States and transitions in succession
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States and Transitions in Succession. Plant Community Succession (Initial Ideas – F.E. Clements). Climax or Potential Natural Community. Large Variation Between Years. Natural Potential. Pioneer/Early. Late. Seral Stage. Plant Community Succession (Initial Ideas -- Clements). Succession.

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States and Transitions in Succession

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States and transitions in succession

States and Transitions in Succession


Plant community succession initial ideas f e clements

Plant Community Succession (Initial Ideas – F.E. Clements)

Climax or PotentialNatural Community

Large VariationBetween Years

Natural Potential

Pioneer/Early

Late

Seral Stage


Plant community succession initial ideas clements

Plant Community Succession(Initial Ideas -- Clements)

Succession

Retrogression

Above average rainfall

Drought

Successional tendency

Grazing Pressure

Climax or PotentialNatural Community

Natural Potential

Pioneer/Early

Late

Seral Stage


Example succession in the western juniper woodland

Example-Succession in the western juniper woodland

Mountain big

sagebrush steppe

Grassland after fire

Stand initiation juniper

Old multistory juniper

Young multistory juniper

Open young juniper


Cyclic patterns creating a dynamic equilibrium

Cyclic Patterns creating a “Dynamic Equilibrium”

1979 - Pre-burn

1980- 1st year after fire

1994

1983

1989


Problems with succession model

Problems with Succession Model

  • multiple pathways of succession

  • multiple stable vegetation types

  • no single and certain end-point

Two examples of stable states for same ecological site

Wyoming big sagebrush/bluebunch wheatgrass steppe, central Idaho

Wyoming big sagebrush/bluebunch wheatgrass steppe near Mtn. Home, ID


Problems with succession model1

Problems with Succession Model

  • multiple pathways of succession

  • multiple stable vegetation types

  • no single and certain end-point

State and Transition Models

1989 - Westoby, Walker and Noy-Meir


States and transitions in succession

Focus on States of communities

and Transitions between states

State A

State D

State B

State C


States and transitions in succession

States and Transitions depend on biotic & abiotic conditions

States are relatively stable but some states are more stable than others

Creosotebush community -this ecological site may have always been creosotebush dominated, or degraded long ago.


States and transitions depend on biotic abiotic conditions

States and Transitions depend on biotic & abiotic conditions

Juniper Present

Low Cheatgrass Risk

Higher Elevation Southwestern Idaho

Higher Elevation Central Idaho

Cheatgrass Risk

Lower Elevation Central Idaho

States and stability depends on factors such as

elevation & climate


States and transitions in succession

Example - Sagebrush Steppe States

Open

Sagebrush

Grassland

Depleted

Sagebrush

Closed

Sagebrush

Transitions= compositional change resulting in the change in plant community (state)

Fire transition

Succession transition

Improper grazing transition


States and transitions in succession

Sagebrush Steppe State

Grazing reduces likelihood of fire

Open

Sagebrush

Grassland

Depleted

Sagebrush

Closed

Sagebrush

Threshold

Annual Grass

Dominated State

Thresholds = transitions that are nearly irreversible & sometimes unpredictable.


States and transitions in succession

The information required to develop these models:

  • potential alternative vegetation states on a site

  • potential transitions between states

  • opportunities to achieve favorable transitions between vegetation states and hazards to avoid unfavorable transitions


Rangelands are dynamic

Rangelands are Dynamic!

Rangeland Ecology and Management

  • But, dynamic patterns can be describe in state and transition models.

  • We manage transitions


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