First of all, thank you very much for your comments, they are very appreciated!
The first photo was intended to show a subtle ornament the tree branches can create when bare. So the subject was to be the trees in the foreground. So, I guess, the only thing to 'cure' this one would reaaly be to climb a little higher and snap the branches against the water of the lake, not against the trees and mist of the opposite shore (thanks, Pete, for this one; but making anyone to cross the view would be hard, because the lake wan't frozen yet then ). Apparently, trying to make the background more washed out wouln't work because of high contrast between trees and mist, right?
About the other ones, I tried to use your advises and attached the results. I'm a very newbie with image processing programs, so I don't know if I opened up the shadows in the second one the correct way. I also tried to crop it (unfortunately, there is no way to crop down, what's in my first post are the full-sized pictures, without crop).
With the third one it took me quite a long time to understand if I'm not leaving too much empty space between the trees and the right border of the picture. Decided to leave it as it is, hoping that this better stresses the detachment and lonelines of the group of trees.
I also tried cropping the last one, but, I'm afraid, it didn't help too much (no more than crop helped to improve the second one, actually).
Thank you for taking your time to comment my photos and to read this many letters