True Christoph and I'm not sure how to get around that. I alway encourage clients to call over and look at the large 9ft piece I have at home and we can view the others on a 50 inch HD Tv but the feel of the images is lost on a computer screen, especially now that more and more people are using tablets and smart phones when viewing sites
I think its the matter of local and global contrast.
When viewed at a large scale, the more smallish features of the image, like roots, twigs, leaves and such can be distinguished.
If you want it to work on a small scale you need to work on the global contrast in a way, that the large feature, like trees and tree shadows become more distinct and identifiable.
I'm afraid you can't get around that, in fact you need to edit the image for being viewed at a certain size / from a certain distance/viewing angle.
When I work on a large file, like a MF scan (100 Mpix), I do contrast adjustment on different scales and view the image at print size (33% on my screen) and at 8.33%, where they are as small as I publish them online.
So I work on global contrast, and I use highpass sharpening with sizes of 500 or 1000 px for smaller frequencies and sharpness for the really small stuff.
But often I fail to make it work on all scales.