People who want to work in outdoors jobs need not only look for positions at the federal level. You might find more opportunities by checking out your state and local governments. The competition to work in Yellowstone National Park or the Grand Canyon is fiercer than a hungry grizzly, and entry-level people may have to work their way up by working at a state-run outdoor park or recreational facility.
State outdoor agencies hire seasonal workers to do things like fight wildfires; build walking, hiking, and biking trails; assist visitors in a customer-service capacity; and run rest and concession areas. There are full-time jobs in agriculture, aquaculture, parks and forests, conservation and geology, research, and maintenance.
Many of these jobs are identical to those with federal agencies. It is an irony that while the federal government has an overabundance of applicants, the states often have trouble filling similar positions. Check with the Web site of your state or local government, and you will very likely find job postings for the above positions as well as many others.