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