Phenology Modulates Carbon and Water Exchange of Ecosystems

Dennis BaldocchiSiyan Ma

Ecosystem Sciences Div/ESPMUniversity of California, Berkeley

AGU 2006B19, Land Surface Phenology, Seasonality and Water Cycle

Objectives

• Phenology and Vegetation-Atmosphere Interactions• Role of Phenology on Carbon and Water Fluxes

– Leaf Area Index, LAI– Photosynthetic Capacity, Vcmax

– Annual Carbon Fluxes – Annual Evaporation– PBL Dynamics

• New Assessment of Phenology– Temperature Deciduous Forest

• When Soil Temperature Exceeds Mean Annual Air Temperature

– Annual Grassland• Amount of Rainfall in the Spring

.

Hopkins Law of Phenology

• Phenology differs by four days for every degree of latitude, every 5 degrees of latitude and every 400 feet of altitude

Andrew Delmar Hopkins

Schwartz, M. D., 1997. Spring Index Models: An Approach to Connecting Satellite and Surface Phenology. In Phenology of Seasonal Climates

Phenology Affects Evaporation, which affects Atmospheric Demand, and Vice Versa

Menzel and Fabian, Nature 1999

Mean annual growing season in Europe increases by 10.8 days from 1981 to 1991.

Phenology, a Measure of Global Change

Spring Temperature Affects Phenology and the Seasonality of

CO2 Exchange: case 1, Deciduous Forests

Temperate Broadleaved Deciduous Forest

Day

0 50 100 150 200 250 300 350

NE

E (

gC m

-2 d

-1)

-7

-6

-5

-4

-3

-2

-1

0

1

2

3

4

5

LAI=0GPP=0;Litterfall (+)Reco=f(litterfall)(+)

snow:

Tsoil(+)

GPP=0; Reco(+)

no snow

Tsoil (-)

Reco (-)

GP

P=f(LA

I, Vcm

ax )

late spring

early spring

Drought:(-)GPP(-); Re(-)

Clouds:PAR(-) GPP=f(PAR)(+)

Day

0 50 100 150 200 250 300 350

Lea

f A

rea

Ind

ex

0

1

2

3

4

5

6

1995199619971998

Walker Branch Watershed, TN

Phenology Modulates Source-Sink via LAI

•Interannual Variability in Length of Growing Season > 30 days

•Latitudinal Variation in Length of Growing Season > 30 days

Spatial Gradients:NEE and Length of Growing Season

Broad-Leaved Forests

Length of Growing Season

100 150 200 250

NE

E (

gC

m-2

yr-1

)

-800

-700

-600

-500

-400

-300

-200

-100

0

100Japan

Denmark

Italy

Massachusetts, USA

Belgium

Tennessee, USA

Prince Albert, CANADA

Ontario

Indiana, USA

Michigan, USA

Baldocchi et al, 2001, BAMS

Temperate Deciduous Forests

Days with NEE < 0

120 140 160 180 200 220 240

NE

E (

g C

m-2 y

ea

r-1)

-800

-700

-600

-500

-400

-300

-200

-100

0

CANOAK, Oak Ridge, TNPublished Measurements, r2=0.89

Year to Year differences in NEE across sites is due to differences in Growing Season Length

Baldocchi et al, 2001 Ecol Modelling

Caveat Emptor

• Growing Season Length has More Explanatory Power across a Latitudinal Gradient than at an Individual Site

• Additional factors explaining annual NEE at a Single Site include:– Absence/presence winter snow– Occurrence of Summer Drought– Extent of cloudiness

Grasslands

Day

0 50 100 150 200 250 300 350

NE

E (

gC m

-2 d

-1)

-6

-4

-2

0

2

4

Mediterranean GrasslandTemperate C4 grassland

Data sources: Valentini et al. 1996; Baldocchi + Xu, unpublished; Verma +Suyker

Late

spr

ing

rain

s

GPP(+

)

Spring/Summer Drought(-)GPP(-); Reco(-)

GPP > 0;AM Frost:GPP(-)

Tmin > 0 oC

GPP =f(LAI) (+)

Rain PulseReco(++)

GPP=0

Autumn Rains:T(-), (++)GPP(+), Reco(-)

snow covereddormant grassGPP=0, Reco > 0

The Duration of Winter/Spring Rain affects Phenology and the Seasonality of CO2 Exchange: case 2, Annual Grasslands

Length of Rain Period affects Phenology of Annual Grassland

Annual Grassland, Ione, CA

Day

0 50 100 150 200 250 300 350

Soi

l Moi

stur

e at

20

cm

0.0

0.1

0.2

0.3

0.4

0.5

200120022003 2004

Interannual variation of Wet season can vary by > 50 days

Annual Grassland, Vaira Ranch

Day of Year

-100 -50 0 50 100 150 200

Le

af

Are

a I

nd

ex

0.0

0.5

1.0

1.5

2.0

2.5

3.0

2001-20022002-20032003-20042004-2005

Timing of Rainfall Can Force Substantial Interannual Variability in LAI

-120 0 120 240

-0.2

0.0

0.2

0.4

-4

0

4

LSW

I MODIS - LSWI

gC

day

-1

Daily NEE

Remote Sensing Can be Used to study Phenology of Carbon Fluxes

PRI and NEE

-120 -60 0 60 120 180

-0.10

-0.08

-0.06-4

-2

0

2

4

6

PR

I

DOY after 1/1/2005

PRI

gC

day

-1

14 day NEE

Land Surface Water Index LSWI = (ρ860 - ρ1640)/(ρ860 + ρ1640)

PRI = (531 - 570) / (531 +570)

Falk, Baldocchi, Ma, in preparation

Humidity Deficits and Phenology:

Annual grassland near Ione California

Xu and Baldocchi, 2003 AgForMet

Tai

r (o C

)

0

10

20

30

40

502000 2001

DOY

100 200 300300

VPD

(kP

a)

0

2

4

6

8

10

Max

Min

Mean annual air temp 16.3 oC

Amount of Rain During the Wet Season Affects NEE of Annual CA Grassland and Savanna Woodland

Open Grassland

PPT3-6 (mm)

0 50 100 150 200 250 300

An

nu

al F

lux

(gC

m-2

)

-200

0

200

400

600

800

1000

1200

Savanna

PPT3-6 (mm)

0 50 100 150 200 250 300

GPP RecoNEE

Ma, Baldocchi, Xu and Hehn, submitted, AgForMet

Seasonality of Model Parameters:e.g. Photosynthetic Capacity

DOY

100 150 200 250 300 350

Vcm

ax

0

20

40

60

80

100

120

140

Quercus alba (Wilson et al)Quercus douglasii (Xu and Baldocchi)

Live Fast, Die YoungIn Stressed Environments

Month

0 2 4 6 8 10 12

v x,25

( m

ol m

-2 s

-1)

-5

0

5

10

15

20

25

30

35

HEHV WB

Wang et al, 2006 GCB

Annual and Spatial Variation in Photosynthetic Capacity, Vcmax, for Deciduous Forests in North America (HV, WB) and

Europe (HE)

Year0 10 20 30 40

v x,2

5 ( m

ol m

-2 s

-1)

0

20

40

60

80

Can

opy

LAI

0123456

Wang et al, 2006 GCB

Interannual Variation in Ps Capacity

0 5 10 15 20 25La

tent

hea

t (F

e)

-40

0

40

80

120

0 5 10 15 20 25

Sen

sibl

e he

at (

Fh)

-100

0

100

200

Month

0 5 10 15 20 25

NE

E (

Fc)

-5

-4

-3

-2

-1

0

Observed Fe (W m-2)-20 0 20 40 60 80 100120140

Mod

elle

d F

e (

W m

-2)

-200

20406080

100120140

Observed Fh (W m-2)

-40 -20 0 20 40 60 80 100120

Mod

elle

d F

h (

W m

-2)

-40-20

020406080

100120

Observed NEE (mol m-2 s-1)-5 -4 -3 -2 -1 0

Mod

elle

d N

EE

-5

-4

-3

-2

-1

0

Wang et al, 2006 GCB

Seasonality of Vcmax is needed to simulate LE, H and NEE

Day

0 50 100 150 200 250 300 350

Leaf

Are

a In

dex

0

1

2

3

4

5

6

1996, Starts d1211997, Starts d108

Oak Ridge, TN

Day

0 50 100 150 200 250 300 350

E (

mm

d-1

)

0

1

2

3

4

5

1996: 492 mm 1997: 519 mm

Growing Season Length and ET, Field Data

Year with Longer Growing Season (13 days) Evaporated More (27 mm).

Other Climate Factors could have confounded results, but Rg (5.43 vs 5.41 GJ m-2) and Tair (14.5 vs 14.9 C)

were similar and rainfall was ample (1682 vs 1435 mm)

Wilson and Baldocchi, 2000, AgForMet

Temperate Deciduous ForestOak Ridge, TN

Day

0 50 100 150 200 250 300 350

ET

(m

m d

-1)

0

1

2

3

4

5

6

7

Leaf out: D90D100D110D120D130

Effect of Timing of Leaf-Out on Evaporation, Theory

CANOAK

Date of Leaf-Out

80 90 100 110 120 130 140

ET

(m

m y

-1)

620

630

640

650

660

670

680

690

700

Slope: -1.68 mm/day

Year to Year differences in LE is partly due to differences in Growing Season Length

Field data show that ET decreases by 2.07 mm for each day the start of the growing season is delayed

Caveat Emptor

• Early Spring can be followed by Summer Drought– ‘Net spring CO2 uptake increased from 1994-2002,

whereas net growing season uptake did not... We have shown that these opposing trends in summer and spring are probably related to a drought-induced reduction in summer photosynthesis…Thus warming does not necessarily lead to higher CO2 uptake’

• Angert et al, 2005, PNAS

Walker BranchData of Davis + Baldocchi

Days

0 50 100 150 200 250 300 350

PB

L (

m)

0

500

1000

1500

2000

2500

3000

Phenology and PBL Growth

Deeper PBL Growth occurred after Leaf Out

Predicting Phenology

• Growing Degree Days• Chill Degree Days• Chill Hours• Chill Degree Hours• Heat Degree Days

GDDT T

Tref

( )max min

2

Critical Heat Units Need Calibration and are not Universal

Oak Ridge, TN 1996

Day of Year

100 105 110 115 120 125 130 135

NE

E (

gC m

-2 d

-1)

-4

-3

-2

-1

0

1

2

3

4

Coefficients:b[0] 21.6b[1] -0.183r ² 0.696

Using the Onset of Photosynthesis as indicator of Phenology

Baldocchi et al., 2005, Int J Biomet

Soroe, DenmarkBeech Forest1997

day

0 50 100 150 200 250 300 350

-10

-5

0

5

10

15

20

NEE, gC m-2 d-1

Tair, recursive filter, oC

Tsoil, oC

Data of Pilegaard et al.

Soil Temperature: An Objective Indicator of Phenology??

Data of: Baldocchi, Wofsy, Pilegaard, Curtis, Black, Fuentes, Valentini, Knohl, Yamamoto. Granier, SchmidBaldocchi et al. Int J. Biomet, 2005

Soil Temperature: An Objective Measure of Phenology, part 2

Temperate Deciduous Forests

Day, Tsoil >Tair

70 80 90 100 110 120 130 140 150 160

Da

y N

EE

=0

70

80

90

100

110

120

130

140

150

160

DenmarkTennesseeIndianaMichiganOntarioCaliforniaFranceMassachusettsGermanyItalyJapan

Mean Air Temperature, C

4 6 8 10 12 14 16 18

Day

of

NE

E =

0

60

80

100

120

140

160

Coefficients:b[0]: 169.3b[1]: -4.84r ²: 0.691

Baldocchi et al. Int J. Biomet, 2005

Onset of Spring is Delayed ~ 5 days with each degree reduction in mean temperature

When Transformed onto a Climate Map, We observe a General Correspondence with N-S gradient Obtained from

the denser Phenology Network

d90

d140

Summary and Conclusions

• The Length of the Growing Season has significant effects on annual Carbon and Water exchange– As long as Warmer Springs are not followed by Summer Drought

• The correspondence between soil temperature and mean annual air temperature has a strong correlation with Spring Leaf-out– The metric does not need tuning/calibration and works across a wide

latitudinal range.• Processes derived from Networks of Flux Measurement Sites can

be Transformed onto Climate Space to produce Phenology Maps• New Technologies for monitoring Phenology

– Eddy Flux, $$$$ – Digital Camera, $$– LED, NDVI/PRI Sensor, $

Acknowledgements

• Funding– DOE/TCP, NIGEC/WESTGEC, CalAgExpt

Station

• Collaborators– YingPing Wang– Matthias Falk– Liukang Xu– Kell Wilson– AmeriFlux/Fluxnet Colleagues