A parliamentary committee has urged Government action on what it called the "public health emergency" of urban air pollution, though without mentioning the role of urban trees in improving air quality.
The report published by the Environment, Food & Rural Affairs Committee states: "Emissions have declined significantly over many decades, but not far enough to prevent the early deaths of 40,000-50,000 people each year from cardiac, respiratory and other diseases linked to air pollution." But the measures it proposed to address this focused on emissions from transport and agriculture.
A London Tree Officers Association (LTOA) representative said: "The LTOA welcomes plans that reduce the amount of pollutants entering the air. However, the vital role that trees play should not be overlooked. Any plan should include measures to reduce emissions and remove pollutants from the air we breathe. Trees and other green infrastructure are an integral part of the long-term and sustainable solution to improve air quality in our cities, and provide multiple other benefits."
A committee representative said: "We were not able to address all of the issues contributing to pollution or potentially improving air quality in a short inquiry hence did not make recommendations on all the potential remedial actions. The committee is, however, interested in maximising the use of natural approaches for multiple benefits including air quality and water management."
Meanwhile, the Government is being sued by activist group ClientEarth over its failure to reduce air pollution "in the shortest possible time", as it was ordered to by the supreme court last year.
A study published in Urban Forestry & Urban Greening last month by researchers in Strasbourg, France, with USDA Forest Service research leader and i-Tree software co-developer Dr David Nowak, found that by applying the i-Tree Eco model to the city - its first application in France - "the contribution of urban trees in air pollution removal is small in comparison with local emission rates", with public trees removing about 12 tonnes, or seven per cent, of particulates of 2.5-10(mu)m in size.
"(The) effect on other air pollutants is small," it concluded. "Urban trees are a significant element to reduce air pollution but are not the only solution to this problem. It's recommended to associate planting and managing urban forest resources to other strategies that take into account the urban environment characteristics - built structures, street design, location of local sources, etc."
Nowak was also involved in a recent study of Texas state capital Austin, the 11th largest city in the USA and fastest-growing among its largest 50 cities. This gave a figure of 33.8 million trees providing a relatively high canopy cover of 30.8 per cent. Based on the number of cases per year of avoided health effects, the researchers estimated that the trees remove 1,253 tons of air pollution per year, a service valued at $2.8m - a relatively small part of the $34m total value of all services.
A separate study also published last month by researchers at Harvard University found higher levels of vegetation, measured from satellite imaging, were associated with decreased mortality in a longitudinal study of more than 100,000 women over eight years, with the effect most pronounced in respiratory and cancer mortality. It concluded: "While planting vegetation may mitigate effects of climate change, evidence of an association between vegetation and lower mortality rates suggests it also might be used to improve health."
Reception - Woodland Trust sets priorities at event in Parliament
Committee chair Neil Parish MP hosted a Woodland Trust reception in Parliament on 27 April at which the trust pressed its priorities for trees in Defra’s 25-year environment plan, currently being drawn up.
The trust’s "vision for a 25-year plan" puts the value of trees’ and woodlands’ benefit to UK society at £270bn, but adds: "Too often these are benefits that we take for granted — delivering cleaner air and water, improving soil stability, reducing traffic noise and helping to tackle flood risk."
As well as urging increased tree cover nationally, and protection for existing, particularly ancient, woodland, it urges "improved access to woodland close to where people are, working to tackle the barriers that hold some people back from enjoying nature by developing innovative approaches to public engagement". Defra minister Rory Stewart told the reception of his desire to see "inspirational" woodland creation projects emerge from the 25-year plan.