Keeping the trees light and without detail is a good choice, but in order to look right each tree should be specifically "that tree, that shadow, that curve of branch", etc. The key is in making specific forms, rather than general ones. Not just "some general tree-like forms", but the particular ones from your reference that you want to depict. That will bring more reality to the scene, even if they are painted lightly and without detail. Just my two cents....

Michelle,

Thanks, that makes a lot of sense to me.

Simon