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News Article

Invasive insects threaten to kill over 1 million trees in urban America

The threat of climate-driven range expansion of invasive species has been well established, but a recent study aims to quantify the impact of these species in the USA over the next 30 years.

Trees and greenspaces are valuable as part of urban areas for many reasons, including improving air quality, providing spaces and corridors for wildlife and for the health and mental wellbeing of local residents. Among the threats facing urban trees are invasive insect species, which can rapidly kill individual trees and disrupt the balance of the wider ecosystem.

A study carried out by researchers from Canada and the USA and published in the Journal of Applied Ecology provides an estimate of the number of trees that will be killed by invasive insect species between 2020 and 2050, along with the associated costs to replace them.

The researchers used a combination of models of invasive insect spread and street tree populations across 30,000 US communities to estimate the impact of these species over the next 30 years. The results demonstrate that as many as 1.4 million urban trees are at high risk of mortality from insect pests. They highlight the spatial variation of tree deaths across the study area, with approximately one quarter of the urban areas reviewed projected to experience 95% of all tree mortality. They also suggest that as much as 90% of all tree deaths are likely to be caused by the emerald ash borer Agrilus planipennis, which is expected to kill almost all ash trees in more than 6,000 urban areas across the USA. The researchers were able to further identify an emerald ash borer high-impact zone of approximately 902,500km2 in which they predict the death of 98.8% of all ash trees.   

Beyond the impacts listed above, the death of urban trees brings a significant cost to the governments and planning authorities who are responsible for their replacement. The researchers estimate that based on their calculations the projected tree mortality due to invasive insects in America will cost an average of $30 million every year.

The researchers state that these predictions may provide information to support mitigation measures and policy changes for minimising the impacts of invasive insect species on urban trees, from species such as emerald ash borer that are highlighted as key threats and the wider list of biotic and spatiotemporal risk factors that is presented in this report.

For more information, the original research article can be found here