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Global warming making trees grow at fastest rate in 200 years | A new study by scientists has determined that global warming is making trees across North America grow at a rate faster now than they have done at any time in the past 200 years. According to a report in The Independent,
the trees in the northern hemisphere appear to have accelerated growth rates due
to longer growing seasons and higher concentrations of carbon dioxide (CO2) in
the atmosphere. Scientists have documented the changes to the growth of 55 plots
of mixed hardwood forest over a period of 22 years, and have concluded that they
are probably growing faster now than they have done at any time in the past 225
years - the age of the oldest trees in the study. Geoffrey Parker, a forest ecologist
at the Smithsonian Environmental Research Centre in Edgewater , Maryland , said
that the increase in the rate of growth was unexpected and might be matched to
the higher temperatures and longer growing seasons documented in the region. The
study suggests that northern forests may become increasingly important in terms
of moderating the influence of man-made carbon dioxide on the climate. Dr Parker
and his colleagues have carried out a detailed census of the trees on a regular
basis since 1987, measuring every tree and sapling that has a diameter of more
than 2cm (0.78in). They calculated that the forest is producing an additional
two tonnes of wood per acre each year, which is equivalent to a tree with a diameter
of two feet sprouting up in the space of a year. The scientists identified a series
of plots with trees at different stages of growth and found that both young and
old trees were showing increased growth rates. More than 90 per cent of the tree
groups had grown by between two and four times faster than the scientists had
predicted from estimates of the long-term rates of growth. The scientists said
that if the trees had grown as quickly throughout their lives as they had shown
in recent years they would be much larger than they are now. They based their
conclusions on 250,000 measurements taken over more than 20 years. During the
same period, the scientists measured the concentration of carbon dioxide in the
forest air and found that it had risen by 12 per cent. The average temperature
had increased by three-tenths of a degree, and the growing season had lengthened
by 7.8 days. The scientists believe that all three factors have played a role
in helping the trees to grow faster. |
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