Community Disturbance

Nonequilibrium Model Early ecologists thought of nature as being in equilibrium. Actually, environments are constantly changing.

Examples: Floods, Fires, drought, storms, overgrazing and human activity

Frequent small scale disturbances sometimes prevent large scale disturbances Yellowstone 1988

Intermediate disturbance hypothesis __________________________________ ______________________

Ecological Succession From bare soil, then… –____________ ______________ –____________ make soil { ______________________________

Ecological Succession Primary Succession: ___________________ ______________________________________

Secondary Succession: __________________ _______________________________________ Mount St. Helens 1980

Climax forest  ___________________ The species mix of climax forest is dependent on the abiotic factors of the region birch, beech, maple, hemlock

A glacial retreat in southeastern Alaska

The Pattern of Succession on Moraines in Glacier Bay

Alders and cottonwoods covering the hillsides

Spruce coming into the alder and cottonwood forest Climax Community: old Growth Forest

Change in soil nitrogen concentration during succession after glacial retreat in Glacier Bay, Alaska

Cedar Creek Higher diversity communities are more __________________________________ ________from environmental stresses, such as droughts. Diverse communities are more __________________ From year to year. Diverse communities ________________ ________________