Carbon & Water Exchange of an
Oak-Grass Savanna Ecosystem
Dennis Baldocchi
Biometeorology Lab, ESPM
University of California, Berkeley
Oak-Grass Savanna: A Two Layer System
Winter:
Trees deciduous; grass green
Spring:
Trees green;grass green
Summer:
Trees green; grass dead
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'
Fluctuation
Mean
Ecosystem Ecology
‘Ecosystem Breathing’
Vaira Ranch, 2007
15
10
0
-2 -1
NEE [  mol m s ]
5
-5
-10
-15
-20
-25
50
100
150
200
250
300
250
300
350
DOY
Tonzi Ranch, 2007
20
15
10
-2 -1
NEE [  mol m s ]
5
0
-5
-10
-15
-20
-25
-30
50
100
150
200
DOY
350
Oak Woodlands are Carbon Sinks, -92 +/- 43 gC m-2 y-1
Annual Grasslands are Carbon Neutral, 30 +/- 116 gC m-2 y-1
Ione, CA
300
oak savanna
annual grassland
-2
-1
NEE (gC m y )
200
100
0
-100
-200
00-01
01-02
02-03
03-04
04-05
05-06
06-07
07-08
Hydrological Year
Oak Woodlands are Risk Adverse, they Experience
less inter-annual variation in NEE than Grasslands
Carbon Fluxes Scale with Spring Rainfall
Open Grassland
Savanna
Annual Flux (gC m-2)
1200
1000
800
GPP
Reco
NEE
600
400
200
0
-200
0
50
100 150 200 250 300 0
PPT3-6 (mm)
Ma et al, 2007 AgForMet
50
100 150 200 250 300
PPT3-6 (mm)
Net Primary Productivity
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.
Interannual Variability in NEE
400
300
200
Interannual Variability in
GPP and Reco scale with one
another
0
-100
-200
-300
-400
-400
-300
-200
-100
0
100
200
300
400
d GPP/dt
California Savanna and Annual Grassland
600
400
dReco/dt
d Reco/dt
100
Trees
Annual Grassland
Woodland understory
Oak-grass savanna
200
0
b[0] 28.21
b[1] 0.605
r ² 0.878
-200
-400
-600
-400
-200
0
200
dGPP/dt
400
600
800
ESPM 2, The Biosphere
PhotoDegradation Can Be a Important Pathway for
Carbon Loss in Semi-Arid Rangelands (~20-30 gC m-2 season-1)
2007
5
soil CO2 flux-gradient
eddy covariance
4.5
4
2
FCO  mole m s
-2 -1
3.5
3
2.5
2
1.5
1
0.5
0
-0.5
200
400
600
Rglobal W m-2
800
1000
Sustained and Elevated Respiration after Fall Rain
Vaira 2008
9
8
-2 -1
NEE [  mol m s ]
7
6
5
4
3
2
1
0
-1
274
276
278
280
282
DOY
284
286
288
Impacts of Photosynthesis and rain pulse on ecosystem
respiration of the Oak Woodland
6
understory
open grassland
Fc (mol m-2 s-1)
5
4
3
2
1
0
150
200
250
Day
Baldocchi et al, JGR, Biogeosciences, 2006
300
350
Respiration and Photosynthesis
Tonzi Under trees
Tonzi Open areas
0.50
1.7
14:50h
0.45
12:50h
Under trees
DOY 211
1.6
12h
0.40
1.5
0.35
16h
10h
1.4
0.30
20h
1.3
0.25
Fo=0.037e0.0525T, Q10=1.69, R2=0.95
6h
0.20
6h
1.2
0.15
30
35
40
45
50
24h
Fu=0.337e0.0479T, Q10=1.61, R2=0.80
1.1
25
o
Soil tempreture ( C)
Tang, Baldocchi, Xu, Global Change Biology, 2005
30
35
o
Soil temperature ( C)
Controls on Ecosystem Respiration of the Grassland:
Soil Moisture, Phenology (reproduction), Temperature and Rain Pulses
2.0
Fast growth
period data
Reco/Rref
1.5
Rain pulse
1.0
0.5
0.0
0.0
0.1
0.2
0.3
Soil volumetric water content (m3 m-3)
Xu + Baldocchi, AgForMet 2004
0.4
Remote Sensing of Canopy Structure and NPP
5
5
0
0
-5
-5
-10
-10
-15
-15
-20
-20
(a) DOY025-040, LAI=1.0
(b) DOY071-080, LAI=1.8
5
5
0
0
-5
-5
-10
-10
-15
-15
(d) DOY130-140
end of senesence
-20
(c) DOY096-105, LAI=2.4
-20
-25
-25
0
500
1000
1500
2000 0
Qp (mol m-2s-1)
Xu + Baldocchi, AgForMet 2004
500
1000
1500
2000
FC (mol m-2s-1)
FC (mol m-2s-1)
Grassland CO2 flux vs Sunlight at different LAI
Refining Spectral Vegetation Indices for
Remote Sensing of Fluxes from Space
Annual Grassland, 2004-2005
1.0
Reflectance
0.8
Oct 13, 2004
Oct 27, 2004
Nov 11, 2004
Jan 5, 2005
Feb 2, 2005
Apr 1, 2005
Mar 9, 2005
May 11, 2005
Dec 29, 2005
0.6
0.4
0.2
0.0
400
500
600
700
800
900
1000
Wavelength (nm)
Ryu, Ma, Falk, Sonnentag, Baldocchi, submitted Frontiers of Ecology
ESPM 111 Ecosystem Ecology
Remote Sensing and Ecosystem Metabolism
Upscale GPP and NEE to the Biome Scale
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
Jingfeng Xiao and D Baldocchi
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/y
Mean Annual Temperature ~ 14-16 C
Climate Trends: Pardee, CA
Temperature Increased by about 1.25 C over 50 Years;
Precipitation Trend is Flat, but with High Inter-annual Variation
1200
18.0
1000
Precipitation (mm/year)
Mean temperature (oC)
17.5
17.0
16.5
16.0
15.5
600
400
200
15.0
14.5
1940
800
1950
1960
1970
1980
1990
2000
2010
0
1940
1950
1960
1970
1980
1990
2000
2010