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Endangered
Species and Spaces
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Vascular Plants
Vascular plants are those which
have a system of vessels or ducts for conveying sap as their primary
means of internal transport of nutrients. British Columbia's bounty
of biological diversity is reflected in the large number of vascular
plants that inhabit the province. There are over 2300 native vascular
plant species, and over 600 are considered rare. More than 200 of
these are rare due to human activities that have affected the habitats
of the plants. The remainder are naturally rare, consisting mainly
of species that are near the periphery of their range (Douglas et
al. 1998).
There are a number of geographic areas where rare
plants are concentrated in the province. Such centres of rarity
may reflect, to a degree, areas that have been botanically explored,
versus unexplored. Also, occurrences along the boundaries of the
province, particularly in the south, may be rare due to the enumeration
of rarity within a narrow definition of range (i.e. provincial).
Nevertheless, the southern Rocky Mountain Trench within the Columbia
Basin is considered one of only a few geographic "hotspots"
representing real centres of rarity in the province (Roemer, 1994).
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2: Distribution of Rare Vascular Plants in British Columbia |
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Circles represent occurrences
of thos taxa which are known fron three or fewer locations in the
Province. Source based on individual distribution maps for taxa
shown in Straley et al, 1985.
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Rarity can be based on geographic
distribution or habitat specificity. The extremes of distributional
rarity are: species that occur in large numbers within a narrow
geographic range; and, species that occur in very small numbers
over a wide geographic range. Habitat-specific species occur in
very specific well-defined habitats that are often rare themselves.
For example, the Southern Maidenhair Fern (Adiantum capillus-veneris)
is so habitat-specific that it only occurs in British Columbia in
the calcareous tufa deposits of Fairmont Hotsprings (Roemer, 1994).
The type of rarity (geographic distribution
vs habitat specificity) has important implications for the protection
of rare plants within a system of protected areas. Rare plants that
are geographically concentrated and/or habitat specific benefit
the most from area-based protection (Roemer, 1994).
Roemer (1994, in Biodiversity in
British Columbia) made the following important recommendations regarding
rare plant protection which warrant repeating here:
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Protect in reserves those
species which have narrow distributions in few localities
and/or are tied to very specific habitats of which all or
a major proportion may be included in a reserve; |
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Provide alternative means
of protection for rare species with diffuse distribution and
for species that are habitat-vague. Such species would be
particularly dependent on suitable management prescriptions
applying outside of protected areas and on a Protected Species
Act; |
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Support research on rarity
type, including life histories and habitat dependencies, for
all provincially-listed rare plants, so that the best mode
of protection can be determined for these plants; |
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Allow for greater density
of protected areas in centres of rarity. |
Notwithstanding the recent work
that has been done, it is important to do much more to identify
and categorize the flora of the province. By the time it is done
it may be too late for many species and populations (Douglas, 1994).
Almost 300 vulnerable and endangered
plants occur in the Columbia Basin - nearly a fifth of the provincial
total (Table 9). The greatest proportion are in the Cranbrook
District, reflecting both the degree of habitat disturbance in this
heavily urbanized and agriculture region, where most valley bottom
land is private, and that fact that, as the northern edge of the
Great Basin (also called the Sonoran or high desert, a sagebrush-dominated
biome that runs from British Columbia to Baja California), it hosts
many species at the northern periphery of their ranges. Therefore,
while many Columbia Basin plants are endangered in British Columbia,
only a few of these are also globally endangered; the rest are "peripheral"
in British Columbia, but more secure in the centre of their population
to the south. Ecologists are divided on the importance of peripheral
species. On the one hand, how important can it be to save a plant
that is secure elsewhere? On the other hand, evolutionary biologists
theorize that peripheral populations are the most important, because
they are adapted to extreme conditions which may increase their
chance of survival in times of environmental stress (Harding, 1999).
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Table 9: Numbers of Red and Blue-listed vascular
plants in the Columbia Basin (by forest district)
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Forest District |
Number of
Red-listed species
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Number of
Blue-listed species
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Total number
of rare species
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Cranbrook |
41 |
70 |
111 |
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Invermere |
16 |
26 |
42 |
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Golden |
7 |
28 |
35 |
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Revelstoke |
2 |
8 |
10 |
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Arrow |
11 |
32 |
43 |
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Kootenay Lake |
14 |
37 |
51 |
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Columbia Basin |
91 |
201 |
292 |
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British Columbia |
488 |
1224 |
1712 |
Source: Douglas, G.W., G.B.Straley,
and D. Meidinger: Rare Native Vascular Plants of British Columbia,
1998
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| Go to: VASCULAR
PLANTS REFERENCES |
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