found equal numbers of females. Corn and mammals, it showed the difficulties that occur in time- Bury (1986) caught predominantly females in their pitfall restricted analyses of vertebrate communities. Three of the traps. four species that had some old-growth association were either weakly linked (the shrew-mole), relatively abundant species The shrew-mole is an insectivore (Terry 1978, Whitaker and in other age-classes (western red-backed vole and the deer Maser 1976) and, in a study in King County, WA, it was mouse), or both (the deer mouse). The deer mouse is of in- found in forested areas with a high organic content to the terest because other authors (for example, Gashwiler 1970a, soil (Terry 1981). We found no such clear delineation of habitat use, although the shrew-mole is a known shallow

265 Hooven 1973, Hooven and Black 1976, Martell and Radvanyi such stands with a previous history of logging, and these 1977) consider the species to be most abundant in early suc- young and mature stands had fewer species and individuals cessional forests. We trapped during a low in the population in the small mammal communities than comparable natural cycle of the deer mouse in the Oregon Cascades, and the stands (Gilbert 1985). Other evidence supports such impacts species seemed to be related to older successional forests. of logging on particular species; Corn and others (1988), Anthony and others (1987) had similar results trapping ripari- state that we have probably already eliminated much of the an zones at Andrews in 1983, as did Raphael (1984) in north- red tree vole habitat by extensive logging of low elevation, em California. Scrivner and Smith (1984) found the species old-growth forests. The habitat features supporting the abun- to be most associated with older successional stages (>80 yr) dance of small mammals we observed in the Oregon Cas- of spruce-fir forests in Idaho, and Monthey and Soutiere cades will be reduced or eliminated in managed forests, cre- (1985) had similar results with a related subspecies in Maine ating a risk that species richness will decline (compare to conifer forests. Sullivan (1979) stated that clearcut areas may Weisbrod 1976) unless forest management practices provide be population sinks for dispersing deer mice. Although the opportunities for maintaining such elements as coarse woody species is not restricted by any means to older successional debris and large trees in the managed Douglas-fir forests of stages, older forests may provide its best habitat. the future. Some of the species we captured were definitely linked with these features of structural diversity (for example, Douglas’ squirrels were not sampled adequately by trapping the red tree vole, flying squirrel, and western red-backed to provide any information on their dependence on old- vole). Therefore, although old-growth may not be itself lim- growth. Data derived from avifauna surveys (Gilbert 1985) iting to very many species, the structural complexity of provided no evidence of dependence on old-growth, although naturally regenerated forests may be required for maintaining Raphael (1984,1988) and Raphael and Barrett (1984) found small mammal diversity. a significant positive correlation with stand age for the Douglas’ squirrel in Douglas-fir forests in northern California. Acknowledgments Flying squirrel abundance was positively correlated with large-snag density (Volz 1986, this study), suggesting this The Oregon Cascades study was made possible by the con- habitat feature is necessary for suitable den trees and cavities tributions of many people, including U.S. Forest Service and may be limiting for that species. Maser and others personnel. Effective field supervision was given by Wynn (1981), however, note that in locations in western Oregon Cudmore, and crew leaders Jim Reichel and Troy Cline at where these more suitable nesting sites have been removed Rogue River-Umpqua, Kathleen Fulmer at H.J. Andrews, by logging, the species will build outside nests. We noticed and Jeff Picton at Mount Hood in 1984. The 1985 crew some of these nests as well. leader was Tony Fuchs. John Teburg, Dick Gilbert, Rich Alldredge, and Betsy Piersone all assisted in data entry and One cautionary note is that virtually all the stands we studied analysis. The hard-working field crews, primarily made up of were natural and not the intensively managed stands that can Washington State University wildlife students, were essential be expected in the future. Even the young stands had large to successful completion of the work. amounts of coarse woody debris and snag numbers almost equivalent to old-growth stands. Vegetational features and This paper is contribution 119 of the Wildlife Habitat coarse woody debris in stands originating from logging rather Relationships in Western Washington and Oregon Research than fire are considerably different. We did sample a few ific Northwest Research Station, USDA Forest

266 Appendix Table 12-Vegetation and site measurements for pitfall and snap trap grids, Oregon Cascades, 1984

I. Measurements on a 100 m2 area (5.6-m radius)

Forest floor: 1. Cover of logs by decay-class (%) (>lO cm diameter). 2. Litter depth at three points (01, 02) (mm). 3. Coverage of forest floor by various substrates: exposed bare rock, exposed bare mineral soil, fine organic litter (10-cm diameter), moss, lichen. (Total - 100%).

A. Vegetation characteristics 4. Coverage of foliage by height interval and life form (%). a. Height intervals 1. 0-0.5 m (100 m2 area) 2. 0.5-2.0 m (100 m2 area) 3. 2.0 m through midstory (shrubs and trees not entering main canopy) (707 m2 area). 4. Canopy trees forming main canopy layer (707 m2 area). 5. Super canopy trees (crowns extending well above main canopy layer) (707 m2 area).

b. Life forms 1. Herbs 2. Graminoids (grass & grasslike plants including sedges) 3. Ferns 4. Berry-producing ericaceous shrubs (Vaccinium and Gaultheria) 5. Evergreen shrubs (including shrubs of #4) 6. Deciduous shrubs (including shrubs of #4) 7. Deciduous trees 8. Broadleaf evergreen trees 9. Needleleaf evergreen trees

B Stand characteris tics 5. Number and species of small diameter, live trees (l-10 cm d.b.h.). 6. Number and species of medium diameter, live trees (l0-50 cm d.b.h.). 7. Number by decay-class of large diameter, medium tall snags (>50 cm d.b.h. and 5-15 m tall). 8. Number by decay-class of medium diameter, medium tall snags (l0-15 cm d.b.h. and 5-15 m tall). 9. Number by decay-class of short snags (any d.b.h., 1.5-5 m tall). 10. Number stumps (

II. Measurements on a 707 m2 area (15-m radius, the distance to next trap station).

A. Stand characteristics 11. Number and species of large live trees (50-100 cm d.b.h.). 12. Number and species of very large live trees (>l00 cm d.b.h.). 13. Number by decay-class of large diameter, tall snags (>50 cm d.b.h. and 15 m tall). 14. Number by decay-class medium diameter, tall snags (l0-50 cm d.b.h. and >15 m tall).

B. Site characteristics 15. Surface water (presence/absence). 16. Type of water: I (intermittent stream), P (perennial stream); S (seep); 0 (pool/pond). 17. Rock outcrop (>l% of area) (presence/absence). 18. Exposed talus (>l% of area) (presence/absence). 19. Number of recent tree-fall mounds-pits with exposed roots and mineral soil.

267

Small Mammal Communities in the Southern Washington Cascade Range

Stephen D. West

Author mammalian presence-absence data or by the abundance of frequently captured species (K-means) did not indicate a STEPHEN D. WEST is an associate professor, Wildlife mammalian community that was strongly organized with Science Group, College of Forest Resources, University of respect to gradients of forest age or moisture. Habitat vari- Washington, Seattle, Washington 98195. ables were weakly correlated with the abundance of mammalian species. The forest-floor small mammal community in Abstract these naturally regenerated forests appears adapted to a broad Small mammal faunas on the western slope of the southern range of conditions related to forest age and moisture. Washington Cascade Range were sampled to describe patterns of abundance along gradients of forest age and moisture Introduction and to identify structural, vegetative, and environmental fea- The small mammal communities of the western slopes of tures associated with these patterns. Forty-five primary sites the southern Washington Cascade Range are composed of were sampled by snap and pitfall trapping in 1984 and 1985, species from two mammalian faunas (Dalquest 1948). Before resulting in the capture of 6751 individuals of 20 species, of the last glacial period (Vashon-Wisconsin), species char- which 11 were regularly caught and statistically analyzed. acteristic of the temperate forests of the Pacific coast, such Four of these 11 species had different abundances between as the shrew-mole, Townsend’s mole, Trowbridge’s shrew, years. The abundance of two species differed between forest the marsh shrew, Townsend’s chipmunk, the deer mouse, age-classes. The deer mouse was caught more often in old- Townsend’s vole, and the creeping vole, probably were the growth than young forest, and the forest deer mouse was most common species in the region. As glacial advance caught more often in mature and old-growth than young proceeded, species associated with boreal conditions to the forest. The abundance of three species differed between north, such as the water shrew, the yellow-pine chipmunk, moisture-classes of old-growth forest. The marsh shrew was the heather vole, the southern red-backed vole, the water caught more often in wet than in moderate old-growth forest, vole, and probably the forest deer mouse, moved southward and the southern red-backed vole was caught more often in through the Cascades. At glacial maximum, species of both dry than in moderate or wet old-growth forest. In 1985 only, faunas inhabited this unglaciated region. With retreat of the deer mouse was caught more often in moderate than in glacial ice, these species expanded their distributions gen- wet old-growth forest. Elevation (404 to 1218 m) was not a erally north and east, colonizing the Cascades as habitats strong factor influencing small mammal abundance. Cluster- became suitable (Dalquest 1948). ing sites by similarity coefficients (Jaccard’s) based on

269 Small mammals, therefore, have inhabited the southern por- years old), 9 sites in mature forest (80-190 years old), and 18 tion of the Washington Cascades longer than areas farther sites in old-growth forest (210-730 years old). All 27 old- north. If consistent associations occur between small mam- growth sites were classified into moisture-classes, yielding 9 mals and naturally occurring gradients of forest age and wet sites, 11 moderate sites, and 7 dry sites. moisture, they might be expected to occur in the south. Do unique species combinations occur along these gradients, or Small Mammal Sampling are the constituent species capable of persisting in an array Sampling techniques varied, reflecting the different natural of forest conditions? These questions have gained importance histories of the small mammal fauna. This study used four in recent years, with increasing attention to the issue of techniques: vocalization frequencies of tree squirrels, track preserving old-growth forests. This study addresses the records from smoked aluminum plates, snap-trapping, and relationships between small mammal communities and pitfall trapping. Vocalization frequency data were collected naturally regenerated forests. Extrapolation of conclusions as part of the spring avian surveys, using variable circular from this work to potential relationships in managed forests plots (Manuwal, this volume). These data were used in con- will be difficult, as discussed below. junction with the other techniques to assess the presence or absence of squirrels on the study sites. Data on track fre- The central objective of this paper is to describe the patterns quency (Carey and Witt 1991) were used in the same fashion. of small mammal species abundances over a gradient of for- They were particularly useful in establishing the presence of est age, and within old-growth forests, to describe patterns of squirrels and chipmunks, species not sampled efficiently by abundance over a gradient of moisture. This paper also will snap or pitfall trapping. By far the most important techniques, investigate correlations between small mammal abundances and the ones yielding information on relative abundance, and selected environmental and vegetational variables. were snap-trapping and pitfall trapping.

Methods As noted by Briese and Smith (1974), Bury and Corn (1987), Study Sites and Williams and Braun (1983), capture efficiency differs consistently between snap and pitfall traps. In general, pitfall This work was conducted on 54 sites on the western slopes traps sample nonjumping rodents and insectivores more of the southern Washington Cascade Range. Sites were effectively than do snap traps, which sample more agile located predominantly within the Western Hemlock Zone rodents most effectively. Species lists exclusively derived (Franklin and Dymess 1973) at elevations ranging from 404 from one technique will reflect this sampling bias. Estimates to 1218 m. Some of the higher elevation sites extended into of relative abundance in this paper consequently combined the Pacific Silver Fir Zone. Most forested sites had Douglas- information from both techniques. West (in press) describes fir as the dominant tree species, although wet old-growth the snap-trapping methods used in this study and a rationale forests had a large proportions of western redcedar. The sites for developing this particular protocol. Briefly, we used two chosen for small mammal studies form a subset of a large Museum-Special traps at each of 144 trapping stations. Most number of sites investigated botanically. For an extensive of the traps were new-model Museum Specials with plastic treatment of the vegetational composition and structure of treadles (West 1985). Stations were arrayed on a 12 by 12 the study stands, see Spies (this volume) and Spies and grid with 15-m interstation distances. Traps were baited with Franklin (this volume). peanut butter and whole oats, and operated for four consecutive days. We trapped each site once during July and August Of the 54 sites, 8 were on areas recently clearcut (cut 6-21 in both years. Trapping grids were relocated within sites years previously). These sites were sampled for small mam- between years to avoid sampling potentially depleted popu- mals in 1984, but could not be included in sampling during lations in 1985. Corn and Bury (1990) also describe methods 1985. One forested site was sampled only in 1985, and the of pitfall trapping that were developed primarily for sampling remaining 45 sites were sampled in both years. These 45 amphibians and reptiles. Mammals and herpetofauna were sites (see frontispiece), which ranged in size from 51 to 1690 sampled simultaneously. Pitfall arrays consisted of 36 traps ha (mean size = 488 ha), are the focus of this paper. on a 6 by 6 grid with 15-m spacing between traps. Pitfall traps were operated continuously for 30 to 34 days each fall, Sites were chosen based on several physical and vegetational beginning in October. Traps were checked once a week and characteristics (Carey and Spies, this volume), and subse- were relocated within sites between years. All captured ani- quently placed into classes along gradients of age and moist- mals were given to the Burke Memorial Museum at the ure (Spies and Franklin, this volume). Of the 45 sites, 36 University of Washington. were judged sufficiently similar in site moisture conditions (moderate vs. very wet or dry) to be compared along an age gradient. Elimination of very wet or dry sites resulted in a chronosequence consisting of 9 sites in young forest (55-75

270 Vegetation Sampling Small mammal responsesto forest-age and moisture gradi- Information on the physical features of the sites and their ents, and to selectedenvironmental variables were investi- vegetational composition and structure was gathered on the gated in three general ways. Analyses of variance (repeated snap and pitfall trapping grids in a similar manner. Variables measuresANOVA) of small mammal abundancewith forest appropriately measuredat a small scale, such as coverageof age (young, mature, and old-growth forest) and moisture- the forest floor by different substrates,percentage cover of classes(dry, moderate, and wet old-growth forest) assessed logs by decay-class,and percentagecover of herbs, ferns, the variation in abundancefor successiveyears aaoss both most shrubs, and small trees, were recorded on 100-m’ circu- gradients. When significant class-by-year interactions were lar plots. Variables of larger scale, such as large trees, large present, I used separateone-way ANOVAs with Tukey’s standing snags,and site characteristics (presenceand type of HSD test for multiple comparisons. I used Pearsoncorre- water, rock outcrops, or talus) were measuredon 707-m cir- lation coefficients to test for associations with selected envi- cular plots centered on rhe smaller plots. Centers of the con- ronmental parameters,and multiple regression to assessthe centric plots were equidistant from four pitfall traps or snap- consistency and strength of association between vegetative trapping stations, resulting in 9 vegetation plots on the pitfall physiographic variables and the abundanceof mammals.The grids and 16 plots on the snap-Impping grids. Becausethese ANOVAs and correlation coefficients were calculated for grids were relocated between years, we collected data from speciesfor which at least 40 individuals were captured. The different grids each year. composition of mammalian communities, based on the presenceor absenceof speciesfor each site, was obtained by Data Analyses combining capture totals in both years with information from the aviao surveys and the track plates. The resulting matrix This paper is concerned with the responsesof small mammal of presence-or-absencedata by sites (speciesin table 1 plus populations at the site or stand scale. Abundance patterns the Douglas’ squirrel) was clustered hierarchically by were.characterized, and correlations with habitat features Jaccard’s similarity coefficients (Jaccard 1912) to reveal were sought, from summations of snap and pitfall captoresin community pattern along the forest-age and moisture each year with site and vegetation variables averagedover all gradients. In addition, K-means clustering (Hartigan 1975) plots in both years. Such an approach was taken to provide a on the abundanceof the most frequently captured species comprehensive data seL As discussedabove, combining snap (11 species)was used to investigate community pattern from and pitfall data enlarges sample sizes and helps reduce the a different perspective. known biasesof each method. By combining information from all vegetation plots (n = 50), a good averagevalue could Table ISmall mammals captured in snap (July and be obtained for most variables. All statistical work was done August) and pltfall traps (Octoberand early November) with SYSTAT microcomputer programs (Wilkinson 1988). on 45 forested sites in the southern Washington Cascade RaIIge Counts of captured animals are reported as numbers per 100 trap-nights. For snap-trap data, these coonts were corrected Comon name 1984 1985 TOtal for empty, snappedtraps, and for traps occupied by another species.Because pitfall traps were multiplecapture imps, hsectivora such adjustments to the capture totals were unnecessary. Vagrantshrd 20 48 68 Montaneshrew” 452 859 1,311 Before statistical analyses,capture data were transfomwd Watershrew 6 3 9 logarithmically @(x+1)). Marshshrew 7.1 25 46 Trowbridge’sshrewb 1,105 x41 1.946 All variables measuredon the vegetation plots were in- Unidentifiedshrew 26 12 38 spectedfor statistical normality and transformed using loga- ShW-IllOk 116 115 231 rithmic @1(x+1)),square root ((x+3/8)), and arcsine (am(x)) Coastmale 11 10 21 functions as appropriate. Redundant variables were either eliminated from furtber analysis or combined with similar Lagomorpha variables after inspecting the Pearson correlation matrix of Pika 1 1 2 the data. Of the field-recorded variables, a subset of 3 1 var- Rodemia iables consisting of original and combined variables was Yellow-pinechipmunk 1 11 12 used to examine correlations between small mammal Townsend’schipmunk 26 16 42 abundanceand habitat features (appendix table 7). Unidentifiedchipmunk 0 1 1 Northernflying squinel 2 27 29 Northernpocket gopher 0 1 1 Deermouse 101 125 226

271