modeling forest ecosystem energy, carbon and water fluxes: impacts of canopy structure conghe song...
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Modeling Forest Ecosystem Modeling Forest Ecosystem Energy, Carbon and Water Energy, Carbon and Water Fluxes: Impacts of Canopy Fluxes: Impacts of Canopy
StructureStructure
Conghe SongConghe Song
Department of GeographyDepartment of Geography
University of North Carolina University of North Carolina
Chapel Hill, NC 27599Chapel Hill, NC 27599
Small Leaves do the Big JobSmall Leaves do the Big Job
26126roplastlight/Chlo
22 O6OHCO6H6CO
CO2
H2O
Losing water is the price to pay for gaining CO2
stoma
Underside
Sunlit and Shaded leavesSunlit and Shaded leaves
phot
osyn
thes
is
Light intensity
Sunlit leaves
Shaded leaves
leavessunlit leaves shaded
lightdirect light diffusePSN
leavessunlit
lightdirect PSN
leaves shaded
light diffusePSN
I1 I2 I3
Research Question
What are the impacts of canopy structure on energy balance, carbon assimilation and transpiration?
Uniform CanopyGappy Canopy
Intercepted Radiation (two leaf scaling up)
Photosynthesis
Transpiration
Eco-physiological
models
Impacts of Canopy Structure on Ecosystem Processes
Sources of Data for Model VerificationSources of Data for Model Verification
AmeriFluxTower
Duke Forest FACE Site
Measured Data: net radiation, evapotranspiration, net ecosystem exchange during May to Sept for 2001, 2002, 2003
Pine density:1377~1299 trees/ha
Understory hardwoods:1470~1389 trees/ha
Leaf area index:
4.7-5.9
Tow-layer Canopy for the Loblolly Pine at DFTow-layer Canopy for the Loblolly Pine at DF
Each layer is independent of the other layer so that the gaps are calculated separately and then an overall gap probability is derived for the entire canopy.
broadleaflayer
Coniferlayer
Model InputsModel Inputs
Incoming radiationIncoming radiationPrecipPrecipAir tempAir tempSoil tempSoil tempSoil moistSoil moistWind speedWind speedVPDVPDLAILAI
All input data are obtained from the on-site measurements.
Net Radiation
Q
Qr
La
Ls
assn LLQR )1(
Radiation Budget:
Energy Budget: Net radiation is used for heat storage in the soil and plant body, evaporate water (latent heat), heating the air near the surface (sensible heat), and photosynthesis
aaa
sss
TL
TL
0.84c0.84c)-(1 0a a
7
1
a0 24.1
a
a
T
e
,7.0/0.1c c
95.0s
Verification of Net RadiationVerification of Net Radiation
y = 1.0501x
R2 = 0.9010RMSE=1.6062
0
5
10
15
20
25
0 5 10 15 20 25
UCR Modeled Rn (MJ/m2/daytime)
Measu
red R
n (M
J/m
2 /dayt
ime)
y = 0.9996x
R2 = 0.9528RMSE=1.0055
0
5
10
15
20
25
0 5 10 15 20 25
GCR Modeled Rn (MJ/m2/daytime)
Mea
sure
d R
n (M
J/m
2 /day
time)
Latent Heat (Evapotranspiration)Latent Heat (Evapotranspiration)
Transpiration Evaporation
Uniform Canopy vs. Gappy Canopy (two-leaf scaling up)
+ = Evapotranspiration
H2O
H2O
)(1γΔ
)]()([ρcΔ
sw
a0
spanT
gg
TeTegRLE
Verification of Latent Heat
0
50
100
150
200
250
300
350
400
450
0 1 3 4 6 7 9 10 12 13 15 16 18 19 21 22
Hours of Day
ET
(w
/m2)
Gappy Canopy
Uniform Canopy
Tower Measured
Carbon Assimilation
Plant Transpiration
NetPSN
)(C iascn CgA
s
n0sc mg
C
hAg
dj
vn min R
A
AA
)O/K1(K
)Γ(
OCi
*cmax
v
C
CVA i
*i
*i
j 5.105.4
)(
C
CJA
Verification of Net Carbon Assimilation
y = 0.8827x
R2 = 0.5866RMSE=1.7266
0
2
4
6
8
10
12
14
0 2 4 6 8 10 12 14
UCR Modeled A (gC/m2/daytime)
Tow
er G
EP
(gC
/m2/d
aytim
e)
y = 0.9787x
R2 = 0.5883RMSE=1.34
0
2
4
6
8
10
12
14
0 2 4 6 8 10 12 14
GCR Modeled A (gC/m2/daytime)
To
we
r G
EP
(g
C/m
2/d
ayt
ime
)
ConclusionsConclusions
Canopy structure has significant impacts on energy interception, carbon assimilation, and transpiration.
A gappy canopy allows more radiation passing through the canopy to reach the forest floor and helps plants trap more heat.
A uniform canopy can lead to overestimate of carbon assimilation and transpiration by plants.