Fraction of absorbed photosynthetically active radiation for a semi-deciduous forest and Vochysia divergens monospecific forest in Brazil

Ecophysiological model employ the fraction of photosynthetically active radiation (f_APAR) absorbed by the plant canopy such as critical input to diagnostic seasonal patterns in the vegetation dynamics. Here, this study focuses on the patterns of variation of transmittance, reflectance and f_APAR for two forests with different canopy structures, a forest located in a climatic transition between Amazonian rain forest (a semi-deciduous forest) and savanna and a V. divergens monospecific forest. Transmittance (t), reflectance (r) and f_APAR were calculated with meteorological data measured from the tower installed in each forest. Our results indicate the annual average f_APAR for the semi-deciduous and Vochysia divergens was 92.3 and 84.8%, respectively. Measurements indicate that the f_APAR for the V. divergens was 9% less than that for the semi-deciduous forest. The values and variation of r, t and f_APAR was due to the fraction of canopy openness, and was influenced by the fraction of canopy openness, solar zenith angle and amount of diffuse radiation.