Carbon & Water Exchange of an Oak-Grass Savanna Ecosystem

Dennis BaldocchiBiometeorology Lab, ESPM

University of California, Berkeley

Oak-Grass Savanna: A Two Layer System

Summer:Trees green; grass dead

Spring:Trees green;grass green

Winter:Trees deciduous; grass green

Oak-Savanna Model System for Studying Ecosystem Ecology

• Structure/Function– Oak and grasses provide contrasting life forms, woody/herbaceous,

perennial/annual– The Canopy is open and heterogeneous, giving us a opportunity to test the

applicability of ecosystem and biogeophysical models, mostly developed for ideal and closed canopies

• Environmental Biology– The Mediterranean climate provides distinct wet/ cool and dry/hot seasons to

examine the ecosystem response (photosynthesis, transpiration, respiration, stomatal conductance) to a spectrum of soil moisture and temperature conditions

• Global Change– The Mediterranean climate experiences great extremes in inter-annual

variability in rainfall; we experience a wider range in precipitation over a few years than long-term predicted changes.

Tonzi Ranch Flux Tower

IKONOS: Savanna & Fetch

Vaira Ranch

IKONOS:Grassland

Canopy Structure: Tonzi Ranch

– Blue oak (Quercus douglasii)– LAI=0.90– Height 7.1 +/- 3.05 m– Diameter at breast height 26.6

+/- 0.11 cm– Understory: annual C3 grasses

• Brachypodium distachyon, Hypochaeris glabra, Bromus madritensis

Canopy Structure:Laser Altimeter Data

Experimental Methods

• Eddy Covariance– above the stand (20 m tower)– below the stand (2 m tower)

• Micrometeorology • Sap flow (heat pulse)• Soil respiration chambers• Leaf Physiology (A-Ci curves)

Eddy Covariance

F w c ' '

Mean

Fluctuation

Ecosystem Ecology

50 100 150 200 250 300 350-25

-20

-15

-10

-5

0

5

10

15

DOY

NE

E [

mo

l m-2

s-1

]

Vaira Ranch, 2007

50 100 150 200 250 300 350-30

-25

-20

-15

-10

-5

0

5

10

15

20

DOY

NE

E [m

ol

m-2 s

-1]

Tonzi Ranch, 2007

‘Ecosystem Breathing’

Ione, CA

Hydrological Year

00-01 01-02 02-03 03-04 04-05 05-06 06-07 07-08

NE

E (

gC m

-2 y

-1)

-200

-100

0

100

200

300

oak savanna annual grassland

Oak Woodlands are Risk Adverse, they Experience less inter-annual variation in NEE than Grasslands

Oak Woodlands are Carbon Sinks, -92 +/- 43 gC m-2 y-1

Annual Grasslands are Carbon Neutral, 30 +/- 116 gC m-2 y-1

Carbon Fluxes Scale with Spring Rainfall

Open Grassland

PPT3-6 (mm)

0 50 100 150 200 250 300

Ann

ual 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 et al, 2007 AgForMet

John Battle's biometric NPP = 235 gC m-2 y-1.

NPP = GPPtree - Ra_tree - Rh = 299 gC m-2 y-1

NPP=NEP+Rh=97+186=283 gC m-2 y-1.

Net Primary Productivity

Interannual Variability in NEE

d GPP/dt

-400 -300 -200 -100 0 100 200 300 400

d R

eco/

dt

-400

-300

-200

-100

0

100

200

300

400

California Savanna and Annual Grassland

dGPP/dt

-600 -400 -200 0 200 400 600 800

dR

eco

/dt

-400

-200

0

200

400

600

TreesAnnual GrasslandWoodland understoryOak-grass savanna

b[0] 28.21b[1] 0.605r ² 0.878

Interannual Variability inGPP and Reco scale with oneanother

ESPM 2, The Biosphere

PhotoDegradation Can Be a Important Pathway for Carbon Loss in Semi-Arid Rangelands (~20-30 gC m-2 season-1)

200 400 600 800 1000-0.5

0

0.5

1

1.5

2

2.5

3

3.5

4

4.5

5

Rglobal

W m-2

FC

O2

mol

e m

-2 s

-12007

soil CO2 flux-gradienteddy covariance

274 276 278 280 282 284 286 288

-1

0

1

2

3

4

5

6

7

8

9

DOY

NE

E [

m

ol

m-2

s-1

]

Vaira 2008

Sustained and Elevated Respiration after Fall Rain

Impacts of Photosynthesis and rain pulse on ecosystem respiration of the Oak Woodland

Day

150 200 250 300 350

Fc

( m

ol m

-2 s

-1)

0

1

2

3

4

5

6

understoryopen grassland

Baldocchi et al, JGR, Biogeosciences, 2006

Soil tempreture (oC)

30 35 40 45 50

0.15

0.20

0.25

0.30

0.35

0.40

0.45

0.50

14:50h

6hFo=0.037e0.0525T, Q10=1.69, R2=0.95

Tonzi Open areas

Soil temperature (oC)

25 30 35

1.1

1.2

1.3

1.4

1.5

1.6

1.7

Under treesDOY 211

Fu=0.337e0.0479T, Q10=1.61, R2=0.80

20h

6h

12:50h12h

16h

Tonzi Under trees

10h

24h

Tang, Baldocchi, Xu, Global Change Biology, 2005

Respiration and Photosynthesis

Controls on Ecosystem Respiration of the Grassland:Soil Moisture, Phenology (reproduction), Temperature and Rain Pulses

Soil volumetric water content (m3 m-3)

0.0 0.1 0.2 0.3 0.4

Rec

o/R

ref

0.0

0.5

1.0

1.5

2.0Fast growth period data

Rain pulse

Xu + Baldocchi, AgForMet 2004

Remote Sensing of Canopy Structure and NPP

Grassland CO2 flux vs Sunlight at different LAI

FC ( m

ol m

-2s-1

) -20

-15

-10

-5

0

5

FC ( m

ol m

-2s-1

)

-20

-15

-10

-5

0

5

Qp (mol m-2s-1)

0 500 1000 1500 2000-25

-20

-15

-10

-5

0

5

0 500 1000 1500 2000-25

-20

-15

-10

-5

0

5

(a) DOY025-040, LAI=1.0(b) DOY071-080, LAI=1.8

(c) DOY096-105, LAI=2.4

(d) DOY130-140 end of senesence

Xu + Baldocchi, AgForMet 2004

ESPM 111 Ecosystem Ecology

Annual Grassland, 2004-2005

Wavelength (nm)

400 500 600 700 800 900 1000

Ref

lect

ance

0.0

0.2

0.4

0.6

0.8

1.0

Oct 13, 2004Oct 27, 2004Nov 11, 2004Jan 5, 2005Feb 2, 2005Apr 1, 2005Mar 9, 2005May 11, 2005Dec 29, 2005

Ryu, Ma, Falk, Sonnentag, Baldocchi, submitted Frontiers of Ecology

Refining Spectral Vegetation Indices for Remote Sensing of Fluxes from Space

Remote Sensing and Ecosystem Metabolism

Jingfeng Xiao and D Baldocchi

area-averaged fluxes of NEE and GPP were -150 and 932 gC m-2 y-1

net and gross carbon fluxes equal -8.6 and 53.8 TgC y-1

Upscale GPP and NEE to the Biome Scale

Conclusions

• Oak Woodlands are Carbon Sinks, Grasslands are Carbon Neutral

• Year to year variability in Carbon Uptake is due to length of wet season.– Oaks are risk adverse and experience less inter-annual variability in

NEE than grasslands• Photosynthesis and Respiration are tightly linked

– Oaks need high N levels to attain sufficient rates of carbon assimilation for the short growing season

• Savanna woodlands need about 80 mm more water to function than nearby grasslands– Trees tap ground-water to sustain themselves during the summer

• Oaks are darker and warmer than grasslands

Biometeorology Team

Funding: US DOE/TCP; WESTGEC; Kearney; Ca Ag Expt Station

Annual Precipitation ~500 - 700 mm/yMean Annual Temperature ~ 14-16 C

Climate Trends: Pardee, CA

1940 1950 1960 1970 1980 1990 2000 2010

Me

an

te

mp

era

ture

(oC

)

14.5

15.0

15.5

16.0

16.5

17.0

17.5

18.0

1940 1950 1960 1970 1980 1990 2000 2010

Pre

cip

itat

ion

(m

m/y

ear)

0

200

400

600

800

1000

1200

Temperature Increased by about 1.25 C over 50 Years;Precipitation Trend is Flat, but with High Inter-annual Variation