130 FOREST PLANTING. 



are allowed to grow, we can prevent the damaging influ- 

 ence of frost upon the plants by covering the rows with 

 a layer of evergreen boughs. 



The Lite frosts in spring when the trees have already 

 developed their buds are the most injurious, killing 

 young trees completely and affecting the older ones so far 

 as to incapacitate them from producing seeds and from 

 making any accretion in wood. This evil appears most 

 frequently in wet or swampy valleys, where the evapora- 

 tion of moisture prevents the access of the warmth con- 

 tained in the upper layers of the atmosphere, and thereby 

 increases the cold developed by evaporation in the soil. In 

 such cases drainage should be applied to let off the excess 

 of water ; but when this is not practicable, hardy trees 

 should be planted for the protection of the young ones, 

 and retained till the latter have reached a size large 

 enough to overshade the ground and to prevent too 

 strong an evaporation of the moisture in the soil. Pines, 

 hornbeams, alders and the American aspen are best 

 adapted for this purpose, and even large bushes may be 

 advantageously used. 



In the swampy parts of mountainous regions there 

 occur, sometimes, late in summer heavy though not last- 

 ing frosts, which may do a great deal of harm insomuch as 

 after such a spell a second growth of wood takos place, 

 which will not ripen by the time the winter sets in, and 

 is then killed by frost. Oaks and beeches are especially 

 subject to this casually The best one can do in such 

 case is to plant sprucet which stand these vicissitudes 

 very well. 



Sun heat does damnge to forests when there is a want 

 of a proper water supply. If this can be procured all 

 danger to the trees is over. Irrigation will seldom be 

 practicable. But a great deal of the natural moisture 

 can be retained in forests by preserving a compact dens- 

 ity of the tree-growth, and keeping the soil well shaded 



