Is There Utility in Simulating Ecosystem-Level Fluxes as a Collection of Fluxes

from Individual Species?

Ian BakerColorado State University

Department of Atmospheric Science/GDPE

With help from:Ken Davis; PSU

Vince Gutschick, Connie Maxwell, Mario Montes-Helu, Erika Mortenson, Alonzo

Soto, Felicia Najera, and Erik Jackson; NMSUJoe Berry, Bob Haxo, Carnegie Institute of Washington

A. Scott Denning, Neil Suits, Niall Hanan; CSU

Motivation/Background

Comparison of model results (SiB) to observations

•Ewers et al (2002) - transpiration calculated from sap flux data

•Vince Gutshick – observations (LI-6200) at the leaf level (i.e. stomatal control, carboxylation capacity)

•Joe Berry – provided a suite of programs that can derive SiB-type vegetation parameters from leaf-level observations

The Model: SiB2

Simple Biosphere Model, version 2 (SiB2) Sellers et al. 1996• Biophysical land surface model• Describes heat, water and carbon transfers in the soil, vegetation, atmosphere continuum• Developed for general circulation models• Useful at many scales, globe to point• Single canopy layer scheme• Highly non-linear• Large number of input parameters

In SiB, WLEF site is ‘mixed forest’-biome 3. All biome 3 sites are parameterized identically wrt time-invariant properties

SiB Vegetation Params:

•20 time-invariant biome-specific variables

•13 soil properties (moisture, thermal and respiration)

•8 NDVI-derived time-varying phenological variables (heterogeneous in space)

•Canopy height•Vegetation fractional cover•Leaf angle distribution•Transmittance/reflectance•Rubisco velocity of sun-leaf•Quantum efficiency (C3/C4)•BB slope/intercept•Coupling parameters for eqn A=min(ωc,ωe,ωs)•Low-and high-temperature inhibition functions•Canopy respiration factors •Respiration fraction of Vmax

These are the variables that we can adjust•Vmax0•BB slope•BB intercept•respcp•hhti•atheta

SiB Time-Invariant Parameters

PROCEDURE

•Sort Vince Gutschick’s leaf-level obs by species•Obtain species-specific values of

•Vmax0 – maximum rubisco velocity•binter – BB intercept•gradm – BB slope•respcp – autotrophic respiration component•hhti – ½ point high-temp inhibition function•atheta – rubisco/light coupling factor

•Create a new SiB vegetation parameter file using these new values•Run SiB

Data from Ewers et al, 2002

Red pineJack pine

Sugar maple

Trembling aspenBalsam fir

White cedarBalsam firSpeckled alder

ASPEN/FIR

-1

0

1

2

3

4

5

6

0 0.2 0.4 0.6 0.8 1

VAPOR PRESSURE DEFICIT (kPa)

TR

AN

SP

IRA

TIO

N (m

m/d

ay)

Ec

Poly. (Ec)

Poly. (MIXED_FOREST)

Obs data asymptotes slightly above 3.0

OBS: trembling aspen, balsam firMODEL: trembling aspen, balsam firComparison looks quite good

CONIFER

-1

0

1

2

3

4

5

6

0 0.2 0.4 0.6 0.8 1

VAPOR PRESSURE DEFICIT (kPa)

TR

AN

SP

IRA

TIO

N (

mm

/day

)

CONIFER_Ec

Poly. (CONIFER_Ec)

Poly. (MIXED_FOREST)

Obs data asymptotes near 2.0

OBS: red pine, Jack pineMODEL: Balsam fir, spruce

WETLAND (Balsam fir, speckled alder)

-1

0

1

2

3

4

5

6

0 0.2 0.4 0.6 0.8 1

VAPOR PRESSURE DEFICIT (kPa)

TR

AN

SP

IRA

TIO

N (

mm

/da

y)

Ec

Poly. (Ec)

Poly. (MIXED_FOREST)

Obs data asymptotes near 2.0

OBS: dominated by white cedar, also balsam fir, speckled alder

MODEL: balsam fir, speckled alder

MAPLE (NORTHERN HARDWOODS)

0

0.5

1

1.5

2

2.5

3

3.5

4

4.5

5

0 0.2 0.4 0.6 0.8 1

VAPOR PRESSURE DEFICIT (kPa)

TR

AN

SP

IRA

TIO

N (m

m/d

ay)

maple_Ec

Poly. (maple_Ec)

Poly. (MIXED_FOREST)

Obs asymptotenear 1.0

OBS: sugar mapleMODEL: sugar maple

SOME QUESTIONS

•Is it reasonable to create species-specific model vegetation for certain parameters, when a number of them, including

•aparc-canopy absorbed PAR•LAI•roughness length•leaf projectionare determined from canopy-level NDVI observations?

•Are the values I obtained internally consistent for each of the species I investigated?

SOME MORE QUESTIONS

•Does this approach have the potential to lead to better simulation of fluxes of carbon, heat and moisture?

•Is there potential to utilize this approach in coupling SiB to mesoscale model(s) (RAMS)?•Will higher-resolution information (both on the

species and spatial/satellite scale) make species-specific land-atmosphere modeling more attractive?•Is the technique I’ve outlined adequate, or do the SiB parameters need to be made more fully self-consistent by including more parameters for each species?