Periodical Literature. 33* 



ly predicted, and, since density also varies according to species, pre- 

 scriptions of a general nature for manner, time and severity of thin- 

 nings cannot be given, each case requiring its own answer. For 

 instance, if spruce in mixture with pine has not reached up to the 

 latter in the polewood stage, then it will never do so, and it remains 

 mere soil cover; the pine spreads into branches. If spruce ever 

 reaches up to the beech, the latter is lost. If oak does not remain 

 permanently ahead of beech, it cannot be preserved without costly 

 individual tending. With the desire to make room for a species in 

 mixture, the rest of the stand may experience such damage that it is 

 questionable whether it pays to maintain the unsuited species. 



On good sites the period of maximum height growth begins earlier 

 and lasts a shorter time than on poor sites. On best sites with spruce 

 the period may begin in the 5 to 10 year with one foot or more. On 

 poor sites in the 40 to 50 year, with three inches as maximum av- 

 erage decennial rate. Hence, neither age nor rate permits judg- 

 ment of the limits and duration of the maximum rate period, which 

 must be always determined by special investigation. 



More detailed account is made of reactions by the different spe- 

 cies to various treatment in this respect. 



Crown Form. Form and dimension of crown are among the best 

 criteria for need and degree of thinnings. The structure of the 

 crown is dependent on biological predisposition and density, besides 

 age and site. Generally speaking, crowns in their youth are more 

 elongated and open than in later age, with a tendency to broaden on 

 better sites. With the same species and height the more compact and 

 rounded form indicates poorer site. During the period of greatest 

 height growth the side branches reach for light, the branches are at 

 an acute angle with the shaft. Only in the open stand does a nat- 

 ural development take place, and here the light-needing species espe- 

 cially, spread out horizontally, for to secure light for the lower 

 branches these must grow more sideways than the upper. With 

 tolerant species this is not necessary, hence the crown is denser, 

 does not lose lower branches as far down, and rounds off later in 

 life. 



The lack of ability to develop adventitious buds is the reason why 

 conifers exhibit more regular crowns than broad-leaf trees, which 

 possess this faculty. Hence, the compacting of the crown by short- 

 ening of internode in conifers gives an easier clue to judgment of 



