BRITISH FOREST TRKI-.> 313 



show the best growth and development, no great demands 

 being made on mineral strength. Along with a sufficiency 

 of soil-moisture, the aspen also requires a considerable degree 

 of relative humidity or atmospheric moisture to enable it 

 to develop into a good timber-producing tree, so that in 

 hilly tracts it is generally to be found near streams and on 

 wet patches in forests of beech, spruce, or pine, and oftener 

 in sheltered dingles or coombs, and along the base of hills, 

 than on exposed and windy situations. For these reasons the 

 cooler and damper northern and eastern aspects are on the 

 whole better suited for it than the drier southern and south- 

 western exposures, although a high degree of atmospheric 

 warmth is in no wise antipathetic to it, as is attested by its 

 sporadic growth on the hotter situations. 



Requirements as to Light. Shade-bearing capacity is not 

 a quality at all attributable to the poplars. That the aspen, 

 with its lofty, open, sparse and lightly-foliaged crown, 

 should be exacting in regard to the enjoyment of light is 

 natural and self-evident. Among broad-leaved trees it is 

 second only to the birch as a light-demanding species, and 

 even in comparison with conifers is only outrivalled in this 

 respect by the larch ; in demand for light and air it must 

 be ranged alongside of the Scots pine, and of its own 

 close relatives the willows. All poplars are light-loving trees, 

 which can bear no measure of shade or overshadow ing, 

 and in their turn cast only a light shade over their under- 

 growth. When once caught up in growth by trees which it 

 has outstripped in the first stages of youthful development, 

 the aspen soon sickens and dies. Even the central in- 

 dividuals in groups or patches only display an energetic 

 growth whilst the crowns obtain the full enjoyment of light 

 and air, and at once become affected by such moderate 

 side-shade as is cast by ash, oak, or Scots pine. When 

 once the beech approaches it in height, the aspen had 



