What biome is the Indiana Dunes?

Well, I doubt I should have done this searching for you if you’re doing a report on it, but i’d thought i’d give you some help. This is from WikiTravel, so i’d find additional sources, but it seems to have some information for you:
http://wikitravel.org/en/Indiana_Dunes_National_Lakeshore

“Many ecosystem types can be readily recognized by amateurs. Ecosystem types, and characteristic grasses and flowering plants, that exist within the Indiana Dunes include the following:

* Sand dunes – marram grass, prickly pear, puccoon
* Wetlands (bogs, marshlands, and swamps) – marsh marigold, skunk cabbage
* Ponds – bladderwort, gentian
* Prairies – black-eyed susan, butterfly weed, goldenrod, lupine, prairie grass
* Savannas – asters, prairie grass
* Dry woods – columbines, hepatica, Solomon’s seal
* Wet woods – Dutchmen’s breeches, hepatica, trillium, violet”

According to this site the Dunes are part of the nearctic grassland/savannah biome of North America.

The seven official land biomes are tundra, taiga, chaparral, rainforest, grassland, desert, and temperate forest according to this site. This is what it has to say about grasslands.

Note: an ecosystem type and a biome are not the same thing.

Biome: A major regional or global biotic community, such as a grassland or desert, characterized chiefly by the dominant forms of plant life and the prevailing climate.

Ecosystem: An ecological community together with its environment, functioning as a unit.