Ash trees and human health

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Published on: January 24, 2013
A lone ash tree in Worcestershire

I have to admit that as a plant scientist plugged into the major social media networks that when I was inundated with articles and posts about ash dieback (Chalara fraxineai) in December, I got a bit fed up with it. Of course I appreciate all species have intrinsic value and it will be sad if Britain loses its ash trees – but I have no emotional attachment to ash trees, and pathogens are a fact of life. British countryside is managed land, so with effective management other trees will fill the gaps. However, a paper published in the February issue of American Journal of Preventive Medicine (Donovan et al., 2013) suggests the health effects on humans of losing trees are significant, and that serious loss of ash trees in the UK could have consequences beyond the financial burden on the forestry industry and the short-term loss of trees. 

Adult emerald ash borer on a penny

The research paper is an analysis of the effects of emerald ash borer (Agrilus planipennis) damage to North American ash trees. Emerald ash borer is a green beetle native to Asia, and was introduced to North America in 2002. It causes significant damage to all North American ash species and an infestation can kill a mature tree within four years. For this study, Donovan et al. looked at human mortality data from 1296 counties across the 15 states where there were confirmed emerald ash borer infestations in 2010. The data were collected from 1990, before the introduction of the beetle, until 2007, by which time the borer had spread to 244 counties. Only deaths caused by lung and heart illnesses were included in the analysis, as these are very common causes of death and both can reasonably be linked to the natural environment, as being outdoors in the fresh air, having an active lifestyle, and low stress levels are all associated with the ‘green-ness’ of a locality, and reduce the likelihood of serious lung and heart conditions. The methods and analysis are described in detail in the paper. The results were clear: In in all age and lifestyle classes, mortality from lung and heart conditions was higher in counties infested with the emerald ash borer, and there was a positive correlation between the number of deaths and any worsening severity of the infestation.

Leaf symptom of ash dieback

Here in the UK, ash dieback is currently off the radar after a blitz of bad news in December, when the number of confirmed findings of dieback in nurseries, recently planted sites, and wilder environments more than doubled from 129 on 7th November to 291 on 5th December.* Chalara fraxinea is still spreading. On 4th Jan there were 339 confirmed findings.** This slow down in new cases is probably due to recently imposed restrictions on importing and transporting ash trees, the warnings to visitors to woodlands to take care to wash their shoes and pets, and the reduction in media coverage. In the spring, when the wilted and dead leaves caused by dieback are easily identifiable, the numbers may rise again. 

Everyone can contribute to limiting the damage from ash dieback. Anyone can get involved with mapping the spread of ash dieback by identifying and infected trees using AshTag. Plant scientists can use their lab, skills, or computing power to contribute to the open science ash and ash dieback genomics project hosted by the Sainsbury Laboratory. The data repository is here. 

Highlighted paper: Donovan, G.; Butry, D.; Michael, Y.; Presternon, J.; Liebhold, A.; Gatziolis, D.; and Mao, M. (2012) The Relationship Between Trees and Human Health: Evidence from the Spread of the Emerald Ash Borer. American Journal of Preventative Medicine 44:139-145

* Emma Downing, Dec 2012; UK Parliament Briefing paper. Standard Note SNSC6498.

** Forestry Commission; data valid 14-21 Jan 2013

Image Credits: Lone Ash Tree by Jonathan Billinger; Adult eab on a penny courtesy of USDA; Chalara ash dieback – symptoms – 29 courtesy of FERA; all via Wikimedia Commons. 


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