brody sandel 1, leah j. goldstein 2, nathan kraft 1, jordan okie 3, michal shuldman 1, david d....

Brody Sandel1 , Leah J. Goldstein2, Nathan Kraft1, Jordan  Okie3, Michal Shuldman1, David D. Ackerly1, Elsa Cleland4 and  Katharine N. Suding2

(1)Department of Integrative Biology, UC Berkeley, Berkeley, CA (2)Ecology and Evolutionary Biology, UC Irvine, Irvine, CA(3)Department of Biology, University of New Mexico, Albuquerque, NM(4)Ecology, Behavior & Evolution Section, UC San Diego, La Jolla, CA

Contrasting predictions of

experimental and observational

studies of the response of plant communities to changing precipitation

How will the composition of plant assemblages respond to climate change?

Precipitation change Weltzin et al. 2003, Bioscience.

Plant functional traits Suding et al. 2008, Glob. Change Biol.

Experimental/observational Rustad 2006, Plant Ecol.

Introduction

Plant responses to climate change

Wright et al. 2005, Glob. Ecol. Biogeogr.

Introduction

Traits and climate change

N:P

Reich and Oleksyn 2004, PNAS

Traits vary with climate Can they predict response to changing

climate?

Advantages of trait-based predictionsMechanistic interpretationsAllows synthesesPredictions are generalizable

Introduction

Traits and climate change

Similar predictions?Direction and magnitude of effect

Shifts in functional trait composition are the bases for comparison

Introduction

Experimental and observational

Introduction

Similar predictions?

Control + Precip

Mea

n tr

ait

valu

e

Precipitation

Mea

n tr

ait

valu

e

Direction

Control + Precip

Mea

n tr

ait

valu

e

Precipitation

Mea

n tr

ait

valu

e

Introduction

Similar predictions?

Direction Magnitude

∆TE =? ∆TO

Control + Precip

Mea

n tr

ait

valu

e

Precipitation

Mea

n tr

ait

valu

e

Equivalent toexperiment

∆TE ∆TO

Introduction

Similar predictions?

Combining resultsSame direction, different magnitude(My a priori expectation)

Precipitation

Mea

n tr

ait v

alue

Experimentalstudies

Observationalgradient

CT

C

CT

T

Introduction

Similar predictions?

Experimental water additions Natural precipitation gradient Match species lists to trait databases Calculate plot mean trait values

Test for effects of increased water

Compare experimental and observational outcomes Direction Magnitude

Methods

Methods overview

Four water addition experiments Konza LTER (1991-2005) Knapp et al. 2001, Ecosystems.

Shortgrass Steppe LTER (2000) Sevilleta LTER (2004-2006) Baez et al. In prep.

Jasper Ridge Global Change Experiment (1999-2002) Zavaleta et al. 2003, Ecol. Monogr.

Between 10% and 190% (mean 50%) precip. increases

Plant community composition data Grasslands or mixed grass-shrublands 219 species total

Methods

Experimental data

VegBank (vegbank.org) 21,566 plots from across the country Plant assemblage of all plots 7813 species total

Used PRISM climate data to obtain 30-year mean precipitation values

Methods

Observational data

TraitsMethods

Matched species lists to trait databasesUSDA PlantsKew Gardens Seed Information DatabaseGlopnet leaf traits Wright et al. 2004. Nature.

More leaf traits Tjoelker et al. 2005, New Phyt.; Reich and Oleksyn 2004, PNAS.

Height Cleland et al. 2008. Ecology.

Exp. Nat. Grad.

Trait Coverage Coverage

LL 30% 21%

SLA 41% 34%

Nmass 42% 43%

Narea 40% 32%

Amass 38% 23%

Aarea 40% 23%

Seed 94% 80%

Form 100% 89%

Lifespan 98% 90%

Height 100%  

TraitsMethods

Abundance-weighted trait means for each plot Percentage cover by a group All analyses performed on these plot-level values

Experimental ANOVA using last year of each study

Observational Aggregated cells at 1 x 1 degree resolution Linear regression

Methods

Analyses

log(Precip (mm))

log(

See

d m

ass

(mg)

)

Results

Seed size example

log(

See

d m

ass

(mg)

)

log(Precip (mm))

Results

Seed size example

log(Precip (mm))

log(

See

d m

ass

(mg)

)

Results

Seed size example

log(Precip (mm))

log(

See

d m

ass

(mg)

)

Results

Seed size example

log(

See

d m

ass

(mg)

)

log(Precip (mm))

Results

Seed size example

Results

Seed size example

Tre

atm

ent e

ffec

tlo

g(S

eed

mas

s (m

g))

per

log(

Pre

cip

(mm

))

Year

Slopes of line segments through time

Results

Summary of all traits Experimental Natural Gradient

Trait Effect P Effect r2

LL - 0.0129 + 0.154

SLA + 0.0297 NS 0.006

Nmass NS † 0.1601 - 0.158

Narea + 0.0003 - 0.309

Amass Mixed † 0.0189 - 0.047

Aarea NS † 0.3116 - 0.101

Seed - 0.0071 + 0.362

Grass NS † 0.0717 - 0.373

Forb + 0.0091 - 0.066

Annual - <.00001 - 0.122

Short - † <.00001    

† indicates a significant site by treatment interaction

Results

Summary of all traits Experimental Natural Gradient

Trait Effect P Effect r2

LL - 0.0129 + 0.154

SLA + 0.0297 NS 0.006

Nmass NS † 0.1601 - 0.158

Narea + 0.0003 - 0.309

Amass Mixed † 0.0189 - 0.047

Aarea NS † 0.3116 - 0.101

Seed - 0.0071 + 0.362

Grass NS † 0.0717 - 0.373

Forb + 0.0091 - 0.066

Annual - <.00001 - 0.122

Short - † <.00001    

† indicates a significant site by treatment interaction

Results

Summary of all traits Experimental Natural Gradient

Trait Effect P Effect r2

LL - 0.0129 + 0.154

SLA + 0.0297 NS 0.006

Nmass NS † 0.1601 - 0.158

Narea + 0.0003 - 0.309

Amass Mixed † 0.0189 - 0.047

Aarea NS † 0.3116 - 0.101

Seed - 0.0071 + 0.362

Grass NS † 0.0717 - 0.373

Forb + 0.0091 - 0.066

Annual - <.00001 - 0.122

Short - † <.00001    

† indicates a significant site by treatment interaction

Experimental studiesTall, long-lived forbs with short leaf lifespans,

high leaf N concentrations, high specific leaf area, and small seeds

Observational analysisLong-lived woody species with long leaf

lifespans, low leaf N concentrations and photosynthetic capacity, and large seeds

Results

How will communities change?

One is right, the other wrongExperimental artifactsUnmeasured covariates

The different responses may reflect a real, two-phased response to climate change

Discussion

Why the mismatch?

Response to climate change may occur over distinct phasesWhy two phases?Why might the responses in each phase differ?What determines the time scale of the phases?

Discussion

A two-phase model

Discussion

Two phases

Premise – Abundance changes happen more quickly than species gain and lossPhase 1 – Changes in local species abundancePhase 2 – Changes in species pool

Calculating plot trait values not weighted by abundance revealed fewer treatment effectsAbundance shifts were critical in experiments

Discussion

Two phases

Phase 1 – Abundance changes

Phase 2 – Species pool changes

Increased water

Time

Discussion

Phase differences

Why might the trait responses differ in the two phases? Changing interactions among

species Shifts in the limiting resource

The traits of local species that increase are not the same as those of immigrating species

Discussion

Phase differences

Increased water

Time

Increasing species are able to take advantage of increased

resource availability (tall, high leaf N, short-lived

leaves, small seeds)

Taller stature - light limitation

Species must cope with low light environment

(woody, low leaf N, long-lived leaves, large

seeds)

Discussion

Time scales Little evidence for phase 2 in the experiments

No convergence through time towards observational results No treatment affect on species-time relationships

JRG KNZ

SEV

What determines the length of phase 1?Spatial extent of climate changeLife histories of local species (annual/perennial)

At least decades in this caseLengthened by experimental limitations

Discussion

Time scales

Traits useful predictors Mismatch between experimental and observational

results Could be due to different time scales captured by

these two types of study

Use the appropriate data to predict for a given time scale

Discussion

Main messages

NCEAS, and the coordinators and participants in the distributed graduate seminar

William Lauenroth Alan Knapp William Pockman Erika Zavaleta Funding –

NSF grant to NCEAS (EF-0553768) UC Santa Barbara LTER network office for cross-site research NSF LTER program (DEB0218210, BSR 88-11906, DEB9411976, DEB0080529,

DEB0217774, DEB0217631) David and Lucile Packard Foundation Morgan Family Foundation Jasper Ridge Biological Preserve

The many VegBank contributors Ian Wright and Peter Reich (Glopnet)

Acknowledgments

Discussion

A two-phase model