330 Forestry Quarterly. 



differently developed in different species, influenced also by soil 

 conditions, the better soil tending to develop a long undivided bole. 

 Density of stand is the only means of forcing this development of 

 long, straight, clear, cylindrical bole. But since quantity depends 

 on open condition, the task is to regulate and even out these tv/o re- 

 quirements, which is the more difficult since besides site, age and spe- 

 cies, its heightgrovpth and character of crown must also be consid- 

 ered. 



Height Growth. The most light-needing species are the most 

 rapid growers (in their youth), the tolerant the slowest, a relation 

 between height growth and tolerance exists to a degree. In each spe- 

 cies a period of most rapid height growth can be found, which is 

 largely independent of the site, but much more influenced by density. 

 The inherent tendency of conifers to be monopodial makes it intelli- 

 gible that density influences their height growth less than that of 

 deciduous trees, which have the tendency of spreading. With these, 

 therefore, the period of maximum height growth may be influenced 

 to a degree. Site influences only the absolute measure of height 

 growth ; since on the same site at same age the tree in the open has 

 less height than that grown in dense stand, we have means to in- 

 crease the absolute height in a given time. Since with conifers this 

 influence cannot be exercised, knowledge of the period of their 

 maximum height growth rate is more important, for during this 

 period any interruptions of crown cover are most readily filled up. 

 Later, when height growth decreases, an opening in conifers is 

 closed less readily than in broad-leaf trees; with these density pro- 

 duces more energetic, open stand slower height growth, and in older 

 age an opening up may arrest height growth entirely. With coni- 

 fers open stand rather stimulates height growth. In other words, the 

 variations of density have the opposite influence on height growth 

 with conifers and with broad-leaf trees. The optimum position 

 has not yet been determined. While with conifers thinnings may 

 be made during the period of maximum height growth without dam- 

 age to shaft form in length and with advantage for diameter de- 

 velopment, clearness of bole alone requiring consideration, with 

 broad-leaf species such openings must be avoided at that period, as 

 detriment to form. 



If a site does not fit two or several species in the same degree, as 

 is usual, their behavior as to relative height growth cannot be sure- 



