How to paint a tree....

I have painted this picture three times so far and am still working on resolving the foreground. I had thought that painting the main trees would be the problem, but it turns out that it is the elements of the picture that I hadn't really focussed on initially which are causing me the greatest difficulty.

I did a 'plein air' watercolour of the trees in Tasmania, then worked from my watercolour sketch and photos to do a black and white charcoal drawing to get some idea of tonal values. I find this a difficult concept to work with because I don't want my paintings to look like photographs (which can be the effect of trying to do a tonal picture from a black and white photo) but I want them to transport the viewer into the scene - which means having tonal values which are 'real' enough to convince the viewer, unconsciously, that the image they are looking at is possible (in a 'through the looking glass' sense).

Ah, the fun and games!

How am I going?