Modeling solar radiation transmission in boreal conifer forests

A hybrid geometric-optical and radiative transfer (GORT) model developed for the radiation regime in discontinuous vegetation canopies, is modified to include branch orientation properties. This new version of the model was used to estimate solar radiation transmission in old jack pine (OJP) and old black spruce (OBS) forests in Canada. Radiation measurements collected in OJP and OBS forests in Canada show that radiation transmission as a function of solar zenith angle and height in the canopy deviates from what is predicted by Beer´s law. By considering gap probabilities between crowns in addition to within individual crowns, GORT estimates more accurately transmission distribution in the canopy. Modification of the GORT model to include branch orientation improves the ability to model the observed patterns of solar radiation transmission as a function of solar zenith angle and height in the canopy in the SOJP site. Branch orientation distributions are derived from PARABOLA measurements by the geometric-optical mutual shadowing (GOMS) model