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The vegetation of the Lake Tahoe Basin is an often overlooked,
yet remarkable, natural resource that ranges from deep water
plants living more than 300 feet below the surface of the lake
to uncommon plant communities on the summit of Freel Peak at
10,881 feet. Plants and plant communities that live between
these extremes are described as common, uncommon, or sensitive.
Common vegetation in the Lake Tahoe Basin can be categorized
by tree-plant type such as, Subalpine Forest, Shrub Association,
Deciduous Riparian, and Meadow Association. Uncommon vegetation
communities, such as the deep waters of Lake Tahoe or Osgood
swamp, are recognized by unique qualities that allow for uncommon
plant communities. Sensitive plants, such as Tahoe Yellow Cress,
are very susceptible to changes in the environment and require
constant conditions to thrive, these are rare plants unique
to Tahoe.
The vegetation conditions and patterns of today in the Lake
Tahoe Basin are a reflection of past and current human activities.
Logging activities began in 1859 and within 40 years about 60
percent of the Tahoe watershed had been clearcut. The remaining
land was characteristically alpine, barren or inaccessible (USDA
2000). After most of the logging was complete, federal and
state governments began acquiring lands in 1899, and intensified
acquisition in the 1930s.
The “second growth” forest that
has grown in the past century has, until recently, received
little active management, except fire suppression. As such,
today´s forest is even-aged and crowded, with many trees suppressed
by the density of the surrounding forest. A drought, which
started in the late 1980s, stressed the overstocked trees, making
them susceptible to insects. In 1991 the United States Forest
Service (USFS) estimated that 300 million board feet of timber
were dying or dead (USDA 2000). This condition has increased
the threat of large catastrophic fire, and is indicative of
a forest where many natural processes have been excluded.
Housing, commercial and infrastructure construction
have also influenced today´s vegetation patterns. Large and
small trees have been removed for these projects and forest
structure and composition are manipulated around the urban area,
as a defensible space for fire protection. In addition, road
salts and soil compaction can stress remaining trees to the
point where the tree is later removed as a hazard. The impacts
of construction and hazard tree removal are not known; however,
the impacts have not been evenly distributed within the Basin.
Roughly 95 percent of the urban area is below 7,000 feet in
elevation and located in the montane major vegetation zone.
Approximately 27 percent of the montane zone is urbanized and,
if a defensible space zone is included around the urban areas,
about 55 percent of the montane zone forest will be manipulated
both in structure and composition.
New impacts as a result of construction will
continue in the montane zone as most of the remaining buildable
lots in the Basin are within the montane. Lost urban trees
are not replaced quickly, nor are there mechanisms to ensure
lost trees are replaced. In May 2001, TRPA adopted a new vegetation
threshold related to late seral and old growth stands. The
threshold standard is that 55 percent of the forested area of
the Recreation and Conservation Plan Areas in the Basin should
exhibit late seral or old growth characteristics.
Sources:
Draft TRPA 2003 EIP Update
Draft TRPA 2001 Threshold Evaluation
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V-1 Common Vegetation
The indicator to evaluate the first vegetation
threshold, common vegetation, is area of vegetation coverage. Both relative
abundance of different vegetation types and the pattern of vegetation can
be evaluated using this indicator. The data used in this evaluation will
be based on the U.S. Forest Service data.
V-2 Uncommon Plant Communities
Although the second vegetation threshold, uncommon
plant communities, is a numerical threshold, the wording of the threshold
does not allow for measurement or quantification to determine the status of
the community. In this regard the indicator to evaluate uncommon plant communities
is unitless. The second threshold states that there is a non-degradation
standard applied to four specific communities. Therefore, if a community
has been degraded the threshold will not be in attainment. Either USFS staff
or TRPA staff will evaluate the status of each uncommon plant community.
V-3 Sensitive Plants
Although the third vegetation threshold (sensitive
plants) is a numerical threshold, the wording of the threshold does not allow
for measurement or quantification to determine the status of the sensitive
plant species. In this regard the indicator to evaluate the third vegetation
threshold is unitless. The language of the third vegetation threshold states
a minimum number of population sites for five sensitive plant species (see
below). However, it is not clear what constitutes a “population” or the protection
to be afforded to each population. The third threshold will be in
attainment when there are a minimum number of
populations for each species and these populations are protected from negative
impact. Agency staff will identify the number of population sites and any
impacts.
V-4 Late Seral/Old Growth
Ecosystems
The fourth vegetation threshold is a numerical
threshold. Fifty-five percent of the region´s forests shall
be in late seral/old growth condition. In specific, 7,600
acres in the subalpine zone, 45,900 acres in the upper montane
zone, and 30,600 acres in the montane zone shall be in late
seral/old growth. This assessment shall be based on the USFS´
vegetation classification. This assessment is scheduled to
occur every five years.
Click
here for more information about vegetation indicators from
the TRPA 2001 Threshold Evaluation
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A goal of TIIMS is housing documents about the past, present and future environmental
research conducted in the Lake Tahoe Basin. Scientific research
conducted by organizations, agencies, and universities aims
to detect, for example, forest fires and discover ways to
monitor and ultimately eliminate environmental impacts. Ongoing
research efforts collecting baseline data will help regulatory
agencies establish regulations and develop limits and indicators
designed to improve environmental health.
The Forest Planning Group (formerly the Forest Health Consensus Group) is
working toward creating policies that achieve healthy forests while maintaining
fire safety for Basin residents. In addition, the Lake Tahoe Interagency
Monitoring Program (LTIMP) and the Tahoe Interagency roadway Runoff Subcommittee
(TIRS) have identified research needs relative to environmental restoration
projects and road cuts. The Tahoe Regional Planning Agency (TRPA) is also
a partner to the Tahoe Yellow Cress (TYC) Conservation Strategy, which is
currently studying three outplantings of TYC to develop the best technique
for future outplanting. These groups, along with the TRPA, will identify
priority studies that will further our understanding of vegetative processes
in the Basin, thereby accelerating our attainment of the vegetation thresholds.
TIIMS is always searching for more documents to include in
this section so please contact tiims@trpa.org
with possible links to other vegetation research.
Vegetation Resources
Murphy, D. and C. Knopp eds. 2000. Lake Tahoe Watershed Assessment: Volume
I. Pacific Southwest Research Station, USDA Forest Service. General Technical
Report PSW-GTR-175. (Chapter 5, page 449-458, “What are the likely effects
of a high severity or large unplanned fire on soil erosion, air quality, lake
clarity, biotic health, old growth and urban areas?” pages 497 – 522,
“What are some of the most ecologically unique and biologically intact
environments and areas in the basin, and what is the state of knowledge about
these areas?”, page 522, “What data gaps were revealed in the process
of assessing ecologically significant areas?”, pages 522 – 526, “What
monitoring, conservation, and research activities are most appropriate for
the ecologically significant areas identified?” In general all of Chapter
5 is relevant.)
Barbour, M. et. al. 2003? In Press. Present and Past Old-Growth Forests of
the Lake Tahoe Basin, Sierra Nevada. I have a copy of this
document.
Tahoe
Yellowcress Draft Conservation Strategy
USDA
Forest Service, Lake Tahoe Basin Management Unit: Fuels and
Vegetation Management Review
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