I'm looking for a good adjective to describe a person who loves experiencing nature, as in a person who has been in the Boy Scouts for most of his life, loves fishing, hiking, mountain climbing, sleeping under an open sky, ice fishing, canoeing, crosscountry skiing and other things along those lines. A true-born “nature freak.”
I'd call that person an outdoorsman
There are a lot of adjectives which describe the physical activeness of somebody:
brisk, alacritous, yary, jaunty, evelié, exilient, sprack
And to modify these words, you can use adjectives which relate to natural wilderness, such as:
bucolic, fielden, agrest, rural, predial
A biophilic is a person driven by curiosity, never wasting an opportunity to know something more about creatures in his neighbourhood.
The Biophilia Hypothesis is an area of research that pertains to such people and systems.
A nemophilist. Maybe it relates to what you need.
One who is fond of forest or forest scenery; a haunter of the woods.
Enthusiast: someone who is very interested in and involved with a particular subject or activity: a computer-games enthusiast
Motivation for my answer: the outdoorsman that was proposed does have a feminine version, outdoorswoman. I've seen it used in the hunting and fishing column in my local newspaper. But having the two versions makes things awkward.