I wasn’t quite sure what was going up at 180 Smith St — I assumed the building’s modern top was an addition to enable airy loft-like apartment space. So I thought it odd that there was a Christmas tree up there — an unnecessary homey touch to a space that was presumably awaiting tenants. But 180 Smith isn’t to be a residential space at all, it’s to be something called the Brooklyn Ecopolis, a non-profit facility aiming to promote sustainable urban living. The building will host a cafe on the ground floor and may include some cool enviro-friendly touches (see the “Ecopolis Defined” page on the site).

So it’s actually quite appropriate for 180 Smith to have a tree on its roof even though there are no people inside. Maybe it’s even a live tree, with roots and everything all snug in a bucket of dirt. But if it’s a dead tree, don’t expect to see it sitting on the sidewalk — no, Ecopolis would likely do the eco-friendly thing and take it to be Cobble Hill Park this Saturday or Sunday, where the Parks Department will be chipping and mulching from 9:30 am to 2:00 pm as part of Mulchfest 2010.