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Climate change, grass invasions, and woody plant
dynamics in semi-arid savannas
Jake Weltzin
Department of Ecology and Evolutionary BiologyUniversity of Tennessee
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CGCM1 HadCM2
Precipitation regimes: wither the future?
NAST 2000
Seed
Seedlingemergence
Seedlingsurvival
Mature plant
• Climate-precipitation-temperature-[CO2]
• Microclimate
• Soil-water-texture-nutrients
• Fire
• Grass neighbors-identity-interactions-density
• Herbivory-direct-indirect
• Seed availability-production-predation-dispersal
Recruitment of woody plants
Recruitment of woody plants
Seed
Seedlingemergence
Seedlingsurvival
Mature plant
• Climate-precipitation-temperature-[CO2]
• Microclimate
• Soil-water-texture-nutrients
• Fire
• Grass neighbors-identity-interactions-density
• Herbivory-direct-indirect
• Seed availability-production-predation-dispersal
Experimental design
• Grass neighborhood- No grass (bare)- Native grass (Heteropogon contortus)- Non-native, invasive grass (Eragrostis lehmanniana)
• Summer precipitation- Wet (LTM + 50%)- Dry (LTM - 50%)
• Soil texture- Sand (Holocene)- Clay (Pleistocene)
Mesquite (Prosopis velutina) demography- Seeds planted August 2002- Seedlings monitored through June 2004
Eragrostis depletes soil moisture faster than Heteropogon
Time since pulse (days)
June 2002
Huxman et al.
ClaySand
Low
Wate
r stress H
igh
Seedlings in summer less water-stressed on clay than on sand
Fravolini et al.
ClaySand
Most summer rain events are smallS
um
mer
rai
n e
ven
ts
Summer rain event size class (mm)Fravolini et al.
Small rain events are transparent to mature mesquite on clay soil
Fravolini et al.
Use
of
iso
top
e-la
bel
ed w
ater
(%
)
Time since pulse (days)
Sand
Clay
Recruitment ultimately depends on soil moisture
• Seed-seedling conflict mediated by grassesFacilitation ---> Competition
• Presence/absence of grass most importantUltimately, identity of grass unimportant
• Importance of summer precipitation depends on soil type
• Seedling dem./phys. inconsistent with landscape patterns
• Seedling-adult conflict mediated by ppt regime and soil
Landscape pattern controlled by interactions between life-history stage and environment
AcknowledgmentsUSDANSFUniversity of Tennessee
Santa Rita Experimental RangeJosh AveyColeen BrownDeborah Angell
David WilliamsTravis Huxman
Nathan EnglishMike MasonBill Cable
Steve ArcherBrian EnquistMitch McClaranGuy McPhersonDon PostSusan Schwinning
NCEAS PrecipNet Participants
Alessandra FravoliniLeigh Thomas
Daniel Potts
Philip AllenMichael Andregg
Enrico BrugnoliDayna BurnsJessica Cable
Janet ChenAlex Eilts
Rico GazalRobbie Hannawacker
Kevin HultineDanielle Ignace
Dan KoepkeCharles Price
Josh PolacheckLara Souza
Lisa SturdivantSam Waskow
PrecipNet
Improving understanding of precipitation effectson ecosystems through cross-disciplinary research networks
http://precipnet.ucsc.edu/index.html
PrecipNet
Improving understanding of precipitation effectson ecosystems through cross-disciplinary research networks
•Research coordination, communication, and integration
•Regional comparisons of precipitation change and its effects
•Fostering multidisciplinary activities
•Promoting skill development and technology transfer
•Participants
PrecipNet Goals
Dennis Baldocchi UC Berkeley biomet@nature.berkeley.edu
Dave Breshears University of Arizona daveb@ag.arizona.edu
Dave Evans Washington State University devens@uark.edu
John Harte UC Berkeley jharte@socrates.berkeley.edu
Travis Huxman University of Arizona huxman@email.arizona.edu
William Lauenroth Colorado State University billl@cnr.colostate.edu
Yiqi Luo University of Oklahoma yluo@ou.edu
Russ Monson Colorado State University monsonr@colorado.edu
Lindsey Rustad USDA Northeastern Lab. rustad@maine.edu
Whendee Silver UC Berkeley wsilver@nature.berkeley.edu
Stan Smith University Nevada, Las Vegas ssmith@ccmail.nevada.edu
Jake Weltzin University Tennessee jweltzin@utk.edu
Claus Beier RISOE National Lab., Norway claus.beier@risoe.dk
Todd Dawson UC Berkeley tdawson@socrates.berkeley.edu
Philip Fay University of Minnesota, Delouth pfay@nrri.umn.edu
Claus Holzapfel University of Massachusetts holzapfe@bio.umass.edu
Robert Jackson Duke University jackson@duke.edu
Michael Loik UC Santa Cruz mloik@ucsc.edu
Hafiz Maherali University of Guelph maherali@uoguelph.ca
Ronald Neilson Pacific Northwest Forestry rneilson@fs.fed.us
Osvaldo Sala University Buenos Aires, Argentina sala@ifeva.edu.ar
Marcelo Sternberg marcelos@tauex.tau.ac.il
David Tissue Texas Tech University david.tissue@ttu.edu
David Williams University of Wyoming dgw@uwyo.edu
Jayne Belnap USGS Moab, Utah jayne_belnap@usgs.gov
Evan Delucia University of Illinois delucia@life.uiuc.edu
Brent Haddad UC Santa Cruz bhaddad@ucsc.edu
Bruce Hungate Northern Arizona University bruce.hungate@nau.edu
Alan Knapp Colorado State University aknapp@lamar.colostate.edu
Steve Long University of Illinois stevel@life.uiuc.edu
Greg Masters CABI Biosciences g.masters@cabi.org
William Pockman University New Mexico pockman@unm.edu
Susan Schwinning Texas State University, San Marcos schwinn@txstate.edu
Eric Small University of Colorado eric.small@colorado.edu
Enrique Vivoni New Mexico Tech vivoni@nmt.edu
John Zak Texas Tech University yzjoz@ttu.edu
Participants
25 sites
9 sites (VULCAN / CLIMOOR)
5 sites (GLOWNET Network)Osvaldo Sala
CABI Bioscience (3 sites)
Participating sites and networks
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