WHEN conceptual artist Roby Paine planted his stainless-steel tree sculptures in Madison Square Park this May, he may have also planted a seed in the mind of several other New York artists looking to literally make their mark on the streets of New York City.

Paine’s frozen-looking limbs are just one of the various pieces of outdoor artwork on display throughout the city, all of which explore how architecture reflects the society that produces it.

At the entrance of Prospect Park in Brooklyn stands sculptor Leonard Ursachi’s “Hiding Place,” a cylindrical military-style bunker which, thanks to its willow branch construction, could barely withstand a well -thrown stone, let alone the onslaught of heavy artillery. It has no entrance or exit, and is adorned with three reflective plates in place of windows.

“The shape of the structure is modeled after a war bunker, but the fact that it’s made out of willow branches, an ancient material in terms of building shelters, is meant to show frailty,” says the Romanian-born Ursachi.

Inspired by his nation’s history of violent conflict, he developed the idea for the sculpture – on display through Aug. 31 – in 2003. “War is really a universal subject, and I think that this piece invites anyone passing by to re-examine the meaning of home, how that meaning changes, and how individual personalities change, especially in times of war.”

Like Ursachi, Donna Dennis also toys with the concept of shelter via her exhibit “Tourist Cabins” on the Park Avenue median between 52nd and 53rd streets. There, two small, playhouse-size cabins sit at opposite ends of a small strip of green grass and trees. According to Dennis, the sculptures were inspired by family road trips that had only the vaguest idea of a destination.

“We’d start out driving very early in the morning, and when it came time to stop for the night we began seeing the typical motel ‘No vacancy’ signs,” recalls the artist. “We wound up stopping one time at this old-

fashioned tourist cabin, and I guess the idea kind of stuck with me.”

Juxtaposed against the surrounding cityscape and designed with satellite dishes, the tiny structures – on display through Oct. 27 – reflect the attempt of an isolated society trying to make contact with the world at large.

Berlin-based, Mexico-born artist Damian Ortega, on the other hand, attempts to portray the ever-shifting balance of world power with his self-styled mobile monument “Obelisco Transportable,” currently on view at Doris C. Freedman Plaza in Central Park until the end of October.

The 20-foot obelisk sits atop a grassy platform that can be wheeled from place to place. Ortega describes this transportable installation, which he designed according to traditional Egyptian obelisks, as a “Napoleonic gesture” because wartime victors used to bring home monuments from their captured cities and install them as symbols of victory.