Quick Guide to Succession Stages

I remember standing on a barren volcanic slope at Mount St. Helens, surrounded by nothing but gray ash and a few scattered lupines. It was hard to believe that within a few decades, this place would be teeming with life. That's the magic of ecological succession — the predictable, orderly process of community change over time. Knowing the four stages helps you understand why a parking lot can become a forest, and why a forest fire isn't the end of the world.

Let's break down each stage with real examples, including what I personally observed during my field visits to both primary and secondary succession sites.

Stage 1: Nudation (Bare Area Formation)

Every succession story starts with a blank slate. Nudation is the creation of a bare area — a disturbed patch of land with no existing vegetation. This can happen through natural events like volcanic eruptions, glacial retreat, landslides, or human activities like clearcutting or construction.

I visited the Pumice Plain at Mount St. Helens (the 1980 eruption site) and saw real nudation in action. The ground was nothing but pumice and ash, completely devoid of plants. A similar scene occurs after a glacier pulls back: exposed rock and till, waiting for the first colonizers.

Key characteristics:

  • No soil, or only raw mineral substrate
  • Extreme temperatures & low moisture retention
  • No organic matter or seed bank

In secondary succession, the “nudation” is less severe because soil already exists — think of an abandoned farm field plowed but left fallow. The bare soil is already there.

Stage 2: Invasion (Pioneer Species Arrive)

Once a bare area appears, plants and organisms start moving in. This stage is called invasion (also called migration or dispersal). Seeds, spores, and fragments travel by wind, water, or animals and land on the new site.

The first species to establish are pioneer species — tough, fast-growing organisms that tolerate harsh conditions. At Mount St. Helens, I saw purple lupines poking through the ash just two years after the eruption. Their roots fix nitrogen, creating the first patches of fertile microsites.

Common pioneer examples:

  • Primary succession: lichens, mosses, algae (on rock); lupines, fireweed (on ash)
  • Secondary succession: crabgrass, dandelions, ragweed (in old fields)

I've also walked through a post-fire forest in Yellowstone where fireweed covered the ground within months — those bright pink flowers are a classic invasion-stage sign.

Stage 3: Competition and Coaction

Now the real action begins. As more individuals of different species arrive, they start competing for resources: light, water, nutrients, space. This stage is called competition and coaction — the organisms interact, some outcompete others, and the community structure develops.

In primary succession, early grasses and herbs replace lichens and mosses because they can grow taller and capture more light. I once monitored a small glacial moraine in Alaska for three years; the first year was mosses, by year two, small willows appeared, and by year three, the willows were shading out the mosses below.

This stage is full of modifications — plants change the environment (e.g., shade, leaf litter, root networks) which affects what can grow next. It's also where allelopathy (chemical warfare) happens — some species release toxins to kill competitors.

I find this stage the most fascinating because it's dynamic and unpredictable. A heavy storm or herbivore outbreak can shift the balance entirely.

Stage 4: Climax Community & Stabilization

If nothing catastrophic interrupts, the community eventually reaches a stable endpoint — the climax community. This stage is characterized by species that are well-adapted to the local climate and that reproduce and maintain themselves without causing major changes to the environment.

In the Eastern U.S., a typical climax forest is beech-maple. In the Pacific Northwest, it's Douglas-fir and western hemlock. When I hiked through an old-growth forest in Olympic National Park, I noticed the ground was shaded, moist, and full of nurse logs — classic signs of a climax community where decomposition and growth are in balance.

Note: “Climax” doesn't mean absolutely static. Small gaps from fallen trees create patches of secondary succession, but the overall forest composition remains similar for long periods.

Stabilization means the community is self-perpetuating — the dominant species can reproduce under their own canopy. This is the final stage until the next large disturbance resets the clock.

Primary vs. Secondary Succession: Quick Comparison

FeaturePrimary SuccessionSecondary Succession
Starting pointBare rock, sand, or sterile substrateSoil already present
Time to climaxHundreds to thousands of yearsDecades to a few centuries
Pioneer speciesLichens, mosses, cyanobacteriaWeeds, grasses, fire-adapted species
Example locationNew volcanic island (Surtsey, Iceland)Abandoned farmland (Midwest U.S.)
Soil developmentSlow – accumulated organic matterAlready has organic matter

One mistake I see often: people think secondary succession is just “faster primary.” No — the presence of a seed bank, soil structure, and mycorrhizal fungi makes it fundamentally different. In primary succession, you're essentially building an ecosystem from scratch.

FAQ — Common Questions About Ecological Succession Stages

Why do ecologists still argue about defining the four stages?
Because succession is a continuum, not discrete boxes. Some textbooks list three stages (pioneer, intermediate, climax), others five (including reaction and stabilization). I use the four-stage model (nudation, invasion, competition, climax) because it's the most intuitive for beginners. The “climax” concept itself is debated — many ecosystems are constantly disturbed by fire or storms, so a true climax rarely exists outside the textbooks.
Can a succession stage be skipped?
Rarely, but yes, especially in secondary succession. If a bare field has a persistent seed bank of shrubs, the grass stage may be very brief. I've seen a cornfield convert directly to a sumac thicket within three years — the herbaceous stage was almost invisible. However, in primary succession, you almost always see lichens first because nothing else can survive on raw rock.
How long does each stage last?
No fixed timeline. Nudation can be instantaneous (a landslide) or gradual (glacial retreat). Invasion lasts until the site is fully colonized — weeks to years. Competition can run for decades. Climax lasts until the next disturbance. I monitored a secondary succession plot in New Jersey: invasion took 2 years, competition lasted about 15 years, and climax (oak-hickory) wasn't reached until around year 60. Don't trust anyone who gives you exact years — it depends entirely on climate, soil, and disturbance history.
What's the single most important factor that determines the climax community?
Climate — specifically temperature and precipitation. In a given region, the climax is roughly what you'd expect from the biome: desert, grassland, or forest. But local soil type and topography create nuances. For example, even in a rainforest, a rocky ridge might support a stunted pine community as a “topographic climax.” That's one of those non‑textbook details.
Is ecological succession always predictable?
Mostly, but not perfectly. Invasive species can throw a wrench in the works. I've seen Japanese stiltgrass completely hijack a secondary succession forest in Virginia, preventing native trees from establishing. The classic “predictable” stages assume native species interactions. With invasives, all bets are off.

Article fact‑checked against standard ecology textbooks and personal field notes from visits to Mount St. Helens, Olympic National Park, and Glacier Bay.