Ecological Succession: A Comprehensive Overview

Ecological succession describes the directional and continuous changes in species composition and ecosystem processes over time. This blog dives deep into the types of succession, the underlying mechanisms, the key changes that unfold, and the concept of climax communities.

1. Types of Succession

1.1 Primary Succession

The gradual colonization and establishment of living communities on substrates that have never supported soil or vegetation. This process begins with abiotic surfaces—such as bare rock, fresh lava, or newly exposed glacial till—and unfolds through a series of biological and physical transformations that create soil and habitat for progressively complex organisms (Clements, 1916; Chapin, Matson, & Mooney, 2002).

• Initial Colonizers (Pioneer Species):  These are the first organisms to arrive and establish on newly exposed or disturbed substrates lacking soil and vegetation.
• Key Characteristics
• High dispersal ability and rapid reproductive cycles to exploit open niches
• Tolerance to extreme abiotic stresses (desiccation, temperature swings, nutrient scarcity)
• Simple structures that demand minimal resources
• Ecological Roles
• Substrate modification: lichens and mosses secrete organic acids that chemically weather rock, initiating soil formation
• Nutrient enrichment: nitrogen-fixing cyanobacteria and bacteria boost soil fertility, making conditions viable for later colonists
• Microhabitat creation: development of a thin organic layer retains moisture and buffers temperature fluctuations
• Begin soil formation by secreting organic acids that break down rock (Odum, 1969)
• Successional Mechanism
• Facilitation: pioneer species alter the environment in ways that allow less hardy, competitively superior species to establish (Connell & Slatyer’s facilitation model)
• Examples
• Lichens and cyanobacteria on glacial till and volcanic lava flows
• Mosses on newly exposed rock faces
• Nitrogen-fixing bacteria in barren sandy soils

 

• Successional Trajectory: The sequential pathway and rate of ecosystem change characterized by orderly shifts in species composition, structure, and ecosystem processes over time. Key Features
• Directional progression from simple to more complex communities
• Predictable stages: pioneer, early successional, mid-successional, late-successional, climax
• Influenced by site conditions, species interactions, disturbance history, and climate

• Underlying Processes
• Colonization and establishment of new species
• Competitive replacement and niche partitioning
• Feedback between biotic communities and abiotic environment (e.g., soil development, microclimate alteration)
• Ecological Significance
• Reflects ecosystem resilience and recovery potential after disturbance
• Guides restoration ecology by identifying reference trajectories for degraded landscapes
• Helps predict carbon sequestration, nutrient cycling, and biodiversity trends through time
• Examples
• Primary succession on Surtsey Island, Iceland: bare lava → lichens and mosses → grasses → shrubs → birch woodlands over ~50 years
• Secondary succession in abandoned Midwestern U.S. farmlands: herbaceous weeds → grasses and legumes → shrubs → oak–hickory forest within 80–120 years
• Glacier Bay, Alaska: Pioneer lichens colonize bare rock; over centuries, spruce–hemlock forest forms (Chapin, Matson, & Mooney, 2002).

 Successional stages from pioneer to climax community

1.2 Secondary Succession

Secondary succession describes the orderly and predictable series of community changes that follow a disturbance in an area where soil and much of the original biotic community remain intact. Unlike primary succession, the substrate already contains organic matter, seeds, and root systems, allowing recovery to proceed more rapidly through familiar stages of plant and animal colonization. therefore, secondary succession takes place in areas where a preexisting community was removed by disturbance, but soil and seed bank remain (e.g., abandoned farmland, burned forest).

Secondary Succession Forest Time Lapse

• Initial Conditions:
• Soil structure, nutrients and propagules are largely intact
• Faster recovery compared to primary succession
• Successional Trajectory:
• Annual weeds and grasses dominate first year post-disturbance
• Perennial herbs and shrubs establish over 3–5 years
• Early successional trees (e.g., birch, poplar) emerge within a decade
• Climax species (e.g., oak, beech) replace pioneers over several decades
• Example:

• Abandoned agricultural fields in the northeastern United States transition from grasses to oak–maple woodlands within 50–100 years (Clements, 1916).
• Post-fire recovery in ponderosa pine woodlands, where grasses and forbs give way to shrubs and young pines within two decades
• Floodplain succession along the Mississippi River, cycling between herbaceous swamps and bottomland forests following periodic inundation

Secondary succession in a post-fire pine forest

2. Mechanisms of Succession

Connell and Slatyer (1977) identified three primary mechanisms that drive species turnover:

• Facilitation:
• Early colonists modify the environment, making it more habitable for subsequent species
• Example: Mosses retain moisture and improve soil fertility, enabling vascular plants to establish
• Tolerance:
• Later-arriving species are neither helped nor hindered by pioneers; they simply tolerate existing conditions better
• Example: Shade-tolerant tree seedlings germinate under pioneer canopy and outcompete them over time
• Inhibition:

• Early occupants actively suppress establishment or growth of newcomers (e.g., through allelopathy or resource preemption)
• Black locust (Robinia pseudoacacia) fixes nitrogen and casts dense shade, inhibiting understory herbs

3. Key Changes During Succession

Ecological succession is marked by predictable shifts in abiotic and biotic factors:

• Soil Development:
• Increase in organic matter, nutrient availability and water-holding capacity (Odum, 1969)
• Species Richness and Diversity:
• Diversity typically rises rapidly during early stages, peaks at mid-succession, and may decline slightly as competitive dominants exclude others
• Biomass Accumulation:
• Net primary productivity increases through mid-succession before leveling off at climax (Odum, 1969)
• Trophic Structure and Interactions:
• Complexity of food webs and symbiotic relationships (e.g., mycorrhizae, pollinators) intensifies over time
• Example:

• In abandoned fields, soil carbon increases by 50–70% in the first 20 years, driving shifts from herbaceous to woody species (Chapin et al., 2002).

4. Concept of Climax Community

A climax community is the stable, self-perpetuating endpoint of ecological succession under a given set of climatic and edaphic (soil) conditions. At this stage, species composition reaches a dynamic equilibrium where rates of colonization and extinction balance, and ecosystem structure and function display minimal directional change over time. So, A climax community is the endpoint of successional change under a given climate and soil regime—a relatively stable assemblage in dynamic equilibrium.

• Classical View (Clements, 1916):
• Succession culminates in a single, stable climax determined by regional climate (“climatic climax”)
• Modern Perspectives:
• Poly climax Theory: Soil, topography and disturbance regimes create multiple climax types within a region
• Climax Mosaic: Landscape comprises patches at different successional stages, continually shifting due to disturbances (Pickett & White, 1985)
• Examples:
• Temperate deciduous forest climax: oak–maple association in eastern North America
• Chaparral climatic climax: evergreen shrubs adapted to Mediterranean climate patterns

Mature Oak–Maple Forest representing a Climax Community

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  video link for Ecological Succession 

References

Chapin, F. S., Matson, P. A., & Mooney, H. A. (2002). Principles of terrestrial ecosystem ecology. Springer.

Clements, F. E. (1916). Plant succession: An analysis of the development of vegetation. Carnegie Institution of Washington.

Connell, J. H., & Slatyer, R. O. (1977). Mechanisms of succession in natural communities and their role in community stability and organization. The American Naturalist, 111(982), 1119–1144.

Odum, E. P. (1969). The strategy of ecosystem development. Science, 164(3877), 262–270.

Connell, J. H., & Slatyer, R. O. (1977). Mechanisms of succession in natural communities and their role in community stability and organization. The American Naturalist, 111(982), 1119–1144.

Pickett, S. T. A., & White, P. S. (Eds.). (1985). The ecology of natural disturbance and patch dynamics. Academic Press.