States and Transitions in Succession
Dec 14, 2015
Plant Community Succession (Initial Ideas – F.E. Clements)
Natu
ral Po
ten
tial Large Variation
Between Years
Climax or PotentialNatural Community
Pioneer/Early LateSeral Stage
Plant Community Succession(Initial Ideas -- Clements)
Natu
ral Po
ten
tial
Pioneer/Early LateSeral Stage
Above average rainfall
Successional
tendency
Succession
Drought
Grazing Pressure
Retrogression
Climax or PotentialNatural Community
Example -Succession in the western juniper woodland
Grassland after fire Stand initiation juniper
Open young juniper Young multistory juniper
Old multistory juniper
Mountain bigsagebrush steppe
Cyclic Patterns creating a “Dynamic Equilibrium”1979 - Pre-burn
1989
1983
1980- 1st year after fire
1994
Problems with Succession Model
Wyoming big sagebrush/bluebunch wheatgrass steppe near Mtn. Home, ID
Wyoming big sagebrush/bluebunch wheatgrass steppe, central Idaho
• multiple pathways of succession• multiple stable vegetation types• no single and certain end-point
Two examples of stable states for same ecological site
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
Creosotebush community -this ecological site may have always been creosotebush dominated, or degraded long ago.
States and Transitions depend on biotic & abiotic conditions
States are relatively stable but some states are more stable than others
States and Transitions depend on biotic & abiotic conditions
Higher Elevation
Central Idaho
Lower Elevation Central Idaho
Higher Elevation Southwestern Idaho
Juniper Present
Cheatgrass Risk
Low Cheatgrass Risk
States and stability depends on factors such as elevation & climate
Example - Sagebrush Steppe States
Fire transition
Succession transitionImproper grazing transition
Transitions= compositional change resulting in the change in plant community (state)
Grassland Open Sagebrush
Closed Sagebrush
DepletedSagebrush
Thresholds = transitions that are nearly irreversible & sometimes unpredictable.
Sagebrush Steppe State
Annual Grass Dominated State
Threshold
Grassland Open Sagebrush
Closed Sagebrush
DepletedSagebrush
Grazing reduces likelihood of fire
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