Succession

Succession

What is Ecological Succession?

  • Ecological succession is defined as the observed process of change in the species structure of an ecological community over time.

    • Source: USDA

Interpreting the Landscape

  • Typical New England forest scene.

    • Resource links:

    • http://www.treehugger.com/tag/new%20england

    • http://ecolibrary.org

    • Image credits: © Dan L. Perlman EcoLibrary.org

Succession Observations

Mount St. Helens

  • Del Moral's studies indicated various stages of recovery in the area after the 1980 eruption.

    • Images of the same general region across three years: 1980, 1998, 2015.

Succession at Glacier Bay

  • Graph indicating the number of plant species over 200 years post-disturbance.

    • Initial rapid increase in plant diversity, leveling off after 200 years.

    • Number of species:

    • Initial spike, graph shows number of species from less than 10 to over 50 in the first 200 years.

Number of Woody Plant Species

  • Similar trend observed with woody plants, where numbers level off after approximately 100 to 150 years post-disturbance.

Number of Bird Species

  • Bird species richness also displays an increase that levels off after 50 to 100 years of forest succession.

Types of Succession

Primary Succession

  • Occurs on previously uninhabited surfaces, such as lava flows or glacial retreated lands.

    • Successive stages include:

    • Pioneer Species: Annual plants (1-2 years).

    • Intermediate Species: Grasses, perennials (3-4 years).

    • Climax Community: Mature oak and hickory forest (150+ years).

Secondary Succession

  • Follows disturbances that do not eliminate all life and soil, such as fires or human activities.

    • Restores the community rapidly.

Dynamics of Succession

Community Composition Changes

  • Changes are due to the relative frequency of species; some species become less abundant while others increase in abundance.

  • New species may invade from adjacent ecosystems.

  • The process is not always predictable.

Factors Affecting Plant Community Composition

  • Components contributing to plant community variations include:

    • Present vegetation: Existing species already in the area.

    • Surrounding vegetation: Influences from nearby ecosystems.

    • Past vegetation (seed bank): Historical flora available in the seedbed.

    • Resource levels: Availability of essential nutrients and water.

    • Disturbance levels: Frequency and intensity of environmental disturbances.

    • Stochastic factors: Random events affecting the community.

Wildflowers and Seed Selection

  • Starting with the Seeds: The following points highlight the factors in establishing wildflower gardens.

    • Wildflowers are gaining popularity for adding aesthetic value with lower maintenance.

    • Misconception: Wildflowers are simple to grow from seed. Many species demand specific conditions for successful growth.

    • Success rates for wildflower planting are categorized on a scale from 10% to 100%.

    • Genetic alterations in seeds are rarer in wildflowers compared to ornamental plants; purity and germination are tested by independent laboratories.

    • Environmental factors, including weather and soil conditions, significantly influence the success of wildflower plantings.

    • Wildseed Farms provides assistance but disclaims liability for performance due to conditions beyond their control.

Succession and Environmental Changes

  • Does Succession Ever Stop?

    • Ecosystems are dynamic; disruptions reset succession to earlier states.

    • Examples of disruptive forces include floods, fires, and storms.

Early and Late Successional Species

  • Early successional species are characterized by:

    • Large seed size, rapid dispersal, and growth rates.

    • Examples of dispersal mechanisms: wind, birds, and mammals.

  • Late successional species typically:

    • Have small seed sizes but higher competitive capabilities over time.

    • Traits include large mature sizes and longer lifespans.

Mechanisms of Succession

Facilitation

  • Involves pioneer species that modify habitat conditions making it more suitable for other species to invade.

  • These species are integral in paving the way for subsequent colonizers.

Tolerance

  • The process consists of species that endure harsh conditions during early colonization phases while waiting for opportunities to outcompete others.

Inhibition

  • Early invaders may alter habitat conditions unfavorably for new species; thus, subsequent arrivals can only occur after disturbances reset the conditions favorably.

Disturbance as a Concept

  • Definition:

    • Disturbance is a discrete event that changes the structure of populations, communities, or ecosystems, impacting resources and physical environments.

    • Source: Johannes Fasolt and Stephen Codrington.

Types of Natural Disturbances

  • Examples include:

    • Natural: Floods, fires, glaciers, volcanoes, hurricanes, and tornadoes.

    • Human-caused: Agriculture, mining, logging, urbanization, and chemical spills.

Disturbance Dynamics

Scale of Disturbance

  • Disturbance scale includes: individual, local, regional, landscape, biome, and planetary scales.

  • Effects vary across different scales and patches.

Patches in Ecosystems

  • Ecosystems are heterogeneous; disturbances impact different patches variably depending on factors like soils and topography.

Fire as a Disturbance

  • Examined through events like the 1988 Yellowstone fires which significantly altered landscape dynamics.

Pulses and Continuous Disturbances

  • Pulsed Disturbances: Events that happen once and conclude quickly (e.g., volcanic eruptions).

  • Continuous Disturbances: Ongoing effects that shift the ecosystem (e.g., oil spills).

Measuring Disturbances

  • Key measures include:

    • Spatial distribution: Area affected, patterns, and connectivity to undisturbed sites.

    • Temporal frequency: Regular intervals and duration of events.

    • Magnitude and Timing: Intensity versus severity of disturbances and their timing in terms of seasonal impacts.

Recovery Post-Disturbance

  • Ecosystems typically recover by way of succession.

  • Larger or repeated disturbances may lead to a permanently altered state.