This is the Valentine's day card I made this year.
I started with a pencil sketch:
It's really rough and was fairly small, but you can see the ideas forming a bit.
Then I started to create the image digitally. It was a combination of vector art, done in illustrator-the trees and their roots- followed by a bit of hand painting in photoshop.
This is the vector drawing I exported from photoshop
It doesn't look nearly as good without the slight shadows beneath the roots, which I painted in afterwards.