They seem very dark and gloomy but I suppose it suits the environment you wanted to create. Number 4 seems to be working the best for me, though I would suggest playing with levels and contrast to help few details stand out more :)
thank you for your advice and your comment
Hey Peta-gaye - yep - if you made this image 'greyscale' you'd quickly see how 'flat' the tonal range is. Don't be afraid to think more 'filmically' about the lighting - so imagine the conifer tree has a number of holes in its trunk allowing 'spot-light' effects and real sense of immersion. Think 'pow'! in terms of the effect on our eyes :)
Number 4 works really well! Can't wait to see when you bring in more contrast and develop these more.