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Home , Quercus garryana, Quercus macrocarpa, Symphoricarpos

The of the , Author(s): John F. Thilenius Source: Ecology, Vol. 49, No. 6 (Nov., 1968), pp. 1124-1133 Published by: Ecological Society of America Stable URL: http://www.jstor.org/stable/1934496 . Accessed: 28/08/2013 19:14

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This content downloaded from 128.193.8.24 on Wed, 28 Aug 2013 19:14:18 PM All use subject to JSTOR Terms and Conditions THE QUERCUS GARRYANA FORESTS OF THE WILLAMETTE VALLEY, OREGON

JOIN F. TIILENIUS' Departmienitof Botany and Pathology, Oregon State University,Corvallis, Oregon (Accepted for publication May 20, 1968)

Abstract. Quiercus garryana forests,prominent at low elevations throughoutthe Willamette Valley, Oregon, have developed from subsequent to settlement of the valley in the mid-nineteenthcentury. Interruptionof the ground fires that were common in the pre- settlement environment probably caused the change. The understory of the oak is dominated by , and well-defined strata are present. Four plant communities occur: (1) Quercus garryana/Corylus cornuta var. californica/Polystichummunitum (most mesic) (2) Quercus garryana/Prunus avium/ albus; (3) Quercus garryana/Arne- lantchieralnifolia/; and (4) Quercus garryana/Rhus diversiloba (most xeric). All are in seral condition because of their relatively recent development and because they have been disturbed throughouttheir existence by man's activities. The soils supporting the oak forest are generally deep and well drained and have developed profiles with illuvial horizons and acidic reaction. They are derived from sedimentaryand basic igneous rocks and old valley-fillingalluvium. Seven established soil series are present: Steiwer, Carlton, Peavine, Nekia, Dixonville, Olympic, and Amity. The Steiwer series and its catenary associate, Carlton, are the most common soils.

INTRODUCTION 00 0 0 0 0 s (N (N (N Forests dominatedby Quercus garryana2are a characteristicvegetation at low elevationsthrough- Vauncouver~ out northwesternOregon. Althoughthe range of 490 Island Canada - the extendsfrom southern Vancouver Is- - -- U.S.A. land, ,to the coastal mountains south of San Francisco, (Fig. 1), it attainsits best developmentas a dominanttree on 470 the cross-valleyranges and borderingfoothills of the central W'illametteValley. In this region it formsalmost pure, closed-canopystands, occurs 450 intermixedwith conifersor otherbroadleaf , Oregon and grows as isolatedtrees in pastures,farmlands, and grassy foothillbalds. This study describes the floristiccomposition, stand structure,physical 430 environment,and successional status of plant communitieswhere Quercus garryana is the major componentof the overstory. 410 a

STUDY AREA

Geographyand physiography 390 The Willamette Valley is located in western Oregon about 65 km inland from the Pacific San Francisco Ocean. It extendssouthward from the Columbia 370 River approximately210 km and is bounded by o a a the Oregon Coast Range on the west and the o0 0 a (N (N (CN (N Cascade Mountainson the east. The widthvaries ( 1 Present address: Rocky Mountain Forest and Range FIG. 1. Range of Quercus garryana. Study area indi- Experiment Station, Forest Service, U. S. Department of cated by crosshatching. Agriculture, Headquarters, Fort Collins, Colorado, and stationed at Rapid City. South Dakota. from40 to 65 km. Average elevationof the val- 2 Where possible, scientificnomenclature follows Hitch- flooris 90 m. The northward- cock et al. (1955-60). Otherwise, Peck (1961) has been ley approximately used, except for Gramineae, where the authorityis Hitch- flowingWillamette River with its many tribu- cock (1950). taries is the major drainage system.

This content downloaded from 128.193.8.24 on Wed, 28 Aug 2013 19:14:18 PM All use subject to JSTOR Terms and Conditions Autumn1968 QUERCUS GARRYANA FORESTS IN OREGON 1125 The valley is a structuraldepression with hills ture of the countryand statedlie was told by the of moderaterelief separatingwide alluvial flats. Indians burningwas for ". . . urging the It is dividedeast and west by a low range of hills to frequentcertain parts, to feed,which they [In- (Salem-ElolaHills) abouthalfway down its length. dians] leave unburned,and of course they [deer] South of these hills it is relativelybroad to the are easily killed," and ". . . that they [Indians] vicinityof the city of Eugene, Oregon. Isolated might better find wild honey and grasshoppers, basaltic buttesare a prominentphysiographic fea- whichboth serve as articlesof winterfood." ture in the southernvalley. In the reportof the \VilkesEIxpedition of 1838- 42 (Wilkes 1845), rollinguplands in the vicinity Geology of Tualatin,Oregon, were describedas ". . . desti- The geology of the WillametteValley is com- tuteof trees,except scattered oak; theselook more plex. Both sedimentaryand volcanic geologic like orchardsof fruittrees, planted by the hand materialsare presentand oftenintermixed. Oua- of man, than groves of natural growth." The ternarygravels, sands, and silts cover most of the minoreffect of fireon matureoak treeswas noted lower portions of the valley. To the west the in the report: "The countryhad been overrunby foothillsof the Oregon Coast Range consist of fire,which had destroyedall the vegetationex- sandstonesand shales of Eioceneand Miocene age. cept the oak trees, which appeared to be unill- The Cascade Mountainfoothills along the eastern jured." Fires set by Indians were describeda-is side of the valley are predominantlyColumbia the causal agent in keeping down the under- River basalts. The valley itselfwas never gla- growthbeneath the , and the commentmade, ciated,but has been inundatedseveral times during since the white have had possession of the interglacialperiods by meltwaterfloods from the countrythe undergrowthis comingrapidly up in Columbia River. The last of these,the Missoula places." This was in 1840. flood,is reportedto have covered the valley to a By 1852 ". . . the hills and had com- depth of over 120 mi above sea level (Baldwin mencedto grow up with a young growthof firs 1959). [Pseudotsuga] and oaks, because the C(alapooiais Climate [local Indian tribe] were no longerthere to burn offthe face of the country"(Clarke 1927). Much In Thornthwaite's(1931) climaticscheme, the of the land once "oak " was covered by a WillametteValley region is classed as a humid, heavy growthof "oakgrubs" and young trees of microthermalclimate with a deficiencyof summer otherspecies in the late 1870's (Nash 1882). precipitation. Average yearly precipitation is Large numbersof immigrantswere startingto about 1,220 mm,occurring mostly as rain between move into the WillametteValley by 1845. Be- the monthsof Novemberand May. Snow is not cause of the abundanceof nativegrasses, livestock uncommonduring the winter,but rarelyremains raisingbecame one of the major occupationsof the on the ground for long periods. Very littlepre- settlers. Wheat farmingreplaced livestockpro- cipitation occurs during the summer months. ductionas the major land use duringthe 1870's, Temperatureextremes are rare as high summer and lands coveredwith dense standsof "oakgrubs" temperaturesare moderatedby an afternoonocean were cleared for planting. By the mid-1880's breeze thatoccurs almostdaily. Wintertempera- wheat productiondeclined because of high crop tures are moderatedby warm-moistsouthwesterly losses from disease and competitionfrom other oceanic winds. Mean wintertemperature is about areas, and manyabandoned fields reverted to oak 5?C; springtemperatures average 10?C; summer scrub. temperatures,21'C; and fall temperatures,120C. These reportsof the vegetationof the Willa- metteValley indicate that coniferousspecies did HISTORICAL ASPECTS not dominatethe vegetationat low elevationsin The firstdetailed account of the vegetationof the valley itself,although Pseudotsuiga menliesii the WillametteValley was given by David Doug- was presenteven in the . las (1914). In 1826 he describedthe northwest- ern portionof the valley as, "Countryundulating, METHODS soil rich,light with beautiful solitary oak and pine Investigationswere confinedto closed-canopy [Pseudotsuga menziesifi]interspersed through it." stands 4 ha or more in area where Quercus gar- Furthersouth, he describedthe appearanceof the ryana was the major componentof the overstory. vegetation as ". . . oaks more abundant and pines Basal area, frequency,and densityof overstory [Pseudotsuga] scarcer and more diminutivein trees were determinedon twenty0.004-ha circu- growth." lar plots spaced at 9-m intervalsin four rows Douglas also emphasized the burned-overna- parallel to the slope contour. Density was re-

This content downloaded from 128.193.8.24 on Wed, 28 Aug 2013 19:14:18 PM All use subject to JSTOR Terms and Conditions 1126 JOHN F. THILENIUS Ecology, Vol. 49, No. 6 corded in fourclasses: saplings (< 10 cm dbh); fornica/Polystichummunuitum community is found poles ( 11-40 cm dbh) ; mature(41-100 cm dbh); on moderateto steep,sheltered slopes. More ex- and relict(> 100 cm dbh). The maximumheight posed slopes and ridgesare occupiedby the Quer- of trees on each plot was measuredwith anl opti- cus garryana/Amelanchier alnifolia/Symphoricar- cal rangefinder. Age-diameter relationshipsof pos albus community. The Quercus garryana/ Quercus garryanawere obtained fromincrement Prunus avium/Symphoricarposalbus community cores and ringcounts of cut stumps. is found on both level and sloping sites on a Frequency and percentagecrown coverage of variety of aspects. The most exposed s-tes in and herbaceous species were recorded on the oak forestare occupied by the Quercus gar- sixty 0.2-M2 quadrats spaced at 3-m intervalsin ryana/Rhus diversiloba communitywhich does four rows coincidentwith the rows of 0.004-ha not have a well-developedtall shrub stratum. plots. Very low crown coverage was recorded Only the genericnames will be used hereafter. as trace and arbitrarilyassigned a value of 0.5% for calculationpurposes. Above trace, the inter- stratum vals were 1%7 and 5 %. Coverage greater than At present Quercus garryana is dominantin 5%o was estimatedto the nearest 10%o. Density the tree stratumof all communities(Table 1). of shrub and herbaceous species was not deter- Two growth forms of Quercus garryana occur. mined because of the high numberspresent and The majorityof the trees have developed under the frequentimpossibility of distinguishingan in- forestconditions. These "forest-form"trees are dividual plant. relativelytall, seldomexceed 60 cm dbh,and have Physical site attributes(elevation, position on ascending branches clustered near the crown. slope, slope angle, slope orientation) were re- Their crowns forma closed canopy. Mean den- corded,and a completesoil descriptionwas made sity of forest-formQuercus garryana is 1,054 for each macroplot (U. S. Soil Survey Staff trees/ha. The average age of matureforest-form 1951). treesis 90 years witha range of 47-135 years. The phytosociologicalimportance of each spe- Scattered throughthe forestare a few large cies in the tree stratumwas determinedby sum- relictQuercus garryanaapparently developed un- ming its percentagebasal area, percentagetotal der nonforestedconditions. These "savanna- density,and percentagefrequency. In the sub- form"trees generallyexceed 1 m dbh and their ordinatestrata (tall shrub,low shrub,herbaceous) boles are short in relationto the total heightof percentagecrown coverage and percentagefre- the tree. They have massivebranches and spread- quency were added to determinespecies impor- ing crowns and are usually spaced so the crowns tance. Species were arranged by strata in de- do not touch. There is an average of 17 savanna- scendingorder of importancein each macroplot, form Quercus garryana per hectare. Annual and the macroplot data serially tabulated in a growthrings froma small sample of freshlycut releve. Physical site attributes,soil features,and trees indicateda mean age of 283 years, with a disturbancefactors were also listed on the releve range of 257-308 years, for trees 76-94 cm dbh. for each macroplot. The releve was rearranged Fowells (1965) indicatesQuercus garryanamay according to similaritiesin species composition, live over 500 years and reaches90 cm dbh at 250 attributes. importanceranks, and environmental years. The groupings formed are the basis for the There are some distinctdifferences in the phy- plant communitiesdesignated. The term "plant tosociologicalattributes of Quercus garryana be- communities"is used to indicatea geographically tween the four communities. Large forest-form repeated assemblage of of relativelyuni- trees-a tree witha tall,generally undivided trunk form species compositionand structuralcharac- and small, ascendingbranches-are most numer- teristics. The dominantspecies in the tree and ous and tallestand the basal area of Quercus gar- shrub strata are used to designatethe communi- ryana is greatest in the Quercus/Corylus/Poly- that most ties. It should be emphasized species stichum community. Basal area and maximum are not confinedto any one plant community. heightof Quercus garryanadecrease in the Quer- There are changes,however, in species dominance, cus/Prunus/Symphoricarposand Quercus/Ame- distribution,vigor, and growthform between com- lanchier/Symphoricarposcommunities and are munitiesthat gives each a recognizablephysiog- least in the Quercus/Rhuscommunity. Savanna- nomy. formQuercus garryana,are least numerousin the VEGETATION Quercus/Rhus community,averaging only three Four plantcommunities have been distinguished. per hectare, but sapling and pole-size Quercus The Quercus garryana/Coryluscornuta var. cali- garryanaare morenumerous and densityof Quer-

This content downloaded from 128.193.8.24 on Wed, 28 Aug 2013 19:14:18 PM All use subject to JSTOR Terms and Conditions Autumn1968 QUERCUS GARRYANA FORESTS IN OREGON 1127

TABLE 1. Phytosociological attributes of major species in the tree stratum

Average denstity/ha

Con- Average Average Saplings Poles Mature Relict Maximum Plant community stancy frequency basal area (< 10cm (1140cm (41-100cm (>100cm height and species (%) (%) (m2/ha) dbh) dbh) dbh) dbh) (m) Quercus/Corylus/ Polystichum Quercusgarryana 100 92 75.6 200 675 156 10 25 Acer macrophyllum 79 24 2.0 126 13 1 1 21 Pseudotsugamenziesii 63 17 1.6 96 10 1 1 30 Rhamnuspurshiana 84 23 0.2 77 1 9 Prunus avium 16 15 0.2 111 1 11

Quercus/Prunus/ Symphoricarpos Quercusgarryana 100 96 66.3 166 613 92 15 22 Prunus avium 100 77 10.4 3912 74 3 12 Pseudotsugamenziesii 100 20 1.7 52 22 3 19 Acer macrophyllum 60 26 1.4 133 20 3 12 Rhamnuspurshiana 60 7 <0.1 25 4 Cornusnuttallii 40 3 <0.1 10 9 Quercus/Amelanchier/ Symphoricarpos Quercusgarryana 100 94 48.5 232 603 96 3 22 Prunus avium 77 9 <0.1 30 1 10 Pseudotsugamenziesii 54 3 <0.1 15 1 23 Acer macrophyllum 46 2 <0.1 7 1 15 Rhamnuspurshiana 46 7 0.2 104 9 Quercus/Rhus Quercusgarryana 100 97 41.3 580 783 55 3 18 Arbutusmenziesii 30 15 1.3 5 17 3 18 Pseudolsugamenziesii 50 19 0.2 59 5 15 Acer macrophyllum 50 6 <0.1 15 14 Rhamnuspurshiana 50 1 <0.1 7 4 cus garryanais greatestin this community(Table mainlyas a tall shrub,but treesequal in heightto 1). the dominantQuercus garryanaare present. An There are 15 otherspecies in the tree stratum, incrementcore from a 40-cm dbh tree had 70 but only seven are overstorytrees. The most im- rings and larger trees occur. Prunus avium portantare Acer macrophyllumand Pseudotsuga grows well under the Quercus garryana canopy mnenziesii.Both are most numerousin the Quer- and producesan abundanceof . cus/Corylus/Polystichumand Q uercus/Prunus/ Othertrees that may enterthe overstorycanopy Symphoricarposcommunities (Table 1). Acer are Arbutus menziesii,Pinus ponderosa, Libo- mnacrophyllumis most common on concave micro- cedrus decurrens,and Abies grandis. Arbutus reliefand along the edges, or near the heads of menziesiiis more commonnear the southernend watercourses. Pseudotsuga menziesii grows on of the WillametteValley where it is codominant convex slopes and ridges as well as along water- withQuercus garryanain some stands. Scattered courses. Large, usuallysolitary trees occasionally treesare foundthroughout the oak forests,but the are presentin the oak forest. These exceed 1 m species is most abundanton sites occupiedby the dbh and 30 m in heightand have branchesthe Quercus/Rhuscommunity. Pinus ponderosaand full lengthof theirtrunks. They appear to have Libocedrus decurrensboth occurred in a single developed under nonforestconditions and are stand located in the Cascade Mountain foothills probably contemporariesof the savanna-form in the southeasternpart of the WillametteValley. Quercus garryana. Abies grandisis foundonly in the Quercus/Cory- The third species to enter the overstorywith lus/Polystichumcommunity and is rare even Qu ercusgarryana is Prunus avium. It was intro- there. duced into the Willamette Valley to provide Subordinatetrees are Rhamnuspurshiana, Cor- disease-resistantrootstock for commercialcherry nus nuttallii,,Pyrus fusca,Pyrus orchards(Horticulture Department, Oregon State malus,Pyrus communes,Acer glabrum,Acer circi- University,personal communication)and has be- natum,and Prunus virginiana.Of these,Rhamnus come establishedin theoak forests. It now occurs purshianais the mostcommon. It occursas a sub-

This content downloaded from 128.193.8.24 on Wed, 28 Aug 2013 19:14:18 PM All use subject to JSTOR Terms and Conditions 1128 JOHN F. THILENIUS Ecology, Vol. 49, No. 6 ordinate tree in all communities,but is most Tall shrubstratutin numerousin the Q'uercus/Amelanchier/Symphori- The understoryof the oak foresthas verywell- carpos and Quercus/Corylus/Polystichurncom- developed shrub strata which give the communi- munities(Table 1). Cornus nuttalliiis less abun- ties their recognizableappearance. However, of dant than Rhamnnuspurshiana and does not occur in the Quercus/Rhuscommunity. Fraxinus lati- the 12 tall shrub species recorded,only threeare folia is most common on poorly drained sites. physiognomic dominants. The indigenousPyrus fusca and the introduced The clustered,arching stems of Corylts cornutda Pyrus malusand Pyrus communesare minortrees. var. californicamay grow 6 m or more high and Acer glabrum,Acer circinatum,and Prunus vir- on some sites form an almost closed secondary giniana each occurredonly in a single stand and canopy. More often,the species occurs as well- are very rare. distributed,individual plants. Average coverage

TABLE 2. Mean cover (%) and frequency (%) of major species in the shrub and herb strata according to plant community

Quercus/ Quercus/ Quercus/ Corylus/ Prunus/ A melanchier/ Quercus/ Polystichum Symhoricarpos Symphoricarpos Rhus

Cover Frequency Cover Frequency Cover Frequency Cover Frequency Species (%) (%) (%) (%) (/) (%) (O) (%)

Tall shrubstratum Coryluscornuta var. californica...... 20 29 11 17 2 3 X Prunusaviuma ...... 4 8 55 63 3 4 1 1 Amelanchieralnifolia ...... 3 8 9 18 23 41 1 6 Osmaroniacerasiformis ...... 3 5 3 7 1 3 X Holodiscusdiscolor ...... 6 11 1 1 X Low shrubstratum Polystichummunitum ...... 34 61 13 29 4 9 -1 2 Symphoricarposalbus ...... 25 60 23 54 46 75 2 8 Rhus diversiloba...... 23 64 15 29 32 76 40 76 Rubusursinus ...... 13 47 11 37 10 22 2 11 Rosa eglanteriaa...... 2 10 1 3 2 7 5 17 Rosa gymnocarpa...... 1 6 1 5 2 10 x Rosa nutkana . .x 2 9 2 13 X Pteridiumaquilinum var. lanuginosum...... 2. 5 X 1 3 X Rubus parviflorus...... 4 10 Dryopterisarguta ...... 2 4 Herb stratum Forbs Ligusticumnapiifolium ...... 2 12 1 2 1 10 X Tellima grandiflora...... 1 12 1 2 1 10 X Galiumspp ...... 1 24 1 17 2 36 1 22 Osmorhizachilensis ...... 1 4 1 4 2 11 1 15 Satejuradouglasii ...... 1 3 1 3 1 3 1 9 Vicia americana X X 1 5 1 11 Hypericumperforatum ...... 1 2 1 3 1 4 1 11 Torilisarvensise ...... 1 6 1 5 2 13 2 37 Circaeapacifica ...... 1 9 X 1 5 Grrasses Holcuslanatusa ...... 2 4 x 1 5 2 22 Bromuslaevipes ...... 1 5 1 10 1 6 1 9 Elymusglaucus ...... 1 2 1 3 1 4 1 16 Poa pratenisa.x XX 1 1 5 33 Agrostisspp ...... 1 2 X 1 2 2 33 Festuca rubra.X 1 3 1 2 2 9 Dactylisglomerata .X X X 3 11 Cynosurusechinatus.. 1 11 Danthoniacalifornica. 1 9 Festucacalifornica 1 2 Tree seedlings Quercusgarryata ...... 1 4 1 4 3 13 6 46 Acer macrophyllum...... 3 6 4 9 2 4 1 5 Pseudotsugamenziesii ...... 2 5 X X X Rhamnuspurshiana ...... 2 5 1 1 1 2 X

aIntroducedspecies. bX=less than1% meancover and frequency.

This content downloaded from 128.193.8.24 on Wed, 28 Aug 2013 19:14:18 PM All use subject to JSTOR Terms and Conditions Autumn 1968 QUERCUS GARRYANA FORESTS IN OREGON 1129 and frequencyare greatestin the Q uercus/Cory- Symphoricarposalbus dominatesthe low shrub luslPolystichumcommunity and decrease in the stratumin the Quercus/Prunus/Symnphoricarpos Q tuercufs/Prunus/Symphoricarposand Q uercus/ and Quercus/Amelanchier/Symphoricarpos comi- A melanchier/Symwphoricarposcommunities. The munitiesand is abundantin the Q'uercus/Corylus/ species is rare in the Q uercus/Rhuscommunity Polystichumcommunity (Table 2). It is sparsely (Table 2). distributedin the Quercus/Rhuscommunity. Oil A melanchieralnifolia is the second species to some sites in the Quercus/Amelanchier/Synpho- becomea physiognomicdominant in the tall shrub ricarpos communityit is particularlyabundant stratum. Its densityis oftengreat enoughto inm- and formsa dense,waist-high layer. pede movement,and it normallyforms a definite The ubiquityof Rhus diversiloba in the low layer beneath the overstorycanopy. Individual shrub stratumof all communitiesis evidentfrom plants 15 cm dbh and over 9 m tall occur. Table 2. In the oak forestit grows as a liana The high densityof Prutnttsavtium in the tall and as a ground cover of single-stemmedplants shrub stratumof the Querctis/Prunus/Symnphori-1.5-2 il tall. A maximumcoverage of 80%o with carpos communitygives it a characteristictwo- 100%,frequency was recorded. The groundcover layered appearance when seen fromthe outside. plants and the lianas are connectedby a dense, Prunus avium has the highest mean coverage shallowroot system,and it is difficultto delimitan and frequencyof all species in the tall shrubstra- individualplant. Rhus diversilobagrows beyond tum (Table 2), and even if it does not becomean the forestedge into adjoiningopenings and forms overstorytree in the future,it should remainan arborescentshrubs 3-4 nmtall. The liana formis importanttall shrub. veryevident in the Querctus/Corylius/Polystichliiin Osmaroniacerasiform.nis and Holodiscus discolor communitywhere lianas with basal stems 15 cm are the only other commontall shrubs. Osuta- or more in diameterare common. ronia cerasiformisis presentin all communities, The genera Rubus and Rosa are well repre- but is never abundant. Holodiscus. discolor oc- sented in the low shrub stratum. There are five casionallyforms small, dense thicketsin the Q0ier- species of each genera present. Ritbus ursinusis cus/Corylus/Polystichumncommunity. It was not commonthroughout the oak forests. Rubus par- present in the stands of the Qiuercus/Pritnits/viflorus is confinedto the Q uercuts/Corylits/Poly- Symnphoricarpos.community examined, but did stichumcommunity and may dominate the low occur in the othertwo communities. shrub stratum on some sites. The introduced Other tall shrubs presentas minor species in species Rifbuslaciniatus and Ritbitsprocerus are all fourcommunities are Crataegus douglasii and less commonmembers of the low shrub stratum. Crataegus oxyacantha. The latter is a garden Rutibusleucodermnis is rarely encountered. The escape. Philadelphus le-zwisiiand Ceanothizsyc- most abundantrose is the introducedRosa eqlaii- lutinus var. iaevigatus are rare membersof the teria. Althoughit grows in all communities,it Qut ercus/Coryl us/Polystich? u1irt community. Phy- is most abundant in the Quiercuis/Rhuiscommu- socarpus capitatitswas representedby one large nitywhere the spreading,heavily armed stems of individual shrub in one stand in the Qiwercts/ individual plants may cover an area 3-4 m ill Prunus/Symnphoricarposcommunity. Viitbitrnm diameter. Native roses are Rosa nutkana,Rosa ellipticumwas similarlyrepresented in one stand gymnocarpa,Rosa pisocarpa,and Rosa durandii. of the Q uercuts/Corvlus/PoiAstichUi?n community. The firsttwo species are rathercommon, but the last two are rare. Louz',shrutb stratumo Other rare membersof the low shrub stratum The low shrub stratumis comp)osedof 1.5 spe- are Berberis aquifolirnt,Ribes sangufineuwi,Spi- cies of woody perennialsand six species of ferns, raea bethlifoliavar. Iucida, Cvtisufsscopariumn, and but only three species are physiognomicdomi- Hedera helix. nants. Several fernsbesides Polystichiunniutiniturin are The woody fern Polystichum unintun is the present in the low shrub stratum. Dryopteris dominantspecies in the low shrub stratumon arguta is a good indicatorfor the Quercus/Corv- manysites. Althoughits average coveragein the lhs/Polystichumcommunity. Pteridium aqu ili- Quercus/Corylus/Polystichunmcommunity is 34%0, num var. lanuginosumgrows in all communities, coverage on the best sites is greater than 80%o but is slightlymore abundant in the Quercus/ and the frondsexceed 1 m in height. In the other Corylus/Polystichumcommunity. Less common communities,coverage, frequency,and height of ferns are Athyriumfilix-femina and Cystopteris Polystichummunitumn decline until in the Quer- fragilis. cus/Rhus communityit grows only as a sporadi- Tree seedlingshave been tabulatedin the low cally distributed,depauperate plant. shrub stratum. Seedlings of Quercus yarryaia

This content downloaded from 128.193.8.24 on Wed, 28 Aug 2013 19:14:18 PM All use subject to JSTOR Terms and Conditions 1130 JOHN F. THILENIUS Ecology,Vol. 49,No. 6 are definitelymore abundant in the Quercus/Rhus crease in importance,and the herb stratumis best community,as are sapling and pole-size trees developedin the Quercus/Rhuscommunity. Ex- (Table 1). Acer m-lacrophyllumseedlings are cept forFestuca californica,the grasses and forbs mostabundant in the Quercus/Prunus/Symnphori-confined to this communityare also common in carpos and Quercus/Corylus/Polystichumcom- adjacent grasslands and hill pastures. A ctaea munitiesand least abundantin the Quercus/Rhus arguta is found only in the Quercus/Corylus/ community.Pseudotsutga mnenziesii and Rhamnus Polystichumcommunity. The most commonin- pirshiana have their greatest coverage and fre- digenous herbs are Galium spp. (G. boreale, G. quencyin the Quercus/Corylus/Polystichurncom- triflorium)and Osmorhigachilensis. munity. Seedlings of the other species are spo- radicallydistributed or rare. PHYSICAL ENVIRONMENT The most common epiphyte is Polypodium The oak foreststend to occur on north-and vulgare var. occidental. It is ubiquitousin the east-facingslopes (Table 3). This is especially oak forest. Phoradendronvillosum occurs mainly true for the Quercus/Corylus/Polystichurnand in the southernWillamette Valley and is missing Quercus/Amelanchier/Symphoricarpos. communi- or very rare in the north. Common epiphytic ties. On the otherhand, the Quercus/Rhuscom- cryptogamsare Camptotheciumpinnatifidium and munitytends to occur on south and west aspects. Orthotrichiumspeciosumn. The firstis especially The small sample of the Quercus/Prunus/Symn- abundantand formsthick mats on the trunksof phoricarposcommunity makes it difficultto draw Quercus garryanaand Acer macrophyllumt. conclusions. Extremelysteep slopes are rare in the border- Herb stratum ing foothillsand cross-valleyranges of the Willa- The herb stratumis relativelyrich in species. metteValley. This is reflectedin the gradientsof One hundred thirty-eightspecies of grasses, the slopes on which the oak forestgrows, the sedges, rushes,and forbswere identified. Table majorityof which have a gradient of less than 2 lists species with a mean frequencyof 5 % or 30%. Only the Quercus/Corylus/Polystichum more in at least one communityand species con- communityhas a tendencyto occur on steeper finedto a singlecommunity. Several of the more slopes. Oak forests are most common on the importantspecies are introduced. upper (includingridgetops) and middlethirds of Althoughmost species are presentthroughout the slope. the oak forest,there is a general increase in the There are no greatelevational differences in the frequencyand coverage as the shrub strata de- oak forest,and most of the stands occur between

TABLE 3. Slope aspect, gradient, and position and elevation of stands in the four plant communities-expressed as percentage of number of stands

Querculs/ Quercus/ Quercus/ Corylus/ Prunus/ Amelanchier/ Quercus/ ARl Environmentalattribute Polystichum Symphoricarpos Symphoricarpos Rhus communities

Slope aspect North. . 47 20 54 10 33 East . 37 40 38 10 32 South...... 5 50 13 West...... 11 40 8 30 22 Slope gradient(%) --10...... 21 40 46 40 34 11-20 ...... 21 20 31 40 28 21-20 ...... 21 40 8 15 + 30 ...... 37 15 20 23 Slope po36t45n Top third...... 32 60 46 50 40 Middle third...... 47 20 38 50 45 Lower third...... 21 20 16 15

Elevation (i) >120 ...... 21 60 46 30 34 -180 ...... 53 20 46 40 45 -240 ...... 21 20 8 30 19 <240 ...... 5 2

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TABLE 4. Percentage of stands on each soil series according to plant communities

Quercus/ Quercus/ Quercus/ Corylusl Prunus/ Amelanchier/ Quercus/ All Soil series Polystichum Symphoricarpos Symphoricarpos Rhus communities

Sedimentarysoils Steiwer...... 53 80 37 30 46 Carlton...... 11 20 23 13 Peavine ...... 5 8 40 13

Basic igneous soils Nekia ...... 16 8 9 Dixonville...... 5 8 20 9 Olympia...... 5 8 4 Alluvial soil Amity...... 5 8 10 6

120 and 240 m. The lower elevationmay be an Weatheredbasalt fragmentsare oftendistributed artificiallimit caused by clearingfor agriculture. throughoutthe solum. At the upper elevationthe oak forestsmay grade Soil series derived from basic igneous rocks into coniferousforest dominated by Pseudotsuga are Nekia, Dixonville,and Olympic. The Nekia menziesii. series is a red soil typicalof the rollinghills and buttesof the centralWillamette Valley. Its cate- ASSOCIATED SOILS nary associate, the Dixonville series, is most Except for the alluvial soils of the floorof the common in the southern part of the Willa- WillametteValley, soils are developedfrom par- mette Valley on the foothillsof the Coast and ent materialsresidual to the underlyinggeological Cascade Ranges. The Olympic series is found formations. These formationsconsist of two forthe mostpart at higherelevations in the Coast major types of materials: sedimentaryrocks and and Cascade Ranges and on the basalt buttesthat basic igneous rocks (mainly basalts). rise fromthe valley floor. Sedimentaryrocks are usually found at lower The soils of the valley floor are derived from elevationsthan basic igneous rocks and are prin- alluvial deposits. Soils fromalluvium are poorly cipallyhorizontally bedded sandstonesand shales. drained and have mottled,compact, clayey sub- The derivedsoils are deep and have profileswith- surfacehorizons and grey brown hues (Munsell out eluvialhorizons (A2), but withwell-developed 2.5Y). The Amityseries, which is derivedfrom illuvial horizons (B2). Soil reactionsare acidic, old consolidated alluvial deposits, is the only and brown hues (Munsell lOYR and 7.5YR) valley bottomsoil supportingoak forest. predominate. Drainage is generally good, al- DIsCUSSION though temporaryhigh water tables caused by lateral water movementmay be present during Developmentof the oak forest the wet season. Althoughthe WillametteValley is, in general, Sedimentarysoils are the principal substrate a forestenvironment, extensive, closed-canopy oak of the oak woodlands (Table 4). Three seriesare forestsappear to have developedfrom present: Steiwer, Carlton, and Peavine. The since the valley was settledin the mid-nineteenth Steiwer series is the most common soil. It oc- century. The severalhistorical references to "oak curred under approximately46% of the oak openings"or oak "orchards"are indicativeof the stands sampled. Carltonseries is foundon lower growthhabit of Quercus garryanaprior to settle- slopes below areas of Steiwer and togetherform ment. Supportingthe validityof these early de- a catena. The Carlton-Steiwercatena was present scriptionsare the large, old, savanna-formtrees under 59% of the stands examined. The Peavine scatteredat low densitythrough the presenthigh series is limitedto uplands on the westernside density stands of smaller, younger forest-form of the WillametteValley and is also related to trees. This patternis repeated throughoutthe the Steiwer series. valley. The mean age of 90 years (determinedat Basic igenous rocks are the parent materials breastheight) for large forest-formQuercus gar- for soils withbrown (Munsell lOYR and 7.5YR) ryana is furtherevidence of the relativelyrecent or reddish (Munsell 5YR) hues. These soils, developmentof the forest. If an arbitrary10 are moderatelydeep and well drained,acidic, and yearsis added to coverthe growth period to breast have illuvial horizons, but not eluvial horizons. height (1.4 m), the date of establishmentof the

This content downloaded from 128.193.8.24 on Wed, 28 Aug 2013 19:14:18 PM All use subject to JSTOR Terms and Conditions 1132 JOHN F. THILENIUS Ecology,Vol. 49,No. 6 oak forestsbecomes 1862 A.D). This is approxi- tivityin adjacent stands would have an influence. mately20 years afterthe period of intensivemi- Removal of disseminulesources or introduction gration and settlement (1842-45) in western of exotic species would directlyor indirectlyaffect Oregon. development. The present oak forestcommune i- The most probablecause for the conversionof ties are, therefore,in a seral state, both because oak savanna to oak forestis interruptionof the they are of relativelyrecent origin and because repetitiousground fires that were an important theyhave been disturbedby the activitiesof manl environmentalfactor of the presettlemeiitsavanna. throughouttheir existence. The climateof the WillametteValley created an A degreeof floristicsimilarity is presentamong environmentparticularly conducive to fire. The the fouroak forestcommunities. Differencesbe- cool, moist winter and spring allowed a dense tweencommunities are due mainlyto shiftsin the herbaceousground cover to develop. This cover importanceof a few shrub species, as this is in- was well dried by the normalsemidrought condi- dexed by theircoverage and frequency,rather than tions of summerand ready to burn in the fall. distinctchanges in species composition. Because The anthropicorigin of manyof the presettlemeiit of the floristicsimilarity it is possiblethe commu- fireswas also reportedby the early writers,but nities representa sere and differencesare caused wildfiresstarted by other causes were common by successionalrelationships. On the otherhand, throughoutthe Pacific Northwestprior to settle- they may represent vegetational expression of ment (Morris 1934). differentenvironments, albeit differentpositions With settlement,fire became an economic as or steps on an environmentalgradient within the well as an ecologic factor,and fire control was oak forestzone. needed to prevent destructionof propertyand The relativelyshort time the oak forest ap- crops. Clearly a rather sensitive ecological pears to have been in existence makes the first mechanismhad operated to perpetuatethe oak possibilityunlikely, and it is more realisticto sug- savanna in an environmentsuitable for oak forest. gest that the Quercus/Corylus/Polystichurncom- Early fire control was crude, but the effectof munityis present on the most mesic sites, the controlin increasingthe densityof the oak was Quercus/Rhuscommunity on the most xeric, and noticedas early as 1840, and by the late 1800's the Quercus/Amelanchier/Syimphoricarpos com- dense stands of scrubbyoak forestwere a promi- munityon sites intermediatebetween these ex- nent part of the landscape. tremes. Because Prunus avium>nis an intro- The above account of the dlevelopmentof oak duced species,the Quercuts/Prunus/Sympthoricar- forestfrom oak savanna in the WillametteValley pos communitymay have developed fromone or is remarkablysimilar to that given by Curtis more of the above communities. (1959) for changes in the The absenceof autecologicalinformation on any dominated "oak openings" of Wisconsin. The of the species makes the classificationonly tenta- overstoryof the WillametteValley oak forestsis tive. The Quercu-s/CorAvlus/Polystichunit com- also quite similarin general physiognomyto that munityhas been called the most mesic community of the Wisconsinoak forests. Both have savanna- for a numberof reasons. The primaryreason is formoak trees scatteredthrough dense stands of the presenceand relativeabundance of understory forest-formtrees. This appears to be an instance species which are also major componentsof the of like ecological processes operating in widely understoryof coniferousforests in the higherpre- separated geographicalareas, resultingin strik- cipitationzones of the Oregon Coast and Cascade inglysimilar vegetation. Mountain Ranges. The most importantof these is Polystichummunitutni which has been recog- Nature of the plant communities nized as a dominantor codomiinantin the under- Ameliorationof environmentalextremes through story stratum of Pseudotsuga nenziesii forests the developmentof closed-canopyoak forestal- by both Spilsburyand Smith (1947) and Corliss lowed plants unable to endure savanna conditions and Dyrness (1965). Corylus cornutavar. cali- to spread and establish. The disseminulesource fornicaand Holodiscus discolor,also commonin would be along watercoursesand around moist the higherprecipitation zones, reach theirgreatest spots presentin the savanna,or in the small areas importancein this community,and a numberof of oak forestthat did exist. othercommon understory species of the Pseudo- Throughouttheir existence the oak forestcom- tsuga menziesiiforest are restrictedto it. Among munitieshave been influencedby man's activities. these are Rubus parviflorus,Dryopteris arguta, Logging, livestock grazing, land clearance, etc., Philadelphus lewisii, Athyriumfelix-femina, and were importantenvironmental factors and even Ceanothus velutinus var. iaevigatus. The high if a stand were to escape actual disturbance,ac- density and greater basal area and maximum

This content downloaded from 128.193.8.24 on Wed, 28 Aug 2013 19:14:18 PM All use subject to JSTOR Terms and Conditions Autumn 1968 QUERCUS GARRYANA FORESTS IN OREGON 1133 heightof large forest-formQuercus garryana as representativeof the Quercus/Corylus/Polysti- well as the greaterdensity of Pseudotsuga men- chum communitywould develop into the Quer- giesniand Acer macrophyllumand the presence cus/Prunus/Symphoricarposcommunity. How- of Babiesgrandis are also indicativeof the mesic ever, the dominanceof Symphoricarposalbus in natureof the Quercus/Corylus/Polystichumcom- the low shrubstratum and the relativelyhigh cov- munity. Finally,the tendencyfor the community erage and frequencyof Amelanchieralnifolia in to occur on relativelysteep northand east slopes the tall shrub stratumalso indicate a relation- also pointsto its mesic nature. ship to the Quercus/Amelanchier/Sysnphoricarpos The Quercus/Rhuscommunity has been called community. Possibly the Quercus/Prunus/Symz- the most xeric communityof the oak forestbe- phoricarposcommunity is developingon sites in- cause of the decreased heightand basal area of termediatebetween the two indigenous commu- Q nercusgarryana and the lower densityof large nities. forest-formtrees. The absence of a tall shrub stratumand the depauperategrowth form of spe- ACKNOWLEDG MENTS cies thatare tall shrubsin othercommunities indi- The National Science Foundation and Oregon State cate thatgrowing conditions are less optimal. The University provided financial and material assistance for presence of Rhus diversilobain adjacent grass- this study. I should like to thank Dr. W. W. Chilcote lands as well as in the oak forest shows it is and Dr. C. E. Poulton for their comments and criticism adapted to relativelyxeric environmentsand it of the manuscript. reaches its greatestabundance in this community. LITERATURE CITED The well-developedherbaceous layer composedof many grasses and forbsalso presentin the adja- Baldwin, E. M. 1959. Geology of Oregon. Edwards further of the generally Bros., Ann Arbor, Mich. 136 p. centgrasslands is evidence Clarke, R. C. 1927. History of the Willamette Valley, xeric environment,as is the tendencyfor the Oreg. Clarke, Chicago, 111. 2 vols. Q nercus/Rhuscommunity to occur on exposed Corliss, J. F., and C. T. Dyrness. 1965. A detailed upperand middleslopes withsoutherly aspects. soil-vegetation survey of the Alsea area in the Ore- The intermediateposition of the Quercus/Ame- gon coast range, p. 457-483. In C. T. Youngberg Fed.] Forest-soil relationships in North America. lanchier/Symphoricarposcommunity is less easy Oreg. State Univ., Corvallis, Oreg. to justify. It is based both on the decline in im- Curtis, J. T. 1959. The vegetation of Wisconsin. Uni- )ortanceof Coryluscornuta var. californica,Poly- versity of Wisconsin Press, Madison, Wis. 657 p. stichunimunitum, and other mesophyllicspecies Douglas, D. 1914. Journal kept by diversiloba,and other during his travels in North America 1823-1827. Wes- and on the decline of Rhus ley and Son, London. 364 p. xerophyllicspecies, indicatingthat sites occupied Fowells, H. A. 1965. Silvics of forest trees of North by the Quercus/ Amelanchier/ Symphoricarpos America. U.S. Dep. Agr., Forest Serv., Handbook communitymay be intermediatebetween the mesic 271. 762 p. and xeric extremes present in the oak forest. Habeck, J. R. 1962. Forest succession in Monmouth Township, Polk County, Oregon, since 1850. Proc. Basal area and the densityof large forest-form Acad. Sci. 21: 7-17. and relictsavanna-form Quercus garryanain the Hitchcock, A. S. 1950. Manual of the grasses of the Q uercus/lArelanchier/Symphoricarpos comnmuni- United States. 2nd ed. U. S. Dep. Agr. Misc. Publ. ty are greaterthan in the Quercus/Rhuscommu- 200. 1051 p. nity,but less than in the Qtuercus/Corylus/Poly-Hitchcock, C. L., et al. 1955-1964. Vascular plants of the . 4 vols. Univ. Wash., Seattle, stichumcommunity which is also indicativeof the Wash. intermediateposition. The communityhas a ten- Morris, W. G. 1934. Forest fires in western Oregon dency to occur on north-and east-facingridges and western Washington. Oreg. Hist. Quart. 35: and slopes which are, in general, more exposed 313-339. Nash, W. 1882. Two years in Oregon. D. Appleton, than sites occupiedby the Quercus/Corylus/Poly- New York. 327 p. stichun community,but less exposed than the Peck, M. E. 1961. A manual of the higher plants of south slopes and ridges generallyoccupied by the Oregon. Binfords and Mort, Portland, Oreg. 936 p. Quercus/Rhuscommunity. Spilsbury, R. H., and D. S. Smith. 1947. Forest site The relativelyhigh coverage and frequencyof types of the Pacific Northwest. Dep. Lands and Forests, British Columbia Forest Serv. 46 p. Corylus cornutavar. californicaand Polystichum Thornthwaite, C. W. 1931. The climates of North inunitumlin the understoryand the abundanceof America according to a new classification. Geogr. Psettdotsugamenziesii and Acer macrophyllumnin Rev. 21: 633-655. the overstoryplace the Quercus/Prunus/Sympho-U. S. Soil Survey Staff. 1951. Soil survey manual. close to the U. S. Dep. Agr. Handbook 18. 503 p. ricarposcommunity floristically Quer- Wilkes C. 1845. Narrative of the United States ex- cus/Corylus/Polystichumcommunity, and possi- pedition during the years 1838, 1839, 1840, 1841, 1842. bily,with a seed source of Prunus avium, stands Vol. 5, Lea and Blanchard, Philadelphia, Pa. 558 p.

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