Beyond tracking and survival I could sure appreciate some brainstorming around good ideas for skill challenges using Nature.
Ability to add in Diplomacy, Bluff, Religion, History and Arcana are pluses
Here's a few:
Nature: Characters stumble out of one heavily overgrown area into an open area where a large beast (grizzly bear?) and her cubs are drinking. players could use nature to calm the beast and backtrack out of the area.
Diplomacy (or bluff?): players have accidentally wandered into a dryad's grove (or done something else offensive), and she has been spending the last hour of travel shadowing the PCs and making the trees fwap them in the face and run them in circles. Eventually she appears, flanked by a pair of treants. Players will have to talk their way out of this situation.
Bluff (or Diplomacy): players run across a pair of satyrs who have charmed an owlbear and are holding a music contest to see who can make the owlbear dance better. Players are called upon to take partin the contest as judges and participants, and of course, if the satyrs get offended, they'll unleash the owlbear.
History: Characters stumble onto an ancient monument (written in elven or even giant), overgrown with trees and scrub. A history check gives them a general sense of where they are in the forest.
Arcana: the spider-webs of a group of monstrous tree-dwelling spiders have been woven into complex and mystifying patterns. An arcana check will show characters a "shortcut" through the feywild outlined by the webs as way-markers. A failed arcana check will strand them there, for a time, near where a hag stalks the woods.
How are those?
One possibility would be to create a complex ritual that you use as a skill challenge, perhaps creating a complex potion. The different stages of the ritual could draw on different skill sets--maybe even using history during a research phase that involves discovering the formula used by a famous figure known to have perfected the ritual.
Natural obstacles: crossing streams or ravines, climbing or repelling down a rock face, horizontal repels in the air or across the face of a glacier, water travel.
Recognizing tribal warning signs to designated sacred or cursed land could add religion checks. Failing and violating sacred land could create a situation where diplomacy, bluff, or religion might be needed to extricate yourself. The later might be escapable (or at least ameliorated) by religion or arcane checks. History could also factor into all three.
Helpful/harmful nature spirits might be influenced by knowledge from a history or arcane check. Noticing a fairy ring is the obvious example, but how to bribe them for help in nature might be possible. See Toot-Toot in the Dresden files for applying that knowledge, especially the change over time indicating diplomacy.