Laurent Misson*; Baldocchi DD; Black TA; Blanken PD; Brunet Y; Curiel Yuste J; Dorsey JR; Falk M; Granier A; Irvine MR; Jarosz N; Lamaud E; Launiainen

Laurent Misson*; Baldocchi DD; Black TA; Blanken PD; Brunet Y; Curiel Yuste J; Dorsey JR; Falk M; Granier A; Irvine MR; Jarosz N; Lamaud E; Launiainen S; Law BE; Longdoz B; Loustau D; McKay M; Paw U KT; Vesala T; Vickers D; Wilson KB; Goldstein AH

* University of California, Berkeleyand soon at CNRS, Montpellier

Funded by: Kearney Foundation of Soil Science, UC Agricultural Experiment Station, US Department of Energy (NIGEC)

Partitioning Forest Carbon Fluxes with Over- and Understory Eddy-Covariance

Most forests are vertically complex

Pinus ponderosa

Ceanothus cordulatus

Soil

Overstory

Understory

Most forests are vertically complex

Pinus ponderosa

Ceanothus cordulatus

Soil

Overstory

Understory

CO2

CO2

CO2

CO2

Photosynthesis

Respiration

CO2

CO2

CO2

CO2

Photosynthesis

Questions1/ how canopy density influences the coupling between overstory and understory meteo?

Respiration

CO2

CO2

CO2

CO2

Photosynthesis


Respiration

2/ how different forest types, structures, and climates influence CO2 flux partitioning?

CO2

CO2

CO2

CO2

Photosynthesis


3/ what factors control understory CO2 fluxes for these different forests?

Respiration

2/ how different forest types, structures, and climates influence CO2 flux partitioning?

Blodgett

Hesse

Le Bray

Tonzi

HyytialaWind River

Metolius

Aspen

Jackpine

Walker Branch

Synthesis Based on FLUXNET Data

• 6 evergreen / 4 deciduous

• 3 boreal, 4 temperate, 3 (semi)-arid

• LAI overstory [ 1 - 9.0 ] m2 m-2

• LAI understory [ 0 - 3.2 ] m2 m-2

10 Sites

CO2

CO2

• Aubinet et al. (2000) and Baldocchi et al. (2001)

• 1 year of summertime data at each site

• NEE above includes storage term (not below)

• GPP and respiration were separated using Q10

10 Sites

Methodology

• 6 evergreen / 4 deciduous

• 3 boreal, 4 temperate, 3 (semi)-arid

• LAI overstory [ 1 - 9.0 ] m2 m-2

• LAI understory [ 0 - 3.2 ] m2 m-2

Results

1/ Micrometeorology

2/ Flux partitionning

3/ Controlling factors

How canopy density influences temperature stratification ?


Tunder > Tover for low LAI

DAY

LAI

Tover – Tunder



Open forest: good mixingClosed forest: weaker mixing

DAY

LAI

Tover – Tunder




Tunder < Tover for low LAI

DAY

LAI

LAI

Tover – Tunder

Tover – Tunder

NIGHT




Tunder < Tover for low LAI

Open forest: strong inversionClosed forest: good mixing

DAY

LAI

LAI

Tover – Tunder

Tover – Tunder

NIGHT

How canopy density influences wind deflection ?

LAI

Wind Dirover – Wind Dirunder (º)


LAI


Wind is strongly defleted in dense forests probably because of stronger drag force


LAI


Wind is strongly defleted in dense forests probably because of stronger drag force

Overstory and understory flux footpint may be different

How much is the understory contribution to whole ecosystem fluxes ?

over

underover1F

FF in %

Understory Contribution


GPP

R(%)



GPP

R

• Evergreen = Deciduous (14%)• Semi-Arid > Temperate > Boreal

20% 13% 6%

(%)



GPP

R


20% 13% 6%

• Deciduous (62%) > Evergreen (49%)

Soil C:N = 16 Soil C:N = 31(%)



GPP

R


20% 13% 6%

• Deciduous (62%) > Evergreen (49%)

• Semi-Arid < Temperate = Boreal

44% 60% 60%

Soil C:N = 16 Soil C:N = 31(%)


What controls understory respiration fluxes across different forests ?

What controls understory respiration fluxes across different forests ?

Soil temperature (ºC)

Mean summertime respiration flux (µmol m-2 s-1)

NS

Normalized flux for soil temperature and soil moisture



R2 = 0.64FluxT,SM


R2 = 0.64FluxT,SM

Soil C (g C m-2)

R2 = 0.82

FluxT,SM



R2 = 0.64FluxT,SM

Soil C (g C m-2)

R2 = 0.82

FluxT,SM

Uncorrelated



R2 = 0.64FluxT,SM

Soil C (g C m-2)

R2 = 0.82

FluxT,SM

Uncorrelated

Partial evidence that respiration acclimates to temperature Zogg et al. 1997, Zhang et al. 2005, Atkin et al. 2005


Relative soil moisture

R2 = 0.67

FluxT,C

Normalized flux for soil temperature and soil carbon

Relative soil moisture

R2 = 0.67

Microbial metabolic activity limited by soil moisture

Normalized flux for soil temperature and soil carbon

FluxT,C

GPP ecosystem (µmol m-2 s-1)

R2 = 0.78


Slope = 0.23

GPP ecosystem (µmol m-2 s-1)

R2 = 0.78

Understory respiration is linked to gross primary productivity


Slope = 0.23

Conclusion

Conclusion

• Eddy-Covariance method: able to measure understory fluxes for a wide range of forest types, structures and climates

Conclusion


• Problems: open forests night inversion dense forests different flux footprint

Conclusion



• Understory can contribute significantly to whole ecosystem CO2 sinks and sources, but variations across sites are important

Conclusion




• Understory LAI and light penetration are important factors influencing understory GPP

Conclusion




• Understory LAI and light penetration are important factors influencing understory GPP

• Substrate availability and quality, soil temperature and soil moisture are important factors for understory respiration

Documents

Laurent Misson*; Baldocchi DD; Black TA; Blanken PD; Brunet Y; Curiel Yuste J; Dorsey JR; Falk M; Granier A; Irvine MR; Jarosz N; Lamaud E; Launiainen