BASKING RIDGE, N.J. — The locals say that George Washington and the Marquis de Lafayette — the Frenchman who bankrolled the American patriots with cold, hard cash — picnicked in the shade it provided. Rank-and-file soldiers are said to have rested under it, gathering strength before going on to beat the redcoats.

It is a huge oak tree, now estimated to be 600 years old. Arborists such as Rob Gillies consider it one of the oldest in North America. It is a local landmark, right there in the cemetery of the Basking Ridge Presbyterian Church.

On Thursday, Mr. Gillies sliced into it with a chain saw.

Not the trunk, rotund and rotted inside and long since shored up with cement, like a cavity in a bad tooth. Mr. Gillies, who is 52 and has long experience in teasing extra life out of old trees, took aim at the upper reaches.

From his perch in the bucket of a cherry picker, he gave the tree a haircut, trimming away trouble spots — thick limbs that hung and could snap if tossed by winter winds or weighed down by snow. They could crash onto the street or slam into the church sanctuary, a relative youngster at only 177 years old, or an adjacent wing that is in its early 60s. Or the ancient headstones in the cemetery, the oldest of which is 280.