. The Canadian field-naturalist. 256 The Canadian Field-Naturalist Vol. 94 primarily by automobiles (, Spergularia Puc- cinellia distans, and Carex praegracilis, see Reznicek et al. 1976). Other species may have been introduced by adhesion to waterfowl (, Solidago senipervlr- ens, Plucheapurpurescens var. succulenta. Aster suh- iilaius): ducks and wading birds frequent alkaline pools in the Windsor and River Canard areas. Zonations of Halophytes In several places in southern Ontario where halo- phytic plants are found, well developed associations occur forming zonations relative
. The Canadian field-naturalist. 256 The Canadian Field-Naturalist Vol. 94 primarily by automobiles (, Spergularia Puc- cinellia distans, and Carex praegracilis, see Reznicek et al. 1976). Other species may have been introduced by adhesion to waterfowl (, Solidago senipervlr- ens, Plucheapurpurescens var. succulenta. Aster suh- iilaius): ducks and wading birds frequent alkaline pools in the Windsor and River Canard areas. Zonations of Halophytes In several places in southern Ontario where halo- phytic plants are found, well developed associations occur forming zonations relative to water content and Na levels. This was well demonstrated in some of the alkaline sites near Windsor (Figure 2). Around the edges of ephemeral or permanent pools containing Poiamogeton fo/iosus, was a fringe of Spergularia marina, followed by a band of Puccinel/ia dislans. followed by Agropyron repens and A triplex patula var. hastata. The Na levels in the rooting medium decreased from over 2000 /ig/g where the Spergularia marina grew to a few hundred micrograms per gram where Agropyron repens was dominant. Similarly, temporary pools at the brine field at River Canard were surrounded by Atrip/ex patula followed by a zone of Puccinellia distans and Solidago sempervir- ens. Beyond this on drier ground was a zone domi- nated by Agropyron repens. Around the brine pond containing Potamogeton pectinatus at River Canard was Atriplexpatula and locally dense stands of Plu- chea purpurescens and Aster subulatus; these graded into a poor growth of Typha angustifolia which grad- ually improved as Na levels in the soil further decreased. Zonations of this general type, although not always so obvious, have been noticed everywhere in southern Ontario where halophytes have been found. Presence of some halophytes is clearly related to the water content of highly alkaline soils. Kochia scoparia grows only in dry alkaline soils and is generally replaced by other species in wetter sites even when
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