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Growing trees in the
By Alistair Johnston
T here are many challenges a tree must
face to reach maturity. Whether
attacked by insects or disease, animal
grazing or environmental stressors,
no challenge is more significant for trees
than human impact. In the naturally
vegetated regions of Canada, trees tend
to grow to maturity in large communities
where soil, nutrients, and moisture are
readily available. These tree communities
follow a cycle of growth, failure, and
regeneration, which maintains a relatively
consistent canopy area. Introduce trees into
the ‘urban jungle’ and a whole new world of
challenges is born.
Before taking a closer look at the challenges
faced by trees in the urban environment,
there are some interesting facts 1,2 to share.
14 May 2014
1. A single tree produces approximately 118 kg
(260 lb) of oxygen (O) per year. That means
two mature trees can supply enough oxygen
annually to support a family of four.
2. A tree can absorb as much carbon (C) in
a year as a car produces driving 40,000 km
3. Over the course of its life, a single tree can
absorb one tonne (2,205 lb) of carbon
dioxide (CO 2 ).
4. The average Canadian uses roughly 340 kg
(750 lb) of paper every year, and 95 per cent
of homes are built using wood. That means
each person uses the equivalent of one 30-m
(98-ft) tall, 0.4-m (1.3-ft) diameter tree
every year for their paper and wood products.
5. A tree on a downtown city site has an
average life expectancy of only 15 years.