Upload
randolf-newton
View
213
Download
0
Tags:
Embed Size (px)
Citation preview
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