Notice the rings of very early pioneer stages on the outer rim and more advanced early seral species. Early seral plants are often annual, herbaceous, and have invasive characteristics. http://botit.botany.wisc.edu

Plant Community Succession (Initial Ideas -- Clements) Above average rainfall Successional tendency Succession Climax or Potential Natural Community Drought Grazing Pressure Retrogression Natural Potential When a perturbation (disturbance or stress as we will refer to it) causes a major ecosystem function to deviate from its normal operating range, the degree of deviation is a measure of relative resistance stability, whereas the time required for recovery is a measure of relative resilience stability. Notes from Steve Bunting – University of Idaho Pioneer/Early Late Seral Stage

Example - Sagebrush Steppe States Grassland Open Sagebrush Closed Depleted Annual Grass Dominated State Threshold Grassland Open Sagebrush Closed Depleted In some areas of the Great Basin we can observe a third state- that dominated by annual grasses such as cheatgrass or ripgut brome. The movement back into either the sagebrush state or the woodland state is difficult in these environments.