Lamb's ears to save the world?
2 November 2012
Research by RHS Tijana Blanusa into plants for green roofs is showing promising results. Her research shows that certain plants may help reduce urban temperatures. One plant in particular, Lamb’s ears (Stachys byzantina), which represents silvery and hairy leaved plants, may be very important in the future.
It is well recognised that air temperatures in urban areas are higher than in surrounding rural areas, a phenomenon called ‘urban heat island effect’. This increase in air temperatures is largely due to vegetation being replaced by dark and impervious surfaces.
A number of studies have shown the importance of green roof plants in decreasing summer-time air temperatures and in counteracting urban heat island effects. They achieve this by cooling surrounding areas through evapo-transpiration, a plant’s equivalent to sweating.
The paper, presented at the World Green Roof Congress, has been produced in collaboration with researchers from the School of Biological Sciences, University of Reading.
Cooling the urban environment
Dr Blanusa looked at the three broad leafed perennial plants and a Sedum mix, the most popular plants for green roofs. The first year of her research showed that Lamb’s Ears (Stachys byzantina) significantly reduced the surrounding air temperature near the surface of the leaf during early afternoon on a hot summer day, by some 1.5 degrees for example when compared to the bare, dry soil.
“Green roofs are not just about looking good,” says Dr Blanusa. “There is much more interest recently in providing additional ecological and economic functions such as regulating internal building temperatures. But this research emphasises the potential in helping reducing air temperatures. If only every building had a green roof and a green wall.”
Earlier research in the UK, based on model predictions, has shown that increasing green space such as parks, gardens and green roofs by 10% would reduce summer-time air temperatures by something like four degrees (*).
“With our climate getting warmer gardeners will be playing an even more important part in helping reduce the effects,” says Tijana. “Getting planting right in urban spaces, which as we all know can be very limited, is particularly important, and can have a major effect in not only helping reduce urban temperatures but will also provide other environmental benefits.”
Green roof experts
The World Green Roof Congress (WGRC) brings together leading green roof experts from across the world, providing a platform for communicating the latest case studies, research and policy initiatives. The Congress encourages the uptake and implementation of green roofs, providing a greater understanding of their benefits and stimulates innovation. It was held in London on the 15 and 16 September.
*Earlier research
Gill SE, Handley JF, Ennos AR, Pauleit S (2007) Adapting cities for climate change: the role of green infrastructure. Built Environment 33; 115-133.