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United States Department of Agriculture

Agricultural Research Service

Title: Developing State-and-Transition Models for Rangelands

Authors
item Bestelmeyer, Brandon
item Brown, Joel - USDA-NRCS
item Havstad, Kris
item Alexander, Robert - BLM
item Chavez, George - USDA-NRCS
item Herrick, Jeffrey

Submitted to: Journal of Range Management
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: May 7, 2002
Publication Date: March 1, 2003
Citation: Bestelmeyer, B.T., Brown, J.R., Havstad, K.M., Alexander, R., Chavez, G., Herrick, J. 2003. Developing state-and-transition models for rangelands. Journal of Range Management. 56. p. 114-126.

Interpretive Summary: State-and-transition models are conceptual models of vegetation response to rangeland management. Unlike traditional succession-based models, state-and-transition models depict the often irreversible changes to rangelands occurring in response to drought and/or mismanagement (e.g., desertification). These models are intended to aid land managers in anticipating consequences of a variety of management decisions and to identify management decisions leading to desired outcomes. Nonetheless, only recently have sets of state-and-transition models been produced that can be used by agency personnel and private citizens, and there is little guidance available for developing and interpreting models. Based upon our experiences developing models for the state of New Mexico, we address the following questions: 1) how is information assembled to create site-specific models for entire regions, 2) how are models constructed, 3) what are the challenges to the validity of the models, and 4) how should models be used? We conclude models should include: 1) reference values for measurable indicators, 2) lists of key indicators and descriptions of changes in them suggesting an approach to irreversible changes in vegetation, and 3) rigorous documentation of the theory and assumptions (and their alternatives) underlying the structure of each model.

Technical Abstract: State-and-transition models have received a great deal of attention since introduction of the to range management concept in 1989. Recently, sets of state-and-transition models have been produced that can be used by agency personnel and private citizens, but there is little guidance available for developing and interpreting models. Thus, we address the following questions: 1) how is information assembled to create site-specific models for entire regions, 2) how are models constructed, 3) what are the challenges to their validity, and 4) how should models be used? We review the general structure of state-and-transition models, emphasizing the distinction between the easily-reversible changes among communities within states and the more persistent, threshold behavior of changes among states (transitions). Both succession and transitions occur, so these models are complementary. Ecological sites serve as a framework for developing and selecting models. We illustrate the importance of clearly delineating ecological sites to produce models and describe how we have dealt with poorly-delineated sites. Producing specific models requires an understanding of ecological mechanisms underlying transitions. Mechanisms tend to fall within discrete categories based upon fundamental ecological processes and their relationships are readily understood. A knowledge of mechanisms is related to the use of ecological indicators to anticipate thresholds. We conclude models should include 1) reference values for quantitative indicators, 2) lists of key indicators and descriptions of changes suggesting an approach to a threshold, and 3) a rigorous documentation of the theory and assumptions (and their alternatives) underlying the structure of each model.

Last Modified: 4/23/2014
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