There seems to be a lot of randomness to the nature. It seems you used every tree available, but I think it would look better if you stuck to more of 1 type or the other. Try sticking to all green trees as it seems to just look better.
Also, for the sand that meets the water, use the correct water/sand border. The paths dont really seem to fit with the bridges, meaning that nothing lines up. You might also look into "drawbridge" tiles instead of wooden floor for the bridges. By looking at the map overview, the nature pic you showed, is no where near a town or anything, so you might even try out dirt pathways instead of all stone, or even a mixture of dirt/stone pathways.
Also, its hard to tell from the pics, but make sure to add details in your nature. Things such as grass tufts, small stones, stones, flowers, mushrooms, etc.
Have a look around the mapping showoff threads, and let them help you to improve your mapping. Not a terrible start though