40 SYLVICULTURE. 



pure forests in Central Europe. But other things are never 

 equal in nature; and trees having light and winged seeds, 

 especially hardy kinds that grow quickly at first (e.g., Birch 

 and Aspen), often establish themselves securely before the 

 kinds previously on the ground have been able to regenerate 

 themselves, so that a mixture of trees varying according to 

 soil, climate, and situation is characteristic of all natural wood- 

 lands, and is the safest method to adopt in forestry. 



Pure Woods can be formed by all kinds of shade-enduring 

 trees, because their dense overshadowing and large fall of dead 

 leaves both preserve and usually increase the soil-productivity. 

 This is also the case with Pines, under which thick moss 

 springs up when the trees begin to thin themselves ; but this 

 mossy protection disappears as the crop ages and the leaf- 

 canopy becomes more and more broken. But much less soil- 

 protection is afforded in the case of light-demanding deciduous 

 trees, which should therefore (theoretically) only be grown in 

 pure woods (1) when they are either to be felled at a com- 

 paratwely early age, or underplanted ; (2) when ihe soil- 

 productivity is not likely to be much impaired by imperfect 

 cover (e.g., mixed Oak, Ash, and Elm on deep, good, fresh 

 alluvial land; Alder, Birch, Willow, and Poplar on low moist 

 tracts, where sun and wind help to evaporate the excess of 

 moisture) ; or (3) where either the soil, the situation, or the 

 local market point to one species as being far more suitable 

 than any other (e.g., Pine on poor, dry sand; Austrian Pine 

 on deteriorated lime ; Ash-groves and Alder-beds on wet land). 

 Practically, however, it often happens that only one sort of 

 wood is saleable at a fair profit, and then, if he plant at all, 

 the landowner may prefer to plant that (e.g., pure Larch, 

 despite the risk there always is of canker). The most suitable 

 trees for pure woods are Beech and the shade-enduring ever- 

 green Conifers (Spruces, Silver and Douglas Firs, and Cypresses). 



Mixed Highwoods are on the whole preferable to pure woods, 



