A selection from the 1500+ images from both reference packs: Nature 1 and 2
https://www.artstation.com/a/42812222
https://www.artstation.com/a/42819420

You'll find a huge image collection from forests in all kind of different times, seasons, conditions and compositions. Images of trees, pathways, grassy forest edges, wet plains, plants and a ton of more interesting things taken straight from nature.