Climate change, grass invasions, and woody plant

dynamics in semi-arid savannas

Jake Weltzin

Department of Ecology and Evolutionary BiologyUniversity of Tennessee

NASA

Clay - Pleistocene Sand - Holocene

-20

-40

-60

-100

-80

20

40

60

>100

80

0 %

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

Annual409 mm

34 events

Irrigation mimics intra-annual variation (daily, seasonal)

Soil types respond differently to irrigation

Clay

Sand

Irrigation controls seasonal soil moisture

Clay

Grass presence and identity control soil moisture

Clay

Eragrostis depletes soil moisture faster than Heteropogon

Time since pulse (days)

June 2002

Huxman et al.

ClaySand

Emergence facilitated by grasses, esp. in wet plots

Sand & Clay

Under grasses, soil moisture inversely related to emergence

Bare

Eragrostis

Heteropogon

Sand & Clay

Grasses do not reduce soil temperature

English et al.

Sand: grass identity not important, irrigation not important

ns 0

Sand

ns 0

Clay: grass identity not important, irrigation is important

WxP: P = 0.008

Clay

Seedlings in bare plots largest on wet, clay soil

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

http://eeb.bio.utk.edu/weltzin/