GRAZING AND BROWSING 123 



Browsing Life Habit 



This coaction type characterizes chiefly the large mammals (ungu- 

 lates) and some of the larger birds and rodents that inhabit the forest. 

 In North America and probably elsewhere, browsing is the primary 

 coaction during the season unfavorable for plant growth. It alter- 

 nates with grazing of aquatic plants, forbs, fungi, etc. (mainly mam- 

 mals), and with scratching for small ground animals or seeds (some 

 birds). In the coniferous forest of North America, the moose browses 

 chiefly on deciduous trees and shrubs, especially in winter, but eats 

 aquatic plants and some herbs in summer, while the Shiras or moun- 

 tain moose apparently browses the year around. The woodland cari- 

 bou uses lichens in winter and browse similar to that of the moose 

 during the remainder of the year. Likewise, various rabbits and the 

 Hudsonian spruce partridge browse on the growing tops of spruce 

 seedlings or trees, and the ruffed grouse eats buds of deciduous shrubs 

 and trees. The effect of this on the plants is not unlike light browsing 

 by large mammals. The tassel-eared squirrels feed on the bark of 

 terminal twigs (Figs. 31, 32). 



Deer browse regularly, but in favorable seasons they may also 

 consume large quantities of mushrooms and sometimes forbs. The elk 

 possesses the ability to live both in open forests with grassy parks 

 and in savanna areas, and at one period it ranged across the northern 

 part of the Great Plains. It divided its time, seasonally and daily, 

 between the timber along the streams and the open prairie (Bailey, 

 1926). Elk browse at all seasons, but especially in winter; they also 

 eat all kinds of herbs, including much grass, thereby differing from 

 the deer. Rabbits browse in the unfavorable season and also take bark 

 from woody plants; the porcupine is similar in this respect but more 

 arboreal, eating the bark at some distance above the ground. Squir- 

 rels, especially the red squirrel, nip off the end buds of conifers in a 

 similar manner (Hatt, 1929). All these rodents resemble the deer 

 in taking herbaceous plants in the growing season, and consequently 

 compete with ungulates in grassy parks as well as in wooded areas. 



Defoliation and Bud and Twig Injury. This is chiefly the work of 

 insects and arachnids; the lepidopterous and hymenopterous larvae 

 play an important role. In the coniferous forest, the hemlock looper, 

 spruce budworm, and larch and jack pine sawflies are of some small 

 importance in competition with the browsers. The subclimax decidu- 

 ous trees are at times defoliated by sawflies and moth larvae. In the 

 deciduous forest, the cicadas, twig girdlers, and twig-boring beetles 

 have somewhat the same effect as the browsers, but native defoUators 



