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| Education | Research | Volunteer
Information | Outreach |
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The Walnut Creek Center for Education and Research provides access to
many, as yet under-utilized, research resources in the Central Arizona
Highlands. The Center’s  leasehold is ideal for intensive research
that needs protection from vandalism, frequent maintenance, water, or
energy. This level of protection is a rarity for field research conducted
in northern Arizona. In the surrounding region, the wide variation in
habitats, the existence of relatively unaltered and protected public lands
and the willingness of the Prescott National Forest to allow manipulative
treatments present tremendous potential for biological research. Ultimately,
we hope that research conducted at WCCER will help land managers in the
region prioritize restoration activities and to develop specific restoration
plans. This is a topic of great interest across multiple ecosystems in
the area. Several specific restoration issues include 1) how best to return
ponderosa pine forests to structures seen before fire suppression/grazing,
2) understanding the implications of pinyon-juniper woodland encroachment
on grasslands, and 3) the need to balance riparian protection and restoration
with ongoing economic uses of the land such as grazing.
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Recent Research at Walnut Creek
Abbott's Riparian Area Survey
Walnut Creek Biological Inventory Final Report
Fire Behavior in Semi-Arid Southwest Ecosystems
Ecological Responses to Climate Change
Abbott's Riparian Area Survey
Abbott (2000) preformed research on the riparian area at Walnut Creek (see riparian area map below) to gain a baseline understanding of the vegetation occurring in this area. During this study 10 transects were established, surveyed and permanently marked for future re-surveying (see Abbott 2000 for transect design and location). Their study measured understory plant vegetation cover as well as foliar high density along these riparian transects. In 2008, 8 transects were re-surveyed and 2 new transects were established in the meadows adjacent to the riparian areas. See examples of data collected and maps below.
Riparian Area Map (click on thumbnail for larger view)
Transects Map (click on thumbnail for larger view)
  
Walnut Creek Biological Inventory Final Report
Download ESRI shapefile of the foliar height density transect locations
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Land Use and Habitat Change
Vegetation change in response to variations in human land use is
a major theme for the WCCER research community and a number of
characteristics of the Walnut Creek region suggest that it could
yield significant insights in this line of research. There are
long-term plots in the Prescott National Forest on which forest
structure and understory vegetation have been monitored. Researchers
from the School of Forestry and the Ecological Restoration Institute
at NAU are working with Prescott National Forest to relocate and
resample these plots. The Prescott National Forest has detailed
vegetation maps of the area from a survey done in 1912. We plan
to follow the model of researchers at NAU who have digitized similar
data for the Coconino National Forest and compared the vegetation
to current data. This will then provide a valuable resource for
many researchers and classes.
Resources for examining pre-historical vegetation change are
rich in the region. There are archaeological resources, which
will aid in the understanding of pre-historical human impacts
and there are records of pre-historical vegetation preserved
in packrat middens and peat deposits. Tree rings and fire scars
also represent an important source of information about processes
controlling vegetation in the area. Initial surveys indicate
longer fire return times than found in other areas of the Prescott
National Forest.
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Restoring Endangered Riparian Ecosystems
The Center’s namesake, Walnut Creek, is itself an important
resource. Walnut Creek and its tributary, Apache Creek, are rare
perennial creeks in this semi-arid region. They are home to lowland
leopard frogs (Rana yavapiensis), canyon tree frogs (Hyla arenicolor),
and speckled dace (Rhinichthys osculus) and native riparian trees
such as willows, cottonwoods, and walnuts occur along the creek and
in its floodplain. This riparian forest habitat is endangered in
Arizona (Noss et al. 2000). The section of the creek that runs through
the Center’s leasehold have been fenced to exclude cattle and
horses since 1999. A detailed biological inventory documented the
condition of the creek and riparian area before the fencing so that
its effects can be studied (Abbott and Glomski, 2000). This lack
of grazing makes this section of Walnut Creek an even more important
resource. WCCER hopes to be a model site for riparian restoration
in the area.
In addition to research on the restoration of this riparian zone,
some unusual species occur there that warrant further study. For
example, asexually reproducing stands of the hybrid species Hinckley’s
cottonwood (Populus x hinckleyana) are thriving near the active
channel of Walnut Creek, where it appears that exposure to air
has stimulated root sprouting. Research has shown that hybrid cottonwoods
may be important for maintaining biodiversity of dependant species
(McIntyre and Whitham, 2003). The variety of habitats present in
and around the riparian corridor supports an impressive diversity
of species. The biological inventory of the field station described
279 species of vascular plants, 17 species of reptiles, 4 species
of amphibians, 131 species of birds and 37 species of mammals (of
which 9 were bats). It also described some unusual vegetation associations,
including a terrace ecotone where flood dependent trees such as
Arizona walnut (Juglans major) and Fremont cottonwood (Populus
fremontii) are found alongside typically upland species such as
Utah juniper (Juniperus osteosperma). This association may be due
to the evolving morphology of the stream channel and consequent
reduction of flood frequency at the terrace level (Abbott and Glomski,
2000).
As an important watering hole for many species Walnut Creek has
been the focus of several surveys of vertebrates and their movements
across the landscape between the creek and upland habitats. However,
much of the population-level research at Walnut Creek has focused
on species interactions between plant and insects or between small
mammals, their food sources, and disease causing organisms. Notable
among these projects are the ongoing studies of rodents that carry
hantavirus. The high degree of variability in precipitation from
year to year make the area valuable for studies seeking to understand
the connections between precipitation, plant growth and insect
and disease outbreaks. The infrastructure at Walnut Creek also
offers the opportunity to back up such correlation field studies
with manipulative experiments.
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Fire Behavior in Semi-Arid Southwest Ecosystems
Before widespread settlement of the West by Euro-Americans a high
surface fire frequency characterized most ponderosa pine forests
of the southwest, including at least portions of the PNF (Brown
et al. 2000, Covington and Moore 1994b, Dietrich and Hibbert 1988,
Sneed et al 2002). Since the late 19th century, natural fire has
been excluded or reduced in many ecosystems by post-settlement
land uses such as mining, logging, livestock grazing (Savage and
Swetnam 1990), fire suppression, and changes in climatic patterns
(Brown et al. 2001,Grissino-Mayer et al. in press, Swetnam and
Betancourt 1990). Understanding and restoring fire is central to
newly emerging paradigms for ecological restoration of forests
and the ecosystem management approach that has been adopted by
federal agencies, including the USFS (Covington and Moore 1994a,
Fule et al. 1997). Fire frequency, intensity, and spatial extent
can be reconstructed quite accurately in ponderosa pine forests
using dendrochronological analysis of fire scarred trees if the
forest historically experienced relatively low intensity fires
(Brown et al. 2000). Recent research has demonstrated that fire
regimes in ponderosa pine forests varied substantially through
time and across space during the several centuries prior to Euro-American
settlement in the mid to late 1800s (Baker and Ehle 2001). Most
forests of pure ponderosa pine in Arizona and New Mexico were characterized
by frequent, low-severity fires that maintained open forests with
trees of many size and age classes (Fule et al. 1997). Despite
a broad network of fire history sites in ponderosa pine forests
throughout western North America, a large gap still exists in central
Arizona, where forest managers are developing new management plans
that will incorporate fire as a natural ecosystem process in the
extensive ponderosa pine forests of the region. One pilot study
(Sneed et al., 2002) has addressed fire history in ponderosa pine
forests of the central Arizona highlands.
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Ecological Responses to Climate Change
There is also reason to believe that ecosystems in the Walnut Creek
region may be particularly sensitive to natural and anthropogenic
changes in climate. Although temperature measurements at Walnut
Creek only extend back into the mid 1950’s, patterns there
are likely to be similar to patterns measured at Prescott, approximately
55 km to the southeast. A linear regression analysis of temperatures
measured in Prescott from 1899 to 2002 indicates that average annual
temperatures have increased by 0.16 + 0.03 °C per decade. The
increase in the annual average of minimum temperatures is 0.32
+ 0.03 °C per decade. There also appears to have been a distinct
shift in the snowfall patterns at Walnut Creek during the 20th
century. Annual snowfall measured at Walnut Creek is shown in Figure
3, along with a 5-year running average. From the beginning of the
winter of 1916-1917 through the end of the winter of 1956-1957,
the average winter season snowfall was 54 cm, with a standard deviation
of 46 cm. From 1957 to 2002, the average snowfall was 5 cm with
a standard deviation of 9 cm. Over this same period there was no
clear trend in total precipitation.
The ponderosa pine type forest found in the Walnut Creek region
exists at the lower end of the elevation range where it is typically
found. Given that winter snowfall is the most important factor
determining availability of soil moisture in the critical spring
germination and growing season, the decrease in snowfall in the
Walnut Creek region could have a dramatic impact on distribution
of plant communities. During the last two years, the Prescott National
Forest has experienced a dramatic die-off of ponderosa pines (50%
in many areas) that resulted from the combination of drought and
an infestation of pine engraver beetles (Ips and Dendroctonus).
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