STUDIES IN TOLERANCE OF NEW ENGLAND FOREST TREES 17 



In table X an attempt is made to show the effect of the forest 

 cover on bright days as compared with cloudy days. Light in the 

 open varied from .25 to 1. The light values in the open were figured 

 as 1 in every case and the percentage of light at each station computed. 

 These data sometimes are confusing rather than helpful. They con- 

 ceal important differences in intensity. For example at the Taxus 

 station the forest cover reduces the light intensity on July 22 to .0277, 

 (Table IX), or it holds back 89 percent of the total daylight at that 

 time. On August 12 the light intensity is .0555, and 94.5 percent of 

 the total daylight has been held by the cover. Nevertheless the plants 

 on August 12 have twice as much light for their development as they 

 had on July 22. 



TABLE X REDUCTION IN LIGHT DUE TO VEGETATION EXPRESSED IN PERCENTAGE OF 

 LIGHT IN THE OPEN. DATA GATHERED NEAR BIG SPRINGS, DOUGLAS LAKE, 



MICHIGAN 



Only a few data are available for studying the effect of forest 

 on light intensities as they vary from hour to hour with the changing 

 of the sun. Two cases are cited by way of example, but since in 

 these trials it was not possible to take simultaneous readings, an un- 

 avoidable source of error was introduced. Four readings taken an 

 hour apart under an Acer-Fagus-Tsuga cover show that the crowns cut 

 off 60, 93, and 81 percents of light respectively. These figures repre- 

 sent a variation in light intensities of from .0166 to .3000. At the time 

 of the latter intensities, the numerous seedlings of Acer and Tsuga had 

 a sufficient light for all purposes. In an adjacent stand of Tsuga, the 

 morning readings were 94 and 95 percents, which show a fairly uni- 

 form cover for that period. (Plate IV). 



Numerous seedlings of Fagus and Acer were found in habitats 

 the light intensities of which were .0250 and even lower. That higher 

 light intensities with proper moisture conditions are favorable for 



