improving gpp, npp, and nee predictions from...
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Improving GPP, NPP, and NEE predictions from space
Improving GPP, NPP, and NEE predictions from space
I R S S
Richard Waring1
Nicholas Coops2
Joe Landsberg3
1 Oregon State University2 University of British Columbia
3 Mt Wilson, NSW 2786, Australia
Richard Waring1
Nicholas Coops2
Joe Landsberg3
1 Oregon State University2 University of British Columbia
3 Mt Wilson, NSW 2786, Australia
Photo: Courtesy of Auro Almeida
Eucalyptus plantationGPP =6,000 g C m-2 yr-1
Brazilian rainforestGPP =3,000 g C m-2 yr-1
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LAI
Eucalyptus Native forest
Brazilian plantation LAI decreases with age as trees approach 40 m in heightat 7 years when harvested. Drought reduces LAI more when stand is young than older
Drought
Auro Almeida, CSIRO Tasmania, unpublished
Drought
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Ava
ilabl
e so
il w
ater
(mm
)Eucalyptus Native forest
In the Atlantic Coastal Region of Brazil,native rainforests and eucalyptus plantations usesimilar amounts of water although LAI differs by > 2 fold.Reason: eucalypts are fertilized & have twice the photosynthetic
capacity and twice the max. canopy conductance ofthe rainforest.
Auro Almeida, CSIRO Tasmania, unpublished
Objective: to provide ecologicalinsights to improve predictions ofGPP, NPP, and NEE from space
I. GPP: set limits and identify constraints
II. NPP: allocation above and below ground
III. NEE: correlation with GPP
Ecosystem Model Structure
Waring, Coops, & Landsberg 2009 For. Ecol & Mgmt (in press)
Leaf chlorophyll conc. linearly related to maximum photosynthetic
capacity (link to soil fertility)
Waring et al. 1995. Plant Cell & Env. 18: 1201-1218. Zhang et al. 2009. Remote Sen. Env. 113: 880-888.
Leaf conductance (g) and photosynthetic capacity (A) decrease with (relative) tree height & hydraulic conductivity
(KL )
Ambrose et al. 2009. Plant, Cell & Env. 32: 743-757.Hubbard et al. 2001. Plant, Cell & Env. 24: 113-121.
Stomatal response to vpd varies by an order of magnitude among species in boreal forests
Dang et al. 1997. Tree Physiology 17: 521-535.
VPD response is a function of maximum canopy conductance
Stomatal sensitivity to vpd is a negative log function (slope =0.6) to maximum conductance at ≤
1 kPa (r2 = 0.75).
Oren et al. 1999. Plant, Cell & Env.22:1515-1535.
As the soil water deficit increases beyond a threshold, water loss through transpiration is progressively reduced below its potential as stomata close
Source: Landsberg & Gower 1997. Fig. 4.5. “Application of Physiological Ecology to Forest Management.” Academic Press, San Diego, CA
Eucalyptus maculata
Root depth determines access to water
28 m
Photo: courtesy of Keith Smettem,University of Western Australia
Eucalyptus
marginata
depth that roots penetrate
Photo: courtesy of E.D. Schulze
To evaluate soil water limitations, need to assess changes in canopy properties
(LAI, fPAR, PRI, & wetness)
Canadell et al. 1996. Oecologia 108:583-595
Photosynthetic Reflectance Index (Gamon et al. 1992. Rem. Sen. Env. 41:35-44)
Suarez et al. 2009. Rem.Sen. Env. 113:730-744.Trotter et al. 2002. Int. J. Rem. Sen.23: 1207-1212.
8 species in New Zealand Olive trees
Hall et al. 2008. Remote Sensing of Env. 112: 3201-3211
Douglas-fir (sunlite) Campbell River, B.C.
Partitioning of forest NPP below ground ranges from 20% to 60% (Waring et al. (1998). When GPP ≥
2500 g C m-2 yr-1
(respiration + NPPb ) ~ minimum
Litton et al.
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GPP, gC m-2 yr-1
Rat
io o
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NPP
Litton et al. 2007. Global Change Biology 13: 2080-2109Chen et al. 2003. Oecologia 137: 405-416Stape et al. 2008. For. Ecol. & Mgmt. 255: 920-930.Waring et al. 1998. Tree Physiol. 18:129-134.
tropical savanna
young ponderosa pine
aspen
black sprucejack pineold ponderosa pine
N =38
plantations
NEE varies seasonally by type of vegetation, as does GPP
After Baldocchi 2008 Aust. J. Bot. 56:1-26.
After Baldocchi 2008. Aust. J. Bot. 56:1-26.
Predicting Ecosystem Respiration or NEE (GPP-Reco )as a function of eddy-flux measured GPP
r2 = 0.9Δ=0.77
Δ=0.94
To improve predictions of GPP, NPP, and NEE from space
• Chlorophyll light absorbance is better than nitrogen content to estimate max. conductance and photosynthetic capacity.
• Max. conductance and photosynthetic capacity are reduced as trees approach site & species-specific maximum height.
• PRI is a good check on modeled constraints on GPP
• GPP is more important to estimate accurately than NPP, although NPPA would be helpful to validate model predictions of growth allocation.
• Allocation of NPP (& respiration) increases below-ground if water and nutrients are not available, generally not the case if GPP ≥
2500 g C m-2 yr-1.
• Ecosystem respiration is ~ 75% of GPP in undisturbed systems, ~ 95% in disturbed systems. Be able to distinguish disturbed systems & recovery.
Email:[email protected] Coops [[email protected]]Joe Landsberg [[email protected]]
Waring, Coops, & Landsberg. 2009. Improving predictions of forest growth using the 3-PGS model with observations made by remote sensing. For. Ecol. & Mgmt. (in press). (RHW Pub. No. 108). www.fsl.orst.edu/~waring