CONSERVATION 



823 



effective because it is based on sound ecologic principles. The rotation 

 of crops, contour farming, the establishment of wind breaks to prevent 

 soil erosion by winds, and the use of proper fertilizers to renew the 

 soil are all measures which are effective in maintaining a balanced 

 ecosystem. Successful farming must follow the principles of good land 

 use. It is not conservation to reclaim marginal land for agricultural 

 purposes or to build expensive dams and canals to irrigate land unless 

 the land can produce crops which will make the irrigation worth while. 

 If the grasslands of regions with slight rainfall are plowed and planted 

 with wheat, a "dust bowl" will inevitably develop, but if the land is 

 kept as grassland and grazed in moderation the soil will be kept in 

 place, no dust bowl will develop, and the land can be used economically 

 year after year. Overgrazing, by destroying the grass covering the soil, 

 can lead to destructive erosion just as plowing does. Overgrazing also 

 leads to the invasion of the grassland by undesirable weeds and desert 

 shrubs. These are difficult to eradicate so that grass may grow again. 

 It is now evident that poor land use affects not only the unwise farmer 

 but the whole population which is eventually taxed to pay for rehabili- 

 tation. 



The ecologists specializing in the management of land have classi- 

 fied land on the basis of its slope, kind of soil and natural biotic com- 

 munities, into eight categories, from Class I, which is excellent for 

 farming and can be cultivated continuously, through three classes which 

 can be used for farming only with special care and another three classes, 

 which are suitable only for permanent pasture or forest, to Type VIII, 

 suitable only to be left as it is for game (Fig. 40.1). 



Figure 40.1. Classification of land according to its usefulness. Types I and II 

 may be cultivated continuously; types III and IV are subject to erosion and must be 

 cultivated with great care; types V, VI and VII are suitable for pasture or forests 

 but not for cultivation; type VIII is productive only as a habitat for game. (U. S. Soil 

 Conservation Service.) 



