Effects of light transmittance on growth and biomass of understory seedlings in mixed pine-beech forests

Abstract

Seedling growth as well as aboveground and belowground biomass allocation is mostly influenced by Light Transmittance (LT) (%) through the canopy. The knowledge of how understory light conditions affect seedling growth and biomass of different species in mixed forests is not well documented. Thus, it is essential to quantify the effects of light on the growth and biomass of understory seedlings. Given their advantages over pure forests, these quantitative understandings are especially crucial in mixed forests with species whose light demand and shade tolerance vary. This research examined the growth responses of natural-origin Scots pine (Pinus sylvestris L.), black pine (Pinus nigra Arnold.) and Oriental beech (Fagus orientalis L.) seedlings to LT (%) through the canopy in their mixed stands. Linear mixed-effect models were utilized to examine the influence of LT (%) on the seedlings. Moreover, allometric equations for estimating the aboveground biomass and belowground biomass of seedlings were developed for each species. Seedling height, and aboveground and belowground biomass after five years of germination were most significantly affected by LT (%) and tree species in the mixed pine-beech stand (p < 0.001). Biomass models for each species included different variable combinations of seedling height, root-collar diameter, LT (%), and their interactions. This study demonstrates the importance of canopy structure and overstory disturbances for the maintenance of mixed pine-beech forests since canopy structure significantly contributes to the understory light environment.