I might suggest "Midworld" by Alan Dean Foster - a ship containing scientists traveling to a research outpost on an extremely dangerous jungle world crashes in the middle of the jungle, and the scientists are saved by the human descendants of the original colonists on the world, who have adapted to live with the world's ecosystem and wildlife. Some environmental moralizing along the lines of "live with the world and environment instead of fighting/conquering it," some vocabulary that 9th graders may have to look up. Possible occasional cusses; it's been a while and I don't remember. Overall a really entertaining story and some nicely realized worldbuilding.