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 in December.

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, Maryland. "In an urban area, that's some problem."

Many of us live in older urban properties where big trees sit cheek by jowl with homes, cars — and 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, Maryland. "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, Virginia. His firm is called TreesPlease. 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.

At Arlington National Cemetery, urban forester Greg Huse said, the cemetery's team of arborists keeps a close eye on each tree, prunes out dead or damaged wood, attends to storm damage, but generally intervenes 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."

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.