The Effects of Ski Resorts in the Lake Tahoe Region of California on
Population Dynamics of the American Marten
This proposal addresses:
Theme 2. Forest Management, Fuels Reduction, and
Watershed Restoration. Sub-theme 2d. Recreation.
Project Team, Contact Information
Principal Investigators:
Keith M. Slauson and William J. Zielinski
Pacific Southwest Research Station, U.S. Forest Service
1700 Bayview Drive, Arcata, CA 95521
kslauson@fs.fed.us, (707)825-2931, Fax 825-2901
bzielinski@fs.fed.us, (707)825-2959
Collaborating Geneticist:
Dr. Michael Schwartz, Rocky Mountain Research Station, Missoula, MT
Local Collaborators:
Theodore Thayer and Shane Romsos, Tahoe
Regional Planning Agency, South Lake Tahoe
Raul Sanchez, Wildlife Biologist, Lake Tahoe Basin Management Unit
Susan Yasuda, Wildlife Biologist, El Dorado National Forest
Grants contact:
Bernadette Jaquint, (510) 559-6309, Fax 559-6440, bjaquint@fs.fed.us
Total Funding Requested:
$ 432,491
Total Value of In-Kind and Financial Contributions:
$ 223,200
1
PROPOSAL NARRATIVE
A. Justification Statement
The American marten (Martes americana) is a carnivore that occupies high-elevation
(5,000-10,000 feet) late-successional conifer forests in the Sierra Nevada (Spencer et al.
1983, Zielinski et al. 2005). The marten is a ‘Sensitive Species’ in Region 5 of the Forest
Service (Macfarlane 1994) and a ‘Species of Special Concern’ for the California
Department of Fish and Game (Bryliski et al. 1997). Current management direction for
American marten in the Lake Tahoe Basin comes from several U.S. Forest Service
documents and the Tahoe Regional Planning Agency (TRPA). The 2001 Sierra Nevada
Forest Plan Amendment (SNFPA) addressed marten (App. E-55) and listed development
of winter recreation as a potential threat to the species. This was presumed to be due to
fragmentation of forest cover usually associated with this management practice. The
2004 SNFPA carried forward den site guidelines for martens, but eliminated 2001
SNFPA vegetation standards and guidelines for developed recreation projects (USDA
2001, 2004). This left decisions for management of marten with regard to developed
recreation to the Lake Tahoe Basin Management Unit (LTBMU). TRPA’s goals and
policies (TRPA 1986) provide for the maintenance of “suitable habitats for all indigenous
species of wildlife without preference to game or non-game species through maintenance
of habitat diversity”.
There are several potential future changes to the management guidelines for marten in
the LTBMU. Revisions to the LTBMU forest plan and TRPA regional plan are
underway which are likely to establish the American marten as a special interest species.
The proposed inclusion of the marten as a special interest species followed guidelines set
forth by the 2005 National Forest Management Act and professional opinion of local
scientists and managers. Elevation of the management level for American martens in the
Lake Tahoe Region will require managers to have an increased understanding of threats
to the species and how they can prescribe management and mitigation alternatives to
favor its persistence. Furthermore, several ski areas are planning expansion. Without
information on whether these are likely to increase impacts on martens, managers cannot
evaluate and potentially mitigate negative effects.
The proposed research project described herein directly addresses the “development of
environmental carrying capacity guidelines for developed recreation [ski resorts]
currently allowed [existing resorts] and proposed [proposed resort expansion]” (Theme 2,
Subtheme: Recreation). The American marten, due to its specialization on old forests
and large area requirements, is one of the best species of management concern to use to
evaluate the effects of ski resorts in the high elevation forests and to use to develop
carrying capacity guidelines for forest management in the Lake Tahoe Region. Letters of
support for this project from the Tahoe Regional Protection Agency, Lake Tahoe Basin
Management Unit, and El Dorado National Forest can be found in Appendix 1.
2
B. Background and Problem Statement
High-elevation conifer forests of the Sierra Nevada have historically provided some
refuge from human impacts including trapping and timber harvest, but these forests have
increasingly become focal areas for winter recreation. Because martens are active yearround and are most energetically stressed during winter, winter recreation has the
potential to have significant negative impacts. The two types of winter recreation most
likely to negatively affect martens are snowmobiling and creation and operation of ski
resorts. There have been very few studies on the effects of these types of recreation on
martens. However, a recent study in the Sierra Nevada found that managed snowmobile
use did not affect marten occupancy or activity patterns (Zielinski et al. in review).
Ski resorts have more permanent and concentrated effects on martens and their habitat
than snowmobiling. There are approximately 25 ski resorts in the Sierra Nevada, nearly
all occur within the range of the marten. The Lake Tahoe region includes about half of
these resorts, constituting the highest density of resorts in the Sierra Nevada and one of
the highest in North America. To create ski runs, chair lifts, and facilities, trees are
removed, creating open areas and fragmenting previously contiguous forest. Martens
typically avoid open areas lacking overhead cover or tree boles that provide vertical
escape routes from predators (Drew 1995), are more susceptible to predation if they must
cross such areas, and have been shown to avoid areas when 25-30% of mature forest is
removed (Bissonette et al. 1997). Snow compaction from grooming alters surface
consistency making it easier for larger-bodied carnivores (e.g., coyotes) which, unlike
martens are not adapted for deep, soft snow, to expand their winter ranges and compete
with or prey on martens. Skiers and staff are active during the majority of the day at high
densities and during the night conducting grooming activities, creating a higher
likelihood for marten-human encounters and their associated disturbances (e.g., decreased
frequency of prey captures due to interruptions while hunting). Finally, ski resort effects
are not limited to winter, as permanent effects (e.g., fragmentation) are present yearround, and because many resorts are developing summer recreation (e.g., hiking,
mountain biking).
Ski areas have some potential beneficial effects on martens as well. Martens have
been reported using anthropogenic food sources (e.g., dumpsters), using resort structures
(e.g., chalets, buildings) as rest sites, and detected via snow tracks under lift lines. Food
available at ski areas, from humans, may also attract small mammals which, in turn, may
be preyed on by martens. We need to evaluate the sum total of costs and benefits of ski
areas on marten populations and we propose to do so by studying the demographic health
of populations in ski areas compared to similar areas unaffected by ski operations.
Kucera (2004) conducted the only intensive study of martens in a ski area. His work
occurred at Mammoth Mountain ski area from 2002-2003. Within the 1855 ha operations
area 12 martens were captured, yielding a density of 6.47 martens per 1000 ha. However,
10 individuals were males, only 1 was female, and 1 was of unknown sex, resulting in a
highly skewed proportional sex ratio of 0.91. Studies of martens adjacent to Mammoth
(Kucera 1997) and in five other areas of North America (Buskirk and Lindstedt 1989)
3
obtained much more balanced proportional sex ratios of 0.57 and 0.52-0.62, respectively.
The single female at the Mammoth ski area did raise two kits, but did not use developed
areas and only used natural rest sites. Martens appeared to move away from the ski area
and into unmanaged forest after winter. Kucera (2004) suggested this fits a seasonal use
pattern where martens occupy ski areas during winter, when natural prey is least available
and human-supplied food is most plentiful, then move into unmanaged forests in spring.
Evidence exists that martens are present at many of the ski resorts in the Lake Tahoe
region. Surveys conducted at Heavenly ski resort have demonstrated that martens
primarily occupy the central and southern portions of the resort, particularly during
winter (Bartholomew & Associates 1993, Cablk and Spaulding 2002). Surveys detecting
martens and sightings of martens have occurred on or near several other resorts in the
region (e.g., Sierra at Tahoe, S. Yasuda pers. comm.; Alpine Meadows, K. Boatner pers.
comm.; Homewood, K. Slauson pers. obs.). Although survey detections and sightings
provide information on occurrence, occurrence alone is insufficient to evaluate the effects
of a ski resort on martens. First, these surveys did not compare marten data from ski
resorts with unaffected (control) areas. Second, these surveys documented presence of
martens only, which provides no information on the demographic health of the
population. Martens can occur in the area but at very low densities, or the populations
may have skewed sex or age ratios or high turnover rates, all suggesting a population that
is not sustainable.
Kucera’s (1994) study provides compelling, if only preliminary, information
suggesting that Mammoth ski area does not support a self-sustaining marten population
due to lack of females. If these results are consistent across ski resorts, their high density
in the Lake Tahoe Region could have significant effects on the regional marten
population. To investigate this possibility, we propose a research project focused on
marten demographic parameters (e.g., sex ratio, age, reproduction) and which compares
data from ski resorts to nearby control areas. Our proposed research design will improve
upon previous research efforts by including multiple ski resorts and control areas,
resulting in a robust design for detecting effects and a broad scope of inference.
C. Goals, Objectives, and Hypotheses to be Tested
The overall goal is to identify whether ski resorts have a net negative, neutral, or
positive effect on marten populations in the Lake Tahoe region. We will gather
information necessary to determine whether any of the following characteristics differ
when ski areas and control areas are compared:
1.
2.
3.
4.
5.
6.
loss and fragmentation of suitable habitat
marten density
marten seasonal movements
marten age structure and sex ratio
proportion of female martens that reproduce
marten population stability
4
For each characteristic listed, our null hypothesis is that there is a negative difference
between the habitat or marten population characteristic at control sites versus ski areas.
D. Approach, Methodology, and Geographic Location of Research
Proposed Study Design
Our proposed design compares 3 pairs of treatment (ski resorts) and control areas (non
ski resorts). To select ski resorts, we reviewed information on the distribution of martens
in the Lake Tahoe region and selected three resorts well within the current range of
martens and that occupied locations composed of large amounts of potential marten
habitat. This process resulted in the selection of the Heavenly, Sierra at Tahoe, and
Alpine ski resorts (Figure 1). Each resort was then paired with a single control site that
best matched it with respect to the overall amount, composition, and suitability of marten
habitat as well as major topographic characteristics. Treatment areas will then be
compared to controls to determine whether population values for the treated differ from
the values from control areas. By including several treatment and control areas, we
include both replication and variation in ski areas, which will allow for a broad scope of
inference. The Sierra at Tahoe resort is outside the Lake Tahoe Basin, but is essential for
inference to the effects of ski areas within the basin. None the less, we will be using nonSNPLMA funds to support the work conducted outside the Lake Tahoe Basin (see budget
for details).
Control Area Selection
The three control areas for this project were selected based on the topographic
(elevation range and major aspect) similarity, vegetation similarity, and proximity to each
ski resort operations area. Topographic and vegetative similarity was assessed using
digital elevation models and remotely sensed vegetation data based on California
Wildlife Habitat Relationships system (CWHR, Mayer and Laudenslayer 1988) habitat
types in a geographic information system (GIS). Control areas were chosen that had the
same basic forest type and size class distribution as present at each ski resort operations
area prior to its development. We used pre-development era aerial photos to determine
the composition of forest habitats at each ski area prior to development. Sites were
selected that were in close proximity to each ski resort operations area to facilitate
assessing seasonal movement, directional dispersal of young, and to better control for
environmental variability (Figure 1).
Statistical Considerations
Prior to committing to a particular study approach, we conducted a simulation exercise
to investigate the relationship between the potential number of martens that could occupy
a typical ski area and the parameters of interest. Because martens have large home
ranges, it may be possible that ski areas only have the potential to affect a few individuals
which would make the study objectives difficult to achieve. Additionally, when sample
sizes are too small it becomes difficult to statistically detect differences.
5
We estimated the potential amount of suitable habitat available for each of the 3 ski
areas. To accomplish this, we used the CWHR types and size classes suitable for martens
and GIS vegetation coverages to identify the amount of potentially suitable habitat in
each ski area. The Heavenly ski area contained approximately 1500 ha of suitable habitat
while Sierra at Tahoe and Alpine Meadows ski areas contained about 1000 ha of suitable
habitat. We created a matrix to estimate marten density over a range of different sizes of
male and female home ranges in 1000 and 1500 ha of suitable habitat (Table 1).
Assuming complete saturation of suitable habitat, we conservatively estimate that 1000
and 1500 ha of suitable habitat could support 4.7-8.0 and 7.1-12.0 martens, respectively.
Using these numbers, we conducted a statistical power analysis to investigate the
range of differences that were statistically distinguishable for several parameters of
interest given the small number of individuals that probably occupy study areas of 10001500 ha. We sought experimental designs that would have a minimum 80% chance of
detecting a significant difference, if it in fact occurred (i.e., statistical power = 0.80). We
calculated power for incremental changes in the observed difference between controls
and ski areas and for a range of potential marten densities. Because we did not have pilot
data, standard deviations were estimated from a Poisson distribution, an acceptable
approach when the counts involved are small. Each calculation was conducted with the
probability of a type one error (alpha) < 0.15 and using a 1-tailed test (We thank J.
Baldwin, PSW Statistician for analysis review).
We investigated the density parameters, including male, female, and total density,
assuming a 10-50% change in marten density between ski area and controls (Figure 2).
Using our design of 3 pairs of treatment and controls, we will be able to detect a 33-36%
(2-4 marten difference) decline in the density of martens. A difference in total density of
≥ 4 martens begins to become biologically relevant, given only 4-16 individuals likely
exist in an area of similar habitat, constituting a 25-100% reduction in the number of
individuals present. Furthermore, a reduction of female density >2 can begin to
significantly reduce reproductive capability in small populations. Thus, our design is
well suited to detect differences in marten density that are biologically relevant with
statistical rigor.
Ski Area Development Forest Fragmentation Analysis
The sensitivity of martens to the loss and fragmentation of forest habitats is one the
main threats that ski are development poses to martens. Martens have been shown to
avoid areas when 25-30% of mature forest has been removed (Bissonette et al. 1997,
Potvin et al. 2000). These studies have all taken place in the context of industrial timber
harvest and there have been no investigations evaluating the effects of forest
fragmentation from ski resort development. To quantify the changes that ski resort
development has caused to forested landscapes and to evaluate the responses by martens,
we will conduct a fragmentation analysis using pre- and post-development vegetation
information. We will measure fragmentation similarly as previous studies (e.g., amount
of mature forest lost / unit area) and through additional metrics (e.g., remnant patch size)
6
using spatial statistical methods (e.g., Fragstats, McGarical and Marks 1995). We will
explicitly test the levels of fragmentation present on ski areas with marten presence and
demographic characteristics (e.g., whether females are present or breed in highly
fragmented areas). This analysis will provide a means to evaluate the vegetation changes
that have occurred and provide predictive tools for managers to evaluate whether other
ski resorts or future expansion of ski resort development will have negative impacts to
martens.
Density Estimation and Demographic Characteristics
To completely census all individuals in each study area, a systematic grid will be
established covering all suitable marten habitat. The grid will be composed of cells with
an area of 100 ha, which is a size similar to a small female marten home range. Within
each grid cell 2-3 stations will be placed where, depending on the season, either live traps
(spring/summer) or hair snares (winter) will be established.
We will determine density by identifying all individuals in each study area. The
effective trapping area will be calculated by buffering individual locations detected along
the edge of the study area by the average radius of a male or female home range (Simon
1980, Spencer 1981). During the spring/summer season, each individual captured will be
chemically immobilized and examined to determine the sex, age class, condition (weight,
evidence of injury), and reproductive status (females lactating, number of teats from
which milk can be expressed, number of suckling rings). One lower first premolar will
be removed for cementum annuli analysis to determine age (Poole et al. 1994). Small
tufts of tail and dorsal body hair will be removed for DNA fingerprinting and parentage
analysis (Riddle et al. 2003). Genetic analysis will be conducted under the direction of
Dr. Schwartz at the USFS Carnivore Genetics Laboratory. Each individual will receive a
uniquely numbered passive integrated transponder tag for future individual identification.
Repeat Sampling to Determine Population Dynamics
Although single season ‘snapshots’ of density and sex ratio may provide some clues to
what is occurring in ski and reference areas, estimating density without knowledge of
survival and reproduction can be misleading (van Horne 1983). The key question we
plan to address is whether marten populations on ski areas are any less productive or
stable than those in control areas. We will use the full suite of demographic parameters,
measured over several years, to parameterize a matrix structured population model (Table
2) to determine the trajectory (declining, stable, increasing) of each population (Caswell
1989). Because we are interested in how the conditions in each study area (ski and
control areas) are affecting the animals that reside there, we will conduct modeling with
and without the effect of immigration from outside each population, to remove the
‘rescue’ effect immigrants can have on declining populations.
Repeat sampling over the course of at least 3 years will be necessary to estimate the
demographic parameters. In the first year, all animals will be marked and age and
reproductive condition (females) determined. In the second year, new animals will be
7
marked, and previously marked individuals provide first estimates of persistence
(surviving and not emigrating) and absence (due to mortality or emigration). The third
year produces the second estimates of persistence and absence for each population and
the first estimates of variation for these parameters. Having ≥ 2 estimates of each
demographic parameter is the minimum amount of information needed to investigate
variation in each parameter and to begin modeling population dynamics.
Each resampling period will occur during the spring/summer reproductive season so
individual identification as well as the full set of demographic parameters can be
collected on each individual. The timing of sampling was chosen such that the kits would
be >2 months of age and weaned (Mead 1994), but evidence of lactation would still be
present in females with kits. To reduce the potential for negative effects of trapping
females with kits and to increase trapping efficiency, each trap will be fitted with a radio
collar that will transmit only when the trap door closes. Re-sampling efforts will likely
include new, unmarked individual martens in each study area. We will use DNA
fingerprinting and parentage analysis to determine the parents of each individual which
will, in turn, help us determine if individuals were born within a study area or originated
elsewhere.
E. Strategy for Engaging with Managers
The development of this study plan and proposal has already led to a working
relationship with managers in the Lake Tahoe region. The letters of support for this
project (Appendix 1) are a testament to our engagement with managers. We have and
will continue to collaborate with local managers (e.g., TRPA, LTBMU, El Dorado
National Forest, ski resort staff) to conduct this study. Upon completion, we will present
and discuss the findings during a regional meeting where all interested managers will be
invited to attend. Managers will be provided an opportunity to review draft final reports
and we will consider their input carefully.
F. Deliverables/Products
Progress reports will be completed annually and final report prepared at the
conclusion of the study. We will present the research findings in public and scientific
meetings both in the Lake Tahoe Region and elsewhere. We will seek to publish this
study in an appropriate professional scientific journal.
G. Schedule of Milestones/Deliverables (quarterly progress reports and invoicing).
Phase I (see budget section) of this study will begin in the winter (December-March)
of 2008-2009 and phase II will begin in late spring/summer (May-July) of 2009. Phase
III, repeating the late spring demographic sampling from phase II, will be conducted in
the late springs/summers of 2010 and 2011. Quarterly brief progress reports and
invoicing will be completed by the 1st of September, December, March, and June.
Annual progress reports will be prepared by 31st of September of 2009 and 2010. The
final report will be completed by 31st December of 2011.
8
III. TABLES AND FIGURES
Table 1. Marten density matrix for the number of male and female home ranges
saturating hypothetical areas of 1000 and 1500 ha of suitable habitat. Shaded cells
identify the most likely range of densities to expect based on average male and female
home range sizes from California.
1a. 1000 ha suitable habitat.
150
200
250
300
350
400
450
500
550
600
150
13.3
11.7
10.7
10.0
9.5
9.2
8.9
8.7
8.5
8.3
200
11.7
10.0
9.0
8.3
7.9
7.5
7.2
7.0
6.8
6.7
250
10.7
9.0
8.0
7.3
6.9
6.5
6.2
6.0
5.8
5.7
300
10.0
8.3
7.3
6.7
6.2
5.8
5.6
5.3
5.1
5.0
350
9.5
7.9
6.9
6.2
5.7
5.4
5.1
4.9
4.7
4.5
400
9.2
7.5
6.5
5.8
5.4
5.0
4.7
4.5
4.3
4.2
450
8.9
7.2
6.2
5.6
5.1
4.7
4.4
4.2
4.0
3.9
500
8.7
7.0
6.0
5.3
4.9
4.5
4.2
4.0
3.8
3.7
550
8.5
6.8
5.8
5.1
4.7
4.3
4.0
3.8
3.6
3.5
600
8.3
6.7
5.7
5.0
4.5
4.2
3.9
3.7
3.5
3.3
500
13.0
10.5
9.0
8.0
7.3
6.8
6.3
6.0
5.7
5.5
550
12.7
10.2
8.7
7.7
7.0
6.5
6.1
5.7
5.4
5.2
600
12.5
10.0
8.5
7.5
6.8
6.3
5.8
5.5
5.2
5.0
1b. 1500 ha suitable habitat.
150
200
250
300
350
400
450
500
550
600
150
20.0
17.5
16.0
15.0
14.3
13.8
13.3
13.0
12.7
12.5
200
17.5
15.0
13.5
12.5
11.8
11.3
10.8
10.5
10.2
10.0
250
16.0
13.5
12.0
11.0
10.3
9.8
9.3
9.0
8.7
8.5
300
15.0
12.5
11.0
10.0
9.3
8.8
8.3
8.0
7.7
7.5
350
14.3
11.8
10.3
9.3
8.6
8.0
7.6
7.3
7.0
6.8
9
400
13.8
11.3
9.8
8.8
8.0
7.5
7.1
6.8
6.5
6.3
450
13.3
10.8
9.3
8.3
7.6
7.1
6.7
6.3
6.1
5.8
Table 2. Population matrix for the demographic parameters that will be collected for
each study area over multiple re-sampling seasons. An X indicates data will be collected
in that cell during the sampling occasion.
Persistence
Absence
Immigration
Sampling (Survivors not
Local
(Deaths +
From another
Occasion
Emigrating)
Recruitment
Immigrants)
Population
____________________________________________________________________
M
F
M
F
M
F
M
F
____________________________________________________________________
First Year
X
X
Second Year
X
X
X
X
X
X
X
X
Third Year
X
X
X
X
X
X
X
X
____________________________________________________________________
Example Diagnostic: (Persistence + Local Recruitment) >< (Absence)
If >, then the population is stable or increasing
If<, then the population is decreasing
10
Figure 1. Locations of the ski resorts and paired control study areas.
11
Figure 2. Results of a 1-tailed, paired t-test power analysis to detect a -10-50% change in
density difference between 3 ski areas and 3 control areas with alpha = 0.15. The
standard deviation was estimated using a Poisson distribution. Three density values (8,
10, and 12 martens / 1500 ha) were used to simulate the range of densities expected.
Power
1
0.9
0.8
0.7
0.6
0.5
0.4
0.3
8 Martens
10 Martens
12 Martens
0.2
0.1
0
-10
-20
-30
-40
Percent Change
12
-50
VII. Literature Cited
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Unpublished report. 2233 Watt Ave, Suite 330, Sacramento, CA.
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spatial scale and scale-sensitive properties on habitat selection by American
marten. Pages 368-385 in J.A. Bissonette, editor. Wildlife and Landscape
Ecology. Springer-Verlag, New York, New York, USA.
Brylski, P. V., P. W. Collins, E. D. Pierson, W. E. Rainey. 1997. Mammal species of
special concern in California. Report submitted to California Department of Fish
and Game, Sacramento, California.
Buskirk, S. W. and S. L. Lindstedt. 1989. Sex biases in trapped samples of the
Mustelidae. Journal of Mammology. 70:88-97.
Cablk, M. E. and S. Spaulding. 2002. Baseline and initial monitoring assessment of
Martes americana, the American marten, at Heavenly Ski resort, Lake Tahoe. U.
S. Forest Service, Lake Tahoe Basin Management Unit. 87 p.
Caswell, H. 1989. Matrix population models. Sinauer Associates, Sunderland,
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Mass.,
Drew, G. S. 1995. Winter habitat selection by American marten (Martes americana)
In Newfoundland: Why old growth? Dissertation, Utah State University. Logan.
83 p.
Kucera, T. 1997. Ecology of American martens on the Inyo National Forest.
Unpublished report, Department of Environmental Science, Policy, and
Management, University of California, Berkeley.
Kucera, T. 2004. Ecology of American martens on the Mammoth Ski area.
Unpublished report.
Macfarlane, D. 1994. National Forest System status information. Pages 176-184 in: L.
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18
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Potvin, F., L. BClanger, and K. Lowell. 2000. Marten habitat selection in a clearcut
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Riddle AE, Pilgrim KL, Mills LS, McKelvey KS, Ruggiero LF. 2003. Identification of
mustelids using mitochondrial DNA and non-invasive sampling. Conservation
Genetics, 4, 241–243.
Simon, T. L. 1980. An ecological study of the pine marten in the Tahoe National
Forest. M.S. thesis. California State University, Sacramento, CA. 143 p.
Spencer, W. D. 1981. Pine marten habitat preferences at Sagehen Creek, California. . M.
S. thesis. University of California, Berkeley. 121 p.
Spencer, W. D., R. H. Barrett, et al. 1983. Marten habitat preferences in the northern
Sierra Nevada. Journal Wildlife Management 47: 1181-1186.
TRPA. 1986. Regional Plan for the Lake Tahoe Basin Goals and Policies,
Tahoe Regional Planning Agency, Stateline, NV, USA
USDA. 2001. Sierra Nevada Forest Plan Amendment Final Environmental
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