Ross: The Dunesland Heritage of Illinois 21 



ferent from the other 50 kinds of stoneflies and nearly 200 kinds of 

 caddisflies that abound in most Illinois streams and lakes. These 

 isolated occurrences of northern species are bits of evidence that 

 furnish clues in detecting movements of the life that once occurred 

 in Illinois, but that now, except for these relict populations, has 

 moved to the north. 



As the ice dissipated and the climate became warmer, the conif- 

 erous forest and its associated plants and animals spread to the 

 north or became restricted to the higher elevations in the eastern 

 and western mountains of North America. 



Temperate deciduous forest also spread northward. At the 

 present time, there is a broad area of overlap nearly 500 miles wide 

 in which the more southerly of the northern coniferous forest trees 

 are intermingled with the northern extensions of some of the tem- 

 perate deciduous forest trees. The main band of this intergrading 

 area (technically called an ecotone) lies only a hundred miles north 

 of northeastern Illinois. Evidence from several sources indicates that 

 the temperate deciduous forest extended a few hundred miles farther 

 north during a warm period several thousand years ago. Since then 

 the Illinois climate became cooler, with the result that the temperate 

 decidous forest again shifted southward and the coniferous forest 

 moved to within a short distance of Illinois. 



These ecotonal or intermingling areas do not form rigid bound- 

 aries. The situation is simply this: In the northern part of the 

 ecotone, between the northern coniferous and the temperate de- 

 ciduous forests, most of the life is typical of the coniferous forest, 

 but with a few outposts of temperate deciduous elements occurring 

 in local areas that favor them. Toward the southern edge of this 

 intermediate area the opposite condition prevails — most of the life 

 is typical of the temperate deciduous forest, but with a few colonies 

 of species chiefly associated with the coniferous forest. Some species 

 of plants and animals that are primarily northern in distribution 

 occur even south of this ecotone, especially species that live in the 

 successional stages which become established on bare areas. Among 

 the plants, excellent examples of northern species whose ranges just 

 barely include Illinois are sand cherry, dune willow, bearberry, dwarf 

 birch, and the two gentians occurring in the dunes. 



The birds contribute several members to the complement of 

 northern species occurring in the Dunesland. In Illinois the piping 

 plover nests only in these lakeshore areas; it nests chiefly northeast 

 and northward to the Arctic. During its migrations this plover can 

 be seen in all parts of Illinois. Not so some of the Arctic birds that 



