The ranger/druid gets a +2 bonus on Hide, Listen, Sneak and Discern while in the favored environment of his choice.
Environment- Examples
Aquatic- sea, ocean (on or under water)
Desert, cold- tundra
Desert, temperate or warm- badlands, sandy desert
Forest, cold or temperate- forest
Forest warm- jungle
Hills- rugged terrain up to 2,000 feet elevation
Marsh- bog, moor, swamp
Mountain- rugged terrain above 2,000 feet elevation
Plains- farmland, grassland, steppe, prairie
Underground- dungeons, caverns