352 JOURNAL OF FORESTRY 



crown densities of all trees of possibly many species in the crown cover, 

 seems almost unavoidable; from this standpoint it is the shade (the 

 complement of the light intercepted) oi the entire crown cover which 

 is the essential point. The second aspect does not necessarily concern 

 the subordinate growth; it relates specifically to the competition, or 

 freedom from competition of the crowns in the crown cover, and has 

 a variety of uses in stand description, as when a stand is thinned 

 to ".8 of perfect closure" (indicating that .8 of the total space is 

 filled with three crowns). Its meaning is the same for aspen as for 

 spruce. It aflfords a necessary means for describing the distance apart 

 of the tree crowns when the sense of shading is either not important 

 or so important as to require separate description. 



I do not believe that these two meanings are sufficiently distinguished 

 and provided for under the definitions suggested by Dr. Fernow. 



Under "crown density," emphasis is correctly placed upon the 

 "density of the individual crown, a biological factor," etc. I believe, 

 however, that this should be only one of two definitions to come under 

 this term, the second to be that given for "crown density" in the original 

 criticism. This is because "crown density" is an established term re- 

 ferring to the crowns of the aggregate trees in the forest, and it is 

 necessary to retain the term as a matter of reference. In its old sease 

 it was, of course, "a loose term, combining the meanings of crown 

 closure and shade density." 



As to the proposed terms, "crown closure" and "crown area," the 

 latter seems to me less desirable, because it does not convey the dynamic 

 sense of coming together, a sense which it will be useful to regard in 

 many cases ; "area" smacks of mathematics, where a biological sig- 

 nificance may be more important; while the crown area vertically pro- 

 jected on the forest floor is a means of denoting the degree of closure, 

 the closure may be important in three dimensions, or within a certain 

 range of depth of crown as well as width. Furthermore, to say that 

 crown area is the "area shaded" (as indicated in Dr. Fernow's defini- 

 tion) seems inapplicable because of variation in the shade cast by 

 crowns, dependent upon season,, time of day, latitude, and length of 

 crown; it is rather a matter of vertical projection of the crowns upon 

 the forest floor. 



I do not believe that the term "crown cover" has the implicit mean- 

 ing of "shade density," while I do believe that the latter term conveys 

 this meaning unmistakably. Finally, "total shading efficiency" is not 



