MAMMALS AND SOIL TURNOVER IOO, 



rainfall, which is very important in arid and semi-arid regions. In this 

 way the work of burrowing mammals compensates for some of the 

 damage they do to crops. On the other hand, the burrows of some of 

 the larger species, such as prairie-dogs, badgers and the like often cause 

 injuries to horses and riders on the western cattle and sheep ranges, and 

 the ridges and mounds of moles and gophers are a serious detriment to 

 lawns, gardens and some fields. Furthermore, the loosening of the soil 

 promotes erosion, which may be serious on steep slopes but little pro- 

 tected by vegetation. 



The burrows of rats, muskrats, beavers, gophers and other mammals 

 of ten. damage earthen embankments, reservoir dams, dikes and canal 

 banks, weakening them, causing leaks and sometimes resulting in flood- 

 ing the adjacent lands. It is said that the American muskrat, intro- 

 duced into Europe, is endangering whole systems of waterways. 4 Beav- 

 ers often flood fields and roads by building their dams across streams, 

 thus backing up the water until it overflows This is usually detrimental 

 to human interests, but not always so. By turning waste lands into 

 ponds, lakes and swamps, they may sometimes provide reservoirs to 

 detain storm waters, retard run-off, and thus lessen damage by floods, 

 as well as providing quiet pools where trout and other fish fry may 

 acquire sufficient size and strength to enable them to safely enter swift 

 streams. 



The biological and environmental interrelations in nature are ex- 

 tremely complicated. It may be that the stirring and aeration of the 

 soil by burrowing mammals are very important, if not necessary, to 

 the thrift of certain kinds of plants. It is well known that some species 

 of plants are at their best only on soil which has been recently dis- 

 turbed by the plow or otherwise. It is also certain that chemical and 

 bacterial characteristics of the soil have a large influence upon plant 

 growth. A thorough study of the influence of the disturbance and 

 aeration of the soil by burrowing animals upon soil bacteria and chemi- 

 cal reactions might prove very fascinating and perhaps fruitful. 



The erosion and destruction that follows forest fires and excessive 

 lumbering operations 6 is observed also to follow overgrazing. In re- 

 gions where slopes are steep, covered with loose soil, rainfall light, but 

 consisting of occasional heavy downpours, the destruction of the scant 

 vegetation in many localities has resulted in very rapid erosion and 



4 Aherns, Muskrats in central Europe, Journ. Mammalogy, n, 236-237, 1921. 

 "Glenn, Denudation and erosion in the southern Appalachian Region and the 

 Monongahela Basin, U. S. Geol. Surv. Professional Paper No. 72, 1911. 



