Title Slide

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Title Slide
Global Change How Will the Mojave Desert
Respond?
Stanley D. Smith Department of Biological
Sciences University of Nevada, Las Vegas
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Why Study Climate Change?
Why Study Global Change?

• Atmospheric CO2 concentration has risen 50
  since the 1800s and will double from todays
  level by the end of this Century
• Scientists now agree that increasing CO2 and
  other greenhouse gases are causing global warming
• Changing precipitation regimes, nitrogen
  deposition, land disturbance and invasive species
  are also critical changes that will affect the
  Mojave Desert

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Why Study Deserts?

• Arid and semi-arid regions constitute 40 of
  the earths terrestrial surface
• Extreme environments, and particularly deserts,
  are predicted to show the greatest responses to
  rising atmospheric CO2 and concomitant global
  change factors

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Mauna Loa Atmospheric CO2 Concentration
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Gas Exchange through Plant Stomata
Water-Use Efficiency CO2 uptake / H2O loss
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GCM-predicted winter temperatures in the 2080s
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EOS 85385 (2004)
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Sierra Nevada Snowpack Projections Based on
Different Emissions/Warming Scenarios
Hayhoe, Cayan, Field et al. (2004) PNAS
10112422-12427
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Predicted Soil Moisture in Late 21st Century
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Past and Future Predicted Global Precipitation
(Hadley GCM)
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HadCM2 trends in precipitation-maps
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Trends in vegetation density -maps
GFDL
Increase in
Vegetation
Density
gt200
100 - 200
50 - 100
25 - 50
10 - 25
1 - 10
No Change
1 - 10
UKMO
10 - 25
25 - 50
50 - 75
75 - 100
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Decrease in
Vegetation
Density
(From Our Changing Planet, 1997)
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Size-Frequency of Summer Rainfall Events in the
SW Deserts Huxman et al. (2004)
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If Total Summer Rainfall Increases, We Will See
Disproportionately More Large (gt 5
mm) Rainfall Events Huxman et al. (2004)
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Differential Use of Large and Small Summer
Rainfall Events
Huxman et al. (2004)
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Potential Ecosystem Change with Changing
Precipitation Regime
from Schwinning et al. (2004)
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Dukes Mooney 99 Table
Possible Impacts of Global Change Elements on
the Prevalence of Invasive Species
Dukes Mooney (1999) Trends Ecol Evol
14135-139
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Ziska, 6 invasive species Graph
Ziska (2000)
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Dukes 2000 Table
Production of Centaurea solstitialis (yellow
starthistle) at elevated CO2 in monoculture
and polyculture
Dukes (2002) Plant Ecology 160225-234
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Smith et al Table
Effects of Elevated CO2 (2X Ambient) on Dry
Weight of Four Great Basin Grasses
Smith, Strain Sharkey (1987) Functional Ecology
1139-143
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Title Slide
The Nevada Desert Research Center
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Project PIs
NDRC Principal Investigators
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NDFF Experimental design
NDFF

• Nevada Desert FACE Facility
• Mojave Desert
• elevation 970 m
• annual precip 140 mm
• max temp 45 C (Jul-Aug)
• min temp -10 C (Dec-Jan)
• Control
• 365 ?mol mol-1
• FACE
• set point 550 ?mol mol-1
• start date April 28, 1997
• 24 h d-1 365 d yr-1
• conditional shutdowns high
• wind cold temperature

Jordan et al. (1999) GCB
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CO2 Tank at sunrise
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Plenum
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Oblique aerial view Ring 3
Oblique aerial view of Ring 3 an elevated CO2
treatment plot
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Walkway Preserve Biological Soil Crust N2
Fixation
Walkway Preserve Biological Soil Crust N2
Fixation
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Nicole measuring productivity
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Variables Measured at NDFF
Variables Measured at NDFF
Physiology Leaf gas exchange Root
physiology Aboveground production Biomass Litter
Carbon pools/fluxes Nitrogen
pools/fluxes Belowground production Root Microbi
al Carbon pools/fluxes Nitrogen
pools/fluxes Soil water content Biodiversity Pla
nts Insects
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Lycium shoot in fruit
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Precipitation at the NDFF 1996-2003
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1998-2001 NDFF perennials cumulative shoot
biomass
NDFF 1998 - 2001
Cumulative Shoot Biomass (mg)
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Seedling recruitment
Housman et al. (2003) Global Change Biology
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Plant-available N (Evans)
Plant available N
Elevated
Ambient
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Bromus in senescence
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Productivity of Annuals 1998
Smith et al. (2000) Nature 40879-82.
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Why does Bromus Respond More to Elevated CO2
Than Do Native Species?

• Accelerated phenology
• Produces smaller, more numerous seeds
• Lower construction cost

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Increased Fire Cycle
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Firecommunity change
Community change
Photos by T. Huxman T. Esque
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Bromus ring
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Bromus madritensis ssp. rubens
Bromus density (plants m-2)
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Bromus aboveground biomass
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Class G Fires gt 2,000 ha in Area
Knapp (1998) Global Ecology Biogeography
Letters

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The Mojave Global Change Facility
The Mojave Global Change Facility
A complementary facility to the Nevada Desert
FACE Facility (elevated CO2 experiment) is
investigating how GCM-predicted increases in
summer precipitation, nitrogen deposition and
crust disturbance may impact important ecosystem
processes in deserts
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MGCF Site Layout
MGCF

• Simulate predicted increases in
• summer precipitation
• nitrogen deposition
• crust disturbance
• 96 plots (ea. 200 m2)
• Results are integrated with NDFF data to predict
  how desert ecosystems will respond to global
  change

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Infrared MGCF
False color infrared image of MGCF from the Probe
1 hyperspectral sensor (5 meter spatial
resolution 11/10/02).
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MGCF Studies Initiated

• Water uptake by roots
• Soil heterogeneity
• Nitrogen Mineralization
• Nitrogen Fixation
• Moss responses
• Soil carbon uptake and respiration
• Leaf/canopy level photosynthesis
• Primary productivity
• Soil moisture/temp differences
• Reflectance measurements
• Aerial photography

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LATR ANPP
Initial Response of Larrea Production to Added
Summer Rain and N-Deposition
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Annuals 2003
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Crust photo
Biological Soil Crusts
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Collema cover
Collema cover Irrigation Disturbance
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MGCF Hypotheses

• Increased nitrogen deposition will result in
  increases in photosynthesis and production,
  particularly in concert with increased rainfall.
• Disturbance of biological soil crusts will result
  in reduced production over time.
• Increased summer rainfall will result in
  increased production growth forms such as
  evergreen shrubs and perennial grasses will
  increase more in production than
  drought-deciduous shrubs or spring annuals.

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Higher Order Responses?
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Ecological Effects of Global Change

• External Variable Internal Variables
  New Regime
• Elevated CO2 Greater plant production
  More productive desert
• 
  Increased invasion
  Fire-controlled grassland
• Higher Temperature Species range shifts
  Community disequilibrium
• Altered Precipitation
• Wetter Greater
  plant production Semiarid ecosystem-type
• Drier
  Increased mortality Species-poor
  system
• Increased N-deposition Greater plant
  production More productive desert
• 
  Increased invasion Community shift
  to invasive

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Global Change How May it Affect Ecosystem
Restoration?

• Uncertainty of future conditions (?)
• Shifting boundaries of reserves/corridors (-)
• Potential decoupling of mutualisms (-)
• Alleviation of environmental stress ()
• Stimulation of invasive species (-)

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Acknowledgements
NDRC Co P.I.s Bob Nowak, UNR Jay Arnone,
DRI Lynn Fenstermaker, DRI UNLV Dene
Charlet, David Barker, Beth Newingham Karen
Nielsen Colleagues Many, but esp. Travis
Huxman, Dave Evans and Jayne
Belnap Funding NSF (Ecosystems EPSCoR) DOE
(PER, TCP NIGEC) Andrew W. Mellon Foundation
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Why Study Deserts?Revisite
Why Study Deserts?
Deserts are quite responsive to elevated CO2,
altered precipitation, and N-deposition. Potentia
l responses to global change have important
implications for land management.