This all depends on what idea you want to convey. Generally you should use “affect” since you are concerned about your presence in the wilderness that could have an overall influence on nature, animals and other visitors.
If you use “effect” you would imply that your presence in the wilderness would definitely bring about changes in nature, animals and other visitors. Your presence could effect changes to nature and animals in the long run, but would it also bring changes to other visitors?
The following is an excerpt from the American Heritage Dictionary about the difference between “affect” and “effect”:
Usage Note: Affect and effect have no senses in common. As a verb affect is most commonly used in the sense of "to influence" (how smoking affects health). Effect means "to bring about or execute": layoffs designed to effect savings. Thus the sentence These measures may affect savings could imply that the measures may reduce savings that have already been realized, whereas These measures may effect savings implies that the measures will cause new savings to come about.
Excerpted from The American Heritage® Dictionary of the English Language, Third Edition © 1996 by Houghton Mifflin Company.