THE PERSISTENCY OF SCIRPUS VALIDUS VAHL

Abstract

Dredging a canal through the marshy ground north of Waukegan, Illinois, from Lake Michigan to the Johns-Mansville asbestos plant in 1919 has resulted in some very interesting successions from the Scirpus validus association. The author's first study of this area was published in a bulletin of the Illinois State Laboratory of Natural History (volume 9, article 5. I9I2). At that time the Scirpus validus association was well developed and very characteristic of most of the swales in the western half of the southern part of the Waukegan flats (Beach area). The association was virtually a pure growth of Scirpus validus across many of the swales, particularly those in the western part of the flat. As one approached Lake Michigan, the swales, while they might have Scirpus validus, were more likely to be vegetated with the Cladium association. The wide swales of Scirpus validus might shade out gradually or abruptly at the edges to various associations, such as the Cladium, Calamagrostis, Salix-Cornus thicket, or the prairie in which Liatris spicata (L.) WilId. was very prominent. Where sand dunes separated the swales from each other, the transition was abrupt to the Liatris scariosa association. The center of a few of the swales near Waukegan was open water of slight depth, bordered by such aquatic plants as water lilies or Polygonum amphibium L. Very few such swales had water as deep as a foot and a half, and more usually it was a matter of only two or three inches. Below the water were a few inches of colloidal mud, in the lower part of which the plants were rooted. Below occurred the sand substratum which underlies all of this area. In the Scirpus validus association one might occasionally find a plant of Polygonum, Castalia, or Utricularia, but such made up so slight an amount of the vegetation as to be practically negligible. During I9I9 a canal some 250 feet in width and 20 feet deep was dredged from Lake Michigan across the entire area to the Chicago and Northwestern railroad tracks. Previously the drainage of the area had been very slight and consisted of little more than seepage. The canal, however, provided drainage whose effect is quite obvious for nearly a half mile north. The water table was thus lowered immediately about 234 to 3 feet. This resulted in complete drainage of all the open-water swales and sufficient drainage to permit a serious drying out of all the other swales for varying