THE YELLOWSTONE GRIZZLY BEAR

STATUS

The Grizzly Bear (Ursus arctos) once roamed much of western North America. Presently it is found in five distinct populations in the conterminous United States, including the Greater Yellowstone Ecosystem (GYE), see map. The species has been listed as threatened with extinction under the Endangered Species Act (ESA) since 1975. Since its listing, a great deal of effort has been made to conserve the species including removal of livestock, especially sheep, from the GYE recovery area; clean-up and lock-up of garbage and other bear attractants; and stronger education and law enforcement to prevent accidental shootings and poaching. While most would agree that substantial progress has been made, there is a great deal of disagreement surrounding the bear’s status and whether to delist the species in the GYE.

In 1993, a recovery plan was implemented with three specific goals that had to be met for six consecutive years. In 2003, those recovery goals were met and the U.S. Fish and Wildlife Service (FWS) proposed to delist the bear in 2005. The proposal was shelved after significant resistance from environmental interests, and the recovery plan was modified with updated population and mortality methodologies. The GYE population continued to meet recovery goals and was removed from the ESA in 2007. Lawsuits were immediately filed and in 2009 a federal district judge overturned the delisting and put the species back on the threatened list. The judge ruled that 1) the Conservation Strategy, under which the bear would be managed by state and federal agencies, was unenforceable; and (2) the FWS did not adequately consider the impacts of the potential loss of whitebark pine nuts, a grizzly bear food source.

Responding to the 2009 decision, an Appeals Court ruled in 2011 that the Conservation Strategy did, in fact, provide an adequate regulatory mechanism, but upheld the lower court’s ruling on whitebark pine and other foods.

In 2013, the Yellowstone Ecosystem Subcommittee, the Interagency Grizzly Bear Committee, and Interagency Grizzly Bear Study Team again recommended the species be removed from the threatened species list, specifically adding that alternative foods are available and the reduction of whitebark pine did not appear to have a significant impact on bears.

In March 2016, FWS again proposed to remove the species from the ESA, by reason of recovery. On June 22, 2017, the Department of the Interior announced that the Yellowstone population of the grizzly bear has recovered to the point where federal protections can be removed and overall management can be returned to the states and tribes.

DOI concludes the population has met and exceeded all criteria for delisting, including: 1) estimated population size, 2) distribution of females with cubs, and 3) mortality rates.

1.      Population Recovery target: ≥ 500 bears in the recovery area (criteria instituted in 2014): achieved in 2014 and 2015. In 2015, there were an estimated 717 grizzly bears in the GYE, an increase from 136 in 1975.

2.      Distribution Recovery target: Objective of 48 females producing cubs annually: achieved since 2006. Earlier target was female grizzlies with young occupying at least 16 of the 18 bear management units that comprise the Primary Conservation Area in the GYE. This goal has been met since 1998.

3.      Mortality:

a) Estimated percent of total mortality of independent-aged females not to exceed 7.6% (lowered from 9% in 2012): achieved 2006-07, 2009-10, 2012-14.

b) Estimated percent of total mortality of independent-aged males not to exceed 15%: achieved 2006-07, 2009, 2012-15.

c) Estimated percent of mortality from human causes for dependent young not to exceed 7.6% (lowered from 9% in 2012): achieved 2006-15. Earlier standard was bear mortality must be limited to no more than 4 percent of the total population. This goal has been met since 1996 with the exception of one year.

·         In 2015, there were 59 known and probable grizzly bear mortalities in the GYE: 34 attributed to human causes; 4 of undetermined cause; 2 were natural deaths; and 19 unknown.

While there are plenty of opinions on all sides, the primary concern by opponents to delisting is the fear that protection for the GYE grizzlies will disappear if they are taken off the ESA list. In fact, years of effort have gone into crafting a conservation package for Yellowstone’s grizzlies to ensure that the bears continue to thrive once taken of the list. Developed by federal and state natural resource management agencies, the Conservation Strategy provides an impressive set of protections including a six-million-acre core Primary Conservation Area, protections against excessive take, and extensive monitoring. A solid framework is in place to ensure that continued grizzly bear conservation will follow delisting. As the needs of Yellowstone grizzlies change or increase, so will the tools and protections needed to meet them.

Outside the courtroom and the court of public opinion, management of bears changes little whether it is listed under the ESA or not. Land agencies will continue to manage the bear and scientists will continue to monitor the long-term recovery goals, and members of the public will sit in judgement.

STAYING SAFE IN GRIZZLY COUNTRY

In 2015, a human-grizzly conflict inside Yellowstone National Park resulting in one dead human, the killing of the mother grizzly, and removal of two, now-orphaned cubs to a zoo. This event was tragic for humans and bears alike. Humans deaths from grizzly attack are rare, especially in light of the number of potential interactions of grizzlies and humans as they overlap in time and space. In Yellowstone National Park, the number of bear-inflicted human injuries has averaged less than one injury per one million park visits each decade from 1970 to 2014. From 1980 to 2014, 37 people were injured by grizzly bears in Yellowstone (an average of 1.1 injuries per year).

Grizzly bears can be dangerous.  Considering their size, strength, and potentially aggressive nature, it is remarkable that they don’t injure or kill people more often than they do. To be prepared one must take responsibility for their own safety in grizzly country.  The following advice is compiled from People and Carnivores:

·         The most important tool for staying safe is situational awareness -- "knowing what is going on around you." 

·         Pay attention to where you are – can you see very far?  Is there terrain or vegetation that could hide a bear from your view?  Many people have an unrealistic ‘search image’ -- they assume that grizzlies are huge, and therefore easy to see.

·         Be aware of wind direction. If the wind is in your face as you walk, that means your scent is being carried away from any bears that may be ahead of you. In our experience, grizzlies that can catch your scent will typically leave once they know what you are.

·         Stay alert for fresh bear sign as well. Tracks may not always be obvious – look also for scat, rub trees, or fresh digging (excavating roots, insects, or rodents).  Bears will often tear apart logs or flip rocks seeking food.

·         One of the most dangerous situations to walk into is a grizzly that has claimed an animal carcass.  The bear’s inclination will be to defend this food source.  Look and listen for scavenger birds like ravens and magpies.   You may be able to smell a carcass from some distance if the wind is right.  If you do detect a carcass, take a wide detour around it, or turn around if there is no option to detour.

·         Bears tend to be most active at dusk and dawn, but that doesn’t mean you can’t encounter one in midday.  Bears often sleep during the day in thick timber.  Move carefully, and stop frequently to listen, when travelling through such places.

·         Have bear spray and know how to use it. Bear Pepper Spray is a highly effective, easily used deterrent against aggressive bears and other animals.  To use bear spray:

ü  Remove safety clip

ü  Aim slightly down and towards the approaching bear.  Adjust angle for wind direction.

ü  Spray a brief shot when the bear is roughly 30 feet away.

ü  Spray again if the bear continues to approach.

ü  Once the animal has retreated or is busy cleaning itself, leave the area as quickly as possible, but do not run.  Alternately, go to an area of safety, such as a car.

ü  REMEMBER: Bear pepper spray is only effective when used as an airborne deterrent sprayed as a cloud at an aggressive animal.  It should not be applied to people, tents, packs, other equipment or surrounding area as a repellent.

Many aggressive encounters with grizzlies happen very quickly.  Some are probably too instantaneous for a person to be able to react with either bear spray or a firearm.  To give yourself a margin of safety, carry your bear spray in a consistent and accessible place on your person (or on your saddle if you are horseback and prefer it not be on your person). Practice reaching for the spray until it becomes second nature to reach for it.

GRIZZLY FACTOIDS

APPEARANCE. The grizzly bear’s color varies from blond to black, often with pale-tipped guard hairs (hence the name “Grizzly”). The coloration of black and grizzly bears is so variable that it is not a reliable means of distinguishing the two species (see comparison of grizzly and black bear below).

DIET. Bears are omnivores with a wide ranging and flexible diet, consuming different foods depending on location and season. Preferred foods include army cutworm moths, whitebark pine nuts, ungulates (elk, bison), and cutthroat trout. Bears in the GYE are known to consume at least 266 species of plant (67%), invertebrate (15%), mammal (11%), fish, and fungi. They will readily eat human food and garbage where they can get it. Their caloric requirements are: normal (May-Sept): 5,000-8,000 kcal/day; hyperphagia (a determined push for calories in advance of hibernation): 20,000 kcal/day; hibernation 4,000 kcal/day.

HIBERNATION. Grizzly bears hibernate in response to seasonal food shortages and cold weather. The location and nature of dens is variable, but typically dug in sandy soils, at base of large trees, on north-facing slopes (30-60 percent grade) at 6,500-10,000 feet elevation. In hibernation, body temperatures fall some 12 degrees F, slowing their metabolism by 50-60%. Bears sometimes awaken and leave their dens during the winter, but they generally do not eat, drink, defecate, or urinate during hibernation. They live off of a layer of fat built up prior to hibernation, and will lose some 15-30% of their body weight.

EMERGENCE. Bears emerge from their dens as temperatures warm and winter-killed ungulates and early spring vegetation become available. In the GYE, bears begin to emerge from their den in early February, and most bears have left their dens by early May. Males are likely to emerge before females.

REPRODUCTION. Female Grizzly bears (sows) rarely breed before age four, and the average age of first reproduction in GYE is 5.8 years. Once of reproductive age, females typically become pregnant once every three years. Implantation of a fertilized egg in the uterus is delayed so the embryo does not begin to develop until late November or December, about one month after the sow has denned. In late January or early February, the sow gives birth to 1-2 cubs, sometimes three, rarely four. At birth the cubs are hairless and blind, are about eight inches long, and weigh 8-12 ounces. The cubs do not hibernate but nurse and sleep next to the mother. At 10 weeks, the cubs weigh about 10–20 pounds. Male (boar) bears take no part in raising cubs, and may actually pose a threat to younger bears (see mortality). Grizzly bear cubs usually spend 2½, and sometimes 3½ years with their mother before she or a prospective suitor chases them away so that she can mate again. Females frequently establish their home range in the vicinity of their mother, but male cubs disperse farther.

GENUS/SPECIES: Ursus arctos is the North American Brown Bear, or Grizzly. Ursus (Latin for “bear”) and arctos (Greek for “bear”). There are several distinct subspecies including the Mainland Grizzly, U. arctos horribilis, found in the lower 48 states and the Kodiak bear, U. arctos middendorffi, on Kodiak Island, Alaska, the largest of the brown bear subspecies.

COMMON NAMES: grizzly bear, brown bear, silvertip.

LIFE SPAN: 20-30 years; oldest known in GYE 31 years.

SPEED: 35-40 mph.

CLAW LENGTH: average 1.8 inches (45 mm), longest 5.9 inches (150 mm); claw length and shape allow efficient digging of foods from the ground but are less efficient for tree climbing than black bear claws.

TREE CLIMBING ABILITY: cubs and younger, smaller bears are proficient tree climbers; however, adult male and female grizzly bears are also capable of climbing trees.

BODY TEMPERATURE: 98-101°F (36.5-38.5°C) during active season; 94-95°F (34.4-35°C) during hibernation.

RESPIRATION: 6-10 per minute; <1 per minute during hibernation.

HEART RATE: 40-50 beats per minute; 8-19 beats per minute during hibernation.

VISION: on par with human vision; exhibits color vision and excellent night vision.

AVERAGE WEIGHT: adult male = 413 lb. (187 kg); adult female = 269 lb. (122 kg).

AVERAGE HOME RANGE SIZE IN GYE: males = 337 square miles (874 km2); females = 109 square miles (281 km2).

GESTATION: 235 days (implantation of embryo delayed until late November/early December).

BIRTH PERIOD/LOCATION: late January/early February in winter den.

DEN ENTRY: pregnant females- 1st week November; other females- 2nd week November; males- 2nd week November.

AVERAGE DENNING DURATION: females with cubs- 171 days; other females- 151 days; males- 131 days.

DEN EMERGENCE: males- 4^th week March; other females- 3^rd week April; pregnant females- 4^th week April.

TYPICAL DEN TYPES: excavated (i.e., dug) = 91%; natural cavity = 6%; snow = 3%.

PERIOD OF MATERNAL CARE: 18 to 42 months; average = 30 months.

SURVIVAL RATE: cubs = 55%; yearlings = 54%; subadults = 95%; adult females = 95%; adult males = 95%

CAUSES OF MORTALITY (GYE): Human-caused (including management actions, hunter-related, vehicle-strikes, etc.) = 85%; Natural causes (including male grizzly attacks, malnutrition) = 15%.

 Everyone likes to watch bears: bear watching enroute to the chapel in Grand Teton National Park, photo © P.Potter

Sources & Resources:

2016 Conservation Strategy for Grizzly Bear in the Greater Yellowstone Ecosystem. U.S. Fish and Wildlife Service. 128 pages.

Grizzly Bear Recovery in the Greater Yellowstone Ecosystem. Yellowstone Science 23(2): December 2015. 98 pages.

Yellowstone Resources and Issues Handbook. U.S. Department of the Interior, 2016. 281 pages.

People and Carnivores. www.peopleandcarnivores.org

Snail Relics

You’re walking through the woods and your eye catches a glimpse of something round and white. On closer inspection, it’s a shell, bleached chalky white with its former occupant long gone. Is this some remains of marine mollusks that dwelt here thousands of years ago or something more recent?

You haven’t found a fossil; you’ve found the shell of one of the numerous species of terrestrial snails roaming Montana. Some of the common names of species you might find in our part of Montana gives you an idea of how varied they are: ambersnail, glossy pillar, mellow column, forest disc, and quick gloss.

The live snails can be found under logs, leaf litter and duff. But keep your eyes out for the sun-bleached shells while you hike around Mountain Sky. Take pictures of the shells or bring them in to the ranch for display.

Here are descriptions of two species common to Paradise Valley.

Forest Disc (Discus whitneyi) Diagnostic Characteristics: A combination of shell shape (flattened heliciform or flattened conic), shell dimensions, number of whorls, shell color (olive-brown and chitinous), the presence of ribbing on the shell, lack of reflected lip, and absence of teeth in the aperture.   Habitat: Forested areas, from mesic (Engelmann spruce, Douglas-fir, secondary canopy including alder, mountain maple, dogwood, willow) to relatively dry (ponderosa pine and Rocky Mountain juniper, but usually in moister sites, such as imbedded pockets of aspen). Found under woody debris and rocks, in downed rotten wood, leaf litter and duff.

Subalpine Mountainsnail (Oreohelix subrudis) Diagnostic Characteristics: Medium to large size, calcareous whitish to gray (some may be brownish), moderately elevated spire (sometimes almost bee-hive shape), variable banding, relatively narrow umbilicus, absence of reflected lip, and surface sculpture help distinguish this from most other larger shells. Habitat: relatively moist sites, along stream courses and near seeps or springs, sometimes in talus slopes. Live animals present mostly in leaf litter, and under downed wood, rocks, and in duff or soil accumulations under wood and rocks.

Sources & Resources:

Montana Field Guide. http://fieldguide.mt.gov/displayFamily.aspx?order=Stylommatophora

Hendricks, P. 2012. A Guide to the Land Snails and Slugs of Montana. A report to the U.S. Forest Service - Region 1. Montana Natural Heritage Program, Helena, MT. vii + 187 pp. plus appendices.

Revisiting Brucellosis in the Greater Yellowstone

Recently a committee of the National Academy of Sciences issued its report, Revisiting Brucellosis in the Greater Yellowstone Area as an update to the 1998 report by the National Research Council. The report examined the changing dynamic of brucellosis in the Greater Yellowstone Area (GYA) and explored various options for addressing the challenge of brucellosis disease management.  

Figure 1. Elk and Bison graze Yellowstone National Park. Photo © by Timothy Pearce, Creative Commons

The Disease

Brucellosis is a contagious disease of ruminant animals that also affects humans. Although brucellosis can attack other animals, its main threat is to cattle, bison, cervids (elk and deer), and swine. The disease is also known as contagious abortion or Bang's disease. In humans, it's known as undulant fever because of the severe intermittent fever accompanying human infection or Malta fever because it was first recognized as a human disease on the island of Malta. As a result of efforts begun more than 80 years ago in the United States, however, the incidence of brucellosis in humans is now less than 0.5 cases/million population, as compared with over 6,000 cases annually in 1947. The disease was first noted in the GYA in 1917, and has been present since.

In cattle, the primary cause of brucellosis is Brucella abortus, a zoonotic bacterial pathogen that also affects wildlife, including bison and elk. Bovine brucellosis posed significant animal health and international trade consequences. In livestock it is known to cause decreased milk production, weight loss, loss of young, infertility and lameness. The generally accepted path of transmission is direct contact with infected animals or with an environment that has been contaminated with discharges from infected animals -- aborted fetuses, placental membranes or fluids, and other vaginal discharges present after an infected animal has aborted or calved (USDA).

Brucellosis in the GYA

The only remaining reservoir of B. abortus infection in the United States is in the GYA, where brucellosis is endemic in bison and elk, and where wildlife transmitted cases spill over into domestic cattle and domestic bison. This spill-over is now occurring with increasing frequency, raising the possibility of brucellosis reoccurrence outside the GYA.

From 1998-2016, 22 cattle herds and five privately-owned bison herds were affected in Idaho, Montana, and Wyoming. During the same period, all other states achieved and maintained brucellosis-free status. A 2010 interim rule enabled the three GYA states to create designated surveillance areas (DSAs) to monitor brucellosis in specific zones and to reduce the economic impact for producers in non-affected areas. However, brucellosis has expanded beyond the original DSAs, resulting in the outward adjustment of DSA boundaries. Most cattle in the GYA are vaccinated with B. abortus strain RB51 which reduces abortions but does not necessarily prevent infection. The increase in cattle infections in the GYA, coupled with the spread in wildlife is a cause of alarm for area producers; moreover, the risk of additional spread to other areas across the United States is increasing due to the lack of guidance and surveillance.

Report Findings

The report’s primary finding is the clear evidence that elk are a primary host for brucellosis and the major transmitter of B. abortus to cattle. All recent cases of brucellosis in GYA cattle are traceable from elk, not bison.[1] This conclusion, long-suspected by ranchers and others in the Paradise Valley, poses greater challenges for control of transmission from wildlife to domestic species.

Ecological changes with the GYA since 1998, including the reintroduction of the gray wolf and increases in grizzly bear numbers, have affected the density and distribution of elk. Elk populations have expanded on the periphery of the GYA but have decreased inside Yellowstone National Park.

The panel observed that reducing the population size of cattle, bison, or elk are all likely to reduce the risk of brucellosis transmission to cattle by reducing the area of potential contact or the number of infected individuals in those areas, even if the disease prevalence in the wildlife hosts remains constant. However, each species has a constituency that would likely oppose any population reduction.

The report’s conclusions:

1.       Brucellosis control efforts in the GYA need to sharply focus on approaches that reduce transmission from elk to cattle and domestic bison.

2.       No single management approach can independently result in reducing risk to a level that will prevent transmission of B. abortus among wildlife and domestic species.

3.       Reducing the elk population is an option for reducing the risk of transmission among elk, cattle, and bison. Unlike bison, transmission among elk appears to be influenced by density. Thus, reducing elk group sizes and/or density may decrease elk seroprevalence over time, and potentially decrease the risk of elk transmission.

4.       While the primary focus would be on elk, bison remain an important reservoir for brucellosis. For this reason, if reduction of brucellosis prevalence is a goal, removal of bison for population management purposes will need to target brucellosis infected individuals, whenever possible.

5.       The weight of evidence nonetheless suggests that reduced use or incremental closure of feedgrounds could benefit elk health in the long-term, and could reduce the overall prevalence of brucellosis in elk on a broad population basis.  This is not a stand-alone solution to control of brucellosis in the GYA, and will need to be coupled with other management actions to address the problem at a systems level.

6.       The lack of data-based guidance and uniformity in conducting wildlife surveillance outside the DSA, the absence of a GYA focused approach for national surveillance, and the infrequent oversight of state brucellosis management plans in the midst of expanding seroprevalence of elk has increased the risk for spread of brucellosis in cattle and domestic bison outside the DSA boundaries and beyond the GYA.

7.       The significant reduction in risk of transmission among vaccinated cattle provides sufficient reason to continue calf-hood and adult vaccination of high-risk cattle when coupled with other risk reduction approaches.

8.       A coupled systems/bioeconomic framework is vital for evaluating the socioeconomic costs and benefits of reducing brucellosis in the GYA, and would be needed to weigh the potential costs and benefits of particular management actions within an adaptive management setting. A bioeconomic framework is also needed to identify appropriate management actions to target spatial-temporal risks, including risks beyond the GYA.

9.       Managing an ecosystem as complex as the Greater Yellowstone Ecosystem will require coordination and cooperation from multiple stakeholders, and will require expertise across many disciplines to understand the intended and unintended costs and benefits of actions.

10.   A strategic plan is needed to coordinate future efforts, fill in critical knowledge and information gaps, and determine the most appropriate management actions under a decision-making frame-work that is flexible and accounts for risks and costs. 

11.   Coordinated efforts across federal, state, and tribal jurisdictions are needed, recognizing firstly that B. abortus in wildlife spreads without regard to political boundaries, and secondly that the current spread of brucellosis will have serious future implications if it moves outside of the GYA.

Report Recommendations

1.       Federal and state agencies should prioritize efforts on preventing B. abortus transmission by elk. Modelling should be sued to characterize and quantify the risk of disease transmission and spread from and among elk which requires an understanding of the spatial and temporal processes involved in the epidemiology of the disease and economic impacts across the GYA. Models should include modern, statistically rigorous estimates of uncertainty. 

2.       In making timely and data-based decisions for reducing the risk of B. abortus transmission from elk, federal and state agencies should use an active adaptive management approach that would include iterative hypothesis testing and mandated periodic scientific assessments. Management actions should include multiple, complementary strategies over a long period of time, and should set goals demonstrating incremental progress toward reducing the risk of transmission from and among elk. 

3.       Use of supplemental feedgrounds should be gradually reduced. A strategic, stepwise, and science-based approach should be undertaken by state and federal land managers to ensure that robust experimental and control data are generated to analyze and evaluate the impacts of feedground reductions and incremental closure on elk health and populations, risk of transmission to cattle, and brucellosis prevalence. 

4.       Agencies involved in implementing the Interagency Bison Management Plan should continue to maintain a separation of bison from cattle when bison are outside YNP boundaries.

5.       In response to an increased risk of brucellosis transmission and spread beyond the GYA, USDA-APHIS should take the following measures:

a.       Work with appropriate wildlife agencies to establish an elk wildlife surveillance program that uses a modeling framework to optimize sampling effort and incorporates multiple sources of uncertainty in observation and biological processes. 

b.       Establish uniform, risk-based standards for expanding the DSA boundaries in response to finding seropositive wildlife. The use of multiple concentric DSA zones with, for example, different surveillance, herd management, biosecurity, testing, and/or movement requirements should be considered based on differing levels of risk, similar to current disease outbreak response approaches. 

c.        Revise the national brucellosis surveillance plan to include and focus on slaughter and market surveillance streams for cattle in and around the GYA. 

6.       All federal, state, and tribal agencies with jurisdiction in wildlife management and in cattle and domestic bison disease control should work in a coordinated, transparent manner to address brucellosis in multiple areas and across multiple jurisdictions. Effectiveness is dependent on political will, a respected leader who can guide the process with goals, timelines, measured outcomes, and a sufficient budget for quantifiable success. Therefore, participation of leadership at the highest federal (Secretary) and state (Governor) levels for initiating and coordinating agency and stakeholder discussions and actions, and in sharing information is critical. 

7.       The research community should address the knowledge and data gaps that impede progress in managing or reducing risk of B. abortus transmission to cattle and domes-tic bison from wildlife. 

a.       Top priority should be placed on research to better understand brucellosis disease ecology and epidemiology in elk and bison, as such information would be vital in informing management decisions. 

b.       To inform elk management decisions, high priority should be given to studies that would provide a better understanding of economic risks and benefits.

c.        Studies and assessments should be conducted to better understand the drivers of land use change and their effects on B. abortus transmission risk. 

d.       Priority should be given to developing assays for more accurate detection of B. abortus infected elk, optimally in a format capable of being performed “pen-side” to provide reliable rapid results in the field.

e.       Research should be conducted to better understand the infection biology of B. abortus.

f.         To aid in the development of an efficacious vaccine for elk, studies should be conducted to understand elk functional genomics regulating immunity to B. abortus.

g.       The research community should (1) develop an improved brucellosis vaccine for cattle and bison to protect against infection as well as abortion, and (2) develop a vaccine and vaccine delivery system for elk.

References

National Academies of Sciences, Engineering, and Medicine. 2017. Revisiting  Brucellosis in the Greater Yellowstone Area. Washington, DC: The National Academies Press. doi: https://doi.org/10.17226/24750.

USDA APHIS. Facts about Brucellosis. https://www.aphis.usda.gov/animal_health/animal.../brucellosis/.../bruc-facts.pdf

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[1] There have been no cases of transmission from GYA bison to cattle in the 27 herds infected with brucellosis since 1998.

Impacts of Juniper Encroachment

Rocky Mountain Juniper commonly grow to be more than 250 years old, and specimens over 1,000 years old have been found. The species’ resinous branches and thin bark make them susceptible to wildfire which historically relegated them to rocky, marginal soils. Decades of fire suppression, however, has enabled Rocky Mountain junipers to spread into grasslands and sagebrush-steppe habitats. Townsend’s Solitaire, waxwings, and other bird species consume the fruit (seed cones) as do mammals such as bighorn sheep. The passing of berries through the animals’ digestive tracts dissolves the fleshy coating and enables germination of the seeds. Juniper has long been prized for use as fenceposts for their durability, though the practice is less common today except where posts are hand-dug. The aromatic wood is also used for wood clips and hand-made furniture. Best known for flavoring gin, the berries also have a long history of traditional medicinal uses.  

Juniper encroachment into otherwise treeless shrub lands and grasslands is one of the most pronounced environmental changes observed in rangelands of western North America in recent decades. This encroachment affects forage production for livestock and wildlife, soils, plant community composition, and water, nutrient and fire cycles.Juniper encroachment into otherwise treeless shrub lands and grasslands is one of the most pronounced environmental changes observed in rangelands of western North America in recent decades. This encroachment affects forage production for livestock and wildlife, soils, plant community composition, and water, nutrient and fire cycles.

Historical Perspective

The shrub-steppe and grasslands of southwest Montana evolved to withstand periodic fire. Before European settlement, species of juniper (predominantly the Rocky Mountain Juniper, Juniperus scopulorum) were found in isolated pockets where fire impacts were minimized. A rangeland ecologist looking for old juniper trees would go to sites with shallow soils and limited understory capable of carrying fire. In the 1880s, the introduction of cattle and consequent heavy grazing led to a decrease in the number of wildfires annually. Cattle cropped most of the grasses that normally became fuel for wildfires. With reduced fire, juniper woodlands began expanding into areas once dominated by sagebrush and aspen. The fire suppression policies of the 20th century also aided the spread of juniper. Today a drier, hotter climate combined with limited opportunities to use prescribed fire, or even allow wildfires to run their course, have further accelerated the expansion of juniper woodlands.

Generalized Effects of Juniper Encroachment

·         High percentage of rain and snow intercepted in the juniper canopy (in Oregon, found to be equivalent to the percentage of juniper canopy cover; e.g., a juniper canopy of 20 percent equates to an interception of about 20 percent of the precipitation the site receives).

·         Precipitation through-fall (water reaching the soil surface through the tree canopy) generally occurs only after rain events of 0.30 inches or more.

·         Increasing juniper dominance is collated to a reduction or die-off of aspen (Populus tremuloides), shrubs, native grasses, and forbs (non-woody broad-leaf plants); a subsequent loss of forage for livestock; and a loss of habitat value (cover, forage) for many wildlife species.

·         As a conifer, juniper is capable of drawing water from the soil year-round with impacts on native shrubs, perennial grasses, and forbs that depend on soil water stored during the dormant period (fall, winter, and early spring) for initiation of growth in the spring.

·         Canopy interception, diminished infiltration rates, overland flow, and increased juniper transpiration (the consumption of stored soil water) can result in a significant reduction of flows from seeps, springs, and streams.

Figure 2. Example of juniper encroachment on pasture

A Fierce Competitor

Juniper is a drought-tolerant evergreen with extensive lateral and deep roots, and the ability to extract water from very dry soil, in part due to a dense mat of fibrous roots at the soil surface. Its deep root system also gives the plant access to water that herbaceous species cannot effectively tap. These adaptations make juniper a successful competitor for water against grass and forbs, both underneath the canopy and in-between trees. Numerous studies have documented the impacts of juniper-induced reduction in light, soil moisture, and soil nutrients resulting in significant reductions in grass production due to increased juniper density. 

As juniper roots expand into the interspaces between trees they compete for water and nutrients with grasses and forbs. This competition, especially when combined with grazing pressure, results in grasses that are sparse, lack vigor and difficult to reestablish in the continued presence of juniper. Another competitive advantage of juniper is that it is not as quickly affected by drought as herbaceous species because the trees have a deep root system which gives them access to a water source that the herbaceous species cannot effectively tap.

Impacts to Rangeland

As juniper come to dominate a site and form dense stands, they commonly outcompete understory plants for nutrients, water, and sunlight forming areas of bare soil between trees and exacerbating soil erosion.  

Increased dominance of juniper in what had previously been grasslands alters the water cycle on rangelands. This has very important ramifications because water is a direct or indirect limiting factor to all aspects of production on semi-arid regions. The impact of juniper encroachment on recharge of streams and aquifers is also a very important consideration.

An increase of juniper cover on rangeland can reduce the amount of precipitation that reaches the soil surface. The extent to which the type of canopy cover influences the amount of precipitation that reaches mineral soil varies from species to species. Interception rates for RM Juniper were not found, but other species commonly capture 25-38% of gross precipitation. In the case of small rainfall events (<5mm), water may not even reach the litter layer because of water retention by the foliage. In a dry environment, much of the canopy-stored water is subject to evaporation.

Figure 3. Junipers commonly arise from multiple stems making mechanical removal a challenge

Water that passes through the canopy (through-fall) must also pass through the litter layer prior to entering the soil. The deposition of leaves, twigs, and branches, coupled with the absence of fire and the resistant nature of the litter to decomposition results in a large accumulation of litter under juniper trees. This litter has a high capacity to retain water falling through the tree canopy. The amount of interception loss associated with the litter layer varies considerably among juniper species (2-40%).

As a result of interception loss via the canopy and litter, a significantly reduced amount of water (20-60%) from annual rainfall reaches mineral soil under juniper. This is a stark contrast to the 80-90% of annual precipitation that reaches the soil under bunchgrass cover.

Research also suggests that the water channeled to the base of juniper via stem-flow (water that runs down the tree stems/truck) may competitively favor the growth and further establishment of juniper species, especially in semi-arid areas.

A Water Hog

Evapotranspiration in semi-arid environments accounts for 80% or more of water loss. While the micro-climate under the canopy of trees and shrubs tends to reduce evaporation from the soil surface (due to shading and protection from wind, etc.), the interspaces between juniper, where severe competition between juniper and herbaceous plants results in barer, more exposed, ground, evaporation from the soil will be greater as compared to areas where good herbaceous cover exists. Additionally, juniper vegetation and litter provides much more surface area for water to adhere on than grass, therefore a much greater percentage of precipitation will be lost to evaporation in a juniper woodland than in a grassland. 

The extensive root system of juniper allows it to access a greater volume of soil water than grasses and forbs. As an evergreen, it also has the capability to transpire water year-round. And it can continue to remove water from the soil long after grasses have gone into a drought or temperature-induced dormancy.

Litter Zone and Water Infiltration

On one hand, the litter layer markedly reduces the amount of water reaching mineral soil. On the other, it contributes to improved soil structure due to the large amounts of organic matter and cover which increases the infiltration rate capacity of the soil. The thick litter layer often associated with juniper also minimizes evaporation loss from soil below the canopy and can help obstruct runoff originating in the interspace areas. As the juniper can harvest this water, the tree gains a further competitive advantage. This also explains why runoff yield from a pasture may not change as juniper density increases. 

When juniper is cut and removed, the soil structure, and the associated high infiltration rate, may be maintained for subsequent years. The area near the dripline commonly exhibits substantially greater forage production for many years after the tree has been cut. It also explains why runoff will not necessarily dramatically increase once juniper is removed. Rather, the water continues to infiltrate at high rates into soils previously ameliorated by junipers, thereby increasing deep drainage potential.

Impact to Water Cycle

As mentioned, Juniper has the potential to impact the water cycle in a number of ways: specifically 1) a large portion of precipitation never reaches the soil due to interception loss, and 2) juniper extracts much of the water that does enter the soil to meet its needs.

The combination of less water entering the soil and strong ability by the juniper to extract water from dry soils translates into significantly less water seeping beneath the root zone. Therefore, invasion of juniper on large areas that were once primarily grassland has strong implications for recharge of aquifers. In the Edwards Plateau of Texas, seeps and springs have been documented to stop flowing in conjunction with increases in juniper cover.

Erosion Potential

Semi-arid rangelands have erosion rates which depend on the interactions of vegetation, soil, and weather events. Because juniper canopies are dense, they protect the soil directly beneath from raindrop impact and prevent detachment of soil particles. The heavy litter layer underneath juniper also impedes overland flow, thus reducing the transport capacity for sediment. But because juniper is highly competitive with interspace grasses, an increase in juniper cover often leads to increased exposure of bare soil. Any time bare soil is exposed, the potential for erosion is increased.

Anticipated Benefits of Treatment

Reducing the density and distribution of juniper on rangelands has the potential to:

·         Reduce the interception of precipitation, resulting in more water delivered to the ground surface.

·         Increase available forage for livestock grazing, and encourage reestablishment of grasses, forbs, and shrubs where juniper competition for space, sunlight, soil water, and soil nutrients has diminished plant community diversity, density, and productivity.

·         Encourage significant increases of herbaceous, deciduous, and semi-deciduous plant cover, reducing the amount of bare soil, increasing surface litter and soil organic matter, improving infiltration of rainfall and snowmelt, reducing overland flow and soil erosion, and increasing soil water retention.

·         Reduce dormant and early-growing-season transpiration and increase amount of soil water available to shrub and/or herbaceous plants for initiation of growth in the spring.

Considerations

·         Juniper management is not juniper eradication. Managers should look to retain old-growth juniper trees and thickets in draws and other areas where they provide shelter and food for wildlife.

·         Noxious weeds present on-site before treatment will take advantage of the newly available water, nutrients, space, and sunlight.

·         Experts warn against attempting to predict changes in surface water yield (seep, spring, and stream flow) that may result as a result of the treatment. Soil conditions and surface and bedrock geology are too variable to permit reliable forecasts. The project should be able to stand alone on the sustainable recovery and/or maintenance of basic ecological functions and processes and their associated environmental and economic benefits.

Resources

Barrett, H. 2007. Western Juniper Management, A Field Guide. Oregon Watershed Enhancement Board.

Miller RF, Bates JD, Svejcar TJ, Pierson FB, Eddleman LE. 2005. Biology, Ecology and Management of Western Juniper. Technical Bulletin 152. OSU, Agricultural Experiment Station. Corvallis, OR.

Thurow, T.L. and J.W. Hester. How an increase or reduction in juniper cover alters rangeland hydrology. Texas A&M (texnat.tamu.edu).

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This brief compiled by Whitney Tilt, Director, Land and Wildlife Conservation, for The Arthur M. Blank Family Foundation. Comments, edits, and corrections welcomed, wtilt@ambfo.com.

Figure 4 & 5. Before/After Treatment of large, multi-stemmed RM juniper. Difficult and time consuming to access stems, many of which are actually in/below the soil. Photo: MSGR Pasture 17-2, November 2016