Models, Mechanisms and Pathways of Succession - OSARA

[Pages:46]Models, Mechanisms and Pathways of Succession Author(s): S. T. A. Pickett, S. L. Collins, J. J. Armesto Source: Botanical Review, Vol. 53, No. 3 (Jul. - Sep., 1987), pp. 335-371 Published by: Springer on behalf of New York Botanical Garden Press Stable URL: Accessed: 03/09/2009 13:02 Your use of the JSTOR archive indicates your acceptance of JSTOR's Terms and Conditions of Use, available at . JSTOR's Terms and Conditions of Use provides, in part, that unless you have obtained prior permission, you may not download an entire issue of a journal or multiple copies of articles, and you may use content in the JSTOR archive only for your personal, non-commercial use. Please contact the publisher regarding any further use of this work. Publisher contact information may be obtained at . Each copy of any part of a JSTOR transmission must contain the same copyright notice that appears on the screen or printed page of such transmission. JSTOR is a not-for-profit organization founded in 1995 to build trusted digital archives for scholarship. We work with the scholarly community to preserve their work and the materials they rely upon, and to build a common research platform that promotes the discovery and use of these resources. For more information about JSTOR, please contact support@.

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THE

VOL. 53

BOTANICAL

JULY-SEPrEMBER, 1987

REVIEW

No. 3

Models, Mechanismsand Pathwaysof Succession

S. T. A. PICKETT'

Department of Biological Sciences Bureau of Biological Research Rutgers University

New Brunswick, New Jersey 08903

S. L. COLLINS2

Division of Pinelands Research Center for Coastal and Environmental Studies

Rutgers University New Brunswick, New Jersey 08903

J. J. ARMESTO3 Department of Biological Sciences

Rutgers University New Brunswick, New Jersey 08903

I. Abstract .

-

--336

Resumen-.-

-336

II. Introduction-..-

--

337

III. Limitationsof the Connelland SlatyerModels-338

A. FundamentalConcepts-..

338

B. Applicationof the Connelland SlatyerModelsto ComplexSeres-341

C. Testabilityof the Models-

345

D. SectionSummary-346

IV. Mechanismsof Succession

--347

A. The Mechanismof Facilitation-347

B. The Mechanismof Tolerance-

349

Currentaddress:Instituteof EcosystemStudies, Mary FlaglerCaryArboretum,The New York BotanicalGarden,Box AB, Millbrook,New York 12545.

2 Currentaddress:Departmentof Botany and Microbiology,University of Oklahoma, Norman, Oklahoma73019.

3 Currentaddress:Laboratoriode Sistematicay EcologiaVegetal,Facultadde Ciencias, Universidadde Chile,Casilla653, Santiago,Chile.

Copies of this issue [53(3)] may be purchasedfrom the ScientificPublicationsDepartment,The New York BotanicalGarden, Bronx,NY 10458-5126 USA. Pleaseinquireas to prices.

TheBotanicalReview53: 335-371, July-Sept.,1987 335 C 1987TheNew YorkBotanicalGarden

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THE BOTANICALREVIEW

C. The Mechanism of Inhibition .

353

D. Generalizations About Mechanisms of Replacement -355

V. A Comprehensive Causal Framework

-

-356

VI. Acknowledgments--364

VII. Literature Cited--364

I. Abstract

The study of succession has been hamperedby the lack of a general theory.This is illustratedbyconfusionoverbasicconceptsandinadequacy of certainmodels. This reviewclarifiesthe basic ideas of pathway,mechanism, andmodel in succession.Second,in orderto preventinappropriate narrownessin successionalstudies,we analyzethe mechanisticadequacy of the most widely cited models of succession, those of Connell and Slatyer.This analysis shows that models involving a singlepathwayor a dominant mechanism cannot be treatedas alternative,testable hypotheses. Ourreview shows much more mechanisticrichnessthanallowedby these widely cited models of succession.Classificationof the mechanisms of specificreplacement,called for by existingmodels, is problematicand less valuablethanthe searchforthe actualmechanismsof particularseres. For example, the "tolerance"mechanism of succession has at least two contrastingmeaningsand is unlikely to be disentangledfrom the "inhibition" mechanismin field experiments.However, the understandingof particularspeciesreplacementsthroughexperimentand knowledgeof the conditions of a particularsere and species life histories is a reasonable and desirablegoal. Finally, we suggestthe need for a broad mechanistic concept of succession. Thus, based on classical causes of succession that have survivedrecentscrutiny,we erecta frameworkof successionalmechanisms. This frameworkaims at comprehensiveness,and specificmechanisms are nested within more generalcauses. As a result of its breadth and hierarchicalstructure,the frameworkperformstwo importantfunctions: First, it provides a context for studies at specificsites and, second, is a scheme for formulatinggeneraland testablehypotheses.The review of specific successionalmechanismsand the generalmechanisticframework can togetherguide futurework on succession,and may foment the development of a broad theory.

Resumen

Laausenciade unateoriageneralsobrela sucesionecologicaobstaculiza el logrode un mayorconocimientoen la materia,creaconfusionen torno a los conceptos m'asfundamentalesde la disciplina,y fomenta el diseiio de modelos inadecuados.Estacriticatiene como metael aclararconceptos fundamentalesacercade la trayectoria,el mecanismo, y el modelo de la

SUCCESSION

337

sucesion ecologica. En segundo lugar, intenta analizar la vtilidad me-

canica de los modelos de la sucesion ecologica mas citados tales como el de Connell y Slatyer. Se sefiala por que aquellos modelos con una trayectoria unica o con un mecanismo dominante no deben considerarse como hipotesis validas por probar.Por otra parte, se sefialatambien la existencia de una riquezamecfanicaque va mas alla de lo admitido por los modelos mas citados.Laclasificacionde los mecanismosde reemplazo esbozadosen los modelos actualescausaproblemasy tienenpocautilidad. El mecanismo de toleranciadurantela sucesion ecologica, por ejemplo, tiene por lo menos dos significadoscontrastantes,y muchasveces resulta dificil distinguiren pruebasde campo entreun mecanismode inhibicion y un mecanismode tolerancia.Un mejorconocimientodel reemplazode una especie-mediante la experimentacion,conocimiento de las condiciones conducentes a la sucesion ecologica y del largo de vida de la especie-no obstante, sigue siendo una meta rezonable y legitima. Se subrayala necesidadde un conceptomecanicode la sucesionecologicamas abarcadory se propone un marco de referenciaparalos mecanismos de la sucesionecologicaque toma en cuentalas causasclasicasde la sucesion ecologica mas escudriniadas.Este marco de referenciadesempefia dos functionesimportantes:provee una estructuraparael estudio de lugares especificos, y provee un esquema para la formulacion de hipotesis generalespor probar.Esta criticatiene tambien como meta el servircomo guiaparafuturostrabajosen la disciplinaquefomentenel disefiode teorias generalesde la sucesion ecologica.

II. Introduction

The study of succession, though central to plant ecology, has proven difficult(McIntosh, 1974, 1980). A numberof factorsmay have contributed to this. First, althoughthere is much informationavailableon patterns of succession, there is currentlyno generaltheory to organizethis information and to relate pattern and mechanisms. Second, the basic conceptsrequiredto focussuccessionalstudyarepoorlyarticulated.Third, the models that have been recentlyproposed,in an attemptto stimulate study of mechanismsand organizethat information,areof limited scope or are poorly used in the literature.

No paperof moderatelengthcouldfullycorrecttheselapses.Additional observationsand experimentson successionare also required.However, raisingthe issues and reviewingthe literaturethat addressesthese problems can indicate the state of the discipline, and encouragefurtherwork towardremedyingthe lapses. While the time may not yet be ripe for the elaborationof a complete theoryof successionand vegetationdynamics,

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THE BOTANICALREVIEW

this review and analysis can advance that goal. In order to focus this undertaking,we orientourreviewaroundthe influentialpaperby Connell and Slatyer(1977). The problems suggestedby that paperor by its use by other investigators,illustratethe threelacunaein the study of succession.

The purposes of this paper are 1) to clarify conceptual and terminologicalproblemsconcerningmodels and mechanismsof succession,2) to demonstratewith examples from various successionalstudies the limits of the Connelland Slatyer(1977, hereafterC + S) models as alternative, testable hypotheses,and 3) to introducea general,inclusive mechanistic frameworkforfuturestudiesof succession,a needemphasizedby Finegan (1984).

III. Limitationsof the Connelland Slatyer Models

In attempting to fill the need for a theoretical context in succession studies, Connelland Slatyer(1977) proposedthat mechanismsof succession could be incorporatedinto three alternative,testable models: facilitation, inhibition,and tolerance(TableI). Facilitationis the Clementsian model of relay floristics(Egler,1954) wherebyearly successionalspecies modify theirenvironmentand facilitatethe establishmentof latersuccessional species. According to the inhibition model, the initial invaders (Egler,1954) regulatesuccessionso that latersuccessionalspeciescannot invade andgrowin the presenceof healthy,undamagedearlysuccessional species. In the tolerance model, floristic changes may be a function of differentialife historytraitsandthe differentialabilityof late successional species to tolerateinitial environmentalconditions. To review the literature that addressesthese models, evaluate the adequacyof the models and ultimatelygeneratea broadframeworkof mechanismsof succession, we will firstdefinethreefundamentalconcepts:pathway,mechanism,and model. Then we will discuss the application of the Connell and Slatyer models to complex seres. Finally, we will discuss the testability of the models.

A. FUNDAMENTAL CONCEPTS

(1) A successionalpathwayis the temporalpatternof vegetationchange. It can show the change in community types with time, the series of systemstates,ordescribetheincreaseanddecreaseof particularspecies populations.A complex successionalpathwayfrom the Lake Michigan dune succession (Olson, 1958) serves as an example (Fig. 1).

(2) A mechanism of succession is an interaction that contributes to successionalchange.A mechanism is an "efficientcause"in the Aristotelian sense.

Table I Abstract of the Connell and Slatyer (1977) models of successiona

Step

Facilitation

Tolerance

A. Disturbance

Open site

Open site

B. Establishment

Only early species

Any species

C. Recruitmentof later species

Earlyspecies disfavored Later species favored

Earlyspecies disfavored No impact on later spec

D. Growthof later species

Laterspecies favored

Laterspecies grow in spite of earlierspecies

E. Continuation

As above until no environmental change

As above until no more tolerant species availa

F. Changeonly with

disturbanceb

To A

To A

a The steps of each model are sequential.Disturbancecan interruptthe processat any point, bu b Specificsite and species pool determinesdisturbanceeffectsin all models.

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THE BOTANICAL REVIEW

INITIAL CONDITIONS

DAMP' DEPRESSION

UPPER BEACH

ERODING SURFACES

DEPOSITING CRESTS

STEEP POCKETS LEE SLOPES

PHYSIOGRAPHIC PROCESSES

PIONEER VEGETATION

RUSH MEADOW

FORDUNE FORMATION

COTTONWOOD

__

BLOWOUT

INITIATION

MARRAM

-

P SAND REE'j

. SHRUBS --

LITTLE BLUESTEM

BASSWOOD

TEMPORARY CONIFERS

JACK WHITE RED

PINES

ARBOR VITAE BALSAM FIR

CLIMASX

TALL GRASS PRAIRIE

RED MAPLE SWAMP

BLACK OAK `'J

OAKS -MAPLES

BEECH HEMLOCK -BIRCHES

Fig. 1. Alternativesuccessionalpathwayson the LakeMichiganDunes. Exceptfor the physiographicprocesses,no mechanismsareincluded.From Olson, 1958.

Which specificinteractionwill be called a mechanismdependson the level of organizationaddressed.At the communitylevel, a mechanism of turnoverin succession can be a generalecological process or interaction(e.g.,competition,predation,establishment).As mechanisms of change in a community, facilitation, tolerance and inhibition fit this description. However, these mechanisms can also be addressedat lowerlevels of organization.Forexample,the interaction of inhibition may be subdividedinto more detailedmechanismsthat encompass the specificenvironmentalresourceand stresslevels, the physiology of nutrient uptake and resource allocation by the interactingplants,andtheirresultantarchitecturaal ndreproductivestatus. In studies where both levels of organizationmust be addressed,we suggestthat the two correspondinglevels of mechanism be differentiated. The most easily understood and least ambiguous way to do this is to specify the level of organizationunder discussion. In this paperwe will needto speakof mechanismsin bothgeneralandspecific senses. (3) A model of successionis a conceptualconstructto explainsuccessional pathwaysby combining various mechanisms and specifyingthe relationship among the mechanisms and the various "stages" of the pathway. To illustrate,we reproducea schematic generalmodel of succession(Fig.2), devised by MacMahon(1980), whichis applicable to many naturalsystems. These constructscan have verbal,diagrammatic, or quantitativeforms.

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LNVIKU~~~ E

,

|

/~~

URVIVAL OF

RESIDUALS

T

S

;

~~~E,R@IG ATI N|

DIVER

(R)

su

o (

tE., R

ar P INTERACTIONS|

i

Fig. 2. A generalized model of succession. Boxes represent system states or stages in the succession (SO, Sl, etc.), diamonds are drivers of the succession, circles are intermediate variables, and bowties are control gates, some of which are equivalent to Clementsian causes of succession (Table I). Dashed lines represent information flows. Environmental drivers (E) and reactions (R) affect control gates at the points indicated. From MacMahon, 1980.

Connell and Slatyeruse "model"in the sense of both mechanismand model as we have defined them. In their diagram of the three models, abstractedhere in Table I, "model"is used in our strictsense. However, in theirdiscussionof mechanismsanddiscriminatingtests,theyusemechanism and model interchangeably.Much of their discussion of specific casesof successionalturnoveris an examinationof mechanismsof species replacementin the strict sense.

B. APPLICATION OF THE CONNELL AND SLATYER MODELS TO COMPLEX SERES

In addition to potential confusion of the ideas of model, mechanism, and pathway,there are several additionalconcernsin applyingthe C +

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