Arboreal arthropod community structure in an early successional c

Great Basin Naturalist 7-31-1988 Arboreal arthropod community structure in an early successional coniferous forest ecosystem in western Oregon T.. 1988 "Arboreal arthropod community st

Great Basin Naturalist

7-31-1988

Arboreal arthropod community structure in an early successional coniferous forest ecosystem in western Oregon

T D Showalter

Oregon State University, Corvallis

S G Stafford

Oregon State University, Corvallis

R L Slagle

Oregon State University, Corvallis

Follow this and additional works at: https://scholarsarchive.byu.edu/gbn

Recommended Citation

Showalter, T D.; Stafford, S G.; and Slagle, R L (1988) "Arboreal arthropod community structure in an early successional coniferous forest ecosystem in western Oregon," Great Basin Naturalist: Vol 48 : No 3 , Article 3

Available at: https://scholarsarchive.byu.edu/gbn/vol48/iss3/3

This Article is brought to you for free and open access by the Western North American Naturalist Publications at BYU ScholarsArchive It has been accepted for inclusion in Great Basin Naturalist by an authorized editor of BYU ScholarsArchive For more information, please contact scholarsarchive@byu.edu, ellen_amatangelo@byu.edu

IN AN EARLY SUCCESSIONAL CONIFEROUS FOREST ECOSYSTEM

T.D.Schowalter', S.G.Stafford^andR L Slagle^

Abstract.—Thisstudywasdesignedto characterize arborealarthropodcommunitystructure inanearly succes-sional coniferousecosystem.Wesampledsix-yeaT-oldsnowbrush(CeanothusvelutinusDougl.exHook) and Douglas-fir{Pseudotsugamenziesii (Mirb.)Franco)at theH.J. AndrewsExperimentalForest inwesternOregonduring1982.

Thearthropod faunawas dominatedintermsof densitiesbypsyllidsandaphidsonsnowbrushand byadelgidsand cecidomyiidsonDouglas-fir Significant associationsamongtaxa, e.g., positive correlationbetweenaphidsandants, indicated trophic interactions or similar responses to host conditions Significant seasonality was observed for individual taxaandfor thecommunity, reflecting the integration of individual life-history patterns Significant spatial pattern (patchiness) in the arthropod community may reflect the influence of faunas on individual plants within neighborhoodsand/or the influence of ant foraging patterns.

Patterns in terrestrial arthropod

commu-nity structure remain poorly understood,

largely because of their taxonomic

complex-ity. Most community-level studies have

re-duced this complexity to indices of diversity

orhave examined only subsets(guilds)ofthe

community(Price 1984) Unfortunately, such

restriction likelymaskspatterns thatcouldbe

usefulin identifyingcommunityresponses to

changes in environmental conditions (e.g.,

Lawton 1984, Thompson 1985) Changes in

community structure may promote or limit

pest population growth (Dixon 1985,

Scho-walter 1986, Strongetal. 1984, Tilman 1978)

and maycontroltemporalandspatialpatterns

in ecosystem nutrient cyclingandsuccession

(e.g., Mattson and Addy 1975, Schowalter

1985, Seastedt and Crossley 1984) At the

sametime, communitystructure reflects the

integration ofpopulation responses to

envi-ronmental conditions (Lawton 1983, 1984,

Schowalter 1985, Schowalter and Crossley

1987, Strongetal. 1984)

Our purpose in this study was todescribe

the pattern(s) of arboreal arthropod

commu-nitystructureinanearly successional

conifer-ousecosysteminwestern Oregon Wetested

thehypothesisthattheintegration of patterns

atthe species levelresults in distincttemporal

and spatial patterns, rather than

unintelligi-ble overlap, at thecommunitylevel (Lawton

1984, Thompson 1985) Multivariate

statisti-cal techniques were used toexamine the ef-fectof seasonality andspatialposition ofhost plants on arthropod community patterns as wellasonindividualarthropodtaxa

Materials and Methods

The study was conducted during 1982 on Watershed (WS) 6 at the H J. Andrews Ex-perimental Forest Long Term Ecological Re-search(LTER) Site inthewestern Cascades,

65kmeastofEugene, Oregon The Andrews

Forest is administeredjointly by the Pacific

Northwest Forest and Range Experiment

Station, theWillamette NationalForest, and OregonState University

Theclimate ofAndrews Forestismaritime with wet,relativelymild wintersanddry,cool

summers Meanannualtemperatureis8.5C,

and mean annual precipitation is 2,300mm,

with more than 75% falling as rain between October and March The Andrews Forest

is dominated by old-growth (>200-yr-old) Douglas-fir {Pseudotsuga menziesii [Mirb.] Franco), western hemlock {Tsuga hetero-phylla [Raf.] Sarg.), and western redcedar {Thujaplicata Donn)(Crierand Logan 1977)

WS 6isa south-facing, 13-hawatershedat 1,000-1,100 m elevation, with an average slope of35% The watershed wasclearcut in

1974, broadcast burned andplanted to

Dou-glas-fir at 3 X 3-m spacing in 1975 The

six-yr-old vegetation in 1982 was dominated by

'Department of Entomology Oregon State University, Corvallis, Oregon 97331.

Department ofForest Science, Oregon State University, Corvallis, Oregon 97331.

328 GreatBasinNaturalist Vol 48, No 3 evergreen snowbrush {Ceanothus velutinus

Dougl ex Hook) and Douglas-fir with a

canopyheightof1-2 m.

A belt transect 50 x 4 m was established

strategically across the middle ofthe

water-shed to represent vegetation diversity and

spatialheterogeneity Becauseother

commu-nity studies have indicated that the various

arthropod taxa are distributed largely

inde-pendently (Schowalter et al. 1981, Strong et

al. 1984),weconsidered oursamplingof a plot

designed to maximize intersection of habitat

patches to sufficiently represent the

arthro-pod community in this relatively simple

sys-tem This design maximized sampling

effi-ciencyandsafetyonthesteep, debris-strewn

slope Furthermore,unlike random sampling

across the watershed, this design permitted

evaluation of potentially important effects of

plant position on insectdemographics

(Scho-walter1986, Thompson1985, Tilman1978)

The 40 snowbrush and 20 Douglas-fir

within this transectwere mapped to explore

spatialpatternsand were sampledeighttimes

at3-4 weekintervals,between19May(Julian

1982 toaddress temporal patterns Sampling

consisted ofquickly enclosing a single,

ran-domlyselectedbranch,bearing2-5g drywt

foliage (or 1-3% of the foliage mass), from

each plant in a large plasticbag, clippingthe

sample, andsealing thebagforreturn tothe

laboratory Samples were chilledat5 Cuntil

processed This sampling procedure was

de-signed torepresent arthropod intensity (#/g

foliage)through timeonaspatiallydiscreteset

of host plants Chemical or otherchanges in

host (juality brought about by periodic

re-moval of small foliage samples (Schultz and

Baldwin 1982) were assumed tohave a

negli-gible effect on successive samples Sample

bias may exist due to selection of healthy,

foliage-bearing plant parts and to the

under-representation or absence of active species

thatleap, fly,ordrop when motionorcontact

in their vicinity occurred during sample

col-lection (Note: Care was taken to minimize

disturbanceduring sampling.)

Samples were sorted into foliage and

ar-thropod components. Foliage material was

driedat45 C toconstantweight Arthropods

weretabulatedbytaxon

Trendsinarthropodintensities(#/gfoliage)

and community were

tistically using the SAS statistical sofhvare package (SAS Institute, Inc 1982) The

square-root transformation was used to nor-malizethe intensitydata inthe analyses

De-greesoffreedom wereadjustedtoaccountfor autocorrelation arisingfromthesampling

pro-cedure (Milliken and Johnson 1984) in the analysisofvarianceforeachof18taxa Corre-lationanalysis, principalcomponentanalysis, clusteranalysis, stepwise discriminant analy-sis, and Spearmansrankcorrelation(Lawton

1984, Steel and Torrie 1960) were used to explore interactionsandtemporal andspatial patternsamongthe 18taxa

Results

Mean intensities of arthropods on WS 6 during 1982aresummarizedinTable1. Prin-cipalcomponentanalysisusingthecovariance matrixverifiedtheobvious importanceofthe sap-sucking Homoptera, especially woolly aphids (Adelgescooleyi[Gillette])andpsyllids {Arytaina rohusta Crawford, some

Craspedo-lepta sp.). Overall, these two principal com-ponentsexplained95%ofthetotalvariance Correlationanalysis revealedsignificant (P

< 05) interactions that we believe indicate trophic relationships or similar responses to host conditions As expected (Dixon 1985, Fritz 1983, Schowalter et al. 1981, Stronget

al. 1984), aphidsandantswerepositively cor-related (r = 0.31, df = 480, P < 0001), re-flecting ant {Camponotus modoc Wheeler)

tendingo{Aphisceanothi Clarkon snowbrush and Cinara pseudotaxifoliae Palmer on

Dou-glas-fir. Positive correlationbetweenpsyllids

andleaf-mininggelechiid larvae (r = 0.31, df

=480,P < 0001)suggestedsimilarresponses

to host conditions Surprisingly, significant negative correlations (P < 05) were found

onlybetween taxarestrictedinoccurrence to differenthosts

Statistically significant (P < 05) temporal trendswerefoundforaphids,psyllids, aleyro-dids,pollen-feedingthrips, defoliating

tortri-cidlarvae, gelechiidlarvae, andantson

snow-brush (ANOVA, F > 4; df - 7, 44; P < 01) (Fig 1) and for adelgids on Douglas-fir

Aphids, aleyrodids, thrips, and tortricid lar-vae were most abundant May-August.

Psyl-lids andgelechiid larvaewere most abundant September-November.Woolly aphidsshowed

Table 1. Mean (± SEM)arthropod intensities(number/kgfoliage)and percentof total arborealarthropodson six-yr-oldsnowbrush(Ceanothusvelutinus, N= 40)andDouglas-fir {Psetidotsuga menziesii, N = 20)onWS6at the

H.J.AndrewsExperimentalForest,Oregon, during1982.

330 Great

O

li.

>-(O

UJ

0.4

JULIAN DATE

314

Fig 1.Mean(± 1SEM)intensities ofarthropods showingsignificant (F<.05)temporaltrendsonyonng snowhrush {Ceanothusvelutinus)fromMay19 (Julian date 139) toNovember10 (Julian date 314) 1982.

Discussion Four species of Homoptera (one woolly

aphid, one aphid, and twopsyllids), all small

phloem-sucking insects, characterized the

arthropod community in this early

succes-sional ecosystem Other species occurred

showed some

evidence of interaction with the dominating Homoptera.

This arthropod community structure is functionally similar to the

aphid-dominat-ed community of an early successional

hardwood forest at Coweeta (Schowalter

and Crossley but distinct from the

"5

h-

0.4|-z

lij

0.04 r

JULIAN DATE Fig 2. Mean(± 1SEM)intensities ofwoolly aphids(Adelges cooleyi)onyoungDouglas-fir(Pseudotsugamenziesii) fromMay19Ouliandate 139) toNovember10Quliandate 314) 1982.

332 Great

defoliator-dominatedcommunities

character-izingmatureforests atbothsites (Schowalter

andCrossley 1987, Schowalter, unpubhshed

data) In particular, thefaunal association on

snowbrush, a symbiotic N-fixer, is

function-allyidenticaltothatontheecologically

equiv-alentblacklocust, Robinia pseudoacaciaL., a

symbiotic N-fixer at Coweetathat was

domi-natedby aphids.Aphis craccivora Koch, and

ants, Formica sp (Schowalter and Crossley

1987) Thus, although theseforest

communi-ties were taxonomically distinct, they were

functionally similar in the dominance of

phloem-sucking Homopteraat similar stages

of forest development These data support

the hypothesis that arthropod communities

are not randomly organized but rather

re-flect functional interactions (Lawton 1984,

Schowalter1986)

Thefaunal structureonDouglas-firalsowas

similartothe faunal structure on 20-year-old

Douglas-fir studied by Mispagel and Rose

(1978) Adelges cooleyi constituted a much

higher proportion ofarthropods on

Douglas-firinour study(96%vs.58%) Thismayreflect

a successional trend or may be due to our

inclusion of immatures Species richness on

Douglas-firwas much lowerin our study (11

vs. 75 taxa ofequivalentrank) as expected if

species richness increases with increasing

habitat complexity (Schowalter et al. 1986,

Strongetal 1984)

Temporal trends in community structure

observed in this study reflected the life

his-tory patterns ofthe constituent species For

example, the appearanceof adult psyllids on

nonhost Douglas-fir in August was the result

of dispersal ofwingedadults; subsequent

re-productionon snowbrush was evident in the

rapidincreaseinintensity(ofnymphs)during

ofthe communitysuggestsagreater

suitabil-ityofenvironmentalconditionsin springand

fall, relative tosummer.

Spatialheterogeneityonascaleofmetersin

arboreal arthropod community structure has

not been reported previously Our data are

consistentwiththe scaleofheterogeneity

re-portedforterrestrialplant (Pickettand White

1985), litter arthropod (Santos et al. 1978,

Seastedt and Crossley 1981), stream

arthro-pod (Reice 1985), and marine intertidal

com-munities (Sousa 1985) Such patch patterns

underlie the demography of outbreaks and

patterns ofherbivory (Schowalter 1985) but

would be masked by randomsampling

Ourdata suggestthat individualplants sup-portingdistinctarthropodcommunities early

inthe growingseason could haveconstituted centersforthedevelopmentof faunalpatches later inthegrowingseason Thepatchpattern

inarthropodcommunitystructurecouldhave

reflected the effect of environmental gradi-entsor of foraging patterns ofkeystonespecies such as ants, as suggested by our stepwise discriminant analysis Ants are attracted to particular plants by floral or extrafloral nec-taryproduction and by honeydew-producing Homoptera (Dixon 1985, Fritz 1983, Scho-walterandCrossley 1987,Tilman 1978) Ants patrolling these plants remove

nonmyrme-cophilous herbivores and predators, thereby

promoting homopteran-dominated

communi-ties. The spatial distribution ofant foraging couldproduceapatchpattern of homopteran-and nonhomopteran-dominated communities

(e.g.,Tilman 1978)

In conclusion, theresultsofthisstudy indi-cate that arthropod community structure in this early successional coniferous forest eco-system was dominated by Homoptera. This

dominance mayreflect the influence of plant architecture interactingwithantforaging pat-tern in young forests Spatial and temporal trends in these factors may contribute to patchiness in arthropod community struc-ture.Thesimilarityofcanopyarthropod com-munitystructurebetweenthiswestern conif-erous ecosystem and an eastern deciduous

ecosystem suggests thatarthropod

communi-tiesarenotorganizedrandomlybutrather are

based on functional interactions common to taxonomicallydistinctecosystems

Acknowledgments

We thank D R Miller and R J. Gagne (US DA Systematic Entomology Laboratory) foridentifying psyllidsand cecidomyiids, re-spectively, and P. Hanson, J. D Lattin, and

A Moldenke (Oregon State University) for identifying aphids, mirids, andchrysomelids, respectively We thank P A Morrow (Uni-versity ofMinnesota) and D A Perry

(Ore-gon State University) for critically reviewing the manuscript Thisresearchwassupported

by NSF Ecosystem Studies Grant

BSR-8306490 and by the Oregon Agricultural

Ex-perimentStation (PaperNo 8101)

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