Workshop on Dynamics and Management of
Juniper Woodlands in the Bighorn Basin
8-9 June 2000
Sponsored by:
The Nature Conservancy
University of Wyoming, Department of Botany
National Science Foundation (Ecology Program)
United States Geological Survey Desert Laboratory
Organizers:
Stephen T. Jackson (UW)
Phil Shephard (TNC)
Julio L. Betnacourt (USGS)
Executive Summary
The expansion of Utah juniper woodlands into rangelands in Wyoming and
adjacent states during the past century is well-documented but poorly
understood. Woodland expansion presents a management challenge for
ranchers and public-land managers committed to maintaining
sage-grasslands and mosaic patterns of vegetation on the Wyoming
landscape. This workshop brought together academic researchers,
resource managers, and ranchers to share information and discuss
management issues.
Four researchers from the University of Wyoming (S.T. Jackson, S.T. Gray,
M.E. Lyford) and the U.S. Geological Survey (J.L. Betancourt)
presented results of an ongoing study of Utah juniper invasion and
dynamics in Wyoming. Key conclusions include:
Utah juniper is a relatively recent constituent of the Bighorn Basin flora
and vegetation. Studies of fossil packrat middens indicate that
populations were established in southern Bighorn Canyon as early as
4700 years ago. However, colonization of foothills sites in the
Bighorn, Pryor, and Bridger Ranges did not occur until 2500-2000
years ago, initiated by a regional change in climate. Similar trends
are noted for other key species in these foothills sites, including
ponderosa pine and curl-leaf mountain mahogany.
Utah juniper has probably not yet colonized all suitable sites and areas
in the region. It appears to be expanding northward from the Dry
Medicine Lodge and Alkali Creek drainages into the Webber Creek and
Trapper Creek drainages. Scattered young individuals in upper Webber
Canyon represent colonization within the last half-century.
The spread of Utah juniper in the Bighorn Basin has consisted of
scattered, individual colonizing events from long-distance seed
dispersal. These colonizations are followed by local infilling and
backfilling. Utah juniper invasion, like most other plant invasions,
occurs as a "spotting" process rather than an advancing
front.
Demographic studies indicate that Utah juniper seedling establishment in the
Bighorn Basin occurs frequently, often under sagebrush and other
"safe-site" shrubs. Once established, Utah juniper
individuals grow slowly; 70 to 90 years may be required for
individuals to reach heights exceeding 4 feet.
Repeat photography (1900-1930 and 1998-1999) indicates substantial local
expansion of Utah juniper populations on shallow rocky and deep
colluvial soils. Field inspection of these photo sites indicates
that much of this expansion may be attributable to recovery from
late 19th Century fires (possibly during the droughts of the 1870s
and 1890s). Fires may have been an important component of
pre-grazing Utah juniper stand dynamics. Utah juniper populations
on steep slopes of the Chugwater Formation have been relatively
stable during the past century, perhaps owing to absence of late
19th Century fires.
Tree-ring climate reconstructions spanning the last 800 years at upper (Powder
River Pass) and lower treeline (Trapper Creek, Big Pryor Mountain,
Tensleep Preserve) indicate that the 20th Century is unique in being
warmer than any of the previous seven centuries, and in being
characterized by warm and relatively wet conditions. Earlier warm
periods were typically accompanied by droughts, and wet periods
tended to be relatively cool. The 1990s were the warmest decade in
the last 800 years. Continued warming will exacerbate the effects of
future droughts on Wyoming ecosystems.
Long-term climate records from tree-rings in the eastern Bighorn Basin region
show unusual persistence of wet or dry, cool or warm conditions over
several years to several decades. For example, wet years tend to be
followed by wet years, dry years by dry years, warm years by warm
years. This natural persistence in Wyoming climate affects land use
and management windows. For a cattle rancher, this means that cow
and calf operations may be subject to prolonged episodes of boom and
bust. For prescribed burning, this means that opportunities lost
during a climatically favorable period may be lost for a decade or
more.
The expansion of Utah juniper populations in the Bighorn Basin is a
complex phenomenon in which long-term population dynamics (i.e.,
migration, post-colonization infilling), climatic change, and
land-use practices are all involved. More information on land-use
history, fire history, and juniper population dynamics and climate
response are desirable for informed and effective management.
In some areas, Utah juniper expansion may be an inevitable outcome of
natural processes, and hence very expensive and difficult to
"control".
The ability of junipers to concentrate nutrients in soils beneath shrub
canopy, resulting in spatial patchiness of soil-nutrient pools, is
documented in the Southwest. If this happens in Wyoming, it may
render conversion of old, established juniper stands to
sage-grassland difficult to impossible. Management efforts may best
be focused on recently invaded sites, where soil nutrients are more
spatially homogeneous. Research is needed to determine the
magnitude and rate of nutrient concentration under Utah juniper
canopy in the Bighorn Basin.
Three managers from The Nature Conservancy (P. Shephard), Bureau of Land
Management (K. Stinson), and Bighorn Canyon National Recreation Area
(S. Morstad) presented summaries of management goals and experience
at their respective situations. Key points included:
Resource managers are committed to reducing encroachment of Utah juniper and
Rocky Mountain juniper into mixed-grass grasslands, sage steppe,
pine woodlands, and cushion-plant communities. Goals vary among
agencies and landowners, ranging from maintaining biodiversity and
endangered species to maximizing forage for livestock and wildlife.
Prescribed fire is the most commonly applied management tool. Mechanical
removal of trees is often applied to manipulate fuel loads and fire
behavior.
Prescribed burns are often hampered by spotting and by lack of sufficient fine
fuels to carry a fire through the woodland understory.
Burning is most successful during drought periods and in old stands where
dead juniper fuel has accumulated.
Following a field trip to examine historical photo sites and a recently burned
Utah juniper stand, workshop participants engaged in a discussion
(D.H. Knight, UW, served as moderator). Key points emerging from
that discussion included:
Landowners and land managers must decide on the desired management outcome.
Managers must determine what they want the landscape to look like
based on their overarching objectives. Managing to "restore"
landscapes to mimic 19th Century configurations may be futile in the
face of a changing climate and dynamic ecosystems.
Careful attention must be paid to identify the key rare species and
biodiversity centers in the foothills regions, and to ensure that
management practices are compatible with maintaining those
populations and habitats.
Managers should keep track of multi-year climate cycles (e.g., El
Niño-Southern Oscillation (ENSO)) and use them in their
management plans. ENSO events can now be predicted 6-8 months in
advance, and this information can be valuable in planning prescribed
burns or anticipating severe fire seasons. Scientists also share
responsibility for keeping managers informed about these cycles and
their implications.
"One size fits all" approaches to management will inevitably result
in serious failures. Factors controlling the dynamics of Utah
juniper woodlands or Ponderosa pine ecosystems are likely to vary
significantly across the western U.S., and even within the Bighorn
Basin.
Management decisions should take into consideration the history and attributes
of individual stands. There is not likely to be a single,
universally applicable strategy for maintaining diversity or
maximizing forage. Each stand is a realization of both natural
processes and human activities. Juniper control can be successful
in some situations, and it may be justifiable based on management
objectives.
Modeling juniper distributions in relation to environmental variables will be
invaluable in identifying areas where invasion might occur in the
near future.
Historical studies of ecosystems and land use are necessary to understand and
manage landscapes realistically and economically. Tree-ring and
fire-scar studies of Ponderosa pine stands adjacent to old Utah
juniper stands would be especially useful in assessing pre-grazing
fire frequencies in Utah juniper woodlands. The USDA/DOI Fire
Sciences Program
(
http://jfsp.nifc.gov/)
may be a
source of funding for studies of fire history and the feasibility
and effects of fuels reduction in Utah juniper woodlands.
Additional studies of juniper demography, including recruitment and mortality,
would be valuable. Local managers can aid researchers by
identifying recruitment and mortality episodes in juniper stands.
Workshop participants agreed that the workshop and discussions provided an
excellent opportunity to share information and develop ideas for
effective and informed management. Public outreach is critical.
Participants identified lack of communication among researchers,
managers, and landowners as a key concern. Follow-up activities
should include:
Organization of a field trip in summer 2001 for a larger group (including
scientists, managers, and ranchers) that will provide an update on
research results as well as discuss management implications.
Creation of a web page for resource managers, ranchers, and scientists to
share data, insights, and information on Utah juniper woodland
ecology and management.
List of Workshop Participants
Jerry Altermatt
Wyoming Game and Fish
P.O. Box 28
Basin, WY 82410
Julio Betancourt
U.S. Geological Survey
Tucson, AZ 85745 jlbetanc@usgs.gov
