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Secondary succession

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2.5.6 Secondary successions happen on bare soil where there has been a pre-existing community, such as a field where agriculture has ceased or a forest after an intense firestorm.

Consider an example of secondary succession, which could be a well-documented example, such as the Broadbalk Wilderness at Rothamsted, or a local example.

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Secondary succession differs from primary succession in one critical respect: soil already exists. This means that a seed bank may be present, root fragments and fungal networks may survive underground, and nutrients are already cycling through the soil. As a result, secondary succession is faster and typically involves fewer seral stages than primary succession.

Examples of triggers for secondary succession:

Trigger Example
Abandonment of farmland Broadbalk Wilderness, Rothamsted
Forest fire Regeneration after wildfire
Flooding Floodplain recovery after inundation
Clearing of vegetation Abandoned building sites
Cessation of grazing Grassland released from livestock

  1. In your own words, explain the key difference between primary and secondary succession.

  2. What advantage does a site with existing soil have over bare rock or bare sand when succession begins? Identify at least three specific advantages.

  3. Suggest why secondary succession typically involves fewer seral stages than primary succession.

Case study: Broadbalk Wilderness at Rothamsted

One of the longest-running ecological experiments in the world. Rothamsted Research in Hertfordshire, England, set aside a section of the Broadbalk wheat field in the 1880s, allowing it to undergo unmanaged secondary succession. The progression over more than 140 years:

Broadbalk Wilderness succession timeline

Time period Community present Key changes
Immediately after abandonment Annual weeds and remaining crop plants Existing soil with nutrient reserves and seed bank
Within 5 to 10 years Perennial grasses and wildflowers Wind-blown and dormant seeds germinate; root competition begins
By the early 1900s Scrub species (hawthorn, blackthorn) Woody plants establish; soil organic matter increases
By the mid-20th century Developing tree canopy (oak, ash, sycamore) Canopy shading reduces ground-level species; leaf litter deepens soil
Present day (140+ years) Closed-canopy mixed deciduous woodland Approaching climax community for lowland England; organic carbon in soil has increased steadily since 1881

The speed of this transition (approximately 100 years from wheat field to woodland) compared with primary succession on Surtsey (still in early stages after 60+ years) or sand dunes (400+ years to climax) illustrates the importance of pre-existing soil and seed bank.

e-RA Broadbalk Wilderness

  1. Explain why secondary succession at Broadbalk was significantly faster than primary succession on Surtsey. Refer to at least two specific differences in starting conditions.

  2. What evidence from Broadbalk shows that soil properties change during succession?

  3. Why does canopy shading in the later stages reduce the number of ground-level species?

How do ecosystem properties change during succession?

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2.5.7 Energy flow, productivity, species diversity, soil depth and nutrient cycling change over time during succession.

Consider data in tables or figures related to succession and the reasons for changes in these factors.

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