The Vegetation of Wisconsin: An Ordination of Plant Communities

15. Sand barrens and bracken-grassland

Sand barrens and brackengrassland NATURE, LOCATION, AND COMPOSITION OF SAND BARRENS On the higher terraces of the Wisconsin and Mississippi rivers and at a few other places south of the tension zone, the oak barrens give way to an open, prairie-like vegetation. In their undisturbed condition, these open plains would probably have qualified as dry-mesic or dry prairies, but disturbances have occurred which have changed their plant cover to something very different from a prairie. These changes have had various initial causes but the result in each case has been the movement of the sandy soil by wind. The new vegetation develops on the windCopyrighted Material SAND BARRENS &. BRACKEN-GRASSLAND 309 influenced areas, either on the blowouts from which the sand is removed , or the dunes or sand deserts on which it is deposited_ As will be seen later, these inland dunes possess a very different flora from the dunes along Lakes Michigan and Superior and must be discussed separately. The sand barrens are most closely related to the dry-mesic prairies and to the oak barrens. No quantitative studies of the type have been made in Wisconsin, although Gleason (1910) and Vestal (1913) have reported detailed investigations in the adjacent areas of northern Illinois. The following discussion is based on a presence survey of 20 stands in Wisconsin, made by J. T. Curtis and H. C. Greene (Figure XV-I). The prevalent species in the P.E.L. stands are listed in Table XV-I and the other species reaching a peak in the sand barrens are also given in the same table. Of the prevalent species which attain an optimum here, all but Gnaphalium obtusifolium and Koeleria cristata are restricted to sandy habitats while several of the other species are essentially confined to the sand barrens, including Croton glandulosus, Krigia virginica, Talinum nlgospermum, Festuca octofiora, Cyperlls filiculmis, Linaria canadensis, Calamovilfa longifolia, and Rhus aromatica . A floristic family analysis shows five families with over 50 per cent of the total species (Compositae, 23.5 per cent; Gramineae, 15.7 per cent; Rosaccae, 5.2 per cent; Leguminosae, 3.3 per cent; Ericaceac, 3.3 per cent). Of interest are the relatively high values of the Euphorbiaceac (2.0 per cent), Cistaceae (2.0 per cent), and Cactaceae (1.3 per cent), which reflect the extreme aridity of the habitat. The phenological pattern of the sand barrens resembles that of the prairies, with a midsummer peak and with about equal numbers of spring and autumn bloomers. Twenty-four species of shrubs were recorded in the P.E.L. stands, but their low importance in the community is indicated by the fact that only one of them, Hudsonia tomentosa, is on the prevalent species list. Among the other biota of the sand barrens grasslands, the cryptogamic plants play an unexpectedly important role. Certain blue green algae form circular, gelatinous masses on the surface of the loose sand and are of great importance in stabilization. The hairy cap moss (Polytrichum piliferum) also produces sand binding mats (Plate 37). Several fleshy fungi somehow obtain sufficient water and nutrients from the sand to develop their fruiting bodies. Prominent among them are the leathery earthstars of the genus Geaster and the unusual Scleroderma geaster (Plate 38). Lichens are numerous on areas that have been Copyrighted Material 310 GRASSLANDS stabilized for some time; these include Cladonia rangiferina, C. cristatella , and other similar forms. Among the animals, the reptiles are of unusual prevalence, with a number of snakes, such as the hog-nosed snake and the blue racer, and one of the few Wisconsin lizards, the six-lined lizard. The lark sparrow, a common bird of the western plains, is largely restricted to the sand barrens grassland in the state. Vestal (1913) indicated a number of characteristic insects in his detailed study of Illinois sand barrens, but no comparable work has been done in Wisconsin. SAND BLOWS When the prairie sad which originally existed on the sand barrens was broken by the plow, the loose sands of the underlying soil were free to move with the wind. In the areas around Muscoda in Grant County and north of Arena, in Iowa County, for example, early attempts at farming the land were quickly doomed by the excessive wind erosion which followed. Frequently the wind caused simply a shifting surface, with as much sand deposited as was picked up on the average. In some places...