16: Disturbance, Fire and Ecological Recovery

Disturbance

a change in abiotic or biotic conditions in a community

(volcanic eruption, species introductions, changes in weather, doctors prescribing antibiotics, gopher mound, lightning burning stuff, species exclusion or extinction)

Disturbance’s measurable dimensions

1. Intensity/severity

2. Frequency

3. Extent/patchiness

4. Timing

5. Biological legacies

Recovery Model

Disturbance Regime: intensity, frequency

Biological legacies: soil, seed bank

Abiotic filters: light, water, space

Colonists: dispersal, traits

Biological Interactions: competition, facilitation

Community trajectory: recovery, shift, loss

Primary succession vs Secondary Succession

Primary: newly exposed/sterilized substrate with little soil, few local propagules, limited biological legacy

Secondary: disturbance removed biomass but soil, seed bank, roots, microbes, or survivors remain

How does the stage of an ecosystem change succession rates?

Early stage: abiotic filters strongest

Middle stage: colonization and facilitation

Later stage: biotic interactions increase

Intermediate disturbance hypothesis

predicts that highest diversity is at intermediate disturbance

low disturbance allows strong competitors to dominate

high disturbance only favors some strong ones or colonists

Which fire-response traits reflect tradeoffs

Above-ground survival: thick bark, tall trunks

Below-ground survival: resprouting

Regeneration from seed: seed dormancy, post-fire germination

Flammability: dead tissue spreads fire, killing neighbors

Serotiny: seeds open after fire