Evaluating the use of Beer's law for estimating light interception in canopy architectures with varying heterogeneity and anisotropy

Abstract

Light interception in plant canopies is most commonly estimated using a simple one-dimensional turbid medium model (i.e., Beer's law). Inherent in this class of models are assumptions that vegetation is uniformly distributed in space (homogeneous) and in many cases that vegetation orientation is uniformly distributed (isotropic). It is known that these assumptions are violated in a wide range of canopies, as real canopies commonly have heterogeneity at multiple scales and almost always have highly anisotropic leaf angle distributions. However, it is not quantitatively known under what conditions these assumptions become problematic given the difficulty of robustly evaluating model results for a range of canopy architectures. In this study, assumptions of vegetation homogeneity and isotropy were evaluated under clear sky conditions for a range of virtually-generated crop canopies with the aid of a detailed three-dimensional, leaf-resolving radiation model. Results showed that Beer's law consistently over predicted light interception for all canopy configurations. For canopies where the plant spacing was comparable to the plant height, Beer's law performed poorly, and over predicted daily intercepted sunlight by up to ∼115%. For vegetation with a highly anisotropic leaf inclination distribution but a relatively isotropic leaf azimuth distribution, the assumption of canopy isotropy (i.e., G=0.5) resulted in relatively small errors. However, if leaf elevation and azimuth were 1

The Role of Spatial Averaging Scale in Leaf‐To‐Canopy Scaling of Non‐Linear Processes in Homogeneous Canopies

“…Agreement was within about ±4%, with a median and mean across all simulations at solar noon about 0.5% higher than the Beer's Law result. This was consistent with comparisons of daily PAR interception carried out by Ponce de Lé on and Bailey (2019). Such a comparison was not strictly necessary for the analysis carried out in this work since the focus was on analyzing differences in canopy fluxes between different scaling methods within a 3D (sub) leaf resolving model, and not on a comparison with turbid‐media based model results directly.…”

Helios: A Scalable 3D Plant and Environmental Biophysical Modeling Framework

“…Models that aggregate trees into homogeneous subvolumes (e.g., see Wang and Jarvis, 1990; Cescatti, 1997; Duursma and Medlyn, 2012) correctly represent tree-scale heterogeneity in absorption, but filter out subtree variability including the tails of the distributions, which were shown to have important contributions to whole-canopy behavior. On the other hand, multilayer models can represent this subtree variability but are not able to represent tree-level heterogeneity in sparse canopies (Ponce de Len and Bailey, 2019).…”

“…Simple models like the “big-leaf” approach described above are very computationally efficient, and thus they can be used to simulate extremely large problems such as global ecosystem fluxes (Churkina et al, 2005; Reichstein et al, 2005; Lawrence et al, 2019). However, errors and biases can be sizable if subcanopy heterogeneity plays a significant role in the biophysical processes of interest (Friend, 2001; Ponce de León and Bailey, 2019). Models that resolve plant-level heterogeneity often incur a significant computational cost, but simulations are usually limited to domain sizes with a few dozen large plants (Duursma and Medlyn, 2012; Vezy et al, 2018).…”

Modeling Transpiration with Sun-Induced Chlorophyll Fluorescence Observations via Carbon-Water Coupling Methods

“…Net radiation is separated into energy intercepted by canopy and soil available energy by one dimensional Beer's law. The simple structure of Beer's law could introduce great uncertainty to energy partition, especially for heterogeneity canopy and plants with highly anisotropic leaves in the azimuthal direction [68], for example, maize at the early growing season at DM and HL sites. Canopy available energy was also used to estimate T in the two-layer Penman-Monteith model in the conductance method.…”