Pine And Oak Forests, Dunes, And Sand Strands

Michael McAllister will use slides and models on Saturday to explain the dynamics of Long Island's groundwater supply, in a program called "Flowing Above, Flowing Below."

The 10 a.m. to noon event will take place at the Bridgehampton headquarters of the Group for the South Fork, which is sponsoring it. Reservations have been requested.

Outdoors on Saturday, Ilmar Ratsep of the East Hampton Trails Preservation Society will lead a five-mile walk on Napeague, beginning at 9:30 a.m. Hikers will pass pine and oak forests, dunes, and sand strands, with Mr. Ratsep pointing out the different ecosystems along the way. Hikers will meet at the Long Island Lighting Company power station on Napeague Meadow Road, north of Route 27.

Elsewhere Saturday, the Long Island Greenbelt Trails Conference is hosting a two-to-three mile hike around the Caleb Smith State Park in Smithtown beginning at 9:30 a.m. The Conference's offices, in Blydenburgh Park in Smithtown, are the meeting place.

The East Hampton Trails Preservation Society will hold the first of a series of "guest speaker" hikes on Sunday, starting at 10 a.m. The East Hampton Town Crier, Hugh King, will relate local history while Richard Lupoletti leads the trek. Those wishing to stretch their minds as well as their legs will gather at the trail entrance on Spring Close Highway, about half a mile north of Route 27 and immediately north of the railroad overpass.

Finally, on Wednesday, the Society's Nancy Kane will lead hikers on a "movable feast" walk through the Nature Conservancy's Merrill Lake Sanctuary in Springs. After exploring a backyard trail system, hikers will repair to the leader's house nearby for bagels, scones, hot liquids, and conversation. The meeting place is the sanctuary entrance, off Springs-Fireplace Road. Ten a.m. is the hour.