Landscape Ecology - Disturbance Dynamics Notes

Disturbance Ecology

  • Disturbance: Discrete events that disrupt ecosystem structure, impacting resource availability and physical environment.
    • Definition by White and Pickett (1985).
    • Includes events like hurricanes, fires, floods, etc.

Key Concepts in Disturbance Ecology

  1. Intensity: Strength of disturbance event.
  2. Severity: Degree to which disturbance alters ecosystem.
  3. Size: Spatial extent of disturbance.
  4. Residuals: Remaining elements post-disturbance.
  5. Frequency: How often disturbances occur.
  6. Return Interval: Time between successive disturbances.
  7. Rotation Period: Time required for ecological recovery.

Intermediate Disturbance Hypothesis

  • Suggests that moderate levels of disturbance can enhance biodiversity.
  • Example: Varies across ecosystems such as Savanna or Pinery Provincial Park.

Patch Dynamics

  • Patch: A spatial unit within the landscape that has different conditions than surrounding areas.
  • A disturbance affects a patch significantly if the scales of the disturbance and patch are similar (Turner et al., 2001).

Landscape Position and Disturbance Susceptibility

  • Landscape Position: Refers to topographical site features (elevation, slope, aspect).
    • Susceptibility and probability of disturbance relate to this position, as highlighted in studies of hurricane impacts in New England (Foster, 1988a,b).

Patterns and Susceptibility to Disturbance

  • Research by Franklin and Forman (1987) showed how different harvest patterns affect disturbance susceptibility.
    • Probability of windthrow increases with edge amount, patch isolation, and fetch.

Models of Disturbance Spread

  • Turner et al. (1989) explored neutral models for the distribution of habitats susceptible to disturbances.
    • Outcomes depended on certain probabilities relating to initiation and spread of disturbances.

Fragmentation and Pest Dynamics

  • Roland (1993) examined the impact of edge density on forest tent caterpillar outbreaks in the GLSL/Boreal region, finding strong correlations with outbreak duration.

Ecological Legacies of Disturbance

  • Disturbance leaves behind biotic (living) and abiotic (non-living) legacies.
  • Examples include the effects of hurricanes, tornadoes, fires, volcanic eruptions, and floods.

Equilibrium Paradigm in Ecology

  • Ecological equilibrium refers to a state where ecosystems are closed, self-regulating, and stable without disturbances.
    • Postulated by Pickett et al. (1994).

Landscape Equilibrium Concepts

  • Shifting Mosaic - Steady State: Concept indicating landscapes are not static but in constant flux (Bormann and Likens, 1979).
  • Stationary Process Model: Proposed by Loucks (1970), emphasizing ongoing processes without alterations.
  • State-Space Model: Turner et al. (1993) outlines relationships between disturbance and recovery intervals.

Summary of Disturbance in Ecology

  • Disturbances alter ecosystem properties across time and space.
  • Landscape position and patterns drastically influence disturbance impacts.
  • Equilibrium, while traditionally understood, is often an oversimplification as ecosystems frequently exhibit dynamic changes.

Exam Information

  • Mid-Term Test Date: February 11, 2025.
  • Weight: 30% of final grade.
  • Covered Topics: Lecture Topics 1 to 5 (Disturbance Ecology).
  • Structure:
    • Section 1: Definitions (10 Marks)
    • Section 2: Short Answer (20 Marks)
    • Section 3: Long Answer (20 Marks)
  • Tasks: Identification, Explanation/Differentiation, Interpretation, Illustration, Synthesis.