CHAP, i i.i The British Sylva 31 



in a purely sylviculture!, and not in any financial, sense ; for, as 

 a matter of fact, the most valuable species of timber are usually 

 to be found among the latter class. To the former belong, 

 among the conifers, Scots Pine, Spruce, Silver Fir, and occa- 

 sionally Larch, and among the broad-leaved trees, Beech, Oak, 

 Birch, and Alder principally ; whilst the latter include all the 

 other indigenous and exotic trees now of woodland growth in 

 Britain, of which the principal are the Douglas Fir, the Menzies 

 Spruce, the Black Pines (Austrian and Corsican), and the Wey- 

 mouth Pines among conifers, and the Ash, Maple, Sycamore, 

 Elm, Hornbeam, Aspen, and Willow among broad-leaved species. 



For the sake of brevity the following details will be con- 

 fined to the above-named trees only. 



Whilst in growth trees extract supplies of nutriment partly 

 from the atmosphere (in the shape of carbonic acid, the 

 carbon being assimilated, and the oxygen being set free) and 

 partly from the soil occupied by their root-systems (mineral 

 nutriment). If the trees were to be allowed to die off and 

 then rot, in place of being utilized as timber whilst still in healthy 

 growth, the supplies of mineral nutrients extracted from the 

 soil would be restored to it, by the formation of humus or 

 mould, on the ligneous tissue becoming decomposed under the 

 action of sunlight, moisture, and a moderate degree of warmth. 

 But, with the removal of the timber crops, the natural balance 

 is disturbed ; and, unless protection be afforded to the agencies 

 active in causing the chemical changes that result in the de- 

 composition of its mineral constituents, the soil runs a risk 

 of becoming gradually deteriorated and finally exhausted. In 

 agriculture, a similar danger is obviated by manuring the land, 

 the manure not only helping to replace the nutrients previously 

 withdrawn, but also stimulating to increased nitrification and 

 decomposition of the soil. In sylviculture, however, such 

 measures would be neither practicable nor remunerative ; and 

 the only recompense that can practically be given consists in 

 the fall of dead foliage, twigs, &c. Fortunately, however, in 



