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An ecological succession modelapplied to environmentalmanagementStephen M. Freedman a & Diane B. Rosenberg ba Department of Natural Science , Loyola University ofChicago , 6525 North Sheridan Road, Chicago, Illinois,60626, U.S.A.b Department of Biology , Loyola University of Chicago ,Chicago, Illinois, 60626, U.S.A.Published online: 24 Feb 2007.

To cite this article: Stephen M. Freedman & Diane B. Rosenberg (1984) An ecologicalsuccession model applied to environmental management, International Journal ofEnvironmental Studies, 23:1, 11-18

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Intern. J. Environmental Studies, 1984, Vol. 23, pp. 11-18 © Gordon and Breach Science Publishers. Inc., 19840020-7233/84/2301-0011 $18.50/0 Printed in the United Kingdom

AN ECOLOGICAL SUCCESSION MODEL APPLIEDTO ENVIRONMENTAL MANAGEMENT

STEPHEN M. FREEDMAN† and DIANE B. ROSENBERG‡

(Received September 2, 1983)

A model is presented which applies current ecological succession theory to land-use management. A briefhistory of succession theory is followed by a more detailed summary of the recently developed facilitation,tolerance and inhibition succession models. The five steps of the management model, designed dis-turbance, selective colonization, inhibitory persistence, removal, and regeneration, are described. Appli-cation of the model for land-use planning is given through specific examples of techniques that manipulatesuccessional processes. It is concluded that successional sequences and rates of replacement can beregulated to develop biotic communities that meet conservation needs.

INTRODUCTION

National and regional land-use policies are being re-assessed in light of resourcedepletion and environmental deterioration.1 Land-use policies are strongly influ-enced by current conceptualizations of ecosystem functioning. Ecological successiontheory has been used as a planning tool in agriculture and range management, as wellas other land-use management areas. This paper describes a model based on currentsuccession theory that can be used for conservation and planning purposes.

Succession refers to an orderly process of change in vegetation, the animalcommunity, or an ecological system. The transitory communities which occur duringa succession are called serai communities, or stages; they are generally thought tolead to a climax or mature community. Since long time periods and a variety ofhabitats are often required for field succession studies, ecologists have relied upontheoretical models to guide their research.

Among the more recent succession models are the facilitation, tolerance, andinhibition models developed by Connell and Slatyer.2 This paper presents a modifiedinhibition model that has been specificially designed for use in environmentalmanagement.

HISTORY OF SUCCESSION THEORY

In the early 1900s Henry Cowles and Frederic Clements formulated the initialconcept of succession. Clements viewed vegetation as an organic entity and sawsuccession as a repeatable deterministic process.3'4 The traditional view of succes-sion, associated with Clements, has been that organisms with superior disperal andecesis abilities, the pioneers, invade an environment first. The pioneer speciesmodify the environment and make it less appropriate for themselves and more

† Department of Natural Science, Loyola University of Chicago, 6525 North Sheridan Road, Chicago,Illinois 60626, U.S.A.

‡ Department of Biology, Loyola University of Chicago, Chicago, Illinois 60626, U.S.A.

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12 S. M. FREEDMAN AND D. B. ROSENBERG

advantageous for other organisms that replace them. A sequence of species changecontinues until no community of organisms can co-exist more efficiently than those thatare present. These organisms persist as the climax community. In addition to Clement'sclimatic climax, other final stages have been identified such as edaphic, physiographic,pyric, and biotic climaxes.5 Clement's holistic model was rejected by many ecologistsand succession began to be seen in terms of individual organisms; the properties ofplant communities depended upon the individual plants comprising them.6

During the 1940s increased emphasis was placed on the structural and functionalcharacteristics of the community. Succession was examined in terms of competitionamong species.7 Gradually, succession came to be viewed as a process of communitydevelopment.8 Mathematical models were applied to the species replacementprocess.9'10 During the 1960s there was also a gradual resurgence of Clementsian ideasabout succession. '12 The Neo-Clementsians correlated stability with the maturity ofthe system, with succession leading to more diverse, stable and mature systems.

Today there are two major views of succession, the ecosystem or organismic positionassociated with Clements, and the population centered or individual position which canbe traced back to Gleason.13 The difference of opinion among ecologists regardingsuccession makes it difficult to develop consistent environmental management policiesthat have general applicability. For example, the belief that over-grazed range land willrecover when grazing is prevented is based upon the traditional premise that thesuccessional series can be repeated.14 If the premise is incorrect, the managementpractice is inappropriate. If land-use policies are to be effectively employed, thesuccession theories underlying their development need to be continuously refined toreflect current ecological thinking.

CONNELL AND SLATYERS' MODELS

Connell and Slatyer2 developed three different succession models, facilitation,tolerance, and inhibition, to describe the mechanisms that might bring about a changein community composition after a disturbance. Each of the three models begins with achance disturbance opening a relatively large space and releasing resources. Thenumber of species replacements possible over time is related to both the intensity of thedisturbance and the size of the area disturbed.

The facilitation model is basically a description of Clementsian, primary succession(see Table I). Only species with early successional, "pioneer" characteristics, initiallycolonize the area. These early successional species modify the environment, making itmore suitable for species that have poorer dispersal abilities or slower growth rates.Successive facilitory changes continue until the species present no longer modify thesite in ways that facilitate the establishment of other species.

The tolerance model begins with the assumption that any arriving species may beable to establish itself. The modification of the environment by colonists makes theenvironment less suitable for other early successional species, but these modificationsby earlier colonists neither facilitate nor inhibit the rates of recruitment and survival oflate successional species. Species with poorer dispersal abilities and slower growth ratesare able to survive in the presence of earlier colonists due to their ability to tolerate lowresource levels. The replacement sequence continues until there are no species that caninvade and grow in the presence of the resident.

Like the tolerance model, the inhibition model assumes that any arriving colonistmay establish itself. In general, early invaders are likely to be species with largenumbers of propagules and good dispersal ability. Once established, a colonizer

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ECOLOGICAL MODEL

TABLE ISummary of Connell and Slatyers' models

13

Model

Disturbance

Invasion

InvironmentalModifications

Effects onIndividuals

Continuationof thesequence

Facilitation

Determinedby chanceOnlysuccessionalspeciesa) Less suitable for

early successionalspecies

b) Advantageous forlate successionalspecies

Late successionaljuveniles facilitatedby early successionalspeciesUntil resident nolonger facilitatesinvasion, growth ofany other species

Tolerance

Determinedby chanceAny colonizer

a) Less suitable forearly successionalspecies

b) Little or no effectlate successioalspecies

Late successionaljuveniles grow despiteearly successionalspeciesUntil no speciesexists that can invadeand grow in resident'spresence

Inhibition

Determinedby chanceAny colonizer

a) Less suitable forearly successionalspecies

b) Less suitable forlate successionalspecies

All other speciesinhibited

Sequence may notoccur colonist persistsuntil removal byphysical extremes ornatural enemies

inhibits the invasion of any subsequent species and persists as long as it continues toregenerate vegetatively, or is undamaged. Replacement is possible only when aresident is eliminated by physical extremes or natural enemies.

The three succession mechanisms hypothesized by Connell and Slatyer have beensupported by some experimental and field evidence.15"20 In the next section amanagement succession model will be presented which is based on the inhibitionmodel suggested by Connell and Slatyer.2

THE MANAGEMENT SUCCESSION MODEL

The management succession model presented in this paper was developed upon thepremise that it is possible to direct successional processes, rather than alter or deflect aknown sequence in an unpredictable direction. It differs significantly, therefore, fromtraditional succession theory which anticipates a directional and repeatable series ofstages that lead to a determined climax community. The model describes the methodsthat can be used to direct species sequencing and rates of replacement. The goal is thedevelopment of a planned, stable biotic community. The management successionmodel utilizes life history characteristics, competitor and predator interactions, andabiotic factors to regulate ecosystem function. It offers an alternative approach tomanagement methods that rely upon chemical manipulation or other intensive meth-ods of environmental control.

The management of a specific land area involves designing a particular disturbanceand selecting colonizers that will influence later patterns of community development(See Table II). The community may be designed and managed to persist andregenerate, or to persist until management directed removal. The entire series and rateof species replacement may be manipulated to achieve specific objectives. The follow-ing discussion of the model provides examples.

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14 S. M. FREEDMAN AND D. B. ROSENBERG

TABLE IIThe management succession model

Designed Disturbance

A selected disturbance modifies physical,spatial, and temporal structure of thecommunity. Subsequent sequence and rateof replacement regulated.

Selective ColonizationAny management selected colonizer canbecome established. Colonizer selectedon basis of preferred characteristics.Diversity of system regulated.

Inhibitory Persistence

Selected colonizer persists and inhibitsundesired sequences or alters rate ofreplacement.

Regeneration

Management aidedregeneration.Successional sequenceprevented. 5.

RemovalManagement directed removal.Successional sequence deliberatelyinterrupted. Subsequent sequencesand rates regulated. 4.

1. Designed Disturbance

The type, frequency, and intensity of a disturbance can be selected to modify thephysical, spatial, and temporal structure of a community so that the subsequentsuccessional sequence and rate of replacement can be controlled. Management tech-niques such as burning, flooding, chaining, or grazing can be designed to releaseresources or to remove or control undesired species. The techniques employed regu-late the successional sequence to maximize the persistence of desired species at latersuccessional stages.

2. Selective Colonization

Establishment of the colonizer is enhanced by choice of the appropriate disturbance instep 1. A management selected colonizer influences the initiation of early successionalsequences. Selection of the colonizer species may be based upon a variety of preferredcharacteristics, such as growth rate pattern, method of reproduction, allelochemicalproduction, predator defense mechanisms or ornamental value. Selecting thenumbers, proportions, and kinds of species for colonization serves to manipulate thediversity of the system and regulate subsequent competitor and predator/prey inter-actions.

3. Inhibitory PersistenceThe objective in designing a disturbance and selecting a specific colonizer is to increasethe probability that the colonizer will persist and inhibit undesired successionalsequences, or alter the rate of species replacement. The established colonizer persistsfor three reasons. First, the disturbance is designed to optimize the population size of

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ECOLOGICAL MODEL 15

that colonizer. Second, the life history characteristics of the colonizer are selected withpersistence in mind. Third, at step 2, the community interactions are manipulated toinsure survival of the colonizer. These factors have an inhibiting effect on the ability ofother species to invade and develop, since the colonizer secures the available space andresources.

4. Removal

The successional sequence can be deliberately interrupted through managed removalof a species, or groups of species, to maximize harvestable biomass and regulatefurther replacement sequences. The cycle represented by steps 4 through 1 can bedesigned to change or maintain community structure.

5. Regeneration

Community replacement can be prevented and species composition maintained toallow for long term survival of desired populations. Mortality rates, especially duringearly and late stages of the growth cycle, can be decreased through careful manipula-tion. For example, management methods can be used to facilitate plant populations inacquiring and maintaining metabolic reserves necessary for regeneration.

APPLICATION

Over the past two decades, succession theory has played an important role in theformulation of environmental management practices. Since there is often a time lagbetween the development of new theory and then application in management, thetraditional Clementsian model has had a strong influence on decision making in thisarea. Frequently, a variety of planning options based on more current ecologicaltheory are not considered in any detail. The management succession model provides aflexible framework that can be used to incorporate current theory. To illustratepossible applications of the model, specific methods of successional manipulation willbe presented for each step.

In range management, a disturbance such as fire, (step 1) can be selected to initiate adesire vegetation-herbivore sequence. For example, a controlled burn can be used toalter patterns of plant replacement or improve soil quality. After the fire, the highernutrient content of plants results in a greater subsequent weight gain of steers grazedon that range.21 In agro-ecosystems, the timing of a disturbance, such as fallowing, canbe manipulated to regulate subsequent replacement patterns.22

For a utility right-of-way situation, a colonizer can be selected, (step 2) on the basisof preferred characteristics such as height, longevity, or ornamental value. Viburnumlentago is regarded as an ideal plant for rights-of-way because it reproduces vegeta-tively, resists tree invasion, and provides both food and shelter for wild life.23

To efficiently utilize rangeland that is topographically and edaphically heterogen-eous, a mixed community of domestic and wild herbivores can be introduced togetheras colonizers. It has been demonstrated in several African grassland studies thatintegrated livestock and game ranching may be a profitable and excellent form of landuse.24-25

If a persisting community (step 3) is desired, as is the case in most managementsituations, practices that encourage an unchanging community structure can beemployed. With regard to rights-of-way, shrub species that reproduce vegetatively can

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16 S. M. FREEDMAN AND D. B. ROSENBERG

persist for years and prevent a successional sequence from occurring.26 Persistingright-of-way communities are more apt to be attained if bulldozing and discing areavoided, since these techniques encourage tree invasion and nutrient loss.27 Thecommunity composition of a forest can also be manipulated for persistence. Forexample, removal of timber through selective thinning is less likely to cause communitychange than other methods of tree cropping.28 Leaving den trees for animals whenharvesting timber, and favoring desirable seed or fruit producing species help tomaintain overall community composition.

Depending upon the management situation, removal, (step 4) could involve bothplant and/or animal species. In agricultural systems, crops can be removed before pestdamage occurs. For example, wheat can be harvested before attack by the wheat stemsawfly.22 Removing the herbivores' resource base decreases the herbivore populationgrowth rate and alters the successional process. In range situations, grazers can beselected for removal on the basis of age, or weight, to maximize economic gain. Specifictypes of grazers can be removed or reduced in size if their grazing preferences aredecreasing the ability of desired species to persist.

An alternative to the removal replacement process is regeneration (step 5). Rotationgrazing, or some other controlled form of predation, can stimulate vegetative reproduc-tion and aid in the regeneration process. Shrub communities often regenerate becausethey reproduce from root suckers; rabbit grazing promotes suckering.29 Manipulationof growth cycles is another method of maintaining or interrupting a regeneration cycle.For example, the dominance of Calluna vulgaris in a vegetation patch is dependentupon the continual production of a fungi-toxic factor.30 During the degenerate phaseof the Calluna cycle allelopathic activity is reduced, and birch may be able to replaceCalluna.30

In summary, the management techniques that are selected to manipulate succes-sional processess can direct the development of three different community structures. Ifshorter lived species are inhibited or removed, a community of longer lived species willdominate.2 Frequent disturbance, severe competition, and predation can be used todevelop a constantly changing community of species at the same successional level.31'32

If management practices emphasize the regeneration cycle, a relatively unchangingcommunity can be maintained.23

CONCLUSION

The management succession model offers an alternative perspective with regard to theconservation of ecological systems. Frequently, environmental management is sitespecific, with little concern for the broader biological implications of long termeffects.1'33 Using the management model approach to manipulating successionalsequences would encourage a greater emphasis on ecosystem function. Inevitably, theenvironment will become more managed. Solutions to environmental degradationneed to be based upon better understanding of the interactions of organisms with theirenvironment.

Life history characteristics of species affect successional sequences and rates ofreplacement and this knowledge should be used to make environmental.responsesmore predictable. The composition of managed systems can be regulated by manipulat-ing predator/prey and competitor interactions to increase stability. In managed sys-tems abiotic factors, fire and flood for instance, are to some extent controllable and canbe used to direct successional processes. The succession model presented in this papercan be used to aid in the establishment of management desired stable communities.

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ECOLOGICAL MODEL 17

ACKNOWLEDGEMENTS

We thank Drs, Anthony Nappi and Nancy Garwood for their comments and suggestions on an earlier draftof this manuscript. We also thank Ms. Deanna Caulfield for typing the final manuscript and preparing thetable and figure. We appreciate the editorial assistance of Maryann Gregory.

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