The vital role of trees: from atmospheric chemistry to architecture

Dr James Levine

As an atmospheric chemist, I am interested in the influence that trees have on the quality of air we breathe and the climate we either enjoy or ‘weather’, depending on where we live.  First off, there’s the appealing synergy between people and trees: as we breathe in oxygen and breathe out CO2, trees draw down CO2 from the atmosphere and top up our oxygen supply.  If we have an immediate need for oxygen, we have a long-term need for a habitable climate, and trees again play a vital role.  In drawing down, or sequestering CO2, they reduce the burden of this greenhouse gas (GHG) that is at the forefront of our minds as we consider the climate our children, and children’s children, will inherit.  But trees have a further, much more subtle means of influencing both air quality and climate.

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The atmosphere is predominantly cleansed of gases harmful to human health, and some potent GHGs (e.g. methane), by a perhaps surprising simple chemical species, the OH radical (just an oxygen atom joined to a hydrogen atom).  Trees emit gases, so called volatile organic compounds (VOCs), that influence the abundance of OH radicals globally.  As part of Prof Rob MacKenzie’s group here at the University of Birmingham, I am involved in the Cooperative LBA Atmospheric Regional Experiment exploring the influence that the Amazon rainforest has in this regard; this is a collaboration with the University of Sao Paulo (Brazil), the University of Lancaster and the Centre for Ecology and Hydrology.  Of course, whilst trees affect the climate, the climate also affects trees; changes in climate also ‘feedback’ on the chemistry stemming from the VOCs trees emit.  Under Rob’s direction, the new Birmingham Institute for Forest Research will explore some of these feedbacks.  In particular, it is tasked with exploring the impact of climate change on UK woodland, both directly via changes in physical conditions (e.g. air temperature and humidity), and indirectly via changes in the incidence of, and resilience to, pests and disease.

I now have a confession to make: I lead a bit of a double life.  Atmospheric chemist by day, I’m an architecture student by night.  Trees and timber have important parts to play in architecture too, including one pertinent to reducing anthropogenic CO2 emissions.  Construction of the built environment, and the energy used to maintain a comfortable environment within it, account for around half the UK’s (and global) CO2 emissions.  If sustainably and locally sourced, timber embodies very little energy, or CO2 emissions; the CO2 locked up in the timber and ultimately released to the atmosphere (upon decay at the end of a building’s life), may be drawn down from the atmosphere by a tree grown in its place.  Timber construction is also readily compatible with approaches to radically reducing the ‘operational energy demands’ of maintaining a comfortable environment, reliant on high levels of insulation and air-tightness.  Built to the Passivhaus standard, for example, a house in the UK may require no more heating, year-round, than the warmth its occupants alone provide.  And it doesn’t stop there.

The use of trees and timber in architecture has a part to play in improving our quality of life and providing uplifting, life-affirming spaces.  Be it the oxygen they ‘breathe out’, the microclimates they yield, or the sense of well-being they inspire, research suggests trees benefit people living and working in their vicinity.  In schools, for example, they appear to increase children’s concentration and ability to learn.  The architect, Louis Kahn (1960), envisaged that “Schools began with a man under a tree who did not know he was a teacher discussing his realization with a few who did not know they were students.”  I wonder what role he imagined the tree played.  Did it simply provide shelter or did it also help cultivate a sense of security, that commodity which is recognised as key to learning?  We only have to look at David Nash’s Ash Dome  to see the potential the boughs of a tree have to offer both shelter and that peculiar sense of ‘rootedness’ a connection to the outdoors inspires.  For an exploration of the many and varied qualities we associate with trees and timber, Roger Deakin’s Wildwood – A Journey Through Trees makes a visceral and evocative read.

So what has motivated this brief reflection on the role of trees in relation to my dual interests in atmospheric chemistry and architecture?  It is the Trees, People and the Built Environment II conference, taking place in Birmingham this week.  Trees clearly have a vital role, be it at present or with a view to the future, and I look forward to learning in the next few days about many more, perhaps equally diverse, facets to this.

Kahn, L. I. (1960). Form and Design (1960). In R. Twombly (Ed.), Kahn (pp. 62-74). New York: W. W. Norton and Company.

Dr James Levine is a Research Fellow at the School of Geography, Earth and Environmental Sciences, University of Birmingham.

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