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Ecological succession

All three mechanisms produce a sequence. Watching the sequence tells you which one you are looking at — nothing.

How the mix of species at a place changes after ground is cleared or exposed. The sequences are often recognisable. What they are not is a march towards a proper final state — that idea belongs to the 1910s.

Clear a patch of ground and something arrives; later, something else replaces it. The sequences are often recognisable enough to predict in outline, which is why the subject became one of ecology’s foundations. What has changed is the explanation. The early-twentieth-century account treated a plant community as a superorganism developing, like an individual, through determinate stages towards a climax fixed by regional climate — and it supplied the vocabulary still in use: pioneers, seres, climax. Against it stood the argument that a community is no such thing: species are distributed individually along environmental gradients according to their own tolerances and dispersal, so associations are coincidences with indistinct edges and no collective development. That view largely prevailed, which leaves us using a losing side’s terminology. Being more careful about mechanism helps. Early occupants can affect later ones in three ways, and they predict different things. Facilitation — the textbook version — means early species change conditions so later ones can establish, so removing the pioneers should slow everything down. Tolerance means they make no difference, and later species arrive and grow regardless. Inhibition means early occupants hold the site and resist replacement until they are damaged or killed, so removing them should speed the sequence up. All three produce a sequence of species when watched from outside, which is exactly why describing the sequence settles nothing. Inhibition turns out to be at least as common as facilitation, and it makes succession look less like development and more like a queue that only moves when something dies.

Early coverage · 36% complete · reviewed 2026-09-04

What this page covers

Studied chiefly in plants, and in marine systems where colonisation of cleared surfaces can be watched over months rather than centuries.

Often confused with: A predetermined sequence towards a stable endpoint, which is not the modern view; Pioneers preparing the ground for later species, which is one of three mechanisms

Quick facts

Three mechanisms
Facilitation, tolerance, inhibition — with different predictions
The textbook one is one of three
Pioneers preparing the ground is facilitation; inhibition is as common
No predetermined endpoint
The climax community belongs to the 1910s, and its vocabulary outlived it
Primary and secondary
Bare rock or new land, against ground that keeps its soil and seed bank

Three ways a species can affect the one that follows it

Only one of them is the story most people were taught.

Early species can help later ones, ignore them, or hold the site against them. Only the first is the textbook story of pioneers preparing the ground — and inhibition, the third, is at least as common.

Established

Specialists would state this without hedging. Multiple independent lines of evidence agree.

Successional replacement can proceed by facilitation, tolerance or inhibition. The three make different predictions about the effect of removing early occupants, and inhibition — where early species resist replacement until damaged or killed — is well documented across systems.

Who this applies to
Documented in terrestrial and marine successional systems.
Studied in
Plantae, Animalia
Why we rate it this way, and what the caveats are
EstablishedHigh confidence

The three mechanisms are distinguished by manipulation, and different systems yield different answers, which is what makes it a framework rather than a story.

How far it can be extended

All three mechanisms are documented across multiple system types.

Caveats

  • The mechanisms are not exclusive: different stages of one sequence can proceed by different ones.
  • Watched from outside, all three produce a sequence of species — which is why describing the sequence establishes nothing about the mechanism.

Still unanswered

  • What determines which mechanism dominates in a given system, which is not resolved.

Last reviewed 2026-09-04

The evidence (1 study)
The mechanisms, and what removing the early species would do
MechanismEarly speciesRemove them and…
FacilitationChange conditions so later species can establishThe sequence slows or stalls
ToleranceNeither help nor hinderLittle changes
InhibitionHold the site and resist replacementThe sequence speeds up

Diagram

Three mechanisms, one visible sequence

Each predicts something different about removing the early species.

Three mechanisms, one visible sequenceFacilitationEarly species improve conditionsRemove them → sequence stallsToleranceEarly species make no differenceRemove them → little changesInhibitionEarly species hold the siteRemove them → sequence speeds upOutlined: the textbook one. All three look identical from outside — which is whywatching a sequence settles nothing, and removing the early species does.
The same explanation in words

Three rows. Facilitation, marked out as the textbook one: early species improve conditions, so removing them stalls the sequence. Tolerance: early species make no difference, so removing them changes little. Inhibition: early species hold the site, so removing them speeds the sequence up. A note records that all three look identical from outside, which is why watching a sequence settles nothing and removing the early species does.

The right-hand column is the test, and it requires a manipulation. Watching a sequence unfold distinguishes none of these, because all three produce a sequence. That is the difference between a description of succession — which ecology had by 1916 — and an account of it, which needed removals.

The climax community, and why the phrase persists

A losing argument that kept the vocabulary.

Vegetation change is contingent, not a march towards a proper endpoint. The climax community was an early-twentieth-century idea, and modern ecology treats communities as coincidences of individual species’ tolerances.

Established

Specialists would state this without hedging. Multiple independent lines of evidence agree.

The Clementsian conception of succession as directional development of a community superorganism towards a climatically determined climax has been superseded by an individualistic view, in which species distributions along gradients are continuous and community composition is contingent on history, dispersal and disturbance.

Who this applies to
Vegetation ecology generally.
Studied in
Plantae
Why we rate it this way, and what the caveats are
EstablishedHigh confidence

A dispute settled largely in favour of the individualistic view over several decades of gradient and long-term work.

How far it can be extended

Supported by gradient studies and long-term vegetation records.

Caveats

  • Rejecting a determined endpoint does not mean succession is unpredictable: sequences are often recognisable and repeatable in outline.
  • Neither original position is held in its 1920s form; the dispute was partly about scale.

Where researchers disagree

  • Sites within a region do often converge on broadly similar mature vegetation, which is the observation the climax concept was built to explain.

Still unanswered

  • How much of observed convergence reflects shared constraints rather than a tendency towards a common state.

Last reviewed 2026-09-04

The evidence (3 studies)

The dispute ran for decades. On one side, communities as integrated units developing towards a state determined by climate. On the other, communities as coincidences — each species where its own tolerances and dispersal put it, with boundaries that look sharp only if you sample coarsely. The second view largely prevailed, and gradient studies showing species turning over continuously rather than in blocks were what settled it.

What survives is the language. "Climax community" implies a destination, and "pioneer species" implies a role in reaching it. Neither implication is current, and both are still taught. The observation underneath — that sites in a region often end up broadly similar — is real, and is better explained by shared constraints than by a shared goal.

Related

Starting from rock, and starting from soil

The difference is what survives the clearing.

Primary succession begins where there is no soil: new lava, a retreating glacier, a fresh dune. Everything has to arrive, and soil has to be built, which is slow — and lichens matter here, because they colonise bare rock and begin its breakdown. Secondary succession begins where a disturbance removed the vegetation but left the soil, the seed bank and the root systems. A burnt or cleared field is not starting from nothing; much of what returns was already present underground.

This distinction does real predictive work. Secondary succession is fast because the site retains its memory — seeds, roots, fungi, soil structure. Primary succession is slow because none of that exists. It is also why land cleared and then farmed for decades recovers differently from land cleared once: the memory has been removed too.

The research behind this page

6 studies, newest first. Each one has a page explaining what it found and what it could not show.

2013Trends in Ecology & Evolution

The intermediate disturbance hypothesis should be abandoned

The proposed mechanism does not reliably generate a diversity peak at intermediate disturbance, and the empirical pattern is absent in the majority of studies testing for it.

2001Nature

Catastrophic shifts in ecosystems

Shallow lakes, coral reefs, rangelands and woodlands show evidence of alternative states with abrupt transitions and hysteresis, so that restoring prior conditions is insufficient to restore the prior state.

1978Science

Diversity in tropical rain forests and coral reefs

Diversity was argued to peak at intermediate levels of disturbance, with low disturbance permitting dominance by superior competitors and high disturbance permitting only rapid colonisers.

1977The American Naturalist

Mechanisms of succession in natural communities and their role in community stability and organization

The three mechanisms make different, testable predictions about what happens when early species are removed, and evidence supports different mechanisms in different systems, with inhibition common.

1926Bulletin of the Torrey Botanical Club

The individualistic concept of the plant association

Species distributions along environmental gradients are individual and largely continuous, so communities have indistinct boundaries and are not repeatable units.

1916Carnegie Institution of Washington

Plant Succession: An Analysis of the Development of Vegetation

Vegetation change after disturbance follows recognisable sequences, and sites within a climatic region tend to converge on similar mature vegetation.

Where to go from here

Each of these follows from something on this page — a relationship in the evidence, a claim people ask about, or the next mechanism along.

How complete this page is, and what it is still missing

NatureHQ publishes its own gaps. This page is at 36% completeness against what we would call a finished subject, and was last reviewed on 2026-09-04. It carries 3 claims and answers 2 mapped search questions.

  • no research from the last few years is attached — check for newer work
  • more experiments could be explained in plain English
  • no popular claim about this subject has been checked yet
  • Chronosequence studies, the main evidence for long successions, are not covered and carry their own assumptions.
  • Animal succession, including on carcasses and dung, is not treated.
  • Soil development during primary succession is described only briefly.