Maples, monocultures, and arboreal courage


West Tisbury has had a spirited conversation this fall about the trees around the parking lot between the Howes House, the Field Gallery and the new public library. The library building committee met with resistance and expressions of alarm when it went before the selectmen in September proposing to remove 11 Norway maples around the new building and parking lot.

Trees are good, so cutting them down must be bad, right? In a case like this, the best approach is usually to start with the simplest answer, throw it out, and proceed from there.

Tim Boland, executive director of the Polly Hill Arboretum, has volunteered his services on the library landscaping committee, and he’s delighted that such passion should be attached to a conversation about the future of a few trees in town. “I think at the very core,” he says, “you want people to value trees.”

But he urges a deeper consideration of the particular trees involved and of how they conflict with a town project whose goal is admirable: the protection of a precious water resource, Tisbury Great Pond.

The plan for this municipal parking lot at the center of West Tisbury is to use pervious pavers and a rain garden filled with plants whose root systems, Mr. Boland says, will capture 93 percent of the hydrocarbons that would otherwise flow into the great pond.

The Norway maples on the site, Mr. Boland says, simply don’t fit into this plan. They do, however, provide an opportunity to tell a little story about the history of our relationship with trees.

A century and a half ago, the tree of choice for towns across New England was the elm. Towns planted them by the thousands, long before the word monoculture had entered the language, and watched helplessly as disease struck them down. Afterwards, rather than learning our lesson and introducing a healthy diversity to our urban forests, many communities planted fresh monocultures of a hardy tree imported from northern Europe, the Norway maple.

Mr. Boland, who doesn’t like to speak ill of anything deciduous, admits that the Norway maple is “kind of a bad tree.” So bad, in fact, that it is banned by the Massachusetts Department of Agricultural Resources. That’s right — buying, selling or planting a Norway maple in this state is a crime.

The problem is that Norway maples are aggressive, colonizing woodlands and displacing New England’s sugar maples. Their root systems release chemicals that act like herbicides, discouraging other plants that try to grow in the maples’ understory. Those toxic roots also promise to upend the new parking lot’s pavers, occasioning frequent and costly maintenance work.

West Tisbury’s Norway maples — Mr. Boland estimates their age at 40 to 50 years — are a monoculture in more ways than one. Not only are they all the same species, but they’re also the same age. “When we have an even-age stand,” he asks, “where are your new trees coming from? They certainly won’t grow under those Norway maples.”

The good news is that trees are a renewable resource. The bad news, if you’re into instant fixes, is that they grow at their own majestic pace.

Looking to minimize the visual impact by replacing the Norway maples with the biggest trees available, Mr. Boland says, is the wrong approach. This simply isn’t the way an arborist thinks about things. In a lifetime of arboretum work, Mr. Boland has developed a more patient attitude toward trees and time. He counsels choosing better trees, cultivating diversity, planting small specimens and letting them grow into their full grandeur.

Looking ahead, he says, “You have to have faith that you can replace these maples with better trees. And in 15 years, this whole property will be grown in. We want to plant some linden trees, which are beautiful and have no pest problems. We’d like to plant some native magnolias, which grow beautifully in these rain gardens. We also want to use some screen plantings of our native arrowwood viburnum — a mix of plants that are local to the site, species like the native spirea which grow in the corridor of the Tisbury Great Pond watershed.

“I look at the rain garden and I think, wow, what an opportunity this is to demonstrate these landscape principles. Kids will be able to go outside and read a sign that says, do you know that these shrubs provide fruits for these native birds?”

The grounds of the new West Tisbury Public Library, the town’s center for lifelong learning, are the perfect spot for this project. Building a new library, like planting a tree, is a forward-looking gesture, an act of faith.

“People look at me funny sometimes when I say this,” says Tim Boland, “but planting a tree is being brave. You’re saying, I’m not certain what’s going to happen with this, but I want to do something good, not just for myself but down the line.”