Nature

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