CraigA. Steele,lEdmund D.Brodie, Jr., Departmentof B ology,Utah State Univers ty. 5305 Old Ma n H Logan UIah 84322 and JamesG. Maccracken, T .nberDepartrnent 300 F breWay, Longv ew F bfeCompany Longv ew Washngton 98632

Influenceof ForestAge on Densitiesof Cope'sand Pacific Giant

Abstract

We suNeled flrst-order streamsin forcst sunds 0 94 )r old on industrial timberlandsin the CascedeNlountains of southcm Washingtonduring the summerof 1998and 1999 ro determinehow short-temrchangcs in lbrest age can rffect rhe abundanccof the \lream-bfeedingCope's and Pacilic giant salananders.Based on resultsfrom cross validatedregression trees, dcnsirics of both specieswere unrelatedto changcsin lbren rge or any othef habitatvariablc mcasured.There was also no differenccin any ofthe measuredhabitat variables bctwccn sreans in $ hich a species$'as present and strcamsin which it wasnot detected.Hou'c\,cr. dcnsiliesof the Pacific giant salamanderr crc ncgalively conelaled to pefcentof riparjan canopy cover in one of the vears. lntroduction old growth statusand are subjectto rcgular, in- tenslveharvest management. Thestream-breeding giant salamanden (DicdnpLr- don spp.) havereceiyed rruch attentionwith re- Many prcvious studies did not differentiate (D. spcctb their habitatassociations (Hawkins ct al. betweenCope's giant copel) and (.D. 19U3,Corn and Bury 1989,Parker 1991, Wilkins Pacific tertebrosus)when andPeterson 2000). Several studies correlated the examininghow this genusresponds to changes presenceof giant salamanderswith streamhabi- in tbrestage or other habitatvariables. It is often tat charactedsticssuch as high gradient riftles difficult to differentiatebetween Cope's giant (Hawkinset al. 1983.Com andBury 1989)and salamanderand larval Pacitic giant salamanders coarsc substrates(Parker 199l, Wilkins and in the field. and there is generally an unstated Peterson2000) or haveshown increasesof giant assumptionthat, despitedilferetces in molphol- salamande$in streamsrunning throughrecently ogy and lile history,the two speciesrespond simi clearcuttimber stands (Muryhy et al. 19ltl, Murphy larly to changesin environmental pammeters. andHall 1981,Hawkins et al. l9U3).Other stud- Cope'sgiant salamanderwas not distinguished ieshave concludedthat girnt salamandersare most trom larval Pacific giant salamandersuntil its oftenfound in ornear streamssurrounded by older descriptionin 1970(Nussbaum l970). Cope's giant .alamander ohligate forest stands(Corn and Bu[y 1989) or in stands is an neonare.remaining in that haveold growth charecteristicssuch as large an aquaticlarval stagethroughout its life. Meta- conifers(Gomez andAnthony 1996).This knowf moryhosedindividuals are lbund rarely.whercas edgeof old growth associationis valuable.how neotony is only occasionallyexhibited in some cver, little old growth exists today in National populationsof the Pacific giant salamander.Thc Forests or on private timberlands.Because the diIficultl oi Ji.tinguishingbel$ecn neotcni(' current rangesof theseamphibians occur panly Cope's giant salamandersand sympatric larval on industrial titnberlandsit is also impofiant to Pacific giant salamandersin the tield is likely study habitat associationsand populationdistri- preventingcomparative tield studieson thesetwo bution oftheseanimals in fbreststhat rffely reach species.Morphological diff'erencesbetween the speciesare slight. making field identificationdif- llcult.lt hasheen us.umed that the turr speeies respondsirnilarly to changesin streamsubstrate (Wilkins Aulhor 10 !rhom correspondenceshould be addrcssed. and Peterson2000), but it has not been Curren!addrcss:School of Biological Sciences.\Vashing!on determinedhow Cope'sgiant salamander responds Sratc Univcrsill. Puilmar. WA 9916,1-.1236.E mail: to chrnge.in lbrestage and whether their response. steele@ mail.\\'su.cdu are similar to thoseof Pacific giant salamanders.

Northwest Science,Vol. 76, No. 4, 2002 31'1

(il00lb)_deNodhrcsSr'.ntili.A*ocilion A l.ighRreselrd This study, perfbrmed in areasof regenerat- commonly plantcdafter timberhan'est. Noble fir ing recondgrouth [ore.t'. intenJeJ li, e\rminc (Abies procer.t), western hemlock (Tsirga how the abundanceof Cope's giant salamander hetercphy-lLa). westem redcedar (Z/ruja p licatu), and sympatriclarval Pacitic giant salamandersare and red alder (A1,,rrisrrlrr.r) also contdbuteto the associatcdwith changesin forestage. This study o\ er\lor) al mosl.ite\. The underlt,r) I unrpri'es alsointended to examinestream habital associa huckleberriesl.Vaccittium spp.). devil's club tionsof cachspecies. (.Opk4tottu horridun), blackberries(Rlbns spp.), salal(Gouhheriu shallor). andwestern sword lem Methods ( PoI y.t t i ch um mtoi turn). The studytook placeon cor?oratetimberlands in We locatedull llr.l-order:.lrerm..u.inB mrl. southemSkami]uria County, . between of the study area,across the mnge of forest ages ,15'46'b 45o38'Nlatirude and l22'l.+' to l2 l'53'w available.Ages of sufounding timber standswere longitudetFigure I t.Annurl prccipit:rtion occur. calculatedfrom the time of replanting.Stands < mostly asruins fiom Octobcr throughMarch and 70 yr had been clearcutup to the streambanks rangesfrom 229 to 305 cm (Daly et al. 1994). and replantedwith Douglas-fir seedlings.S|ands Geology ofthe arcais mostly basaltand andesite > 70 yr were rare and likely regeneratednatu- flows with their associatedbreccias and tulTs rally atier one of the rcgional fires. While timber (Franklinand Dymess 1988).Elevations range hanestwas rot theprimary disturbance fi)rstreams from 2,+0to 800 m. Thc rcgion experiencednine in theseoldest stands, t\\"o streams were sampled localizedsland-replacing fires between1902 and to provide additional data fronr older agcd lbr- 1952(Felt l9?7).The areais managedprimarily eststhat areuncommon on industrialtimberlands. lbr the production of wood pulp and small sau- Streamswith continuouspennanent flow were logs with evenaged silvicultureand 50-70 yr locatedin the field to confirm their presenceand rotations.Dominint vegetationvaries with har- to determineif they mct the selectioncriteda for vest management,but Douglas-flr (P.r"r.,i.rtrrg4 siunpling.Streams selected for samplingmeasured neirr:lesil)is usually the dominantconifer as it is (2 m wide, had a rnarimum depthof (15 cm, and

A lN T

30 Km -

Figure 1. Locadon of strcainssampled in SkamaniaCount]. \'ashinglon.

348 Steele,Brodie. and MacCracken had an unembeddedsubstrate that was visually aticallyplacing a squareframed dip net in the estimatedto comprisemorc than halfcobble and plot. removing all cover items. raking the sub glarel.The.e criterir en.ured thrl appropriirte stratetbr approximately0.5 m in fiont of the dip streamhabitat fo[ giant salamanders(i.e., unsilted net,and repeating the processwith the intention rocky substrates)was sampledin strcamsof a that all salamanderswould either be caught by manageablesize while mininizing vadation of hand or swept into the dip net. Periodically dur- physicalstream characte.istics. Because of thc ing the sample.the large net spanningthe stream high gradientand smallsizc of theseheadwater was searchedfor salamanders.Because large larvae streams,sampling was precludedin slow-u'ater will leavea streamduring intensive sampling, a habitatssuch as pools. runs, or glides.All streams l-m wide plot on the streambank on eitherside meetingthese criteria in the study area were of the slream was also intensively searchedfor sampled.Twenty-nine streamsthat met the se- amphibiansthat had either Ieft the streamduring lectioncriteria were survcycdin 1998.ln 1999 samplingor were associatedwith streamedges. thcsc samestreams were resampledalong with This l-m wide tenestdal plot was subjectedto a an additional four streams.AII streiuls were within \) .lemJli(al :'eJr(hin u hi,.h rll corer itctn. u crc 29 km ol eachothcr. tumed over and the substratewas raked. Cover Three plots in each strean were sampledbe- itenrswere replaccdin all plots at &e end of the tweenJune and Augustduring 1998and 1999. search. Selectionof plots within a streambegan 10 m Becauselarlae are often difficult to identify beloll, thc immcdiate headwaters(i.e.. wherethe to speciesin the field, it was necassffy to pre- headwatersfirst fomed a recognizablechannel). serve! l capturedlllrvae in fbrmalin forlater iden- Plotswere 2 m long,as wide as the wcttcd widlh. tification in the laboratory.Using criteria estab and scparatedliom each other by at least l0 m. Iishedby Nussbaum( 1970,1976). preserved lawae All plots were locatedupstream from roads.We were identified as cither Cope's or Pacilic giant measuredthese stream and riparian habitatchar- salamander.The Pacific giant salamandcr usually rcteristicsat eachplot bcforesampling for sala has6 7 gill rakerson the first and secondgill arches mandersbegan: water temperature. stleam depth, whileCope's giant salamander has 4-5. Also, thc width,gradicnt. aspect, elevation, and percent cover Pacific giant salamanderusually has 5-6 rakers of treesand tall shrubs.A singlemeasurement of on the tilih and sixth gill arches*hile Cope's sh'eamdepth for eachplot was obtainedby aver- gianthas 3-,1 (Nussbaum 1976). Gill rakerswere a-singnine depth measurementsto the neargst countedtbr each specimento determinethe centineter: depth of the thalweg (deepestchan- species. nel of the strean) at the middle. upstrcam,and Salamanderabundance and habitat dataofeach do\\'nstrcamedges olthe plot. and depthsat mid strcamwere averagedftom the threeplots to give points between each thalweg measurementand an overall measurementof streamhabitat char- either bank. Strean width was averagedto the acteristicsand salamanderabundance fbr an in- nearest10 cm fron measurementsat the middle, dividual streamin eachyear. Data from eachyear upstream,and downstreamedges of the plot. uere unulyzetl.epuratel) u\ing regre\\ir\nlree Upstream gradient of thc streamwas measured analysiswith the computerprogram S Plus 2000 with a clinometer.Elevation and aspect were taken forWindows (S-Plus 1999).Regression trees are from topographicmaps. Percent canopy closure usedto uncoverstructure or patternsin datowhen u'asrneasured with a sphericaldensiometer at the eithera setor a singlepredictor variable is used niddle ofeach plot. The timber standssurround- to estimatea singleresponse variable (Clark and ing the streamswerc relatively homogenous, even- Pregibon1992) and are appropriate when classi- aged stands.Measurernents of habitat variables ticationofdata based on thresholdvalues is needed wereaveraged hom thethree plots to givean overall ratherthan a linearasscriation (Verbyla 19ti7). measurcmcntof the standand strcamchancter- Regressionffees are advantageousbecause data isticslbr individualstreams. may be assumedto bc non-norrrally distrib- Sampling for salanandersbegan at the upstre?un uted.both continuous and categorical data may portion of eachplot and moved downstreamto a be used.and data also do not nccd to bc lin- net placed acrossthe streamat the lowcr end of early related to predictor vadables.We per the plot. Salamanderswere collectedby system- formedregression tree analysis to examinethe

lnfluence of ForestAge on Giant Salamanders 349 mean number of salamanderscaught per stream in l6 (557o).Twelve streamscontained both spe- relative to fbrest age.Optimally sizedregression cies;the ratio of Cope'sto Pacificgimt salamanders treeswere selected based on the resultsofa cross- in thesestreams was I .0:1.2.In 1999,l05 larval validationprocess (Breiman er al. 1984)repeated Cope's and ll4 larval Pacitic giant salamanders 500times. The presence or absenceofeither species werecapturcd fiom the33 streamssampled. When in a stueamwas determinedfuom both years of presentjranges of densitiesfor Cope's and pa- sampling.Comparative, two{ailed Student'st{ests, cific giant salamanderswere 0.06-l .43/mr and or Welch's t-test in the caseof unequalvariance 0.06-2.5/m2.Of thesestreams sampled, Cope's betweengroups. were usedto testfbr differences giant salamanderswere detected in 19 (582a)and in habitatvadables between streams in which the Pacific giant salamande6in l6 (48ol.).Both spe- specieswas presentand streamsin which it was cies of giant salamanderswere detectedin l0 of not detected.The 57, significancelevel ofrhe p lhe sfeams; the latio ofCope's giant salamande$ values for these tests were adjusted using the to Pacific giant salamandersin thesesrreams was Bonterroni correctionmethod described by Rice 1.0:1.1. (r989). Densitiesbetween years were signiticantly correlatedfor both Cope's(r= 0.65,p < 0.01) Results andPacific giant salamanders(r= 0.4,1,p = 0.02). Regressiontrees basedon the capture data fbr In 1998a totalof l66larval Cope'sand 98 larval eitheryear(Figure 2) werenot suppoftedthrough Pacific giant salamanderswere captured from the cross-validationand are not presented.Of the 33 29 streamssampled. When present,the range of streamssampled over the 2-yr period, none of densitiesofCope's andPacific giant salamanders the measuredhabitat variableswas significantly were0.05-1.16/m2, and0.05 0.79lm2.Ofthe29 dill'erent between streamsin which either spe- streams sampled,Cope's giant salamanderswere cies waspresent and streamsin which they were rn 23 (79Ea)and Pacific giant salamanderswere not detected(Table 1).

.o a.) E ". 1998 1999 =.r 40 F 201 30 s lc 20 o 10 1'1 f n. - I ..1r_r ^ z-6 u.. F-..J--p 20 40 60 80 100 0 20 40 60 80 100

b) 9 rc 40 Fzo 30 i,t 20 o-' I5..' - tv . 5 '.-l '..1 . . zo20o. 9. i"-i -.r' - . 40 60 80 100 0 20 40 60 80 100 ForestAge (yr) ForestAge (yr)

Figure 2 Scatterplolsshowing changc in densityofPacific gianr salamanders(a.) and Cope'sgianr salamanders(b.) in 1998and 1999.Some daraare obscuredby overtappingpoinrs.

350 Steele,Brodie, and Maccracken TABLE l. Comparisonof mean(SE) measuredrariables werc seenin streamslocated in recentlyclearcut betweenstreams in which a species\ias detected forcsts (Figure 2). Elevateddensities of Pacific lvhich " and streaDrsn it was undelected. indi giant in catesthatwelch s I len of uncquallariancc\ was salamandersare ofien observed streams pcribnncd. runningthrough recently han'ested timber (Murphy ct al. 1981.Murphl, and Hall 1981.Hawkins et I)ctccted L.ndetected al. 1983)and are considered to reflectthe rcmoval riparian covcr!which tcmporarilyin- Cope'sgi.mt salanander of canopy 21 9 creasesaquatic production and produces an abun- Canopycoler (tl) 79.1(5.1) 85.1(.1.6) 0.13" danceof invertebrateprey. As in theseprevious (;radient(degreet 16.511.2) 17.3(2.2) 0.'71 studies,densities of Pacific giant salamandersin ,{!eragesidrh (cn) 82.1t(3.5) 75.0(,1.5) 0.21 1991|]are negatively corrclated with canopycovcr A\eragedepth (cm) 1.3(0..1) 3.9(0.5) 0.61 (r = 0.65.P < 0.001).Patterns ofdensity ofCope's Forestage (,vf) 29..1(:1.3) 13.7(10.2) 0.1'1 giant salamandersdiffered from thoseof Pacific \\'lterrenpenrure (Cll 9.,1(0.3) 9.E(l.l) 0.71' giant salamandersand were not correlatedwith (n) (32.,1) (59.l) Ele\arion 55:.2 504.0 0.,16 canopycover Becauseofthe high degreeof varia- Paciicgiant salamander tion in the numberofcapturcs betweenyears for Numberofstreams l8 l5 both species,it remainsunclear if densitiesof Canopycovef (C ) 76.1(6.9) rJ6.5c.6) 0.r9" Gradient(dcAlcs) l5.l I l.,l) llJ.5(1.5r 0.1:l Cope's giant salamanderrespond to changesin ,\,efage width (cm) 85.9 (,t.2) 7,1.5(3.3) 0.05 habitatpanmeters in the sameway that hasbeen ,{veragedeplh (cm) 1.6 (0.5i 3.7(0.2) 0.ll" documentedtbr Pacifiogiant salamanders by other Foresr.rge(tr) 10.6(5.3) -16.6(6.9) 0.5 authors.A concertedefTon by rcsearchersto bc- \\'alcr tcmpcraturc(C) 10.3rc.5) 8.5(0.1) 0.01" come familiar with dillerentiating Cope's and Elevation(m) 550.0(31.6) 5r5.5(.17.s) 0.67 Pacificgiant salamanderswill be necessaryto fuflher our understandingof the ecological dif ferencesbetween these species.

Discussion Acknowledgements The inability to cross validateany of the regres- This paperbenelited from commentsmade by Dr. sion treessuggests that either none of the habitat JosephBeatty and one anonymousreviewer Re variableswe measuredwas an effectivepredic- searchwas made possibleby the Washington tor of salamanderdensity or that the high levels Departmentof Fish andWildlife permit #98 173 of variancein thc data preventeda consistentre C andwas funded by LongviewFibre Company. sponsepattern fiom bcin-edctermined. However. Specimenswere depositedin the Collection of an examinationof the data showsthat high den- Vertebrates,Depafinent of Biology, University sitiesof Pacificgiant salamandersduring 1998 of Texasat Arlington.

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lnflucnccof ForestAge on GiantSalamanders 351 streamsofthc CascadeMountains. Oregon. Canadian Parker,M. S. 1991.Reiationships between cover availabilitr JoumaiofFisheries and Aquatic Sciences38:137 l'15. and lan:rl Pacific giani salanander density.Journal Murphy.M. L.. C. P Ha$kins,aDd N. H. Anderson.l9ltl. of Hcrpctology 25:355-357. EllecNof canopymodification andaccumulated sedi- Rice, $'. R. 1989.Analvzing |ablesof staiisrical tesis.Evolu ment on strcamconmunities. Transactions of thc don,13:223225. American FisheriesSocietv I 10i469'+78. S Plus.1999. S Plus2000 Professional Rclcasc 3 Useis Guide. Nussbaum.R. A. 1910.Dinn\odo t:try.r, n. sp.. from rhe Data Analysis ProducrsDi!ision, \4athSott. Sealtle. Pacific No(hwirs1. U.S.A. (Amphibia: Caudata: Washinglon. Amb)stomatidae).Clopeia 1970:506 51,1. Verbyla, D. L. 1987.Classification trees: a ne\, djscrirnina \ussbaun. R. A. 1916.Geographic variation and s)sten t- tion tool. CanadianJournal of Forest Rcscarch ics ofsalamandcrsoflhe genusDrcdr,?ra./rr Srauch 17:1150I152. (Anbystomatidae). Miscellaneous Publicadons of the Wilklns. R. A.. and N. P Peterson.2000. Faclorsrelated to Nluseumof Zoology. Uni! ersity of Michigan I .19:1 occurrcncc and abundancein headwarcr streaDrsdmining recond growth Douglas-fir forests in routhwestern \Vashington. Forcs! Ecologj- and Man.rgement139i79 91. Receivecl26 December2001 Acceptedfor publication I0 Jwre 2002

352 Steele,Brodie. and MacCracken