Hi Scott, thanks for the reply and I am glad you like the composition etc and let me see if I can give you some answers to your observations, not by way of disagreeing with you, but more of an explanation of the circumstances of the shot as it were:
for example the ferns hanging from the trunk are brighter than those on the floor
I was standing on a well used tourist path near the side of the rain forest and looking into the edge of the forest, the ferns hanging from the trunk are near to me and lit by the light coming down through the more open canopy where I am stood, the darker ferns on the floor are actually several feet further into the forest and not lit by the same level of light, I was using a medium zoom lens and so even though it appears that the darker ferns are directly below, they were not and it is more likely to be the foreshortening effect of the zoom lens I am using.
Why are their tips so bright?
Not really sure, but I can only guess that they are the newer growth areas of the ferns hanging from the tree, they may well be thinner and therefore more transparent to the light behind them, or just brighter green because it was fresh growth, but I certainly don't have the skill to add the same amount of light to each tip of each fern selectively.
Why is there so much variation in colour, sometimes even on the same tree (sapling lower left)?
Could this also be new growth and its subsequent colour variation? Or just the rays of the sun breaking through the variously toned upper leaves of the canopy to highlight some parts of the scene and not others? Again I admit I am pretty good with PS, but I am still not able to selectively lighten or change the colour/tonality of some leaves within a scene and not others to this accuracy.
Both issues would be resolved if there was clear directionality in the light that accounted for the variation
It was taken in a rain forest, yet the light still has to break through the canopy sometimes to allow the ground plants to survive, therefore it is dappled beams of light that change and move throughout the day. Also as can be observed, there is a larger light source much further back into the scene, which I assume is from a larger hole deeper in the canopy, throwing more light into some of the back areas of the scene - when taking a picture in any dense wood or forest in bright daylight, the light is sort of sprinkled around where it breaks through or shines through the upper leaves to give variations in that light.
but to my eye the variation has been introduced during processing as opposed to captured in the field. Clearly this is a matter of taste.
I can only work with what was there at the time, and yes I freely admit I have worked on the image to enhance and bring out as much detail, colour and tonality as I could to represent what I was seeing while I was there, as I am sure we all do, but for this image I have only enhanced what was already in there and not added anything that was not.
Scott, I would also like to say thanks to you for posting your reply, I have really enjoyed thinking about my answers and mentally revisiting the scene and wish I was there again right now.