The Accidental Tree Killers

In Brighton, England, there are about 17,000 beautiful elm trees lining its streets and adorning its parks. Known as Elm City, Brighton is the last great refuge of trees that once shaped the English landscape. Unfortunately, the UK lost most of its elm trees due to an epidemic of Dutch elm disease back in the 1970s.

Britons witnessed a terrible transformation of sorts. They watched their local countryside decline in beauty as the elms became nothing more than lifeless skeletons. In more than a decade, more than 30 million elms died. Elms were the nation’s second most important source of hardwood timber, a key component of hedgerows and woodlands. Elms are also home to at least 80 species of invertebrates which suddenly disappeared when the elms died.

Due to a quirk in geography and a policy of fell-and-burn at the first sign of infection, Brighton’s elms survived. For almost half a century, the elms in Brighton have stood as a salutary reminder of the dangers posed by globetrotting plant pathogens. Tree-killing microorganisms responsible for Dutch elm disease have been criss-crossing the world for centuries. They ship along with exotic trees and shrubs, timber and wood products as well as packaging. In the 20th century, a slew of epidemics hit the point home that these hitchhiking bacteria and fungi are seriously bad news for agriculture, forestry and natural wooded habitats. Despite this knowledge, we are doing nothing to stop the spread of these diseases.

With wildfires growing fiercer and more frequent and world leaders promising to plant trillions of trees worldwide to help restore nature and tackle the climate emergency we’re facing, there’s an urgent need to figure out how to handle these epidemics. We’re not doing well in this process but there is still hope. As plant disease epidemiologist Stephen Parnell at the University of Salford says, “We need to get ahead of these epidemics, not just monitor the damage. If we don’t, we stand to lose many more species and billions of trees that we depend on for so much.”

In their native ranges, trees and pathogens evolve in tandem. For example, trees acquire resistance so pathogens try harder. Trees then ramp up their defenses another notch and do so until they reach a sort of truce where the trees can tolerate infection and the pathogen does little harm. The problem occurs when you transport the pathogen elsewhere. At that point, all bets are off. Loosed among defenseless trees, even the mildest of microbes can turn nasty and destroy entire forests.

Cures and treatments remain elusive. Fungicides and pesticides can sometimes help in commercial settings but not in the wider environment. In almost every case, the solution seems to be culling trees so that they pathogens don’t arrive in the first place. That leads to tougher ‘quarantine procedures’, rigorous health checks and tighter regulation of the plant trade.

Yet, they still come. Hopefully, as time goes on, we’ll find better ways to save trees from these pathogens. However, we’re still waiting for that time to arrive.

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