My son loves all things nature so when he turned 7 we threw him a nature themed party. Thankfully we live in an area that has excellent nature centers that you can rent out (including the time and talent of a naturalist) for parties.
I wanted the party to feel like a day at camp. I DIY'ed lots of the decor including the camp sign, party napkins, and animal tracks table runner. It didn't hurt that the nature center had a cool mural to serve as a backdrop.
When it comes to parties, over the top and FUN!
You can read all about this project on my blog, http://www.namesakedesign.com/2014/09/a-nature-themed-7th-birthday.html.
Oh it so hard to choose! I think its a tie between the campfire cake, the table runner, and the camp sign.
Stick with natural colors. Don't over look opportunities like straws and cutlery to enhance the theme. I found "wood" printed paper straws and wooden utensils online.