![]() | NatureVital Signs and Select Park Resources 2017 |
Yellowstone National Park’s "Natural Resource Vital Signs" report is a valuable tool used to assist park managers and scientists more fully understand the status of important indicators of resource condition. Published by the National Park Service (NPS).
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covered parks
Yellowstone National Park
Greater Yellowstone Network, Inventory & Monitoring Program
Montana, Wyoming, Idaho
National Park Service
U.S. Department of the Interior
The State of Yellowstone Vital Signs and
Select Park Resources
2017
Clockwise from top left: stemless mock goldenweed flowers growing along a ridgeline. NPS Photo-J. Frank;
Brewer’s sparrow nest and eggs. NPS Photo-J. Frank; bull bison grazing in Lamar Valley. NPS Photo-J. Frank;
and land snail along Sepulcher Mountain Trail. NPS Photo-N. Herbert.
Cover photos, clockwise from top left: NPS Photo-N. Herbert; NPS Photo-J. Frank; and NPS Photo J. Frank.
Suggested Citation: Yellowstone Center for Resources. 2018. The State of Yellowstone Vital Signs and Select
Park Resources, 2017. YCR–2018–01. Yellowstone Center for Resources, Yellowstone National Park, Wyoming,
USA.
The State of Yellowstone Vital Signs
and Select Park Resources
2017
Edited by Yellowstone Center for Resources,
Science Communications Program
National Park Service
Yellowstone National Park
Post Office Box 168
Yellowstone National Park, Wyoming, USA 82190
www.nps.gov/ycr
NPS Photo-N. Herbert
The Vital Signs Report Series
In 2008, 2011, and 2013, Yellowstone National Park (YNP) published Vital Signs reports. Initially, these reports provided information on the park’s key natural resources; but in 2013, key cultural resources were also included. These reports
referred to all resources as vital signs, even if they were not recognized as a “vital sign” in the National Park Service’s (NPS)
2005 Vital Signs Monitoring Plan for the Greater Yellowstone Network. In this updated report, our goal is to provide information on a more robust set of park resources, which includes resources that were specifically identified as vital signs in the
Vital Signs Monitoring Plan. As a result of the greater inclusion of park resources, we changed the report’s title to The State
of Yellowstone Vital Signs and Select Park Resources, 2017. Vital signs resources that help measure the overall health or pulse
of the park and will be identified by this symbol (h he). Instead of reporting on reference conditions, we have highlighted
key concerns for each resource. We recognize that, at this time, most resources do not have defined reference conditions.
However, all resources have identified concerns that may cause managers to take action to protect resources (rather than
attempting to return the resources to an unknown past condition).
In this report, we highlight 41 natural and cultural resources; 21 are identified as vital signs and 20 as select park resources.
Each resource summary includes a resource history and background information, recent research and monitoring findings,
current status and trends, and future concerns and management priorities.
NPS Photo-J. Frank
4
State of the Resources Report - 2017
Table of Contents
Report Contributors ������������������������������������������������������������������������������������������������������������������� 6
What Are Vital Signs? ����������������������������������������������������������������������������������������������������������������� 6
Why We Monitor Vital Signs and Key Park Resources ������������������������������������������������������������������ 7
Vital Signs Summary Table ���������������������������������������������������������������������������������������������������������� 8
Select Resources Summary Table ����������������������������������������������������������������������������������������������� 10
Ecosystem Drivers ��������������������������������������������������������������������������������������������������������������������� 12
Environmental Quality �������������������������������������������������������������������������������������������������������������� 17
Birds ����������������������������������������������������������������������������������������������������������������������������������������� 20
Amphibians and Reptiles ���������������������������������������������������������������������������������������������������������� 27
Fishes ��������������������������������������������������������������������������������������������������������������������������������������� 28
Insects �������������������������������������������������������������������������������������������������������������������������������������� 30
Mammals ��������������������������������������������������������������������������������������������������������������������������������� 31
Plant Resources ������������������������������������������������������������������������������������������������������������������������ 39
Cultural Resources �������������������������������������������������������������������������������������������������������������������� 43
Ecosystem Stressors ������������������������������������������������������������������������������������������������������������������ 46
Relevant Publications ���������������������������������������������������������������������������������������������������������������� 53
NPS Photo-J. Frank
Yellowstone National Park
5
Report Contributors
Yellowstone Center for Resources
The Yellowstone Center for Resources (YCR) is entrusted
to research, monitor, and manage YNP’s unique and valuable resources. Since the 1872 act that created the park for
conservation and recreation, National Park Service (NPS)
staff and cooperators have inventoried and studied many aspects of the park. Today, the YCR staff strive to understand
and protect a wide range of resources, from hot springs
to wildlife to the park’s archeological sites, and how these
resources may be affected by stressors such as a changing
climate and visitation.
In 2014, the park completed a Foundation Document,
identifying key park resources and values and serving as
a basis for ongoing park planning, research priorities, and
management actions. Documenting general conditions,
trends, threats, opportunities, and data needs for various
park resources, the Foundation Document took a broadbrush approach at reviewing these resources (e.g., YNP’s
large, nearly intact temperate ecosystem). Yellowstone’s
Vital Signs report series provides detailed, up-to-date information on individual resources (grizzly bears, alpine plant
communities, etc.), building upon the information in the
Foundation Document. To read Yellowstone’s Foundation
Document, go to https://www.nps.gov/yell/learn/management/upload/YELL_FD_508.pdf.
Greater Yellowstone Inventory and Monitoring
Network
The Greater Yellowstone Network (GRYN) is one of 32
networks of the NPS Inventory and Monitoring Division
designed to support park managers to improve their understanding of key natural resources and to provide the best
available science for decision making. Each NPS network
collaborated with park specialists and scientists to develop a long-term monitoring strategy. In 2005, the GRYN
published the Vital Signs Monitoring Plan for the Greater
Yellowstone Network. This plan identified and prioritized
a number of vital signs for Yellowstone and Grand Teton
national parks, Bighorn Canyon National Recreation Area,
and the John D. Rockefeller, Jr. Memorial Parkway. Twenty-one of the GRYN-identified vital signs are featured in
this report. Currently, GRYN leads research and monitoring
on seven of those 21 vital signs, while the others are overseen by specialists in the YCR. For a full copy of the Vital
Signs Monitoring Plan, go to https://www.nps.gov/im/gryn/
index.htm.
6
In addition to the YCR and the GRYN, YNP has over 135
independent research groups that conduct work annually.
Of these groups, and others, the following have contributed
directly to this report: Phil Farnes, Snowcap Hydrology;
Marie Gore; C. Barre Hellquist, Massachusetts College of
Liberal Arts, Emeritus; C. Eric Hellquist, SUNY-Oswego; Infographics Lab, University of Oregon; Barkley Sive,
USGS-Air Resources Division; Mike Tercek, Walking Shadow Ecology; USGS-Water Resources Division; Yellowstone
Volcano Observatory.
What Are Vital Signs?
As defined by the NPS Inventory and Monitoring Program, vital signs are “a subset of physical, chemical, and
biological elements and processes of park ecosystems that
are selected to represent the overall health or condition
of a park, known or hypothesized effects of stressors, or
elements that have important human values” (e.g., air and
water quality). While some vital signs may be a species (e.g.,
whitebark pine), others have been categorized as ecosystem
drivers, ecosystem stressors, or environmental quality:
• Ecosystem Drivers - The major external driving
forces that have large-scale influences on natural
systems. Drivers can be either natural forces or
anthropogenic influences.
• Ecosystem Stressors - Physical, chemical, or biological agents that cause significant changes in the
ecological components, patterns, and relationships
in natural systems or cultural resources. The effects
of stressors on park resources can be positive or
negative. In this report, most of the stressors are
having negative effects on other resources.
• Environmental Quality - Parameters that are part of our
environment and have a direct effect on humans and
other organisms (e.g., water, soundscapes). The effect
can be positive, neutral, or negative, depending on the
state of the environmental quality parameter. In addition, environmental quality can be affected by human
activities and natural influences (e.g., fire, geothermal
influences) that occur both inside and outside of the
park.
In this report, we will summarize 21 vital signs and 20
select park resources. Some of the individual species we report on (e.g., grizzly bears) are not a vital sign but are part of
a larger vital signs group (e.g., large carnivores). Therefore,
State of the Resources Report - 2017
for the select park resources that fall under an umbrella of
a larger vital sign, we will identify their original vital sign on
the tables in this report.
Why We Monitor Vital Signs and Key
Park Resources
Yellowstone National Park was established in 1872, primarily to protect geothermal areas that contain about half
the world’s active geysers. At that time, the natural state
of the park’s other landscapes, waters, and wildlife was
largely taken for granted. As development throughout the
West increased, the park’s 2.2 million acres containing
forests, mountains, meadows, rivers, and lakes became an
important sanctuary for the largest concentration of diverse
wildlife in the lower 48 states. The park also preserved important prehistoric and historic cultural resources, such as
archeological sites and historic buildings.
Today, YNP and the surrounding Greater Yellowstone
Ecosystem (GYE) are recognized as one of the largest,
nearly intact temperate ecosystems in the world. The park
has been designated by the United Nations Educational,
Scientific, and Cultural Organization as a Biosphere Reserve
site and as a World Heritage site. These designations reinforce the international significance of YNP as a critically
important conservation area.
safeguard individual resources, it remains critical to continue monitoring the status and trends of the park’s natural
and cultural resources. To determine whether observed
changes to resources are a result of natural, ecological, or
human influences requires careful study. These influences
can occur both within and outside of the park; for example,
the survival of some animal species depends on seasonal
migrations or the use of habitat that extends beyond the
park’s boundaries. Within the park, introduced non-native
plant and animal species may reduce the presence of native
species through competition, predation, or disease, or even
change natural ecological processes such as fire regimes.
High levels of visitation can lead to soil compaction and trail
degradation, resulting in disturbance of natural vegetation
and cultural sites. For these reasons, it is important to pay
careful and regular attention to the state of park resources.
In our effort to monitor the status and trends of the park’s
ecosystem, we focus on select resources, including those
that are defined as vital signs by the NPS’s Greater Yellowstone Network. While a number of resources have had data
collected over a long time period, thereby enabling us to
determine trends for these resources, others have shorter
data records not yet conducive to trend reporting. This
report summarizes the status and, when available, the trend
of the park’s natural and cultural resources, and makes this
information available for use in science-based decision
making by park managers.
Although YNP is largely protected due to its status as a
national park, and there are federal laws and policies that
NPS Photo-J. Peaco
Yellowstone National Park
7
VITAL SIGNS SUMMARY TABLE
Vital
Sign
Vital Sign
Category
Climate
Fire
Ecosystem
Drivers
Geothermal Systems/
Subsurface Geologic
Processes
Geomorphology
River and Stream
Hydrology
Daily temperature (Mammoth)
2010–2017: average min = 30°F,
average max = 54°F
Annual precipitation (Mammoth)
2010–2017 average annual
precipitation = 14.9 inches
Accumulated growing degree days above 40°F
(Mammoth)
2010–2017 average AGDD40 =
3,072
Peak snow water equivalent (Northeast Entrance)
2010–2017 average peak SWE =
10.4 inches
Peak streamflow (Corwin Springs)
2017 peak = 20,500 cfs
Average acres burned per year (1972–2017; minus
1988)
5,936
Average number of fires per year (1972–2017;
minus 1988)
26
Thermal output (chloride discharge through major
rivers, heat flux in hydrothermal areas)
Within normal variation
Earthquakes per year (2017)
3,427; elevated due to Maple
Creek swarm
Ground deformation in caldera (2016)
Subsiding few cm/year in
caldera; uplifting few cm/year
near Norris
Yellowstone Lake level (peak, 2017)
~3.5 m peak relative to
benchmark at Grant dock
River discharge, peak rates (2017)
Increased nearly twofold from
2016 at some major rivers
Timing of peak flows
Shifting earlier in spring
Variable and site specific
Base flows
Earlier and lower
Visibility, 5-year average (2011–2015)
2.7 deciviews
Ozone (W126), 5-year average (2011–2015)
8.6 ppm/hr
Nitrogen in precipitation, 5-year average
(2011–2015)
4.9 kg/ha/yr
Sulfur in precipitation, 5-year average (2011-2015)
1.7 kg/ha/yr
Particulate matter, annual 98th percentile 24-hour
average, West Yellowstone (2016)
43.1 mg/m3
CO, winter max 1-hour average, West Yellowstone
(2016)
13.0 ppm
NO2, winter max 1-hour average West Yellowstone
(2016)
25.2 ppb
Arsenic, dissolved nitrogen, and phosphorus in
Yellowstone, Lamar, and Madison rivers (2016)
Within natural variation and
not outside historical range
Soda Butte Creek iron, copper, and lead levels
Improved, after 7 decades of
mine-related impairment and
reclamation
Median sound levels, West Entrance sound station,
(July 2017)
52.2 dBA
Median sound levels, West Entrance sound station,
(Winter 2017)
28 dBA
Potential sites suitable for breeding (2016)
66%
Catchments occupied by boreal chorus frogs (2016)
75%
Major drainages with 4 native species (2016)
75%
Alpine Plant Communities
Species richness (at GLORIA site)
127 species
Soil temperature; growing degree days above 5°C
(2011–2016; at GLORIA site)
100 days
Beavers
Beaver colonies (2015; partial survey with colonies
in northeast YNP estimated)
102
Insects
Butterflies-species present, butterfly species counted (1997–2007)
Xeric affinity species increased;
hydric affinity species
decreased
Dragonflies-mercury (Hg) levels in larvae
Hg increasing in some areas
and decreasing in other areas
Environmental
Quality
Water Quality
Natural Soundscapes
Amphibians
8
Current Conditions
Magnitude of peak flow
Air Quality
Resources
Current
Status
Key Monitored Indicators
Resource Concerns
Average
temperatures
are exceeding
historical
norms
• seasonal rain, snow, stream
flow changes
• reduced water supply or
shift in seasonal water
supply
• longer growing season,
shift in plant species
composition
• declining snow pack
Stable
• increase in size and
frequency of fires due to
climate change
Stable
• degradation of
hydrothermal features by
visitors
• changes to hydrothermal
system recharge due to
changes in precipitation
patterns
Stable
• changes to annual snowpack
and precipitation patterns
• changes in river incision and
erosion patterns
Stable to
Declining
• increased temperatures
• shifts in precipitation
patterns
• earlier snowmelt
SummerStable to
Declining;
WinterStable
• increase in magnitude and
frequency of wildfires
• damage to plants,
disruption in soil nutrient
cycling
• increasing Western U.S.
nitrogen (and other)
emissions
Stable with
exception
of Soda
Butte Creek
(Improving)
• earlier snowmelt and runoff
• increasing water recreation
(fishing, swimming,
boating)
SummerStable to
Declining;
WinterImproving
• increase in extent/events
of human-caused noise in
summer months
Stable
• spread of chytrid fungus
and other diseases
• climate-induced effects on
wetlands/breeding
Unknown
• warming climate
• competition from invasive
species
Stable
• willow recovery and
recolonization of historical
areas
Unknown
• effects of changing climate
(i.e., drought) on host
plant availability
• increase in mercury levels
in air
• shifts in phenology
State of the Resources Report - 2017
Vital
Sign
Category
Resources
Current
Status
Vital Sign
Key Monitored Indicators
Current Conditions
Shrub-steppe
Communities
Percent cover of native and non-native species,
bare ground, and litter in all plots across the
landscape (2016)
Landscape is largely comprised
of native species, with few
locations heavily impacted by
invasives
Whitebark Pine
GYE percent blister rust infection (2015)
14–26%
GYE tree mortality, 4-year trend (2015)
26%
GYE trees with reproduction potential (i.e., cone
producing; 2015)
25%
GYE regeneration
51 understory trees/500m2
Inspected watercraft with AIS (2016)
Less than 0.5% detection of
suspected AIS on inspected
watercraft
Gastropods (red-rimmed melania, New Zealand
mud snails) in select waterways (2016)
2
Aquatic invasive vegetation (2016)
0
Change in density of targeted invasive species
after treatment
Varies by species
Invasive plant species (as ratio of known park
vascular plants)
18%
Reduction in lake trout, age 2+ (2012–2017)
-15%
Removal of lake trout (2017)
397,000
Reduction in lake trout, age 6+ (2012–2017)
-60%
Reduction in lake trout biomass (2012-2017)
-33%
Population estimate-GYE (2010)
924,000
Land use changes (public to private)
No known changes since 2010
Mountain Goats
(non-native)
Estimate of numbers in and near Yellowstone's
boundary (2016)
More than 200
Increasing
• potential competition for
resources and potential for
disease transmission with
bighorn sheep
• effects on alpine vegetation
Visitor and
Recreational Use
Annual visitation (2017)
4,116,525
Backcountry person use nights (2016)
44,507
Backountry
recreationStable;
VisitiationIncreasing
• increase in wildlife habituation and interactions
• increase in visitor impacts (invasive species
introduction, social trails,
thermal area damage)
• increase in unsanitary conditions (human waste, trash,
contaminated water)
Wildlife Diseases
Brucellosis prevalence (adult female bison and elk)
Bison ~60%; elk ~10%
Chronic wasting disease (mule deer and elk)
Detected in mule deer outside
park's east boundary
Stable to
Increasing
• wildlife, domestic animals,
and humans share an
increasing number of
infectious diseases,
which pose a risk to
high densities of visitors
and wildlife within
Yellowstone
• proximity of confirmed
diseases near the park
boundary or within
adjacent states (chronic
wasting disease, whitenose syndrome)
Aquatic Invasive
Species (AIS)*
Invasive Plants*
Lake Trout (non-native) in Yellowstone
Lake*
Land Use
Few locations
near North
Entrance
Declining,
majority are
Stable
• increased temperatures,
change in timing of spring
runoff, loss of native
species to non-natives
• changes in fire regime due
to warm, dry conditions
and increased fuel from
non-natives
Stable to
Declining
• increased temperatures
leading to drought
and increased
intensity/frequency of fires
• white pine blister rust
infection rates
• exposure to insect and plant
pathogens
• competition from other tree
species
Stable
• increased in AIS from visitor
boats and fishing gear
• effects of warming
temperatures, making
park waters more optimal
for AIS
• expansion of known AIS
beyond current locations
Increasing
• warmer temperatures
increase habitat suitability
for invasive species
• increased introduction of
invasives plants via visitors
and vehicles
• spread of invasive plants in
disturbed sites (e.g., road
corridors, construction
areas)
Decreasing
• logistical difficulties and
financial cost of long-term
suppression operations
Stable
• change in private land use
(including recreational
use) outside the park
• potential mineral, gas, or
geothermal development
near park boundary
Ecosystem
Stressors
Chytrid fungus, ranavirus prevalence (amphibians)
Widespread
Distemper and mange prevalence (wolves)
Distemper not detected since
2008; mange low
Hantavirus (deer mice)
Seasonally 30–40% at actively
infected sites
West Nile virus (birds)
Mosquito host present; virus
not detected
White-nose syndrome (bats)
Not detected
Yellowstone National Park
Resource Concerns
9
SELECT RESOURCES SUMMARY TABLE
Resource
Key Monitored Indicators
Current Conditions Current
Status
Resource Concerns
Archeological Sites
Percentage of park inventoried
<3%
Percentage of documented sites in good
condition
57%
• effects of environmental change
(wildfire, floods, erosion, retreating
ice patches, insect infestation, etc.)
• unauthorized collecting
Arctic Grayling and
Westslope Cutthroat
Trout*
Occupied stream habitat-kilometers (past
decade)
Restored 74 stream
kilometers and 20 lake
surface hectares
Bald Eagles
Productivity (average, 1984–2016)
0.71
Nest success (average, 1984–2016)
50%
Stable
Improving
• competition and hybridization with
invasive species
• potential climate-induced changes to
habitat (temperature), affecting food
availability, disease exposure, survival
Stable
• prey availability and switching among
prey species due to decrease in
cutthroat trout in Yellowstone Lake
• potential for exposure to white-nose
syndrome
• protection of maternal colonies in
buildings
Brood size (average, 1984–2016)
1.4
Bats
Number of species identified
13
Unknown
Bighorn Sheep**
Northern range count (2017)
353
Stable
Lambs per 100 ewes (2017)
27
• exposure to pneumonia-inducing
pathogens
• potential competition/disease
transmission with mountain goats
Bison**
Population estimate-summer (2016)
5,500
Stable
• large-scale management reductions
due to limited tolerance in
surrounding states
• limited capacity within park
• recent shifts in preference for habitats
on the northern range
Colony Nesting Birds+
American white pelicans fledged (2016)
308
Declining
Caspian terns fledged (2016)
0
California gulls fledged (2016)
0
Double-crested cormorants fledged (2016)
34
• high water levels in Yellowstone Lake
• decreased availability of primary food
source, Yellowstone cutthroat trout
• disturbances by visitors
• increased predation by eagles
Adult loons (2016)
31
Loonlets fledged (2016)
9
Stable to
Declining
• human disturbance of shoreline nests
• loss of breeding habitat
• mercury toxicity in prey fish
Population count-northern range (2017)
5,349
Recruitment (2017)
21 calves/per 100 adult
females
Stable to
Improving
• combined effects of a diverse and large
predator guild, including human
harvests outside the park
Nesting success (2016)
41%
Unknown
Productivity (2016)
0.45 per occupied
territory
• reproduction is low in most years due
to unknown factors; research has
been initiated
Wolves in Yellowstone (2016)
108
Breeding pairs, Yellowstone (2016)
7
GYE population estimate (2016)
690
Distribution of females with cubs (2016)
18/18 bear management
units occupied
Annual mortality: Adult female (2016)
6
Annual mortality: Adult male (2016)
19
Annual mortality: Dependent young (2016)
9
Historic properties documented
66%
Historic properties documented in good
condition
77%
Cultural landscape properties documented
25%
Cultural landscape properties in good condition
85%
Museum objects cataloged (2016)
81%
Common Loons++
Elk**
Golden Eagles
Gray Wolves◊
Grizzly Bears◊
Historic Structures,
Districts, and Cultural
Landscapes
Museum Collections
Stable
• habituation to park visitors
Stable to
Improving
• human-caused disturbance and
mortality, especially to females
Stable to
Declining
• ongoing need for maintenance and
improvements due to continual
human use
• backlog on evaluations, documentation
Improving
• storage space (including vehicle
storage) and staffing
*Park resource that is included in the Greater Yellowstone Network (GRYN)-identified Native Aquatic Assemblages vital sign.
**Park resource that is included in the GRYN-identified Ungulates vital sign.
+Park Resource that is included in the GRYN-identified Land Birds vital sign.
++Park Resource that is included in the GRYN-identified Birds of Concern vital sign.
◊Park resource that is included in the GRYN-identified Large Carnivores vital sign.
10
State of the Resources Report - 2017
Resource
Key Monitored Indicators
Current Conditions Current
Status
Resource
Concerns
Peregrine Falcons
Annual nesting success (2016)
43%
Brood size (2016)
1.8
• low nesting and productivity levels
over the last decade
Productivity per occupied territory (2016)
0.8
Northern range spring count (2017)
506
Recruitment: fawns/100 adult females (2016)
37
Abundance-birds per survey plot (2016)
6.6
Species richness per survey plot (2016)
18.6
Resident adults and subadults, fall count
(2016)
29
Nesting pairs (2016)
2
Cygnets fledged (2016)
3
Percentage of wetlands dry (2016)
35%
Stable
Improving
Pronghorn**
Songbirds+
Trumpeter Swans++
Wetlands
Yellowstone Cutthroat
Trout*
Average fish/net-fall (2017)
20.5
Average observed-spawning streams (2017)
157 in 4 streams
Average caught/hour by anglers (2017)
0.85
Stable
Stable to
Improving
Stable
Declining
• limited forage availability on winter
range
• reestablishing migration and dispersal;
removal of barriers to movements
• increased fequency/magnitude of fires
• range-wide decreases in songbirds
• climate-induced changes to habitat
availability
• decrease in nesting pairs and low
productivity
• human disturbance
• flooding of nests
• Increasing annual percentages of dry
wetlands
• loss of species diversity and wetland
habitat
• predation by non-native lake trout
**Park Resource that is included in the GRYN-identified Ungulates vital sign.
+Park Resource that is included in the GRYN-identified Land Birds vital sign.
++Park Resource that is included in the GRYN-identified Birds of Concern vital sign.
NPS Photo-J. Frank
Yellowstone National Park
11
ECOSYSTEM DRIVERS
Climate
Climate is the set of long-term, average meteorological
conditions that occur over several decades or longer. Unlike
weather, which fluctuates greatly in the short-term and is
difficult to predict, climate is relatively stable and many organisms have adapted to its predictable rhythms. As a result,
climate is a driving force behind many ecological processes.
For example, average temperature and moisture determine
which species can live in an area, the rate at which they
grow, and the frequency and severity of forest fires. Temperature and precipitation regimes also strongly influence
the intensity and timing of stream flows, which are important factors in both agricultural and natural ecosystems.
The GYA is becoming more arid, and global climate models project this trend will continue in the future. Precipitation has declined in many locations throughout the GYA in
recent decades as temperatures have increased. At Mammoth Hot Springs, the five-year running mean of average
annual daily maximum temperature has increased by 1.2°
Celsius (2.1°F) and the average annual daily minimum temperature has increased by 2.2° Celsius (3.9°F) during 1941–
2016. Total annual precipitation at Mammoth Hot Springs
since 1976 has been generally below the long-term mean of
15.3 inches (38.9 cm; see figure bottom left). The five-year
running mean of annual peak snowpack (expressed as peak
snow water equivalent, or PWE) at the Northeast Entrance
has declined 30% since 1966, from 15.02 inches to 10.44
inches (from 38.2 cm to 26.5 cm; see figure above right).
Peak snow water equivalent (PWE) at YNP’s Northeast
Entrance, 1966–2017. Five-year running average included
current year and 4 previous years.
Snowy conditions have been prevailing for a shorter period
during the year. The 10-year running mean of winter length
(annual number of days with snow water equivalent > 0) at
the Northeast Entrance SNOTEL station has decreased 15%
during 1966–2017, from 216 to 183 days. Even if precipitation
recovers to historical levels, which models indicate is possible, increased temperatures and evapotranspiration will
reduce water availability.
In the future, changes in the seasonal patterns of rain,
snow, and stream flow will be as important to management
as the reduction in total water availability during the course
of the year. Also, a greater proportion of annual precipitation will likely fall as rain rather than snow. Instead of being
stored in the snowpack and gradually released during the
year, this rain will be rapidly lost to streams and unavailable
for plants and animals during the growing season. The snow
that does accumulate will likely melt more quickly as a result
of the projected warming trends, producing earlier and
more intense spring runoff. Total annual stream discharge
may remain steady or decline; but as a greater proportion
becomes compressed into an increasingly intense spring
runoff, streams could be lower in summer months, contributing to water scarcity. Hotter, drier summers and shorter
winters will likely cause larger and more frequent wildfires,
as well as changes in the amount and type of motorized
winter recreation that will be possible in the park.
Annual precipitation at Mammoth Hot Springs, YNP, 1941–
2016. The running mean is based on a time series with 21.1%
missing values. The five-year moving mean includes the
current year and previous four years.
12
State of the Resources Report - 2017
Fire
Fire has been a key factor in shaping the ecology of YNP;
vegetation has adapted to fire, and in some cases, species
like lodgepole pine rely on it to regenerate. Park policy is to
allow naturally ignited fires to burn when at all feasible for
resource benefits, and to suppress fires which are human
caused or endanger people or property. During the last 45
years of reliable fire records, YNP has averaged 26 fires per
year (an average of six human-caused and an average of 20
lightning-caused), and an average of 5,936 acres (2,402 ha)
burned per year from 1972 to 2017, excluding 1988. In 2017,
less than one acre (.4 ha) burned from eight known wildfire
starts. Six fires were caused by human activity and were
suppressed, while two fires went out naturally. The summer
of 2017 had the least amount of acreage burn in the park
since 1983.
The size and frequency of fires are affected by several factors such as location, amount of lightning, type and amount
of fuels, fuel moisture, weather, drought, and long-term
climate. Within the park, climate trends show precipitation
is declining and temperatures are increasing. Current statistics show there are fewer fires burning an equal or greater
number of acres on average, per year, than in the past. In
the last 10 years (2008–2017), the