Arlo Guthrie celebrates the 50th anniversary of the event that inspired the seminal song “Alice’s Restaurant Massacree,” while influential folksinger-songwriter Tom Paxton, who plans to retire from the road later this year after more than a half-century as a performing and recording artist, are among the dozens of artists and acts slated to perform during the 2015 Philadelphia Folk Festival. Scheduled for August 13 -16 at the Old Pool Farm in Upper Salford Township, near bucolic Schwenksville, Pennsylvania, the festival is produced and presented by the Philadelphia Folksong Society. Now in its 54th year, it is the longest continuously running musical festival of its kind in North America. To continue reading this article, click on the headline.