ROMULUS, Mich. (AP) - Officials say some trees planted at the site of a memorial for 1987 plane crash that killed 154 people aboard and two on the ground near Detroit Metropolitan Airport are being replaced. WXYZ-TV reports the pine trees were planted more than two decades ago where a memorial now stands to those who died in the Northwest Flight 255 crash in Romulus. The station says some have been cut down and others are dying because of what an arborist Kevin Schible describes as healthier trees overtaking weaker trees. Thursday marks the 31st anniversary of the crash of the Phoenix-bound plane, which had one survivor. The Michigan Department of Transportation, which contracts out maintenance of the area, says trees that were removed or will be removed will be replaced. --- Information from: WXYZ-TV,