Forests and woodlands play a vital role in determining climatic conditions on landscape scale. However individual trees also possess the capability to effect climatic conditions on a micro scale. Trees can provide a cooling service via evapo-transpirational latent heat loss, by energy reflection in the long wave part of the spectrum and by shading. The informed selection of particular species can help optimise the cooling services provided by trees when planning an urban area. Greater cooling has potential to increase energy efficiency via reduced need for air conditioning and raise human wellbeing via the reduction in severity of extreme temperatures alongside other aesthetic, ecological and environmental benefits.
The ultimate aim of the project, funded by the University’s Walker Institute, was to ground-proof the initial hypotheses that A) tree species differ in the extent of the cooling service provide via differential rates of water use and B) the cooling of adjacent wall is linearly influenced by leaf temperature.
With the supervision and guidance of Dr Tijana Blanusa (RHS) and DrMartin Lukac at the School of Agriculture, Policy and Development, the project involved implementing a field experiment. A total of 27 six-year-old containerised trees of the species Platanus x hispanica (London Plane) and the ‘Crimson King’ and ‘Princeton Gold’ varieties of Acer platanoides (Norway Maple) were placed against the walls of the TOB buildings at the Earley Gate side of the campus (see the image below). Thermocouples and thermistors measured leaf and wall temperature, respectively, while Hydrochron buttons recorded relative humidity. To estimate tree water loss pots were weighed, soil moisture regularly recorded, leaf stomatal conductance measured using an Infrared Gas Analyser (IRGA) and tree sap flow estimated using Grainer sensors. Measurements of reflectance and irradiance were also measured, thanks to an EngD student Thomas Chung, to explore the influence of species of the canopies radiative properties.
As the majority of the data was collected autonomously the experiment’s preparation consumed a large proportion of the 10 week project. With the help of the technician Lawrence Hansen at PEL, and fellow students Maria Eduarda Moreira and Ana Montalvão, Grainer sensors and thermocouples were constructed by hand. Along with the thermistors these were wired to DL2e dataloggers and attached to the wall or tree on site. After three weeks of data collection the results were collected and analysed. The statistical package Genstat was used to carry out ANOVA and linear regressions analysis to draw conclusions from the huge dataset. It is hoped that the data provided by this project should be sufficient to produce a paper for publication. To have a recognised contribution to a published paper before leaving University would be an undeniable bonus.
Being involved with project from its initial stages provided a priceless insight into the processes of environmental research. When reading scientific paper no real appreciation is gained for the amount of work, or even the individuals, involved in the process. Personally, it also helped indicate that even if not everything goes to plan it’s not the end of the world, plans can always be adapted. For someone contemplating a career in forestry research the freedom and independence granted by this particular project gave a real impression of what a pursing in a research career would be like.
Jon Tanner