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Beetlemania as invasive species spreads north

A southern pine beetle, yesterday A southern pine beetle, yesterday KC Film
07 Sep
After an ‘unprecedented’ surge northwards into New Jersey, New York and Connecticut, the southern pine beetle is expected to continue expanding its range into large portions of northern US and southern Canadian forests

Nova Scotia by 2020. Southern New England and Wisconsin by 2060. Canada by 2080. These are the years that researchers believe regions could make the ultra-destructive southern pine beetle ‘southern’ no longer.

At just half the length of a grain of rice, the bugs don’t look threatening. However, they burrow themselves within the inner bark of pine trees, where they feed on its vital tissue – or phloem. Enough beetles prevent the transportation of essential nutrients within the tree, damaging it beyond repair. Infestations were responsible for a loss of 14 million cubic metres of timber across the southeastern states of Pennsylvania, Ohio and Maryland between 1990 and 2004.

A southern pine beetleThe southern pine beetle (Image: US Department of Agriculture)

‘Our projections indicate that the southern pine beetle will continue to spread into forests that have never seen it before,’ says Corey Lesk, graduate student at the University of Columbia and lead author of the research published in Nature Climate Change. According to his findings, the beetles’ range depends on winter temperatures, specifically those of the phloem. The team found that once the inner bark stays above -10ºC for a decade, the beetles begin to appear. So far, infestations have followed warmer winters in New Jersey since 2001, while populations were found in New York in 2014 and Connecticut in 2015. The study predicts that forests further up the east coast to Nova Scotia could be hospitable to beetles by 2020, southern New England and Wisconsin between 2040 and 2060 and much of southern Ontario and Quebec in Canada before 2080. Overall, ‘there is huge vulnerability across a vast ecosystem,’ states Lesk.

Pine tree covered in resinA pine tree covered in tell-tale blobs of resin, or ‘pitch tubes’ (Image: Bugwood.org)

The predictions combined 27 different global climate models and two greenhouse gas emission models. Because these models don’t unanimously or perfectly predict the climate, they show different years when the beetles could emerge. Overall, they found a 43-year range between the earliest and latest year a suitable climate for the beetles would become established. ‘There are also ecological uncertainties that the study doesn’t cover, such as whether beetles will be successful in northern pine species that they have never seen before, or whether increased droughts could make trees more vulnerable to the beetle,’ explains Lesk. ‘Although we haven’t yet fully answered these questions, we think our results suggest that we should consider how we will prepare for these new threats to our forests.’

Infestations are difficult to control once they are underway. ‘The main strategy to prevent damage is to cut and remove infested trees so that the beetles can’t reproduce,’ says Lesk. ‘That’s effective for keeping down the intensity of an outbreak.’ Sometimes, removing strips of forest can also hinder the spread of pests. ‘But,’ warns Lesk, ‘there is some evidence that these beetles can travel very large distances, so that will likely not work in this case.’

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