18 LOCAI.ITY AND Fdl^HST VEGETATION. 



of lifiht required by the several species little is known at 

 present, but much experience has been collected which 

 demonstrates their relative light requirements. On 'the 

 whole it is known that certain species cannot thrive unless 

 the.v enjoj' a large measure of light throughout life, while 

 others will bear a certain amount of shade. Accordingly, 

 the former species are termed lijiht dcinandhui, and the 

 latter sliade hcariuii or tolrnitiiif/. In a general way it may 

 be said, that trees with a dense crown are shade Ijearing, 

 and those with a thin crown light demanding, though the 

 light requirement does not always stand exactly in inverse 

 proportion to the density of the crown. 



Some species, which are shade bearing, require a certain 

 amount of shelter, or protection, during early youth ; they 

 have therefore been called " shade demanding." Such a 

 definition is, however, misleading, as these plants require 

 protection against heat and cold, and not against light as 

 such. In young plants of beech and silver lir, for instance, 

 transpiration frequently reaches such a high degree, if they 

 are not sheltered, that they lose water more quickly than 

 they can take it up from the soil, and consequently die. 

 Hence they require either a thorough wetting of the soil, 

 or shelter. In tlie former case more water is availal)le, 

 and in the latter the temperature and thereby the transpi- 

 ration is reduced. Species are called tender or luirdi/, 

 according as to whether they require shelter during early 

 life, or can do without it. 



By summing up the available experience of the light 

 requirements of a number of species, scales have been 

 prepared by various authors, which, though generally agree- 

 ing, differ somewhat in details. The following scale begins 

 with the most light demanding species and finishes with the 

 most shade bearing. Lime and Weymouth pine stand in the 

 centre of this scale; the species above them are considered 

 light demanding, and those below shade bearing, the degree 

 in each case depending on the distance from the centre line. 



