Secondary succession is the type of ecological succession that begins in an area where soil already exists. Unlike primary succession, which starts on bare rock or newly formed land with no soil at all, secondary succession occurs after a disturbance disrupts an existing ecosystem but leaves the soil and its nutrients largely intact.
Why Soil Makes the Difference
The distinction between primary and secondary succession comes down to how severe the disturbance was. Primary succession happens on surfaces that have never supported life before, like cooled lava flows, newly exposed rock after a glacier retreats, or sand dunes. There is no soil, no seed bank, no organic matter. Organisms have to start from scratch, with lichens and a few hardy plants slowly breaking down rock into the beginnings of soil over centuries.
Secondary succession skips that entire soil-building phase. The disturbance, whether it’s a wildfire, a flood, a hurricane, or the abandonment of farmland, removes or damages the plant community but doesn’t strip away the ground beneath it. Because soil, seeds, roots, and microorganisms remain, recovery happens far more quickly.
What Triggers Secondary Succession
Any disturbance that wipes out vegetation without destroying the soil can set secondary succession in motion. Common triggers include:
- Wildfire: Burns plant life above ground but leaves root systems and seed banks in the soil.
- Logging or deforestation: Removes trees but keeps the forest floor and its nutrient-rich organic layer.
- Flooding: Can flatten vegetation and deposit sediment while the underlying soil structure persists.
- Abandoned agriculture: When a farmer stops plowing, the field still has deep, fertile soil ready to support new growth.
- Overgrazing: Intensive livestock grazing can strip vegetative cover almost completely, but the soil remains and succession begins once the pressure is removed.
The key idea is that these disturbances modify an existing set of conditions rather than creating an entirely new surface. A burned forest still has organic matter, fungal networks, and buried seeds. A plowed field still has topsoil rich in nutrients. That biological legacy is what separates secondary from primary succession.
The Role of Seeds and Roots in the Soil
One of the biggest reasons secondary succession moves so fast is the soil seed bank: seeds buried underground from the previous plant community, waiting for the right conditions to germinate. Research on degraded landscapes shows that aboveground vegetation often reestablishes directly from seeds already present in the soil, especially during the early stages of recovery. In the first phases, herbs and grasses dominate both the seed bank and the new plant cover, with high overlap between what’s buried and what sprouts.
As succession progresses into later stages, shrub and tree seeds accumulate in the seed bank as well. However, the similarity between what’s in the soil and what’s growing above ground decreases over time. Reaching a mature, stable ecosystem eventually depends on seeds arriving from surrounding areas, not just what was stored underground. Still, the seed bank provides the critical jumpstart that makes secondary succession so much faster than primary.
Beyond seeds, surviving root systems, soil fungi, bacteria, and decomposing organic matter all contribute. These organisms cycle nutrients, retain moisture, and create the conditions new plants need to establish quickly.
How Secondary Succession Unfolds
Abandoned farmland in the eastern United States offers one of the best-studied examples of secondary succession. The process follows a predictable sequence, though the specific species vary by region.
In the first one to two years after a field is abandoned, annual plants like crabgrass and horseweed colonize the bare soil. These fast-growing species thrive in open sunlight and disturbed ground. By year three, perennial grasses such as broomsedge take over, outcompeting the annuals. Around year five, shrubs like blackberry and tree seedlings, including pines and eastern redcedar, begin to appear wherever seeds are available nearby.
These early trees are still considered pioneer species. They need full sunlight, grow fast, and are relatively short-lived. Over the next several decades, they form a young woodland. As the pines age and die, shade-tolerant hardwoods like white oak and hickory gradually replace them. By about 100 years, a former field may have as many hardwoods as pines. After 200 years, the forest is dominated by hardwood trees, closely resembling the mature forest that might have stood there before the land was ever farmed.
How Long Each Type Takes
Primary succession is extraordinarily slow. Building soil from bare rock requires physical weathering, colonization by lichens and mosses, and the gradual accumulation of organic material. This process takes centuries to even produce enough soil for small plants, and reaching a mature ecosystem can take a thousand years or more.
Secondary succession operates on a much shorter timescale. Because soil, nutrients, and often seeds are already in place, a recognizable plant community can establish within a few years. A full return to mature forest typically takes 100 to 200 years, depending on climate and the severity of the original disturbance. Research across global ecosystems shows that recovery is generally more successful in cold and humid climates than in warm or arid ones, for both types of succession.
Primary vs. Secondary Succession at a Glance
- Starting surface: Primary begins on bare rock or new land with no soil. Secondary begins on land where soil already exists.
- Pioneer species: Primary pioneers are lichens and mosses that can survive without soil. Secondary pioneers are grasses, herbs, and fast-growing shrubs that root directly into existing soil.
- Speed: Primary succession takes centuries to millennia. Secondary succession reaches maturity in decades to a couple hundred years.
- Biological legacy: Primary succession has none. Secondary succession benefits from seed banks, surviving roots, soil microbes, and residual nutrients.
- Species diversity trends: Primary succession is more likely to show steady increases in species richness over time. Secondary succession starts with higher diversity because of the existing seed bank and surrounding plant communities.
Ecologists continue to use the primary and secondary distinction as a foundational framework. Modern models have expanded the concept to include factors like land-use history, landscape context, and feedback loops between plants and soil microbes, but the core question remains the same: did the disturbance leave soil behind? If it did, what follows is secondary succession.