26 ELEMENTARY FORESTRY. 



EFFECT OF SLOPE AND ASPECT ON TREE GROWTH. 



The slope of the land affords drainage and so affects the 

 growth of trees, but trees will grow on any slope, even on 

 precipices, if they can find room for their roots and the soil is 

 somewhat moist. The direction of the slope usually has a very 

 marked effect on the growth of vegetation. This is especially 

 the case where high ranges of hills and other local conditions 

 modify the climate. 



A Northern Slope receives no full sunlight; the sun's rays 

 fall obliquely in the morning or toward evening, according to 

 the angle of elevation. The winds it receives in winter are 

 colder than those received by the southern slope, but the few 

 winds which strike it during the growing season are not strong, 

 hot or very dry. As the vegetation is a little delayed on a 

 northern slope, there is less danger from late spring frosts than 

 on a sunnier aspect, and, as the snow melts slowly, there is a 

 better chance for its waters to soak into the ground. In con- 

 sequence of these facts trees are less liable to suffer from drouth 

 on the same kind of land with a northern than with a southern 

 exposure. The trees keep a more regular form and growth is 

 more uniform and certain. It will generally be found that 

 where timber is cut off from a northern slope growth renews 

 itself very quickly, for tree seeds are most likely to grow undei 

 the conditions found there. 



An Eastern Slope receives the sun in the cool morning 

 hours when the temperature and light are moderate. It is not 

 exposed to our hot, dry winds nor to the intense heat of the 

 sun. The soil retains its moisture fairly well and trees make a 

 good growth. For trees it ranks next in value to a northern 

 slope. 



A Southern Slope receives the most direct rays of the sun, 

 and the full force of our hot, dry winds and beating rains 

 during the growing season. Consequently vegetation is more 

 liable to injury by late spring frosts, because of starting earlier 

 in the spring, than in any other location. The soil is most 

 liable to erosion from beating summer rains and dries up most 

 quickly after the spring rains. The trees grow irregular in 

 form, the seeds seldom start well on southern or western slopes. 



