If you want a tree that will last a century, what should you plant?

  • So far, the emerald ash borer hasn’t brought tree-killing diseases to this huge, gorgeous ash tree near where I live. But it almost certainly will before too long. Courtesy Shelley Brooks

  • So far, the emerald ash borer hasn’t brought tree-killing diseases to this huge, gorgeous ash tree near where I live. But it almost certainly will before too long.

  • So far, the emerald ash borer hasn’t brought tree-killing diseases to this huge, gorgeous ash tree near where I live. But it almost certainly will before too long. CourtesyShelley Brooks

Published: 7/6/2020 6:19:08 PM

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Everybody knew that COVID-19 would bring a lot of changes but I’m not sure many people anticipated society’s sudden love of bushy trees.

“This is our busiest spring ever. We have never sold as many big trees as we have this year,” is how Rob Farquhar, garden center manager at Brochu Nursery in Concord, put it.

What’s the COVID connection? Social distancing.

“People say: How can I hide my neighbor? I’ve never been home this much!” Farquhar said. “They want big shade trees and evergreen screening.”

Even without neighbors to hide from, I’ve spent a lot more time contemplating the trees on my property during these stay-at-home months and have become positively Lorax-like in my admiration. When you really look at trees you have to admit that they are weird, monstrous, incredibly cool things.

But they also seem imperiled. I’ve lost track of how many of our tree species are being attacked by invasive insects, invasive plants, new diseases, the shifting climate or a combination of all four. Pine, oak, maple, hemlock; varieties of each seem like potential candidates to join elm and chestnut – and, soon, ash – on the list of tree species wiped out in North America.

That leads to a question: What should I plant if I want the tree to last for a century or more and turn into a gorgeous giant like a century-old ash tree I’ve admired in a neighboring town?

That ash tree is more than 100 feet fall, with branches that could shade half a football field and a trunk that’s at least eight feet across, but even so it’s doomed because of the emerald ash borer, a beetle that chews into trees and carries a fungus which strangles them. You probably have seen ash trees in your neighborhood that were killed in the last year by this unstoppable pest.

I wrote about this ash in October 2018 after stumbling across it and wondering whether it could be saved. The answer is probably yes through the use of expensive and never-ending pesticide applications, but also definitely no, because the effort should be saved for younger ash trees with more potential to stay alive until we find a solution to the pest.

I revisited the tree last weekend expecting to lament its decay but happily it is just as green and healthy as ever. Probably the beetle just hasn’t gotten there yet in big enough numbers to affect such a  giant, although there’s a very slim chance that it has some sort of immunity. We’ll keep an eye on it.

Nonetheless, I’m not going to be planting ash trees any time soon. So what should I plant?

I approached Farquhar in hopes he would give me a short list of choices but since we’re talking about the natural world, it’s not that simple. His advice boiled down to two things: Plant trees that are already around the region because you know they’re adapted to the soils and surroundings, but don’t stick to one species.

“Diversification is the biggest thing. We have a history of planting large groups of one species of tree. If a new insect or disease comes up, it wipes out everything,” he said.

Indeed. We’re increasingly being hit with the environmental equivalent of what economists call the black swan event, the unpredictable item that has huge impact – such as the emerald ash borer. The past is no longer prologue.

John Gunn, a professor of forest management with UNH Cooperative Extension, agreed with Fahrquar’s advice. “You should be keeping eggs in many different baskets,” he said. “Diversity within a stand is helpful, gives you a lot more to work with in the future.”

Before I asked for advice my idea was to just plant whatever trees are thriving in the next climate zone south of here because warm weather is moving north. I even poked through the Climate Change Atlas, a publication of the U.S. Forest Service, designed to give advice about this very approach – although it’s aimed at people managing woodlots not plunking down a few trees in a former field.

Kyle Lombard, forest health program coordinator with the state Division of Forests and Lands, disabused me of that idea.

“Phenotypes and genotypes from other regions may or may not grow well depending on a whole host of factors.  Climate is only one of those factors to consider,” he wrote in an email. “My general advice is to accept the natural regeneration that fits best on the site today and encourage native species that naturally do well and compete strongly on the soils and climate. …  Trying to be ‘proactive’ and plant mid-Atlantic hardwoods north of their range today because you think they might do well in the future is not necessary.”

Aside from lots of various evergreens, my property has mostly oak (not sure which varieties), sugar maple, and white and black birch trees. So I won’t be planting more of those.

What I obviously need to do is get advice from somebody like Farquhar, since I can’t tell a fir from a pine. Ironically, my decision is more complicated because things have gotten better.

“Thirty, forty years ago there weren’t a lot of different options. Now with the breeding that’s been done, making trees more durable, there are choices now,” he said, pointing to certain types of flowering dogwoods that old-timers couldn’t have planted.

As for people buying those neighbor-hiding trees, Farquhar says for most multi-generational longevity is not uppermost in their minds.

“The No. 1 thing people want a really big tree – they don’t have time to watch it grow before they die,” he said. “I don’t think they’re thinking about the lifespan of the tree: ‘I don’t care how big the tree gets – I’ll be dead before it gets that big and it will be my neighbor’s problem!’ ”

(David Brooks can be reached at 369-3313 or dbrooks@cmonitor.com or on Twitter @GraniteGeek.)

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