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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.
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.
Tahoe
Yellowcress Draft Conservation Strategy
USDA
Forest Service, Lake Tahoe Basin Management Unit: Fuels
and Vegetation Management Review
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