I5RITISII FOKKST TREES 15 



made is found in the fall of leaves after fulfilling their 

 function, flowers, fruits, twigs, and the like, whilst the leaf 

 canopy also assists mechanically by preserving the soil- 

 moisture from being evaporated by the sun's rays and 

 by winds, thereby allowing the moisture more opportunity 

 of rendering soluble the mineral constituents of the soil. 

 Under the shade of the forest trees lowlier forms of 

 vegetation thrive, and these in turn die, decompose, 

 and aid in the great work of forming humus or leaf-mould 

 which, being strongly hygroscopic, absorbs and retains 

 the atmospheric moisture and precipitations, and regulates 

 the motion of moisture within the soil. The roots of trees 

 also in ramifying penetrate the soil in every direction, 

 first of all cleaving and breaking up the rocks mechani- 

 cally, and then on decaying assist indirectly in the 

 subsequent chemical changes. 



Retention of soil-moisture and formation of humus or 

 vegetable mould, by which is meant all organic matter in 

 process of decomposition two of the important factors in 

 determining the quality of soils from a sylvicultural point 

 of view are therefore the principal benefits conferred by 

 tree-growth on the soil. Without considering the excep- 

 tional cases of very fertile or very moist soils, whose mineral 

 strength or supply of moisture is not likely to be affected, 

 these objects are most satisfactorily attained by maintaining 

 growth in closed canopy although the crowns of the trees 

 need not necessarily be all at the same level, as in planta- 

 tions so that the soil should not be exposed to the disturb- 

 ing and inimical influences of sun and wind, blowing away 

 the dead leaves, evaporating the moisture, and otherwise 

 interfering with the gradual process of decomposition of the 

 humus. If the canopy be too light or broken, rank growth 

 of grasses and weeds gains a foothold, and consumes the 

 nutriment unprofitably, so that the crops best adapted for 



