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State and Transition Modeling Workshop

Updated 06/09/2006

Summary

One of the major differences between the ecological site description and traditional range site description is the description of known plant communities, which may occur on the site, rather than just one potential or natural plant community. Ecological site descriptions will utilize the state and transition model to described the dynamics of rangeland vegetation associated with each site. State and transition models offer a method to organize and communicate complex vegetation management information. Some of the models currently being developed are very broad and others very specific applications. Common understanding and application of definitions for state, transition, and threshold is needed to ensure consistency in development of state and transition models.

A state is a recognizable, relatively stable complex whose attributes include its physical environment (abiotic foundation) and biotic community (biotic framework). Stability refers to the capability of the state to return to its original ecological structure when stresses or disturbances are removed.

Boundary of a state, although represented by the sides of the boxes in the model, is actually a region along the transition continuum where a threshold is crossed. Threshold is defined as the boundary in which return to the previous state is not possible on a practical time scale without significant inputs. Significant inputs are associated with accelerating practices as defined in the National Range and Pasture Handbook. These are conservation practices that help achieve desired changes in plant community more rapidly than is possible through grazing management practices alone, such as brush management, range planting, and prescribed burning.

Transition is the trajectory of system change between states, triggered by natural events, management actions, or both, that will not come to rest before the establishment of a new state. Some transitions may occur very quickly and others over a long period of time.

States are not static as they encompass a certain amount of variation due to climatic events, management actions, or both. Dynamics within a state do not represent a state change since a threshold is not crossed. In order to organize information for management decision-making purposes, it may be desirable at times to describe these different expressions of dynamics within the states. We will refer to the different assemblages within the states as communities and the cause of changes between these communities as community pathways.

Community pathways and transition.

Within the ecological site description format, the major sections of the site description dealing with the vegetation component are:

  • Ecological Dynamics of the Site
  • State and Transition Model Diagram
  • Plant Communities (more than one plant community can be described)
    Sections within the Plant Communities are:
    • Community Narrative
    • Total Annual Production
    • Species Composition
    • Growth Curves
    • Cover and Structure
    • Photo

Ecological Dynamics of the Site - should be utilized to describe the general dynamics of the site. States could be described at the level of growth form, life form or functional group. Other information pertinent regarding the dynamics of the site in general should be added.

Plant Communities – utilized to describe the states or communities in the detail that site description developers feel is needed to make the site description an effective management tool. One or more communities for each state can be described. If only one community is described for a state, the community narrative can be utilized to describe the dynamics of the state. If more than one community is described for each state, the amount of detail entered into site description for each community is at the discretion of site description developers. As a minimum, information should be entered into community narrative describing dynamics of the community and causes of community pathway changes.

Information in regards to transitions between states should be described in the plant community narrative. Incorporating as much information as is known concerning the triggers and drivers of changes and any known probabilities associated with the transitions.

A detailed species composition list will be entered for the historic climax plant community or naturalized plant community. Any other states or communities that are considered acceptable desired plant communities in which similarity index will be calculated will need to have a detailed species composition list.

The site description format is flexible enough to allow site description developers to enter desired detail of information.

As site descriptions are being developed, we must remember for whom the site descriptions are being developed and why. The site description should provide enough information to assist land managers in making timely, well informed decisions.



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