Ecological succession is the process by which the species composition and structure of an ecological community change over time. It occurs when organisms colonize new habitats, respond to disturbances, and influence the conditions that determine which species can survive.
For example, a burned forest may gradually develop new grasses, shrubs, and trees, while newly exposed volcanic rock may slowly become suitable for plants. Understanding succession is an important part of biology because it explains how ecological communities develop, recover, and respond to environmental change.
Succession does not always follow a predictable path toward a mature forest. Climate, soil conditions, species interactions, and repeated disturbances can produce different outcomes, including grasslands, wetlands, shrublands, and forests.
What Is Ecological Succession?
Ecological succession describes changes in the organisms occupying an area over time. These changes occur as species establish populations, compete for resources, modify their surroundings, and respond to environmental conditions.
A newly disturbed habitat may initially support fast-growing plants that tolerate exposed conditions. As vegetation develops, changes in shade, moisture, soil nutrients, and habitat structure can favor different species.
Succession is closely connected to ecological stability, which examines how ecosystems maintain or recover their functions despite change. Understanding the environmental drivers of ecosystem change also helps explain why succession progresses differently across habitats.
Interactions among organisms influence these changes. Competition, herbivory, and mutualism are examples of ecological interactions that affect which species become established. Changes in vegetation also influence biomass distribution, as living material accumulates or shifts among organisms.
Scientists apply these principles to ecosystem restoration in environmental science, where understanding natural recovery helps guide the rehabilitation of damaged habitats.
Primary vs. Secondary Ecological Succession
Ecologists distinguish two major types of succession according to the conditions present when community development begins.
| Feature | Primary Succession | Secondary Succession |
|---|---|---|
| Starting conditions | Newly exposed surfaces with little or no developed soil | Previously occupied habitat where soil remains |
| Typical locations | Volcanic rock and land exposed by retreating glaciers | Burned forests, abandoned farmland, and disturbed grasslands |
| Early colonizers | Microorganisms, lichens, mosses, and other tolerant species | Grasses, herbs, surviving plants, and seedlings |
| Soil availability | Soil must develop or accumulate | Existing soil supports regrowth |
| Typical recovery rate | Often slower because soil development is required | Often faster because soil and biological resources remain |
| Possible outcomes | Grassland, shrubland, forest, or another community | Recovery of previous vegetation or development of a different community |
The distinction is useful, but actual recovery depends on local conditions. Secondary succession can be slow when disturbances damage soil or remove seed sources, while some primary succession sites develop vegetation relatively quickly.
Primary Succession: Life Establishing on New Surfaces
Primary succession begins where a developed soil community is absent. Examples include newly formed volcanic surfaces, exposed bedrock after glacier retreat, and certain newly created landforms.
Early colonizers must tolerate limited nutrients, exposure to sunlight, and fluctuating moisture. Microorganisms, lichens, mosses, and specialized plants may establish themselves depending on the environment.
Weathering breaks down rock, while accumulating dust, decomposed organisms, and other organic materials contribute to soil development. As growing conditions change, additional species may become established.
Typical Stages of Primary Succession
- Exposed surface: Bare rock or another newly available surface provides limited resources for plants.
- Early colonization: Microorganisms, lichens, or other tolerant organisms establish populations.
- Soil development: Weathered minerals and organic material accumulate, creating conditions suitable for more organisms.
- Vegetation establishment: Mosses, grasses, herbs, or shrubs spread as resources become available.
- Community development: Additional plants, animals, fungi, and microorganisms establish increasingly varied relationships.
These stages describe a common pattern rather than a fixed sequence. Some environments remain sparsely vegetated because temperature, water availability, or soil conditions limit further development.
Secondary Succession: Recovery After Disturbance
Secondary succession occurs when an existing ecological community is disturbed but much of its soil remains. Common triggers include wildfires, storms, flooding, logging, and agricultural abandonment.
Unlike primary succession, recovery may begin with surviving roots, seeds, soil microorganisms, and nearby populations. These biological resources can accelerate recolonization.
Grasses and flowering plants often establish quickly in open areas. Shrubs and trees may subsequently expand, although their success depends on climate, competition, grazing, and disturbance frequency.
Worked Example: A Forest Recovering After Fire
Consider a hypothetical 10-hectare forest where a wildfire removes most aboveground vegetation but leaves much of the soil intact. The following timeline illustrates one possible secondary succession sequence in a temperate environment. It is not a prediction for every burned forest.
- Year 0: Fire removes vegetation across much of the 10-hectare area. Some roots, seeds, microorganisms, and trees survive.
- Years 1–3: Grasses, flowering plants, and resprouting shrubs begin covering exposed soil. Surviving trees may produce new growth.
- Years 4–10: Young trees establish where suitable seeds, moisture, and growing conditions are available.
- Years 10–30: Tree cover may expand, increasing shade and changing which understory plants can survive.
- After 30 years: Some areas may develop substantial tree cover, while others remain dominated by shrubs or grasses.
The example demonstrates how vegetation structure can change over decades. Actual recovery may be faster, slower, or follow another pathway entirely. Severe soil damage, repeated fires, drought, or limited seed availability can prevent the previous forest community from returning.
How Pioneer Species Change Their Environment
Pioneer species are organisms that establish early in succession. They often tolerate environmental conditions that prevent many other species from surviving.
Some lichens contribute to rock weathering, while plants add organic matter through fallen leaves, dead roots, and other material. Root systems can stabilize soil, and vegetation can modify temperature, moisture, and light availability near the ground.
These changes may help later species establish, a process called facilitation. However, early colonizers do not always benefit newcomers. They may compete for resources or prevent other species from becoming established.
Ecologists therefore recognize several mechanisms of succession, including facilitation, inhibition, and tolerance. Which mechanism dominates depends on the organisms involved and the environmental conditions.
Climax Communities and the Limits of a Final Stage
Traditional ecological models describe succession as progressing toward a climax community: a relatively stable community associated with local environmental conditions.
For example, a temperate region with sufficient rainfall may support a mature forest, while a drier region may support grassland or shrubland. Climate, soils, and disturbance patterns influence which communities persist.
Modern ecology recognizes that succession does not necessarily produce one permanent endpoint. Ecosystems experience ongoing disturbances, species turnover, and environmental variation. Several different community states may persist under similar regional conditions.
A mature forest is therefore not automatically more successful or ecologically valuable than a grassland. Each ecosystem supports organisms adapted to its particular conditions.
Environmental Factors That Control Succession
The direction and speed of succession depend on interacting biological and physical factors.
- Climate: Temperature, precipitation, and seasonal conditions influence survival and growth.
- Soil: Nutrients, moisture, texture, and microbial communities affect plant establishment.
- Seed availability: Nearby vegetation and seed dispersal determine which plants can colonize.
- Species interactions: Competition, herbivory, and mutualism influence community composition.
- Disturbance patterns: The frequency, intensity, and type of disturbance can redirect succession.
- Human activity: Land management, pollution, invasive species, and habitat fragmentation may alter recovery.
For example, repeated fires may maintain an open grassland or shrubland rather than allowing extensive tree establishment. In other environments, fire suppression may encourage woody vegetation to expand.
Ecological Succession and Biodiversity
Succession changes biodiversity by altering the species and habitats present in an area. Early communities may contain relatively few species, while later communities can provide more varied resources and shelter.
However, biodiversity does not always increase continuously. Some intermediate communities support particularly high species richness because open-habitat and developing-forest species coexist. Dense vegetation may later reduce opportunities for species that require sunlight.
Different successional stages also support different animals. Open grasslands may provide habitat for ground-nesting birds, while mature forests support species that depend on large trees, cavities, or shaded conditions.
Maintaining a mixture of habitats at different stages can therefore support regional biodiversity more effectively than managing every area toward the same vegetation type.
Ecological Succession in Restoration and Conservation
Restoration projects often use knowledge of succession to help damaged ecosystems recover. Rather than assuming that planting trees is always the best solution, restoration specialists examine the habitat’s natural conditions and the factors preventing recovery.
Restoration activities may include reintroducing native plants, controlling invasive species, rebuilding wetlands, improving soil conditions, or restoring natural water movement.
Successful restoration does not necessarily recreate an exact historical community. Environmental conditions may have changed, and some species may no longer be available. Projects often focus on restoring ecological functions, supporting native biodiversity, and improving resilience to future disturbances.
Examples of Ecological Succession in Nature
Volcanic Landscapes
New volcanic surfaces provide opportunities to study primary succession. Microorganisms and other early colonizers may establish on exposed material before substantial soil develops. Vegetation patterns depend on moisture, substrate characteristics, and the arrival of seeds.
Land Exposed by Retreating Glaciers
As glaciers retreat, newly exposed surfaces become available for colonization. Scientists can compare areas exposed at different times to investigate soil formation and changes in vegetation, although differences between locations can complicate comparisons.
Forests After Wildfire
Wildfires can initiate secondary succession when soil remains. Recovery may involve surviving trees, resprouting plants, seed germination, and the gradual establishment of new vegetation. Some fire-adapted species depend on periodic burning for successful reproduction.
Abandoned Agricultural Fields
When farming stops, grasses and other herbaceous plants may colonize abandoned fields. Shrubs and trees can establish later if environmental conditions permit. Soil degradation, grazing, and invasive species may alter or delay this process.
Common Misconceptions About Ecological Succession
Misconception 1: Succession Always Ends in a Forest
Forests are only one possible outcome. Grasslands, wetlands, shrublands, and other communities may persist because of climate, soil conditions, and recurring disturbances.
Misconception 2: Biodiversity Always Increases During Succession
Species richness may increase, decrease, or fluctuate. Some species disappear as shade increases or habitat conditions change, while others become established.
Misconception 3: Secondary Succession Always Restores the Original Ecosystem
Recovery does not guarantee a return to previous conditions. Invasive species, repeated disturbances, climate changes, and soil damage may produce a different community.
Misconception 4: A Climax Community Never Changes
Even relatively stable communities experience disturbances, population fluctuations, and species replacement. Ecologists generally view ecosystems as dynamic rather than permanently fixed.
Frequently Asked Questions
What is ecological succession in simple terms?
Ecological succession is the gradual change in the species living in an area. It occurs as organisms colonize habitats, interact with one another, and respond to changing environmental conditions.
What is the difference between primary and secondary succession?
Primary succession begins on surfaces without developed soil, such as newly exposed rock. Secondary succession begins after a disturbance in an area where soil remains, such as a forest recovering after fire.
How long does ecological succession take?
Succession can occur over years, decades, centuries, or longer. Its duration depends on soil development, climate, species availability, disturbance severity, and the type of community developing. There is no universal completion time.
What are examples of pioneer species?
Examples include lichens, mosses, certain microorganisms, grasses, and fast-growing flowering plants. The pioneer species present depend on whether succession begins on bare surfaces or in a previously occupied habitat.
Does ecological succession always happen in stages?
Ecologists often describe succession using stages to make community changes easier to understand. In nature, however, stages may overlap, species may arrive in different orders, and disturbances can interrupt or redirect development.
Ecological succession reveals how communities respond to changing conditions rather than following one fixed path toward maturity. Understanding the processes that influence colonization, species replacement, and recovery helps scientists explain ecosystem change and develop more effective conservation and restoration strategies.
Sources: OpenStax, Biology 2e; Eugene P. Odum and Gary W. Barrett, Fundamentals of Ecology, Fifth Edition; Michael L. Cain, William D. Bowman, and Sally D. Hacker, Ecology, Third Edition.
