ANIMAL ECOLOGY OF JOHNSON COUNTY — 23 
In treating the animal associations of such formations, 
Shelford* recognizes four strata of life: (a) subterranean- 
ground stratum, (b) field stratum, (ce) shrub stratum, and (d) 
tree stratum. Adams,{ in a similar consideration of the same 
subject, which he treats under the head of ‘‘communities,’’ 
recognizes and discusses in detail six such divisions, as follows: 
(a) forest soil community, (b) forest fungus community, (c) 
forest undergrowth community, (d) forest crown community, 
(e) tree-trunk community, (£) decaying wood community. This 
analysis will follow the plan of the same six subdivisions of the 
forest habitat brought out in Adams’ ‘‘communities’’ in so far 
as it is applicable to the various forest formations herein treated. 
Scattered oak groves. The scattered oak groves occur for the 
‘most part on the uplands and usually are much more exposed 
to evaporating influences than any of the other forest forma- 
tions. They are found regularly on hillsides, and not infre- 
quently on slopes that show out-croppings of rock. The main 
distinguishing physical characters are excellent drainage, rela- 
tively low moisture content of the atmosphere, and abundant 
light in all parts (due to the scattered condition of the trees). 
Not all of such groves are absolutely natural, as conditions have 
frequently been created by the thinning out of the trees in an 
ordinary solid piece of oak or oak-hickory until but a few re- 
main. As these are uniformly pastured, but little of the original 
vegetation has been preserved save the trees themselves. The 
surface of the ground has become set in a blue grass sod in which 
there is some intermingling of other grasses, a few composites, 
ete. 
From the standpoint of the life strata, only the soil commum- 
ties, the tree-trunk communities, and the tree-crown commumty 
need be considered. The lack of underbrush eliminates the 
‘undergrowth community and the comparative scarcity of fungi 
renders the fungus community of only occasional importance. 
The decaying wood community will deserve consideration only 
when the grove is the result of the thinning out of former solid 
*Shelford, ‘Animal communities in temperate America,’ Bulletin No. 5, the Geo- 
graphic Society of Chicago, University of Chicago Press, 1913; 362 pages, maps and 
plates. 
yAdams, ‘An ecological study of prairie and forest invertebrates,’ Bulletin of the 
Illinois State Laboratory of Natural History, XI (1915), Article II, pp. 34-279; 63 
plates. : 
