Researchers join educators and children on walks in a nearby urban forest. Toddlers negotiate jackets, snow pants and boots, and then move, as fast as layers of winter clothing would allow, across a sports field. On the other side of a chain-link fence is the forest. The group moves along its edge to a small clearing they’ve come to regard as the entrance. It’s marked with a fallen tree and, on rainy days, a large puddle at the edge of the path. The entrance is different today. Smaller shrubs and trees have been cut down, and a wave of orange markings – bright flags and smears on tree trunks leads…