My previous post was entirely flippant, but I do photograph trees a lot.
For me, there is usually a moment when I see a certain fall of light and form that says "photograph". If I don't do it (take the picture, I mean) then and there, but wait and try to get it "just right" then I end up with a photograph of some trees. Rather than the particular emotional fizz of that thing I saw. But sometimes I go back to the same tree or trees, month in and month out, waiting for something to be there. And sometimes it is. and often it isn't.