this control even more desirable. Damage done to the 

 range by increased populations of rodents and rabbits 

 has undoubtedly been much greater than the mone- 

 tary value of an occasional killed lamb, calf, or 

 chicken. In the great grasslands of the West, where 

 human populations are low, there would be advan- 

 tage not only in reducing the amount of grazing by 

 livestock to the carrying capacity of the land but in 

 restoring balanced populations of herbivorous and 

 carnivorous species. 



THE FOREST-EDGE COMMUNITY 



Grassland animals are usually restrained 

 from penetrating forests in the same way that true 

 forest animals are restrained from penetrating grass- 

 land, although the home ranges of these species may 

 overlap at the forest margin and in shrubby areas. 

 Since shrubs are especially numerous at the forest- 



FIG. 9-5 Interior of a virgin 

 coniferous forest of Engeimann 

 spruce in Colorado (courtesy 

 U.S. Forest Service). 



edge and animals have an opportunity to make use 

 of these as well as both grassland and forest, the 

 forest-edge biocies is well developed for some groups 

 of animals. There are probably no soil or small 

 ground animals characteristic of the forest-edge. 

 There are some foliage insects that find their pre- 

 ferred niches here. Many insects of grassland and 

 agricultural crops that overwinter as adults migrate 

 into the forest-edge to hibernate. Since many game 

 species of interest to man reach their greatest abun- 

 dance on the forest-edge, he has become impressed 

 by this so-called edge effect. When total populations 

 of all species are measured, however, the density of 

 birds (Table 9-11 ) or mammals is not always higher 

 than in the forest. When tw^o forest types come in 

 contact, for instance different deciduous forest types 

 or deciduous and coniferous forests, there is no con- 

 sistent change in the density of animal species 

 (Barick 1950 ) . The forest-edge is the preferred nest- 

 ing site of many birds (Johnston 1947). 



Grassland, forests, and forest-edges 1 29 



