Primary succession occurs whenever a completely barren surface is exposed for the first time, with no existing soil, seeds, or living organisms present. This includes freshly cooled lava flows, land revealed by retreating glaciers, newly formed volcanic islands, and sand dunes that emerge along coastlines. The key trigger is a surface so new or so thoroughly scoured that life must start entirely from scratch.
The Conditions That Trigger Primary Succession
The defining feature of primary succession is the absence of any biological legacy. There is no soil, no seed bank buried underground, no root systems waiting to regrow. The substrate is essentially sterile: bare rock, volcanic ash, glacial sediment, or raw sand with negligible organic matter and almost no nutrients. This distinguishes it from secondary succession, which happens after a disturbance like a wildfire or flood where soil and seeds still remain. In primary succession, the disturbance is so severe that it creates a completely new surface that doesn’t resemble whatever existed before.
The most common situations that set primary succession in motion:
- Volcanic eruptions that deposit lava or ash, burying or replacing all previous ecosystems
- Glacial retreat that exposes crushed rock and sediment (glacial till) as ice melts back
- New island formation from volcanic activity rising above the ocean surface
- Sand dune creation along coastlines or lakeshores
- Landslides or rockfalls that expose fresh rock faces
- Mining operations that strip away all soil and vegetation down to bedrock
How It Starts: Pioneer Species
The first organisms to colonize bare rock are lichens and mosses. Lichens are particularly important because they can grow directly on stone, slowly breaking it down through both physical and chemical processes. As they grow, they trap tiny particles of organic material and moisture, creating the thinnest possible layer of what will eventually become soil. This process is extraordinarily slow, but it’s the foundation everything else depends on.
On volcanic lava flows, colonization begins almost immediately after the surface cools. According to the U.S. Geological Survey, wolf spiders and crickets are often the first animals to take up residence on new Hawaiian lava flows, feeding on invertebrates that wander onto the barren rock. Meanwhile, a steady rain of organic debris, seeds, and spores accumulates in cracks and pockets. Some of these sheltered spots retain enough moisture to support scattered tree seedlings and a few hardy ferns.
On sand dunes, the pioneers look different. Along the shores of Lake Michigan, for example, sea rocket and beach pea are among the first plants to survive the harsh, wind-blasted lakefront. Marram grass then begins building the first dunes, trapping sand and stabilizing the surface so other species can follow. Eastern cottonwood trees eventually join as another important dune-builder.
The Stages From Bare Rock to Forest
Glacier Bay in Alaska offers one of the best-documented examples of primary succession unfolding in real time. As glaciers have retreated over the past two centuries, they’ve left behind a timeline of succession visible across the landscape. The sequence follows a predictable pattern: mosses colonize the bare glacial till first, followed by wind-dispersed plants like fireweed. Then comes dryas, a low-growing plant that enriches the soil by pulling nitrogen from the air, something all later plants need to survive. Alder shrubs follow, further fixing nitrogen into the soil. Eventually, spruce trees begin growing beneath the alder thickets, and over time, hemlock joins to form a mature old-growth forest with trees at all stages of growth and decay.
Each wave of species changes the environment in ways that make it more hospitable to the next wave. Nitrogen-fixing plants build soil fertility. Shrubs provide shade that retains moisture. Fallen leaves and dead roots are broken down by soil organisms into rich organic material. Each community essentially engineers the conditions for its own replacement.
How Long Primary Succession Takes
Primary succession is one of the slowest ecological processes on Earth. In wet tropical regions like Hawaii, a forest can develop on a lava flow in less than 150 years. In colder or drier climates, the process takes far longer, often many centuries to reach a mature forest stage. The bottleneck is soil formation. Without existing soil, every grain of organic matter must be produced from scratch by lichens, mosses, and the slow chemical weathering of rock.
One of the most famous case studies is Surtsey, a volcanic island that emerged off the coast of Iceland in 1963. By June 1965, just a year and a half after the eruption ended, the first vascular plant seedlings were already growing on the island. Over the following 25 years, researchers documented over 10,000 individual plant occurrences as species gradually established themselves. Birds played a critical role, using the island as a stopover during migration and bringing seeds with them. Still, decades later, Surtsey remains in the early stages of succession, a reminder of just how long the full process takes in cold climates.
What a Climax Community Looks Like
Primary succession doesn’t continue forever. It eventually reaches what ecologists call a climax community: a relatively stable assemblage of species that persists until something disrupts it. In the Pacific Northwest, that might be an old-growth redwood forest where species composition changes very little for decades or even centuries. In the midwestern U.S., it might be a hardwood forest dominated by oaks and hickories.
Climax communities remain in rough equilibrium, with ancient trees dominating the canopy and few opportunities for new plants to establish themselves. But “stable” doesn’t mean frozen. Recent research shows that even in climax communities, shifts in water and nutrient availability can gradually change which species dominate, even without a dramatic disturbance like fire or storm. And when a major disturbance does occur, the clock resets. If the disturbance is severe enough to strip away all soil and biological material, primary succession starts over from the beginning. If soil remains, the faster process of secondary succession takes over instead.
Why Animals Arrive Later
Animals depend on plants for food and shelter, so they colonize primary succession sites on a delay. The first to arrive are typically invertebrates: ants, worms, and snails that can survive in sparse vegetation. On new volcanic islands, birds are often early visitors because they can fly in from nearby land, and they play a dual role by depositing seeds in their droppings. Larger animals like mammals arrive last, usually only after enough vegetation exists to support a food web. The progression mirrors the plant stages: as the ecosystem grows more complex, it can support increasingly complex animal life.