. The Canadian field-naturalist. 1994 Catling and Porebski: Glossy Buckthorn in Southern Ontario 307. Figure 2. Collections of Rhamnus frangula in southern Ontario based on herbarium speci- mens examined (see methods). A, up to 1970. B, up to 1994. Rhamnus alnifolia by 1930 (Figure 3). The edaphic tolerance of R. frangula appears to overlap complete- ly with that of R. alnifolia, so that a habitat difference cannot be advanced as an explanation for the differ- ent distributions of these two species. By 1930, the much shorter and less conspicuous R. alnifolia had been collected over a broad are
. The Canadian field-naturalist. 1994 Catling and Porebski: Glossy Buckthorn in Southern Ontario 307. Figure 2. Collections of Rhamnus frangula in southern Ontario based on herbarium speci- mens examined (see methods). A, up to 1970. B, up to 1994. Rhamnus alnifolia by 1930 (Figure 3). The edaphic tolerance of R. frangula appears to overlap complete- ly with that of R. alnifolia, so that a habitat difference cannot be advanced as an explanation for the differ- ent distributions of these two species. By 1930, the much shorter and less conspicuous R. alnifolia had been collected over a broad area of southern Ontario and was not associated with urban centres, suggesting the extensive collecting of the early botanists. Thus the early confinement of R. frangula to the urban centres is not an artefact of collecting locations, but is an accurate picture of the first stages of its invasion. Spread from urban centres By 1950, R. frangula appears to have spread up to 40 km from initial sites of establishment in Ottawa and 20 to 30 km from initial sites of establishment in London and Guelph (Figure IB). By 1970, it had spread to sites up to 150 km distant from the three urban centres but still appeared to have a sparse dis- tribution in the southern part of the province (Figure 2A). In 1982, Soper and Heimburger noted that it was rather local and chiefly near cities in southern Ontario. Their 1982 map is basically the same as the "up to 1970" map (Figure 2A).. Please note that these images are extracted from scanned page images that may have been digitally enhanced for readability - coloration and appearance of these illustrations may not perfectly resemble the original Ottawa Field-Naturalists' Club. Ottawa, Ottawa Field-Naturalists' Club
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