430 RELATIVE EFFECTS OF DIFFERENT KINDS OF TREES. 



the case of the elm and of the Scotch fir — one would naturally sup- 

 pose that the diversity of their effects in improving the land is in some 

 measure to be ascribed to the quantity and kind of the inorganic mat- 

 ter which the leaves of these several trees contain. And to this 

 cause, no doubt, some effect is to be ascribed in localities where all 

 the trees thrive equally. 



But upon the quantity of leaves produced, as much in general will 

 depend, as upon the relative proportions of organic and inorganic 

 matter vdiich these leaves may respectively contain. And as the 

 quantity of leaves is always greatest where the tree flourishes best or 

 finds a most propitious soil — the improvement of the soil itself, by 

 any particular tree, will be always in a great measure determined by 

 its fitness to pronnote the growth of that kind of tree* 



On the soil planted by the Duke of Athol, the larch shot up luxu- 

 riantly, while the Scotch fir lingered and languished in its growth. 

 Thus the quantity of leaves produced and annually shed by the 

 former was vastly greater than by the latter tree. Had the Scotch 

 fir thriven better than the larch, the reverse might have been the 

 case, and the value of the soil might have been increased in a great- 

 er proportion by plantations of the former tree. 



Other special circumstances also will account for the relative de- 

 grees of improvement produced by the larch and by some of the 

 other trees — for example, the oak. In the oak copse the soil in 16 

 years become worth 6s. or 8s. an acre. If, therefore, instead of being 

 cut down for their bark at the end of 24 years, \\^ trees had been al- 

 lowed to grow up into an oak forest, the permanent improvement of 

 the pasture, even on this soil, would probably have been at least as 

 great as under the larch. The above experiments, therefore, are in 

 reality not so decisive in regard to the relative improviJig- power of 

 the several species of trees as they at first sight appear. The most 

 rational natural rule by which our practice should be guided seems 

 to be contained in these three propositions — 



1°. That the soil will be most improved by those trees which thrive 

 best upon it. 



2°. Among those which thrive equally, by such as yield the 

 argest produce of leaves, and — 



3°. Among such as yield an equal weight of leaves, by those whose 

 leaves contain the largest proportion of inorganic matter — which 

 bring up from beneath, that is, and spread over the surface in largest 

 quantity, the materials of a.fertile soil. 



The mode in which the lower branches of the larch spread out and 

 overshadow the surface is not without its influence upon the ultimate 

 improvement which the soil exhibits. All vegetation being prevented, 

 the land, besides receiving a yearly manurg of vegetable mould, is 

 made to lie for upwards of 20 years in uninterrupted naked fallow. 

 It is sheltered also from the beating of the min drops, which descena 

 slowly and gently upon it, bearing principles of fertility instead of 

 washing out the valuable saline substances it may contain. 



Beneath the overshadowing branches of a forest, the soil is also pro- 

 tected from the wind, and to this protection Sprengel attributes much 

 of that rapid improvement so generally experienced where lands are 



