Canadian Forest Service Publications
Solar radiation over a snow pack in a dense pine forest. 1964. Vézina, P.E. Agricultural Meteorology 1: 54-65.
Issued by: Laurentian Forestry Centre
Catalog ID: 16184
Availability: PDF (request by e-mail)
This paper reports the results of a study conducted during the 1961-62 winter season to determine the daily solar radiation ratios in a 24-year old Pinus resinosa Ait. (red pine) plantation with 66% crown closure situated on a steep southeast facing slope at Valcartier, near Quebec City. Ratios are the percentage of the daily amount of solar radiation beneath canopy (expressed in langleys) to that in the open.
The average daily solar radiation ratio beneath canopy in a 104-day period was 8.0%, and varied 1-28% on individual days. It was directly related to the degree of cloudiness, but unrelated to the amount of solar radiation in the open. This is explained by the fact that in this study cloudiness was only moderately correlated with the amount of solar radiation in the open. The daily solar radiation ratio, however, had the tendency to approach the average ratio as the amount of solar radiation in the open increased. This suggested that a shortcut method of estimating the average solar radiation available below a softwood canopy would consist of making observations on a calm, cloudless day, with radiation in the open exceeding 350 langleys. The radiation penetration process is discussed in terms of radiation absorption in the crown cover, and its implications in regeneration silviculture are mentioned.