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(148')), i n , 2.1. 243

ofxerophyticandhalophytic of acoastal alluvial plainin

Y E. MEDINA', W, J.CRAM ,H, S. J.LEE' U.LUTTGE''*, M.POPP' ',SMITH'' ANDM.DIAZ'deEcologiay Ciencias Ambientales, Instituto Venezolano de Investigaciones

Caracas 1020-A , Venezue la ofBiology, TheUniversity, Newcastle upon Tyne, NEl 7RU, UKInstitut fur Botanik, Technische Hochschide Darmstadt, D-6100 Darmstadt, FRGInstitut fiir Pflanzenpliysiologie derUniversitdt, A -1091 Wien, AustriaInstitut fiir Angew andte Botanik, Westfdlische W ilhelms- Universitdt, FRGDepartment ofBotany, University ofEdinburgh, Edinburgh, EH9 3JH, UK

deInvestigaciones enEcologiay Zonas Aridas, Universidad NaciottaldeMiranda, Coro, Venezuela

8March 1988;accepted 22 July 1988)

theecology of a coastal alluvial p lain atC hichi r iviche in north ern Venezuela . Theareaagreat diversi tyofplant comm uni t ies , ranging from m angrovesonthe seaward edgeofthe plainton o n -

onthelandw ard side. Small differences ontopograp hy resul t in amosaicofandless-saline env iron me nts. Rainfal l isstron gly season al, caus ing superficial floodingofthe alluv ial plain

the rainy seasonand thecreat ionof ahypersa l ine subst ra tum during the dryseason.Asaconsequence , muchisdevoidoivegeta t ion. T ow ardsthelandward s ideofthe p lain thereare numerous smal l 'vege ta t ion

byha lophi lic succu lent herbs ,andm a d eup ofdec iduous andsemi -dec i duous sh rubsandtrees CAMplants such ascacti and bromel iads . In subsequent pape rs theresultsofofthese diverse plant sp eciesare presented.

RODUCTION habitat patchine ss. De ciduo us and sem i -dec iduousnon-ha lophy t i c sh rubs andtrees coexist withman-f lats associated with estuarine mang roves und er groves and shru bb y and herba ceous t rue haloph ytes, in thetropics cons t i tute an W ithin this heterog eneo us vegetat ion terrestr ialand and non- epiphyt ic CAMplants maycons t i tu te a significant to the coast and percentageofthe total bio mas s,as isthecaseoftheofrainfall resu ltinpronou nced column ar cact i andopu n t i a s, andB romehaceaeof

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23 4 E. Medina and others

1 C H I C H I R I V I C H E2 TOCUYO DE LA COSTA3 C U R A M I C H A T E* STOD Y SITE

Figure 1 Location of the study site on the northern coast ot Venezuelaferential distribution of active absorbing roots(Walter, 1973). Non-halophytic cacti and terrestrialbromeliads have supeflcial root systems which areactive only during the rainy season, when superficialsoil salinity is washed away by free running water.Shrubby and herbaceous halophytes on the contrary,are able to obtain water and nutrients from deepersoil layers, with higher chloride content throughoutthe year. The present project aims to document thevariety of ecophysiological types co-occurring in suchan environment, and characterise differentiation ofmicrohabitats. The field work was undertakendur ing the months of November-December 1985and March-Apri l 1986.

create a mosaic of saline and less or non-saline environments. Areas in lower geomorphologlevels are heavily flooded during the rainy seasonbecome brackish and salty as the dry seprogresses. These areas may be completely devoivegetation, probably as a result of the strong seaschanges in salinity and flooding (Walter, 1W alter & B reckle, 1984). To w ard s the C hichirivbay the influence of sea water becomes mpronounced and flooding tends to be permanThere, a typical estuarinc mangrove vegetadominates the landscape. At the other extrdeciduous forest vegetat ion surrounds the aflooded seasonally by the Tocuyo river.

STl'DV ARK AThe study area, locally known as the Cienega elOs tiona l, is located abo ut 6 km w est of the town ofChichiriviche in Estado Falcon in north-westernV e n ez ue la ( 1 O 5 5 ' N , 6 8 2 1 ' W ) ( F ig . 1 ). T h ewhole area is made up of alluvial sand plains andharr ier beaches created by the Tocu yo and T ucu rerc

LIM TELong-term climatoiogical data are available fromtown of To cu yo de la Costa, appro xim ately 16north-west of the study site (Fig. 1) for the pe1963 -86. Annu al rainfall av erages 1029 m m . annual distribution of rainfall (Fig. 2) shows clear peaks, a small one in April and a

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Ecophysiologv of xerophvtic and halophvtic vegetation in Venezuela. I 235

Ed 200

oQ.ao 100ooCC

TOCUYO DE LA COSTA (20m)( 1963 -1985 ) o R a in f a l l av 1020 m m Evaporat ion av 2325 mmA Tem pera ture av 26 4 C

Oo

30 S.Ecu2 0 '

10

J F M A M J J A S O N DAxera^c tnonllily \alue.s of raitil 'all, cxaporatioti

cuy o dc la Costa, Estado I 'alcon, V enezuela.

vaporat ion is very high throughout the year and isDecember . The evapora t ion curve shows two smal leaks, the first in March and the second in August,in both cases ju st before the onset of the respec tiverainy periods, associated with the apparent path ofhe sun towards and from higher lat i tudes during thesummer in the nor thern hemisphere . Lowest evap-rat ion rates are registered in the period Novemberto February, when they reach 5-5+0-3mm d^ ' ;du ring the rest of the year daily eva por ation is signifi-cantly high er reach ing 6-4 +0-3mm d ' . Averagemonthly temperature varies very l i t t le during theear; dai ly temperature differences between meanma xima and m ean m inim a (7-1 C on average) arelarger than the differences between mean tempera-tures of the hot test and the coldest month (Augustand January respect ively) , which amounts to 2-1 C.

Th e period analysed shows a pro nou nce d rainfallVariation between successive years (Fig. 3). Thisvariation is of ecological importance because it canregulate the expansion or contract ion of the halo-phobic vegetat ion through the degree of surface-soi lWashing occurrin g every year . B esides, occu rrence ofhumid years probably causes erosive impacts whichrnay reduce the soil level in the vegetation coveredislands, thereby decreasing survival of non-halo-phytic elements. The 23-year observat ion period canbe roughly dif lerent iated into two phases. Theperiod between 1964 and 1975 was rather humidvv'ith a rainfall ave rage of 11 70 348 m m y '. T h eperiod from 1976 to 1986 was much drier with a

2000-TOCUYO DE LA COSTA {20m

64 68 72 76 e r s

80 84Figure 3 .\tintial variations in total rainfall registeredthe last 2.^ \ears m the TocuNO df la Costa station.

ISO150-70 -60-50-40-

_ 30El 2 0 10

15 20 25 30October 5 10 15 20 25 30 5 10 15November Decem ber 1985

15 20 25 28 5 10 15 20 25 30 5 10 15Februa ry March April 1986

Figu re 4 Daily rainfal l distributiot i during the studperiod of the rainy seasoti ot 1985 and the dry season o1986.

error occurred after 1975. However, variability ihigh. In the mo nth of No vem ber 1985, du ring thperiod when the first series of field measurementwere undertaken, rainfal l was nearly twice the longterm average recorded in Fig. 3. Rainfall figureregistered durmg the periods of f ieldwork characterize the strong seasonal distribution of rain (Fig. 4)Du ring No vem ber 1985, 8 d had rainfall x 'alueabove 25 m m , am ong them 1 d with m ore than150 mm.

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236 E. Medina and others

F i g u r e 5. Gen eral vegetation map of the study areadeveloped from aerial photographs provided by theMinister io del Ambiente , Caracas. L , lagoon with brackishwater; M, tall mangrove vegetation ; B, decidu ous forest ,G, secondary grassland; I.V., island vegetation complex ;vf, mainly vegetation-free, f looding-prone areas; C, longterm fresh-water flooded areas dominated by sedges; S ,the broken l ine indicates th e border of areas of pre-dominan t ly saline soils in the east from higher non-floodedareas in th e west.

found (Fig . 5). The lowest geomorphological level isoccupied by a lagoon (L) with brackish water and iscompletely su r rounded by tall mangrove vegetat ion(M) [mainly Rhizophora mangle L. and Avicenniagerminans (L.) Stearn and scattered Lagunculariaracemosa CJaertn.] . The highest geomorphologicallevel is occupied by several areas of deciduous forest(B) and grassland (G), probably of secondary origin,dominated by the grass,Paspalum plicatulum Michx .The area between the mangroves and the deciduousforests contains a mosaic of vegetation units desig-nated by us as an island-vegetation complex (I .V.)where very slight changes in the soil level, in theorder of 5-20 cm, determine changes in salinity andflooding and th e coexistence of halophylic andhalophobic plan t species. Between the mangrovearea and the island-vegetation units extend areascompletely devoid of vegetation or occupied by

Vegetation units emerging from the plain, cluding pure mangrove associations, can be ferentiated as follows:(1) Flooded areas with fresh water accumuladuring the rainy season. These areas are dominaby species of Cyperaceae such as Eleocharis genicuR. Br. Prod. , E. nutans R. Br. Prod. , Fymbriscymosa Vahl and F. spadicea Vahl. Some spe

such as Nyniphaea sp ., with floating leaves in owater, are ephemeral and disappear during the season (Fig. be).(2) A Batis maritima-Sesuvium protulacastunit, bordering the vegetation-free salt fiats, whcan be temporarily flooded after heavy rains [6(a) and (6)].(3) A grassland eleva ted be twee n 5-10 cm frthe salt flat dominated by Sporobolus virginKunth , in termixed wi th Oxycarpha suaedifolia Band isolated individuals of the cacti, Opuntia z

tiana B rit ton & Rose and Acanthocereus tetrago(L. ) Humik . (Fig . 6a) .(4) Small islands, 3-10 m in diameter, where soil surface can be 10-40 cm higher than the salt-[Fig. 6(c) and {d)~\. The vegetation on top of islands is frequently dom inated by a man grassociated species, Conocarpus erectus L . ( Tlinson, 1986), reaching ap proxim ately 2 m in statufrequently a ccomp anied by a colum nar cactus Spilosocereus ottonis Backeb. , and a broad-joiOpuntia species (unit 4a in Ta ble 1). On isiawi thout C. erectus a number of isoiated nhalophylic tree species such as Prosopis fulifD . C . , Capparis hastata Jacq. and Maytenus karstReiss. may be found. Another occasional speciethe cactus, Pereskia guamacho Weber, a smdeciduous tree or shrub covered with succulfleshy ieaves ciuring the rainy season (unit 4/;Ta bie 1). As an epiphyte on the shru bs and cacti ,bromeliad Tillandsia flexuosa Sw. is ab und ant .islands nearby and in deciduous lorest relicts, orchid Schomburgkia humboldtiana Re ich b. is

frequently found. The floor of these islands maycovered by dense thickets of Bromelia humilis Jor scattered tufts of Sporobolus virginicus.The contact between the islands and the splains on lower ground is occupied by the BaSesuvium community. During the rainy season reddish-flowered Portulaca riibricaulis H.B.K. , wwell developed underground tubercules, is qoften seen.(5) The deciduous woodland. These areas

represented hy deciduous forest remnants of variasize which have been clearly isolated from the mforest core by erosive influences of running w

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Ecoph ysiology of xerophy tic and halophytic vegetation in Venezuela. I 23

Figu re 6 Vegetation units within the study area, {a ) General view of the alluvial plains showing Sporobolusvirginicus and Acanthocereus tetragonus (foreground), Batis maritifna and Sesuvium portulacastrum (middle) andConocarpus erectus. Background shows the main core of deciduous forest towards the north-east border of thestudy area, (6) Edge of the vegetation zone with Sesuvium potulacastrum leading to higher ground with mixedgrass species, (c) View of the island vegetation in the rainy season, (d ) View of a typical island during the dryseason, (e) Example of fresh water vegetation with Nymphaea sp, and Eleocharis geniculata. (f) R e m n a n t s ofdeciduous forest vegetation.

saline soils. The borders of these forested areas^re characterised by the presence of Capparisodoratissima Jacq, , C. hastata, Capparis cf. pachacaJacq. (broad, round leaves) , Caesalpinia coriariaWilld, Prosopis juliflora, Jac quinia revoluta Jacq, ,^aytenus karenii, Erythroxylon cumanense H, B, K,3nd shrubs of Croton sp, and Pereskia guamacho.Occasionally there are dense thickets of the terrestrial

A profi le through the study area which includes athe vegetat ion uni ts described above and a n u m bof the most representat ive species shows the specidistr ibut ion pat tern associated with topographicposition and the fluctuation of the water tab(Fig, 7),

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23 8 E. Medina and othersmetres 20 AO 60 80 100 120 U O 160 180 200 220 240 260 280

Bare soilConocarpus erectusCupparis flexuosaProsopisjulifloraEugenia sp.Croton heliasterCapparis odoratissimaMimosa oligocanthaCapparis hastataMaytenus karsteniiTrichilia trifoliataGuapira sp.Capparis IinearisFimbristylis spadiceaFimbristylis cymosaCarexsp.Desmanthus virgatusPaspalum pUcatulumLeptochioa sp.Sporobolus virginicus canthocereus tetragonusOpuntia wentianaSubpiiosocereus ottonisBastardia viscosaCissus sicyoides nthurium crassinerviumPhilodendron sp.Evolvulus tenuisSesuvium portulacastrumBatis maritimaOxycarpha suaedifoliaBromeiia humilisTillandsia flexuosaPhoradendron mucronaturTillandsia recurvata

c m15010050

island deciduous foresthalophytes grassland remnant grassland halophytes- soil pit water table - rainy seasons o i l pit

water table dry season

Figure 7 Transect indicating location of the three soil pits excavated for measurement of ground-water depthand vertical variations in soil salinity. The transect reveals distribution of most frfqiicnt plant species as relatedto topographical variations.season differences in soil salinity (expressed aschloride content) among vegetation units are re-latively small but it is clear that salinity decreasesfrom the salt fiats towards the deciduous forestremnants (Table 1). Differences among vegetationunits increase markedly during the dry season. InApril 1986, in th e to p 0-10 m soil, salinity decreasesfrom a high of 340 me quiv . C r kg ' soil in th e saltflats to a low of 18meq uiv. C r kg ' in tbe deciduousforest remnants. T h e sodium/cbloride equivalentratio wasO-88+O-O3,indicating tbat most of tbe saltin these soils is Na CI. Seasonal variation in salinity isquite large in tbe salt flats, particulary in theBatis-Sesuvium zone (unit 2) and the Sporobotuszone (unit 3). Those are the typical halophylic plantcommunities along th e Caribbean coast in Ven-ezuela. Least variation in salinity is observed in theremnants of the deciduous forests (unit 5). In-dividuals of Subpitosocereiis ottonis are found only in

the dry season. Individuals oi B. humilis are found a wider range of superficial soil salinity. For thspecies however, soil chloride content is of nconsequence because functional roots are not in tsoil but grow between the leaf sheaths into the tanconstituted by tbe leaf bases (Pittendrigh, 1948).Soil profiles were excavated during the dry seaso(in March and April 1986 and 1987) to determine tvertical variations in nutrients and salinity and measure tbe depth of the ground water (Fig. 8Sodium and chloride were by far tbe dominant iospecies in tbe profile. The ground water from ttbree vegetation sites (units 1, 4a an d 4-b) hsignificantly higher concentrations than sea watcollected nea rby (F ig. 9). In all cases Cl cocentration increased witb soil depth (Fig. 10Moreover, there vvere considerable differences in t

profiles depending on the location in relation to tvegetation un its. D own to 0-50 m in a profile d

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Ecophysiology of xerophytic and halop/iytic vegetation in Venezuela. I 23Table 1.Seasonal changesinsuperficial soil chloride contents.Cienega el Ostional Chichiriviche, Stado Falcosee text for description of vegetation units)

(1) Vegetation-free salt flats(2) Batis+Scsuiiuni zone(3) Spnrobolus + Oxxcarpha zone4() Conocarpus island withBromelia humilis4(6) Non-halophil ic t reesandBromeliasp.undernea th, mosscovered soil surface(5) Deciduous forest withBromelia sp. beneath

Chloride contentDept h(cni)

0-1010-200-100-1010200-1010-200-1010-200-1010-20

in nict |uiv.kjDry season3 4 0 +133219+ 49203+10711 +8770 + 2646+341 1 4 + 1 4 928+2044+918+212 1 + 2 7

X' drysoilRainy season

65107371711-3611

16

Na/Cl equivalent rat io= 0-88+0-03

F i g u r e 8. Depthofground waterinsoilpitIIIof Figure7 excavated during the dry season of 1986. The wholeprofile sho ws a predom inantly sandy fine clay con-iposition.Red colour is anindicationof thepresenceof ferric oxideand grey of ferrous oxides which indicates pron oun cedseasonal oscillationsof theground water.( S o i l pit III sa l i n it i e s we re even h i ghe r . G ro un d

2iOO

2000

1500

1200

n

inI s o i l p i t I

D - - II

sea water

K'Co'MgFigure 9. Ionic composition of groun d water in the dryseason from pits excavated near a 6-5mtall Subpilosocereusottonis (Soilpit II, Fig. 7) at theborder of a small islanddominatedby aConoca rpus erectustree (Soilpit I, Fig. 7),onthe alluvial plain (SoilpitIII andsea water fromtheChichirivichebay.

wat e r we re 1-73, 1-75 and 2-30o s m o l kg ' r e s p e c -t ive ly, c o r r e s p o n d i n g to an o s m o t i c p r e s s u r e ofm o r e t h a n 4-5MPa, i.e. a b o u t 1-8 t i m e s t h a t ofseaw a t e r . At a d e p t h of 0-50 m the prof i le n ear thel agoon (Soi l pit III had a m u c h h i g h e r sa l i n i t y ,a p p r o a c h i n g 600m e q u i v .kg ' s o il . G r o u n d w a t e rwas a l ready s t ruck at 0-70 m as s t a t ed a b o v e .Differences it-i gro un d wa t e r l eve l i nd i ca t e t ha t the

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240 E. Medina and others

100100 200 300m eq C l / kg soil 400

Figure 10 Variations of chloride concentrations withdepth in soil pits. I, Conocarpus profile (A ); H, Cactusprofi le ( ) ; H I , Batis profile (O) (cf. also Fig. 7).

flooded after heavy rain[Fig. 6(c) and (e)]. In th e dryseason of 1983 most of the vegetation-free plain wascovered by acontinuous salt crust (Fig. 11 a). Th i swas the dry season following the driest year in the 22year period shown in Fig. 3 and was exceptionallydry in the whole Caribbean region (Smith, Griffiths& Luttge, 1986). During th e period of the presentinvestigation, in th e dry season of March to April1986, a continuous salt crust was not observed,although crystallized salt was frequently found ontop and in the upper layers of the soil (data in Table1). Extensive formation of salt crusts was observed

again in the dry season of 1987 (Fig. 11b) ,followingyear with below average rainfall (see Fig. 3).O R I G I N O F T H E I S L A N D V E G E T A T I O N A N DC O - O C C U R R E N C E O E H A L O P 111LIC A N DH A L O P H O B I C V E G E T A T I O NThe distribution of vegetation units, as related ttopographical positions and soil salinity, clearlindicates that soil salinity is very heterogeneoucontrasting soils occurring side by side. In mocases however, non-saline patches are slightly elevated above the salt flat level. This level differencranges from 5 to 40 cm. M oreov er, salinity in thupper soil layers changes dramatically throughouthe year. During the rainy season superficial salt washed away, while it is concentrated througevaporation during the dry season. This last situatiowas considered by Walter (1973) when explaininthe co-occurrence of halo-intolerant succulent cacwith succulent halophytes rooting in the same soiWe have observed similar behaviour in Opuntwentiana, a salt-intoleran t succu lent cactus and thalophytes Sporobolus virginicus and Oxycarphsuaedifolia (unpu blished data). T he cacti grow anrecharge their water reserves only during the rainseason when salinity is low (Table 1).

One of the main objectives of the Chichirivichproject is to explain the vegetation dynamics in thsalt flats and to clarify the origin of island vegetatioAre those islands in the process of formation, gaininland from the inhospitable salt flats, or do therepresent phases of disintegration of vegetation unioriginally growing on salt-free areas? Three hyptheses are worth considering.(1) Walter (1973, pp. 411-12) assumes that tsuccession leading to the formation of the vegetatioislands starts with individual rosettes of B. humi

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Ecophysiology of xerophytic and halophvtic vei^etatioit in Jetteziiela. I 241

pWtej^vsj,

Figure 12 A.spectsofisland ve getation witliin tlie alluvial plains, (a )Typical small island with Sidtfyi/osoccrcusottonisand Capparis odoratissimawith Boniclici huniilisutiderneath.Inthe b ackgrotitid th e coreofthe deciduou sforest with which these typesof v'egetation islands seemto be originally associated, (h ).A.spectof plants growingon slightly elevated ground within the salt flat {Sporohoiusvirffiniciisand Sesuvium portulacastrum). c), d)Aspect of disintegrating island during the rainy and the following dry season respectively. Noticethat twoBromeiia humilis specimens atid the small Subpiiosocereus ottonis died in the intervening period. The treeremnants behind also itidicate that this partictilar island is in the process ot decay.

transported to the sand |Jain by gu.sty wind.s. 'Iliis ispossible because the tank torminj rosettes of B.humilis do not need to root in the substratum andonly loosely He on it for tiiccbanical support.According to Walter's hypothesis tbese rosetteswould then form large colonies by \-egetati\e pro-pagation. The wind could accumulate sand aroundthese colonies so tbat otber plants, including cacti,may establish themselves. However, from pro.,ductivity measurements performed in tbe presentproject, it appears improbable that a single rosette ofB. humilisloosely laid down on tbe sand could giverise to a community of rosettes rapidly enough toform a new island,

(2) Vegetation-free areas may be occupied by salt-toleratit herbs, sbrubs and/or trees (such as Spo-robolus virginicus, Batis maritima atid Conocarpuserectus)wbicb, by their presence, cause accumulationof soil in their surroundings so ele\'ating tbe soil levelabove the salt Hat itself. Tbis cle\ation of the soillevel allows leaching of salts during tbe rainy season

itions are associated witb tbeerosive effects broughtabout through flooding by the river and after beavyrainfalls. It is proposed thattbe deciduous forest soilis being eroded away leading to tbe formation ofdeciduous forest patcbes surrounded by soils proneto salinizatit)n from percolation of sea water. Tbismay explain the occurrence of salt-intolerant treesand shrubs in small islands surroundedby balopbyticvegetation.

Field observations suggest tbat both processes ofaggregation and disintegration of \-egetation islandsas stated in bypotheses (2) and (3) areco-occurringin tbe area. Small islands, constituted by salt-intolerant species, appear to be separated from tbemain core of deciduous forest asaresult of erosiveprocesses [bypotbesis (3), Fig, Ma]. Conversely,slightly elevated areas arising from changes inbydrological patterns maybeinvaded bysalt tolerantspecies. This is an alternative mode of islandformation [bypotbesis (2), Fig. \2h\.

While hypotheses (2) and (3)and Fig 12/; andaare

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242 E. Medina andothershypothesis (3) of island formation. Conversely,degradation mayoccur w ith juvenile islands formedaccordingto hypothesis(2), i.e. for such cases youngislandsareunstab le .

STUDIES AND AIMS OF THE C H t C H l R l V I C H EPROJECT

The s tudiesofthe Chichiriviche project presentedinthis series of art icles were primarily devoted tocomparative ecophysiologyofplantsintherainyandthe dry season and to the physiological chang esbrought about hy the transit ion between seasons.Several species were studied. They represent anarray of life-forms such as halophyte , mangrove,deciduous and evergreen sh rubs, tank-formingbro-meliads, leaf and stem succulen ts and epiphytes .They comprise species with C. |-photosynthesisandcrassulacean acid metabolism (CAM). The com-parative ecophysiology led to synecologicalcon-siderations part icularlyby theworkon thevegetationislands (units 4a andb). Each island c overed arelatively small area on theplain andpossessed al imi ted numberofspecies. Th us ,thespecies selectedfor measurements were representativeandallowedacomparative evaluation ofadaptive strategiesofco-occurrence. Terrestrial speciesofthe islandandtheBatis-Sesuvium zone (unit2)borde ring them , whichareallaffected byseasonal chang esinsalinityofthesubs t ra tum,aredescribedinseparate p apers :II, III,VandVI.

The dominan t sh rub of the islands, Conocarpuserectus, wasinvestigated in greater detail. It alsooccursinsandand sand dunes closetothe seashoreand these were included in the s tudy . At suchlocations, fundamentally different from theplainsofthe CienegaetO st ional, C.erectus also behavesin adifferent way and hasbeen c ompare d with a saltexcret ing mangrove growing in the same area,Avicennia germinans (PaperVI).Another monographic t reatment isdevoted toB.humilis (Paper III).It isoneofthemost typicalandabundant terrestrial plantsofthe islandsbut italsooccurs within the fringe of the decidu ous forestremnants (uni t 5).Th is tank-forming hromel iad isnot directly exposed tothesubs tratum since mostlyithasfew or nofunctional roots in thesoil. It onlyusesthesubs t ra tum as asup por t, occasionally evenbecoming semi-epiphyt ic , res t ing on other vege-tation from a few decimetersup to a1mabovetheground . Thespecies occurs in habitats withcon-

trasting light climates, from partially shaded habitatsunder tree groves, where theplants arelargerand

these epiphytes, frequency of rainfall is mimportan t than amount . This factor is part iculcritical forS. humboldtiana, which has to abswater when it isavailable throug h theroot velamand accumulate it insucculent bu lbsand leavesflexuosa forms a small tank w ith its leaf sheaallowing the retention of rain w ater for lonper iods . T.flexuosa leaves areheavily coated wtrichomes which arehighly effective in absorbrain water.Finally, investigations of mangroves werelimitedto theplantsoi A.germinans occurr ingonplainsof the CienegaelOstional . Fxtensive sampof mangroves includingA.germinans,R.mangleL. racemosaalongthelagoon were performed durthe rainy season inN o v e m b e r / D e c e m b e r 1 98 5,during the dryseason in M a r c h / A p r i l 1986 (PaV I I , in preparat ion) .A C K N O W L E D G E M E N T SThis project was a mul t inat ional endeavour wi thparticipation ofthefollowing in sti tut ions :(1) Institut Botanik derTechn i schen Hochschu le , Darm stad t ,FR(2) Centro de Ecologia, In sti tuto Venezolano de vestigaciones Cientif icas, I VI C, Caracas , Vene zuela;Inst i tu t fur Pflanzenphysiologie der Universi ta t WAustr ia ; (4) The D e p a r t m e n t of Plant B iology, TUniversity of Newcast le upon T yne , UK; (5)Cen t roInvestigaciones deZonas Ar idas, Universidad Fransde Miranda, Coro, Venezuela .Theproject was suppomainly bygran ts from theDeu t sche For schungsgemschaf t , Bonn-Bad Godesberg , FRG (U.L. and J . A . Cand FondszurFode rung der wissenschaf tl ichen Forsch(project no.5784), Austr ia (M .P .) . Additional funds wreceived from The Royal SocietyofL o n d on ( W . J . C .H . S . J . L . ) , the DaxCopp Travel l ing Fel lowship ofInst i tu teofBiology (H .S.J. L.) and theStudienst i f tungdeutsclien Volkes (C.S.) . Local laboratory facil i t iesasupplies were providedby theCen t rodeEcologiaofI VD r R.Wingfield andLiesG.Carnevali and G.Colonassisted in theidentification of plant samples. Me teological data was supp ' ied by thece ntra l Fal con officethe Minister io delAmbien teyRecursos Naturales . RHeger prepared thehalf- tone pictures andDoris Schand Lelis Oehoa the india ink i l lustra t ions. Technassistance wassuppl ied by Frika B all, Eileen Go undSabas Perez andEl isa M ar t inez. Th an ks a lso to DGorham (Universi ty Col lege of Nor th Wales) for exchange chromatography ofsoilandwater samples.

R E E E R E N C E SG O D D A R D , D . & PIC C AR D, X. (1972). Geomorfologia y imentacion en lacostadelEstado F'alcon, C abo San Roma

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Eeophvsiologv of.xerophvticandhaloph vtic vegetation in Venezuela. I 24complex in Trinidad. 1. Tho bronieliad Hora, Evolution 2, W A L T E R ]]. {\'-)73). Die l'i%'ct(ition der Ertie in okopliysiologiscli58-89, Betrrichtuiif;.Band 1: Die tropischeii iiiul suhtropmhen Zone

S M I T H , J, A, C , G R I F F I T H S , H, & L I T T G F , U, (1486), Com- VF.B Gustav Fischer Verlag, Jena,parative ecophysiology of ChM and C., bromeliads, I, The WM.TFR, 11, &HRFCKLE,S,-\V,(1984), OWoi'/f rfc) AV(A, Band ecology of the Iirotncliaceae in Trinidad, Plant, Cell and Spezielle Okologie der tropischen und siibtropischen Zonen, pEnvironment 9, 359 376, 180 182, Gimta\' iM.scher, Stuttgart,

ToMLiNSON, P, B, (1986), The Botany of Mangroves. CambridgeUniversity Press, Cambridge, L ,K,

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