Forest Ecology Notes

A relatively event in and that alters the of , , and and causes changes in and/or the ___ ___.

Timing determines impact.
Example:
- Fire or freeze during bud break causes much more mortality.
- Fire in summer is more severe than in winter.

The effect of one disturbance on the probability of another disturbance occurring (Picket and White 1985).
Example:
- Beetle-killed spots within a loblolly pine stand may be relatively small in proportion to the stand.
- However, they are areas of high fuel loading, increasing the risk that a lightening-ignited wildfire will start in these areas and spread to the surrounding stand.

Perturbation: An external force that displaces a system from equilibrium.
Response: Describes the direction and magnitude of change in system after perturbation.
Resistance: Tendency of the system to remain in a reference state in the face of perturbation (i.e., maintain certain structures and functions despite being disturbed).

Recovery: The extent to which a system returns to its original state after perturbation.
- Recovery depends on the magnitude of response and time since perturbation.
Resilience: Rate at which a system returns to a reference state.

Systems that maintain properties despite disturbance (i.e., resistant) and return rapidly to their original state (i.e., resilient) are more stable and predictable.

Disturbance maintains communities in a "non-equilibrium state" (never reaching equilibrium).
By renewing colonizable space, disturbance allows the persistence of species that might otherwise go extinct due to competitive exclusion.
Attribution: Joe Connell

Species diversity is low at low disturbance frequency because of competitive exclusion.
Species diversity is higher at intermediate disturbance frequency due to a mix of good colonizer and good competitor species.
Species diversity is low at high disturbance frequency because only good colonizers or highly tolerant species can persist.

A directional change in ecosystem structure and function resulting from biotically-driven changes in resource availability following the formation of barren land (primary) or a disturbance (secondary).
- Organisms respond to changes in resources, and the presence of those organisms alters resources, creating a cascade effect.

Different stages of communities are seral stages that are distinct.
Transitions between seral stages are usually gradual rather than abrupt.
Each stage transforms the ecosystem’s environment, creating conditions that foster the next stage’s development.

Occurs when a community develops on a site without established biota (no soil, plants, or seeds).

Bare rock left after the retreat of a glacier.
In time, mosses and lichens start to colonize the rock.
As they die, organic matter is added to weathered rock particles, making simple soils.
As the soils develop, grasses and small herbaceous plants start to grow.
More organic matter is added, and roots of plants aid breakup of rock material.
Deeper soils hold more water; small shrubs colonize these better soils.
Nutrient availability increases
More root action
Eventually, trees establish, leading to the development of a climax community on mature soils.

The depth of all major soil layers increased during the first 200 years of succession.