ANIMAL ECOLOGY OF JOHNSON COUNTY = 21 
The plants which have been able to establish themselves with 
any degree of permanence upon these summits are naturally the 
most xerophytie of all the prairie forms. Descending these 
dunes, from the summit toward the base, is a constant increase 
in the number of individuals and of species. A corresponding 
increase, therefore, in the number of animal forms and in the 
complexity of the animal associations in the same ratio is to be 
expected. This is the region of the greatest abundance of the 
land tortoise, whose tracks were visible on the dry sandy summit 
of every naked dune in April, 1917. Of the more common in- 
vertebrates, Tiger beetles and digger wasps command attention. 
The location of these dunes is given on the County Map, Plate 
III. They are to be found at the areas indicated by A-shaped 
marks. It will be seen that their distribution is limited to the 
west part of Madison township and the north part of Oxford 
township. The one found in the southeast quarter of Section 12 
of Oxford township is the best example in the county at present 
of a shifting dune. A similar semi-barren sand area in Penn 
township, Sections 29 and 30, Township 80 north, Range 6 west, 
is also given on this map. It is somewhat similar in reference to 
its physical characters and vegetation, although it is evidently 
of alluvial origin, and has been listed because of its availability 
from Jowa City as a working center. 
Forest HABITATS 
The forested areas of Johnson County, while they are of much 
more limited extent than the original prairies and while they 
have been very much reduced and modified by man, present such 
a great number of varied conditions that they easily afford a 
life’s work in any attempt to do justice to a proper. intensive 
study of their animal associations. The tree-covered lands vary 
dn character from steep, rocky bluffs to low-lying, semi-swamp= 
stretches on the alluvial plain. The trees themselves vary from 
the burr oak of the uplands to the willow and water birch along 
the sloughs and streams, which actually stand in water several 
weeks of the year. Between such extremes as these there are all 
stages of intergradation, all possible types of intermingling. 
Any classification of these formations under a few headings is 
of necessity arbitrary and artificial. That which has been adopt- 
