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Sagebrush Demography on the Idaho National Laboratory

Investigators and Affiliations

Amy D. Forman, Plant Ecologist, Environmental Surveillance, Education and Research Program, S.M. Stoller Corporation, Idaho Falls, ID
Roger D. Blew, Ecologist, Environmental Surveillance, Education and Research Program, S.M. Stoller Corporation, Idaho Falls, ID

Funding Sources

U.S. Department of Energy Idaho Operations Office

Background

As more and more sagebrush steppe habitat in good ecological condition is lost, it becomes increasingly important to understand the ecosystem dynamics of that vegetation type, especially the biology of the dominant species, sagebrush. An understanding of the population dynamics, or demography, of sagebrush should allow land managers to make better decisions about remaining healthy sagebrush steppe vegetation. An understanding of what the historical population dynamics of a sagebrush stand may have been like will also allow land managers to begin to understand how to make improvements in sagebrush steppe communities that are in somewhat degraded conditions.

At the INL, the DOE is responsible for the stewardship of 2300 km2 of relatively pristine sagebrush steppe habitat. This land comprises one of the largest remnant of this type of ecosystem that has been largely exempt from anthropogenic disturbance. Some of the primary issues DOE must address as a land manager include: fire risk and fuel management, post-fire vegetation recovery, rangeland health, wildlife habitat management (including habitat critical to the survival of threatened, endangered, and sensitive species), and land use planning. Sagebrush is an important component of managing for all of these issues. Unfortunately, the population biology of sagebrush is not well understood. In particular, very little information is available on the typical age structure of sagebrush stands, the frequency of recruitment events, the dynamics of shrub die-off, and the typical lifespan of sagebrush.

The overarching goal of this proposed study is to describe sagebrush stand age structure for a representative sample of sagebrush stands and to identify the population dynamics that influence that structure at the INL. Characterizing sagebrush stand age structure is a critical component to managing sagebrush steppe ecosystems, and understanding some of the basic biology of sagebrush can add tremendously to DOE’s ability to make knowledgeable land management and land use decisions. A simple study to establish a working knowledge of the age dynamics of sagebrush stands can yield information useful to those land management issues listed above. Many of the results from this study may also be applied to sagebrush stands with similar climatic conditions and disturbance regimes range-wide, allowing range managers throughout the West to use these data.

Objectives

The working knowledge of the dynamics of stand age structure gained from this study will allow managers to better address all of the land management issues mentioned above. The specific objectives for this project are:

  1. To determine the typical stand age structure or range of stand age structures for mature sagebrush stands.
  2.  To investigate how stand age structure relates to stand condition and shrub die-off for sagebrush.
  3.  To examine the dynamics of sagebrush stand replacement in the absence of wildland fire.

By addressing these goals, the proposed study will facilitate a comprehensive understanding of sagebrush population biology on the INL and on climatically similar rangelands. That improved understanding of sagebrush ecology will include the normal age structure of sagebrush stands, the typical range of variation of sagebrush stand age structure, how age structure of a sagebrush stand relates to stand condition, the dynamics of shrub die-off, the typical lifespan of sagebrush, the frequency of recruitment events, and the relationship between recruitment and disturbance.

The expected deliverables for the project will support the development of the Conservation Management Plan and include (1) specific habitat management recommendations for sagebrush at the INL and (2) guidance for assessing the status of sagebrush habitat health on the INL.

Accomplishments through 2006

During 2006, 14 stands of Wyoming big sagebrush (Artemisia tridentata ssp. wyomingensis) were sampled. The vegetation data collected as a component of this study included; shrub cover, sagebrush density, and individual shrub rank data for use in developing criteria for measuring stand condition. At each stand, cross section samples of sagebrush were also collected. The cross sections were labeled and archived in preparation for sanding and ring counts.

Results

Because data collection was initiated in 2006 and no data analyses have yet been completed, no results are reported here.

Plans for Continuation

Funding for this project has been discontinued.

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