Mikkel Eye is an Architectural Designer who posts pictures of trees to his site, Meye.dk.
Mikkel explains: "All the trees are available as high quality PNG’s with transparent background. The trees are free to use for anyone who wants to add plantings to their visualizations, sections, and diagrams within the fields of landscape architecture, architecture, or urban planning. However, your project should be in focus. The trees of Meye are not to be used as free standing pictures or for advertisements."
Norway Maple // Windmill Palm // Scarlet Oak
You can filter by Species and Season. Niche-y, but for those in need: great resource well done.
The Teacher-Friendly Guide to Climate Change offers links to chapters on Paleontological Research Institution's Digital Encyclopedia of Earth Science and Here on Earth: Regional Guides.
Michelle Thompson is a "British digital illustrator, cutting-up and reassembling images from recent history, to reflect contemporary themes and popular culture."