Arborist Sue Nicol is usually asked to consult when a tree has dead wood or changes color, or neighbors complain about it.

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DO YOU CRINGE when you hear autumn winds blowing through big trees near your house? Do you worry about conifers dropping limbs or a favorite maple showing decline?

For many gardeners, trees are beloved friends. They lend structure, shelter, bark, flower, fruit, leaf and needles to our gardens while offering a home to birds, insects and wild creatures. They filter the air, soaking up carbon dioxide and exuding oxygen. Their majesty speaks of the passing of time.

They’re also the biggest investment we make in our gardens and can be their most problematic, destructive and even deadly component.

When to call an arborist? I posed this question to Sue Nicol, a professional arborist certified in risk assessment. After managing the landscape at Woodland Park Zoo for 16 years, she’s also an accomplished horticulturist.

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Nicol is usually asked to consult when a tree has dead wood or changes color, or neighbors complain about it. “Most people who call me are looking to save their tree, but their neighbors are looking for a reason to take the tree down,” she explains.

While it’s easier for an arborist to suggest removing rather than rescuing a tree, usually the goal is to save it, Nicol says. The International Society of Arboriculture offers risk-assessment training to help arborists determine which trees are hazardous and which are not.

When called to evaluate a tree, Nicol looks first for what part of it is most likely to fail. Is the entire tree dying, or is a single branch cracked? What will a tree hit if it falls? She’d make a different recommendation for a tree looming over the roof of a house than she would for a tree farther away from structures, driveways or roads.

Arborists peer attentively at branch attachments, roots, wounds and decay. She adds that it helps to know a little about lots of species to understand how they look and grow.

Premature death from girdled roots is becoming a big concern. It’s only been in the past 40 years or so that trees have been sold in pots. And once tree roots start circling in a pot, they continue to do so in the ground unless properly teased apart and even sliced to facilitate spreading. If the roots just keep circling, the base of the poor tree is sorely restricted, and it’s unable to take up adequate water or nutrients. “So many landscape companies plant the trees fast and don’t pay attention,” says Nicol. All those trees have now grown old enough that we have an epidemic of dying and falling trees.

Nicol makes a point of talking to clients about soil and good watering practices. “Even our native conifers get drought stressed,” she says. She includes a pruning lesson on what tools to use and where to make cuts. “I bring binoculars with me, but sometimes the tree is 90 feet tall, and I recommend an aerial inspection for a closer look.”

Why spend the money for an arborist when you could call in a tree-service company? Nicol has a ready answer: “You need an opinion from someone who won’t make money from the tree’s removal.”

Valerie Easton is a Seattle freelance writer and author of “petal & twig.” Check out her blog at Ken Lambert is a Seattle Times staff photographer.

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