Techniques used:
For this image I actually duplicated a picture and flipped it to make it look like it was a whole image together. (The original picture was just half of the yellow forest)
Then, I selected different sections of the trees on the image and put them together to create the forest in the front. I changed some of the levels and colors for the trees to each of them look a little different from the one next to it. I also added a shadow overlay to give the picture a 3D effect.