Trees in Winter by Eric Sloane, N.A. Notice how well the bark of the Birch trees is rendered – look closer and you’ll see how Eric used the flat side of a razor blade, working gently to pull the blade across the trunk horizontally to produce the effect of Birch bark. Eric also includes “Tree Wells”, the area around the trunks where the snow looks like it has melted. Indeed, it has, as these wells are formed because sunlight has reached the trunks, warming and reflecting upon the snow that has come to rest nearest the trunk.