g94 ANIMALS AND THEIR ENVIRONMENT 



The control of insect pests by chemicals such as DDT must be 

 carried out cautiously, with possible ecologic upsets in mind. Spraying 

 orchards, forests and marshes may destroy not only the pests but also 

 useful insects such as honeybees which pollinate many kinds of fruit 

 trees and crops, and useful insect parasites. In some cases the insect pests 

 have actually increased after the use of DDT because the chemical 

 killed off greater numbers of insect enemies of the pest than of the 

 pests themselves. A number of strains of insects resistant to DDT have 

 developed. 



DDT and related chemicals kill other animals in addition to in- 

 sects; amphibians and reptiles are the most vulnerable vertebrates. The 

 vertebrates are less sensitive than insects, and DDT applied at a level of 

 about 1 j)ound per acre is effective in insect control without endanger- 

 ing the vertebrates. However, when applied at a level of 5 to 10 pounds 

 per acre some of the useful animals are killed along with the insects. 

 Some of the newer, stronger insecticides have been used without ade- 

 quate testing of their effects on other animals. 



370. Forestry 



The management of our forests is an important aspect of applied 

 ecology. Careful forest management has been carried on in Europe for 

 many decades but is only beginning in this country. Proper timber 

 management in our national and state forests has been important in 

 demonstrating to the owners of private forests the results which can be 

 obtained in this way. Since in some regions the desirable timber trees 

 are members of the climax community, the ecologic problem is simply 

 to find the best way to speed the return of the climax community after 

 the trees have been cut. In other regions the desirable trees are earlier 

 serai stages of the ecologic succession, and forest management involves 

 establishing means of preventing the succession from proceeding to the 

 climax community. This is also true of many kinds of animals; most 

 game birds and many of the most valuable game fish are members of, 

 and thrive best in, an early serai stage of their community. 



371. Wildlife 



The management of our fish and wildlife resources is a field of 

 applied ecology which is supported by wide public interest, especially 

 by sportsmen's clubs and associations. "Wildlife" used in this connec- 

 tion usually means game and fur-bearing animals. Since the various 

 types of wildlife are adapted to different stages of ecologic succession, 

 their management requires a knowledge of and the proper use of these 

 stages. As the Middle West became more and more intensively farmed, 

 and the original forests and prairies were reduced to small patches, the 

 prairie chickens and ruffed grouse which were adapted to these habitats 

 were greatly decreased in numbers. However, this region has been par- 

 tially restocked with game birds by introducing pheasants and par- 



