CHAP, ii.] The British Sylva 33 



well and is thickly foliaged, though, as the leaves are thin in 

 texture, the amount of humus formed is only slight ; the Chest- 

 nut has a thick crown of foliage yielding good mould. None of 

 these last three genera occur, however, to any great extent form- 

 ing pure woods in Britain. Oak, Elm, Ash, Maple, Sycamore, and 

 the other valuable broad-leaved species are, owing to the com- 

 parative lightness of their crowns of foliage, not naturally well 

 endowed with capacity for protecting the productive power of the 

 soil, when they form crops by themselves, without the assistance 

 of other trees with denser crowns, although they may be found 

 doing well on soils of so moist a character that insolation and 

 evaporation are rather beneficial than prejudicial in diminish- 

 ing the amount of soil-moisture. Among conifers the species 

 best endowed with soil-improving and soil-protecting qualities 

 are in particular Spruce, Menzies, Douglas, and Silver Firs, and 

 in a less degree the Weymouth and the Austrian and Corsican 

 Pines, the fine growth of mosses beneath which also acts like 

 humus in sponge-like absorption and retention of moisture. 

 Scots Pine and Larch are, owing to the sparseness of their foliage, 

 least endowed in this respect, although during the earlier stages 

 of their development a good layer of moss is usually to be 

 found covering the soil, and protecting it from the inimical 

 and exhausting effects of sun and wind. When once the canopy 

 begins, however, to get broken, this beneficial covering of moss 

 disappears ; and then the soil, with its new growth of rank 

 grasses, whortleberry, or heather, rapidly begins to deteriorate, 

 unless underplanting is taken in hand. Where marshy land is 

 planted up with Alders, Birch, Willows, and Poplars, the action 

 of sun and wind is often beneficial, just because it tends to 

 reduce the quantity of moisture, which is apt to be excessive 

 on such low-lying situations. 



One of the leading principles in the Management of Forests is 

 that in woods of normal composition, having crops of all ages and 

 classes properly represented from zero up to maturity on areas 

 of equal productive capacity, the annual fall of mature timber 



D 



