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Ecological
Succession

Explore how ecosystems change over time, from bare rock to complex forests, through predictable stages of community development.

AP Environmental Science

What Is Ecological Succession?

Ecological succession is the process by which the structure of a biological community changes over time. Species replace one another in a largely predictable sequence as environmental conditions shift, ultimately leading toward a stable climax community.

Why Does Succession Matter?

★ Biodiversity
Succession increases species richness and ecosystem complexity over time.
★ Resilience
Understanding succession helps predict how ecosystems recover after disturbance.
★ Conservation
Guides restoration ecology, land management, and habitat preservation efforts.

Key Terms to Know

1
Pioneer species: The first organisms to colonize a barren or disturbed area (e.g., lichens, mosses, grasses).
2
Climax community: A stable, mature community that persists with little change until the next major disturbance.
3
Sere: A particular stage in the succession sequence; the full series of stages is called a seral series.
4
Disturbance: Any event (fire, flood, volcanic eruption, human activity) that disrupts an existing community.

Two Types: Primary vs. Secondary

Primary Succession Bare Rock / New Surface Lichens + Mosses (Pioneers) Grasses + Small Plants ... Shrubs ... Trees ... Climax Secondary Succession Disturbed Area (Soil Remains) Grasses + Herbs (Fast Growth) Shrubs + Young Trees Mature Forest (Climax) Hundreds to thousands of years Decades to centuries

Primary Succession in Detail

Primary succession occurs on newly exposed surfaces where no soil exists: cooled lava flows, retreating glaciers, or newly formed islands. The process is slow because soil must be created from scratch.

1
Bare substrate: Rock, sand, or volcanic material with no organic content.
2
Pioneers arrive: Lichens and cyanobacteria break down rock, acids create thin soil.
3
Mosses and ferns: Retain moisture, add organic matter as they die and decompose.
4
Grasses and shrubs: Deeper roots stabilize soil; animals begin colonizing.
5
Climax community: Mature forest (or other biome-dependent community) with stable biodiversity.

Secondary Succession in Detail

Secondary succession occurs where a community has been disturbed but soil remains intact: after wildfires, logging, hurricanes, or abandoned farmland. It proceeds much faster than primary succession.

Explain how seed access and interventions can change succession.

Use this illustration to explore the concept described in its caption.

Matched retained-soil scenes compare passive recovery with assisted recovery using a planted root plug and nonnative-plant removal. Outcomes are conditional.
Both recovery branches begin with soil intact. Native planting and invasive removal represent an assisted pathway whose outcome depends on site conditions.

Succession depends on soil and biological legacies

Two rows compare bare glacial rock becoming vegetated with burned woodland recovering above visible retained soil and roots; later patches contain mixed open vegetation and trees.Bare substrate and retained soil create different starting conditions for succession. Colonization and later communities depend on climate, dispersal, surviving organisms and further disturbance.

Succession depends on soil and biological legacies

Succession depends on soil and biological legacies. Bare substrate and retained soil create different starting conditions for succession. Colonization and later communities depend on climate, dispersal, surviving organisms and further disturbance.Bare substrate and retained soil create different starting conditions for succession. Colonization and later communities depend on climate, dispersal, surviving organisms and further disturbance.

Disturbance regime and recovery are separate dimensions

Three pine-woodland states show a surface burn, surviving trees after fire and later regeneration.Return interval, fire intensity, ecological severity and time since a fire describe different properties of a disturbance. A single event and its recovery sequence cannot establish a frequency–diversity relationship.

Disturbance regime ≠ recovery time

Disturbance regime ≠ recovery time. Return interval, fire intensity, ecological severity and time since a fire describe different properties of a disturbance. A single event and its recovery sequence cannot establish a frequency–diversity relationship.Return interval, fire intensity, ecological severity and time since a fire describe different properties of a disturbance. A single event and its recovery sequence cannot establish a frequency–diversity relationship.

Primary vs. Secondary: Side by Side

Feature Primary Secondary
Starting condition No soil present Soil intact
Pioneer species Lichens, mosses Grasses, weeds
Timeframe Hundreds to thousands of years Decades to centuries
Trigger examples Volcanic eruption, glacial retreat Fire, logging, farming
Soil formation Must be created from scratch Already exists with seed bank
Speed to climax Very slow Relatively fast

Biodiversity Trends During Succession

Time Biodiversity Pioneer Early Seral Mid Seral Climax Species Richness Biomass

The Climax Community

The climax community is the final, relatively stable stage of succession. It is determined primarily by the region's climate (temperature and precipitation). Different biomes have different climax communities.

★ Temperate
Deciduous forest with oaks, maples, and beeches as dominant canopy species.
★ Boreal
Coniferous forest (taiga) dominated by spruce and fir trees.
★ Grassland
Prairies maintained by fire and grazing: grasses are the climax species.

How to Identify the Succession Type

1
Check for soil: Is there existing soil with seeds and nutrients? If no soil, it is primary succession.
2
Identify the disturbance: Did it remove all life and soil (volcanic eruption, glacier) or just above-ground life (fire, hurricane)?
3
Look at pioneer species: Lichens and mosses = primary. Grasses and weeds = secondary.
4
Estimate timeframe: If it takes centuries to millennia, it is likely primary. If decades, secondary.

Example: Mount St. Helens

Lava + Pyroclastic Debris (No Soil) 1980 Eruption Lichens + Lupines Fireweed + Grasses Alder + Willow Trees Primary Succession: soil destroyed by eruption

Example: Abandoned Farmland

Time (decades) Year 0 Bare field (soil intact) Years 1-3 Annual grasses + weeds Years 3-20 Perennial herbs + shrubs Years 20-100+ Mature forest (climax) Low diversity High diversity

Example: Aquatic Succession

Stage 1 Deep Lake Stage 2 Shallow Lake Sediment fills in Stage 3 Marsh / Bog Emergent plants Stage 4 Land Forest Aquatic Succession: Lake to Land Sediment accumulation gradually fills in the lake

Models of Succession

★ Facilitation
Early species improve conditions for later species (e.g., nitrogen fixation enriches soil). The classic model.
★ Inhibition
Early species resist replacement: they inhibit later species until they die or are damaged. Succession slows.
★ Tolerance
Later species are neither helped nor hindered: they simply tolerate lower resource levels and eventually outcompete pioneers.

A seedling’s neighbors can help, tolerate or inhibit

Focal seedling grows among low vegetation and lichens. This is habitat context, not a measured three-treatment comparison; the exact hypothetical panel supplies the mechanism comparison.Compare how a seedling responds when neighboring plants improve conditions, have little effect on establishment, or inhibit it. These patterns distinguish facilitation, tolerance and inhibition.

Pioneer present vs removed

Pioneer present vs removed. Compare how a seedling responds when neighboring plants improve conditions, have little effect on establishment, or inhibit it. These patterns distinguish facilitation, tolerance and inhibition.Compare how a seedling responds when neighboring plants improve conditions, have little effect on establishment, or inhibit it. These patterns distinguish facilitation, tolerance and inhibition.

Common Mistakes

✕ Confusing the Two Types
The key factor is whether soil exists: not the type of disturbance. A landslide that removes soil down to bedrock is primary, even though it is not volcanic.
✕ Climax = Permanent
Students assume climax communities never change. In reality, disturbances (fire, storms) constantly reset parts of the ecosystem.
✕ Ignoring Pioneer Diversity
Pioneer species vary by succession type: lichens for primary, grasses/weeds for secondary. Don't list lichens for farmland recovery.

Question 1 of 5

A volcanic island rises from the ocean, creating a surface of cooled lava with no soil. What type of succession will occur?

Question 2 of 5

A forest fire destroys all above-ground vegetation, but the soil and root systems remain intact. Which pioneer organisms are most likely to colonize first?

Question 3 of 5

Which statement best describes the facilitation model of succession?

Question 4 of 5

A retreating glacier exposes bare rock in Alaska. Over 200 years, ecologists observe the following sequence: lichens, mosses, fireweed, alder, spruce forest. What is the climax community?

Question 5 of 5

Secondary succession typically proceeds faster than primary succession. Which of the following best explains why?