GLOBAL RADIATION WITHIN SUB-ARCTIC OPEN FOREST CANOPIES

Measurements of global solar radiation were made at six sites with var ying architecture within a subarctic open forest near Churchill, Manit oba. Below-canopy radiation was determined from a network of nine sens ors and the mean was compared with global radiation above the canopy. The ratio of below- to above-canopy radiation, R, ranged from 0.52 to 0.7 for the six sites. This range falls within the range of observatio ns from other subarctic sites. At all sites, R was smaller for clear t han for overcast skies; however, the differences were not statisticall y significant. The data from this study were combined with data from t he literature in order to develop predictive equations for solar radia tion at the floor of subarctic forests, based on easily derived forest parameters. Linear relationships were found between R and canopy clos ure (r2 = 0.76) and between R and tree height (r2 = 0.88).