Periodical Literature. 329 



the density period i. e. when the crowns are smallest and therefore 

 retain least water, the main cause of the death of branches must 

 be sought in withdrawal of light. The behavior of the dominant 

 stems, which do not participate in the decrease of increment, are also 

 a potent argument for this theory. Yet, we may assume, that the 

 water conditions of the soil have an important influence in the change 

 of density, i. e. loss of branches, at least where the soil humidity falls 

 to a degree which corresponds to minimum requirements of the spe- 

 cies in hand. 



Since Heyer, the relative demands of different species for light 

 have been the foremost basis for their treatment. 



With light-needing species, irregular forms of stands as regards 

 height and density are rare and are possible only on best sites. The 

 reason is that the lower stand is soon eliminated. While no light- 

 needing species can persist under the shade of its own mother trees, 

 tolerant species can persist in the shade of their own mother trees, 

 if only not overtopped. For these reasons selection forest with 

 light needing species is possible only in very open stands and natural 

 regeneration with them is more difficult, especially if as in pineries 

 soil moisture approaches a minimum. Hence, also, the well-known 

 rule, that in mixed plantations the light-needing species must be 

 more rapid growers or that the "filler" must be tolerant. Practi- 

 cally, this rule is difficult of execution because light requirements 

 are so much influenced by site, hence it is impossible to formulate 

 rules for the tending of mixed forest in which the mixture is in 

 single specimens ; the general deduction may be made, that it is 

 easier to tend stands mixed in groups, than those mixed as single in- 

 dividuals. Nor is it possible to readily formulate a scale for the re- 

 quirement of species as regards density and form of crown cover. 



Shaft Form. A maximum of value is the object of forestal oper- 

 ations, hence when quantity production cannot any more be stimu- 

 lated, quality, i. e. timberwood percent or shaft form must be im- 

 proved, to secure straight, clear, cylindrical logs of largest diame- 

 ter. Species diff'er as to their capacity of securing this result. The 

 conifers are physiologically predisposed to it, even without a dense 

 stand. These are, therefore, least influenced by density. The char- 

 acteristic of the broad-leaf trees dividing the shaft into a crown is 



