The damage to the tree from which a branch fell and killed schoolgirl Bridget Wright would not have been discovered by the audit of all trees in NSW schools, according to one of the country's top arborists.

Mark Hartley, a director of Arboriculture Australia, who visited the Pitt Town Public School and took this picture of the damaged branch, also said the audit was a ''knee-jerk reaction''.

Tragedy: Bridget Wright (inset) and the damaged branch that killed her when it fell from a tree in her Pitt Town school.

The tree limb sustained a fracture probably about three months before last month's accident when it crashed to the ground, he said.

He said the crack would not have been picked up by the audit of trees every school in the state had been told to undertake to find ''extreme or unacceptable risk''.