Relative Abundance of Yellow Pine and Red Fir Forest in Seral Stages other than Mature

Status and Trend

Interpretation and Commentary

Relative Abundance of Yellow Pine Forest in Seral Stages other than Mature

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Status: Considerably Worse Than Target
Trend: Unknown
Confidence: Low

Relative Abundance of Red Fir Forest in Seral Stages other than Mature

Status: Considerably Worse Than Target
Trend: Unknown
Confidence: Low

Relevance - This indicator measures the relative proportion of tree stands classified in seral stages other than mature for Yellow Pine and Red Fir Forests in the Lake Tahoe Region. For this evaluation, “seral stages other than mature” was equated with stands dominated by small diameter trees (<10.9” dbh). The relative abundance of small-tree dominated stands is important because it provides a measure of forest sustainability; without young trees, Tahoe’s forests will not be sufficiently stocked to replace dead and dying trees over time. Today, Tahoe’s forests are dominated by an intermediate age/size class (ranging in diameter from 11” to 23”), due to past Comstock-era logging and ongoing fire suppression (Taylor 2007; USDA 2000; Raumann and Cablk 2008).
Adopted Standards - (Relative Abundance) Of the total amount of undisturbed vegetation in the Tahoe Basin - 1) Maintain 15-25% of the Yellow Pine Forest in seral stages other than mature. 2) Maintain 15-25% of the Red Fir Forest in seral stages other than mature.
Indicator - Relative proportion of tree stands dominated by small diameter trees (<10.9” dbh) for Yellow Pine and Red Fir Forests (percent [%])
Status – Based on the most current vegetation distribution data, the Region was determined not to be in attainment with Management Standards adopted for “seral stages other than mature” (interpreted for this evaluation as stands dominated by small diameter trees [<10.9”]) for both Yellow Pine and Red Fir Forests. The current percentage of small diameter (<10.9” dbh) Yellow Pine Forest cover is 3.6% (or 24% of the low end of the target); an estimated additional 11,570 acres of small diameter Yellow Pine Forest is needed to achieve the lower limits of this Management Standard. The current percentage of small diameter Red Fir Forest is 10.9% (or 72% of the low end of the target); an estimated additional 1,380 acres of small diameter Red Fir Forest is needed to achieve the lower limits of this management target. Past evaluations indicate that the Region was not meeting numeric targets, with the exception of Yellow Pine Forest documented in the 2006 TRPA Threshold Evaluation.
Trend – Earlier forest vegetation evaluations used lower resolution vegetation mapping approaches, and evaluation procedures were not sufficiently documented in the past. Most importantly, the 2006 evaluation used a diameter limit of <20” dbh to represent “small trees,” while this evaluation uses a diameter limit of <10.9” dbh to represent “small trees,” based on current interpretations of why the Threshold Standard was created. Thus, comparison of trend determinations among years is inappropriate and uncertain, so the trend determination for both small diameter Red Fir and Yellow Pine Forests was determined to be “unknown” because of insufficient data. The apparent improvement in the percentage of Red Fir Forest is most likely due to improvements in mapping and the change in diameter limit for “small trees” than to real ecosystem change. Areas affected by the Angora Fire (2007) and Gondola Fire (2002) are likely to eventually contribute about 3,800 acres of forestland occupied by first shrub, and then small diameter trees; however, these changes could take decades.

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Confidence
- Status - Vegetation data presented here met U.S. Forest Service mapping standards (Warbington et al. [no date]; FGDC 1997). Calculated overall accuracy of the map layer used for this evaluation was 70% confident that the vegetation characteristics represented on maps is similarly situated on the landscape(USDA 2009c). This level of accuracy equates to a “moderate” confidence determination for status.
- Trends - Due to differences in mapping resolution and evaluation methodologies across years, a trend determination was not presented and consequently confidence in trend was determined to be “low.”
- Overall Confidence - Because there is low confidence in trend, a “low” confidence determination is assigned to the overall status and trend determination.
Human and Environmental Drivers - The primary natural driver in creating patches of small diameter trees in the Lake Tahoe Basin is wildfire and other natural disturbances such as avalanche and wind-throw. Contemporary forest management practices do not substantially contribute to the creation of small diameter patches because the focus is to reduce understory ladder fuel loads (D. Fournier, personal communication, 2011).

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 evaluation, stands dominated by trees <10.9” were enumerated from the following California Wildlife Habitat Relationship (CWHR 2011) Types attributed in the U.S. Forest Service - Remote Sensing Lab Pacific Southwest Region TMU_Strata_07 map layer (published 2009).

TRPA Association	California Wildlife Habitat Relationships Type	California Wildlife Habitat Relationships Size Class
Red Fir Forest	Red Fir	1”-5.9” and 6”-10.9”
Yellow Pine Forest	Eastside Pine	1”-5.9” and 6”-10.9”
Yellow Pine Forest	Jeffrey Pine	1”-5.9” and 6”-10.9”
Yellow Pine Forest	Sierran Mixed Conifer	1”-5.9” and 6”-10.9”
Yellow Pine Forest	White Fir	1”-5.9” and 6”-10.9”

Monitoring Partners – U.S. Forest Service, US Geological Survey and Tahoe Regional Planning Agency

Map

Geographic distribution of small diameter (< 10.9” dbh) Yellow Pine and Red Fir Forests (red areas in figure) in the Lake Tahoe Basin (USDA 2009c).Note: source data precedes 2007 Angora Fire.

Trend Charts

Chart data not available at this time.

Estimated percent cover of small diameter tree size-classes (<20"dbh in 2001 and 2006; <10.9" dbh in 2011) for Yellow Pine and Red Fir Forests in the Lake Tahoe Basin by evaluation year (TRPA 2001; TRPA 2007c; USDA 2009c) relative to adopted management target (the range within red lines, 15 to 25%). Differences In percent cover were attributed to different evaluation criteria across evaluations.

Additional Info

References

Additional Information

Conceptual Model:
Monitoring Plan:

tahoemonitoring.org