broadcasters learned in the first half of the 2006-07 season that scheduling too many serialized dramas was a fool’s errand, then the season’s second half taught them that keeping viewers, even for successful serialized shows, isn’t easy, either. The networks hope to bolster ratings next season by airing an increasing number of those series continuously.

Earlier this month, ABC announced it would air Lost consecutively over 16 episodes next spring. CBS’ midseason drama Swingtown also will air nonstop, as will The CW’s One Tree Hill. Along with Fox’s 24 airing continuously, so will The Sarah Connor Chronicles and Canterbury’s Law. In addition to ordering 24 episodes of Heroes, NBC will produce six stand-alone episodes of the series entitled Heroes: Origins, each of which will introduce a new character for whom viewers will vote to keep on the show the following season.

Most of these scheduling moves are in response to a challenging season, in which Heroes, Lost, and CBS’ Jericho returned after midwinter breaks to lower ratings than they enjoyed last fall. Whether due to scheduling disruptions, creative missteps, or sheer exhaustion on the part of the audience, those declines point to a shifting landscape, in which viewer loyalty continues to fragment.

“It’s very easy for the audience to get distracted by other forms of entertainment,” said Laura Caraccioli-Davis, exec vp of Starcom Entertainment. “So the networks have to be creative in thinking of ways to keep these shows alive.” NBC programming chief Kevin Reilly even coined a term for the strategy, calling it the “bulk-up challenge.” During a press briefing prior to the net’s presentation last week, Reilly described that challenge as “trying to stay more consistent in our scheduling for the audience.”

But ABC Entertainment president Stephen McPherson took a different approach. “I think you have to be careful not to push it too much,” he said in reference to NBC’s expansion strategy. “If you back up the calendar, there’s a limited amount that you can get done and still keep the quality level up.”

CBS’ programming chief Nina Tassler addressed the decision not to renew Jericho for a second season, saying the show had “lost a lot of steam.” And she acknowledged that Jericho’s split broadcast schedule “informed” the decision to air Swingtown uninterrupted.

Of course, there is a downside. Traditionally, networks have recouped their investments on series through the repeat broadcasts of those programs. “It is a challenge financially to make hay from a show like 24 without the ability to repeat it,” said Fox Entertainment president Peter Liguori. “But I think it would be absolutely foolhardy—both for this network and our competitors—not to continue to invest in broadcast television with big event-like shows.”