found no speciality full pattern but perhaps you could adapt another pattern.
Here is an idea.
http://community.livejournal.com/knitting/7873887.html
Elann has several patterns that might work.
Full Skirts, Half round shawls could do more segments to make round, Lace poncho,
http://www.elann.com/freepatterns.asp
or these show how to do flat circle with Feather & fan lace, you would just do it open and start further out with more sts. That would look amazing around a tree.
http://tiajudy.com/circfnf.htm
http://tiajudy.com/omaslace.htm