dennis baldocchi biometeorology lab, espm university of california, berkeley
Post on 24-Feb-2016
77 Views
Preview:
DESCRIPTION
TRANSCRIPT
Carbon & Water Exchange of California Rangelands:An Oak-Grass Savanna, Annual Grassland and Peatland
Pasture Ecosystem
Dennis BaldocchiBiometeorology Lab, ESPM
University of California, Berkeley
Scientific and Management Questions
• What are the magnitudes and temporal variability of the exchanges of energy, CO2 and water vapor in terrestrial ecosystems?– Is my rangeland a Carbon Sink?– If, not, How can I manage it to become one?
• How does climate, vegetation type, physiological conditions phenology, changes in land use, management and disturbance history modulate the exchange of energy, carbon and water; and vice versa?– Can my rangeland off-set global warming?– Can it conserve water for the watershed and reservoir?
Take Home Messages
• Oak Woodlands are modest Carbon Sinks, Grasslands are Carbon Neutral, & Peatland pastures are Carbon Sources
• Year-to-year variability in Carbon Uptake is due to length of the wet season.– Oaks are risk adverse and experience less inter-annual variability in NEE
than grasslands• Savanna woodlands use/need more water than annual grasslands
– Trees tap ground-water to sustain themselves during the summer• Oak woodlands are darker and warmer than annual grasslands
Oak-SavannaTonzi Ranch Flux Tower
Annual GrasslandVaira Ranch
Oak-Grass Savanna: A Two Layer System
Summer:Trees green; grass dead
Spring:Trees green;grass green
Winter:Trees deciduous; grass green
Oak-Grass Savanna are Model Systems for Studying Ecosystem Ecology
• Structure/Function– Oak and grasses provide contrasting life forms, woody/herbaceous,
perennial/annual– The Canopy is open and heterogeneous
• gives us a opportunity to test the applicability of ecosystem and biogeophysical models, 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.
Sherman Island Peatland Pasture
Peatland Pastures are a Model for studying Land Subsidence and Carbon Management in the Delta
Background Conditions
http://www.carolsatriani.com/img0005.html
Annual Precipitation ~500 - 700 mm/yMean Annual Temperature ~ 14-16 C
Cool Wet, Winters...Hot, Dry Summers
Camp Pardee, CA
Climate Trends: Pardee, CA
1940 1950 1960 1970 1980 1990 2000 2010
Mea
n te
mpe
ratu
re (o C
)
14.5
15.0
15.5
16.0
16.5
17.0
17.5
18.0
1940 1950 1960 1970 1980 1990 2000 2010
Prec
ipita
tion
(mm
/yea
r)
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
Environmental Conditions
Ma et al, in prep
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
Results and Discussion
http://www.terrysteinke.com/pixpages/etchingpages/valleyoak.html
50 100 150 200 250 300 350-25
-20
-15
-10
-5
0
5
10
15
DOY
NEE
[m
ol 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
NEE
[ mol
m-2 s-1 ]
Tonzi Ranch, 2007
‘Breathing of the Ecosystem’
0 100 200 300 400 500 600 700 800-6
-4
-2
0
2
4
6
DOY after Jan 2008
nee
(gC
m-2
d-1
)
Sherman Island Peatland Pasture
NEE = +27 gC m-2 y-1, 2008NEE = +82 gC m-2 y-1, April, 2007-April ,2008
mowing
Pasture is a Carbon Source
Ione, CA
Hydrological Year
00-01 01-02 02-03 03-04 04-05 05-06 06-07 07-08
NE
E (g
C 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
Perspective
16.86 sheets of 8 ½ by 11 inch paper is 1 m2 in area and equals 76 g
Carbon Fluxes Scales 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
Vaira Grassland + Sierra Foothills
Year
1975 1980 1985 1990 1995 2000 2005
DM
(gD
M m
-2)
0
100
200
300
400
500
600
700
800
data of Bill Frost, L Xu, S Ma and D Baldocchi, Mel George et al
Dry Matter Production, Grasslands
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
dRec
o/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
274 276 278 280 282 284 286 288
-1
0
1
2
3
4
5
6
7
8
9
DOY
NEE
[m
ol m
-2 s
-1]
Vaira 2008
Sustained and Elevated Rates of 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
Remote Sensing of Canopy Structure and NPP
IKONOS: 1 m resolution in b/w; 4 m res. in color
LIDAR Measurement of Tree Height
-600 -400 -200 0 200 400 600-600
-400
-200
0
200
400
600tree height; mean=9.6299 m
0
5
10
15
20
25
30
35
40
Vaira 2006-2007
DOY
30 60 90 120 150 180 210 240 270 300 330 360 390 420 450 480 510 540
ND
VI (a
vera
ge 1
000
to 1
500)
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1.0
GPP
(gC
m-2
day
-1)
0
2
4
6
8
10
12
NDVIGPP
Canopy Photosynthesis Follows changes in Canopy Structure
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
Water, Energy and Evaporation
http://www.carolsatriani.com/2019.html
Sherman Island Peatland Pasture, April 2007-2008
Week
0 10 20 30 40 50
ET
(mm
wee
k-1)
0
5
10
15
20
25
30
ET= 731 mm y-1
Evaporation from Irrigated Pasture
Inter-annual Variation in Rain and EvaporationTonzi Ranch, Ione, CA
Year
2001 2002 2003 2004 2005 2006 2007 2008 2009
E,P
(mm
y-1
)
300
400
500
600
700
800
900
EP
On Average, Woodland Uses 410 mm of Water on 540 mm of Rain
156 158 160 162 164 166158
158.02
158.04
158.06
158.08
158.1
158.12
158.14
158.16
158.18
158.2
DOY
grou
nd w
ater
ele
vatio
n [m
]groundwater elevation at Tonzi
G. Miller, Y. Rubin, D. Baldocchi unpublished data
Oak Trees Tap Ground Water, and Must to Survive
G. Miller, Y. Rubin, S. Ma, D. Baldocchi unpublished data
Oak Trees Access a Significant Fraction of Water from Water Table
Role of Land Management on Water and Energy Exchange and Climate
Case Study:Savanna Woodland vs Grassland
2006
Day
0 50 100 150 200 250 300 350
Air
Tem
pera
ture
(C)
0
10
20
30
40GrasslandSavanna
Mean Potential Temperature difference Equals 0.84 C; grass: 290.72 K vs savanna: 291.56 K
2006, Ione, CA
Potential Temperature, Grassland
275 280 285 290 295 300 305 310 315
Pote
ntia
l Tem
pera
ture
, Oak
Sav
anna
275
280
285
290
295
300
305
310
315
b[0] -2.67b[1] 1.012r ² 0.953
Oak Woodlands are Warmer than Grasslands
2006
Day
0 50 100 150 200 250 300 350
Ene
rgy
Flux
Den
sity
(MJ
m-2
d-1
)
0
5
10
15
20
25
30
35
Solar RadiationNet Radiation, GrasslandNet Radiation, Savanna
1. Savanna absorbs much more Radiation (3.18 GJ m-2 y-1) than the Grassland (2.28 GJ m-2 y-1) ; DRn: 28.4 W m-2
Available Energy Drives Heat Exchange and Evaporation
u*, oak woodland, daily average
0.0 0.2 0.4 0.6 0.8 1.0
u*, g
rass
land
, dai
ly a
vera
ge
0.0
0.1
0.2
0.3
0.4
0.5
2002
Tall and Rougher Savanna Promotes Turbulent mixing over Short, Smoother Grassland
Savanna injects more Sensible Heat into the atmosphere because it has more Available Energy and it is Aerodynamically Rougher
2006
Day
0 50 100 150 200 250 300 350
Sen
sibl
e H
eat F
lux
Den
sity
(MJ
m-2
d-1)
0
2
4
6
8
10
12
14GrasslandSavanna
Gs (mm s-1)
0 2 4 6 8 10 12 14 16
LE/L
Eeq
0.0
0.2
0.4
0.6
0.8
1.0
Savanna WoodlandAnnual Grassland
Monthly Averages
Landscape Differences on Short Time Scales:Grass ET > Forest ET
California Savanna
Hydrological Year
N.a.N. 01_02 02_03 03_04 04_05 05_06 06_07
Eva
pora
tion
(mm
y-1
)
240
260
280
300
320
340
360
380
400
420
440
Oak WoodlandAnnual Grassland
Role of Land Use on ET on Annual Time Scales:Annual Oak ET (400 +/-35 mm/y) > Grass ET (322 +/-48 mm/y)
Photosynthesis >Respiration
DOY100 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)
CO2
Ps Capacity must be Great,For Short Period to Facilitatehigh rates of photosynthesis
Leaf N and Leaf Thicknessmust be adequate tosupport Ps Machinery
At Ecosystem scale LeafArea is limited enabling theSparse Canopy to Reduce
ET, too
20 40 60 80 100 120 140 160 180
20
40
60
80
100
120
140
160
180
200
Broadleaved, Deciduous Trees
Specific Leaf Area (m2 g-1)
60 80 100 120 140 160 180 200
Am
ass
(nm
ol g
-1 s
-1)
0
50
100
150
200
250
300
Quercus douglasii
data of Reich et al and Xu and Baldocchi
v (%
)
0.0
0.1
0.2
0.3
0.4
0.5
0.6
0.05 m0.50 m
Savanna, 2005
Day
0 50 100 150 200 250 300 350
Wat
er F
lux
0
100
200
300
400
500
600
700
ET ppt
E T (m m d-1
)
0 1 2 3 4
GP
P (
gC
m-2d-1
)
0
2
4
6
8
10
Synthesis/Conclusions
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; NASA; WESTGEC; Kearney; Ca Ag Expt Station
Questions
• How would you use these data to make land mgt Decisions?– Are you compelled to cut-trees for grass, to save water and
cool the climate?• What about Topography and the role of trees to maintain soils and
serve as habitat– Encourage trees on grasslands to sequester carbon?
• Do you have enough rain?– Should Delta Peatland Pastures revert back to tules and
wetlands?• What about methane emissions (20x CO2), mosquitoes and water
quality?
Annual ET and Interannual Variation
Vaira 2004
Day
0 50 100 150 200 250 300 350
E (m
m d
-1)
0
1
2
3
4
5
2001: 301 mm 2002: 292 mm 2003: 353 mm 2004 : 284 mm
Savanna Soil Stores about 80 mm water and uses that much extra to sustain a sparse woodland, over a grassland
Oak Savanna
Day
0 50 100 150 200 250 300 350
ET
(mm
d-1
)
0
1
2
3
4
5
2002: 389 mm2003: 422 mm2004: 340 mm2005: 484 mm2007: 385 mm2008: 350 mm
Canopy Structure:Laser Altimeter Data
Goals of Research
• Quantify the Biophysical Controls on Ecosystem Metabolism (carbon gains and losses) and Water Balance of Oak Woodlands and Peatland Pastures
• Quantify and understand mechanisms controlling net annual budgets and inter-annual variability of carbon, water and energy exchange of oak woodland and annual grassland and Peatland Pastures
• Produce predictive and mechanistic ability to quantify future conditions, e.g. global warming, elevated CO2 and ozone, perturbed water supply, and land use change, land subsidence, methane emissions and in order to manage rangelands
• Upscale fluxes to the region for management decisions
Kueppers et al 2005 PNAS
IKONOS:Grassland
Sherman Island Peatland Pasture
365 456 547 639 730 821 912 1003 10950.01
0.10
1.00
10.00
100.00
1000.00
At-mo-sphereLeaf MiddayLeaf Predawn
Day after 1/1/2006
Tota
l Wat
er P
oten
tial (
MPa
)
G. Miller 2009, PhD Dissertation
Evidence of Trees Tapping Ground Water
Grassland
weighted by roots (cm3 cm-3)
0.00 0.05 0.10 0.15 0.20 0.25 0.30 0.35 0.40
E/ E eq
0.00
0.25
0.50
0.75
1.00
1.25
summer rain
Oak Savanna
weighted by roots(cm3 cm-3)
0.00 0.05 0.10 0.15 0.20 0.25 0.30
E/ E eq
0.0
0.2
0.4
0.6
0.8
1.0
ET and Soil Water Deficits:Root-Weighted Soil Moisture
Baldocchi et al., 2004 AgForMet
Grassland
weighted by roots (cm3 cm-3)
0.00 0.05 0.10 0.15 0.20 0.25 0.30 0.35 0.40
E/ E eq
0.00
0.25
0.50
0.75
1.00
1.25
summer rain
Oak Savanna
weighted by roots(cm3 cm-3)
0.00 0.05 0.10 0.15 0.20 0.25 0.30
E/ E eq
0.0
0.2
0.4
0.6
0.8
1.0
Dynamics of Grassland Canopy Structure
Annual Grassland, Vaira Ranch
Day of Year
-100 -50 0 50 100 150 200
Leaf
Are
a In
dex
0.0
0.5
1.0
1.5
2.0
2.5
3.0
2001-20022002-20032003-20042004-2005
Grass Understory, Tonzi Ranch
Day of Year
-100 -50 0 50 100 150 200
Leaf
Are
a In
dex
0.0
0.5
1.0
1.5
2.0
2.5
3.0
2001-20022002-20032003-20042004-2005
top related