This white oak in Section 2 of Arlington National Cemetery is among the oldest trees on the property. (Adrian Higgins/TWP/Adrian Higgins/TWP)

Old magnolias never die, they just fade away. That seems to be the fate of the most historic tree at the White House, a Southern magnolia planted by Andrew Jackson and now so ancient and fragile that part of it was dismantled last month.

The decision to take down or at least dismember an old tree is neither easy nor always objective, but professional arborists are guided by a risk assessment protocol that brings a rationality to the process. The evaluation assesses the tree's vigor, the thickness of its sapwood shell, its disease stresses, the state of the roots and the like. Arborists also consider its location and the proximity to what they call "targets" — property and people.

"A tree in the middle of the woods is not a problem," said arborist Paul Wolfe of Integrated Plant Care in Rockville, Md. "In an urban area, that's some problem."

The Jackson magnolia could not be less out of the way. It stands between the Rose Garden and the west side of the South Portico, and though sheltered by the executive mansion, it is buffeted by the rotor wash of the presidential helicopter.

Gardeners, by the way, tend to be highly ambivalent about Southern magnolias. These emblems of the Deep South are stately and evergreen and have exquisite blossoms, creamy white chalices surrounding a column of beautiful stamens. The fragrance is sweet and lemony.

But the leaves are tough as old boots, and they drop continually from June until the fall. Also, it is virtually impossible to grow anything else beneath a Magnolia grandiflora.

"It's a wonderful tree, but in my neighbor's yard, not mine," Wolfe said.

Many of us live in older urban properties where big trees sit cheek by jowl with homes, cars and with us.

There is a prevailing mentality among many homeowners that big old trees are inherently threatening and should be removed. This is sort of like refusing to get on a plane because it can crash.

With the 2012 derecho and other destructive storms before and since, "people are fearful that large trees around their houses might fall," said Michael Guercin of Branches Tree Experts in Kensington, Md. "We have had to tell people these trees don't represent a danger and are safe."

"The worst thing they can do is have somebody take a very healthy tree and hat-rack it back," said Wolfe, referring to the practice of lopping the top sections from trunks and limbs. "And after the derecho there were people who just took down every tree on their property."

If you're worried about limbs or whole trees crashing down, what should you do? I would ask a consulting arborist or one certified by the International Society of Arboriculture to offer an expert opinion on a tree you're worried about, but an opinion only. A consultation is typically $75 to $150, Guercin said. This removes any impulse to suggest work to generate business.

Dead wood should be removed, but experts will tell you that decay and cavities alone are not enough to condemn trees. It comes down to the extent of the decay and whether it reaches into the roots, Guercin said.

"A tree with a cavity often responds by growing reaction wood" that strengthens it, said Ed Milhous, an arborist in Haymarket, Va. His firm is called TreesPlease. "Anybody who says, 'There's a cavity in that tree, it needs to be removed,' is out of line."

An ancient tree with problems can be managed: A decayed limb might be removed, a fungal disease addressed, soil compaction mitigated. Competent cabling is an effective way to prevent an old tree from breaking apart, at least for several additional decades, but it needs to be adjusted periodically as the tree grows.

I asked Greg Huse, an urban forester at Arlington National Cemetery, to show me some of the oldest trees in what is Washington's other national arboretum (albeit across the river in Virginia). The 624-acre cemetery has approximately 8,800 trees, some as old as 300 years, and, yes, is a certified arboretum. On a windswept hill on the cemetery's southern fringes, Huse pointed out a dwarf hackberry tree that is the co-champion in size in Virginia. I noticed on the brow of a nearby hill a large shade tree with its main trunk skillfully removed about one third of the way up. This is an old black locust that lost its central leader in a storm but is otherwise a healthy-looking specimen.

"It's not that great-looking, but when leafed out in the growing season it's going to have a completely different look to it," he said. Huse then took me to a specimen white oak in Section 2 below Arlington House that is close to 100 feet tall, with limbs as thick as the trunks of most trees. It's one of the oldest trees on the property, with a broad spreading silhouette. Three of the old secondary leaders have been removed, surgically, after storm damage. The oak has soldiered on beautifully.

Finally, he showed me an old but low-growing littleleaf linden with obvious decay in some of its branches; it has been cabled and braced. It is not a pretty tree, but it's one full of character and age, and even on some of the decayed branches it's showing vigorous growth.

Huse said the approach by the cemetery's team of arborists is to keep a close eye on each tree, prune out dead or damaged wood, attend to storm damage, but generally intervene as little as possible. "We only like to take a tree out if it's dead or irretrievably damaged in a big storm," he said.

Ultimately, the fate of an old and compromised tree comes down to the owner's comfort level for risk or to the sentimental attachment to the tree. "We find on older trees that people are emotionally tied to them and we go to incredible lengths to keep trees up that otherwise would fail," said Jason Grabosky, a professor of urban forestry at Rutgers University. "We try to engineer our way out of the biology."

Sometimes a tree appears vital when it's not. "We were contracted to take down a very large tulip tree in Chevy Chase, and I thought it was perfectly sound," Wolfe said. When he cut into it, the interior was hollow.

"There was no indication it was rotten," he said. "Now we are further along" with diagnostic tools.

If I had several old and precious trees on my property, I would develop a long-term connection with an arborist I trusted for their preventive care. Old trees decline and die (middle-aged ones, too), and sometimes you have to accept that a friend's time has come. The loss of a beloved tree can provide its own silver lining: the opportunity to put in sun-loving perennials, shrubs or a new tree.

Most of my trees were planted by me. Some are now large but relatively young, and I have positioned them a very safe distance from the helipad.

@adrian_higgins on Twitter

Tip of the Week

January is a good month to order vegetable and flower seeds — the early bird gets the best selection — but it's too early to start the great majority of plants indoors. Take the next month to set up equipment and materials for seed starting, which ramps up in mid- to late February for the Mid-Atlantic.

— Adrian Higgins