Review on Forest Canopy Structure,Radiation Transfer and Canopy Photosynthesis

Canopy structural factors with radiation distribution and canopy photosynthetic modelling inclued crown shape,leaf angle distribution,leaf distribution within canopy,penumbra effect,reflection and scattering of leaf on radiation etc.The radiation within canopy was mainly described with Poisson distribution or binomial distribution,depending on the uniformity of leaf distribution.Crown shape was closely related to radiation transfer and canopy photosynthesis,however,influenced by latitude,sun height and stand density,there were no specific crown shape that was absolutely favorable for canopy photosynthesis.Leaf angle was believed to be important at leaf scale but could be neglected at canopy scale.Spherical and /or elliptical leaf angle distribation were proposed hypothesis in canopy radiation and photosynthetic modelling.Leaf distribution within canopy was one of the most important structural factors affecting radiation transfer and canopy photosynthesis.The uneven canopy surface,clumped,regular and/or random crown distribution,and clustered or random leaf distribution within crown would greatly influence radiation transfer and canopy photosynthetic modelling.Penumbra effect within high canopy with small leaf were believed to be significant,however,since penumbra effect was currently estimated on circular leaf,it is necessary to develop a more practical estimation method particularly for coniferous forest. The reflection and scattering of leaf on radiation are also important factors in radiation transfer and canopy photosynthetic modelling although they account for only several percent of total radiation.