Well first off there is an issue with the tree because you use two styles, both incomplete becausee they share. The left side of the tree that you are trying to inact shading over is more detailed, and tree like then the faded remainder of the tree. Usually when shading you do it was a whole, not just the change in the under brush. The base is alright, and not much to complain over. Though my advice would just be to follow through with the style that you example on the left side of the tree throughout the entire tree. Now about the ground. Usually unless you intended it to be tiled ground for farming, it never has lines. i would suggest ditching the lines, and adding detail through other manners. Finally on the grass you have created it to look like there are shrubs among the grass because of the large portions of differently shaded areas that you use. If your going for a grass style it should be diverse, and not have any same color blotches/connections in one area unless you intend to make a larger creation such as a bush, etc. Finally, if this is a tileset add variation, not just the same tiles copied over and over again, because it ruins it. Diversity is key in any artistic creation, especially landscape.