36 SYLVICULTURE. 



the thickness of their foliage and by the length of time over- 

 shadowed twigs of evergreen Conifers retain their leaves. 



(4) As regards root-system, stem, and crown, trees grown as 

 woodland crops have always a smaller growing-space than when 

 growing freely in the open ; but while the roots and the crown 

 are kept smaller, the growth in height (due to the struggle for 

 existence) is greater, and there is less tendency to spread side- 

 wards into branches. And, of course, it is only when deep- 

 rooting and light-demanding kinds of trees have their natural 

 requirements satisfied that good growth can be maintained, and 

 more especially as the trees approach maturity. 



(5) As regards rate of growth as timber-crops, few of those 

 which grow rapidly in height at first furnish very large mature 

 crops, though the Pacific Douglas Fir and Menzics Spruce are 

 exceptions in this respect. Among European trees the largest 

 crops per acre are yielded by Silver Fir and Spruce, though 

 both are slow in establishing themselves and beginning to shoot 

 ahead. Increment or growth in cubic contents is the combina- 

 tion of growth in height and growth in girth. As the number 

 of stems per acre has to be sooner lessened (by thinning) to pro- 

 vide the necessary growing-space, light-demanding trees culminate 

 in increment and become less energetic sooner than shade-bearing 

 trees, though, of course, much depends on the soil and situation. 

 Hence shade-enduring trees (Douglas Fir, Spruces, Silver Fir, 

 and Red Cedar ; Beech) produce larger crops per acre than light- 

 demanding trees (Larch and Pines, most hardwoods and soft 

 woods), and larger crops are usually obtainable on a fresh than 

 on a dry soil, in which food-supplies are scarce. 



(6) Reproductive power in throwing up stool-shoots and root- 

 suckers and Regenerative power in producing seed are different 

 forms of utilising reserve nutrients, in the one case for main- 

 taining individual life, and in the other for propagation of the 

 species. Reproduction is strongest in the younger stages of 



