Comment – So
Trees Are Polluters? Huh?
Copyright © Tony Burfield 2002
It was widely reported in the UK
National Press at the end of October 20021 that trees are
adding to the pollution of the atmosphere – trees were even graded with
respect to their allegedly sinful emissions, with Silver Birch trees coming off
with a cleaner image that Oak trees apparently. The basis of these curious
statement are worth examining – how can something which is deeply green by its
very nature be causing these problems?
The source information for the articles, apparently, stems from a team from
Lancaster University, lead by Professor Nick Hewitt, who are studying the
effects and the interactions of trees with the local atmosphere. Instead or in
addition to trees being “the lungs of the world”, the team found that trees
produce volatile organic carbon compounds (VOC’s). This information is hardly
new2, but it is the interaction of these VOC’s with oxides
of nitrogen under the action of sunlight which goes on to produce a nasty
cocktail of chemicals (including ozone) which produces photochemical smog which
often hangs over our cities in summertime.
According to the press the team surveyed some 32,000 trees in the West
Midlands recording species, age, condition, height, trunk diameter, leaf area
etc. in order to estimate VOC emission rates. The data was fed into a chemical
lower-atmosphere simulating computer-model, and results scrutinised, paying
attention to what would happen by varying the species. It was found that more
pollution would occur when oaks, poplars and willows were more evident. Finally
the conclusion was that planting trees in urban areas does lower pollution, but
only if certain species are planted. A policy of discrimination was therefore
advised to local councils, planners etc. whereby ash and maple trees should be
encouraged, at the expense of poplars, oaks etc.
It seems to me that trees are not the culprits here – they are doing what
they have been doing for thousands of years – quietly growing, and adding
beauty, shelter and a sense of permanence to the environment. To say therefore
that trees are polluters in this situation is a nonsense – the true culprits
are motor engines that pump out noxious gases which kill and disable and affect
the health of so many of our citizens. Instead therefore of altering the ecology
of our local environments to better accommodate the polluting nature of
motorcars, wouldn’t the research money that sponsored this study have been
better spent on designing or campaigning for a cleaner motor engine?
I happen to think that the oak tree is as much an abstract symbol of what
England represents as the Houses of Parliament. Although Guy Fawkes failed in
his mission, I would hate to think that the Lancaster University team will
succeed in theirs – towns full of silver birch and maple are not so appealing
as the present diversity of species which grace our drives, parks and gardens.
Refs: