594 FOKEST LITTER. 



Khould also be notocl, viz., that it falls off in quantity with the 

 altitude. 



(c) Weather. — Any casual observer must have noticed that 

 according to the changes of weather in different years, the 

 forest presents different appearances, being in certain years 

 fresher, greener and possessing denser foliage than at other 

 times. Spring-weather is most decisive in this respect. Years 

 with severe late frosts and dry seasons produce less foliage than 

 moist years free from frost. According to Krutzsch, there may 

 be a difference of 60 % in the amount of foliage produced by 

 Scotch pine and beech in wet and dry years. 



The duration of the foliage of evergreen trees depends on 

 their shade-bearing properties and age, on the climate, the com- 

 parative density of the crop, frosts and nature of the weather in 

 spring. As a rule, leaves persist longer in southern than in 

 northern latitudes. The amount of rainfall is very influential ; 

 with heavy rainfall needles which should fall normally remain on 

 the trees, and whenever a dry year follows a damp one, needles 

 of two or three consecutive years may all fall together. 



(d) Density of growth and system of management. — The pro- 

 duction of foliage depends on the free admission of light to the 

 trees ; the more a tree is exposed on all sides to light, the larger 

 its crown. A tree, therefore, standing in the open produces 

 far more litter annually than a tree of the same species grown 

 in a dense wood. 



The densest woods do not produce most litter, nor do open 

 woods where each tree is completely exposed to the influence 

 of light, the number of individual trees being then too few. 

 The most litter is produced annually when there are as many 

 stems as possible in a wood, with the proviso that each stem 

 has ample room for its growth — a density which results from 

 well executed thinnings. 



Even-aged woods exercise a similar influence to that of the 

 density of woods on the animal supply of litter. When all trees 

 in a wood are of the same height and their crowns form a dense 

 leaf-canopy at a uniform level above the ground, the influence of 

 light is far less than when the heights of the trees vary, when 

 lateral light is admitted between the groups of the taller trees 

 and their crowns consequently grow lower down their stems. 



