States and Transitions in Succession

1. States and Transitions in Succession

2. Plant Community Succession (Initial Ideas – F.E. Clements) Climax or PotentialNatural Community Large VariationBetween Years Natural Potential Pioneer/Early Late Seral Stage

3. 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

4. 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

5. Cyclic Patterns creating a “Dynamic Equilibrium” 1979 - Pre-burn 1980- 1st year after fire 1994 1983 1989

6. 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

7. 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

8. Focus on States of communities and Transitions between states State A State D State B State C

9. 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.

10. 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

11. 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

12. 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.

13. 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

14. Rangelands are Dynamic! Rangeland Ecology and Management • But, dynamic patterns can be describe in state and transition models. • We manage transitions