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What trees are killed, and what is the impact?

In North America, emerald ash borer (EAB) attacks and kills most ash trees regardless of their species, health, size or location. Most native ash species are vulnerable, with the possible exception of blue ash (Fraxinus quadrangulata) which often survives EAB attack[1,2]. Mountain ash (Sorbus americana) is not a true ash species so is not at risk. Although EAB has been reported to infest non-ash tree species in Japan, this is not seen in China where the beetle is more common. In experimental tests on North American tree species, EAB offspring only developed on ash tree hosts [3,4]. Recently, EAB was found in a small number of white fringe trees in Ohio [51]. Research is being initiated to re-examine whether tree species closely related to ash (such as lilac and privet) could be at risk. There is no scientific evidence at this time that EAB will attack tree species other than ash here in Canada. All saplings and trees greater than 3-4 cm diameter at breast height (dbh) are considered vulnerable to EAB[5,6]. In its native range, ash trees on city streets, in city parks, and in plantations are more vulnerable than those in forests - it remains to be seen whether a similar pattern will occur here[7]. A small number of ash survive and remain healthy in heavily infested areas; these trees are being studied to determine whether they will eventually succumb to infestation or remain resistant to EAB[8].

ash trees dying of emerald ash borer attack Ash trees dying from emerald ash borer attack.
Image: Chris Gynan, Silv-Econ Ltd.

In cities:
Economic and ecological impacts will be considerable in urban areas with a high proportion of ash street trees. The financial impact (in 2010 dollars) of EAB in urban centres over the next 30 years will be upward of $890 million dollars in direct costs for treating suitable trees with insecticide, and removing and replacing dead ones[9]. Trees in urban areas perform a variety of ecological functions including reducing household energy use, attenuating storm water, improving air quality, and increasing carbon storage; these benefits provided by ash will be reduced until canopy cover is restored[10]. There are also health, social and aesthetic benefits to urban trees; the presence of urban trees is associated with lower crime rates and higher house re-sale prices, while the loss of ash has been linked to higher death rates in EAB-infested areas of the US[11,12,13,14].

In woodlots and forests:
Loss of ash in woodlots and forests will have significant ecological impact where ash forms a large component of the stand. Studies in Michigan show that 98% of ash trees in forest ecosystems die within six years of initial EAB attack[15]. This loss may be especially significant in riparian forests where the loss of ash could result in increased stream bank erosion, altered stream water quality and loss of shoreline habitats[16]. Because of this insect's ability to attack and kill all age and size classes of ash including larger saplings (>3 cm dbh) the ash seed bank in affected forests will be lost; this phenomenon is already evident in some Michigan forests[5,17]. In forests and woodlots, invasive understory species such as buckthorn outcompete tree species in the understory; with the loss of ash, invasive species may exploit canopy gaps and dominate the regenerating stand[18].

emerald ash borer killed ash stand Woodlot with dying ash.
Image: Troy Kimoto, CFIA

Loss of ash species:
Ash wood is strong and resilient and has a broad range of uses. It is used for making sports equipment (e.g. hockey sticks and baseball bats), tool handles, furniture, veneer and flooring. Black ash is used by some First Nations communities to make traditional woven baskets. If ash species are lost or drastically reduced in population, this will have both economic and cultural consequences.

References


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