Agencies are a part of the executive branch of government that has been created by a legislature to carry out the legislative will. Legislatures often enact statutes that create a broad framework for an area of law and then create an agency with the power to make regulations to fulfill the purpose of the laws and fill in the details, enforce the laws and regulations, and adjudicate disputes.
Regulations (aka rules or administrative code sections) are laws enacted by agencies. Just like statutes, they have the force of law with criminal and civil penalties for violations.
There are a variety of agencies involved in natural resources law! The EPA, Forest Service, U.S. Fish and Wildlife Service, Bureau of Land Managment, Departmnet of the Interior, Department of Agriculture, etc.
Many federal agencies have the power to issue opinions/decisions to enforce their regulations and adjudicate disputes that arise under them.
Congress doesn't want national forests randomly burning all the time, but individual Representatives and Senators don’t know anything about fire or forests… So, Congress created a agency and subagency with expertise, the Department of Agriculture and the Forest Service, to enact regulations to regulate and prevent fires in national forests, and to enforce those regulations and also the federal statutes.
Congress created the Forest Service and gave it (and the Department of Agriculture) to power to enact regulations to protect forests.
The Department of Agriculture/Forest Services enacted regulations to protect forests.