ESTABLISHING FORESTS BY PLANTING 373 



It was found that the roots undergo a cessation of growth in 

 summer due to drought, but in October there is a new period of 

 activity, which is much more intense and more prolonged in decid- 

 uous species than in the conifers. It appears from these investi- 

 gations that the autumn planting of broadleaved species should be 

 just before this new period of root activity begins. It also appears 

 that deciduous species, because of the greater growth of the roots 

 in late autumn, are more acceptable for autumn planting than are 

 spruce, pine, and other conifers. 



16. Winter Planting 



Over most parts of the United States winter planting should 

 be avoided, because it .is harmful to the young trees if there is 

 frost either in the ground or in the air at the time of planting. 

 Only in the southern part of the country is it safe to plant forest 

 stock during the winter months. 



17. Summer Planting 



Summer planting also is objectionable because the trees are then 

 in active growth. This new growth is young and tender, and re- 

 quires a large amount of moisture to sustain the transpiration cur- 

 rent. The soil at this season is more likely to be dry, and the loss 

 of soil moisture through evaporation is at its maximum. In those 

 localities, however, which have a well-defined rainy season during 

 the summer months with little or no rain during the winter and 

 spring, planting ordinarily begins at the commencement of the 

 summer rains. It is extremely doubtful whether there is any por- 

 tion of the United States where the summer rains are sufficiently 

 abundant to make this season preferable to the spring months for 

 forest planting. 



18. Autumn Planting 



In most parts of the United States the planting season falls 

 between September 15 and May 15. Between these dates the 

 planting should be done at such times as there is no frost in the 

 air or soil. At high elevations, particularly in the Rocky Moun- 

 tain region, because of the shortness of the growing season and 

 the long time required for the frost to disappear completely from 

 the soil in the spring, planting is often delayed as late as June. 



