18G FOREST PLANTING. 



gions, trees which are generally found only in lower locali- 

 ties, while on the other hand trees will not grow in their 

 particular region if exposed to more than ordinary hard- 

 ships, and that in such case as the forester calls it 

 the trees " step downward." 



Those parts of the mountain slopes which are exposed 

 to the scorching sun rays (south) and the parching 

 winds (west) suffer often by the rapid evaporation of 

 the moisture contained in the soil, and, therefore, do not- 

 favor the growth of deciduous trees, but allow only such 

 evergreens as are not so pretentious in this regard, as 

 for instance, pines, cedars and larches. 



Sometimes the prevailing winds, being either un- 

 usually cold or excessively dry or very wet, change the 

 character of a mountain situation to the worse and do 

 not permit the growth of a vegetation which commonly 

 thrives there ; while surrounding higher mountains exer- 

 cise a protecting effect against such physical influence, 

 and often allow the growth of trees otherwise entirely 

 unknown in such a locality. 



The average humidity of the air, in growing forest- 

 trees, should also not be undervalued. So, for instance, 

 the fir, hemlock, spruce, beech, birch, ash and maple, 

 grow better in a more moist air than do pines and even 

 oaks. At all events the effects of excessive warmth upon 

 trees will be considerably counteracted by an excess of 

 moisture in the currents of the air. 



The quantity of warmth, light and humidity received 

 by any locality, depends, to a great extent, on the angle 

 with which the sun rays fall upon the same, and there- 

 fore the particular inclination of the soil towards the 

 horizon must not be left out of consideration. 



While the leaves of the trees feed mostly on the con- 

 tents of the air, the roots have to draw their support 

 from the soil in which they grow. Therefore, in ordef 



