The headstones go up this weekend :

UPN. Born: Jan. 16, 1995. Died: Sept. 15, 2006.

The WB. Born: Jan. 11, 1995. Died: Sept. 17, 2006.

The death of the two ``netlets’’ — their viewership was a fraction of the audiences drawn by the big boys — was pronounced earlier this year when their parent companies, CBS Corp. and Time Warner Inc., merged them into the new CW. That decision pulled the plug on more than a decade of heavy financial losses as UPN and the WB had battled over young viewers, buzz and even the rights to shows (most famously, ``Buffy the Vampire Slayer’’ back in 2001).

So after this weekend, they’ll be gone, replaced by a niche network that will combine the ``best’’ of their old schedules. The new CW will make its debut Monday, although much of its new lineup won’t be in place until the week of Sept. 25. (Locally, the new CW will be KBCW, Ch. 44, the old UPN station, while KBWB, Ch. 20, the old WB outlet, will be scrambling for programming.)

One never wants to speak ill of the dead, but it’s hard to believe too many viewers will be mourning the passing of UPN. It had its moments: ``Star Trek: Voyager’’ in its early days, the last couple of seasons of ``Buffy’’ and the more recent ``Veronica Mars’’ and ``Everybody Hates Chris.’’ But it never established a clear identity, and its programming development also produced some of the worst shows in TV history.

The WB played on a different, higher plain. Until its final months, when things started to crumble creatively, it had a very clear sense of what it was and what worked for its audience. Over the years, it had a fistful of memorable and often influential series: ``Buffy,’’ ``Angel,’’ ``Felicity,’’ ``Dawson’s Creek,’’ ``Gilmore Girls,’’ ``Smallville,’’ ``Everwood.’’ Even its commercial failures — ``Jack & Bobby,’’ ``Popular,’’ ``Grosse Pointe’’ — had real artistic snap and pop.

It also provided a launching pad for some of television and film’s most distinctive voices, including J.J. Abrams (``Alias,’’ ``Lost’’), Joss Whedon (``Serenity’’), Amy Sherman-Palladino (who just left ``Gilmore Girls’’), Ryan Murphy (``Nip/Tuck’’), Kevin Williamson (``Scream’’) and Greg Berlanti (the new ``Brothers & Sisters’’).

The differences between the two remain right to the bitter end. UPN will end its run with yet another installment of ``WWE Smackdown!’’ (8 p.m. Friday, Ch. 44). The WB goes a classier route one more time with an evening of the original pilots for its top shows. (Don’t go looking for it locally, though, because sore loser KBWB has decided to pre-empt the night for syndicated programs.)

Just exactly how things shake out at the CW remains to be seen.

Perhaps wisely, it is building its first schedule almost entirely on returning WB and UPN shows with just one new drama (``Runaway’’) and one new sitcom (``The Game’’). That gives it a certain stability while it decides how to shape its identity. (It needs to move fast because such series as ``7th Heaven,’’ ``Smallville’’ and ``Gilmore Girls’’ are nearing the end of their TV lives.)

One can only hope that there will be more WB than UPN on the new CW.

Falling from `Trees’

ABC’s ``Men in Trees’’ got a sneak preview earlier this week, but if you missed its opening episode, you can catch up with it Friday (8 p.m., Ch. 7), followed by the show’s second hour at 9. And you should give this newcomer a shot.

The romantic comedy-drama is perhaps the most pleasant surprise of the fall season, especially given all the tabloid baggage that star Anne Heche brings with her. But as written by Jenny Bicks (who cut her teeth on ``Sex and the City’’) and directed by James Mangold (``Walk the Line’’), this ``Northern Exposure’’-esque series about a relationship guru (Heche) who decides to find love and happiness in the small Alaska town of Elmo is sweet, charming and often witty. Some of the key moments are totally unbelievable, but Heche and an engaging supporting cast (John Amos and Abraham Benrubi — Jerry on ``ER’’ — are particularly good) make them work.

At one point, this show was part of what looked like a solid, chick-lit-style night of TV with the buzz-heavy ``Ugly Betty.’’ Now, ``Betty’’ has become such a hit-in-the-making that ABC moved it to Thursdays, when there is a bigger audience. That leaves ``Men’’ hanging out to dry — which is too bad, because this could a very enjoyable diversion.

Spy world

A&E finally brings back the marvelous ``MI-5’’ for its fourth season this week (11 p.m. Friday). The British equivalent of ``24,’’ it’s a taut, thrill-a-minute drama about a crack anti-terrorist unit. The big difference is that ``MI-5’’ is much more grounded in reality than its American counterpart. And if you think ``24’’ is fatalistic and bloody, this series makes Jack Bauer’s day look like a bright, sunny stroll in the park.

This season’s opening two-parter, involving a group triggering a bomb every 10 hours until its leader is released from custody, will have you on the edge of your seat as the MI-5 unit deals with myriad surprise twists in the case. It’s a most welcome return for a very good series.