2 FORESTRY IN NEW ENGLAND 



Besides temperature there are other chmatic 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 killed out by the prolonged drought 

 and hot weather of 191 1. 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 

 trees are 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. Each genus, and in some respects each species, reaches its 

 best development under a certain set of conditions of soil, 

 climate, etc., called its optimum, and varies whenever found 

 under different conditions. Since topography, exposure, and 

 altitude affect these factors, they must also be taken into account. 

 Near their northern limits of distribution all trees ascend the 

 mountains to a greater height on the southern than on the 

 northern sides, because of warmth requirements. 



Trees derive most of their nourishment from the carbonic 

 acid of the atmosphere, but they depend upon the soil for water 

 and mineral supplies; these can only be taken up when held in 

 solution by the soil. Water is a chief essential of tree growth, 

 part of it being retained in the wood. Greenwood often contains 

 as much as 50 per cent by weight of water. Water in the plant 

 serves as a carrier for the minerals (the salts, oxides, etc.), which, 



