Photosynthesis in Sitka Spruce (Picea sitchensis (Bong.) Carr.) V. Radiation penetration theory and a test case.
[Cf. FA 35, 7073] A general theory is presented which describes the interaction between radiation and a Spruce forest. The canopy is divided into a series of layers so that all the radiation fluxes can be computed if the layer interception, reflection and transmission properties are known. The effects of multiple scattering at any wavelength and variable angular distribution are included. Two different radiation models were tested: (a) a simple random canopy model, and (b) a more comprehensive, non-random (grouping) model with measurements of structural elements of the canopy as inputs. Theoretical results were compared with measurements made in a visible (0.51-0.57 mu m) and a near infra-red (0.73-1.0 mu m) waveband. The best correlation was obtained with (b). Predictions with this theory require data solely on canopy structure, spectral information and incident radiation above the canopy; measurements of radiation within the canopy are not required.