Plant material theft has gone on for years. Out in LA, they install anchors in the ground to secure the new plantings along the highways. I would tend to agree it's probably a landscraper/jackleg that sees a chance to pocket extra money by reducing cost of buying the stuff. And I have also heard of large quantities of Jap Maples being stolen from garden stores and nurseries. This was done by someone who knew their value. Sadly, material is virtually untraceable. With this harsh economy, thefts industry-wide are going to get worse, so be vigilant about securing your goods.