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Precipitation (blue) and weighted number of creosotebush budding or
flowering (red) on randomly selected days of 2003 at a site in the
Sevilleta NWR. Notice the many gaps in knowledge that this type of data
collection fails to address.
Figure by L. Benton
Example photo from one camera in the eddy covariance footprint at the
creosote site of the Santa Rita Experimental Range.
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Project Title: Tracking the Phenological
Triggers of the Repeat-Blooming Creosotebush
Current Project Participants: Lisa Benton
(UA-SNR),
Shirley Kurc (UA-SNR)
Project Summary:
Previous studies suggest that creosotebush
blooms in response to rainfall at all seasons (Shreve 1951; Humphrey
1975; Barbour et al. 1977; Abe 1982) or once in the spring and
successively throughout the summer following precipitation events
greater than 12 mm (Bowers and Dimmitt 1994). However, these studies
are based purely on observational data that are discrete in time,
subject to bias (descriptors have included “sparsely budding”, “entire
population budding”, “population with sparse leaf fall”, etc.), and
rely on minimal variables to characterize environmental conditions. In
addition, this commonly-used transect methodology to track bloom and
green-up is very time consuming and is rarely conducted more than once
weekly. We argue that this method is insufficient for explaining what
is causing creosotebush to initiate phenological activity.
In this study, the central research initiative
is to decipher what
conditions and soil moisture levels must be present in order to produce
floral development in the creosotebush by monitoring with digital
photography Our hypotheses are (1) blooming in creosotebush is
controlled by temperature in the spring and moisture in the summer and
(2) soil moisture below the depth
of atmospheric demand will be the main trigger for flowering of
creosotebush in the summer and that this is independent of geographic
location and individualized variations in the species. Obtaining a
greater understanding of the
reproductive biology and growth of this woody species is essential for
addressing regional concerns over climate change in the desert
southwest for avian and entomological
researchers, land managers concerned with soil stability and/or woody
encroachment by the creosotebush, and climate modelers needing better
inputs for the phenological behaviors of this dominant species and
other repeat-blooming functional types found within water-limited
regions.
Current Funding From: Kurc University of
Arizona Start-Up
Package, and Lisa Bentons's Eco-Hydrology Fellowship through the USDA
and CSREES
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Project Title: Controls on
transpiration in creosotebush dominated ecosystems
Current Project Participants: Michelle
Cavanaugh (UA-SNR, USDA-ARS),
Shirley Kurc (UA-SNR), Ross Bryant (USDA-ARS), Russ Scott (USDA-ARS)
Summary: In this study is to
compare transpiration losses by creosotebush (Larrea tridentata) at two
study sites in southeastern Arizona using the heat balance method of
sap flow measurement.
Our objective is to understand the unique water use of these woody
creosotebush under different environmental conditions. This species
covers much of the desert southwestern United States in areas differing
in soil type and precipitation regime. In southeastern Arizona,
creosotebush can be found in the transition zone between the Sonoran
and Chihuahuan deserts at the Lucky Hills field site within the Walnut
Gulch Experimental Watershed and within the Sonoran Desert itself at
the northern boundary of the Santa Rita Experimental Range. Both of
these locations are equipped with eddy covariance towers, associated
micrometeorological measurements, and profiles of water content
reflectometers for soil
moisture making them ideal locations for this study.
Here, we propose
three hypotheses in regards to the measurement of transpiration in
creosotebush at the two study sites. Firstly, we hypothesize that we
will not see transpiration responses for storms less than 5 mm at both
sites. Secondly, we hypothesize, that at both sites we will see a
lagged response of T to large precipitation events, with evaporation
being the dominate component in the partitioning of ET for the first
two days. Thirdly, we hypothesize the ratio of plant transpiration to
total evapotranspiration (T/ET) will be less at SRER due to the larger
amount of bare soil exposed at this site.
Current Funding From:Kurc University of
Arizona Start-Up
Package, Michelle Cavanaugh's Peace Corps Fellowship, USDA-ARS
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Components of ET following a precipitation pulse greater than 10 mm A.
at the Lucky Hills Site of the Walnut Gulch Experimental Watershed
(from Scott et al. 1996) and B. as anticipated at the Creosote Site of
the Santa Rita Experimental Range.
Figure by M. Cavanaugh
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Before the 1950s, much of the SRER was
grass-dominated.
Photo by: S.A. Kurc
Since the
1950s, the SRER has become dominated by woody
shrubs.
Photo by: J. Costa
Eddy
covariance tower in the cresotebush area of the SRER.
Photo by: S.A. Kurc
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Project Title: Vegetation controls on
water, energy, and carbon cycling in water-limited ecosystems
Current Project Participants: Shirley A.
Kurc (UA-SNR), Michelle Cavanaugh (UA-SNR, USDA-ARS), Lisa Benton
(UA-SNR)
Summary:The report released in February
2007 by the Intergovernmental Panel on Climate Change, anticipates the
continuation of trends in both gradual and abrupt climatic change at
the global scale with the additional projection that global
temperatures will continue to rise. Already, nearly 40 percent of the
global land surface is classified as arid to semiarid; a percentage
that is almost certain to increase based on current climate trends.
Historically, these water-limited areas have also been locations of
major population increase [e.g. Falkenmark, 1990; Oki and Kanae, 2006].
In fact, from Pakistan to the southwestern United States, desert
communities continue to grow at higher rates than much of the rest of
the world [UNFPA, 2001]. This combination of sustained climate change
and population growth essentially guarantees the continuation of major
shifts in dominant vegetation.
One might visualize that a shift in vegetation from grassland to
shrubland is a shift from shorter, denser vegetation to a taller more
sparse vegetation type. A more difficult task is the visualization of
how the changes in associated plant physiology, canopy structure, and
canopy density alter the way that energy, water, and carbon are cycled
throughout ecosystem.
The main objective of this
research is to identify key aspects of vegetation and how they control
the processes associated with dynamics of energy, water, and carbon
cycling. Specifically, the following three questions will be addressed
concerning (1) spatial scale, (2) temporal scale, and (3)
transferability:
(1)
Vegetation structure affects the cycling of energy, water and carbon.
What are the important spatial scales at which vegetation structure
influences these cycles?
(2)
Timing of physiological activity depends on plant phenology. How does a
plant phenology change associated with a vegetation shift affect the
temporal variability of water and carbon exchange in the desert
ecosystems?
(3) We found a difference in available energy of 70 W m-2 between
grassland
and shrubland at the Sevilleta NWR. How robust is this observation such
that it may be applied as a generalization to grassland and shrubland
ecosystems in other locations?.
Funding "Current" From: University of
Arizona Agriculture Experiment Station, through the USDA and CSREES
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Project Title: Characterization of
microclimate and vegetation structure within riparian areas along
urbanized and non-urbanized ephemeral streams
Current Project Participants: Jonathan Martin
(UA-SNR), George Zaimes (UA-SNR), Mike Crimmins (UA-SWES), Doug Green
(ASU-ABS), Shirley Kurc (UA-SNR)
Summary: In Arizona, urban growth has the
potential to impact riparian areas along ephemeral streams in ways that
are not fully understood. In addition, the ecological functions of
riparian areas along ephemeral streams are not well known. In Arizona
these functions might be very important since most streams are
ephemeral. Comparisons of microclimatic and vegetative data from
riparian areas along ephemeral streams with different levels of
urbanization will provide a better idea of what the ecological
functions of these riparian areas are and how urbanization impacts them.
Current Funding From: EPA
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Photo by G. Zaimes
Photo by G. Zaimes
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Project Title: Quantifying
relationships
between water, carbon, and nutrient cycles
Summary: Quantify linkages between water,
carbon, and nutrient cycling over a range of ecosystems to develop a
predictive understanding of how climate or vegetation change will
affect water balance
Funding by: Sustainability of semiArid
Hydrology and Riparian Areas, SAHRA,
a Science and Technology Center of the National Science
Foundation.
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