Modelling of light transmission under heterogeneous forest canopy
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Transcript of Modelling of light transmission under heterogeneous forest canopy
Modelling of light transmission under heterogeneous forest canopy
Da SILVA David, BALANDIER Philippe, BOUDON Frédéric,André MARQUIER, Christophe PRADAL,
Christophe GODIN, SINOQUET Hervé
FSPM 07 - Napier
Light influence
Understorey microclimate :Light, temperature,
air humidity, …
Transmited irradiance
Soil water, soil temperature
Soil biological activity, humus
Flora, wildlife, regeneration saplings
FSPM 07 - Napier
Understorey developement
0 10 20 30 40 50
Rel
ativ
e B
iod
iver
sity
Transmittance (%)
Bare soil
Classicalforest flora
Maximum biodiversity
Invasion by competitives
speciesRegeneration
Larch stands, France and Belgium
[Balandier et al., Forestry, 2006]
FSPM 07 - Napier
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
= x 0.93
FSPM 07 - Napier
Light interception model
• Crown discretization using regularly spaced beams• Beam opacity evaluation according to components
distribution hypothesis
Known positions
Uniform distribution
[Sinoquet et al., 2005]
FSPM 07 - Napier
Light measurements :
• PAR sensors
• Hemispherical photos
Experimental unit
Dendrometric measures :
• X, Y positions
• Total height
• Base crown height
• DBH (diameter at breast height)
• 4 to 8 crown radii Tree height
Tree height
Buffer zone, no light measurement
64 PAR sensor grid
Interest zone
FSPM 07 - Napier
Crowns opacity
Thresholding and pixel countusing PiafPhotem[UMR Piaf, INRA, Clermont-Ferrand]
Tree opacity = 93,5%
FSPM 07 - Napier
Stand reconstruction
Fitting the hulls to measured radii
3D tree reconstruction using height informations
FSPM 07 - Napier
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
Weighted merging according to elevation [Campbell G.S. and Norman J.M., 1998]
FSPM 07 - Napier
Combining direct and diffuse
Image are merged using PDIF ratio(diffuse PPFD / diffuse+direct PPFD)
FSPM 07 - Napier
Extracting interest zone information
Tree opacity = 93.5%Simulation
Mean : 48.972Std : 8.071
FSPM 07 - Napier
Calibration
• Unsuficient edge
• Unique opacity
Measures
Mean : 38.081Std : 9.455
Tree opacity = 93.5%Simulation
Mean : 48.972Std : 8.071• Ongoing work
• First results for one stand
FSPM 07 - Napier
Stand replication
Tree opacity = 93.5%Simulation
Mean : 42.68Std : 12.08
Measures
Mean : 38.081Std : 9.455
FSPM 07 - Napier
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
FSPM 07 - Napier
Multi-scale light interception model
Known positions
Uniform distribution
[Sinoquet et al., 2005]
FSPM 07 - Napier
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
FSPM 07 - Napier
Acknowledgment
Virtual Plants team
• CHAUBERT Florence• CHOPARD Jérôme• STOMA Szymon
UMR Piaf
• 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