Analysing species-specific light transmission and related crown characteristics of Pinus sylvestris and Betula pendula using a shoot-level 3D model

This is a first attempt to analyse species-specific light attenuation in mixed boreal forests created by shoot-level 3D tree models. The models are configurations of real individual Scots pine (Pinus sylvestris L.) and silver birch (Betula pendula Roth.) trees grown in mixed-forest stands. We study species-specific differences in radiation transmission by using the ray-casting method. Light transmission was found to be higher in dense birch-dominated stands compared with dense pine-dominated stands because of the higher total foliage area and the higher location of foliage in the pine canopy. Transmission of light per leaf area index (LAI) was nevertheless higher in the pine canopy compared with the birch canopy because of foliage clumping. Especially in clumped canopy, species-specific shoot-level light simulations enable a more realistic estimation of light transmission compared with simpler calculations based on LAI and Beer-Lambert's law. The observed differences in light-transmission characteristics of the studied species may influence the development of target crowns in the neighbourhood. Light attenuation caused by the dense foliage zone in the upper pine canopy could be avoided in dense stands by mixing species with different vertical foliage distributions.