. The Canadian field-naturalist. Figure 1. Distribution of Isoetes engelmannii in North America after Taylor et al. (1985) with the disjunct Georgian Bay locations and Michigan locality included. Ecology At both sites /. engelmannii was rooted in a fine sandy or silty substrate. Also at both sites, Isoetes echinospora, Isoetes X eatonii, Eleocharis acicula- ris, Najas flexilis, Sagittaria graminea, Vallisneria americana and small plants of Potamogeton richardsonii were growing nearby. At Big Chute additional associated species in approximate order of importance included Potamogeton gramineus,
. The Canadian field-naturalist. Figure 1. Distribution of Isoetes engelmannii in North America after Taylor et al. (1985) with the disjunct Georgian Bay locations and Michigan locality included. Ecology At both sites /. engelmannii was rooted in a fine sandy or silty substrate. Also at both sites, Isoetes echinospora, Isoetes X eatonii, Eleocharis acicula- ris, Najas flexilis, Sagittaria graminea, Vallisneria americana and small plants of Potamogeton richardsonii were growing nearby. At Big Chute additional associated species in approximate order of importance included Potamogeton gramineus, Sagittaria rigida, Elodea canadensis, Potamogeton spirillus and Ranunculus flammula. At Big Chute the conductivity of water near the dam and near Pretty River Channel was 259 to 260 ^ohms/cm and the pH ranged from to At the West Guilford site the conductivity of Gull River water was 49 to 53 juohms/cm and both the rooting medium and the water had a pH range of to While fluctuating water levels are clearly essential to the survival of some of the coastal plain flora in the Georgian Bay region (Keddy and Reznicek 1982), the relationship between /. engelmannii and amount and perodicity of fluctuation in water levels is not yet clear. At Big Chute, the water level has fluctuated very little since 1917. A stable water level is important for navigation and hydroelectric generation, and is maintained by dams at Pretty Channel and Big Chute and also by an Ontario Hydro generating station. Prior to 1917, the level was two feet ( m) lower and fluctuated much more through natural causes and because of development for the logging industry. The only recent fluctuations have involved periodic drawdowns at intervals of several years, to facilitate repairs. The Gull River at West Guilford is subject to naturally fluctuating levels and was probably near, but not at, its lowest level, with some of the Isoetes X eatonii plants growing as terrestrials on wet silt with Leersia
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Keywords: ., bookauthorottawafi, bookcentury1900, bookdecade1910, bookyear1919
