Geoscience Reference
In-Depth Information
growth, disease species and climate interactions is a theme that we shall return to
when we look at human ecology in Chapter 7.
The early-21st-century outbreak of the mountain pine beetle in western Canada is
an order of magnitude greater in area than previous outbreaks. Beginning just before
2000, it was facilitated by higher minimum winter temperatures, higher summer
temperature and reduced summer rainfall. By the end of 2006 the outbreak had
covered some 130 000 km 2 , with commercial timber losses estimated to be more than
435 million m 3 and additional losses outside commercial areas. But in addition to
the commercial costs arising from the biological impact of this climate-facilitated
outbreak, there were also changes to the forests' ecosystem function with regards to
carbon balance. In 2008 researchers primarily from the Canadian Forest Service (Kurz
et al., 2008), reported that between 1990-2002 the average net biome production (net
primary and secondary production 3 ) for the south central region of British Columbia
(an area of approximately 660 000 km 2 and the region most extensively affected by
the outbreak) was 0.59 Mt C year 1 : that is to say, it was acting as a carbon sink. The
researcher used actual ecological data from the area between 2000 and 2006 and then
modelled the outbreak's likely course through to 2020, with an expected peak around
2008. They found that net biome production was changing and, including the modelled
future prognosis for the outbreak, concluded that the forest would be a net source of
carbon of some 17.6 Mt C year 1 until 2020 but with peak carbon release years seeing
between just below 20 to just under 25 Mt C year 1 . Again, this is another example of
the many biosphere feedback cycles in the global climate system discussed in section
1.5. The researchers also predict that outbreaks of other forest insects are likely to
affect forest carbon balance, including the eastern spruce budworm ( Choristoneura
fumiferana ) and forest tent caterpillar ( Malacosoma disstria ), by reducing tree growth
and increasing tree mortality. With tree mortality comes the risk of increased forest
fires, and the research team postulated that such insect outbreaks together with fire
could turn current North American forest carbon sinks into carbon sources. Their
study is one example of how climate change biology has an impact on the global
carbon cycle providing a positive feedback to the global climate system. (Of course,
climate change can also work the other way to increase other carbon sinks so it is the
overall global balance between sources and sinks that will determine the trajectory
of the global system.)
Returning to climate change and altitude, an example of a plant species restricted by
altitude and which may see a population decline with warming is Britain's Snowdon
lily ( Llodia sevotina ).
In this section on species' climate-induced range shifts we have noted that some
high-latitude species have nowhere to go with warming that takes the Earth above
the temperature of the warmest times of the current and past interglacials (above the
warmest global climate level of the Quaternary to date, the past 2 million years): they
have run out of biome in which to live. We have also noted that high-altitude species
on the tops of mountains face a similar problem. However, in the tropics in addition to
3
Gross primary production is the dry biomass produced (mainly) by photosynthetic organisms and
secondary production is the dry biomass by those species living on primary producers. Net primary
production is gross primary production minus biomass lost by respiration.
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