Roosevelt’s Elk: Research
ELK HABITAT SELECTION IN WESTERN
OREGON AND WASHINGTON:
Models for a new century
By Mary M. Rowland
Wildlife Biologist
USDA Forest Service, PNW Research Station
La Grande, Oregon
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Elk are big business in western North America, with millions of dollars spent annually on viewing and hunting
these magnificent animals. But management of Roosevelt and Rocky Mountain elk in the Pacific Northwest, including direction in federal land management planning documents, has relied for many years on outdated guidelines for
elk habitat. Three key reasons justify the need for new information to support updated guidelines:
l Elk are highly sought by the public for hunting and viewing – they are a prime recreational resource.
l The economic effects of managing for elk are substantial, whether through direct habitat improvements or other costs like
those associated with damage hunts for problem herds.
l Habitat management for elk is likely to benefit many other native species that depend on early-seral (e.g., grass and shrub)
habitats or that are sensitive to human disturbance.
First-generation models of elk habitat in the Northwest
focused heavily on minimizing effects of human disturbance (like
traffic on roads) on elk, but failed to address the limiting effects of
specific habitat elements. Declines in elk populations in the 1990s
led researchers to pay more attention to these elements, especially
summer nutrition, which was previously not considered a problem
for elk populations. The last two decades have seen a surge in new
research addressing these factors, including elk nutrition. These
new studies also reaffirmed the impacts of human disturbance on
elk. It was time to put these results to use in new evaluation tools
for elk habitat.
Enter Mike Wisdom, a research wildlife biologist with the
Pacific Northwest (PNW) Research Station of the Forest Service.
Wisdom mobilized a team of scientists from state, federal, private,
and tribal entities in 2009 to develop and apply new elk nutrition
and habitat models for management use in western Oregon and
western Washington (“Westside” region - MAP). The project is
nearing completion and has incorporated modern modeling techniques to provide a strong foundation for guiding future management direction and habitat restoration for elk.
The new models focus on summer range, which is a critical
time for elk productivity. The team developed two new models –
the first was the elk nutrition model, which then became part of
a more comprehensive elk habitat model. The nutrition model
predicts dietary digestible energy (DDE) that elk can acquire from
each plant community during summer. The predictions from the
model are based on diet data collected during years of grazing
trials with tame elk across the Westside region, led by ungulate
ecologists John and Rachel Cook of the National Council for Air
and Stream Improvement. Digestible energy levels in elk diets in
summer are affected by the nutritional adequacy of the various
vegetation communities used by elk while foraging. Importantly,
the DDE levels are related to reproduction and survival of elk in
summer and subsequent seasons. This new nutrition model has
been applied across the entire Westside region for all land ownerships, based on current conditions, to produce a wall-to-wall map
of DDE – the first of its kind.
The next step was to integrate the summer nutrition model
with several other variables in a “resource selection” modeling process to predict elk habitat use at regional levels. A resource selection
model—a special kind of habitat model—estimates the probability
of an animal using a particular part of a pre-defined landscape,
based on the environmental conditions that most affect or account
for landscape use. The model selection process was guided by the
expert skills of Ryan Nielson, a biometrician with WEST, Inc., in a
complex, iterative process. The team initially considered over 50
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environmental variables related to nutritional, human disturbance,
and biophysical conditions, such as distance to nearest water or
open roads, slope, and aspect. The scientists then considered subsets of these variables in different combinations to identify which of
the many models tested were best supported by patterns of observed
elk use, based on radio telemetry locations of elk.
To obtain the telemetry data, the team scoured wildlife agencies and Tribal Nations in both Oregon and Washington for such
information. The search yielded a variety of data sets, with all but
one from Tribal sources. One of the project’s objectives was to
build an elk habitat model without spending thousands of dollars
putting new radio-collars on elk throughout the Westside, but
instead relying on existing radio telemetry data. In the end, usable
radio telemetry locations were found in eight areas ranging from
the Coquille River in southwestern Oregon to the Nooksack area in
north-central Washington.
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Models for a new century
By analyzing the fit between model predictions and elk locations, the scientists were able to determine the top-performing habitat models. These analyses demonstrated that a combination of four
variables was consistently and strongly associated with elk locations:
l elk dietary digestible energy (higher DDE, higher pre-
dicted elk use)
l distance to roads open to public access (farther from
roads, higher use)
l percent slope (flatter slopes, higher use); and
l distance to cover-forage edge (closer to edge, higher use).
This 4-variable model was head and shoulders above any other
combination tested, which was a surprising but welcome result.
But answering the next question was even more important – how
good a job does this model do in predicting where elk will be in
other areas? The modeling team used locations of elk from three of
the study areas to build the model, but the true test was application
of the model in new areas to evaluate its predictive capability.
The remaining five radio telemetry data sets were used for
model evaluation. These telemetry data sets were independent of
the ones used in the model selection process, an important distinction in a sound scientific process. The 4-variable model performed
remarkably well during these tests - the correlation coefficients
between predicted use from the model and observed use from elk
locations in the five areas ranged from about 0.30 to 0.95 - with
most values greater than 0.80. Given that the highest possible correlation is 1.0, the results showed the strength of this model across
a variety of diverse landscapes in western Oregon and Washington.
“Our results were extremely encouraging, with close matches seen
between predicted elk use from the model and locations of elk in
the study areas,” said Wisdom. “This information can help set goals
for changing elk use in certain areas and guiding management
prescriptions for elk habitat.”
The model performed most poorly at the very southern
reaches of the Westside study area. The modeling team was
not surprised – in this corner of Oregon, square in the range of
Roosevelt elk, the climate is warmer and the vegetation becomes
much more diverse and unlike that of the forests farther north. To
address questions raised about the suitability of the Westside model
for southwest Oregon and northern California, the Cooks hauled
the tame elk around this area for most of the summer of 2011, re-
cording what elk ate in different habitats and measuring vegetation
in hundreds of plots. These data are now being analyzed to develop
a new “variant” of the nutrition model, which will be plugged into
the elk habitat model to predict elk use in this area.
A key objective of the modeling project sponsors was the
creation of management-based tools – not obscure research to be
published in scientific journals with little relevance to management. In partnership with land managers and biologists of the Forest Service, Bureau of Land Management, Washington Department
of Fish and Wildlife, and Tribal Nations in the Pacific Northwest,
the new models were tested with data from a suite of “real life”
management scenarios, such as timber thinning projects. This allowed the modeling team to gain users’ perspectives and to obtain
constructive feedback about the models and how well they worked
for end users. Months of web meetings and conference calls yielded
extensive comments and gave the modelers a better understanding
of how the models could be applied at a ranger district or regional
office level. The modeling results were also shared at two workshops open to the public, held in 2010 and 2011. The modeling
team will continue to work with management partners to assist in
applying the models on local units and to develop guidelines for
best management uses.
To recap – what was learned about Roosevelt’s
elk populations and habitat?
l Elk needs are best met through active management, particu-
larly silviculture and fire. Elk benefit substantially from a
variety of management practices that reduce overstory cover,
but use of the resulting forage depends on managing human
disturbance, for example through seasonal road closures.
l In general, within our Westside modeling region, the lower
the canopy closure and the higher the elevation, the greater
the abundance of high quality forage species and dietary
digestible energy (DDE). Digestible protein also tends to
follow this pattern.
l Nutritional resources for elk are relatively poor in the Coast
Range and many areas in the Cascades. Even with clearcuts,
forage quality is often below maintenance level during summer for lactating elk in these areas.
l During summer in western Oregon and Washington, elk select gentle slopes close to cover-forage edges, but away from
open roads; consideration of these preferences in planning
management activities on public and private lands that sup-
port elk is necessary to maximize benefits to elk.
l The importance of summer range conditions cannot be
underestimated. Forage available to elk during summer
directly affects growth of young elk, pregnancy rates of cow
elk, and body fat levels of elk entering winter. Consequently,
evaluation and management of summer range conditions is
essential to year-round management of healthy elk herds.
Now that we have these models, what can they
do to help elk management?
l The new habitat model predicts the probability of elk use
across landscapes. The model can be used as the basis for
setting goals for changing elk use in certain areas, and to assess how to get more “bang for your buck” with management
prescriptions. It can also show the consequences of NOT
improving habitat.
l Users can compare different management scenarios: for example, using modeling tools that simulate vegetation change,
one could “remove” canopy cover in units across a management landscape and then estimate DDE at specific time intervals to make predictions of elk use. If management speeds up
or retards vegetation succession, the model will reflect that.
l The models are suitable for application across large regional
landscapes that cross multiple ownerships and include multiple elk populations. This big-picture approach is designed to
help landowners work strategically to integrate management
objectives and habitat treatments for elk across ownerships.
Management of public lands involves a complex balance
between sometimes competing demands. Regardless of the management objectives on a given piece of forest, these new models
provide key insights about impacts of different land uses on elk
populations and their habitats, and help practitioners weigh possible alternatives. As one workshop participant said, “Having these
nutrition maps could really help us from an administrative standpoint because they justify creating openings.”
A comprehensive monograph is now being prepared for publication that will ultimately provide the scientific foundation for
long-term, credible management use of these new evaluation tools.
For those who want more information, a project website has been
developed with summary reports and presentations from the two
workshops that have been held to demonstrate the modeling results: http://www.fs.fed.us/pnw/calendar/workshop/elk/index.shtml.
Acknowledgments
The success of the Westside elk habitat modeling project resulted from a
diverse array of partners. Key sponsors of the research included the National
Fish and Wildlife Foundation, Boone and Crockett Club, Rocky Mountain Elk
Foundation, Sporting Conservation Council, the US Forest Service (Pacific
Northwest Research Station and Pacific Northwest Region), and Bureau
of Land Management. Many other entities contributed data or personnel,
including Oregon Department of Fish and Wildlife, Washington Department
of Fish and Wildlife, the National Council for Air and Stream Improvement,
WEST, Inc., Oregon State University, and Oregon State University Extension
Service. The project would not have been possible without the help of Tribal
nations that provided all of the elk radio telemetry data, with the exception of
data from Oregon State University from southern Oregon. Participating Tribes
included the Lower Elwha Klallam Tribe, Makah Nation, Muckleshoot Indian
Tribe, Quileute Indian Tribe, and Sauk-Suiattle Indian Tribe.