REACTIONS ON LAND 85 



acteristic of swine and their relatives, and produces the maximum local 

 disturbance of this type. Pawing resembles it closely in effect when 

 roots and bulbs are dug out of the soil by this method, but as a rule 

 the effect of pawing is merged in the greater reaction due to trampling. 

 Trampling acts primarily by destroying the plant cover and working 

 the remains into the loosened soil, improving the penetration of rain- 

 fall, and perhaps hastening the incorporation of organic material. On 

 the other hand, the damage done to the plant matrix directly and as 

 a consequence of increased erosion by water and wind far overbalances 





■4----'- ••■•^ ..r -»m»t^^- 



'"mim. 



Fig. 18. — TeiTaces produced by gi-ound .■^^qmrii 1-, upper ."^lui Joaquin Valley. 

 (Photo by Edith Clements.) 



any beneficial action. The formation of blowouts in sandhills is a 

 frequent outcome of the trampling reaction, particularly about water- 

 ing places. 



Somewhat akin to pawing and rooting are the scratching and 

 pecking of most ground birds and some perchers, utilized for the 

 finding of food or gravel, for "dusting," making hollows for nests or 

 "forms," and so forth. Aside from gallinaceous birds, those that nest 

 on the ground away from water are relatively few, the lark bunting 

 being an example. Surface disturbance is also a reaction in the 

 case of reptiles. The effects of all such habits are of much the same 

 nature as those of burrowing, the uppermost layer of the soil being 



