Nature and Structure of the Climax

Transcription

NATURE AND STRUCTURE OF THE CLIMAX
BY FREDERIC E. CLEMENTS
Santa Barbara, California)
(CarnegieInstitutionof Washington,
(WithPlates VI-XI)
CONTENTS
PAGE
...253
INTRODUCTION
THE CLIMAX CONCEPT .253
NATURE
OF THE
.254
CLIMAX
Unity of the climax.254
Stabilisationand change.255
Originand relationship.257
Tests of a climax .257
.261
CLIMAX AND PROCLIMAX
261
262
Essential relations.
Proclimaxes
Subelimax .262
Disclimax
265
266
267
Preclimax and postclimax.
Preclimax
Postclimax .269
STRUCTURE
OF THE CLIMAX .270
270
270
Community functions.
Roles of the constituent species: dominants
.271
.
Influents
Climax and seral units
.
Climax units
..273
Association
..274
..274
Consociation
Faciation
Lociation ..
Society
Sociation
Lamiation
Sation
Clan
TABLE
AND
Panclimax
.278
.
..280
CORRESPONDENCE
OF CLIMAX
275
..275
..276
..277
..277
..278
Seral units
Serule
RANK
.271
.272
.
AND
SERAL
and eoclimax
280
OF UNITS
UNITS
.
.
.
.
.
.
Prerequisites to research in climaxes
REFERENCES
..
281
.
.
.
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283
FREDERIC
E.
CLEMENTS
253
INTRODUCTION
MOREthan a centuryago whenLewis and Clarkset out upon theirmemorable
journeyacrossthe continentofNorthAmerica(1803-6), theywerethe firstto
traversethe greatclimaxesfromdeciduouswoodsin the east throughthe vast
expanse ofprairieand plain to the majesticconiferous
forestofthe north-west.
At this timethe oak-hickorywoodlandbeyondthe Appalachianswas almost
untouchedby the ax except in the neighborhoodof a fewstragglingpioneer
settlements,and west of the Mississippihardlyan acre of prairiehad known
the plow. A few years later (1809), Bradbury states that the boundless
prairiesare coveredwiththe finestverdureimaginableand willbecomeone of
the mostbeautifulcountriesin the world,whilethe plains are of such extent
and fertility
as to maintainan immensenumberof aniimals.It appears probable thatat thistimeno othergrasslandin the worldexhibitedsuchmyriadsof
large mammalsbelongingto but a fewspecies.
The naturalinference
has been that the prairiesweremuchmodifiedby the
grazingofanimalsand the firesofprimitiveman, and thishas been reinforced
by estimates of the population of each. Seton (1929) concludes that the
originalnumberof bison was about 60 millionwith a probable reductionto
40 millionby 1800, and that both the antelope and white-taileddeer were
equally abundant,whileelk and mule-deereach amountedto not more than
10 millionat the maximum. However, these were distributedover a billion
or two acres,and the averagedensitywas probablynevermorethan a scoreto
the square mile. Estimatesofthe Indian tribesshowthe greatestdivergence,
but it seems improbablethat the total populationwithinthe grasslandever
exceeded a half million.The generalhabit of migrationamong the animals
furtherinsuredthat seriouseffectsfromovergrazingand tramplingwere but
whilethe influenceoffiresset by the Indians was even less
local or transitory,
in modifying
the plant cover. As to the forests,thoseofthe northsignificant
westwerestillprimevaland in the east theywereyetto be changedoverwide
areas by lumberingand burningon a large scale.
THE
CLIMAX CONCEPT
The idea of a climaxin the developmentof vegetationwas firstsuggested
by Hult in 1885 and thenwas advanced moreor less independently
by several
investigatorsduringthe next decade or so (cf. Clements,1916; Phillips,1935).
It was applied to a more or less permanentand finalstage of a particular
ofa restrictedarea. The conceptofthe
successionand henceone characteristic
climaxas a complexorganisminseparablyconnectedwithits climateand often
continentalin extentwas introducedby Clements(1916). Accordingto this
view,the climaxconstitutesthe majorunitofvegetationand as suchformsthe
basis forthe naturalclassificationofplant communities.The relationbetween
climateand climaxis consideredto be the paramountone, whilethe intimate
254
Nature and Structureof the Climax
ofthetermsfromthe
bythederivation
bondbetweenthetwois emphasized
underthisconceptclimaxis invariably
same Greekroot. In consequence,
alone,namely,the forto the climaticcommunity
employedwithreference
mationoritsmajordivisions.
that animalsmustalso be considered
At the outsetit was recognized
members
oftheclimax,and thewordbiomewas proposedforthepurposeof
1916b;
layingstressuponthe mutualrolesofplantsand animals(Clements,
thattheprimary
1936). Withthiswenttherealization
andShelford,
Clements
by virtueofthefact
different
to thehabitator ece werenecessarily
relations
and animalsconsuments.On land, moreover,
that plantsare producents
withthe
thefixedmatrixofthebiomein directconnection
plantsconstitute
climate.
to
to
well
as
as
relation,
plants
a
dual
climate,whiletheanimalsbear
oftheoneis displayedin reactionupontheece,ofthe
effect
The outstanding
the primarybond of the
otherin coactionupon plants,whichconstitutes
bioticcommunity.
Becauseofits emphasisuponthe climaticrelation,the termclimaxhas
whichis regardedas an
comemoreand moreto replacethewordformation,
and thisprocessmayhave beenfavoredby a tendencyto
exact synonym,
"
" climatic
use.Thedesignation
formation
withthegeological
avoidconfusion
to
is
accentuate
its
nature
but
this
merely
been
employed,
has nowand then
climaxandbiome
lessdefinite
itfrom
usages.Furthermore,
andto distinguish
is to be indicated,
though
whenthebioticcommunity
synonyms
arecomplete
forthe matrixwhenplants
continueto be employed
climaxwillnecessarily
aloneareconsidered.
NATURE
OF THE CLIMAX
detailin earlierworks
This themehas been developedin considerable
1929),as wellas ina recent
1916,1920,1928;WeaverandClements,
(Clements,
accountof
treatment
byPhillips(1935),andhencea summary
comprehensive
inthepresent
willsuffice
place.Thesemaybe conveniently
themajorfeatures
andchange,
i.e. unity,stabilization
fourcaptions,
groupedunderthefollowing
and objectivetests.
originand relationship,
Unityoftheclimax
unity'oftheclimaxrestsuponthefactthatit is notmerely
The inherent
and
climate,butis at thesametimetheexpression
to a particular
theresponse
the
and
theindicatorofit. Becauseofextent,variationin space and time,
human
ofthe
to saynothing
intoadjacentclimates,
usuallygradualtransition
equation,neitherphysicalnorhumanmeasuresof a climateare adequately
and sessilenatureofthe
thevisibility,
continuity,
By contrast,
satisfactory.
limits
the fluctuating
are peculiarlyhelpfulin indicating
plantcommunity
growthand
of a climate,whileits directresponsein termsoffood-making,
factors.Naturally,
ofphysical
thefullest
possibleintegration
life-form
provides
FREDERIC E. CLEMENTS
255
both physicaland human values have a part in analyzingand in interpreting
the climateas outlinedby the climax,but these can onlysupplementand not
replace the bioticindicators.
It may seem logical to inferthat the unity of both climax and climate
but reflection
willmake clearthat
shouldbe matchedby a similaruniformity,
such is not the case. This is due in the firstplace to the gradual but marked
shiftin rainfallor temperaturefromone boundaryto the other,probablybest
illustratedby the climateof the prairie. In termsof precipitation,the latter
may range along the parallel of 40? fromnearly40 in. at the easternedge of
the true prairieto approximately10 in. at the westernborderof the mixed
grassland,or even to 6 in. in the desertplains and the Great Valley of California. Such a change is roughly1 in. for50 miles and is regionallyall but
imperceptible.The temperaturechange along the 100th meridianfromthe
mixed prairiein Texas to that of Manitoba and Saskatchewanis even more
striking,since only one association is concerned. At the south the average
periodwithoutkillingfrostis about 9 months,but at the northit is less than 3,
while the mean annual temperaturesare 70 and 330 F. respectively.The
variation of the two major factorsat the extremesof the climatic cycle is
likewisegreat,the maximumrainfallnot infrequently
amountingto threeto
fourtimesthat of the minimum.
The visible unity of the climax is due primarilyto the life-form
of the
dominants,which is the concreteexpressionof the climate. In prairieand
steppe, this is the grass form,with which must be reckonedthe sedges, especially in the tundra. The shrub characterizesthe three scrub climaxes of
North America, namely, desert, sagebrush,and chaparral, while the tree
appears in threesubforms,
coniferous,
deciduous,and broad-leavedevergreen,
to typifythe corresponding
boreal,temperate,and tropicalclimaxes.The lifeformis naturallyreflectedin the genus,thoughnot withoutexceptions,since
herbor shrub,deciduousor evergreen,annual
two or moreformsor subforms,
or perennial,may occur in the same genus. Hence, the essentialunity of a
climaxis to be soughtin its dominantspecies,sincetheseembodynot onlythe
life-form
and the genus,but also denotein themselvesa definiterelationto the
climate. Their reactionsand coactions are the most controllingboth in kind
and amount, and thus they determinethe conditionsunder which all the
remainingspeciesare associated withthem.This is trueto a less degreeofthe
animal influents,thoughtheircoactionsmay oftenbe more significantthan
those of plants.
Stabilizationand change
Under the growingtendencyto abandon static concepts,it is comprehensiblethat the pendulumshould swingtoo far and changebe overstressed.
This consequenceis fosteredby thefactthat mostecologicalstudiesare carried
out in settledregionswheredisturbanceis the rulingprocess. As a result,the
256
or evenabsentoverwideareasand subseresare
climaxis badlyfragmented
or entirely
impossible
difficult
legion. In all suchinstancesit is exceedingly
to
andchange,andit becomesimperative
to strikea balancebetweenstability
by man,whereclimaticcontrolis still
turnto regionsmuchless disturbed
measureoftime,
paramount.It is likewiseessentialto employa conceivable
ratherthanin eons. No
inhumantermsofmillennia
suchas canbe expressed
a doubtthat climaxeshave evolved,
studentof past vegetationentertains
of greatclimaticchanges
migratedand disappearedunderthe compulsion
thattheypersistthrough
fromthePaleozoiconward,buthe is also insistent
disturbances
millions
ofyearsintheabsenceofsuchchangesandofdestructive
the
limitations
of
within
evidence
and
even
conclusive
is
by man.There good
has
been
in
existence
for
several
millions
thattheprairieclimax
fossilmaterials
speciesofto-day.Thisis even
ofyearsat leastandwithmostofthedominant
onthePacificCoast,owingto thewealthoffossil
trueofforests
morecertainly
ofthedeciduous
evidence(Chaney,1925,1935),whilethegenericdominants
similar.
and ofto-dayarestrikingly
oftheDakota Cretaceous
forests
is the universal
that stabilization
affirmed
It can still be confidently
underthe rulingclimate,and that climaxesare
tendencyof all vegetation
inthousands
whenreckoned
oreven
characterized
bya highdegreeofstability
the
devotee
than
one
more
of
No
realizes
succession
ofyears.
clearly
millions
at work,but in the absenceof
and universally
that changeis constantly
ofit.
civilizedmanthisis withinthefabricoftheclimaxand notdestructive
developedas the MiddleWest,the prairie
Even in a countryas intensively
and subdominants
in
relictsexhibitalmostcompletestabilityof dominants
(cf.Weaverand Flory,1934). It is
by cultivation
spiteofbeingsurrounded
obviousthat climaxesdisplaysuperficial
changeswiththe season,year or
thematrixitselflittle
but
these
and
in
as
modify
annuation,
aspection
cycle,
in
be
oneyearand
of
the
desert
annuals
ornotat all. The
may present millions
oneseasonand a
grassmayseemprevailing
absentthenext,oronedominant
or
one the following
different
year,but thesechangesare merelyrecurrent
by bareareasand
represented
indeedonlyapparent.Whilethemodifications
theseareall intheirresistible
process
byseresineverystagearemorestriking,
climateandtheinterference
of
ofbeingstabilizedas rapidlyas thecontrolling
manpermit.
annuationor naturalcoactionare
In brief,thechangesdue to aspection,
no
and
leave
or
whilethoseof
impress,
permanent
fleeting periodic
superficial,
process.Man alone can
successionare an intrinsic
part of the stabilizing
destroythe stabilityofthe climaxduringthe longperiodof controlby its
inconsequence
ofa destruction
thisbyfragments
climate,andheaccomplishes
renewed.
and continually
thatis selective,
partialor complete,
FREDERIC
E.
257
CLEMENTS
Originand relationship
Like otherbut simplerorganisms,each climaxnot onlyhas its owngrowth
and developmentin termsofprimaryand secondarysuccession,but it has also
evolved out of a precedingclimax. In otherwords,it possessesan ontogeny
studied,much
and phylogenythat can be quantitativelyand experimentally
as with the individualsand species of plants and animals (Plant Succession,
1916, pp. 181, 342). Out of the one has come widespread activity in the
investigationofsuccession,whileinterestin the otherlingerson the threshold,
chieflybecause it demands a knowledgeof the climaxes of more than one
continent.With increasingresearchin these,especiallyin Europe and Asia, it
willbe possibleto test criticallythe panclimaxesalreadysuggested(Clements,
1916, 1924, 1929), as well as to determinethe originand relationshipsof the
constituentformations.
This task will also require the services of paleo-ecologyfor the reconstructionof each eoclimax, which has been differentiated
by worldwide
climatic changes into the existingunits of the panclimax or panformation.
As it is, therecan be no seriousquestionofthe existenceofa greathemispheric
clisereconstitutedby the arctic,boreal,deciduous,grassland,subtropicaland
tropicalpanclimaxes. Desert formationsfor the mostpart constitutean exception and may well be regardedas endemic climaxes evolved in response
to regionalchangesof climate(Clements,1935).
It is a significantfact that the boreal formationsof NorthAmerica and
Eurasia are morecloselyrelatedthan the coniferousones of the former,but
thathave
thisseeminganomalyis explainedby the greaterclimaticdifferences
produced the forestsof the Petran and Sierran systems.The five climaxes
concernedare relativelywellknown,and it is possibleto indicatetheirrelationshipswithsome assurance,and all the morebecause oftheirparalleldevelopmenton the two great mountainchains. In the case of deciduousforestand
grassland,onlya singleformationofeach is presentin NorthAmerica,and the
resolvesitselfintotracingthe originand relationship
problemofdifferentiation
of the several associations. It has been suggestedthat the mixed prairieby
virtueof its position,extent and commondominantsrepresentsthe original
formationin Tertiarytimes,an assumptionreinforced
by its close resemblance
to the steppe climax (Clements,1935). It is not improbablethat the mixed
hardwoodsof the southernAppalachians bear a similarrelationto the associationsof the moderndeciduousforest(Braun, 1935).
Testsofa climax
As has been previouslyindicated,the major climaxes of NorthAmerica,
such as tundra,boreal and deciduousforest,and prairie,stand forthclearlyas
distinctunits,in spite of the fact that the prairiewas firstregardedas comprisingtwo formations,as a consequenceof the changes producedby overJourn.of Ecology XXIV
17
258
grazing.The otherconiferousand the scrub climaxes emergeless distinctly
because ofthe greatersimilarityoflife-form
withineach group,and henceit is
necessaryto appeal to criteriaderivedfromthe major formationsjust mentioned.This insuresuniformity
of basis and a highdegreeof objectivity,both
ofwhichare qualitiesofparamountimportanceforthe naturalclassification
of
biomes. In fact, entireconsistencyin the application of criteriais the best
warrantofobjectiveresults,thoughthisis obviouslya procedurethatdemands
a first-hand
acquaintance withmostif not all the unitsconcernedand over a
large portionof theirrespectiveareas.
The primarycriterionis that affordedby the vegetation-form,
as is illustratedby thefourmajorclimaxes.The othersofeach group,suchas coniferous
forestor scrub,are characterizedalso by the same formin the dominants,but
this is not decisive as betweenrelated climaxes and hence recoursemust be
taken to the othertests. The value of the life-form
is mostevidentwheretwo
climaxes of different
physiognomyare in contact,as in the case of the lake
forestofpine-hemlockand the deciduousforestofhardwoods.The staticview
would make the hemlockin particulara dominantofthe deciduousformation,
but the evidence derivedfromthe vegetation-form
is supportedby that of
phylogenyand by early recordsof compositionand timber-cutto show that
two different
climaxes are concerned. Secondary formsor subformsrarely
if ever mark distinctionsbetweenclimaxes,but do aid in the recognitionof
associations.This is well exemplifiedby the tall, mid and shortgrassesof the
prairieand somewhatless definitely
by the generallydeciduouscharacterofthe
Petran chaparraland the typicallyevergreennatureof the Sierran.
As wouldbe expected,the mostsignificant
test ofthe unityof a formation
is affordedby the presenceof certaindominantspecies throughall or nearly
all of the associations,but oftennot in the role of dominantsby reason of
reducedabundance. Here again perhapsthe best examples are furnishedby
prairieand tundra,thoughthe rule applies almost equally well to deciduous
forestand onlyless so to coniferousones because of a usually smallernumber
of dominants. For the prairie,the numberof such species,or perdominants,
found in all or all but one or two of the five associationsis eight,namely,
Stipa comata,Agropyrumsmithi,Boutelouagracilis,Sporoboluscryptandrus,
Koeleriacristata,Elymussitanion,Poa scabrellaand Festucaovina. Even when
a speciesis lackingover most of an association,as in the case ofStipa comata
and the true prairie,it may be representedby a close relative,such as S.
spartea,whichis probablyno morethan a mesicvarietyofit. As to the three
associationsof the deciduousforest,a stilllargernumberof dominantspecies
occurto some degreein all; the oaks compriseQuercusborealis,velutina,alba,
stellataand marilandica,and the hickories,
macrocarpa,coccinea,muhlenbergi,
Carya ovata,glabra,alba and cordiformis.
It was the application of this test by specificdominantsthat led to the
recognitionof the two climaxes in the coniferousmantle of the Petran and
FREDERIC
E.
CLEMENTS
259
Sierrancordilleras.The naturalassumptionwas that such a narrowbelt could
not contain more than one climax, especiallyin view of its physiognomic
uniformity,
but thisfailedto reckonwiththe greatclimaticdifferences
of the
two portionsand the corresponding
responseof the dominants.The effectof
altitude proved to be much more decisive than that of region,dominants
commonto the montaneand subalpinezones beingpracticallyabsent,though
theruleforthe same zone in each ofthetwo separatemountainsystems.Long
afterthe presenceof two climaxes had been established,it was foundthat
Sargenthad anticipatedthis conclusion,thoughin otherterms(1884, p. 8).
As wouldbe inferred,
the dominantsofrelatedassociationsbelongto a few
commongeneraforthe most part. Thus, there are a dozen species of Stipa
variouslydistributedas dominantsthroughthe grassland,nearlyas many of
Sporobolus,Bouteloua and Aristida, and several each of Poa, Agropyrum,
Elymus, Andropogon,Festuca and Muhlenbergia.In the deciduous forest,
Quercus,Carya and Acer are the greatgenera,and forthe various coniferous
ones, Pinus, Abies and Picea, with species of Tsuga, Thuja, Larix and Juniperushardlyless numerous.
The perennialforbsthat play the part of subdominantsalso possess considerablevalue in linkingassociationstogether,and to a higherdegreein the
deciduousforestthan in the prairie,owingchieflyto the factorsof shade and
protection.Over a hundredsubdominantsbelongingto two score or moreof
genera,such as Erythronium,
Dicentra,Trillium,Aquilegia,Arisaema,Phlox,
Uvularia,Viola, Impatiens,Desmodium,Helianthus,Asterand Solidago,range
fromNova Scotia or New England beyondthe bordersofthe actual climaxto
Nebraska and Kansas. Acrossthe wide expanse of the prairieclimax,species
in commonare onlyexceptional,thesefewbelongingmostlyto the composites,
notably Grindeliasquarrosa,Gutierreziasarothrae,Artemisiadracunculusand
vulgaris. On the otherhand, the numberof genera of subdominantsfound
throughoutthe grasslandis verylarge.
The greatermobilityof the largermammalsin particularrendersanimal
influents
less significant
than plants as a criterion,but severalofthesepossess
definitevalue and the less mobilerodentseven more.The antelopeand bison
are typicalof the grasslandclimax,the firstbeingpracticallyrestrictedto it,
while jack-rabbits, ground-squirrelsand kangaroo-ratsare characteristic
dwellersin the prairie,as is theirchieffoe,the coyote.
The remainingcriteriaare derivedfromdevelopmentdirectlyor indirectly,
thoughthisis less evidentin the case ofthe ecotonebetweentwo associations.
Here the mixing of dominants and subdominantsindicates their general
similarityin terms of the formation,withinwhich range their preferences
associations.The evidencefromprimarysuccessionis
assignthemto different
of value only in the later stages as a rule,since initialassocies like the reedswamp may occur in severalclimaxes. With subseres,however,all or nearly
all the stages are related to the particularclimax and such seres denote a
17-2
260
corresponding
unityin development.This is especiallytrueof all subelimaxes
still are
and most evidentlyin the case of those due to fire. More significant
postclimaxesin bothgrasslandand forest.For example,the associesofspecies
of Andropogon,which is subelimax to the oak-hickoryforest,constitutesa
postclimaxto fiveout ofthe six associationsofthe prairie. On the otherhand,
the communityof Ulmus, Jubglans,Fraxinu?s, etc., found on flood-plains
throughtheregionofdeciduousforest,formsa commonsubelimaxto thethree
associations.
In additionto such ontogeneticcriteria,phylogenysuppliestests of even
greatervalue. Thisis notablythecase withthetwo associationsofthe montane
forestsof the west,thoughperhapsthe moststriking
and subalpineconiferous
is in,connectionwith the lake forestof pinethis
criterion
application of
hemlock.Though the concreteevidenceforsuch a climax recursconstantly
throughthe regionof the Great Lakes to the Atlantic,it is fragmentary
and
thereis no evidentrelated associationto the westward. However, the four
genera are representedby related species in the two regions,namely,Pinus
strobusby P. monticola,P. banksianaby P. contorta,
Tsuga canadensisby T.
Larix laricina by L. occidentalis,and Thuja occidentalisby T.
heterophylla,
plicata,thoughthe last two generahave changedfroma subelimaxrolein the
east to a climax one in the west. As suggestedearlier,phylogeneticevidence
of still more direct nature is supplied by the mixed prairiewith the other
enclosingassociationsand by the remnantsof a virgindeciduousforestthat
exhibits a similar genetic and spatial relation to the associations of this
climax (cf. Braun, 1935).
Finally,it is clear that any test will gain in definiteness
and accuracy of
applicationwheneverdependablerecordsare available withrespectto earlier
compositionand structure.These may belongentirelyto the historicalperiod,
as in the case of scientificreportsor land surveys,they may bridgethe gap
betweenthe presentand the past as withpollen statistics,or theymay reach
furtherback into the geological record, as with leaf-impressions
or other
fossils(Chaney,1925, 1933; Clements,1936). Two instancesof the scientific
recordthat are of the firstimportancemay be givenas examples.The firstis
the essentialrecognitionby Sargent of the pine-hemlockclimax under the
name of the northernpine belt (1884), at a time whenrelativelylittleof this
had been logged,by contrastwith 90 per cent. or more at present(cf. also
Bromley,1935). The second is an account,discoveredand communicatedby
Dr Vestal, of the prairiesof Illinois as seen by Short in ca. 1840. This is of
heightenedinterestsince its discoveryfollowedlittlemorethan a year after
repeated field trips had led to the conclusionthat all of Iowa, northern
Missouriand mostofIllinoiswereto be assignedto the trueprairie,'a decision
1 The true prairieis characterizedby the three
eudominants,Stipa spartea,Sporobolusasper
and S. heterolepis.
The presenceof tall-grassesin it to-day,particularlyAndropogon
fiircatu-s
and
nutans,is the markof the discimax due to the varied disturbancesassociated withsettlement.
JOURNAL OF ECOLOGY
VOL. XXIV, PLATE VI
Phot. i. Sierransubalpineclimax: Consociationof Tsuga
CraterLake, Oregon.
mertensiana;
*....
Z
..
-
Phot. 2. ProclimaxofSagebrush(Artemisia
a disolimaxdue
tridentata),
to overgrazing
ofmixedprairie;climaticallya preclimax.
CLEMENTS-NATURE
Face p.
AND STRUCTURE OF THE CLIMAX
26I
FREDERIC
E. CLEMENTS
261
confirmedfor Illinois by Short's description,and supported by the more
generalaccountsof Bradbury(ca. 1815) and Greeley(1860).
CLIMAX
AND PROCLIMAX
Essentialrelations
that developmentregularlyterminatesin the
view
the
with
In accordance
communitycapable of maintainingitselfunder a particularclimate,except
when disturbanceenters,thereis but one kind of climax,namely,that controlledby climate.This essentialrelationis regardedas not onlyinherentin all
naturalvegetation,but also as implicitin the cognatenatureofthe two terms.
While it is fullyrecognizedthat successionmay be halted in practicallyany
stage, such communitiesare invariablysubordinateto the true climax as
determinedby climatealone. From the verymeaningof the word,therecan
notbe climaxesscatteredalongthe developmentalroutewitha genuineclimax
at the end. There is no intentionto questionthe realityof such pauses, but
orderfromthe climax.
onlyto emphasizethe factthat theyare of a different
Whileit is naturalto expressnewideas by qualifyingan old term,thisdoes
not conduceto the clearestthinkingor the most accurate usage. Even more
undesirableis the fact that the meaning of the originalword is gradually
shifteduntil it becomes eitherquite vague or hopelesslyinclusive. At the
thisfate,and fire,disease,insects,
hands of some,climaxhas alreadysuffered
and human disturbancesof all sorts are assumed to produce corresponding
climaxes(cf. Chapman,1932). On such an assumptioncornwould constitute
one climax, wheat another,and cotton a third,and it would then become
imperativeto begin anew the task of properlyanalyzing and classifying
vegetation.
In the light of two decades of continuedanalysis of the vegetation of
NorthAmerica,as well as the applicationof the twinconceptsof climax and
complex organismby workersin otherportionsof the globe and the strong
supportbroughtto themby theriseofemergentevolutionand holism(Phillips,
of the climax as givenin Plant Succession,in 1916,
1935), the characterization
still appears to be both completeand accurate. " The unit of vegetation,the
is an organicentity. As an organism,the formationarises,
climax formation,
grows,maturesand dies. Its responseto the habitat is shownin processesor
functionsand in structuresthat are the recordas well as the resultof these
functions. Furthermore,each climax formationis able to reproduceitself,
repeatingwithessentialfidelitythe stages ofits development.The life-history
of a formationis a complex but definiteprocess, comparable in its chief
of an individualplant. The climax formationis
featureswiththe life-history
the adult organism,of which all initial and medial stages are but stages of
development.... A formation,in short, is the final stage of vegetational
developmentin a climaticunit. It is the climax communityof a succession
possiblein the climateconcerned."
that terminatesin the highestlife-form
262
onlyto theextentofsubwouldneedmodification
To-daythisstatement
and "biotic" forvegetational.
stituting"biome" forclimaxor formation
by Phillips'
beenannotatedand confirmed
has recently
Thischaracterization
as citedabove,a treatise
ofclimaxandcomplexorganism,
masterly
discussion
inthefieldofdynamic
interested
byeveryone
thatshouldbe readanddigested
ecologyand itswideapplications.
Proclimaxes
thatsimulate
includesall the communities
As a generalterm,proclimax
but lack the
the climaxto someextentin termsofstabilityor permanence
ofthistypewere
climate.Certaincommunities
oftheexisting
propersanction
calledpotentialclimaxesin PlantSuccession(p. 108; 1928,p. 109),and two
To avoid pronamely,preclimaxand postclimax.
kindsweredistinguished,
to do double
was
made
need,
subclimax
posinga newtermin advanceofits
duty,denotingboth the subfinalstage of succession,as well as apparent
climaxesof otherkinds.This dual usage was criticizedby Godwin(1929,
by Tansleyin an appendednoteon theground
justified
p. 144)and partially
just given. However,thisdiscussionmadeit evidentthata newtermwas
1934).While
suggested(Clements,
desirableand proclimaxwas accordingly
thistakescareoftheuse ofsubclimaxin thesecondsensenotedabove,it is
to applyto all kindsofsubperbetteradaptedby reasonofits significance
thereis stillan
manentcommunities
otherthantheclimaxproper.However,
have been
postclimax
and
preclimax
subclimax,
after
residuum
important
as indicatedlater.
and it is proposedto call thesedisclimaxes,
recognized,
community
as anymoreorlesspermanent
Theproclimax
maybe defined
the climaxin one or morerespects,but graduallyreplaceable
resembling
by the latterwhenthe controlof climateis not inhibitedby disturbance.
forany one ofits
it maybe usedas a synonym
Besidesits generalfunction,
suchas in
further
investigation,
divisions,
as wellas in casesofdoubtpending
are subclimax,disclimax,
waterclimaxes.The fourtypesto be considered
and postclimax.
preclimax
Subclimax
As the stage precedingthe climaxin all completeseres,primaryand
wellunderstood.
The
is as universal
as it is generally
secondary,
thesubclimax
belongto the subsere,especiallythat
greatmajorityof such communities
isto-daya practically
constant
following
fire,
owingtothefactthatdisturbance
incultivated
processes
featureofmostclimaxes.Fireandfallowarerecurrent
subsereuntil
and theyserveto maintainthecorresponding
regionsgenerally
is
thedisturbance.
Thoughthesubclimax
terminates
orconversion
protection
thesehavelongago endedin theclimax
just as regulara featureofpriseres,
are
Qvermostof the climaticarea and the relatedsubclimaxcommunities
in size and widelyscattered.Smallnessis
muchrestricted
consequently
JOURNAL OF ECOLOGY
VOL. XXIV, PLATE VII
Phot. 3. Fire subclimaxofdwarfPinus and Quercus;the "Plains",
New JerseyPine-barrens.
Phot. 4. Subclimaxof consociesofAristidapurpureain field
abandonedI5 years; GreatPlains.
CLEMENTS-NATURE
Face p. 263
FREDERIC
E.
CLEMENTS
263
naturallya characteristicof nearlyall subelimaxes,the chiefexceptionsbeing
due to fireor to fireand loggingcombined,but by contrastthey are often
exceedinglynumerous.
Because of its positionin the succession,the subclimaxresemblesthe preclimax in some respectsand in a few instanceseithertermmay be properly
applied. The distinctionbetween subclimax and disclimax presents some
now and then, as the amount of change necessaryto produce the
difficulty
lattermaybe a matterofjudgment.This arisesin part also fromthe structural
and association,as a consequenceofwhichthedominants
diversityofformation
areas. When thereis but a
of a particulartype of subserevary in different
singledominant,as in manyburnsubclimaxes,no questionensues,but if two
or more are present,the decisionbetweensubclimax and disclimaxmay be
less simple,as is not infrequentin scrub and grassland.
Examples of the subclimaxare legion,the outstandingcases beingmostly
due to fire,alone or afterlumberingor clearing. Most typical are those composed of " jack-pines" or species with closed cones that open most readily
afterfire. Each greatregionhas at least one of these, e.g. Pinus rigida,virginiana and echinatain the east, P. banksianain the north,P. murrayanain
muricataand radiata on the Pacific
the Rocky Mountains,and P. tuberculata,
rolein the " piney" woodsofthe
similar
a
play
taeda
and
palustris
Pinus
Slope.
in the north-west.The
taxifolia
does
as
Pseudotsuga
Atlantic Gulf region,
ofaspen (Populus
are
composed
subclimaxesofthe borealforest
characteristic
balsam-poplar(P. balsamifera),and paper-birch(Betula papyritremuloides),
fera), eithersinglyor in various combinations. Aspen also formsa notable
subclimaxin the Rocky Mountains,forthe most part in the subalpinezone.
Prisere subclimaxesare regularfeaturesof bogs and muskeags throughout
much or all of the boreal and lake forests,the threedominantsbeing Larix
laricina,Picea mariana and Thuja occidentalis,oftenassociated as zonal consocies. Wherepines are absentin the regionof the deciduousforest,two xeric
oaks, Quercusstellataand marilandica,may constitutea subclimax,and this
roleis sometimesassumedby smalltrees,Sassafras,Diospyrusand Hamamelis
being especiallyimportant.
Subclimaxesin the grasslandare composedlargelyof tall-grasses,usually
in the formof a consocies. In the true prairie,this part is taken by Spartina
cynosuroidesand in the desert plains by Sporoboluswrighti,while Elymus
condensatusplays a similarrole in the mixed prairieand in portionsof the
bunch-grassprairies.The functionofthetall Andropogonsis morevaried; they
are typicallypostclimaxratherthan subclimax,though they maintain the
latterrelationalong the fringeof the oak-hickoryforestand in oak openings.
They occupy a similarpositionat the marginof the pine subclimaxin Texas
especially,and hencetheyare what mightbe termed" sub-subclimax" in such
situations. Beyondthe forestand in associationwithElionurus,Trachypogon,
etc., they appeaT to constitutea faciationof the coastal prairie. Chaparral
264
proper
is tobe regarded
as a climax,butwitha changeofspeciesitextends
into
themontane
andeventhesubalpine
a fire
zoneandthereconstitutes
subclimax.
In thefoothills
ofsouthern
the coastalsagebrush
California,
behavesin like
mannerwhereit liesin contactwiththechaparral.
The disposition
ofseralstagesbelowthesubclimax
thatexhibita distinct
retardation
orhaltfora longeror shorter
periodis a debatablematter.It is
entirely
possibleto includethemamongsubclimaxes,
but thiswouldagain
failinaccuracyanddefiniteness
andhenceleadto confusion.
Thedecisionmay
well be leftto usage by providinga termforsuch seralor sub-subclimax
communities
as persistfora longorindefinite
periodbecauseofcontinued
or
recurrent
edaphiccontrolorhumandisturbance.By virtueofitssignificance,
" serclimax
" is suggested,
andaccordwithrelatedterms,
thedesignation
brevity
withthemeaningofa seralcommunity
usuallyone or twostagesbeforethe
subclimax,
whichpersists
forsuch a periodas to resemble
theclimaxin this
and agreement,
one respect.For reasonsof brevity
the connecting
vowelis
butthee remainslongas in sere.
omitted,
arefoundin standing
Forthemostpart,serclimaxes
waterorin saturated
soils as a consequenceof imperfect
drainage.The universalexampleis the
withone or moreof severalconsocies,suchas Scirpus,Typha,
reed-swamp
and Glyceria:
thisis typicalofthelowerreachesofrivers,
Zizania,Phragmites
of deltasand of certainkindsoflakes,the greattule swampsof California
instances.Anothertypeoccursin coastalmarshesin
affording
outstanding
whichSpartinais oftenthesoleormajordominant,
whilesedge-swamps
have
a widerclimaticrangebut are especiallycharacteristic
ofnorthern
latitudes
and highaltitudes.The Evergladesof Floridadominatedby Cladiumconstituteperhapsthemostextensive
exampleofthegeneralgroup,thoughCarex
swampsoftencovergreatareasand the grassArundinaria
formsjungle-like
cane-brakes
the south. Amongwoodyspecies,Salix longifolia
through
is an
consociesof sand-barsand river-sides,
omnipresent
but the most unique
exemplaris thecypress-swamp
ofthesouth,typified
by Taxodium.In boreal
and subalpinedistrictsthe distinctive
serclimaxis the peat-bog,mooror
associatedwithotherseralcommunities
muskeag,moreor less regularly
of
Carexand usuallyofLarixorPicea also in theproperregion.
Frequentburning
mayretardor preventthedevelopment
ofthenormal
firesubclimaxand causeit to be replacedby a preceding
stage.Thismaybe
a scrubcommunity
oronekeptin theshrubformbyrepeatedfires,
butalong
theAtlanticand GulfCoastsit is usuallyoneofAndropogon
virginicus,
owing
toitssufferance
ofburning.
Theso-called" balds" ofthesouthern
Appalachians
areseralcommunities
ofheathsorgrassesinitiatedand maintained
primarily
byfire.Finally,thereareserclimaxes
ofweeds,especially
incultivated
annuals,
anda somewhat
similar
districts,
ofnativeannualsis characteristic
community
ofwidestretches
in thedesertregion.
JOURNAL OF ECOLOGY
VOL. XXIV, PLATE VIII
.44"
Phot. 5. Serclimaxof Taxodium.,
a
Nyssa and Quercusforming
cypressswamp; Paris,Arkansas.
Face
p. 26
Phot. 6. Disclimax of Bouteloua, Muhlenbergia and Opuntia, due to
overgrazing of mixed prairie, Great Plains.
CLEMENTS-NATURE AND STRUCTUJREOF THE CLIMAX
Face p. 265
FREDERIC
E.
CLEMENTS
26,5
Discllmax
As withthe relatedconcepts,the significance
ofthistermis indicatedby a
prefix,dis-, denotingseparation,unlikenessor derogation,much as in the
Greekdys,poor, bad. The most frequentexamples of this communityresult
fromthe modification
or replacementof the true climax,eitheras a whole or
in part, or froma change in the directionof succession.These ensue chiefly
in consequenceofa disturbanceby man or domesticatedanimals,but theyare
also occasionallyproducedby mass migration.In some cases, disturbanceand
the introductionof alien species act togetherthroughdestructionand competitionto constitutea quasi-permanent
community
withthegeneralcharacter
of the climax. This type is best illustratedby the Avena-Bromusdisclimax
of California,whichhas all but completelyreplacedthe bunch-grassprairie.'
A similarreplacementby Bromustectorum
has morerecentlytaken place over
large areas of the Great Basin, while Poa pratensishas duringthe last halfcenturysteadilyinvaded the nativehay-fields
and pasturesofthe trueprairie,
an advancefirstnotedbyBradburyin 1809. An evenmorestriking
phenomenon
is the steadilyincreasingdominanceofSalsola overrangeand cropland in the
west, and this is imitatedby Sisymbriumand Lepidium in the north-west.
It is obviousthat all cultivatedcropsbelongin the same generalcategory,but
this point hardlyrequiresconsideration.
Probably the example most cited in NorthAmericais that of the shortgrassplains,whichactually representa reductionof the mixedprairiedue to
overgrazing,supplementedby periodicdrouth. Over mostofthis association,
the mid-grasses,Stipa, Agropyrum,
etc., are still in evidence,though often
reducedin abundanceand stature,but in someareas theyhave beenpractically
eliminated. Similar though less extensive partial climaxes of short-grasses
characterisepasturesin the true and both pasture and range in the coastal
prairie,the dominantsregularlybelongingto Bouteloua,Buchloeor Hilaria. Of
essentiallythe same natureis the substitutionof annual species of Bouteloua
1 The grassland climax of North America comprisessix well-markedassociations (Plant
Indicators,1920; Plant Ecology,1929). The mixed prairie,so-called because it is composed of
both mid-grassesand short-grasses,
is more or less centralto the otherfiveand is regardedas
ancestralto them. To the east along the Missouriand MississippiRivers, it has become differentiatedintothe trueprairieformedby otherspeciesofmid-grassespertainingmostlyto the same
genera,and this unitis flankedalong the westernmarginof the deciduousforestby a proclimax
oftall grasses,chiefly
Andropoqon.Southwardthe trueprairieis replacedby coastal prairie,which
in the main occupiesthe GulfregionofTexas and Mexico and is constitutedby similardominants
but of different
species. The desertplains are characterizedprimarilyby species of Boutelouaand
Aristida,whichrangefromwesternTexas to the edge of the desertsof Mexico and Arizona. In
the north-westthe short-grassesdisappear and the Palouse prairie of easternWashingtonand
adjacent regionsis formedby mid-grassesof the bunch-grasslife-form,
among whichAgropyrum
spicatumis the eudominant.The same life-form
signalizesthe Californiaprairie,foundfromthe
northernpart of the state southwardinto Lower California,but its especial characteris derived
fromendemicspeciesofStipa. As indicatedin the discussion,the short-grass
plains, composedof
Bouteloua,Buchloe,and Carex,are not climaticin nature,and this statementapplies likewiseto
the tall-grassmeadows of Andropogonmentionedabove.
266
Nature and Structureof the Cllimax
onesofthesamegenera,which
and Aristidain thedesertplainsforperennial
ones.
by stillshorter
beingfollowed
is a case ofshort-grasses
a community
is
to
produce
of
disturbance
the
effect
instances,
In other
is thatofan
concerned
whenthelife-form
ofa postclimax,
withtheappearance
or tall grass.Thisis notablythe case in themixedprairiewhen
undershrub
sodandperup theshort-grass
is carriedto thepointofbreaking
overgrazing
In essence,
orGutierrezia
sarothrae.
ofArtemisiafrigida
thedominance
mitting
and of creosote-bush
tridentata)
the wideextensionof sagebrush(Artemisia
thougheachoftheseis a climax
is thesamephenomenon,
(Larreatridentata)
dominantin its ownregion.In the case of Opuntia,the peculiarlife-form
but the numerousspeciesbehavein all
difference,
suggestsan important
respectslike othershrubs,thaughwiththe two advantagesof
significant
spinesand readypropagation.
originally
byspeciesofAndropogon
formed
oftall-grasses
Thecommunities
have all theappearanceofa
sincethesenaturally
somedifficulty,
presented
numberareto be assignedto
to theprairie.Probablythegreater
postclimax
thatinthe
indicates
andrecord
from
reconnaissance
thistype,buttheevidence
in partifurcattus
Andropogon
trueprairieand especiallytheeasternportion,
in some
and
mowing
pasturing,
a
to
due
disclimax
now
constitutes
cular
miniature
in
disclimax
characteristic
A
1933).
measureto firealso (Clements,
is to be foundin the "gophergardens"ofthealpinetundra,wherecoaction
and reactionhave removedthe climaxdominantsof sedgesand grassesto
and
forbs." Towns" ofprairie-dogs
gardensofperennial
makeplaceforflower
communities.
oftenproducesimilarbutmuchmoreextensive
kangaroo-rats
as may likewise
initiatesdisclimaxes,
Selectivecuttingnot infrequently
the similaractionof otheragentssuchas fireor epidemicdisease.The most
from
ofthe chestnut(Castaneadentata)
dramaticexampleis the elimination
extreme
the
been
has
importance
greater
even
canopy,butof
theoak-chestnut
of
of the lake forestthroughthe overcutting
reductionand fragmentation
a disclimaxmayresultfromclimatic
whitepine. Finally,whatis essentially
such as in the Black Hills of SouthDakota has brought
mass migration,
fromthemontaneclimaxoftheRockyMountains
Pinusponderosa
together
fromtheborealforest.
and Picea canadensis
andpostclimax
Preclimax
(1916,1928)
werefirst
advancedinPlantSuccession
Theserelatedconcepts
organisation
the
in
and
(1929)
Ecology
in
Plant
and havesincebeendiscussed
ofthe principle
oftherelictmethod(1934).Theyare bothdirectcorollaries
thespatialseriesofclimaxesthatare setin motionby a major
oftheclisere,
climaticshift,suchas thatoftheglacialepochwithits oppositephases.The
in the case ofhighrangesor summits,
clisereis mostreadilycomprehended
suchas PikesPeak wheretheentireseriesofclimaxesis readilyvisible,andis
describedon MountAraratin his famousjourneyof 1700.
whatTournefort
FREDERIC
E. CLEMENTS
267
However,thisis but an expressionofthe continentalcliserein latitude,which
achievesperhapsits greatestregularity
in NorthAmerica. A similarrelationis
characteristicof the longitudinaldispositionof climaxes in the temperate
zone between the two oceans, the portion fromdeciduous forestthrough
prairieto desertbeingthe most uniform.
With the exception of the two extremes,arctalpineand tropical,each
climax has a dual role, being preclimaxto the contiguouscommunityof socalled higherlife-form
and postclimaxto that of lowerlife-form.
This may be
illustratedby the woodlandclimax,whichis postclimaxto grasslandand preclimax to montane forest.The arctic and alpine tundras exhibit only the
preclimaxrelation,to borealand subalpineforestrespectively,
sincea potential
lichenclimax attains but incompleteexpressionnorthwardor upward.While
thegeneralprimaryrelationis one ofwaterin termsofrainfalland evaporation,
temperatureconstantlyenters the situation and at the extremesmay be
largelycontrolling,
as in thetundraespecially. However,in ourpresentimperfect knowledgeof causal factorsit is simplerand moredefiniteto determine
rankby positionin the cliseralsequence,each communityhigherin altitudeor
latitude being successivelypreclimaxto the precedingone. This relationis
likewiseentirelyconsistentin the cliserefromdeciduous forestto desert,as
it is amongthe associationsofthe same climax,thoughin boththesecases the
zonal groupingmay be moreor less obscured.
Wherever concrete preclimaxes or postclimaxes occur, either between
climaxesor withina singleone, theyare due to the compensationaffordedby
edaphic situations.The major examplesof the latterare providedby valleys,
especiallygorgesand canyons,long and steepslope-exposures,
and by extreme
soil-typessuch as sand and alkali. The serationis a seriesof communitiesproduced by a graduated compensationacross a valley and operatingwithina
formationor throughadjacent ones, while the ecocline embracesthe differentiationbroughtabout by shiftingslope-exposuresarounda mountainor on
the two sides of a highridge. In the case of such soils as sand or gravelat one
extremeand stiffclay at the other,the edaphic adjustmentmay sometimes
appear contradictory.
Thus, sand affordsa haven forpostclimaxrelictsin the
dryprairieand forpreclimaxones in the humidforestregion,whilethe effect
ofheavy soilsis just the reverse. However,thisis readilyintelligiblewhenone
recalls the peculiar propertiesof such soils in termsof absorption,chresard
and evaporation(Clements,1933).
Preclimax
Since theyoccupythe same generalantecedentpositionwithrespectto the
climax,it is necessaryto distinguishwith some care betweensubclimaxand
preclimax,especiallyin view of the factthat theyoftenexhibitthe same lifeform. However,this is not difficult
whenthe priseresand subsereshave been
investigatedin detail, as the actual compositionand behavior of the two
268
reactionleads
in thefirst,
Moreover,
areusuallyquitedifferent.
communities
whilein the
withultimateconversion,
to the entryoftheclimaxdominants
within
to be overcome
is rarelyifever,
bylocalfactors
secondthecompensation
disturbance.
man-made
of
short
climate,
theexisting
are
are mostclearlymarkedwheretwo adjacentformations
Preclimaxes
eitherprairieand forestor desertand prairie.Examplesof the
concerned,
firstkind are foundin the grassy"openings"and oak savannahsof the
andin theso-called" naturalparks" alongthemarginofthe
deciduousforest
Theyare also welldevelopedon warmdryslopemontaneand borealforests.
is
in theRockyMountains.In theone,compensation
orxeroclines
exposures
to
due
by
a
local
climate
in
the
other
soil,
or
rocky
a
sandy
by
afforded
usually
beartheproperrelationto circumjacent
insolation.Desertclimaxesregularly
whichwould
obscuredbytheshrublife-form,
butthisis somewhat
grassland,
Thismaybe explained,
theless xericformation.
be expectedto characterize
bythewidecapacityforadaptationshownbysuchmajordominants
however,
a qualitythatis lackingin most
and Artemisia
tridentata,
as Larreatridentata
in desertplainsand
oftheirassociates.Leftstrandedas relictcommunities
bythe
ofthelast dryphase,theyhaveprofited
mixedprairiebytherecession
in
that
than
larger
much
a
territory
across
extend
to
of
grasses
overgrazing
postclimax,
of
a
appearance
the
all
have
whichtheyare climax. Here they
attainsa statureseveral
especiallyin the case of Larrea,whichcommonly
timesthatfoundin thedesert.However,sincethisis thedirectoutcomeof
in termsof grazing,it is betterregardedas a disclimax,partidisturbance
cularlysincetheclimaxgrassesstillpersistin it to somedegree.
or consociations
the morexericassociations
Withinthe sameformation,
are preclimax
to theless xericones.Thisis thegeneralrelationbetweenthe
theformer
ofthedeciduousforest,
associations
and beech-maple
oak-hickory
ortype
by
insolation
produced
sites
drier
in thelatterthewarmer
occupying
the Quercus
of soil. A similarrelationmayobtainin the case offaciations,
oftenbeinga borderof marginalpreclimax
community
stellata-marilandica
persist
naturally
faciations.Suchpreclimaxes
to themoremesicoak-hickory
properas relictsin valleysor sandysoils
beyondthelimitsoftheassociation
grassland,a
to the surrounding
and thenassumethe role of postclimaxes
" of Texas. In the
in the "Cross Timbers
exemplified
situationstrikingly
is preof Pinus ponderosa
montaneforestof the Rockies,the consociation
in all
recurs
condition
similar
a
and
taxifolia,
climaxto thatofPseudotsuga
ofconsociations.
forests
wherethereis moreorlesssegregation
of the desertplainsoccurall alongthe
In the mixedprairie,fragments
the Colorado
the most extensiveone confronting
marginas preclimaxes,
tothedesert.Themixedprairie
Valley,whereitis at thesametimepostclimax
relictsofthistypewhereit meetsthetrueprairie.The mostfreconstitutes
cryptandrus,
gracilisandSporobolus
byBouteloua
quentexamplesareprovided
in thisrole,grazinghasplayedsomepart.
thoughas withall theshort-grasses
JOURNAL OF ECOLOGY
VOL. XXIV, PLATE IX
.~~~~~~~~~~4
..
Phot. 7. Postclimaxof Quercus,Juglans,Ulmus,Fraxinus,etc.,
Canadian River,near OklahomaCity.
Phot. 8. Postclimaxoftall-grasses,Andropogon,
Calamovilfaand
Paniciumin sandhills;Thedford,Nebraska.
CLEMENTS-NATURE AND
STRUCTURE OF THE CLIMAX
Face p. 269
269
Postclimtax
As a generalrule,postclimaxrelictsare much moreabundant than those
that representpreclimaxes,owingin the firstplace to the seculartrendtoward
desiccationin climateand in the secondto the large numberof valleys,sandhills and sandy plains, and escarpmentsin the grassland especially. Postclimaxesof oak-hickoryand of theirflood-plainassociates,elm, ash, walnut,
etc., are characteristicfeaturesof the true and mixed prairies,holdingtheir
own farwestwardin major valleysbut limitedas outlierson ridgesand sandy
stretchesto the eastern edge. However, the compensationaffordedby the
last two is incompleteas a rule and the postclimaxis typicallyreducedto the
savannahtype.The latteris an almostuniversalfeaturewhereforest,woodland
or chaparraltouches grassland,owingto the fact that shrinkageunder slow
desiccation operates gradually upon the density and size of individuals.
Savannah is derivedfromthe reductionof deciduousforestalong the eastern
edge of the prairie,of the aspen subclimax of the boreal forestalong the
northern,and of the montane pine consociation,woodland or chaparral on
the westernand southernborders,recurringagain on the flanksof the Sierras
and Coast Ranges in California. On the south, the unique ability of the
mesquite(Prosopisjulifjora)to produceroot-sproutsafterfire,its thorniness,
palatable pods and resistantseeds have permittedit to producean extensive
savannah that oftencloselysimulatesa true woodland climax.
As would be expected,a pointis reachedin the reductionofrainfallwestward in the prairiewheresand no longeraffordscompensationadequate for
trees. In generalthisis alongthe isohyetof30 in. in the centerand south,and
of about 20 in. in the north. Southwardfromthe parallel of 37? the further
shrinkageofthe oak savannah may be tracedin the " shinry", whichdwindles
fromfouror fivefeetto dwarfsonly "shin" high. With these are associated
tall-grasses,principallyAndropogonand Calamovilfain the formgigantea.To
the northof this line, the shin oaks are absent and the tall-grassesmake a
typical postclimax that extends into Canada, though the compensatory
to permitan abundance of such low bushes
influenceof sand is still sufficient
as Amorpha,Ceanothus,Artemisiafilifoliaand Yucca, as well as depauperate
hackberryand aspen. In the vast sandhillarea of centralNebraska,the tallgrasspostclimaxattainsits best development,whichis assumedto reflectthe
climatewhen the prairieswere occupied by the Andropogonsand theirassociates some millionsof years ago. The gradual decreaseto the rainfallof the
presenthas led to the tall-grassesfindingrefugein all areas of edaphic compensation,not only in sand but likewiseon foothillsand in valleys, and in
additionalong the frontof the deciduousforest.
270
Nature and Structureof the Cliawx
STRUCTURE OF THE CLIMAX
functions
Community
The natureof communityfunctionsand theirrelationto the structureof
climax and sere have been discussedin considerabledetail elsewhere(Plant
Succession,1916, 1928; Plant Ecology,1929; Bio-ecology,1936), and for the
in significance
presentpurposeit maywell sufficeto emphasizethe difference
The former
functiohs.
secondary
or
minor
and
primary
or
major
between
cooperation,
competition,
reaction,
ecesis,
compriseaggregation,migration,
disoperation,and coaction, togetherwith the resultingcomplexes,invasion
and succession. Anyone ofthesemay have a profoundeffectupon community
and
structure,but the drivingforcein the selectionand groupingoflife-forms
speciesresideschieflyin reaction,competition,and coaction. Migrationdeals
forthe most part with the movementand evolutionof units under climatic
compulsion,and succession with the developmentand regenerationof the
climax in bare or denuded areas.
In contrastto thesestandsthe groupofminorfunctionsthat are concerned
with numbersand appearance or visibilityas it may be termed.The firstis
annuation, in accordance with which the abundance of any species may
fluctuatefromdryto wet phases of the various climaticcyclesor the growth
beingcombined.
the two effectsnot infrequently
in termsofprominence,
differ
For the grassland,a season of rainfallmoreor less extremein eitherdirection
oftenemphasizesone dominantat the expenseofothers,thoughthe balance is
usually redressedby the followingyear, whilein the desertin particularthe
swingin numberof annuals may be fromalmostcompleteabsence to seasonal
dominance,again withone or fewspeciestakingthe major role. Aspectionis
mainlythe orderlyprocessionof societiesthrougheach growingseason, more
or less modifiedby changesin numberensuingfromannuation. Hibernation
and estivationmerelyaffectseasonal appearance and are formsof aspection,
withthe temporarysuspensionofcoactioneffects.Whileusuallyappliedto the
animalmembersofthebiome,it is obviousthatplantsexhibitcertainresponses
of similarnature. Diurnationis likewisebest knownin the case of animals,
especiallynocturnalones,but it is exhibitedalso by the verticalmovementof
formby the openingand closingof flowersand the
planktonand in different
"sleep" movementsof leaves.
species: dominants
Roles of constituent
werelong
The abundant and controllingspecies of characteristiclife-form
ago termed dominants(Clements,1907, 1916), this propertybeing chiefly
determinedby the degreeof reactionand effectivecompetition.In harmony
withthe conceptof the biome,it has become desirableto considerthe role of
animalslikewise;sincetheirinfluenceis seen chieflyin coactionby contrastto
the reaction of plants, the term influenthas been applied to the important
FREDERIC
E.
CLEMENTS
271
species of land biomes (cf. Clementsand Shelford,1936). It is an axiom that
the life-form
ofthe dominanttreesstampsits characterupon forestand woodland, that of the shrub upon chaparral and desert,and the grass formon
prairie,steppe and tundra. Thereare seral dominantsas well as climax ones,
and these give the respectiveimpressesto the stages of prisereand subsere.
Finally, there are considerabledifferences
in rank or territoryeven among
the dominantsof each formation.The mostimportantare those ofwide range
that bind togetherthe associationsofa climax; to thesethe termperdominant
(per,throughout)maywellbe applied. In contrastto thesestandthedominants
more or less peculiar to each association,such as beech or chestnutin their
respectivecommunitiesand Sporobolusasper in the true and Stipa comatain
the mixedprairie,forwhicheudominantmay be employed.
Subdominantsregularlybelong to a. life-form
different
fromthat of the
dominantsand are subject to the controlof the latterin a highdegree,as the
name indicates. They are best exemplifiedby the perennialforbs,though
biennials and annuals may serve as seral subdominants;all three may be
actual dominantsin the initial stages of succession and especially in the
subsere. The term codominanthas so far had no very definitestatus; it is
hardlyneededto call attentionto the presenceoftwo or moredominants,since
this is the rule in all cases with the exceptionof consociationand consocies.
In contrastto the types mentionedstands a large numberof secondaryor
accessory species that exhibit no dominance,which may be conveniently
referred
to as edominants,
pendingmoredetailed analysis.
Influents
As indicatedpreviously,the designationofinfluent
is applied to the animal
membersof the biome by virtueof the influenceor coactiontheyexertin the
community.The significanceof this effectdepends much upon the life-form
and to a large degreeupon the size and abundanceof the species as well,and
is seen chieflyin the coactions involved in food, material,and shelter. Influentsmay be groupedin accordancewith these properties,or they may be
arrangedwithrespectto distributionand role in climax or sere,or to time of
appearance (Clementsand Shelford,1936). For generalpurposesit is perhaps
most convenientto recognizesubdivisionssimilarto those fordominantsand
withcorresponding
termsand significance.
Thus, a perfluent
would occurmore
or less throughoutthe formation,while the eufluentwould be more or less
typicalorpeculiarto an association.Subfluents
wouldmarkthenextlowerdegree
of importance,roughlycomparableto that of subdominant,whileminuteor
microscopicinfluentsof stillless significance
mightwellbe knownas vefluents.
Climaxand seralunits
No adequate analysis of vegetationor of the biome is possible without
taking full account of development. As the firststep, this involves a distinctionbetween climax communitiesproper and those that constitutethe
272
Nature and Structureof the Climwax
in commovement
towardthefinalstages.The twogroupsdiffer
successional
and typeof control,but theyagreein the possessionof
position,stability,
madeit
differences
Theseprimary
subdominants,
and influents.
dominants,
seral
and to
viz.
climax
and
of
communities,
recognize
two
series
desirableto
suffixes,
-ation
by therespective
terms,distinguished
proposecorresponding
1916).Thesehave graduallycomeintouse as thefeeling
and -ies(Clements,
basis
a permanent
fordynamicecologyhas grownand bid fairto constitute
forall suchstudies.It is notsupposedthattheyembraceall theunitsfinally
to thegreat
but theirconstantapplication
necessary
fora completesystem,
climaxesofNorthAmericafornearlytwodecadesindicatesthattheymeet
presentneedsin thematterofanalysis.
at the
placedin thepropercategory
can be certainly
Not all communities
smalland fewofthese
casesis relatively
outset,butthenumberofdoubtful
undercombinedextensiveand intensiveresearch.
presentseriousdifficulty
wideandlong
an experience
sufficiently
Thisstatement,
however,
presupposes
to permit
betweenclimaxesandthevarioustypesofproclimax,
distinguishing
in particular.
ofsubelimaxes
features
as wellas recognizing
thecharacteristic
and thedifficulties
studiesovera wideregionare indispensable
Comparative
willdisappearto thedegreethatthisis achieved.Whileecotonesand mictia
thesein turnare
necessarily
giveriseto somequestionsin thisconnection,
as theyaredetailed.
as extensive
resolvedby investigations
Climaxunits
rankandimportance
ofthese,fourtypesofdescending
In theorganization
weredistinguished
withinthe formation,
namely,association,consociation,
thefirst
twowerebaseduponthe
itself,
society,and clan. Liketheformation
whilethe last wereestablishedupon the subdominantand its life-form,
life-form.
It was recognized
at thetimethatthe
dominantand its different
units
formed
(cf.
by the dominants
associationcontainedwithinitselfother
faciationand
divisions,
PlantIndicators,
1920,pp. 107,276),and twofurther
seralones,faciesand locies,weresuggested
and
withcorresponding
lociation,
Thesehave
to Prof.Tansleyforhisopinionas to theirdesirability.
submitted
fieldstudiesand havenowand thenbeen
beentestedin thecourseoffurther
used in print,thoughthe completeserieswas not publisheduntil1932 (cf.
the following
units3viz.
1932). The climaxgroupnow comprises
Shelford,
faciation,lociation,society,and clan. At the
association,consociation,
itwasintended
to replacesocietybysociation
forthesakeofgreater
beginning,
had attainedsuchusagethattheidea was
interms,
buttheformer
uniformity
sensebystudents
theuseofsocietyin quitea different
However,
relinquished.
of socialrelations,
especiallyamonginsects,againraisesthe questionofthe
in viewofthegrowing
ofsucha substitution,
emphasisuponbiodesirability
ecology(cf.also Du Rietz,1930;Riibel,1930).
JOURNAL OF ECOLOGY
VOL. XXIV, PLATE X
Phot. 9. Associationof mixed prairie,Stipa, Agropyrum,
Bouteloua,etc.: Monument,Colorado.
Phot. io. Foothillfaciationof the desert-plains
association,Bouteloua
eriopoda, B. gracilis, B. hirsuta,B. fliformis,etc.: Safford,Arizona.
CLEMENTS-NATURE
Face p. 273
FREDERIC
273
E. CLEMENTS
Association.
Underthe climaxconceptthisrepresentsthe primarydivisionofthe biome
entirelyfromthe generalizedunit of the plant
or formation,and hence differs
is to be preferred.Each biome
sociologists,for which the term community
consistsregularlyof two or moreassociations,thoughthe lake forestand the
desertscrubembodytwo apparentexceptions,each seemingto consistof one
associationonly. However,these are readilyexplained by the fact that the
westernmemberofthe formerhas been obscuredby the expansionofmontane
whileone or moreadditionalassociations
and coast forestsin the north-west,
of the desert climax occur to the southwardin Mexico, and apparentlyin
South Americaalso.
The numberof associationsin a particularformationis naturallydeterand thesein turndependupon the
minedby the numberofprimarydifferences
presenceof eudominants. Just as,the unityof the formationrestsupon the
wide distributionof several major dominantsor perdominants,so the associationis also markedby one or moredominantspeculiarto it, and oftenas
in the rank and groupingof dominantsheld in common.
well by differences
Thus, in the true prairie association, the eudominantsare Stipa spartea,
Sporobolusasper and heterolepis;for the desert plains, Bouteloua eriopoda,
rothrockiand radicosa and Aristida californica,while Stipa comata and
Buchloe take a similar part in the mixed prairie. In the deciduous
climax, the characteristicdominantsof one associationare suppliedby the
beech and hard maple, of a second by chestnut and chestnut-oak,
though the oak-hickoryassociation,of widerrange and greatercomplexity,
is comparativelypoor in eudominants by contrast with the number of
species.
The structuraland phyleticrelationsof the associationsof a climax are
of all
best illustratedby the grassland,whichis the mosthighlydifferentiated
extent.
of
The
its
great
North Americanformations,largelyas an outcome
mostextensiveand variedunitis the mixedprairie,whichoccupiesa generally
median position with respect to the other five associations of this climax.
Originally,it derived its dominants from three separate regions, Stipa,
and Koeleria comingfromHolarctica,Sporobolusfromthe south,
Agropyrum
and the short-grassesfromthe Mexican plateaux, and it still exhibitsthe
closest kinshipwith the Eurasian steppe. It contains nearly all the genera
that serve as dominantsin the related associations,while many of the eudominantsof these have all the appearance of direct derivativesfromits
The evolution
species,as is shownby Stipa, Sporobolus,Poa, and Agropyrum.
of both species and communitiesis evidentlyin responseto the various subclimates,that ofthe trueprairiebeingmoister,ofthe coastal warmeras well;
the desertplains are hotterand drier,the Californiaprairiemarkedby winter
rainfalland the Palouse by snowfall.
Journ.of Ecology XXIV
18
274
Consociation.
In its typicalformthe consociation
is constituted
by a singledominant,
thetermis also appliedto casesin whichother
butas a matterofconvenience
dominantsare but sparingly
presentand hencehave no real sharein the
'controlof the community.It has likewisebeen convenient
to referin the
abstractto each majordominantoftheassociationas a consociation,
though
withtherealization
thatit occursmorefrequently
in mixture
thanbyitself.
In thissenseit maybe considered
a unitoftheassociation,
thoughtheactual
area ofthe latteris to be regardedas dividedintodefinite
faciations.Consociationdominants
fallintoa moreorlessregularserieswithrespecttofactor
requirements,
especiallywatercontent,and oftenexhibitzonationin consequence.Thisis a generalfeatureofmixedprairiewhereAgropyrum
smithi
and Stipa comataare thechiefmid-grasses,
theformer
occupying
swalesand
lowerslopes,thelatterupperslopesand ridges.
Theconsociation
achievesdefinite
expression
overa considerable
areaonly
whenthefactors
concerned
fluctuate
withinthelimitssetbytherequirements
ofthedominant
orwhentheotherdominants
arenotfoundin theregion.The
firstcase may be illustratedby Pinus ponderosain the lowerpart of the
montane
forest
andbyAdenostomafasciculatum
while
intheSierranchaparral,
thesecondis exemplified
byPicea engelmanni
intheFrontRangeofColorado,
itsusualassociate,Abieslasiocarpa,
beingabsentfromthedistrict.In rolling
terrainlikethatoftheprairie,each consociation
willrecurconstantly
in the
propersituationbut is necessarily
fragmentary
in nature.Such behavioris
ofdominants
characteristic
witha postclimax
tendency,
as withStipa minor
and Elymuscondensatus
in swalesand lowerlevelsofthemixedprairie.
Faciation.
Thisis the concretesubdivision
ofthe association,
the entirearea ofthe
latterbeingmadeup ofthevariousfaciations,
exceptforseralstagesorfragmentsoftheseveralconsociations.
Each faciation
corresponds
to a particular
regionalclimateof real but smallerdifferences
in rainfall/evaporation
and
It maybe characterized
temperature.
by one or two eudominants,
suchas
HilariajamesiandStipapennatainthesouthern
mixedprairie,
butmoreoften
it derivesits individuality
froma sortingout or a recombination
of the
oftheassociation.As is evident,
dominants
thetermis formed
fromthestem
fac-,show,appear,as seen in face and facies,and the suffix-ation,which
denotesa climaxunit.
Duringthepastdecade,muchattention
has beengivento therecognition
and limitation
offaciationson the basis ofthepresenceor absenceofa eudominant,such as Hilaria, Buchloe,or Carex,or a changein the rankor
ofcommondominants,
grouping
likeStipa,Agropyrum,
Sporobolus
or Bouteloua. In theprairiethistaskhas beencomplicated
cultivation
byovergrazing,
andrelateddisturbances,
whileselective
andfirehaveaddedto the
lumbering
275
in the deciduousforestespecially. In general,temperatureappears
difficulties,
offaciations,sincetheyusually
to play the leadingpart in the differentiation
fall into a sequence determinedby latitude or altitude, though rainfall/
evaporationis naturallyconcernedalso. The mixedprairieexhibitsthe largest
number,but it is approached in this respect by the deciduous forestas a
consequenceof wide extentand numerousdominants. Over the GreatPlains
fromnorthto south,the successivefaciationsare Stipa-Bouteloua,BoutelouaBouteloua-Buchloe,
Carex,Stipa-Agropyrum-Buchloe,
Hl'ilaria-Stip'a-Bouteloua,
However,the short-grasscommunitiesare to be
and Agropyrum-Bouteloua.
regarded as disclimaxeswhereverthe mid-grasseshave been eliminatedor
nearlyso, a conditionthat fluctuatesin relationto dry and wet phases of the
climaticcycle.
Lociation.
In its turn,the lociationis the subdivisionofthe faciation,the termbeing
derivedfromlocus,place, as indicatinga generallocalityratherthan a large
region. Nevertheless,a lociationmay occupy a relativelyextensiveterritory
up to a hundredmilesor morein extent,by comparisonwithseveralhundred
in the
forthe faciation. It is characterizedby more or less local differences
abundance and groupingof two or more dominantsof the faciation.These
oraltitude,
correspondto considerablevariationsin soil,contour,slope-exposure
but all withinthelimitsofthefaciationconcerned.As a consequence,lociations
hereand thereas alterneswitheach other,
recurring
are veryoftenfragmented,
and frequently
withproclimaxesofvarioustypes.Like mostclimaxunits,they
have been modifiedby disturbancein some degree,and this fact must be
themfromsubelimaxor
constantlykept in mindin the task of distinguishing
disclimax.
A detailed knowledgeof the faciationis prerequisiteto the recognitionof
the various lociationsin it. The numberfor a particularfaciationnaturally
dependsupon the extentofthelatterand the numberofdominantsconcerned.
Consequently,lociations are more numerousin the faciationsof the mixed
prairie and desert plains, of the chaparral and the oak-hickoryforest. As
would be expected,they are oftenmost distinctin ecotonesand in districts
wherethereis local intrusionof anotherdominant. In correspondencewith
theirlocal character,it is importantto eliminateor diminishsuperimposed
differences
throughrestorationof the originalcover by means of protection
enclosuresand thus renderit possibleto disclosethe true composition.
Society.
This termhas had a wide range of application,but by dynamicecologists
it has generallybeen employedfor various groupingsof subdominants,of
whichthose constitutedby aspects or by layers are the most important. In
addition,thereis a host of minorcommunitiesformedby cryptogamsin the
groundlayeror on host-plantsand othermatrices.The soil itselfrepresentsa
18-2
276
major layer,divisibleinto moreor less definitesublayers. Animalsregularly
assume roles of varyingimportancein all of these, especially the insects,
arachnids and crustacea, and hence most if not all societiescompriseboth
subdominantplants and subinfluentanimals. It is doubtfulwhetheranimals
form true societies independentlyof their food-plantsor those used for
materialsor shelter,but this is a questionthat can be answeredonly after
the simplestunits, namely, family and colony, have been recognizedand
coordinatedin termsof theircoactions.
In view of what has been said previously,it seems desirableto employ
society as the general term for all communitiesof subdominantsand subinfluentsabove the rank of familyand colony, much as communityis the
inclusivetermforall groupingsofwhatsoeverrank.This thenpermitscarrying
out the suggestionmade two decades ago that the major typesof societiesbe
set apart by distinctivenames. In accordance,it is here proposedto call the
aspect societya sociationand the layer societya lamiation,while the correspondingseral terms would be socies and lamies. Many of the societies of
cryptogamsand minuteanimals would findtheirplace in these,particularly
so for those of the surfaceand soil layers,but many otherstake part in a
miniaturesereor serule,such as that of a molderinglog, and may best receive
designationsthat suggestthis relation.
Sociation. Whereversocietiesare welldeveloped,theyregularlymanifesta
fairlydefiniteseasonal sequence, producingwhat have long been known as
aspects (Pound and Clements,1898). As phenomenaof the growingseason,
these were firstdistinguishedas early spring or prevernal,vernal proper,
estival, and serotinalor autumnal,but there may also be a hiemal aspect,
especiallyfor animals, in correspondencewith an actual and not merelya
calendarwinteras in California.
Sociationsare determinedprimarilyby the relationbetweenthe lifecycle
of the subdominantsand the seasonal marchof directfactors,temperaturein
particular. So faras the matrixofplantsis concerned,the constituentspecies
may be in evidencethroughoutthe season, but theygive characterto it only
duringthe periodof flowering,
or fruitingin the case of cryptogams.They are
presentlargelyor whollyby sufferance
of the dominants,and they are to be
related to the reactionsof these and competitionamong themselvesrather
more than to the habitat factorsas such. In grasslandand desert,they are
often more strikingthan the dominants themselves,sometimesowing to
stature but chieflyas an effectof color and abundance, and they may also
attain muchprominencein woods withthe canopy not too dense.
Sociations are usually most conspicuousand best developedin grassland,
fouror even fivedistinctaspectsoccurringin thetrueprairiefromearlyspring
to autumn. In the mixed prairiethese are usually reduced to three,and in
the desertplains and desertproper,to two major ones, summerand winter,
in which howeverthere may be subaspects marked by sations,as indicated
JOURNAL OF ECOLOGY
-
Phot. ii.
-
54b?i
VOL. XXIV, PLATE XI
Dr
eS
SociationofErigeronand Psoralea,estivalaspect; Belmont
Prairie,Lincoln,Nebraska.
Phot. I2. Lamiationofmid-herbs,
Laportea,Physostegia,
Impatiens,etc.,
in Oak-Hickoryforest.
CLEMENTS-NATURE
Face p. 277
FREDERIC
E.
CLEMENTS
277
later. Short seasons due to increasinglatitude or altitude affordless opportunity,and the tundra, both alpine and arctic, usually exhibits but two
aspects,the sociationshowevertakinga conspicuousrole as in the prairie. In
woodlandthe numberand characterofthe sociationadepend largelyupon the
sociationsregularly
natureofthe canopy,and fordeciduousforestthe flowery
belongto the springand autumnaspects,whenthe foliageis eitherdeveloping
or disappearing.
It is convenientto distinguishsociationsas simpleor mixedwithrespectto
of
the plant matrixin accordancewiththe presenceofa singlesubdominant,or
two or more. However, when animals are includedin the grouping,such a
distinctionappears misleadingand may well be dropped.The word "mixed"
would be more properlyapplied to plant-animalsocietieswereit not foTthe
factthat thisappears to be the universalcondition. Since seasonal insectsare
legion,manyofthesocietiesin whichtheytake partare bestdenotedas sations.
Lamiation. The termfora layersocietyis derivedfromthe stemlam-,seen
in lamina and lamella. As is well known,layersare best developedin forests
witha canopyofmediumdensity,so that underthe mostfavorableconditions
as many as fiveor six may be recognizedabove the soil. In such instances,
thereare usuallytwoshrubstories,an upperand lower,oftenmuchinterrupted,
followedby tall, medium and low forblayers,and a groundcommunityof
mosses,lichensand otherfungi,and usually some delicate annuals (cf. Hult,
1881; Grevillius,1894). The soil populationis perhapsbest treatedas a single
unit,thoughit may exhibitmoreor less definitesublayers.When the various
layersbeneaththe dominantsare distinct,each is regardedas a lamiation,but
organizedto warrantdesignation,
in manycases onlyone ortwo are sufficiently
e.g. shrubor tall-herblamiation.
Layers are oftenreducedto a singlelamiationof low herbsin the climax
forest,especiallyof conifers,and even this may be entirelylackingin dense
chaparral. Two or three layers of forbs may be presentin true prairie in
particular,the upper lamiationbeingmuchthe most definiteand oftenconcealingthe grassdominantsin the estivalaspect,but the structureofgrassland
generallyreflectsthe greaterimportanceof sociations. Climaxesof sagebrush
and desertscrubexhibitno properlamiations,owingto the intervalbetween
the individualdominants,but the herbaceoussocietiesofthe interspacesshow
somethingof this nature.
As a rule, well-developedlamiations also manifesta seasonal rhythm,
correspondingto aspects or to subaspects. These constituterecognizable
and analysismay
groupingsin the lamiationand forthe sake ofdetermination
be termedsations.This wordis a doublet of season, both being derivedfrom
the root sa-, sow, hence growor appear. Because of the frequentinterplayof
aspects and layers,the sation may forthe presentbe employedforthe subdivisionofboth sociationand lamiation,and especiallywhereseasonal species
of invertebrates
play a conspicuousrole.
278
Clan. This is a smallcommunityofsubordinateimportancebut commonly
of distinctivecharacter. It is markedby a densitythat excludesall or nearly
all competingspecies,in consequence of types of propagationthat agree in
the possessionof short offshoots.Extensionis usuallyby bulb, corm,tuber,
stolonor shortrootstock,each ofwhichproducesa moreor less definitefamily
grouping;in fact,most clans are familiesdevelopedin the climax matrixand
sometimeswitha blurredoutlinein consequence. Clans ofa particularspecies
such as Delphiniumazureumor Solidago mollis are dotted throughoutthe
respectivesociation, often in large numbers,and contributea distinctive
impressmuchbeyondtheirabundance. Like all units,butsmallonesespecially,
theyare subjectto muchfluctuation
withthe climaticcycle,as a resultofwhich
theymay pass into societiesor be formedby the shrinkageof the latter.
Seral units.
The conceptsof dominanceand subdominanceapply to the sereas theydo
to the climax, as does that of influencealso, and the correspondingsets of
units bear the same generalrelationto each other. Each of the fourmajor
units is the developmentalequivalent of a similarcommunityin the climax
seriesand thisis likewisetrueofthe variouskindsofsocieties.They constitute
the successivestages of each sere,both primaryand secondary,includingthe
subclimax,wherethey oftenachieve theirbest expression. It has also been
customaryto employ seral terms for preclimax and postclimax,and this
appears to be the betterusage fordisclimaxand proclimaxesin general.From
the fragmentary
natureof bare areas and suitablewaterbodies in particular,
seral communitiesare oftenbut partiallydeveloped and one or more units
will be lackingin consequence. Thus, the reed-swampassocies is frequently
representedby a single one of its several consociesand the minorunits are
even morecommonlyabsent.
The associes is the major unit of everysere,the numberbeing relatively
large in the prisereand small in the subsere.The universaland best understood examples are those of the hydrosere,in which Lemna, Potamogeton,
Nuphar, Nymphaea,Nelumboand othersformthe consocies of the floating
stage, and Scirpus, Typha, Phragmites,etc., are the dominantsof the reedswampor amphibiousassocies. As alreadyindicated,everyconsociesmayoccur
singlyand oftendoes whenthe habitat offersjust the properconditionsforit
or the othershave failedto reach the particularspot. When the ecial rangeis
wider,various combinationsof two or three dominantswill appear, to constitutecorresponding
facies. Locies are less definitely
markedas a rule,except
in swampsof vast extent,but are to be recognizedby the abundance of reedlike dominantsof lower stature, belongingto other species of Scirpus, to
Heleocharis,Juncus,etc. Both faciesand locies seemto be betterdevelopedin
sedge-swampwith its largernumberof dominants,though the Everglades
withthe singleconsociesof Cladiumforma strikingexception.
279
United States containa considerable
The tree-swampsofthe south-eastern
Nyssa aquatica,bijioraand
numberof consocies,such as Taxodiumdistichum,
ogeche,Carya aquatica,Planera aquatica, Persea palustrisand borbonia,Magnolia virginiana,Fraxinus pauciflora,profundaand caroliniana,and Quercus
facies,thougha more
nigra.These are variouslycombinedin severaldifferent
detailed and exact study of the swamp sere may show the presenceof two
woody associes,distinguishedby the depth or durationof the water. As with
otherscrub communities,the heath associes of peat-bog and muskeag comwealth of
prises a large numberof dominantsand presentsa corresponding
faciesand locies.
In the hydrosereof the deciduousforest,the typicalsubelimaxis that of
the flood-plainassocies, composed of species of Quercus,Ulmus, Fraxinus,
Acer,Betula,Juglans,Celtis,Platanus,Liquidambar,Populus and Salix forthe
most part. There are at least three well-markedfacies, namely,northern,
centraland southern,each with a numberof moreor less distinctlocies. The
swamp associes or subelimaxof the lake and boreal forestsconsistsof Larix
laricina, Picea mariana and Thuja occidentalis,occurringoftenas consocies
but generallyin the formof zoned facies. A large numberof firesubclimaxes
appear in the formof consocies,as with many of the pines,but associes are
frequentalong the Atlantic Coast, as they are in the boreal climax, where
aspens and birchesare chieflyconcerned.The numberof shrubs and small
treesthat play the part of seral dominantsin the deciduous climax is much
larger,producingnot merelya wide rangeofassociesbut offaciesand lociesas
well. Morethan a dozen generaand a scoreor so ofspeciesare involved,chief
among them being Sassafras,Diospyrus,Asimina,Hamamelis,Prunus, llex,
Crataegusand Robinia. The subclimaxof the xerosereis constitutedforthe
most part by species of Quercus,formingan eastern,a south-easternand a
westernassocies, the last with two well-markedfacies, one of stellataand
marilandica,the otherof macrocarpaand Carya ovata.
Amongpostclimaxassocies,those of grasslandand scrub possess a large
varietyoffaciesand locies,
numberof dominantsand exhibita corresponding
togetherwithfairlydefiniteconsocies. In the sandhillsof Nebraska,the tallgrasses concernedare Andropogonhatli,furcatus and nutans, Calamovilfa
Elymuscanadensisand Panicumvirgatum;some
Eragrostistrichodes,
longifolia,
ofthesedrop out to the northwardand othersto the south,thus producingat
least three regionalfacies. The mesquite-acaciaassocies of the south-west
possesses a largernumberof dominantsand manifestsa greatervarietyof
faciesthroughits wide area, and this is likewisetrue of the coastal sagebrush
of California.
With referenceto seral societies,it must sufficeto pointout that theseare
of necessitypoorly developed in the initial stages of both hydrosereand
xerosere,as the dominantsare relativelyfew. Even in the reed-swamp,true
layers are the exception,being largelyrestrictedto such subdominantsas
280
Nature and Struetureof the Climax
Alisma,Pontederia,
Hydrocotyle
and Sagittaria,
whichare foundmostlyin
the
borders
andintervals.However,
inextensive
subelimaxes
andpostelimaxes
situation
is quitedifferent.
Thetall-grass
is oftenquiteas
associesofsandhills
richinsatiesandlamiesas thetrueprairie,
ofthe
whilethevarioussubelimaxes
severalgreatforest
typesmayequal thelatterin thewealthofsubdominants
for each season and layer,the actual communities
beingverymuchthe
same.
Serule.
Thisterm,a diminutive
ofsere,has beenemployed
fora greatvarietyof
miniature
successions
thatruntheirshortbutsomewhat
complexcoursewithin
thecontrol
ofa majorcommunity,
theclimaxand subelimax.
especially
They
resembleordinary
seresin arisingin bare spotsor on matricesof different
sorts,such as earth,duff,litter,rocks,logs,cadavers,etc. Parasitesand
roleinthem,andplantsand
saprophytes
playa prominent
andoftenexclusive
animalsmay alternatein the dominantparts.The organisms
rangefrom
microscopic
bacteriaandwormsto mites,larvaeandimagoesontheonehand
and largefleshy
ofthesein
and shelffungion theother.The mostimportant
termsof coactionand abundanceare knownas dominules
(Clementsand
as termsforthetwodegrees
and edominule
Shelford,
1936),withsubdominule
oflesserimportance.
On thesamemodelareformed
associule,
consociule,
and
sociulein generalcorrespondence
withtheunitsofthesereitself.In addition
therearefamilies
andcoloniesoftheseminuteorganisms,
whichareessentially
similar
tothoseoftheinitialstagesofthemajorsuccession.Up tothepresent,
littleattention
has beendevotedto thedevelopment
and structure
ofserules,
but theyare comingto receiveadequateconsideration
in connection
with
bio-ecological
problems.Manyofthecoactions,
however,
havelongbeenthe
subjectofdetailedresearch
in theconversion
oforganicmaterials.
RANK
AND CORRESPONDENCE
OF UNITS
Thefollowing
theactualunitsofclimaxand sere,as wellas
tableexhibits
theircorrespondence
witheachother.However,
forthecomplete
andaccurate
thecontinental
analysisofa greatclimaxand especially
massofvegetation,
it
is necessary
to invokeotherconcepts,chiefly
that of the proclimaxand of
communities
mixedin space or in time.The severalproclimaxes
have been
characterized
(pp.262-8),andtheecoclineandseration
briefly
defined
(p. 267).
To theseareto be addedtheecotone
andmictium,
bothtermsoflongstanding,
theformer
appliedto themixing
ofdominants
between
twounits,thelatterto
the mixedcommunity
thatintervenes
betweentwo seralstagesor associes.
Finally,therewill be the severaltypesof seresin all possiblestagesof
the priserein the formof hydrosere,
development,
xerosere,halosereor
in regionsless disturbed
psammosere
and a myriadofsubseresin thoselong
settled.
FREDERIC
E. CLEMENTS
281
TABLE OF CLIMAX AND SERAL UNITS
Climax
Association
Consociation
Faciation
Lociation
Sociation
Lamiation
Sation
Clan
Eoclimax
Panclimax
Climax (formation)
Serule
Associule
Consociule
Sociule
Sere
Associes
Consocies
Facies
Locies
Socies
Lamies
Saties
Colony
Family
is employedas a generalterm
As indicatedpreviously,the wordcommunity
to designateany or all ofthe precedingunits,whilesocietymay well be used to
includethoseofthe seconddivision,i.e. sociation,etc. These are characterized
by subdominantsin contrastto the dominantsthat markthe firstgroup. It
has also been pointedout that the entirearea ofthe associationis dividedinto
faciationsand that the consociationis the relativelylocal expressionof complete or nearlycompletedominanceon the part of a singlespecies. The clan
correspondsto the familyas a rule,but in some cases resemblesthe colonyin
beingformedby two species.
Families and coloniesmay also appear in climax communities,but this is
regularlyin connectionwiththe serule.
Panclimaxand eoclimax
The comprehensivetreatmentof these conceptsis reservedfor the succeeding paper in the presentseries,but it is desirableto characterizethem
meanwhile.The panclimax(wav,all, whole) comprisesthe two or morerelated
climaxes or formationsof the same generalclimaticfeatures,the same lifeformand commongeneraofdominants.The relationshipis regardedas due to
theiroriginfroman ancestralclimax or eoclimax(qcos',dawn), of Tertiaryor
even earliertime, as a consequence of continentalemergenceand climatic
In the past, eoclimaxesformeda seriesofgreatbioticzones in
differentiation.
the northernhemispherewiththe pole as a focus,and this zonal disposition
or clisereis still largely evident in the arrangementof panclimaxes at the
present. It is strikingin the case of the arctic tundra and taiga or boreal
forest,fairlyevidentfordeciduous forestand prairie-steppe,and somewhat
obscureforwoodland and chaparral-macchia,whilethe positionof desertsis
largelydeterminedby interveningmountainranges. This is true likewiseof
grasslandin some degree,and taken withthe formerbroad land connection
betweenNorthand South Americaexplainswhyboth prairieand desertpanclimax containat least one australformation.
282
that
In the lightof whathas been said earlier,it is readilyunderstood
as are eoclimaxand eoforare exactsynonyms,
panclimaxand panformation
termswhenthebiotic
mation.Panbiomeand eobiomearethecorresponding
research.
for
the
basis
is takenas
community
in climaxes
toresearch
Prerequisites
to statethatthe majordifficulty
in the
superfluous
It wouldbe entirely
wereit notforthefactthatit is too
is its complexity,
analysisofvegetation
in the
Thiswas embodied
forthestaticviewpoint.
oftentakenas thewarrant
wereassembled
as a unitin whichcommunities
original
idea oftheformation
andphyletic
composition
ofgeneric
basis,quiteirrespective
ona physiognomic
shouldhave
It is notstrangethatthisviewand its corollaries
relationship.
what
happened
is
exactly
since
this
of
usefulness,
period
its
long
past
persisted
fully
systemofLinnaeus,butthetimehascometo recognize
withtheartificial
upon
mustbe builtjust as certainly
that a naturalsystemof communities
as mustthatofplantfamilies.Comrelationship
andconsequent
development
in view
forthisratherthanagainstit, and especially
plexityis an argument
patternwhenthetouchdisclosesa definite
ofthefactthatthe complexity
is appliedto it.
stoneofdevelopment
kaleidoscope
mayappearto be a veritable
Thoughthemosaicofvegetation
uponit are readily
longoccupiedby man,thechangeswrought
in countries
the
previously,
concerned.As emphasized
intermsoftheprocesses
intelligible
scaleofunitsthatcorrespond
ina descending
is thatofclimate,
control
primary
arewrought
pattern
andfaciation.Uponthisgeneral
association,
toformation,
and
andsoil,andbothclimatic
ofphysiography
effects
themorecircumscribed
witha
obscured
areoverlaidandoftenmoreorlesscompletely
edaphicfigures
ofall possiblekinds.Even abovethismaybe
veneerappliedby disturbance
apparent,of such recurrent
transientbut nonetheless
discernedthe effect,
theorderly
patternofclimate
andaspection.Moreover,
changesas annuation
such
climaxesas tundraand
rangesso that
is complicated
by greatmountain
is further
variedbythe
taigaoccurfarbeyondtheirproperzone,andtheeffect
relativepositionoftheaxis.
sourceoffragmentary
Themigrations
ofclimaxesin thepastarea prolific
exceptin termsofdynamics.
theinterpretation
ofwhichis impossible
relicts,
theshrinkage
offorest
and
Thisis likewise
trueofsavannah,whichrepresents
modified
by fireor
scrubundera dryingclimateand is thenusuallyfurther
ofevery
fromthisand othercausesis characteristic
grazing.Fragmentation
enters
the
utilization
when
human
andreachesitsmaximum
diversified
terrain
thoughnotin processis
sceneupona largescale. Somewhatsimilarin effect
that
ofnumberofdominants
bydistance,withtheconsequence
thereduction
ofone. Sucha
intoa consociation
an associationofseveralmaybe converted
naturallybearssomerelationalso to climateand physiography,
shrinkage
in the
especiallyas seenin the glacialperiod,and findsits bestillustration
FREDERIC
E. CLEMENTS
283
generalpovertyof dominantsin the coniferousand deciduous climaxes of
Europe,by contrastwiththoseof easternAsia and NorthAmerica. A similar
contrastobtains betweenthe grasslandof Asia and of North America,the
latterbeingmuchricherin dominants,whileSouth Americaapproximatesit
closelyin thisrespect.
On the part of the investigator,
the difficulties
in the way of an extensive
and thoroughgoing
study of climaxes are usually more serious. They arise
partlyfromthe handicap too oftenset by state or national boundariesand
partlyfromthe limitationsof fundsand time.They are also not unrelatedto
the fact that it is easiest to know a small districtwell and to assume that it
reflects
largerones withmuchfidelity.As a consequence,it is impossibleto lay
too muchstressupon the needforcombiningintensiveand extensivemethods
in the researchupon climaxes,insofaras theirnature,limitsand structureare
concerned.The detaileddevelopmentin termsof primaryand secondarysuccessionlends itselfmuch morereadilyto local or regionalinvestigation,but
even here a widerperspectiveis essentialto accurategeneralization.
REFERENCES
Bradbury, J. "Travels in the InteriorofNorthAmerica,ca. 1815." In Thwaites' Early Western
Travels,5, 1904.
Bromley, S. W. "The originalforesttypesofsouthernNew England." Ecol. Mon.5,61-89,1935,
Chaney, R. W. "A comparativestudy of the Bridge Creek flora and the modernredwood
forest." Publ. Carneg.Instn,No. 349, 1925.
Chaney, R. W. and E. I. Sanborn. "The Goshen Flora of West-centralOregon." Publ.
Carneg.Instn,No. 439, 1933.
Chapman, H. H. "Is the longleaftype a climax?" Ecology,13, 328-34, 1932.
Clements, F. E. Plant Physiologyand Ecology,New Yoik, 1907.
Clements, F. E. Plant Succession,Washington,1916.
Clements, F. E. "Development and structureof the biome." Ecol. Soc. Abs. 1916.
Clements, F. E. Plant Indicators,Washington,1920.
Clements, F. E. "Phylogenyand classification
of climaxes." Yearb. Carneg.Instn,24, 334-5,
1925.
Clements, F. E. Plant Successionand Indicators,New York, 1928.
Clements, F. E. "The relictmethodin dynamicecology." This JOURN. 22, 39-68, 1934.
Clements, F. E. " Originof the desertclimateand climaxin NorthAmerica." This JOURN. 24,
1936.
Clements, F. E. and E. S. Clements. "Climate and climax." Yearb.Carneg.Instn,32, 203,
1933.
Clements, F. E. and V. E. Shelford. Bio-ecology,
1936.
Du Rietz, G.E. "Classificationand nomenclature
ofvegetation."Svensk.Bot. Tid. 24,489, 1930.
Godwin, H. "The subclimaxand deflectedsuccession." This JOIURN.17, 144, 1929.
Greeley, H. An OverlandJourneyto Californiain 1859,New York, 1860.
Grevillius, A. Y. "Biologisch-physiologische
Untersuchungeneiniger SchwedischenHainthiilchen." Bot. Z. 52, 147-68, 1894.
Hult, R. "Fors6k til analytiskbehandlingaf viLxformationerna."
Medd. Soc. Faun. Flor. Fenn.
8, 1881.
Medd.
utvecklingshistorie."
Hult, R. " Blekingesvegetation. Ett bidragtill viaxformationernas
Soc. Faun. Flor. Fenn. 12, 161, 1885. Bot. Zbl. 27, 192, 1888.
Lewis, M. and W. Clark. Journal,1803-1806.In Thwaites' TheOriginalJournalsoftheLewis
and ClarkExpedition,1904-05.
Phillips, J. "The biotic community."This JOuRN. 19, 1-24, 1931.
284
Phillips, J. "Succession, development,the climax and the complex organism:an analysis of
concepts. Part I." This JoURN.22, 554-71, 1934.
Phillips, J. "Succession, development,the climax and the complexorganism:an analysis of
concepts. Part II." This JouRN.23, 210-46, 1935.
Phillips, J. "Succession,development,the climax and the complex organism:an analysis of
concepts. Part III." This JouRN.23, 488-508, 1935.
R-ibel, E. Pflanzengesellschaften
derErde, Bern-Berlin,1930.
Sargent, C. S. Reporton theForestsof NorthAmerica(exclusiveof Mexico),Washington,1884.
Seton, E. T. Lives of GameAnimals,3, New York, 1929.
Shelford, V. E. "Basic principlesof the classificationof communitiesand habitats and the use
of terms." Ecology,13, 105-20, 1932.
Short, C. W. " Observationson the botanyof Illinois." West.J. Med. Surg.3, 185, 1845.
Tansley, A. G. "Editorial note." This JouRN.17, 146-7, 1929.
Tan'sley, A. G. " The use and abuse ofvegetationalconceptsand terms." Ecology,16, 284-307,
1935.
Tournefort, J. P. Relationd'un Voyagedu Levant,Paris, 1717.
Weaver, J. E. and F. E. Clements. Plant Ecology,New York, 1929.
Weaver, J. E. and E. L. Flory. " Stabilityof climax prairieand some environmentalchanges
resultingfrombreaking." Ecology,15, 333-47, 1934.

Nature and Structure of the Climax

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