BRITISH FOREST TREES 5.5 



by the various species when advancing in age. Light-loving 

 species, like the Scots pine or the oak, have earlier and 

 greater requirements as to growing-space than those with 

 denser foliage, like the spruce or beech. Trees grown in 

 the close canopy of high forest have not the same freedom 

 and enjoyment of light and air, and in consequence are less 

 vigorous than, and do not attain so high an age as, those 

 grown in a more isolated position, or in the open. Unless 

 due development of all assimilative organs takes place, 

 full vigour and health are not attainable ; but the capacity 

 for regaining normal vigour on being admitted to larger 

 growing-space differs considerably in the various species 

 of trees, being greater in oak, lime, willow, elm and Cembran 

 pine than in alder, aspen, maple, sycamore, beech, horn- 

 beam and spruce (Gayer, op. cit. p. 44). 



The second essential condition is that soil and situation 

 must continue to supply the demands made by each species 

 relative to its normal development. In general the locality 

 where a certain species is indigenous affords it all the 

 conditions necessary for the maintenance of healthy vigor- 

 ous growth, and the attainment of sound old age. The 

 longer the natural term of life, and the greater the demands 

 of the species on the qualities of the soil, the more danger 

 there is of its healthy development being interfered with, 

 and at the same time the greater the risk of the soil deterio- 

 rating, and losing its moisture and power of decomposing 

 humus. Localities differing from that in which the species 

 is indigenous may offer too much or too little warmth of 

 soil and air, considerable variations from the normal 

 requirements being in either direction injurious ; or the soil 

 may offer more or less than the favourable degree of moisture, 

 mineral strength, or depth, richness of soil tending towards 

 precocity and immature development beyond the limits of 

 healthy vigour and power of resisting the action of conditions 



