136 Forestry Qjiarierly 



light-needing species, the former allowing perhaps 10 to 20 per 

 cent, of active light to reach the soil, when under similar condi- 

 tions the latter may allow twice that amount to pass through. 

 Of interest is the observation that parallelism between cross-sec- 

 tion area or stem number and light intensity exists only to a cer- 

 tain degree. " The numerous, but in crown and shaft form less 

 developed beech stems of the lightly thinned area do not absorb 

 in their crowns proportionately the same amount of chemically 

 active light as the fewer, but in crow^n and shaft better developed, 

 stems of the moderately and severely-thinned stand." 



The "shade coefficients"! ~ioo; when i =light absorbed, n= 



number of trees), which express relatively the amount of light 

 absorbed by a single tree in the average, showed the following 

 relations. 



Light i\foderate Severe 



Thinning Thinning Thinning 



r • , , T , , Leafless .28 .36 .44 



Light Intensity „ ,, , , „ 



Full leaf 032 038 .059 



or J £r ■ . Leafless xi 5.3 6.4 



Shade coefficient ^ ,, , ^ ■' ^ -^ 



Full Itaf 4.4 7.9 10.7 



Difference it! coeflBcients 12 2.6 4.3 



In other words, each crown in the more open position absorbed 

 double (or more) the amount of light taken by those in the dens- 

 er position : the crowns in the lightly-thinned stand are less fully 

 foliaged, more open. 



The differences between the shade-coefficients in leafless and 

 leafy condition, namely 1.2, 2.6, 4.3, furnish a tolerably good 

 measure of the amount of foliage (assimilation apparatus) in the 

 three areas. They express that the stems in the moderately- 

 thinned area work with an assimilation apparatus of double the 

 size, those in the severely-thinned, of nearly four times the size, 

 of the lightly thinned area. 



The shade coefficient can also be used to express the relative 

 rate of crown expansion. For instance, the relation of the light 

 intensities of four differently thinned areas varied as follows : 



1899 I : 1.5 : 2.2 : 3.3 



1903 (5 years after thinning) 1 : 1.6 : 2.4 : 3.8 



Difference o : .01 : .02 : .05 



i.e., crown expansion and crown density had progressed at a rela- 

 tively greater rate, the more open the position. 



