Secondary Succession
Historical Background
Early Concepts of Ecological Succession
The study of succession has its roots in the nineteenth century when naturalists first recognized that ecosystems are not static but change over time. Early observations of abandoned farmlands, burnt forests, and floodplains revealed that vegetation follows predictable patterns of replacement. These patterns were considered evidence of nature’s capacity for self-repair and regeneration.
Contributions of Clements and Gleason
Frederic Clements, in the early twentieth century, formalized the concept of succession, describing it as a linear and orderly process culminating in a stable climax community. He compared plant communities to superorganisms that develop through sequential stages. In contrast, Henry Gleason proposed the individualistic concept, arguing that succession is influenced more by chance dispersal and environmental factors than by predetermined pathways. Together, their contrasting perspectives shaped the framework of modern ecological thought.
- Clements: succession as an orderly, predictable process leading to climax communities.
- Gleason: succession as a product of individual species interactions and environmental variability.
Modern Perspectives on Secondary Succession
Contemporary ecology integrates both deterministic and stochastic views. Succession is now seen as a dynamic process influenced by disturbance, species traits, soil conditions, and climate. Models of succession account for facilitation, inhibition, and tolerance mechanisms, providing a more nuanced understanding of how ecosystems recover after disturbance.
Definition and Characteristics
Secondary succession is the process by which biological communities reestablish themselves in areas where a disturbance has altered but not eliminated soil and some components of the ecosystem. Unlike primary succession, where life colonizes newly formed or barren substrates, secondary succession begins on pre-existing soil that retains seeds, roots, and organic matter.
- Distinction from primary succession: primary succession occurs on bare rock, lava flows, or newly formed sand dunes, while secondary succession occurs in environments where life previously existed but was disrupted by fire, agriculture, storms, or logging.
- Key features: faster recovery due to the presence of soil and seed banks, early colonization by opportunistic species, and progressive replacement by more competitive species.
- Typical habitats: abandoned agricultural fields, burnt forests, storm-damaged woodlands, and flood-affected grasslands.
| Feature | Primary Succession | Secondary Succession |
|---|---|---|
| Starting substrate | Bare rock, sand, lava | Soil already present |
| Soil fertility | Absent, develops slowly | Present, enriched with organic matter |
| Seed bank | Absent initially | Often present and viable |
| Time scale | Hundreds to thousands of years | Decades to centuries |
| Examples | Retreating glaciers, volcanic islands | Abandoned farmland, burnt forests |
Causes and Initiating Factors
Secondary succession is triggered by disturbances that alter existing communities without destroying the underlying soil. These disturbances can be natural or anthropogenic, and they shape the trajectory of ecosystem recovery by influencing species composition, soil properties, and resource availability.
Natural Disturbances
- Wildfires: fires clear above-ground vegetation but often leave soil, roots, and seed banks intact, allowing rapid regrowth of fire-adapted species.
- Floods: floodwaters deposit sediments and nutrients, reshaping habitats while leaving soil suitable for recolonization.
- Storms and hurricanes: high winds and water damage create canopy gaps and open ground for colonization by fast-growing pioneer plants.
Anthropogenic Disturbances
- Deforestation and logging: removal of trees changes light, temperature, and soil conditions, initiating succession in cleared areas.
- Agricultural abandonment: when farmland is no longer cultivated, weeds, grasses, and shrubs quickly colonize, leading to secondary succession.
- Mining and industrial activity: extraction and construction disturb plant communities but often leave behind soils that can support recovery once activities cease.
| Disturbance Type | Immediate Effect | Successional Impact |
|---|---|---|
| Wildfire | Removes vegetation, enriches soil with ash | Rapid colonization by fire-resistant species |
| Flood | Deposits sediments, alters soil structure | Promotes germination of flood-tolerant plants |
| Hurricane | Uproots trees, opens canopy gaps | Encourages fast-growing pioneer species |
| Agricultural abandonment | Cleared land left unused | Weeds and grasses dominate initially, later replaced by shrubs and trees |
| Mining | Soil disruption, vegetation loss | Succession begins with hardy colonizers once soil stabilizes |
Stages of Secondary Succession
Secondary succession proceeds through distinct but overlapping stages, each marked by characteristic species and ecological interactions. The process culminates in a relatively stable climax community, although disturbances may reset succession at any stage.
Pioneer Stage
The pioneer stage is dominated by hardy, fast-growing species that colonize disturbed soils. These species improve soil structure, increase organic matter, and create conditions favorable for later successional species.
- Colonization by grasses, mosses, lichens, and herbaceous plants.
- Rapid growth and high reproductive output.
- Soil stabilization and initiation of nutrient cycling.
Intermediate Stage
As conditions improve, shrubs and young trees establish, and biodiversity increases. Competition, herbivory, and symbiotic relationships become more prominent during this stage.
- Expansion of shrubs and shade-tolerant herbaceous plants.
- Increase in species richness and trophic complexity.
- Formation of layered vegetation, supporting diverse animal life.
Climax Community
The climax community represents the relatively stable endpoint of succession, characterized by a balance between species composition and environmental conditions. The specific climax state varies with climate, soil, and regional factors.
- Development of mature forests in humid regions, dominated by long-lived tree species.
- Grasslands or shrublands in arid or semi-arid climates.
- High ecological stability with efficient nutrient cycling and complex interactions.
| Successional Stage | Dominant Vegetation | Key Features |
|---|---|---|
| Pioneer | Grasses, weeds, mosses | Rapid colonization, soil stabilization |
| Intermediate | Shrubs, young trees | Biodiversity increase, trophic interactions |
| Climax | Mature forest or grassland | Stable ecosystem, high complexity |
Mechanisms of Secondary Succession
The progression of secondary succession is influenced by interactions among species and environmental factors. Three primary mechanisms—facilitation, inhibition, and tolerance—explain how communities change over time and how different species influence each other’s establishment and survival.
- Facilitation: early colonizers modify the environment in ways that benefit later-arriving species. For example, nitrogen-fixing plants enrich the soil, allowing other plants to thrive.
- Inhibition: some pioneer species hinder the establishment of others through competition or allelopathy. Succession proceeds only when these inhibitors die or are removed.
- Tolerance: certain species are unaffected by the presence of others and can establish at any stage of succession, eventually outcompeting less tolerant species.
| Mechanism | Process | Example |
|---|---|---|
| Facilitation | Early species improve conditions for later ones | Legumes enriching soil nitrogen for grasses |
| Inhibition | Early species prevent colonization by others | Allelopathic chemicals released by weeds |
| Tolerance | Species establish regardless of prior community | Shade-tolerant trees growing under pioneer plants |
Soil and Nutrient Dynamics
Soil plays a central role in secondary succession, serving as the foundation for plant regrowth and microbial activity. Nutrient dynamics evolve throughout the process, influencing which species can establish and how ecosystems recover.
- Soil fertility restoration: after disturbance, soil fertility improves gradually as organic matter from decomposing plants accumulates, enhancing water retention and nutrient availability.
- Nitrogen fixation and microbial activity: pioneer plants, particularly legumes, introduce nitrogen into the soil, while microbial communities decompose organic matter and recycle nutrients.
- Role of decomposers: fungi, bacteria, and detritivores break down litter and dead biomass, returning essential elements such as carbon, nitrogen, and phosphorus to the soil.
| Soil Component | Successional Change | Ecological Impact |
|---|---|---|
| Organic matter | Increases as plants and microbes establish | Improves soil structure and water retention |
| Nitrogen content | Enhanced by nitrogen-fixing plants and microbes | Supports growth of nutrient-demanding species |
| Microbial diversity | Expands with vegetation complexity | Promotes efficient nutrient cycling |
| Decomposition rate | Accelerates with increased litter input | Recycles nutrients for plant uptake |
Biodiversity and Community Structure
Secondary succession profoundly alters biodiversity and the structure of ecological communities. As ecosystems recover from disturbance, changes in species richness, abundance, and trophic interactions occur, leading to a more complex and stable community over time.
- Changes in species richness over time: biodiversity typically increases during succession, starting with a few opportunistic pioneers and expanding to include shrubs, trees, and animal species.
- Successional guilds and niches: groups of species occupy distinct ecological roles at different stages, such as early colonizers specializing in disturbed habitats and later species dominating shaded environments.
- Impact on animal communities: as vegetation structure diversifies, habitats for herbivores, pollinators, predators, and decomposers expand, leading to more intricate food webs.
| Stage | Dominant Flora | Associated Fauna | Biodiversity Trend |
|---|---|---|---|
| Pioneer | Weeds, grasses, mosses | Insects, small herbivores | Low but increasing |
| Intermediate | Shrubs, young trees | Birds, pollinators, small mammals | Moderate and diverse |
| Climax | Mature forest or grassland | Large herbivores, predators, decomposers | High and stable |
Secondary Succession in Different Ecosystems
Secondary succession occurs across diverse ecosystems worldwide, each exhibiting unique patterns of recovery depending on climate, soil, and disturbance type. Studying these variations helps in understanding ecological resilience and management strategies.
- Forests: in temperate forests, succession often begins with fast-growing deciduous trees that are later replaced by shade-tolerant species. Tropical forests show rapid recovery due to high biodiversity, while boreal forests recover slowly due to harsh climates.
- Grasslands: succession in grasslands is driven by fire and grazing. Disturbed patches are recolonized by perennial grasses and herbaceous plants, maintaining ecosystem balance.
- Wetlands: floods and drainage events reset communities, with reeds, sedges, and aquatic plants reestablishing habitats for fish, amphibians, and birds.
- Coastal ecosystems: dunes and mangroves regenerate after storms or human interference, with salt-tolerant plants stabilizing soil and creating niches for marine-associated fauna.
| Ecosystem | Disturbance | Pioneer Species | Climax Community |
|---|---|---|---|
| Temperate forest | Logging, fire | Birch, aspen | Oak, beech, maple forest |
| Tropical forest | Clear-cutting, storms | Pioneer shrubs and vines | Diverse evergreen canopy |
| Grassland | Overgrazing, fire | Annual grasses, herbs | Perennial grasses, legumes |
| Wetland | Flood, drainage | Sedges, rushes | Stable marsh or swamp ecosystem |
| Coastal dune | Storm surge, erosion | Salt-tolerant grasses | Mature dune vegetation or mangrove forest |
Human Influence on Secondary Succession
Human activities significantly alter the course and pace of secondary succession. While some actions accelerate recovery, others hinder natural processes and reduce ecosystem resilience. Understanding these influences is essential for sustainable land management and ecological restoration.
- Agricultural practices and land abandonment: when farmland is abandoned, succession typically begins with weeds and grasses before shrubs and trees recolonize. Crop type, soil degradation, and pesticide residues influence recovery trajectories.
- Urbanization and landscape fragmentation: construction, roads, and settlements interrupt natural successional processes. Fragmentation reduces species dispersal and can permanently alter community structure.
- Restoration ecology and rehabilitation efforts: intentional human interventions such as reforestation, controlled burns, and seeding of native species accelerate recovery and promote biodiversity in degraded landscapes.
| Human Activity | Impact on Succession | Outcome |
|---|---|---|
| Agricultural abandonment | Soil retains fertility and seed banks | Rapid regrowth of pioneer species |
| Urbanization | Land sealing, habitat fragmentation | Delayed or altered succession |
| Deforestation with replanting | Artificial initiation of succession | Accelerated recovery with managed species |
| Restoration projects | Human-assisted recovery | Enhanced biodiversity and ecosystem stability |
Medical and Environmental Relevance
Secondary succession has direct and indirect implications for human health and environmental quality. By restoring ecological balance, it influences air, water, and soil conditions while also shaping interactions between humans and disease vectors.
- Impacts on air and water quality: regrowing vegetation improves air quality by sequestering pollutants and enhances water quality through filtration and stabilization of watersheds.
- Role in carbon sequestration and climate regulation: successional forests and grasslands act as carbon sinks, mitigating the effects of greenhouse gas emissions and contributing to global climate stability.
- Implications for human health: changes in vegetation can influence allergen levels, such as pollen production, and alter habitats for disease vectors like mosquitoes, affecting public health outcomes.
| Aspect | Successional Effect | Relevance |
|---|---|---|
| Air quality | Vegetation absorbs pollutants | Improved respiratory health |
| Water quality | Wetlands and forests filter runoff | Reduced contamination and erosion |
| Carbon sequestration | Increased biomass accumulation | Mitigation of climate change |
| Allergens | High pollen production in early stages | Potential triggers for allergies and asthma |
| Disease vectors | Changes in habitats for insects and rodents | Impact on vector-borne disease risk |
Case Studies
Case studies of secondary succession provide real-world examples of how ecosystems recover after disturbances. These instances highlight the variability of successional processes depending on disturbance type, climate, and human intervention.
- Mount St. Helens eruption recovery: following the 1980 volcanic eruption, the landscape was covered with ash and debris. Secondary succession began in areas where soil remained intact, with lupines and other nitrogen-fixing plants paving the way for shrubs, trees, and animal recolonization.
- Forest regrowth after Amazon deforestation: in abandoned agricultural plots of the Amazon, secondary succession led to the rapid return of grasses and shrubs, followed by native tree species. However, soil degradation and invasive species often slow full forest recovery.
- Succession in abandoned agricultural fields: old farmlands in temperate regions show predictable patterns of succession, starting with annual weeds, progressing to perennial grasses and shrubs, and eventually forming woodlands or forests over several decades.
| Case Study | Initial Disturbance | Pioneer Species | Long-term Outcome |
|---|---|---|---|
| Mount St. Helens (USA) | Volcanic eruption (1980) | Lupines, mosses | Mixed forest recovery over decades |
| Amazon rainforest | Deforestation, land abandonment | Grasses, shrubs | Gradual regrowth of native forest species |
| Temperate farmlands | Agricultural abandonment | Annual weeds (ragweed, crabgrass) | Woodlands and forests in 50–100 years |
Recent Advances in Research
Advances in ecological research have improved understanding of secondary succession by integrating technology, molecular biology, and computational modeling. These tools provide greater precision in monitoring and predicting successional dynamics.
- Remote sensing and satellite monitoring: high-resolution imagery allows scientists to track vegetation recovery, biomass changes, and land cover transitions across large areas in near real time.
- Molecular tools in microbial succession studies: DNA sequencing technologies reveal changes in soil microbial communities that drive nutrient cycling and plant colonization during succession.
- Modeling successional dynamics: computer models simulate how disturbances, climate change, and species interactions influence recovery, enabling better conservation and restoration planning.
| Research Tool | Application | Benefit |
|---|---|---|
| Remote sensing | Tracking land cover and vegetation regrowth | Provides large-scale, long-term monitoring |
| DNA sequencing | Analyzing microbial community changes | Reveals soil health and nutrient cycling drivers |
| Successional modeling | Predicting community recovery patterns | Improves restoration strategies under climate change |
Conclusion
Secondary succession represents a fundamental ecological process that governs the recovery and regeneration of ecosystems following disturbances. It highlights the resilience of nature, showing how soil, microbial activity, and species interactions collaborate to restore balance over time. From pioneer species establishing initial footholds to the development of complex climax communities, each stage contributes to rebuilding biodiversity and ecosystem functions.
The study of secondary succession has practical importance for conservation, restoration ecology, and climate change mitigation. Understanding how disturbances influence ecological pathways allows for better land management strategies, habitat restoration, and preservation of ecosystem services. While human activities can both hinder and assist successional processes, advances in ecological research provide tools to guide recovery in sustainable directions.
Ultimately, secondary succession underscores the dynamic relationship between disturbance and stability in ecosystems. By examining its mechanisms, stages, and outcomes, ecologists and policymakers can work together to foster healthier environments that support both biodiversity and human well-being.
References
- Clements FE. Plant succession: an analysis of the development of vegetation. Carnegie Institution of Washington; 1916.
- Gleason HA. The individualistic concept of the plant association. Bull Torrey Bot Club. 1926;53(1):7-26.
- Odum EP. Fundamentals of ecology. 3rd ed. Saunders; 1971.
- Connell JH, Slatyer RO. Mechanisms of succession in natural communities and their role in community stability and organization. Am Nat. 1977;111(982):1119-44.
- Pickett STA, White PS. The ecology of natural disturbance and patch dynamics. Academic Press; 1985.
- Walker LR, del Moral R. Primary succession and ecosystem rehabilitation. Cambridge University Press; 2003.
- Turner MG, Dale VH. Comparing large, infrequent disturbances: what have we learned? Ecosystems. 1998;1(6):493-6.
- Foster DR, Aber JD. Forests in time: the environmental consequences of 1,000 years of change in New England. Yale University Press; 2004.
- Dale VH, Swanson FJ, Crisafulli CM. Ecological responses to the 1980 eruption of Mount St. Helens. Springer; 2005.
- Chazdon RL. Second growth: the promise of tropical forest regeneration in an age of deforestation. University of Chicago Press; 2014.
