Environmental Engineering Reference
In-Depth Information
Figure 7.11
Changing vegetation patterns in Canada following a doubling of CO
2
Source:
After Hengeveld (1991)
(Wittwer 1984). There is some concern, however,
that the improvement in the growth rates would
be accompanied by a reduction in the quality of
plant tissue (Melillo
et al.
1990).
The predicted higher temperatures, working
through the lengthening and intensification of the
growing season, would have an effect on the rates
of plant growth and crop yields. The regional
distribution of vegetation would change,
particularly in high latitudes where the
temperature increases are expected to be greatest
(Shugart
et al.
1986). Across the northern regions
of Canada, Scandinavia and Russia, the trees of
the boreal forest would begin to colonize the
tundra, as they have done during warmer spells
in the past (Viereck and Van Cleve 1984; Ball
1986), at a rate of about 100 km for every 1°C
of warming (Bruce and Hengeveld 1985). The
southern limit of the boreal forest would also
migrate northwards, under pressure from the
species of the hardwood forests and grasslands
which would be more suited, to the new
conditions. An expansion of the grassland in
western Canada would push the southern
boundary of the forest north by 250-900 km
(Wheaton
et al.
1989), and ultimately the boreal
forest might disappear completely from northern
Alberta, Saskatchewan and Manitoba (see Figure
7.11).
The changing nature and distribution of the
northern forest biomes would be the clearest
indication of prolonged warming. Accompanying
these changes, and contributing to them, would
be a series of less obvious factors. Rising soil
temperatures, for example, would speed up the
provision of soil nutrients through the more rapid
decay of organic matter, and contribute to
improved plant growth (Van Cleve
et al.
1983).
