Longtime Lawrence Public Library Director Bruce Flanders announced his sudden retirement Thursday, vacating the position he’s held for 16 years after recently taking a medical leave of absence.

“Bruce is a great guy, and he has brought us to this point,” said Deborah Thompson, chair of the library’s Board of Trustees. “We just have to move forward as a board and as a staff to bring that next phase of the library to fruition.”

Former Lawrence City Manager Mike Wildgen was named as the interim director of the library. Thompson said the board will begin a search process for a new director after the first of the year.

Thompson confirmed that Flanders has been on medical leave since August. His retirement is effective immediately. Flanders was not at Thursday’s meeting of the library board, and he did not make a statement in a press release distributed by the library. An attempt to reach Flanders for comment was not successful.

The library board praised Flanders’ service, noting that circulation at the library had doubled to 1.4 million items over the last decade, and that he had pushed hard for the library to adopt new technologies such as self-check stations and social media.

Flanders also played a key role in planning for an $18 million expansion of the library that voters approved in November. The expansion project currently is being designed and is scheduled to be under construction in 2013.

Thompson said the board would look for a new director that has strong library experience.

“Being a public library in a university community is unique,” Thompson said. “That may be a factor in our search. You have a very educated population, and there are very high expectations for the library.”