CHOICE OF SPECIES. 7 



subject to damage by insects than any other European 

 species, &c. All these macters influence the choice of 

 species under a given set of conditions. 



4. Capacity of Species to preserve or improve the Fertility 

 of the Locality. 



From the point of view of Political Economy the 

 improvement, or at any rate the maintenance, of the 

 yield capacity of the land is the most important con- 

 sideration. Whether the owner of a forest be the State 

 or a private person, he will find a system of manage- 

 ment recognizing that principle to be the most profitable 

 in the long run. Hence it must be the forester's en- 

 deavour to grow species not only suited to the locality, 

 but also tending to improve it.* 



In the first place the quality of the locality must 

 be carefully ascertained, so as to avoid growing a species 

 which has no chance of thriving on it. This task is by 

 no means an easy one, because the effects on tree growth 

 of some of the factors of the locality are as yet im- 

 perfectly understood. The climatic factors are of special 

 importance ; hence the effects of the geographical posi- 

 tion, altitude, aspect, gradient, contour and surroundings 

 of the locality upon the temperature, degree of moisture, 

 and air currents must be carefully considered. The soil, 

 and, if necessary, the subsoil as well must be examined 

 as to depth, degree of porosity and moisture, composition 

 and admixture of humus. The development of any trees 

 already growing on the locality, or in its vicinity, should 

 be carefully studied.! An investigation of this kind will 



* See Chapter I. of Part. II. of Volume I., especially pages 137 150. 

 t See pages 150 157 of Volume I. 



