Plant life forms in the Golfo Dulce region and other neotropical rainforests

2008·17.8 MB·English

by  Hietz, Peter

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Plant life forms in the Golfo Dulce region and other
neotropical rainforests
Formas de vida vegetal en la región de Golfo Dulce y en otros
bosques lluviosos neotropicales
Peter HIETZ
Abstract:Thespectrumofplantlifeformsstronglyreflectsthelocalclimate,andtosomeextentinteractionsbetweenplantsand
biogeography,i.e.thepoolofspeciespresentinawiderregion.Thetraditionalcategoriesdistinguishinglifeformsaccordingto
thepositionofwinterbudsareoflimitedapplicabilityinecosystemswithyear-roundgrowthsuchastropicalrainforests.Themost
species-richlifeformintheforestoftheGolfoDulceregionaretrees,followedbyherbs,smallerwoodyplantsandepiphytes.15%
ofallvascularplantspeciesareshrubsorpygmytreesgenerallynotexceeding5minheight,10%aresmalltreesreaching10m,
and26%aretreesgrowingto>10m.Terrestrialherbsaccountfor19%,woodyandherbaceousepiphytesfor12%,hemiepiphytes
for3.3%,lianasfor7%,non-woodyvinesfor5.4%,andhemiparasites,parasites,andaquaticplantseachforlessthan1%ofthe
localflora.Thissurveydiscussestheadaptivesignificanceofthedifferentlifeformsandcomparesthelifeformspectrumfound
intheGolfoDulceareawiththatofotherneotropicalforests.
Keywords:plantlifeforms,neotropicalrainforest,CostaRica.
Resumen:Lavariedaddeformasdevidavegetalreflejafuertementeelclimalocal,yenalgunamedida,lasinteraccionesentre
plantasybiogeografía,esdecirlasespeciespresentesenunaregión.Lascategoríastradicionalesdeformasdevida,diferenciadas
deacuerdoalaposicióndelasyemasinvernales,sondelimitadaaplicaciónenlosecosistemasconcrecimientotodoelaño,co-
mosucedeenlosbosqueslluviosostropicales.LasformasdevidamásricasenespeciesenelbosquedelaregióndeGolfoDulce
sonlosárboles,seguidosporlashierbas,pequeñasplantasleñosasyepífitas.El15%detodaslasespeciesdeplantasvascularesson
arbustosoárbolespigmeos,queusualmentenoexcedenlos5metrosdealtura,10%sonpequeñosárbolesquealcanzan10m,y
26%sonárbolesquecrecensobrelos10m.Lashierbasterrestresalcanzanal19%,epífitasleñosasyherbáceasal12%,hemiepí-
fitosel3,3%,lianasel7%,enredaderasnoleñosasel5,4%yhemiparásitas,parásitasyplantasacuáticasalcanzanmenosdel1%
delafloralocal.Estainvestigacióndiscuteelsignificadoadaptativodelasdiferentesformasdevidaycomparalavariedaddefor-
masdevidaencontradasenelareadeGolfoDulceconladeotrosbosquesneotropicales.
Palabrasclave:formasdevidavegetal,bosquelluviosoneotropical,CostaRica.
Introduction life-formclassificationfortemperateareashasitslimits
whenappliedtotropicalvegetationasitgroupslianas
Globally,ecosystemsareoftendefinedbythecom-
with trees in megaphanerophytes on the one hand,
position of plant life forms present. They characterise
whileontheotherhandtherearehardlyanygeophytes
the structure of the ecosystem and reflect the adapta-
andtherophytesorbiennialsinrainforests.ELLENBERG
tionsandadvantagesthatindividuallifeformspresent.
(1979)drewacoarsecomparisonbetweenthelifeform
Plant life forms have been popularised by Raunkiaer’s
spectra of tropical lowland forests, and characterised
classification, which distinguishes plants according to
rainforests by the dominance of evergreen trees, the
the location of their hibernating buds from megapha-
presence of epiphytes, lianas and chamaephytes, and
nerophytes, with buds well above the snow cover, to
theabsenceofallothergroupssuchastherophytesand
therophytes,whichsurviveasseeds.Althoughrainfor-
geophytes.Laterauthorsmorecommonlydistinguished
est plants need no hibernating buds, most of Raunki-
at least trees, shrubs, lianas, epiphytes and terrestrial
aer’slifeformscanbereadilyrecognisedinrainforests. Stapfia88,
herbs,asdefinedbelow. zugleichKatalogeder
To account for tropical life forms, Raunkiaer himself
oberösterreichischen
lateraddedaerophytesfornon-parasiticplantsgrowing Life form spectra are strongly affected by sample Landesmuseen
NeueSerie80(2008):
onotherplants,i.e.epiphytes.Evenso,thetraditional size.Whensamplingisbasedonforestplots,often1ha
129-142
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orless,treestendtobeunderrepresented,iffornooth- ferentspecimensofaspeciesweredescribedwithdiffer-
erreasonsthansimplybecauseofthemuchlowernum- entlifeforms,cross-checkedwithotherpublishedinfor-
ber of individual trees relative to other life forms pres- mationoracceptedasspeciesthataredifficulttoassign
entinsmallareas.Therelationshipbetweenagradual- toasinglelifeform(seediscussionbelow).Inthecase
ly increasing area and the number of species (the of woody plants, which were distinguished into three
species-area curve) in epiphytes often levels off above sizeclasses,thelargestsizesreportedweretaken.Inmost
anareaofca.1.000m2,sothatonehectare,ifsampled cases this information was unambiguous, but a number
intensively, includes most epiphyte species found in a ofspeciesweredifficulttoassigntoasinglelifeform.
givenforest(HIETZ&HIETZ-SEIFERT1995).Bycontrast,
Asothershavenoted(MORIetal.2002),acompar-
thenumberoftreespeciesfoundinonehectareofadi-
isonofplantlifeformspectraiscomplicatedbythefact
verse tropical rainforest trees, is nowhere close to in-
that a part of the flora cannot easily be classified as
cluding all species (CONDIT et al. 1996). As a conse-
therearecontinuafromherbstosubshrubs,toshrubs,to
quence, the ratio of epiphytes to ground-rooted plants
treesofvarioussizes,fromvinestolianas,fromaquatic
(particularly trees) tends to decrease with larger plot
toterrestrialandfromterrestrialtoepiphytesandsome-
sizesorareassurveyed(NIEDERetal.2001),andsimilar
times also between self-supporting woody plants and
biasesarelikelytobefoundforotherlifeforms.Because
climbers or epiphytes. In addition to this, scientists do
largeplantswillalwaysbeunderrepresentedinsmallor
not always agree on how to define these terms, which
evenfairlylargeplots,localflorasofintensivelycollect-
complicatescomparisonsbetweenstudies.Thisproblem
ed locations may be more suitable to analyse life form
spectraofforests. isacknowledgedbyothers,andMORIetal.(2002)sug-
gestedauniversalterminologytoclassifytropicalplant
Another bias when comparing larger areas may be lifeforms,towhichthiscompilationoflifeformsfrom
foundinthedegreeofdisturbanceandfocusofthecol- theGolfoDulceareaadheresasfaraspossible.Thefol-
lection activities. Open habitats tend to have more lowingclassesandsub-groupsareusedinthispaper.
herbaceousspeciesandspeciesthatarenotfoundinthe
Aerial–describesthehabitatofaplantneitheraquatic
forestbygrowinginhighlight,beingweedy,exotic,or
norterrestrial,whoselifecycleiscompletedwholly
simply cultivated plants. The La Selva flora includes
orpartiallywithoutgroundcontactgrowingonoth-
220exoticspecies:197oftheseareherbsandthebulk
of these are grasses and Asteraceae (HARTSHORN & erplants.MORIetal.(2002)considersthisahabitat
ratherthanalifeform.
HAMMEL 1993). Given the number of species in the
Aquatic – plants with or without anchoring roots,
Poaceae (42) and Asteraceae (47) in the checklist of
whoselifecycleiscompletedwhollyorpartiallyin
theGolfoDulceflora,thelistseemsnottobestrongly
water.
affectedbyexoticspeciesthatarenotrepresentativeof
Epiphyte–anon-terrestrial,non-parasiticplantusually
theoriginalvegetation,althoughanumberofnon-rain-
growinguponanotherplantwithnocontacttothe
forestspeciesarecertainlyincludedandnoattemptwas
soilthroughouttheirlifecycle(trueepiphytes)orat
made to identify and eliminate these. In addition, the
leastduringpartsoftheirlife(hemiepiphytes).Ac-
collectionsincludeafewcultivatedplantspeciessuchas
CinnamomumorCitrus,butannualcropssuchaswheat, cording to MORI et al. (2002), the term epiphyte
maize, squash or tomatoes that are certainly cultivated refers to the habit of non-parasitic aerial plants,
intheareahavenotbeensampled(althoughricewas). whereastheirlifeformscanbeherbs,shrubs,etc.A
Cultivated plants are therefore unlikely to distort the number of plants can grow terrestrially or as epi-
pictureofthelifeformspectrum. phytes(facultativeepiphyte),butinthemajorityof
speciesthedistinctionbetweenepiphyticorground-
rootedisclear.Accidentalepiphytes,plantsthatal-
Methods
most invariably grow terrestrially but on rare occa-
Information on life forms of all vascular plant sionsarefoundgrowingontrees,werenotincluded
species collected from the Golfo Dulce region (WEBER inthisgroup.
etal.2001).Apartfromthepublishedfieldguide(WE- Hemiepiphyte – an epiphyte that is attached to the
BERetal.2001)andpersonalexperience,themostim- groundatsomestageofitslifecycle.Hemiepiphytes
portantsourcewas“Tropicos”,theonlineherbariumof areclassifiedaseitherprimaryorsecondary(though
Missouri Botanical Gardens (Tropicos.org), which in- seethediscussionunderthelatterterm).
cludes the original specimen description of the collec- Hemiparasite–achlorophyllousparasiticplantthatde-
tors. For each species where no other information was rives part of its nutrition from its host but obtains
available,theinformationonlifeformsofseveralspec- carbon mostly through photosynthesis. Plants that
imensatTropicoswaschecked,andincaseswheredif- may be partially mycotrophic, particularly orchids,
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arenotincluded hereasthe degreeofparasitismis Trueepiphyte–anepiphytethatisnotattachedtothe
generally unknown. All but one known hemipara- groundatanystageofitslifecycle.
sitesintheareaaremistletoes(whicharenotclassi- Vine–aherbaceousclimbingplantcontinuouslyroot-
fiedasepiphytes). ed in the ground. Since any degree of lignification
Herb–generallyanon-woodyplant,buthereexcluding can be found in climbing plants, some are difficult
plantsalreadycategorisedasaquatic,epiphyte,vine, toassigntoeithervinesorlianas.
orparasite.
To simplify and to compare with other studies,
Holoparasite–aplantwithoutchlorophyllthatderives
groups were sometimes combined as described below.
all carbohydrates and nutrients from its host, in-
Also,severalgroupsthatmaybedifficulttoallocateto
cludingmycorrhizalfungi.
asinglelifeformarediscussed.
Liana – a woody climbing plant always rooted in the
Lianas, which would fall into the megaphanero-
ground.
phytecategoryofRaunkiaer,aredistinguishedfromoth-
Primaryhemiepiphyte–aplantthatstartsitslifeasan
er climbers in being large and woody. As non-woody
epiphyte but later becomes ground-rooted, usually
climbers could be placed either into the herb category
byextendingaerialrootstotheground
ortogetherwithlianasintoagroupofclimbersorvines,
Secondary hemiepiphyte – a plant that starts its life
lianas and vines were distinguished, as far as possible.
rootingintheground,becomesaclimberandsubse-
Some herbs with minor climbing tendencies and
quently loses soil contact. While SCHIMPER (1898)
climberswithminorlignificationweredifficulttoallo-
didnotconsiderplantsthatmaylosetheirsoilcon-
catetooneofthesethreegroups.Lianarecordswereal-
tactashemiepiphytes,laterauthors(BENZING1990;
socheckedwithGILBERTetal.(2006),PUTZ&WIND-
PUTZ & HOLBROOK 1986) and many scientists
SOR (1987), and NEPSTAD et al. (2007). Many aroids
recording epiphytes have used the term secondary
germinate on the ground, become climbers and may
hemiepiphytes.MOFFETT(2000)arguedagainstthis
eventuallylosecontactwiththesoil.Inthiscase,they
practice, preferring the term “nomadic vine” for
can be classified as secondary hemiepiphytes, though
climbers that change their position by growing on
mostindividualswillbecomereproductivebeforelosing
theoneendanddyingoffattheother,wherebythey
soilcontactandifsoilcontactislostatalldependson
cancontinuouslyrootinthesoil,neverrootinthe
species,treeheightandlightclimate.Forsimplicity,all
soil,orcontactthesoilatsomestagesduringitslife.
climbingaroids,exceptforHeteropsis,wereclassifiedas
TheseincludeparticularlyAraceaeandsomeMarc-
secondary hemiepiphytes in so far as they can at least
graviaceae, Cyclanthaceae and possibly a few potentiallybecomeindependentofsoil.Ifonedoesnot
speciesinotherfamilies. wanttoclassthese“nomadicvines”hemiepiphytes,all
Shrub–generallyawoodyplantthatisbranchedclose 35 hemiepiphytic aroids would be placed in the vine
toitsbase(butexcludingmulti-stemmedtreesthat category as they hardly lignify. Also, monocots do not
branchonlyatgroundlevel)irrespectiveofheight. normally show the secondary growth typical of lianas,
Here, shrubs are all ground-rooted, self-supporting but the climbing palmDesmoncus was classified as a
woodyplantsnotnormallyexceeding5minheight. lianaasitsstemisdistinctlywoodierthanthatofaroids.
Strangler – a primary hemiepiphyte whose aerial roots Also, many primary hemiepiphytes can become fertile
anastomoseandbecometightlyencirclingthehost and conclude their life cycle before rooting in the
tree, which may eventually cause the death of its groundorwillneverdosoifperchedhighinthecanopy.
host. Here,allthataredesignedtorootinthesoilbysending
Subshrub–aplantintermediatebetweenanherbanda long aerial roots downwards are considered primary
shrub,andonlyslightlywoodyorwoodyonlyatthe hemiepiphytes,irrespectiveofhowoftenthisisseenin
base. thefield.Sincethedistinctionbetweenshrubsandsub-
Tree–awoody,erectplant,occasionallywithmultiple shrubs (subfrutices) is particularly gradual, the ca. 20
stems, that grows to >10 m (MORI et al. 2002) de- subshrubswerealsoclassifiedasshrubs.
finedtreesasplantswithadiameteratbreastheight Ultimately,whichlifeformaspeciesisputintoalso
(d.b.h.) ≥ 5 cm, others distinguish trees above and dependsontheresearchquestion,andscientistswitha
below10cmd.b.h.,butthisinformationislessread- particular interest in epiphytes (such as the author of
ilyavailableforallplantslisted). thismanuscript)tendtoseeanepiphyteineveryplant
Smalltree:awoody,erectplantthatreaches>5mbut thatmaypossiblybecomeone,andpeopleinterestedin
rarely > 10 m (according to MORI et al. 2002, a climbers,treesorotherlifeformsdolikewise.Tostillbe
treeletisasmalltree<5cmd.b.h.and>2mtallat abletocomparethelifeformspectrumoftheareawith
maturity);othersgrouptreesofdifferentsizesdiffer- otherlistsorre-groupclassestosuitotherinterests,the
ently. mainclasseshaveinsomecasesbeensubdivided.
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Results
800 Outof2.378vascularplantspeciesreportedforthe
Golfo Dulce region, 851 are trees, including four tree
fernsand238woodyplantsthatgrowbetween5and10
s 600 m tall, but excluding 27 primary hemiepiphytes, more
e
ci than half of which can also grow into free-standing
spe >10m trees. 352 species are classified as shrubs, woody, free-
of standing plants < 5 m height, including some 20 sub-
er 400
mb sec. HemiE. shrubs (Fig. 1). Of the 303 climbing plants, 131 were
u prim HemiE herbaceous(vines)and172woody(lianas).Inaddition,
N
there are 52 climbers (woody or herbaceous) that are
Lianas
200 classified as secondary hemiepiphytes or nomadic
<10m True HemiP climbers.290speciesaretrueepiphytes,includingafew
Vines
HoloP facultativeepiphytesbutexcluding27primaryhemiepi-
phytes, 17 hemiparasitic mistletoes and one parasitic
0
Trees Shrubs mi)Epiphytes Climbers mi)Parasites Aquatic Rppaaarrfaaflsseiittseeiasc(aeXraeiemtee(nArriaepsotdaramianelt,rhieacsanndcaa,1se9Oanrliaoacena)-.cpeaOarean)seitaiocnthdpelar1n7htsetmrauriee-
(He (He aquatic. 449 plants are classified as herbs, which are
herbaceousplantsthatdonotfallintoanyoftheprevi-
Fig.1:LifeformspectrumofvascularplantsfromtheGolfoDulceregion.
ous categories of (hemi)epiphyte, climber, aquatic, or
(hemi)parasite.
Fig.2:Familiesof Trees Shrubs
trees(left)and
shrubs(right)with Fabaceae Rubiaceae
themostspeciesin Rubiaceae
theGolfoDulce Melastomataceae
Lauraceae
area.Shrubsare
Moraceae Piperaceae
free-standing
woodyplants<5m Sapotaceae Arecaceae
tall,treespecies Annonaceae
Fabaceae
typicallyreachinga Melastomataceae
sizebeloworabove Euphorbiaceae Solanaceae
10mare Chrysobalanaceae Euphorbiaceae
<10 m
distinguishedon Clusiaceae
theleft-hand Flacourtiaceae >10 m Asteraceae
graph. Arecaceae Acanthaceae
0 20 40 60 80 100 120 0 20 40 60 80
Number of species Number of species
Fig.3:Familiesof Climbers Herbs
climbers(left)and
herbs(right)withthe Fabaceae Pteridophyta
mostspeciesinthe Bignoniaceae Poaceae
GolfoDulcearea. Sapindaceae Asteraceae
Climbersaredivided Marantiaceae
Apocynaceae
intowoodylianasand Cyperaceae
Cucurbitaceae
non-woodyvines. Acanthaceae
Passifloraceae
Araceae
Convolvulaceae
Fabaceae
Malphigiaceae
Costaceae
Dilleniaceae Heliconiaceae
Ferns Rubiaceae
Liana
Hippocrataceae Euphorbiaceae
Vine
Dioscoreaceae Gesneriaceae
0 20 40 0 20 40 60 80
Number of species Number of species
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Epiphytes Hemiepiphytes Fig.4:Familiesofepiphytes
(left)andhemiepiphytes(right)
withthemostspeciesinthe
Orchidaceae Araceae
GolfoDulcearea.Primary
Pteridophyta Clusiaceae hemiepiphytesgerminateona
treeandlaterrootinthe
Bromeliaceae
Moraceae groundsoil;secondary
Araceae hemiepiphytesgerminateinthe
Marcgraviaceae
Gesneriaceae soil,climbatree,andlaterlose
Cecropiaceae soilcontact.
Piperaceae
Cyclanthaceae
Cactaceae
Primary H
Ericaceae Araliaceae Secondary H
Melastomataceae Scrophulariaceae
0 20 40 60 80 100 0 20 40
Number of species Number of species
In addition to trees, shrubs and lianas, all primary limited water supply limits the establishment of large
hemiepiphytes and all hemiparasites are woody plants, woody plants, which explains the dominance of trees
butonlyaboutonedozenofthenomadicclimbers,most overotherlifeformsoratleastthehigherproportionof
ofwhichareherbaceousaroids.Intotal,1.450speciesare treesinrainforestscomparedtoothervegetationtypes.
woodyand928herbaceous,1691speciesareself-support- Thehightreediversityintropicalforestsisasomewhat
ingand687aredependent,i.e.epiphyticorclimbing. differentquestion,sinceananswerofthatmustalsoex-
plainhowthishighnumberofspeciescancoexistwith-
Trees
50
All forests are dominated by trees, but, in contrast Trees Shrubs
to most other forests, trees may dominate in tropical 40 r2=0.90 r2=0.22
rainforestnotonlyintermsofbiomassbutalsointerms 30
ofdiversity.Ofthe851treespeciesrecorded(represent-
20
ing36%oftheentirevascularflora),238donotgener-
ally grow to > 10 m in height. These small trees were 10
dominated by Rubiaceae and Melastomataceae, fol- 0
lowedbyFabaceae,FlacourtiaceaeandLauraceae.Taller 50
Herbs Vines
trees were strongly dominated by Fabaceae s.l. with 97 es 40 r2=0.95 r2=0.74
species,withInga,themostspecies-richgenusoftrees, ci
e 30
comprising 34 species. Of the leguminous trees, 48 be- p
s
longtotheMimosaceae,31totheFabaceaeand18to of 20
theCaesalpiniaceae.Othertreefamiliesdominatingthe % 10
forest are Lauraceae, Sapotaceae (with 23 species in
0
Pouteria)andMoraceae(Fig.2).Ficusispresentwith23
50
species,ofwhich14wereclassifiedastreesandtherest Lianas Epiphytes
asprimaryhemiepiphytes.Foursmalltreesaretreeferns 40 r2=0.04 r2=0.05
and17treesarepalms. 30
20
Many shapes of tropical trees have been described,
which are not always easy to recognise in the field 10
(HALLÉ et al. 1978). In the Golfo Dulce area, as in 0
other rainforests, buttresses are common in large trees 1 10 100 1000 1 10 100 1000
(Fig. 6). Individual emergent trees in the forest can Area (km2) Area (km2)
reach60morevenmore,typicallyhavelargebuttress-
esandastraight,unbranchedstemtotheuppercanopy. Fig.5:Contributionofdifferentlifeformstovascularplantdiversityin
Treesofthisheightandwithad.b.h.substantiallyover neotropicalwetforests(filledcircles),moistforests(half-filledcircle)anda
dryforest(emptycircle)relatedtotheareasampledforaregionalplant
than1marerareandtheclosedforestcanopyreachesa
list.IndicatedisPearsonr2fordatapointsonalogarithmicscale,excluding
heightof30-40minmostplaces.
thedryforest.DataarebasedonTable1,withtheexceptionofCapeira,
forwhichnoareawasavailableandtheflorawasneverfullypublished.
Treesarethelogicalandmostcompetitivelifeform
Epiphytesincludehemiepiphytes.Thewetforest(fullsymbol)at560km2
in an environment where neither low temperature nor representstheGolfoDulceforest.
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Fig.6:Buttressesare pressedunderstoryplantsandepiphytes(forreviewssee
commoninlarge e.g., HARMS et al. 2000, WRIGHT 2002, LEIGH et al.
rainforesttrees,but
2004). Thisquestion iscentral in understandingtropi-
giantssuchasthis
Ceibapentandraare caltreeandgeneralforestdiversitybutbeyondthepres-
rare. entcomparisonoflifeforms.
Shrubs
The term shrub generally refers to a woody plant
with basal branching, irrespective of plant height. In
temperate areas, shrubs are common, sometimes more
species-richthantreesandinallbutafewcasesreadily
distinguishable from trees (Fig. 7, 8). In tropical rain-
forests,thislifeformislesscommon,mainlybecausethe
lowlightatthegroundlevelmakesbasalbranchingand
therebyexposingleavesclosertothegrounduneconom-
ic.Somesmallwoodyplantsarethussometimescalled
pygmy trees as they have a tree-like habit but remain
small.Inourareashrubs/pygmytreesaredominatedby
Rubiaceaewithmanygenera,themostimportantbeing
Psychotria,followedbyMelastomataceae(withMiconia)
andPiperaceae(onlyPiper)andsmallpalms(Fig.2).It
is noteworthy that Piper, Psychotria, andMiconia, with
Fig.7:Manywoody 41, 40 and 35 species, respectively, are the three most
plantsinthe
species-rich genera of all life forms in the area, which
rainforestunderstorey
meansthatalmostoneinthreeofthe352shrubspecies
arepygmytrees,
includingsmallpalms belongstooneofthesethree.
suchasthis
Asterogynemartiana. Herbs
Among the 449 non-aquatic, non-parasitic and
non-epiphytic herbs, pteridophytes are by far the
largest group with 76 species (Fig. 3). Pteridophytes
(mainly ferns plus a number of clubmosses and two
horsetails), of course, comprise several families, and
withintheterrestrialferns,themostspecies-richfami-
lies are Pteridiaceae, Thelypteridaceae, Dennstaedti-
aceae and Tectariaceae (Fig. 9). Poaceae as well as
Cyperaceaeareveryuncommonintheunderstoreyand
sign of natural disturbance or other open habitat such
as riverbanks, or were collected from anthropogenic
habitats,whichtoalesserextentisalsotrueforAster-
aceae and Fabaceae. By contrast, most ferns, Gesneri-
aceae,Acanthaceaeandsmallpalmsgrowintheshady
understorey of rainforests. The low light available on
the rainforest soil challenges any plant to maintain a
out most being displaced by the most competitive
positive carbon balance. As an adaptation to very low
species.Thisfacthasbeenmuchdiscussedandvarious light, several rainforest herbs and also small shrubs
theorieshavebeenbroughtforward,somebynowwell- have corrugated upper leaf surfaces and an antho-
founded in ecological theory and field studies. Parts of cyanin-richlowerepidermisthatcollectivelymaximise
theanswerappeartobehigherratesofspeciationinthe the proportion of light absorbed by the leaves which
tropics,alonghistoryofspeciationwithoutlarge-scale canthenbeusedforphotosynthesis(Fig.10).
extinction, density-dependent mortality driven by
Marantiaceae, Costaceae and Heliconiaceae and
pathogensandpests,nichedifferentiation,intermediate some Araceae (Diffenbachia, Anthurium) are monocot
rates of disturbance, non-equilibrium between poten- herbswithoftenverylargeleafareas.Many,thoughnot
tiallycompetingspecies,and littlecompetitioninsup- allorthese,tendtogrowabundantlyingaps,forestmar-
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gins, steep slopes, rivers margins or other spots where
more light reaches the forest floor but where they are
lessexposedtodryairthanincompletelyopenhabitats
(Fig.11).Heretheabundantsunlightcapturedbylarge
leaves allows for high rates of photosynthesis. These
plantsconsequentlygrowfast,butastheyinvestlittlein
anystructurethatcouldhelpthemgrowupwards,they
aresoonerorlateroutgrownbytallerplantswhenforest
successionclosesthegap.
The19aquaticplantsarefrom12differentfamilies,
the largest with only five species being the Pontederi-
aceae(Fig.12).
Onelifeformwhichisnotreportedfromevergreen
tropical regions is annual. For this study, annuals were Fig.8:Rubiaceae(Psychotriaelata)arethedominantfamilyofshrubsand
notclassified,amongotherreasonsbecausethisisrarely smalltrees.
notedonherbariumvouchers,butquiteprobablynone
oftheplantsrecordedclassifiesasanannualsincethere
isnounfavourableseasonthataseedmighthavetosur-
vive.Similarly,geophytesandhemicryptophytesarenot
normally present in tropical rainforests (ELLENBERG
1979). Where rainforest plants have a short live span,
this is mostly due to death caused by herbivores,
pathogens, competitors or a combination of these fac-
tors and these species tend to invest most resources in
rapidgrowthandlittleindefence.Alsorarebutnotun-
heard-of are monocarpic rainforest plants, which may
beperennialbutdieafterfruitingandthushavealimit-
ed life-span. These include some bromeliads and, sur-
prisingly,thetreegenusTachigalli.
Fig.9:Filmyferns(Hymenophyllaceae:Trichomanesreniforme)areadaptedto
veryhumidandshadyenvironmentsandfoundasepiphytesonthelower
Climbers stemorontherainforestfloor.
While herbaceous climbers (here, the term vine is
limitedtoherbaceousplants)arealsocommonintem-
perateareas,lianas(woodyclimbers)arewithafewex-
ceptionslimitedtotropicalzones,thoughnotnecessar-
ilytoveryhumidclimates.Mostofthe128vinespecies
arefoundintheFabaceaeandCucurbitaceae(bothalso
common in temperate zones) and the largely tropical
genusPassiflora.Inaddition,35climbingaroidsatleast
starttheirlivesasvines.Themostimportantlianafam-
ilies are Bignoniaceae, Fabaceae, Sapindaceae, Apocy-
naceae and Malpighiaceae (Fig. 4). If secondary hemi-
epiphytesornomadicclimbersarecountedasclimbers,
thenumberofvinesincreasesto163andthenumberof
lianasto189.Manyepiphyticfernshavelongcreeping
rhizomesandwouldthusclassifyasnomadicvines(sen-
suMOFFETT2000),but,beingmostlyepiphyticandnot
reallychangingtheirpositionbygrowingattheoneand
dyingoffattheotherend,theyareallclassifiedasepi-
phytes.Afewfernsinseveralfamilies(Bolbitis,Danaea,
Metaxya, and Lygodium) are true climbers with very
Fig.10:Leavesofrainforestplantsinextremeshadearesometimesrichin
long,thinrhizomesthatcanclimbmanymetresupona
anthocyansattheabaxialsideandhavecorrugatedadaxialsurfacesto
treebutdonotnormallylosesoilcontact(Fig.13). maximiselightcapture.
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Lianas are perennial, woody plants that have their
regenerationbudsabovegroundandwouldbeclassified
as phanerophytes in the Raunkiaer system (Fig. 14).
Whilemanytreespeciesareabletosurvivethetemper-
atewinter,mostlianasapparentlyarenot,andtheirdi-
versity strongly declines outside the tropics at higher
latitudes than ca. 25° (PUTZ & MOONEY 1991). The
likelyreasonisthatthewater-supplysystemoflianasis
designedforveryefficienttransportofwaterthrougha
comparatively thin stem. To do so, they produce very
largevesselsinwhichwatercanbetransportedfast,but
which are vulnerable to freezing in winter. Within the
tropics, liana diversity is highest in wet forests with
rainfall>3.000mmperyearandashortornodrysea-
son(CLINEBELLetal.1995).
Climbers differ in the strategies they employ to
Fig.11:Megaphyllherbsdominategapsandotherareaswheremorelight
moveintothecanopyandthesedifferencesarealsore-
reachestheunderstorey.
flectedindifferentecologicalroles.Intwinerseitherthe
main stem or branches grows clockwise or anti-clock-
wisearoundthesupport.Intendrilclimbers,stemorleaf
(or rarely root) tendrils show autonomous circular
movements and react upon contact by making a few
loopsaroundthesupport.Twinersandtendrilclimbers
can only hold onto relatively thin stems and branches
and are therefore not able to climb upwards on a large
tree. To reach the canopy they normally establish on
youngtreesandgrowupwardswiththeirsupport.Once
there,theycanbuildlargecrowns,whichcanspansev-
eral tree crowns and connect these. Scramblers attach
with hooks, thorns, rigid trichomes or simply stiff
branches that can find some hold in neighbouring
plants. A typical scrambler is the palm Desmoncus
costaricensis, which scrambles between branches with
spiny stems, petioles and rachis, and stiff spreading
Fig.12:Eichhorniacrassipes,afree-floatingaquaticplant. leaves.Desmoncusandsomeotherlargewoodyclimbers
wouldbeclassifiedassmalltreesintheirjuvenilephase
whenthesmallstemismoreorlessself-supporting,but
are clearly climbers later. Plants climbing with their
rootsattachingtothetreestem(rootorboleclimbers:
common in Araceae, Cyclanthaceae, Marcgraviaceae
and 11 climbing ferns), are able to climb branchless
stemsofanydiameter,butrarelyreachtheoutercrowns.
Somerootclimbersalsohavelongaerialrootsthatcan
growdownwardsformanymetresandwhenthesegrow
intothesoil,theycanprovideadditionalsupplyofwa-
terandnutrients.Twinershavetypicallyhighergrowth
ratesthanrootclimbers,whichisimportantforthemas
theyhavetokeeppacewiththeupwardgrowthofthe
tree.
Byinvestingrelativelylittleintheirstem,lianascan
build a massive leaf biomass, which can represent
10-30% of the entire forest, and become serious com-
Fig.13:Vines,non-woodyclimbers,includeseveralfernssuchasBolbitis
nicotianafolium. petitors with trees. Most lianas have small, wind-dis-
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persedseedsthatgerminateinlightasdothoseofpio- Fig.14:Aristolochia
neer trees. Others germinate in the shade and are re- grandiflora,aliana
withlargeflowers
leasedwhenagapformsorgrowtowardsatreestemin
andadissectedxylem
theunderstoreyandstarttheirupwardmovementfrom typicalformany
lowlightconditions.Becausemostlianasarelight-lov- lianas.
ing,cangrowtowardslightveryfast,andusuallysurvive
atreefall,theygrowmostdenselyindisturbedsites,par-
ticularlyingapsbutalsoforestmargins(Fig.15).Here,
they compete with trees and can dominate and deter-
mine the succession for many years and thus become
important players in the dynamics of rainforests
(SCHNITZER&BONGERS2002).
Epiphytes
The current plant list includes 290 true epiphytes,
27 primary hemiepiphytes, 17 plants that grow as
woodyclimbersbutcouldeventuallylosecontactwith
thesoil(groupedhereareseveralMarcgraviaceae,Cy-
clanthaceae, Schlegelia in the Scrophulariaceae and a
fewothers)and35climbingaroidsthataregenerallyin
the group of secondary hemiepiphytes (Fig. 4). The
most species-rich groups of true epiphytes are Orchi-
Fig.15:High
daceae, Pteridophytes (with the main families being abundanceoflianas
Polypodiaceae, Lomariopsidaceae and Grammiti- intheclosedforest
daceae), Bromeliaceae, Araceae (Anthurium with 20 oftencharacterises
ancientgaps.
species), Gesneriaceae, and Piperaceae (Peperomia)
(Fig. 4, 16, 17). Primary hemiepiphytes as classified
hereareallwoodyplants.Some(particularlyFicus,but
sometimes also Coussapoa) grow into free-standing
treeswhentheirhosttreedies,othersrarelygrowtoin-
dependent trees and remain supported by their host
throughout their life cycle. Ficus, Clusia, Coussapoa,
Oreopanaxandpossiblyothersformanastomosingroots
thatcanencirclethestemoftheirhost.Ifastrangleris
a hemiepiphyte that kills its host by restricting lateral
growthandultimatelyphloemtransport,probablyonly
Ficusspp.andrarelyindividualsofotherspeciesclassi-
fy as true stranglers. There are rather few herbaceous
plantsthatarefacultativeepiphytes(afewaroidspecies
can regularly be found growing either on a tree or the
soilorrocks),butthereismoreambiguityinthegroup
of woody (hemi)epiphytes. For simplicity, Ericaceae,
Gesneriaceae, Melastomataceae, Rubiaceae (Hillia)
and Solanaceae (Juanolloa) were classified as woody
epiphytes though some species of Drymonia (Gesneri-
dendron, Syngonium, Fig. 18). Whether ground-rooted
aceae),Blakea,Clidema(Melastomataceae)andJuanol-
climbers eventually lose soil contact depends on the
loacanalsobefoundgrowingaslianas.
species, the light climate and water availability. On a
Aroids present a particularly diverse group of life well-illuminatedstem,plantsflowerearlyandthelower
forms,growthhabitsandlocations(CROAT1988).Some parts receive enough sunlight to maintain a positive
arestrictlyterrestrial(Diffenbachia,Spathiphyllum,anda biomass balance, or at least are useful enough in terms
few species of Anthurium) while others are strictly epi- ofsupplyingwatertobemaintainedbytheupperleaves.
phytic (most Anthurium species). Many are climbers, Bycontrast,plantsthatescapetheshadyunderstoryare
someofwhichareentirelyepiphytic(Stenospermation), lesslikelytomaintaintheloss-makinglowerparts,par-
but more commonly start rooted in the ground (Philo- ticularly when adventitious roots can absorb sufficient
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Fig.16:Orchids(Plerothallisorbiculare)arethemostspecies-richgroupof
epiphytes.
Fig.18:Manyaroidsareclimbers(Philodendron
scandens)thatmaylosesoilcontactastheygrow
upwardsonthestem.
Thediversityofvascularepiphytesisclearlyrelated
totheyear-roundhightemperatureandwatersupplyin
rainforests (BENZING 1990). Without access to soil wa-
ter, they rely on rain percolating through the canopy
and only species with special provisions to survive
longer drought can grow in drier forests. Even more
than drought, low (freezing) temperatures exclude all
Fig.17:Cochliostemmaodoratissima,ofafamilywithfewepiphytes but very few epiphytes from temperate forests. The
(Commelinaceae)hasadaptedtotheepiphytichabitatbyarrangingitsleaves abundance of epiphytes is generally higher in tropical
inarosettethatensuresthatwaterandleaflitteristrappedanddirected
montane forests, where branches can be completely
towardstheroots.
covered with epiphytes and decomposing organic mat-
ter builds thick layers of canopy soil. By contrast, in
waterfromtheabundantrainfallandstemflow.Thus,a
most lowland forests including the one of the Golfo
species that never loses soil contact and remains a
Dulce area, epiphytes may be species rich but their
climber in a drier forest may well be found as an epi-
abundanceismostlymoderate.Thecauseoftherather
phyteinawetrainforest.Afewclimbingaroids(Philo- sparse growth of epiphytes in most lowland forests is
dendronsagittifolium)willgerminateeitheronthesoilor mainly an effect of water supply and demand. First,
onthetree.Ifthesehavebecomelargeplants,itisim- thoughtotalrainfallisveryhigh,onlytherainthatre-
possible to tell if they started life on the soil (are sec- mains on the branches or can be readily absorbed or
ondary hemiepiphytes) or in the canopy (true epi- storedbyepiphytesisofanyuse.Inlowlandrainforests
phytes).Finally,ifanindividualthatgerminatedonthe whereprecipitationcomesmainlyinstrongdownpours,
tree sends long aerial roots to the soil, it will have be- the amount intercepted is a small proportion of total
comeaprimaryhemiepiphyte(Fig.19). rainfall.Andsecond,thehighertemperatureinlowland
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