Comparative Biomass and Growth of Cypress in Florida Wetlands


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Comparative Biomass and Growth of Cypress in Florida Wetlands
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The American Midland Naturalist
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Mitsch, William J.
Ewel, Katherine C.
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cypress swamps
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United States -- Florida


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Pages: 417-426

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University of Florida
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Comparative BiomassandGrowthofCypressinFloridaWetlands'WILLIAMJ.MITSCH'Center for WetlandsandDepartmentofEnuironmental Engineering University0/Florida, Gainesville 32611 and KATHERINEC.EWELCenterfOTW.etlandsand of Forest Resources and Conservation,University of Florida, Gainesville 32611ABSTRACT:Treebiomassandincreaseinbiomass weredetermined[or cypress (Taxodiumdistichum)indifferent systems inFlorida.Tentrees were harvestedto terminebiomass re$ressions. Lowest biomassandtreegrowthrates werefound.Incypress-pine associationsindicativeoflow water, inmonospecificstandsofcypress areindicativeofhighwaterlevels,andinapoorlydrainedcypress dome. IncreasesInindividualtreegrowthrangedfrom 1.0 to3.5 kg/y-l inthese groupings.Highestcypress treegrowthrateswerefoundincypress-tupelo systemsandcypress-hardwood systems.Thelatterarelessdominated by cypress, however, so individualtreegrowthisgreater(7.719/yvs. 4.0 kg/y).Cypress-hardwoodassociationsareknowntobe generallybetterdrainedthancypress-tupelo systems.Twoexperimentalcypressdomescurrentlyreceivingtreatedsewage effluentandgroundwatershowedhighindividual treegrowth(5.0and4.2kg/y,respectively),butlittledifference wasnotedbetweenthetwo domes.Treediameterincrease showed nonnal cypresstreegrowthtobe1.0-2.0oooo/ywithhighervaluesof2.8-3.3incypress-hardwood associationsandtheexperimentalcypress dome. Cypressinthepoorlydraineddomeincreasedbyonly2.0mm/y.INTRODUCTIONCypress trees(Taxodium distichum)arefound in a variety of wetland eco systemsthroughoutsoutheasternUnitedStates, along the Atlantic CoastanduptheMississippi River Valley to southern Illinois. Cypress-dominated ecosystemsarecharacteristically still-water pondsordomes, fringes around lakes, floodplain back swampsorslowly flowing sloughs or strands.Thesingle feature commontoall cypress habitats is standing water foratleastpartoftheyear. Cypress seedlingscanonly germinate on dry land (Demaree, 1932), so a fluctuatingwaterlevelisnecessary for a cypress system to suzvive over long periods.Maturecypress trees, however,canadaptto continual flooding(Matoon,1916; Demaree, 1932; DicksonandBroyer, 1972). Because cypressOCCursina widerangeofwetland systems, itispossible to identifythehydrologicconditions bythetreesthatgrowinassociation withthe cypress. Cypress.hardwood associationsareindicative of bottomland riverine forestsandsloughs which experience a short hydroperiod(Carteret al., 1973; ConnerandDay, 1976).Herecypressdonotdominate,andgrow in association with species such as red maple (AceT rubTum), ash (FTaxinus sp.) box elder (AceTnegundo),cotton wood (Populus heteTophylla)andwateroak (QueTcus nigTa).Ifdrainage is poorerandthe hydroperiod is longer in the riverine swamp, the cypress is found withwatertupelo (Nyssa aquatica).Theeqnivalenttowatertupelo fonnd in still-water ponds1WorkdoneatCenterforWetlands.UniversityofFlorida.Anthematerialsincorporatedinthis workweredevelopedwiththefinancialsupportoftheNationalScienceFoundation,GrantGf-38721andRockefellerFoundationGrant RFa73039. 2Presentaddress:PritzkerDepartmentofEnvironmentalEngineering, IllinoisInstituteofTechnology,Chicago60616.417


418THEAMERICANMIDLANDNATURALIST101(2)ordomes with a similar hydroperiod hut with stagnant waterisswamp black gum(Nyssa biflora)(Penfound, 1952; MonkandBrown, 1965).A associationisindicativeofseverely drained conditions which allowslash pine(Pinus elliottii)orlongleaf pine(P. palustris)toinvade cypress. Thiscondition was notedbythe authors to be common in N-centraI Florida where drain age ditches lowered water levels near cypress domes.Thisassociation is also commonatthe edgeofcypress domes where waterisoften intermittentandshallow (Mo'lk andBrown, 1965). Cypress in pure stands generally indicatetheotherextreme'Jfcontinuous high water. Several investigators (Penfound, 1952; BroadfootandWil liston, 1973) have statedthatcypressisone of the swamp trees most toleranttocontinual flooding. AndersonandWhite (1970) report on a cypress-tupelo swamp .insouthern Illinois where many hardwoods were killed whenthewater level was suddenly raised by a beaver dam.While several ecological studies have been performedonthe floristic structureofcypress swamps(e.g.,HallandPenfound, 1939, 1943;KurzandWagner, 1953;MonkandBrown, 1965; AndersonandWhite, 1970; MontzandCherubini,1973),few data are available on the comparative growthofcypress in its various ecosys ternsandwhatfactors may affect this productivity.CarteretaI.(1973)madesome measurements ofnetproductivity of cypress in slough areasinthe Big Cypress Swamp.ConnerandDay(1976) recently reportedonnetproductivityofa bottomlandforestanda cypress-tupelo swamp in Louisiana.Thisstudy will present some and tree growth data collected from Florida cypress swamps'aspartofan ongoing studyofthese wetlandsaswater conservation and nutrient recycling areas(seeOdumet al.,1977). Particular emphasisispaidtothe variation in productivityamong sites due to environmental variables, especially hydrologic conditions. Pre liminary determinationsofcypress growthincypress domes subjected to high nutrient loadings from secondarily treated domestic wastewater and groundwater-arealso given. WI'HLAOOOOIEEsrAn'QltESTSTUOTAII.FLORIOA Fig.I.-Locationoftwo cypress study areas in Florida: Alachua County and Withlacoochee State ForestII.,.,


1979MITSCHANDEWEL:CYPRESSBIOMASS419METHODSSludysiles.-Twogeneral areas with cypress wetlands inFloridawere used in this study (Fig.I).Oneareaincludes cypressdomeecosystems inAlachuaCounty in N-central Florida.Threegeneral sites within thisareawere utilized:(I)a cypressdomeabout10kmNWofGainesville intheAustinCaryMemorial Forest, where cypress trees were harvestedforbiomass regressions;(2)twoexperimental cypress domes 5 kmNofGainesville associatedwithanongoing st,,:! ofwastewater re cyclingandwaterconservation,and(3)a forest inventory siteoftwocypress domesnearsite(2)whichisownedby Owens-Illinois Inc.andforwhichseveral years of cypress treegrowthdatawere available. All sites were knowntobedominated by pond cypress(Taxodiumdistichumvar.nulans) ,Thesedomesarelocated inanareadominatedby theOcalalimestone formation(Eocene),overlying formationsofHawthornesands, claysandlimestones (Miocene)andsurficial sands (Pleistocene).Solution holesthatform intheOcalalimestonearethoughttocause slightsurface slumpages in Hawthorne and sand formations that in turn resultincypressdomes (PirkleandBrooks, 1959).Thetwo experimental domes mentioned above are part of an experiment beingconducted to studythepotentialofthese domes as areasoftertiarytreatmentfordomestic wastewater andasareasofwater conservation. Some preliminary resultshave been published elsewhere(Odumel al.,1977).Thetwo domes utilized hereinclude one which received secondarily treated sewageata rateof2.5em/week(SewageDome)anda second dome which receivedanequivalent loadingofhardgroundwater(GroundwaterDome).ThetwodomesattheOwens-Illinois site were-characterized according to observed hydrologic conditions with one having verydryconditionsandinvading pine(DrainedDome)andtheotherhavingpoordrain age conditions(PondedDome).A wetlandareaintheWithlacoocheeStateForest (Fig.I)inW-central Florida was also included inthestudyduetotheavailabilityofcypresstreegrowth data.Partsofthe forest are located in theNWcornerofGreen Swamp, a recharge areafor the Floridan Aquiferandthe headwatersoftheWithlacoochee River. BecauseofslowdrainagetotheNW,thispartofthestate forest isdominatedbycypresswetlands interspersed among pine flatwoods.Nodistinction was made between baldcypress(Taxodiumdislichum),if any,andpondcypress(Taxodiumdistichum)var. nutans)in data collected in this area.Biomass.-Tenpond cypress trees, representative ofthe wide rangeofsizes encountered in most cypressdome_s,were harvested at the Alachua County Austin Cary Memorial Forest site for biomass detennination. Diameter at breast height(dbh)andtotal tree heightweiemeasured with diameter tapeandclinometer priortofelling each tree,Thetree wascutatapproximately 0.6 m above the groundsurface with a chain saw, and the biomass was separated into leaves, small branches (less than 1emindiam),large branches and main stem. Wet weights were sured for each with a beam scale and subsamples were taken to detcnnine moisture "Content. Totalheightandbranchlength were also measured onthefelled trees.Rootsofseven trees were pulled out with a tractor. Becauseofunderlying claylayers, these rootshadnotpenetratedmorethan2m deep.Anestimateof75% recoverywas made,judgingprimarily fromthetaperoftheroots(D.Post, Univ. ofFla., pers. cornm.). Moisture content was detennined for each setofroots and forstem cross sections by drying in a kilnat100 C for72hr.Dryweightsofleaves,-_branches,stem and roots plus stump were used as dependent variables (y) in regres-sion analyses withthe independent variable chosen as x= V dbhx height. Bothdbhand height were expressed in centimeters.Thisindependent variable was found mostsatisfactory for cypress byCarterelal.(1973),Theregression equationhadthe form


420THEAMERICANMIDLANDNATURALIST101(2)y=axbwitha and b as regression coefficients. Biomass values were then determinedforothercypress ecosystems by using the regression relationsanddbhandheightdataforeach cypress tree inthatecosystem.Treegrowth.-Changesin biomass (AB/At) wer'.jdeterminedforAlachuaCounty and Withlacoochee State Forest study areasby utIlizing data on changes in dbh over time. Spring-loaded aluminum dendrometers were used to record changesindbhon12treesovera I-year periodattheSewageDomeandGroundwaterDomeinAlachuaCounty.Thetwo Owens-Illinois domes inAlachuaCountyhadfour setsofdbhmeasurementsforcypress trees overanlI-yearperiod. MeasurementsofdbhatWithlacoocheeStateForestweremadeatthebeginningandendofa 6-year period inthe1960s byFloridaDivisionofForestry as apartofa Continuous ForestInventory(CFI)datacollection effort.Datafrom21circular plotsof809m'eachwere used from this inventory. Biomass regressions developed from harvested treeswere used togetherwithchangesindbhto calculate changeintotal biomass change (AB/At) foreach cypress tree inthestudy plots overthemeasurement period. Hydrologic conditions were inferred for cypress plotsinWithlacoocheeStateForest based on trees growing in association with the cypress. This led to determinationoffourclassifications: (1) cypresshardwood;(2)cypress-tupelo;(3)cypress pine,and(4)purestandofcypress.RESULTSANDDISCUSSIONCypress harvestandbiomass regression.-Datafor the 10pondcypress trees harvestedinAlachuaCountyareshown inTable1.Thedbhrangedfrom 8.4-36.8cmandheight varied from 7.8-24.9 m.Groundleveldiameterwas generally fromtwoto four times greater than dbh due to swollen buttresses characteristicofcypress(KurzandDemaree, 1934). Most roots werefoundwithin 2mofthesurface be <:ause ofunderlying clay layers.Thelateral spreadofroots seemed to be one-thirdthe height in most cases;nodataonroot distribution with depth were measured.Treerings showed the trees to vary in age from 50-162 years. Constants for regres sion relationships used to determine pond cypress biomass were calculated from bio mass data and are given in Table 2. A significant correlation was obtained for eachrelationship.Rootbiomass averaged35%of total biomass.Thisis intermediate be tween51%reportedformangroves (Golleyetat.,1962)and11%reported for forested sphagnum bogs(RodinandBasilevic, 1968). Cypress biomass of study sites.-Regressionswere used to determine cypress biomass in bothAlachuaCountyandWithlacoocheeStateForest cypress wetlands.Results are summarized in Table 3. These calculations include only the contributionofcypress(>10cmdbh)tototal ecosystem biomass;dataforcalculating regressions were not found for other species present in the wetlands. However, since thetwoexperimental cypress domes are almost exclusively cypress, biomass for these sites was characteristicofthe entire ecosystem.Thetwo other plots in Alachua County,theDrainedDomeandthePondedDome,hadlow biomass values. These plots werelocated on the edgesofcypress domes where trees are generally smaller (Vernon,1947; Kur< andWagner,1953).Moreover,theplot inthePondedDomewas only50%cypress.Four cypress associations were distinguished in the Withlacoochee State Forest according to presenceofor absenceoftrees besides cypress.Thisenabled sites tobeIcharacterized according to their hydrologic regime. Subdominants in the cypresshardwood site were ash, maple or water oak. These species are indicativeofriverineI srste'!'s withhigh.waterfluctuatiOl:'sandshort hydroperiods.Thecypress-tupelo,IsItes mcluded specIesof Nyssa, espeCIally swamp blackgum,asthesubdominant.TheI


1979MITSCHANDEWEL:CYPRESSBIOMASS421TABLEl.--Pondcypress biomass data for trees harvestedinAlachua County. FloridaTreenumber2 3 4 5 TreedimensionsDBH,em8.4 11.212.7 15.0 19.0Height, m7.8 14.013.3 16.6 17.8Age, years 5250 66 66 63Branch length, m17.0 12.8 26.9 19.6 28.0Height to 4-in diam, m.8 2.2 4.6 6.4 11.1Root depth, m.9 .8 .8 .9 t.2 Rootdiameter, m2.4 2.4 3.6 3.3 5.0Ground diameterJem23.6 33.8 25.6 31.2 50.3Dryweight,kgLeaves.37 .80 1.7 .84 1.8Small branch a.57 1.3 2.7 2.3 3.5Large branchTotal branch.57 1.3 2.7 2.3 3.5Stem7.9 21.4 31.0 47.1 77.2Stumpb5.2 7.0 4.2 6.7 18.8 RootsC 7.0 16.319.8 29.7 62.1Total21.0 46.8 59.4 86.6 163.4 Dryweight distribution % in:Leaves1.7 1.7 2.9 1.01.1Branches2.7 2.8 4.5 2.62.1Stem37.6 45.7 52.2 54.4 47.3Stump24.7 33.3 34.3 38.0TABLEl.-(continued)Treenumber6 7 8 910Tree. dimensionsDBH,em 22.1 25.429.2 32.3 36.8Height,m16.818.0 20.6 20.9 24.9Age, years119 147 123-133 162153Branch length, m16.5 37.1 40.9 45.545.5Heightto4-indiarn, m 12.4 14.2 16.9 17.5 18.1Rootdepth,m1.21.5Rootdiameter, m3.66.1Ground diameter, em45.7 53.1Dryweight,kgLeaves1.6 3.8 4.2 2.5 5.8 Smallbranchll.2.9 6.8 5.4 6.3 7.8Large branch8.1 9.0 23.0 12.7 \2.1 Totalbranch11.0 15.8 28.4 19.0 20.9Stem116.5 161.4 218.5 258.6 399.4 16.1 28.2RootsC69.1 158.8Total214.3 368.0Dryweight distribution%in: Leaves.8 1.0Branches5.1 4.3 Stem 54.4 43.9IStump 7.5 7.7IRoots32.2 43.1 : Small b;anche.s are considered finger size (approximatelyIcmdiam) and smanerI'Stump IS conSIdered to be the stem from ground level to the levelatwhich the tree was cut (approximately 0.6 m above the ground)I C Seventy.five percent recoveryofroots is assumediI


422THEAMERICANMIDLANDNATURALIST101(2) association contained either slash pineorlongleaf pine. Pure cypressstandshadno other trees growing with the cypress. Cypress biomass values ranged from 3.1-38.0kg/m'for allWithlacoochee sitesandaveraged 13.5kg/m'.Table3 givestheaveragesandstandard errors for cypressbiomass in the four associations.Thecypress-tupelo association had the highest age (19.0kg/m')butalsohadthe highest standard error range (14.3 to 23.7kg/m').Thenexthighest cypressbiomass was in the cypress-hardwood association. Cypress hardwood siteshadlarger cypress treesthanthe cypress-tupelo sites (27.8vs.22.6emdbh),sothedifferenceinbiomass is reflected in the higher densityofcypressintupelo sites.Therewere 560 cypress/ha in the hardwood sites while the cypress tupelo sites averaged 800 cypress/ha.Inboth pure cypress stands andcypress pineassociations, size and biomass weresubstantiallylessthaninhardwoodandtupelo sites. These two areas probablyrepresent thetwoextreme conditions for cypress. A pure standofcypress is generally indicativeofa highwaterlevel which excludes allothertree species, evenNyssa(Penfound, 1952). A cypress-pine association, conversely, reflectss a dry environment that has allowed water-intolerant pine to invade the cypress habitat.Cypress treegrowth.-Treegrowth values for cypress in the ecosystems studiedaregiven inTable4.Itis again stressedthatthese numbers are for cypress onlyanddoTABLE2.-Regressionanalysis for pond cypress biomassy ... axby =0 biomass,gx Vdbh'htdbh = diameteratbreast height,ht """ tree height, ememNumberoftreesnRegression constantsabCorrelation coefficientrLeaves BranchesStemStumpandroot10 10 1077.16X 10-' 3.66 x10-'8.25x 10-' 6.55x10-'1.95 3.20 3.10 2.68 0.91 0.95 0.99 0.95TABLE 3.--..'Cypress biomass and numbers calculated for AlachuaCountyand With lacoocheeState Forest study areas in Florida Withlacoochee State Forest Cypress-hardwood32362 (4 sites)CypresstupeJo 485P (6sites) Cypresspure stand32362 (4 sites) 56632(7sites)95 510 23.7 80 720 21.0 90 450 18.6 20.3152 220 22.1 22.3162 12' 560'27.8.6'8080022.6.210058019.5.876 460154 20.3.3Cypress ecosystemAlachuaCountySewageDomeGroundwaterDomeDrainedDomePondedDomePlotarea(m')5272 6900 578 578%oftotal treesNo./haCypressMeandbh(em)Biomass(kg/m')13.6 17.5 6.8 8.4 5.1 5.3 15.4.9' over llyear period 2 Combined areaofall sites 3 Average and standard errorofsite values


1979MITSCHANDEWEL:CYPRESSBIOMASS423not reflect the entire ecosystem productivity. Biomass increase showed the samepatterns as standing biomass did for different ecosystems.Itisconvenient to dividediscussion on data into three categories.Thefirst caregory includes cypress ecosystems stressedbyeither too much or toolittle drainage.Theponded cypress dome in Alachua Countyhadthe lowest treegrowthofanysystem examined. Both densityofcypressandtree growth rates arelower than in any other cypress system considered. Larger cypress biomass increaseswere calculated for Withlacoochee State Forest cypress wetlands that were inter spersed with pine trees and that were pure stands, and for the DrainedDomeinAlachuaCounty. ValuesattheDrainedDomeandthe cypress-pine system reflectcompetition stress from pine trees which have invaded following drainage. Growthinthe pure cypress ecosystem is low, presumably becauseofwater stress. Individual cypress treesinthese three ecosystems were similarbutlowat2.5-3.5 kg(y.TheAlachuaCountydomehada very low valueof1.0 kg(y.Thus,either tooIowawater level, through increased competition, or too high a water level apparently duetoflooding stress has a depressing impactoncypress productivity. A second category includes cypress domes under experimental manipulation. Hydrologic conditions in both the Sewage and Groundwater domes are continualhigh water levelswhichcould generally lead to lower productivities. However, each domeisreceiving high levels of nu trients (rangesoftotal phosphorus were 0.1-0.7mg-P(Iand0.5-6.8mg-P(literfortheGroundwaterDomeandSewage Dome waters,respectively) ; this apparently contributes to greater productivities.Thecypress domereceivinggroundwaterhada high cypress biomass increase foreachtree of 4.2 kg(ywhile the value for the dome receiving sewage was5.0kg/tree. Indications are, therefore, that thetwocypress domes are responding similarly to the inputofaddi tional nutrients although the SewageDomeis receiving considerably more.Thecomparison, however,isnot complete because measurements were begun only about 1 year after sewage application began.Theeffect of a forest fire which burnedbothdomes prior to experimentation (EwelandMitsch, 1978) is also unclear. However, increase in biomass per treeishigher than that seen for the othertwoAlachua County domes discussed above.Itis also higher than 3.1kg/yfor the harvested cypress trees listed inTable1.A third category includes a comparisonofproductivitiesofthe cypress-hardwoodTABLE4.-Cypresstree growth data measured in Alachua County and Withlacoochee State Forest study areas in Florida Increase in biomass Cypress ecosystem Alachua County SewageDomeGroundwaterDomeDrainedDomePondedDomeWithlacoochee State ForestlCypress-hardwood(4sites) Cypress-tupelo(6sites) Cypress-pure stand(4sites) Cypress-pine(7sites) Average diameter increase,mm/y3.0 2.8 1.5 4.2 304 15922336289154117I'1Values are averagestandard error


424 THE AMERICAN MmLANDNATURALIST101(2)associations (riverine)andcypress-tupelo associations in Withlacoochee State Forest. Overall growthpercypress trec was much higher in the cypress-hardwood associa tionthaninthecypress-tupelo system (7.7kg/yvs. 4.0 kg/y).Thus, cypress were growingmuchbetterinthe hardwood associationbutthere were fewer of them;maples, water oak and ash were important subdominants.Thegreater densityofcypressinthe tupelo association makes its overall cypress productivity higher. An analysis of variance showed significant differences(oc=0.05) among the associa tionsintree growth, whether expressed asmm/y, kgtree-t.y-', or g-m-'y-'. Also shown on Table 4areannual increases in diameterofcypress treesinthe various ecosystems expressed as rom/yo Here,thecypress seem tobegrouped in a range of 1.0-2.0mm/ygrowth with these exceptions: (1) the ponded dome in Alachua County which showedanincrease of only 0.2mm/yoveranll-yearperiod;(2)cypress-hardwood systems whichhadstem increases averaging 3.3mm/y,and(3) the experimental domes which had valuesof2.8-3.0mm/y.A regression of the dbhvs.ageof harvested trees listed inTable1 gave a diameter increaseof1.6mm/y;this sampling areahadnormal drainage conditions. Langdon (1958), on theotherhand, found an increase of 4.6-5.3rom/yfor bald cypressinLouisiana, slightly higherthanthevalue found for cypress-hardwood grouping here.Plot productivityestimations.-Anestimateofplot productivity was made byassuming that subdominant trees had the same growth characteristics and size as thecypressandthatlitterfall was related to total biomass according to litterfall turnover rate of 0.0165/year, a value measuredatthe Alachua County sites. Productivity values were dividedbythepercentageoftrees thatarecypress.This gavean aver age net productivity of 950 g'm-'l'-I for the cypress-hardwood associationand760 g'm-"y-t forthecypress-tupelo association. A cypress-hardwood swampanda cypress-tupelo swamp in Louisiana were found byConnerandDay (1976) to haveCYPRESSCYPRESS_PINECYPRESS-HAROWOODALLTREESCYPRESS_TUPELO X-C'fPRESSOOMEWITH AOOEDWASTE_WATEROR GROUNDWATeR PURESTANDOFCYPRESS CONDITIONS----.+_ WET INCREASING DIFFERENCE BETWEEN WETANDDRYSEASONSFig. 2.--Generalized diagram showing the jnfluenceofdrainage conditions on net productivityofcypress and cypress ecosystems


1979MITSCHANDEWEL:CYPRESSBIOMASS 425 productivity valuesof 1374 gom-"y-' and1120 gom-'T', respectively.Carteretal.(1973) reportedonmeasurementsofcypress productivity in S Florida inbothundrainedanddrained cypress strands. Productivities were 858 gm-2.y-' fortheundrainedswampand387 g'm-2T' forthedrainedswamp.Thisseemstocontradictthe findings in Alachua County wheretheDrainedDome main tained a higher productivitythanthe Ponded Dome. However, a cypressstrandisa slow-flowing system withmanyspecies (especiaJly redmaple)incommonwiththecypress-hardwood riverine system. Conditionsarethus equivalent to a highly productive cypress.hardwood system; drainage would force the system towards a dry, low productivity cypress-pine association.Cypress treegrowthand environmental conditions.-Cypresstree growth andecosystem productivity have been showntovaryindifferent typesofcypress ecosys tems.Therelationships between cypressandecosystem productivity for differentdrainage conditionsinwhich cypressisfound are summarized in Figure2.TheeffectofartificiaJlyaddingwastewater with nutrientsisalso shown.Onthebasisofthisfigure SOJ)1e generalizationsabout theimportanceofenvironmental variablesin pro ductivity of cypress system in Floridacanbe made.1.Cypress-hardwood associations, found primarily in riverine and flowing strand systems, have the most productive cypress trees.Theshort hydroperiod favors both root aeration during the long, dry periods and eliminationofwater-intolerant species during the short, wet periods.Thecontinual supplyofnutrients with the flooding river system conditions may be a second portantfactor inmaintainingthese high productivities. Although highestproductivities per cypress tree are found in this system, the cypressisalso least dominant. 2.Totalcypress production in gom-2or1 inthe cypress-tupelo association is similar to the cypress-hardwood association. However, cypress are more numeroUS in the association and thus the growth ratesofin dividual trees are less. Here the water levels are not extreme but the period tends tobelonger than in the cypress-hardwood association (ConnerandDay, 1976).3.Cypress tree growth is generally slow inpurestandsofcypress.Thiscondi tion probably indicates relatively highwaterlevelsthatdonot even allowforsurvivalofNyssa(Penfound, 1952).Nyssa aquaticain a southern Illinoiscypress swamp under study by the senior author recently suffered high mor tality rates when water levels were raised by beaver dams. 4. Cypress tree growth is likewise lowindry conditions where pine has invaded. There is some evidence that cypress grows much faster in dry conditions when competition is eliminated. However, in Florida, cypress is at an extreme com petitive disadvantage relative to the several speciesofpine well-suited to dry conditionsofthe upland. Fire could eliminate cypress completely from thesesystemsifconditions remained dry (EwelandMitsch,1978).5.Theadditionofboth secondary sewage with high nutrients and groundwater with some nutrients may increase cypress tree growth over levels foundinnatural cypress domes.Noevidenceisyet available that sewage application results in higher productivities than equivalent groundwater application.Acknowfedgments.-Treegrowth data were suppliedbyJ.Lewisofthe Florida Division of Forestry and \V. SchlitzkusofOwens-Illinois Inc.H.T. Odum, Directorofthe Center for Wetlands, provided directionofthe senior author's dissertation,ofwhich thisisa part.D.Post,P.Straub andJ.Ordway assisted with the cypress harvest. Computer facilities were providedbytheNortheastRegionalDataCenter at the UniversityofFlorida. ArielLugomade valuable comments on the manuseript.


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