A female jogger who was struck and killed by a large tree branch in Fairmount Park yesterday evening has been identified as a 23-year-old high school teacher new to Philadelphia.

Police said Mary Katherine Ladany, a 2008 graduate of Bucknell Univeristy who majored in math, orginally was from Montclair. N.J.

Known as Katie to her friends and family, Ladany taught last year at Dobbins Techical High School in North Philadelphia.

Police say she was listening to an iPod while jogging and may not have heard the 30-foot-long branch crack and fall from a tulip tree, also known as a tulip poplar.

The iPod was still playing when police arrived, said Chief Inspector Scott Small.

He said the branch fell about 50 feet before hitting the woman round 6:35 p.m. on the Forbidden Drive, a popular gravel trail through Wissahickon Valley Park.

"She was at the wrong place at the wrong time," said Small. ". . . It was a freak accident."

A passer-by called 911 but did not stay until police arrived.

According to Julianne Schieffer, urban forester for Pennsylvania State University in the Philadelphia area, tulip poplars are known to be "weak-wooded as a species," but for a branch to snap off, "usually there are mitigating factors," such as rot or an extreme wind storm.

Ninety percent of a tulip poplar's roots are in the top 18 inches of soil, and sometimes heavy rains over a prolonged period can cause a tree to topple. But in this case, with a very heavy branch falling from 50 feet up, Schieffer said, "It sounds like it was just an unfortunate circumstance."

Tulip poplars generally are extremely large trees, topping out at 100 to 120 feet, she said, "so even the smallest branch can hurt you if it falls."