Trees are resilient. In the face of natural events – drought, floods, lightning, wildfires, tropical storms, and tornados, to name a few – woodlands can rebound from such challenges with persistence, displaying new growth within weeks. But the challenges created by humans are another matter, such as accidental or deliberate wildfires, as well as invasive species, insects, and diseases that have been introduced to ecosystems around the world. Some of these have been the result of “best intentions.” Plants such as kudzu or Japanese honeysuckle were imported for erosion control, and others (including English ivy and Norway maple) were touted as plantings that would enhance your landscaping. Insects such as emerald ash borer and the nematode responsible for beech leaf disease arrived more discretely – likely in contaminated imported stock. Diseases including chestnut blight and Dutch elm disease apparentlly arrived the same way.
I was reminded of Dutch elm disease recently when I read an article documenting efforts to manage the disease. I must admit that I was unaware of such efforts. My high school in New England had an elm grove that hosted decades of graduations; by the 1990s, the trees were gone. Learning that so many had succumbed to the disease, I had the impression that if any survived, they were as few and far between as the American chestnut.
Yet, like the few remaining surviving chestnuts that are resilient in the face of the blight, elms are still out there, and scientists are working to combat the disease with patience and determination. Two commercially available fungicides used by urban forestry crews across the country help prevent infection by disabling the fungal spores. But these only limit the spread of the disease and are not 100% effective.
On the other hand, scientists have developed methods that can attack some infestations affecting our woodlands on a larger level. One that comes immediately to mind is aerial spraying to combat the spongy moth. Unfortunately, no such method has been developed to combat emerald ash borer, which devastated native tree populations far more swiftly than spongy moth. When I worked on the Hiawatha National Forest in northern Michigan in the early 2000s, EAB was still only a regional concern. By the time I started with UME in 2012, it had arrived on Maryland’s western shores of the Chesapeake Bay before crossing the Bay not too much later. And new populations are now in Oregon and British Columbia. Communities and homeowners can protect individual trees with chemical treatments that need to be repeated every few years, even if the EAB population has crashed locally (because there are no more mature, healthy trees to attack).
All of this brings us back to resilience. Researchers at Ohio State University report that trees that have received chemical treatments for more than ten years remain healthy. Because EAB do not affect a tree’s root system, some ash survive to sprout new growth, forming what they call “bush ash.” Some survive to maturity; others are then attacked by insects still in the area. More encouragingly, they also report that some trees remain unaffected by the invaders. These “lingering ash” may hold the key to the species’ survival in the same way that surviving chestnuts and elms are contributing to scientific research. Perhaps future generations will see these resilient species once again filling our woodlands.