Using a stand-level model to predict light absorption in stands with vertically and horizontally heterogeneous canopies

Abstract

Background: Forest ecosystem functioning is strongly influenced by the absorption of photosynthetically active radiation (APAR), and therefore, accurate predictions of APAR are critical for many process-based forest growth models. The Lambert-Beer law can be applied to estimate APAR for simple homogeneous canopies composed of one layer, one species, and no canopy gaps. However, the vertical and horizontal structure of forest canopies is rarely homogeneous. Detailed tree-level models can account for this heterogeneity but these often have high input and computational demands and work on finer temporal and spatial resolutions than required by stand-level growth models. The aim of this study was to test a stand-level light absorption model that can estimate APAR by individual species in mixed-species and multi-layered stands with any degree of canopy openness including open-grown trees to closed canopies. Methods: The stand-level model was compared with a detailed tree-level model that has already been tested in mixed-species stands using empirical data. Both models were parameterised for five different forests, including a wide range of species compositions, species proportions, stand densities, crown architectures and canopy structures.

Can Vegetation Indices Serve as Proxies for Potential Sun-Induced Fluorescence (SIF)? A Fuzzy Simulation Approach on Airborne Imaging Spectroscopy Data

“…We assume that after some training the use of different APAR images composed with different irradiance values can be considered as a prime variable to scale the SIF fuzzy at a different time of the day. The overestimation of SIF fuzzy-APAR has been particularly observed for dense forest canopies (i.e., DF, SFPS, SFAG, SeFPS) in reference to SIF 760 which was in agreement with Jung et al [85] and Forrester et al [86]. For SIF 687 , the modelled overestimations of SIF fuzzy-APAR have been observed in overall vegetation groups.…”

Calibration of the process-based model 3-PG for major central European tree species

“…3-PG consists of five sub-models: light, biomass production, water balance, allocation and mortality. The light sub-model calculates light absorption using speciesspecific light extinction coefficients, leaf area indices and, in the case of multi-species or multi-cohort stands, the vertical positioning of each cohort based on species-specific mean height and crown length (Forrester et al 2014). The biomass production sub-model calculates gross primary productivity based on a species-specific canopy quantum efficiency (α C ) that is reduced by limitations caused by temperature, frost, vapour pressure deficit, soil moisture, soil nutrient status, atmospheric CO 2 and stand age (Almeida et al 2009;Landsberg and Waring 1997;Sands and Landsberg 2002).…”

Disponibilidad de luz bajo dosel en rodales de Abies religiosa

“…Esta ley considera la cantidad total de radiación interceptada por el dosel y depende de la radiación incidente, de la estructura del dosel y de las propiedades ópticas del mismo. Para estimar la transferencia de radiación solar a través del dosel forestal, en este estudio, se ha adoptado y modificado dicho modelo para describir la atenuación de la radiación solar a través de un dosel horizontal y homogéneo (Monsi y Saeki, 2005;Forrester et al, 2014).…”

“…La estimación del índice de área foliar a partir de parámetros de transmisión de luz y estructura del dosel por medio del modelo Beer-Lambert, mostró que la relación existente entre los parámetros de radiación trasmitida (directa y difusa), apertura del dosel e índice de transmisión de luz del dosel se ajustan a un modelo de tipo exponencial, indicando que la transmisión de luz disminuirá siguiendo dicha tendencial al aumentar el área de intercepción del dosel, debido a un incremento en la cobertura y densidad de copas. El modelo de Beer-Lambert resulta ser adecuado para doseles simples y homogéneos, como el caso de rodales puros; sin embargo, investigaciones recientes indican que para doseles heterogéneos y complejos dicho modelo podría no proporcionar resultados satisfactorios y es necesario utilizar otro tipo de modelos (Forrester et. al, 2014).…”