44 PLANTING. 



sand (the maximum at which the successful culture of the white field- 



turnip is supposed to be limited) to one-twentieth, the supposed point of 



ute sterility for even common herbage, are properly termed simple 



; d on which the pine, fir, larch, and perhaps the birch, can 



only le planted. Soils consisting of from seven-eighths to a larger pro- 



on of chalk will rear the beech chiefly; and when the proportion of 



half of vegetable matter to one-half of sand and loam meet in a soil, it 

 :oprrl\ simple vegetable earth, and comes under the denomination of 



. of which there are se\eral kinds, but which will be more particularly 

 mentioned under the head of soils. On this last-mentioned soil the 

 planter is chiefly confined to the abele, poplar, and alder : the willow and 

 birch only partially succeed, or when the vegetable matter is in a less pro- 

 portion to the other ingredients above stated. 



The elevation of the site of the intended plantation above the level of 



the sea. where that is considerable, influences the local climate so much as 



D to confine the choice of the planter to one or two species of trees 



only, i ven thong-h the soil should be otherwise favourable for mixed 



planting. 



Jt is calculated that an elevation of six hundred feet diminishes the 

 temperature of a site equal to that of one degree of north latitude ; ihe 



re of dryness or humidity of the atmosphere, and the force of the 

 winds seem also to increase in proportion to the elevation of the land. 

 Accordingly we find that different species of trees occupy different regions 

 and degrees of elevation on the mountains of the torrid, temperate, and 

 frigid /one-. 



According to Humboldt, the trees which grow in the highest elevation 

 are the pine and the birch, (these also it may be observed will flourish in 

 the lowest situations, the birch in particular will grow in soils periodically 



tlowed or covered with water for two or three months in a year). The 

 highest altitude of the growth of the pine is stated to be from twelve 

 thousand to fifteen thousand feet above the level of the sea, in latitude 

 20 ; and the limits of the growth of the ouk appears to be confined to ten 

 thousand three hundred. The last species of trees found nearest to the 

 limits of perpetual snow on Mount Caucasus, in latitude 42j, and on the 

 Pyrenees, are the common birch (Bctula alba), and the hooked pine 

 (Pinifj uncinafa) t and the red spruce fir (Pinua rubra). On the Alps, 

 latitude fio:n !."> to 1<>, the common spruce appears limited to an elevation 



..out live thousand nine hundred feet. In Lapland the birch is found 

 at the altilude of one thousand six hundred feet in latitude (J7 and 70. 

 The influence of dillercnt altitudes on the distribution and growth of 

 n in the interior elevations of the forests of 



Britain. The pine, fir, and birch occupy the highest points*; next the 

 sycamore and mountain elm ; lastly, the oak, beech, poplar, ash, and 



tout When the ground to be planted is, therefore, so high above the 

 le\el oi t to influence materially the nature of the climate, the 



to be planted should be selected according to the above 

 principles. In practice this ni..\ be tinned region planting. I3y imitat- 

 ing the natural process in this respect, not only tin- most profitable returns 

 which the site and soil are capable of producing will be secured, but also 

 the most ornamental cliccls produced on the landscape, and the useful ones 

 ol judicious shelter obtained. It generally happens in extensive planting 



the soil varies in different parts of the site in its properties and fitness 



* T/ir Mountain a$h ccupie* tome of the moit expoted of the Dartmoor Fern. Mr. 

 ton. 



