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Home Land Upland Habitat and Vegetation

Relative Abundance of the Shrub Vegetation Type

Status and Trend

Interpretation and Commentary

Relative Abundance of Shrub Vegetation Type


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Status: Considerabley Better Than Target
Trend: Unknown
Confidence: Low

  • Relevance - This indicator measures the proportion of land cover dominated by shrub vegetation in the Tahoe Basin. Shrub vegetation represents an early successional stage of forest vegetation. The relative proportion of shrub type is important because it provides habitat for a wide diversity of wildlife species (USDA 2011c; Coppeto et al. 2006; Airola and Barrett 1985) and complements vegetation diversity in the Basin (USDA 2000). The relative abundance of shrub vegetation type in the Tahoe Basin is intended not to exceed 25% since it is most valued as habitat by an array of wildlife species when interspersed between other vegetation types, such as forests and meadows. Shrub vegetation is comprised of sagebrush, whitethorn, manzanita, bitterbrush, huckleberry oak, and chinquapin. This indicator does not provide an accurate measure of the extent and distribution of understory shrub vegetation or provide a measure of the relative condition of shrub vegetation.
  • Adopted Standards  - (Relative Abundance) Of the total amount of undisturbed vegetation in the Tahoe Basin - Maintain no more than 25 percent dominant shrub association vegetation.
  • Indicator - Percent of the landscape dominated by shrub vegetation (percent [%]).
  • Status – The most recent data (which does not include the area affected by the 2007 Angora Fire) indicates that about 15% (approximately 30,041 acres) of the land area in the Region is covered by the shrub vegetation type. The management target for this Threshold Standard sets an objective to achieve and maintain less than 49,728 acres (or < 25% of the land area) of this vegetation type. Based on this target, the region is meeting this target by 39%. Consequently, a determination of “considerably better than target” was assigned to this indicator.
  • Trend – The trend determination was “unknown” due to differences in mapping approach and resolution across years.

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  • Confidence 
    • Status - According to an accuracy assessment conducted by the U.S. Forest Service Remote Sensing Lab (2009) on the most recent vegetation type map, there is 88% confidence that the mapped data accurately represents the distribution and extent of this vegetation types (shrub) on the landscape. Therefore a confidence of “moderate” was assigned to status.
    • Trends - Due to differences in mapping resolution and evaluation approach over time, there was “low” confidence assigned to trend.
    • Overall Confidence - Confidence assigned to status was “moderate” and to trend “low,” therefore according to rules established for this report, overall confidence was assigned a “low” determination.
  • Human and Environmental Drivers - Several factors can influence the extent of shrub vegetation in the Tahoe Basin. The primary factors responsible for shrub vegetation are light exposure, soil type and moisture content, and extent and frequency of wildfire and other natural disturbances. Canopy-replacing wildfire is suspected of creating openings conducive to the establishment of contiguous shrub vegetation on the landscape, although shrub vegetation is known to also occupy the understory of most mixed conifer forest landscapes in the Region.
  • Monitoring Approach – Every five years, the Tahoe vegetation map is updated with new satellite data (if available) and/or modeled and calibrated using field-based Forest Inventory and Analysis (FIA) data to assess the extent of different vegetation types and associated forest structure characteristics for the Basin (USDA 2009c; Warbington et al. [no date]). For this analysis, CWHR vegetation types associated with shrubs were queried and enumerated from the most recently available vegetation map (U.S. Forest Service - Remote Sensing Lab Pacific Southwest Region: TMU_Strata_07 [published 2009]). The following CWHR types were queried to represent shrub vegetation in this evaluation:
    TRPA Association California Wildlife Habitat Relationship Type
    Sagebrush Scrub Bitterbrush
    Sagebrush Scrub Low Sagebrush
    Sagebrush Scrub Sagebrush
    Shrub Alpine Dwarf Shrub
    Shrub Montane Chaparral
  • Monitoring Partners – U.S. Forest Service, US Geological Survey and Tahoe Regional Planning Agency

Links

 
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Map

Recent distribution and extent of shrub vegetation type (red areas in figure) in the Lake Tahoe Basin prior to the 2007 Angora Fire (USDA 2009c).

 

Trend Charts

Chart data not available at this time.
Estimated percent of land area occupied by shrub vegetation in the Lake Tahoe Basin by evaluation year (TRPA 2001; TRPA 2007c; USDA 2009c).

Additional Info

References

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Additional Information

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  3. Conceptual Model:
  4. Monitoring Plan:
Last Updated on Tuesday, 13 November 2012 11:24