Explore how plant and soil biological succession shape ecosystems, manage nutrients, and control weeds in natural and agricultural settings.
Nature operates through cycles of change, with each stage laying the groundwork for the next.
One of the most important ecological processes is succession—how ecosystems naturally evolve and shift over time. Succession is fundamental to soil health, biodiversity, and plant communities. Understanding this process not only deepens our knowledge of ecosystems but also provides practical applications for sustainable land management.
Introduction to Plant Succession
Succession refers to the gradual process by which ecosystems change and develop over time. It occurs in predictable stages, where plant and animal communities replace one another until a stable, mature state is reached, known as the climax community.
Succession can occur in two forms:
Primary succession begins on barren landscapes where no previous soil or vegetation existed—such as newly formed volcanic islands or areas left behind by retreating glaciers.
Secondary succession happens in areas where an existing ecosystem has been disturbed but not entirely destroyed—such as after wildfires, floods, or human activities like farming.
These successional stages progress towards a climax community, which represents a stable, self-sustaining ecosystem. However, the form and composition of climax communities vary widely depending on climate, geography, and local conditions. A climax forest in temperate regions might consist of towering oaks and maples, while grasslands in arid zones could settle into a diverse mixture of hardy perennials.
Soil Biological Succession: The Foundation for Plant Succession
Plant succession is deeply intertwined with changes occurring beneath the surface. Soil biological succession is the progression of soil organisms—bacteria, fungi, protozoa, nematodes, and more—that helps shape the aboveground plant communities.
In early stages, bare or disturbed soil is first colonized by bacteria and fungi. These microorganisms begin to break down organic matter, converting it into forms that plants can use. As soil life develops, these simple organisms give way to more complex organisms, like protozoans and nematodes. Protozoans feed on bacteria, releasing nitrogen into the soil, while nematodes regulate bacterial and fungal populations, maintaining balance in the soil ecosystem.
Earthworms, arthropods, and larger organisms also begin to contribute to soil health. They aerate the soil, improve its structure, and facilitate deeper rooting for plants, allowing more advanced plant communities to thrive.
As the soil ecosystem grows more diverse, so do the plants it can support. Simple, fast-growing species—such as grasses and annuals—dominate the early stages of plant succession. Over time, as soil health improves and organic matter accumulates, more complex plants like perennials and trees take root.
Nutrient Progression During Plant Succession
Succession also transforms the nutrient dynamics of the soil. In early stages, pioneer plants rely on readily available nutrients in the soil. These nutrients, such as nitrates, are simple and require little processing. However, as plants die and decompose, they enrich the soil with organic matter, and more complex nutrient cycling begins to take place.
Over time, perennial plants with deep root systems begin to dominate. These plants release root exudates, which feed soil organisms and drive further nutrient cycling. The slow release of nutrients from organic matter supports long-term plant health. This dynamic also creates a positive feedback loop: healthy plants contribute to the soil, which in turn nurtures future generations of plants.
Disturbances and Their Effect on Plant Succession
Disturbances, both natural and human-induced, significantly impact plant succession by altering soil structure, nutrient availability, and the composition of plant communities. These events create opportunities for pioneer species to establish or, in some cases, disrupt the natural successional process.
Natural Disturbances
Fire: Wildfires remove mature vegetation, exposing bare soil. In fire-prone ecosystems, this can reset the successional stages, allowing fire-adapted species to thrive. However, repeated fires may deplete soil organic matter and nutrients.
Flood: Flooding, particularly in riparian zones, can deposit nutrient-rich sediments, aiding early successional plants. However, prolonged flooding may suffocate root systems and lead to anaerobic soil conditions, altering soil biology.
Temperature (Freeze/Thaw): Seasonal freeze-thaw cycles can cause soil heaving, which disturbs roots and soil aggregates. This creates space for opportunistic species but can also compact soil and reduce microbial activity.
Moisture (Wet/Dry Cycles): Extreme wet or dry conditions can inhibit plant growth. Dry conditions lead to dormancy or death of plants and soil life, while excess moisture reduces oxygen in the soil, harming aerobic organisms like protozoa and nematodes.
Human-Induced Disturbances
Tillage (Intensity, Repetition, Timing): Excessive tillage disrupts soil structure, breaks up macroaggregates, and reduces microbial habitat. It accelerates erosion and decreases organic matter, making it harder for later successional plants to establish.
Monoculture: Monocultures disturb natural successional processes by eliminating biodiversity, leading to reduced soil fertility and increased pest and disease pressure. Succession is halted, preventing the soil from evolving toward a more complex ecosystem.
Overgrazing: Grazing livestock too frequently removes vegetation, compacts soil, and reduces organic matter. This limits plant regrowth and allows invasive or early-successional plants, such as weeds, to dominate.
Compaction: Activities like heavy machinery use or overgrazing lead to soil compaction, limiting root penetration, air, and water movement. Compacted soils disrupt both plant and soil biological succession, slowing down the process of ecosystem recovery.
Clear Cutting & Thinning: These forestry practices remove tree cover, drastically changing the light, temperature, and moisture levels in an ecosystem. Clear cutting resets succession, while thinning may encourage intermediate successional species.
Air Pollutants: Pollutants like sulfur dioxide, nitrogen oxides, and particulate matter affect plant health, inhibiting photosynthesis and reducing biodiversity. Acid rain from air pollutants can alter soil pH and disrupt the biological processes essential for succession.
Fertilizers, Pesticides, and Herbicides: Overuse of synthetic fertilizers can disrupt the natural nutrient cycling process, favoring fast-growing plants and preventing later successional species from establishing. Pesticides and herbicides harm non-target organisms in the soil, including beneficial microbes and nematodes, which are vital for unlocking nutrients and maintaining a balanced successional pathway.
Weeds and Succession
Weeds are often viewed as undesirable in agricultural or landscaped settings, but they play an important role in the early stages of succession. Weeds are pioneer species—plants that can quickly colonize disturbed soils. They are well-adapted to harsh conditions, thriving in compacted or nutrient-poor soils.
In natural ecosystems, weeds help stabilize the soil and prevent erosion. They also draw nutrients from deep in the soil profile, accumulating them in their tissues. When weeds die and decompose, they release these nutrients into the topsoil, making them available for other plants.
Over time, as succession progresses, more complex plants outcompete weeds. Perennial grasses, shrubs, and trees create shade and build up organic matter, creating conditions where weeds can no longer dominate. In this way, succession naturally limits the spread of weeds as soil health improves.
How Soil Biology Manages Weeds
Soil life plays a crucial role in managing weeds throughout succession. Protozoans, nematodes, and other soil organisms help maintain a balanced ecosystem where weeds struggle to take over. Protozoans consume bacteria that thrive on decomposing weed matter, cycling nutrients back into the soil. Nematodes, which feed on bacteria and fungi, regulate microbial populations and maintain soil health, further preventing weeds from dominating.
Mycorrhizal fungi are another key player in managing weeds. These fungi form symbiotic relationships with plant roots, helping them absorb nutrients more efficiently. In well-developed soils, mycorrhizal networks can give perennial plants an advantage over shallow-rooted weeds by providing them with greater access to water and nutrients.
By promoting soil biodiversity and maintaining healthy microbial communities, succession can naturally reduce weed pressure, minimizing the need for chemical or manual weed control.
Examples of Plant Succession in Permaculture Systems
Succession isn’t just a natural process—it can be intentionally designed and managed in sustainable agricultural systems like permaculture. Permaculture mimics natural ecosystems, starting with hardy pioneer species that improve the soil and gradually transitioning to more complex and permanent plant communities.
For example, in a new permaculture garden, fast-growing cover crops might be planted to protect the soil and build organic matter. As the soil improves, perennial vegetables, fruit trees, and shrubs can be introduced. Eventually, the system evolves into a self-sustaining food forest, with minimal input required to maintain its productivity.
By understanding and working with natural successional processes, permaculture designers can create resilient landscapes that improve soil health, enhance biodiversity, and support long-term food production.
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