A NATIONAL PLAN FOB AMERICAN FORESTRY 511 



INFLUENCE OF FORESTS ON FISH LIFE 



That forests have a profound effect on fish and other aquatic life 

 must be evident to even the most casual observer. This influence is 

 far-reaching and affects almost every phase of the life and activities 

 of these animals. In streams, the growth and well-being of fish are 

 affected by the temperature of the water, the speed of the current, the 

 presence or absence of food, the nature of the bottom, the amount of 

 shade and shelter provided by the vegetation on the banks and in the 

 water, and by variations in the water level. In lakes and ponds the 

 relative extent of deep and shallow water is also an important factor. 



One of the most obvious effects of forests on stream conditions is 

 in connection with the temperature. Forests tend to keep cool the 

 stratum of air overlying the water and prevent the stream bed and 

 surrounding ground from warming during the day. The result is 

 that in forested regions the temperature of the water is usually con- 

 siderably lower than in streams exposed to the full force of the sun's 

 rays. Not only is the average temperature lower but the daily 

 fluctuations are much less. The cooling effect of the forest is so 

 pronounced that we have numerous instances of streams in which 

 the temperature is lowered several degrees as a result of flowing 

 through a forested area. 



The influence of the temperature on fish is most noticeable in the 

 case of trout, which are classed as cold-water fishes as distinguished 

 from such game fishes as bass or sunfish, which require warmer water. 

 The eastern brook trout thrives best at temperatures between 50 and 

 60 F. but may for short periods withstand temperatures as high as 

 75 F. when the water is well aerated. Under similar conditions ram- 

 bow and brown trout can survive temperatures of 80 F., and .pos- 

 sibly even higher, without apparent injury. This means that in 

 forested areas many streams are suited to trout which if fully exposed 

 to the sun would be uninhabitable by these fish. In many localities 

 as a result of deforestation streams which formerly provided ideal 

 conditions for trout are now unable to support these fish. Others 

 have become too warm for brook trout, which formerly were present 

 in great abundance, but are still suitable for brown or rainbow trout. 



Forests usually exert a favorable influence on the supply of food 

 available for fish, but in some instances they may have an opposite 

 effect. As in the case of land animals, fish are, in the last analysis, 

 dependent on plants especially the algae for most of their food. 

 When the trees and shrubs on the banks of a stream are crowded 

 closely together the shade may be so dense as to seriously interfere 

 with the growth of plant life in the water. This, of course, results 

 in a marked scarcity of animals, and we frequently find such areas 

 to be almost devoid of fish. OccasionaUy dead leaves may accumulate 

 to such an extent in pools and quiet streams as to seriously interfere 

 with the growth of food organisms. 



In most cases, however, the effect of forests on the production of 

 fish food is distinctly beneficial. Fallen trees in the bed of a stream 

 or along the shores of a lake furnish support for insects and other 

 aquatic organisms which can usually be found in such places in large 

 numbers. They also provide an ideal shelter for fish. Trout delight 

 to lurk in the cool depths of pools containing fallen logs and branches 

 beneath which they can retreat from their enemies. The impor- 



