modeling forest ecosystem energy, carbon and water fluxes: impacts of canopy structure conghe song...

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Modeling Forest Modeling Forest Ecosystem Energy, Carbon Ecosystem Energy, Carbon and Water Fluxes: and Water Fluxes: Impacts of Canopy Impacts of Canopy Structure Structure Conghe Song Conghe Song Department of Geography Department of Geography University of North Carolina University of North Carolina Chapel Hill, NC 27599 Chapel Hill, NC 27599

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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

Big-Leaf Scaling upBig-Leaf Scaling up

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

Two-Leaf Scaling upTwo-Leaf Scaling up

Sunlit leaf

Shaded leaf

Uniform vs Gappy CanopyUniform vs Gappy Canopy

Uniform CanopyGappy Canopy

Sun flecks

Gap Effects on Light AbsorptionGap Effects on Light Absorption

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.