2 A M. \\r.\L OF FORESTRY 



an explanation of the inability of the eucalyptus of southern 

 California to live in New England, and of the fact that the canoe 

 birch, although growing from the Atlantic to the Pacific, does 

 \tcn.l as far south as Long Island Sound. In a less notice- 

 able way it is probably the extreme cold of winter which limits 

 the chestnut to southern New England and the region farther 

 south. Aside from this matter of extremes it is not so much the 

 winter's cold that is injurious to species, as the late frosts in 

 spring when the young leaves and shoots are still tender, and the 

 early frosts of the autumn before the summer's growth has 

 sufficiently hardened to withstand the cold. The late frosts of 

 the spring of 1910 killed back the new growth of pine and fir 

 in northern Vermont. Ash seedlings are frequently killed by 

 late frosts. 



IK sides temperature there are other climatic factors influenc- 

 ing tree growth. It has been found, for example, that the 

 southern limits of forest trees are mainly determined by the 

 quantity and the regularity of the rainfall during summer. 

 Taken as a whole, broadleaf trees consume on the average about 

 ten times as much water as conifers, and, owing to the light 

 foliage of pine, this species requires much less soil moisture than 

 .spruce or fir. The lack of rain for even two or three days may be 

 fatal to young seedlings. White pine plantations established two 

 years previously were badly injured by the prolonged drought 

 and hot weather of 1911. With age and development of the 

 root system the ability of the tree to resist drought increases. 

 A mature tree with the assistance of its reserve supplies of water 

 can withstand a drought of several months' duration. Precipita- 

 tion outside of the growing season is also valuable, in thoroughly 

 wetting the soil, because during the growing season when the 

 in foliage the soil is seldom thoroughly wet. 



Aside from these climatic factors, heat and rainfall, which 

 influence the general distribution of forests, the factors most 

 important to individual tree growth are light and soil moisture, 

 and to a lesser extent the physical and chemical character of the 

 soil. K:i< li genii-, and in some respects each species, reaches its 



