Successional describes the step-by-step process through which biological communities replace one another over time on a given piece of ground, water, or even an artificial surface. In ecology, succession is the closest thing nature has to a storyline: bare rock gets colonized by lichens and mosses, grasses move in, shrubs follow, and eventually a forest or other mature community develops. The concept applies far beyond forests, though. Rocky shorelines, abandoned farmland, lava flows, microplastic particles drifting through wastewater, and the decaying logs on a rainforest floor all undergo their own successional sequences, each shaped by a distinct set of environmental pressures and biological interactions.
Primary Versus Secondary Succession
Ecologists split succession into two broad categories. Primary succession starts from scratch on surfaces that have never supported life or where previous biological material has been completely stripped away. Think of a glacier retreating to expose bare rock, a new volcanic island cooling, or a mine spoil heap. Secondary succession picks up where a disturbance left something behind: soil, seeds, root fragments, a microbial community. A forest regrowing after a wildfire or a farm field returning to grassland after abandonment are classic examples.
The practical difference between the two is speed. A global review of vegetation recovery found that total plant cover comes back significantly faster in secondary succession than in primary succession, which makes intuitive sense given that secondary sites already have soil and a seed bank to work with.1Land Degradation & Development. Potential of vegetation and woodland cover recovery during primary and secondary succession, a global quantitative review Among primary sites, post-mining areas recovered the fastest, while glacier retreats were the slowest. Among secondary sites, abandoned agricultural fields led the pack. The factors that controlled recovery speed also differed: latitude, soil pH, temperature, and the size of the disturbed area all mattered for primary succession, whereas secondary succession was influenced mainly by latitude.2Land Degradation & Development. Potential of vegetation and woodland cover recovery during primary and secondary succession, a global quantitative review
The two types also differ in biological outcomes. A cross-biome comparison found that primary seres were more likely to show increases in species richness over time, tended to follow divergent trajectories (meaning similar starting points could end up looking quite different), and were less influenced by invasive alien species than secondary seres.3Journal of Ecology. Differences between primary and secondary plant succession among biomes of the world Secondary succession, by contrast, often inherits the legacy of whatever came before, including any non-native species that had already established themselves.
What Drives Species Replacement
The core puzzle of succession is why one set of species gives way to another. Several mechanisms operate simultaneously, and the relative importance of each shifts as the community ages.
Facilitation is the idea that early-arriving species make conditions better for later ones. On nurse logs in temperate rainforests, early-colonizing mosses create a moist, stable surface where tree seedlings germinate far more readily than on bare wood. Seedling density is highest on young logs covered with these early bryophytes. But as the log ages and a thick mat of long-lived moss builds up, the interaction flips from helpful to competitive: later moss species actually suppress seedling establishment.4PubMed Central. Plant-plant interactions change during succession on nurse logs in a northern temperate rainforest In drylands, pioneer shrubs that act as “nurse plants” tend to facilitate the growth of neighboring species more effectively than plants from later successional stages, though the variation within any single stage is large.5PubMed Central. The role of nurse successional stages on species‐specific facilitation in drylands: Nurse traits and facilitation skills
Competition is the other side of the coin. As resources shift over the course of succession, the traits that make a plant competitive change too. A plant that thrives in full sun on nutrient-poor soil may be a poor competitor in the shade of a closed canopy. These inverse correlations among life-history traits produce predictable species replacements, but the patterns only make sense when you look at competition among individual plants rather than averaging across whole populations.6The American Naturalist. Plant succession: Life history and competition
A study in karst ecosystems captured this shift in strategic emphasis neatly. Early successional communities were dominated by stress-tolerant plants, but as succession progressed, competitive and ruderal (fast-growing, disturbance-adapted) strategies became increasingly prominent. The transition tracked closely with changes in woody species diversity and leaf nutrient traits.7PubMed Central. Shifts and Trade-Offs of Ecological Strategy Associated With Species Diversity and Functional Traits During Vegetation Succession Progress in Karst Ecosystem
How Plants Change Their Playbook Over Successional Time
If you could line up early and late successional plants side by side, the differences would be visible even under a microscope. Pioneer tree species in tropical moist forests have dramatically higher stem glucose content, larger water-conducting vessels, denser stomata, and more chlorophyll than their non-pioneer counterparts. Non-pioneers invest instead in thicker cell walls and larger mesophyll cells.8Ecological Indicators. Stem and leaf functional traits allow successional classification in six pioneer and non-pioneer tree species in Tropical Moist Broadleaved Forests Pioneers are essentially built for speed: grow fast, capture light, reproduce quickly. Non-pioneers are built for endurance: tougher tissues, slower metabolism, better defenses.
On a broader scale, primary succession on oceanic islands reveals a shift from “acquisitive” leaf traits (thin, high-nutrient leaves designed to grab resources fast) to “conservative” traits (thick, durable leaves that hang onto resources) as the substrate ages. Dispersal mode shifts too: wind-dispersed species dominate early because they are the ones that can reach a barren surface, while animal-dispersed species become more common later as the community develops enough structure to support wildlife.9Journal of Ecology. Primary succession and plant functional traits on an oceanic island
The Underground Succession You Cannot See
The visible turnover in plants is mirrored by an equally dramatic turnover in the soil. During secondary succession, the ratio of fungi to bacteria rises steadily. Early successional soils are bacteria-dominated: microbes that grow fast, burn through carbon quickly, and hold relatively little of the soil’s nutrients in their biomass. As succession proceeds, fungi take over. Fungal communities are slower-growing but more efficient, locking a larger share of carbon and nitrogen into their biomass and releasing less through respiration.10Soil Biology and Biochemistry. Trends in soil microbial communities during secondary succession The overall abundance of both bacteria and fungi tends to increase in early successional stages and then plateau, while microbial diversity continues to climb in a roughly linear fashion over time.11Land Degradation & Development. Changes in soil microbial community structure during long‐term secondary succession
Mycorrhizal fungi, the root-associated partners that help plants acquire nutrients, also change with successional stage. In older successional communities, networks of arbuscular mycorrhizal fungi become more species-rich and more robust to the random loss of a plant partner than in younger ones.12PLoS ONE. Arbuscular Mycorrhizal Fungal Networks Vary throughout the Growing Season and between Successional Stages Mid- and late-successional tree seedlings appear to benefit more from these fungal partners than early-successional species do, suggesting that the fungi may actually help accelerate the transition from pioneer to mature forest.13PubMed. Associations among arbuscular mycorrhizal fungi and seedlings are predicted to change with tree successional status
Nutrient cycling follows its own successional trajectory. In primary succession, the capacity of soils to convert organic nitrogen into plant-available forms rises through the first several stages and then levels off. In secondary succession, nitrogen mineralization tends to remain relatively steady except at the very oldest sites, where it spikes.14Ecology. Nitrification Potentials in Primary and Secondary Succession
Animals Follow the Plants, But Not Always in Step
Because animals depend on habitat structure and food resources shaped by vegetation, their recovery during succession generally tracks with plant recovery. A synthesis of tropical secondary forests found that vertebrate recovery increased with successional stage across the board, but the details depended on the animal group. Amphibian and reptile communities recovered their species composition more rapidly on islands than on mainlands, mammal recovery was faster in drier regions, and landscape context mattered: more forest patches in the surrounding area sped up compositional recovery for amphibians, reptiles, and mammals alike.15Oikos. Recovery of amphibian, reptile, bird and mammal diversity during secondary forest succession in the tropics
Insects tell a more nuanced story. In boreal forests recovering from logging, beetle assemblages shifted significantly during the first few decades. Ground-dwelling and flying beetle communities in stands that were roughly two to three decades post-harvest looked distinctly different from those found in old-growth forests. Interestingly, the beetle communities in both very recent cuts and in stands that had matured beyond that intermediate window were not statistically distinguishable from old-growth assemblages.16PLOS ONE. Temporal dynamics in animal community assembly during post-logging succession in boreal forest The implication is that early post-disturbance conditions and late-recovery conditions can sometimes support similar suites of species, while the transitional middle period is the odd one out.
Carbon Storage and the Productivity Question
One reason policymakers care about successional stage is carbon. Older, late-successional forests generally store more carbon in their trees than younger ones. A comparison of an early-successional birch forest and a late-successional mixed broadleaf-Korean pine forest in northeastern China found that tree carbon storage in the mature forest was about 120 metric tons per hectare compared to roughly 79 in the birch forest.17Ecological Research. Stand density and species richness affect carbon storage and net primary productivity in early and late successional temperate forests differently Yet productivity, the amount of new biomass produced each year, was not significantly different between the two. What did differ was what controlled that productivity: in the young birch forest, tree density was the main driver, while in the mixed forest, both density and species richness mattered.18Ecological Research. Stand density and species richness affect carbon storage and net primary productivity in early and late successional temperate forests differently
Whole-ecosystem carbon exchange along a successional gradient in the southeastern United States broadly followed the classic theoretical prediction that both photosynthesis and respiration rise with successional age. But the late-successional hardwood site produced a surprisingly large net carbon uptake, bucking the expectation that old forests should approach a near-zero carbon balance as respiration catches up with production.19Global Change Biology. Role of vegetation in determining carbon sequestration along ecological succession in the southeastern United States That finding matters for climate models, which have sometimes treated old forests as carbon-neutral.
Disturbance as Part of the Process
Succession is not a one-way street ending at a single stable destination. Disturbances reset parts of the landscape to earlier stages, creating a patchwork of communities at different ages. One of ecology’s most debated ideas, the intermediate disturbance hypothesis, predicts that species diversity peaks when disturbances happen at a moderate frequency or intensity: too little disturbance allows dominant species to crowd out weaker competitors, while too much disturbance wipes the slate before slower species can establish.
Tests of this idea have produced mixed results across ecosystems, but some systems fit the prediction well. On shallow reef spurs in Belize, coral diversity was highest at intermediate levels of physical disturbance. Storm-generated debris reduced the cover of the dominant coral species, opening space for competitively subordinate species to gain a foothold.20Journal of Experimental Marine Biology and Ecology. Landscape patterns of reef coral diversity: a test of the intermediate disturbance hypothesis A two-year experiment on rocky intertidal walls also found a unimodal relationship between disturbance intensity and diversity, consistent with the hypothesis, though the differences were modest.21PubMed Central. The intermediate disturbance hypothesis underlies community structure in rocky intertidal forests
In some marine systems, succession is not a slow march toward stability but a cyclic loop. Along certain rocky shores, bare rock gets colonized by barnacles and crustose algae, which are then overgrown by mussels, whose eventual detachment returns the surface to bare rock again. This cycle generates persistent, irregular species fluctuations that never approach equilibrium.22PubMed Central. Species fluctuations sustained by a cyclic succession at the edge of chaos
The Classic Debate That Shaped the Field
Much of what ecologists argue about regarding succession traces back to a disagreement from over a century ago. Frederic Clements proposed that plant communities develop in a coordinated, almost organism-like way toward a predictable “climax” state. Henry Gleason countered that species respond independently to their environment and that community composition is largely a product of individual species’ tolerances and dispersal abilities, not of communities acting as integrated wholes.23PubMed. Method and metaphysics in Clements’s and Gleason’s ecological explanations Modern ecology has mostly sided with Gleason’s individualistic view, but a recent study on Pikes Peak, Clements’s own lifelong study site, revisited the question and found the truth is, unsurprisingly, messier than either extreme. Whether species distributions look “Clementsian” or “Gleasonian” depends on how you measure them.24PubMed. Revisiting Clements and Gleason: Insights from Plant Distributions on Pikes Peak, Clements’s Life-Long Study Site
The practical legacy of this debate is the recognition that succession does not always converge on one predetermined endpoint. The forests regrowing in and around Rio de Janeiro, for instance, recovered structural and functional attributes over centuries of secondary succession following charcoal production, but their species composition now includes a substantial exotic component. These are “novel ecosystems,” structurally sound forests that provide ecosystem services to millions of people but that do not resemble the pre-disturbance community.25Royal Society Open Science. Land use and social-ecological legacies of Rio de Janeiro’s urban Atlantic forests: from charcoal production to novel ecosystems
When Restoration Tries to Steer Succession
Understanding successional dynamics matters most, perhaps, when people try to speed the process up. Ecological restoration often aims to shortcut succession by planting seeds, removing invasive species, or reintroducing soil organisms. But whether active intervention actually outperforms simply letting nature take its course depends heavily on the reference point you choose.
A 24-year experiment in a Minnesota old-field grassland found that adding native tallgrass prairie seeds boosted native grass and forb abundance in the treated plots, especially when the original vegetation was first removed with herbicide, burning, and tilling. At the small scale, though, even the unrestored plots within the same field achieved similarly high native abundance after 24 years, possibly because seeds drifted from nearby treated areas. When the researchers compared their actively restored plots against passively recovering fields across the broader landscape, the benefit of active restoration was clearer but still variable: many fields in the surrounding area had transitioned to native grass dominance on their own.26Journal of Applied Ecology. Active restoration after three decades: Seed addition increases native dominance compared to landscape‐scale secondary succession The takeaway is that the scale of your comparison can change whether restoration “works” or merely matches what passive succession would have done anyway.
A related distinction in the restoration world is between restoring a landscape to a specific historical target and “rewilding,” which leans more heavily on natural processes. Rewilding accepts that the endpoint may not match the historical baseline and instead focuses on reestablishing ecological processes, including successional dynamics, that allow the landscape to organize itself.27Journal of Applied Ecology. The differences between rewilding and restoring an ecologically degraded landscape
Climate Change and the Unpredictability of Future Succession
All of the successional patterns described above were established under relatively stable climatic conditions. As climate shifts, the rules may change. Multiple lines of evidence indicate that forest recovery dynamics are sensitive to temperature, precipitation, and atmospheric carbon dioxide. Growth rates generally increase with CO₂ and warmth, but drought can devastate seedling recruitment and survival, particularly in younger forests. Because species within a community respond differently to changing conditions, climate change can alter competitive hierarchies and push successional pathways in unexpected directions. In extreme cases, forests may cross thresholds after disturbance and fail to recover to their previous state entirely.28PubMed. Altered dynamics of forest recovery under a changing climate
Recent work in boreal forests reinforces this concern while adding an important nuance. Widely predicted climate-driven transitions in boreal systems, such as shifts from conifer dominance to deciduous dominance, appear to be more context-dependent and variable than earlier models suggested. The ecological pathways driving successional transitions are complex and interlocking, and a simple “warmer means more deciduous” rule does not capture what is actually happening on the ground.29Forest Ecology and Management. Complex ecological pathways drive boreal forest successional dynamics
Succession on Surfaces No One Expected
One of the stranger frontiers in successional ecology is the discovery that microplastics in wastewater serve as substrates for microbial colonization, and the biofilms that form on them undergo succession just like any other community. Plastic particles attract bacteria and fungi that form layered biofilms with distinct metabolic activities.30PubMed Central. Microbial Succession on Microplastics in Wastewater Treatment Plants: Exploring the Complexities of Microplastic-Microbiome Interactions Research comparing microplastics to natural polymers in river water found that biofilms on plastic particles exhibit secondary succession characteristics, resembling communities that recolonize after disturbance, while biofilms on natural polymers persist in a state resembling primary succession. Among the colonizers are bacteria with the capacity to degrade the plastic itself, suggesting that succession on synthetic surfaces may eventually recruit organisms capable of breaking down their own habitat.31PubMed. Distinctive patterns of bacterial community succession in the riverine micro-plastisphere in view of biofilm development and ecological niches
The fact that the same successional logic, early colonizers modifying conditions for later arrivals, competitive displacement, gradual increases in diversity, plays out on a fragment of polyethylene drifting through a wastewater treatment plant speaks to how fundamental the process is. Succession is not a property of forests or grasslands. It is a property of biological communities encountering new space.