Ecosystem Change in AP Environmental Science: Disturbance and Recovery

Natural disruption (natural disturbance)

A naturally occurring event that alters an ecosystem’s structure and function by changing resource availability, physical conditions, or species interactions.

Disturbance regime

The characteristic pattern of disturbance in an ecosystem, described by features like frequency, intensity, duration, and spatial scale.

Frequency (of a disturbance)

How often a disturbance occurs (e.g., seasonal flooding vs. rare major hurricanes).

Intensity (severity)

How strongly a disturbance changes conditions or removes biomass (e.g., low-intensity ground fire vs. high-intensity crown fire).

Duration (of a disturbance)

How long a disturbance lasts (e.g., a short storm vs. a multi-year drought).

Spatial scale

The area over which a disturbance affects an ecosystem (e.g., a small landslide vs. a regional drought).

Resistance (ecosystem response)

How much an ecosystem changes when disturbed; high resistance means relatively little change in structure or function after the event.

Resilience (ecosystem response)

How quickly an ecosystem returns to its previous state (or a stable functioning state) after a disturbance.

Biodiversity

The variety of life in an ecosystem; can increase resilience by providing backup species, genetic diversity, and buffering through complex food webs.

Functional redundancy

When multiple species perform similar ecological roles, so ecosystem processes can continue if one species declines.

Wildfire

A natural (and sometimes human-ignited) disturbance that rapidly oxidizes biomass and releases heat, gases, and ash.

Crown fire

A high-intensity fire that burns through the forest canopy, typically removing more biomass than a low-intensity ground fire.

Nitrogen volatilization

Loss of nitrogen to the atmosphere during intense fires, which can reduce soil nitrogen availability.

Water-repellent (hydrophobic) soil layer

A soil condition that can form after severe fires, reducing infiltration and increasing runoff and erosion.

Storm surge

Coastal flooding pushed inland by severe storms, which can drive saltwater into freshwater wetlands and stress salt-intolerant plants.

Defoliation and treefall

Storm impacts that remove leaves and knock down trees, increasing light on the forest floor and restructuring habitat.

Flooding

A disturbance that redistributes water, sediment, and nutrients, reshaping floodplains and river channels.

Waterlogging (oxygen-poor soils)

Soil conditions caused by flooding where low oxygen stresses plants that need well-aerated roots.

Drought

A prolonged period of below-average precipitation that reduces water availability and can weaken ecosystems.

Heat wave

A period of unusually high temperatures that can intensify drought stress by increasing evaporation and plant transpiration.

Ecological succession

A predictable (but not perfectly linear) process where species composition and community structure change over time after a disturbance as conditions like soil, light, and nutrients shift.

Primary succession

Succession that begins where there is little or no soil (e.g., new volcanic rock or land exposed by retreating glaciers); typically slow because soil must form.

Secondary succession

Succession after a disturbance that leaves soil intact (e.g., fire, hurricane, flood, abandoned farmland); usually faster because seeds, roots, and microbes remain.

Pioneer species

The first organisms to establish in harsh conditions (often lichens and mosses on bare rock) that help start soil formation and community development.

Intermediate disturbance hypothesis

The idea that biodiversity may be highest at intermediate levels of disturbance: too little allows competitive exclusion, too much prevents many species from establishing.