I reread your original post, and it is the opposite of what i was thinking. I thought you wanted all the trees to be the same.
So, to separate your trees, you will need to use a selection. Probably the best way would be to use Select>Color Range
You can then select that color, then using the selection tools or the quick mask, to remove part of that selection
I would then copy that selected portion of the trees to a new layer
Now repeat for another section
What you could do with each layer before removing the selection is to create a mask, then you can use that mask to easily reselect if necessary. (Should not be needed, but it is an option)
Now select a layer and use the hue/saturation command or adjustment layer to adjust the hue. (With the adjustment layer you will need to clip it to that layer so it does not affect the remaining layers below it. That means the adjustment layer must be just above that layer no higher or lower)
When you are done, save as a psd or tiff for your master (just in case you need to change something later on. When you save as a png or jpg the layers will be merged in that file because they do not support layers. Just so you are aware.