PARENT SESSION
Contributed Oral Session 100: Modeling: Forest Systems
Wednesday, August 10, 1:30 PM - 5:00 PM, Meeting Room 519 B, Level 5, Palais des congrès de Montréal
Light distribution in a mixed species canopy based on constant versus variable clumping factor and leaf angle distribution.
Kim, Hyun-Seok*,1, Palmroth, Sari1, Therezien, Mathieu1, McCarthy, Heather1, Parashkevov, Yavor1, Oren, Ram1, 1 Nicholas School of the Environment and Earth Sciences, Duke University, Durham, NC, U.S.A
ABSTRACT- In order to evaluate the sensitivity of canopy light models to leaf characteristic parameters, a combined and modified Campbell and Norman (1998) and Stenberg(1998) model was employed at Duke Forest with constant versus variable clumping factor and leaf angle distribution at a wide range of LAI (2.1 to 4.2 m2 m-2). Photosynthetically active radiation (PAR) on the horizontal surface was slightly lower in early morning and late evening with variable parameters (clumping factor (top: 0.56, bottom: 0.82) and leaf angle distribution (top: 0.5, bottom:3.0) ) than constant parameters(clumping factor: 0.6, leaf angle distribution: 1), but higher from mid-morning to mid-afternoon. The impact of variable parameters increased with increasing leaf area, so the increase of absorbed PAR (APAR) at noon was greater during the period of maximum leaf area (from 82.7% to 86.2 %) than the period of minimum leaf area (48% to 48.4%). On the leaf surface the proportion of surface area receiving over-saturation of average PAR with respect to photosynthesis decreased at the top of canopy, while the proportion of the surface receiving low PAR values decreased and the average PAR increased in the deeper canopy creating about 3.6% increase in photosynthesis throughout a year. Due to the non-linearity of the photosynthetic response to light, using average PAR overestimated photosynthesis by only 6% compared with when we simulated, using a Monte Carlo approach, finer distribution of PAR on leaf surfaces.
Key words: light model, photosynthesis, leaf angle distribution, clumping factor