. The Canadian field-naturalist. Natural history. 176 The Canadian Field-Naturalist Vol. 109 To explore the phytogeographic pattern of ah ar \egetation in Ontario and further e\aluale confine- ment, the geographical distribution of potential ah ar landscapes was compared with plant distribution pat- terns. The limestone plains map was redrawn from Chapman and Putnam (I984j. Since most Ontario alvars occur within the combined area of limestone plains and more or less flat melanic brunisol soil landscape (melanic brunisol of loamy texture with morainal parent material, either undulating or hum-
. The Canadian field-naturalist. Natural history. 176 The Canadian Field-Naturalist Vol. 109 To explore the phytogeographic pattern of ah ar \egetation in Ontario and further e\aluale confine- ment, the geographical distribution of potential ah ar landscapes was compared with plant distribution pat- terns. The limestone plains map was redrawn from Chapman and Putnam (I984j. Since most Ontario alvars occur within the combined area of limestone plains and more or less flat melanic brunisol soil landscape (melanic brunisol of loamy texture with morainal parent material, either undulating or hum- mocky with slopes of 0 to 9%; Llm Mul M14. see Edwards. 1988: Shields et al. 1991). these two largely but not completely overlapping features rep- resent potential alvar landscape for correlation with plant distributions. Base maps were produced using the Canada Soil Information System in the cartogra- phy unit of the Land Resource Division of the Centre for Land and Biological Resources Research of Agriculture Canada. The soil landscape associated with alvar sites and the plant distributions were also plotted using this system. All dot distribution maps for plants are based on specimen's at the herbaria list- ed above, with some additional records from the herbaria at the University of Michigan (MICH), and the University of Waterloo (WAT), and also from the Canadian Museum of Nature's rare Ontario plant database. Authorities for scientific names may be found in Morton and Venn (1990). Results and Discussion Limestone plains and the fiat melanic brunisol soil landscape are largely, but not entirely overlapping (cf. Figures 1 and 2). Forty-five of the best (in terms of native species diversity, rare species presence, and lack of disturbance) alvar sites in Ontario occur within the region of limestone plains physiography (Figure 3). which thus appears to be a fairly reliable "alvar landscape". This landscape corresponds approximately to the edges of the Canadian S
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