Slideshow

Modelling of light transmission under heterogeneous forest canopy Da SILVA David, BALANDIER Philippe, BOUDON Frédéric, André MARQUIER, Christophe PRADAL, Christophe GODIN, SINOQUET Hervé

Light influence Transmited irradiance

Understorey microclimate : Light, temperature, air humidity, …

Soil water, soil temperature FSPM 07 - Napier

Flora, wildlife, regeneration saplings

Soil biological activity, humus

Understorey developement Relative Biodiversity

Maximum  biodiversity

Classical forest flora

Regeneration

Invasion by  competitives species

Bare soil 0

10

20 30 Transmittance (%)

40

50

Larch stands, France and Belgium FSPM 07 - Napier

[Balandier et al., Forestry, 2006]

Objectives • Determine a minimal set of simple measurements to obtain satisfactory light transmission classes  Basal area  Height  Closest neighbour distance

• General model  Coarse or detailed parametrization  Mono or multi-scale

• Output : light transmission classes FSPM 07 - Napier

Method • Model developement • Starting from detailed description of stand at tree scale • Sensitivity analysis  spatial distribution, clustering  size of tree crown  shape and orientation of tree crown

• Simplify the measures requirement FSPM 07 - Napier

Light interception model • Porous envelope based • Fraction of light intercepted is related to the crown projection area and its envelope projection area in the direction

= FSPM 07 - Napier

x 0.93

Light interception model • Crown discretization using regularly spaced beams • Beam opacity evaluation according to components distribution hypothesis Known positions

Uniform distribution

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[Sinoquet et al., 2005]

Experimental unit Buffer zone, no light measurement

Light measurements : • PAR sensors • Hemispherical photos

Interest zone 64 PAR sensor grid

Tree height Tree height

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Dendrometric measures : • X, Y positions • Total height • Base crown height • DBH (diameter at breast height) • 4 to 8 crown radii

Light measurements Grid of PAR Sensor

[Chaboche K., 2006]

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Full light reference

Crowns opacity Thresholding and pixel count using PiafPhotem [UMR Piaf, INRA, Clermont-Ferrand]

Tree opacity = 93,5% FSPM 07 - Napier

Crown reconstruction using Skinned Surfaces Constructed from different profiles

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Stand reconstruction

Fitting the hulls to measured radii FSPM 07 - Napier

3D tree reconstruction using height informations

Computing direct & diffuse incident light • Direct light depending on latitude, longitude, julian day, time step, start and stop hour • Diffuse light simulated by 46 directions of Turtle Sky [Den Dulk 89] FSPM 07 - Napier

Simulation steps

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Simulation steps

Weighted merging according to elevation FSPM 07 - Napier

[Campbell G.S. and Norman J.M., 1998]

Combining direct and diffuse

Image are merged using PDIF ratio (diffuse PPFD / diffuse+direct PPFD)

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Extracting interest zone information Simulation Tree opacity = 93.5% Mean : 48.972 Std : 8.071

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Calibration Simulation Tree opacity = 93.5%

• Ongoing work • First results for one stand

Mean : 48.972 Std : 8.071

Measures

• Unsuficient edge • Unique opacity FSPM 07 - Napier

Mean : 38.081 Std : 9.455

Stand replication Simulation Tree opacity = 93.5% Mean : 42.68 Std : 12.08

Measures Mean : 38.081 Std : 9.455

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Calibration options • Duplicates positioning and/or introducing randomness • Use of porous wall as calibrating device • LAD determination to take beam travel distance in crown into account • Usage of the multi-scale possibilities of the model

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Multi-scale light interception model

Known positions

Uniform distribution

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[Sinoquet et al., 2005]

Perspectives (after calibration…)

• • • •

Stand type caracterization [Marie-Ange NgoBieng, 2007] Simulation of n stands Variability caracterization Sensitivity analysis  Spatial distribution  Crown shape  Intra and inter-tree clustering

• Determination of descriptors of main interest

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Acknowledgment Virtual Plants team

UMR Piaf

• CHAUBERT Florence • CHOPARD Jérôme • STOMA Szymon

• DONES Nicolas

ANR Project ECOGER

“Bases of mixed stands sustainable management of mixed stands: ecophysiology, growth and demogenetics of constitutive species.” Collaboration between INRA, the French National forestry commission and CEMAGREF FSPM 07 - Napier

Existing models • Simple : [Monsi & Saeki,1953 ; Ross, 1981] – Output = mean an std

• Layers : [Kimes & Smith, 1980 ; Hanan 2001 ] – Not adapted for heterogeneous stands

• 3D cells : [Kimes & Kirchner, 1982 ; Sinoquet et al., 2005] – Difficulty to characterize canopy cells in the field

• Tree crown : [Cescatti, 1997 ; Brunner, 1998 ; Canham et al., 1999] – Different level of shape complexity – High and fixed requirement

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