How do current GORT models describe the bidirectional reflectance distribution function of forests?

This work aims in long time to investigate how do GORT models describe the radiative transfer within forest. In other words, how such model could approach the actual forest BRDF (Bidirectional Reflectance Distribution function). The 5SCALE model describes forest BRDF considering various architecture levels (stand, crowns, foliage elements...). The effect of some architectural parameters on BRDF, of this GORT model is presented in addition to a comparison with maritime pines reflectance simulated by a radiosity model using numerical scenes