I don't think I have done any of a forest, unless you count this one:
http://www.flickr.com/photos/104696694@N02/10577226474/sizes/o/in/photostream/
I guess not.
But here are a few of other kinds of natural settings...
Hi,
I have developed a tool for converting normal photos into what appear to be digital art portraits. It has not been publicly released yet, but here are some "before & after" examples of what it can do.
http://www.flickr.com/photos/104696694@N02/10500219425/sizes/o/in/photostream/...