Solar Radiation Beneath Conifer Canopies in Relation to Crown Closure

Abstract

Abstract Observations were made in Quebec on solar radiation available daily below canopies of Abies balsamea L. (Mill.), Pinus resinosa Ait., and Pinus banksiana Lamb. during summer and winter with Bellani radiation integrators. A relationship between crown closure and the solar radiation ratio—defined as the proportion, in percent, of the amount of solar radiation available beneath canopy (in langleys), to that available in the open— was calculated for a wide range of crown closures. Variations in solar radiation in the open did not change the average ratio in the stands, but with increasing radiation in the open the scatter of values around the mean of daily solar radiation-ratios decreased. This suggested the feasibility of a short-cut method for estimating the average solar radiation ratio in coniferous stands by integrating solar radiation on a few calm and clear days. Results are discussed in relation to the radiation-intercepting properties of forest canopies, the solar radiation requirements of Abies balsamea seedlings, and silvicultural management.