APPLIED ECOLOGY 327 



forest. To be sure, largely by trial and error, the farmer has learned 

 to grow crops so that they give a reasonable return for his labor. 

 But, on the whole, this has been done at the expense of the soil as 

 a natural resource. The natural fertility of most of our soils is 

 largely depleted, erosion has ruined thousands of acres and re- 

 duced the productivity of many more, and water tables have been 

 lowered to such an extent that crops in areas with rainfall suffi- 

 cient for hardwood forest are suffering during dry spells as much 

 as they would in grassland climate. Thanks to increased knowledge 

 of fertilizers, the development of productive hybrid strains of 

 various crop plants, and modern mechanized methods, our yields 

 have steadily increased, but this cannot proceed indefinitely, espe- 

 cially since much of the increase in yield has resulted in further 

 depletion of the soil. 



To counteract the inevitable downward trend of productivity, 

 soil conservation and erosion control are receiving greater atten- 

 tion. Increased knowledge of crop ecology is imperative so that 

 the highest yielding species will be grown under the proper con- 

 ditions of cultivation and on the right sites. If possible, yields must 

 be maintained at high levels at the same time that soils are im- 

 proved rather than being depleted. The ecology of weeds, pests, 

 and diseases must be studied so that the depredations of these prod- 

 ucts of cultivation may be held in check effectively. These things 

 are not being neglected by agronomists and horticulturists, but 

 there are special contributions that can be made if the investigator 

 has the ecological point of view. 



Land Use.— It has been customary to clear all workable land for 

 agriculture, permit plowland to revert to pasture only when it 

 becomes unprofitable, and permit pasture in turn to revert to for- 

 est only under the same conditions. It may be desirable to reverse 

 this procedure completely. Perhaps the soundest ecological ap- 

 portionment of the landscape would be represented by a minimum 

 of carefully selected, skillfully operated plowland with a max- 

 imum of natural vegetation. Where this natural vegetation consists 

 of grassland, regulated pasture is an aspect of its normal develop- 

 ment; where it consists of forest, it should be scrupulously pro- 

 tected against grazing, and whatever pastures are required should 

 be handled with the same measure of skill that has been suggested 



