Final answer:
The US Forest Service is the federal agency that protects ecosystems and supervises public access to forests.
Step-by-step explanation:
The federal agency that protects ecosystems and supervises public access to forests is the US Forest Service. The US Forest Service is responsible for managing and protecting national forests and grasslands. They work to conserve the nation's forests for future generations and allow for recreational activities while maintaining the ecological balance.
Learn more about US Forest Service