Geoscience Reference
In-Depth Information
100 meters (300 feet) lower than today and the coastal plain was emergent. According to this scenario, as the
glacier retreated the plants extended their range to Nova Scotia, where they became isolated.
It is now evident, however, that the Wisconsinan glacier advanced to the outer edge of the continental shelf
of Atlantic Canada and that the emergent areas of Georges Bank and Browns Bank were separated from the
Nova Scotia mainland by 150 kilometers (90 miles)—too far for the plants to have crossed a supposed postgla-
cial “land bridge.”
Instead, researchers now believe that coastal plain species reached Nova Scotia by stepwise migration
through Maine, New Brunswick, and north-central Nova Scotia during a period of warmer climate. Subsequent
cooling and vegetation change led to the loss of intermediate populations. Alternatively, coastal plain species
may have reached southwestern Nova Scotia by long-distance dispersal from populations in the eastern United
States, either by birds or by strong winds generated by tropical storms and hurricanes that track northward up
the east coast of the United States, then often veer eastward toward Atlantic Canada.
Once there, the coastal plain plants found the conditions in southwestern Nova Scotia conducive to their
permanent establishment. It is the warmest area of the province, with the longest frost-free period, and it has
an exceptionally high density of lakes. Many of these plants are adapted to limited, nutrient-poor sites along
lake and river shores, as well as bogs, fens, and estuaries. Often they are subject to the physical stress of wind,
waves, ice-scouring, and fluctuating water levels. Such limiting factors work in their favor, however, because
they do not compete well with more aggressive plants on more fertile and less stressful sites.
Eleven of these plants are protected by federal or provincial legislation as species at risk of extinction, and
five of Nova Scotia's
ACPF
are globally rare: pink coreopsis, New Jersey rush, Plymouth gentian, Long's bul-
rush, and goldenrod. Human activities probably now pose the greatest threat to its survival. These include use
of all-terrain vehicles, alteration of the shorefront habitat, eutrophica-tion, and hydroelectric development,
which can change the natural fluctuations in water level.
