202 DRAINAGE BY ROOTS OF TREES. 



vation and human inhabitation not less than 1,100,000 acres of 

 ground once well wooded, well drained and productive. 



It is an important observation that the desiccating action of 

 trees, by way of drainage or external conduction by the roots, is 

 greater in the artificial than in the natural wood, and hence that 

 the surface of the ground in the former is not characterized by 

 that approach to a state of saturation which it so generally mani- 

 fests in the latter. In the spontaneous wood, the leaves, fruits, 

 bark, branches, and dead trunks, by their decayed material and 

 by the conversion of rock into loose earth through the solvent 

 power of the gases they develop in decomposition, cover the 

 ground with an easily penetrable stratum of mixed vegetable and 

 mineral matter extremely favorable to the growth of trees, and at 

 the same time too retentive of moisture to part with it readily to 

 the capillary attraction of the roots. The trees, finding abundant 

 nutriment near the surface, and so sheltered against the action of 

 the wind by each other as not to need the support of deep and 

 firmly fixed stays, send their roots but a moderate distance down- 

 wards, and indeed often spread them out like a horizontal net- 

 work almost on the surface of the ground. In the artificial wood, 

 on the contrary, the spaces between the trees are greater ; they 

 are obliged to send their roots deeper both for mechanical support 

 and in search of nutriment, and they consequently serve much 

 more effectually as conduits for perpendicular drainage.* 



It is only under special circumstances, however, that this func- 

 tion of the forest is so essential a conservative agent as in the two 

 cases just cited. In a champaign region insufficiently provided 

 with natural channels for the discharge of the waters, and with a 

 subsoil which, though penetrable by the roots of trees, is other- 

 wise impervious to water, it is of cardinal importance ; but though 

 trees everywhere tend to carry off the moisture of the superficial 



* It has been remarked that with the planting of trees [on the Landes] the 

 sheets of water on the surface have disappeared. This is attributed to the 

 powerful tap-roots of the maritime pine, which, in time, pierce the pan and 

 furnish an ingress for the surface waters into the porous strata beneath. — 

 French Forestry, etc.: Journal of Forestry, March, 1879, p. 771. The same 

 Journal, p. 813, contains the account of a bog which was planted forty years 

 ago with Italian black poplars. These trees, which grew rapidly, have drained 

 the bog by their roots, these having penetrated, through many feet of bog and 

 clay, into a porous underlying stratum. 



