Succession 🌱

students, imagine a volcanic island that is completely bare after an eruption. No soil, no grass, no insects, and no birds. Now imagine that a few years later, tiny lichens appear, then mosses, then grasses, shrubs, and eventually a forest. This slow, predictable change in the living community is called succession. In Ecology, succession helps explain how ecosystems change over time, how communities recover after disturbance, and how energy and nutrients move through living systems.

What is succession?

Succession is the gradual change in the species composition and structure of a community over time. It happens because organisms change the environment around them, making it more suitable for some species and less suitable for others. In other words, an ecosystem is not fixed; it develops and changes as conditions change.

A community may begin in a harsh place with few organisms, or it may change after a disturbance such as a fire, flood, storm, or human activity. Over time, more species can move in, survive, reproduce, and compete. This creates a new balance in the ecosystem.

The important idea is that succession is a process, not a single event. It can take years, decades, or even centuries. The speed depends on factors such as climate, soil, water availability, and the distance from nearby seed sources.

Key terms you need to know 📘

To understand succession clearly, students, it helps to know the main terms used in IB ESS.

A pioneer species is one of the first organisms to colonize a new or disturbed area. These species are usually hardy, meaning they can survive difficult conditions such as little soil, high sunlight, wind, or drought. Examples include lichens and mosses in some environments.

A climax community is a relatively stable community that develops at the end of succession, when the ecosystem has reached a more balanced state under the local climate and environmental conditions. This does not mean “unchanging forever.” It means the ecosystem is more stable compared with earlier stages.

A disturbance is an event that changes an ecosystem by removing organisms or changing resources. Disturbances can be natural, such as volcanic eruptions, hurricanes, or wildfires, or human-caused, such as deforestation and agriculture.

A bare substrate is a surface without soil or established vegetation. This could be fresh lava, rock exposed by a glacier, or land left after mining.

Primary succession and secondary succession

Succession is usually divided into two main types: primary succession and secondary succession.

Primary succession

Primary succession begins in an area where there is no soil and usually no living community at all. This often happens on newly formed volcanic rock, land exposed by melting glaciers, or sand dunes where life has not yet become established.

Because there is no soil, the first species must be able to live on bare rock or very poor substrate. Lichens are a classic example. They are not a single organism, but a partnership between a fungus and an alga or cyanobacterium. Lichens help break down rock physically and chemically. Over time, this contributes to soil formation.

As soil depth increases, more plants can grow. Mosses may appear, then grasses, then shrubs, and eventually trees if climate conditions allow. Each stage changes the environment by adding organic matter, increasing water retention, and reducing exposure to wind and sunlight.

Secondary succession

Secondary succession happens where a community already existed, but the soil remains after a disturbance. Examples include farmland abandoned after use, forests regrowing after a fire, or vegetation recovering after a flood.

This type of succession is usually faster than primary succession because soil, seeds, roots, fungi, bacteria, and nutrients are already present. The recovery starts with fast-growing species such as grasses and small herbs, then moves toward shrubs and larger plants.

For example, after a forest fire, some seeds may survive in the soil, and underground roots may sprout again. This gives the ecosystem a head start compared with primary succession.

How succession works in real ecosystems 🌍

Succession happens because species interact with their environment and with each other. Early species often modify the habitat in ways that help later species. This is called facilitation.

For example, pioneer plants may:

• reduce wind speed at the ground surface
• increase soil fertility when they die and decompose
• create shade that lowers temperature
• improve water retention in the soil

These changes make the habitat less harsh. Later species can then survive more easily.

However, succession is not always a simple straight line. Sometimes later species compete strongly with earlier ones, and some species may prevent others from establishing. Also, disturbances can interrupt succession, causing the community to start changing again.

A useful IB idea is that succession is linked to community change and ecosystem development. As succession proceeds, biodiversity often increases, soil becomes richer, and biomass usually increases. The ecosystem becomes more complex, with more feeding relationships and more stable nutrient cycling.

Example: succession after lava flow 🌋

Imagine a lava flow that cools into bare rock. At first, there is no soil, so few organisms can survive. Over time:

1. Pioneer stage: lichens and some microorganisms colonize the rock.
2. Soil formation stage: rock breaks down slowly, and dead organisms add organic matter.
3. Herb stage: mosses and grasses begin to grow.
4. Shrub stage: larger plants root into deeper soil.
5. Forest stage: trees establish if the climate supports them.

This example shows why succession is connected to energy flow and nutrient cycling. As plant cover increases, more sunlight is captured by photosynthesis, and more biomass is produced. Decomposition also increases, returning nutrients to the soil.

Succession, productivity, and biomass

Succession is closely linked to productivity and biomass in ecosystems.

At early stages, productivity is usually low because there are few producers and little soil. As succession continues, more plants grow, so gross primary productivity generally increases. More plant matter means more energy is stored as chemical energy in biomass.

The amount of living material in an ecosystem, called biomass, often rises during succession because plants become larger and more numerous. This is why a mature forest usually has much more biomass than a young grassland or bare rock surface.

However, net ecosystem changes depend on both production and respiration. In younger stages, respiration may be lower because there are fewer organisms. In later stages, total respiration also increases as the food web becomes more complex.

Nutrient cycling during succession ♻️

Succession also changes how nutrients move through the ecosystem. In a newly formed area, nutrient stores are small. Over time, nutrients are added from weathering, decomposition, and biological activity.

As plants and animals establish, they absorb nutrients from soil and later return them through waste and decay. This strengthens nutrient cycling. Soil organisms such as bacteria, fungi, and detritivores become more abundant, helping break down dead matter and release nutrients for plant uptake.

In primary succession, nutrient cycling starts slowly because soil is poor at first. In secondary succession, nutrient cycling can restart faster because some soil nutrients and living organisms already remain after the disturbance.

Why succession matters in IB ESS

students, succession is important because it connects many big ideas in Ecology:

• Ecosystems and communities: succession shows how communities change over time.
• Energy flow and biomass: more plants usually mean more energy captured and more biomass stored.
• Nutrient cycling: soil development and decomposition increase recycling of nutrients.
• Productivity and change: succession is a clear example of ecosystem change and recovery.

Succession also helps people understand conservation and land management. For example, if a forest is cleared, the recovery pathway depends on whether soil remains and whether the area is protected from repeated disturbance. In restoration ecology, scientists may help succession by planting native species, preventing erosion, or removing invasive species.

How to apply IB-style reasoning

When answering exam questions about succession, think in terms of cause and effect.

If asked why primary succession is slower than secondary succession, explain that primary succession begins without soil, seeds, or nutrients, while secondary succession begins with soil already present.

If asked how pioneers help later species, explain that they improve conditions by forming soil, adding organic matter, and reducing harsh environmental conditions.

If asked to compare early and late stages, mention that early stages have low biomass, low species diversity, and simple food chains, while later stages usually have higher biomass, greater diversity, and more complex food webs.

A strong IB answer often includes an example. For instance, after a wildfire, grasses may grow first because they germinate quickly and use open sunlight. Later, shrubs and trees may return as soil stability and shade increase.

Conclusion

Succession is the gradual change of a community over time, from pioneer stages to more stable later stages. It can be primary, when no soil exists, or secondary, when soil remains after disturbance. Succession matters because it shows how ecosystems develop, how biomass and productivity change, and how nutrient cycling becomes more efficient over time. It is a key idea in Ecology and a useful way to understand ecosystem recovery, resilience, and long-term environmental change 🌿

Study Notes

• Succession is the gradual change in a community over time.
• Primary succession starts without soil; secondary succession starts with soil remaining.
• Pioneer species are the first colonizers, often lichens, mosses, or fast-growing plants.
• A climax community is a relatively stable final stage under local climate conditions.
• Succession changes species composition, biomass, productivity, and nutrient cycling.
• Early succession has low biomass and simple food webs; later succession usually has higher biomass and more complex interactions.
• Disturbances such as fire, floods, storms, and human land use can trigger secondary succession.
• Succession connects directly to Ecology because it shows how ecosystems change and recover over time.
• In exams, always explain why changes happen, not just what happens.
• Use real examples such as volcanic rock, forest fires, abandoned farmland, or glaciers to support answers.