CHOICE OF SPECIES IN ARTIFICIAL REGENERATION 23 



through a long period of years has developed within the species 

 a number of races of variable degrees of hardiness. In seeding 

 and planting operations it is important that we recognize this 

 difference of hardiness within the species. When restocking is un- 

 dertaken on exposed sites where the climate is severe, we should use 

 seed collected over that portion of the range of the species having the 

 most severe climate. 



As a rule, forest trees should not be seeded or planted in a 

 locality much colder than the habitat where the seed is collected, 

 even if the distribution of the species extends into much colder 

 regions. Experience has demonstrated that transportation from 

 a warmer to a colder habitat is almost always unfavorable. On 

 the other hand, present evidence indicates that most trees thrive 

 when transported to a habitat somewhat warmer than their native 

 home. 



Trees in the juvenile stage are much more subject to injury 

 from temperature conditions than older ones. Serious injury is 

 often escaped by underplanting, i.e., by starting the young forest 

 under an old stand. The effect of the larger growth is to render 

 the temperature conditions under it more uniform and, thus, less 

 harmful to the young growth. 



Individuals of all species which occur on the outskirts of their 

 geographical range are single or in isolated groups where local 

 temperature conditions are suitable. In the extension of a 

 species northward or to a higher elevation, it occurs only in warm 

 local situations as expressed in southern aspects. In its exten- 

 sion southward or to lower elevations, it occurs only in cold local 

 situations. When seeding or planting at the northern geograph- 

 ical range of a species, or when an exotic species is introduced 

 from a warmer region, warm local situations should be selected 

 as expressed in southern slopes with their drier soil, over which 

 the air is warmer. When done at the southern geographical 

 range or when an exotic species is introduced from a colder region, 

 cold local situations should be selected as expressed in northern 

 slopes with their moister soil, over which the air is cooler. 



9. Light in Its Relation to the Choice of Species. Light 

 is necessary for the life, growth, and development of trees. It is 

 necessary for photosynthesis, chlorophyll formation, and the 

 metabolism of green plants. In general, other factors being 

 equal, the greater the light intensity the more rapid the growth 



