EDIT: After fighting this thing three times, we determined that it's definitely NOT a lottery (it popped about the same time as a Treant). It pops on its own, in the 21-24 hour time block.
Weeping Willow spawns, as the map shows, up by the Aged Arbor, only accessible via Beaucedine. This tree spawns 21-24 hours after its last death, like an HNM, although no title is given. It's quite easy, like a normal Treant (also in that area), except that it spawns 6 Sobbing Saplings at 1/2 life. At 0 life, right about when it fades from the screen,Lumber Jack appears. He's the "real" NM, and requires at least a party of 65s to have no trouble (we did it with 4 65s, but it was a small challenge).
Edited, Fri Aug 13 19:02:16 2004