144 PRINCIPLES OF AMERICAN FORESTRY. 



Occasional strips of grass are also a preventive of this 

 injury, or mulching may be resorted to. 



Snow Crust. The settling of a snow crust that has 

 formed on the top of deep snowdrifts may cause injury 

 to young trees by stripping off their branches and break- 

 ing the stems. It may be prevented by breaking up the 

 crust or by thinly scattering over the snow some sand, 

 ashes, or other material that will absorb the sun's heat 

 and cause the crust to melt before the snow underneath 

 melts. This injury seldom occurs except under drifts, 

 and a little good judgment in selecting the location and 

 arranging the windbreak so as to prevent drifts may 

 obviate this source of injury. 



Drought. Injuries from drought may be prevented to a 

 great extent by constant cultivation, but where this can- 

 not be done mulching is a good substitute. Attention to 

 thinning at the proper time so as not to get the soil filled 

 with roots will also help to prevent injury from drought. 

 Willow windbreaks can be grown without any cultivation, 

 after being once well established, in the driest portion of 

 Minnesota, if they are kept mulched with straw or litter 

 for six feet on each side. Mulching also prevents injury 

 from severe freezing of the roots. 



Sun-scald. Nearly all of our cultivated trees may be 

 injured by sun-scald. This occurs, almost without ex- 

 ception, on the southwest side of unprotected trees of 

 Hard and Soft Maple, Basswood, Box-elder, Black Walnut, 

 etc. Oaks and all other trees are occasionally affected. 

 It never occurs when the trees are sufficiently close together 

 to shade their trunks, and for this reason the growth of 

 shrubs and low branching trees should be encouraged 

 on the south and west sides of groves where they do not 

 crowd the principal kinds. Street trees liable to this 

 injury may be protected by burlap sacking, straw, or 

 other similar material. W T hen injuries from sun-scalci 



