Ancient forests are mentioned only in P1. That reference to ancient forests has nothing to do with the meaning of “maintenance burns” in the last paragraph.

To understand the meaning of the phrase, think about the point made earlier in the paragraph. The author has just described a fire management policy designed to reduce fuel available for large fires to burn. “Maintenance burns” refers to fires that will be required to reduce the fuel available for large, devastating fires. These burns aren’t designed to reduce the larger, fire-tolerant trees. They’re designed to reduce the smaller, less fire-tolerant trees.

To understand the meaning of the phrase, think about the point made earlier in the paragraph. The author has just described a fire management policy designed to reduce fuel available for large fires to burn. “Maintenance burns” refers to fires that will be required to reduce the fuel available for large, devastating fires.

“50 years” is a number mentioned in connection with ponderosa forests in P2. It has nothing to do with the meaning of “maintenance burns” in the last paragraph.

To understand the meaning of the phrase, think about the point made earlier in the paragraph. The author has just described a fire management policy designed to reduce fuel available for large fires to burn. “Maintenance burns” refers to fires that will be required to reduce the fuel available for large, devastating fires. This is the only answer that sounds anything like the idea of fires designed to control the amount of fuel. There’s nothing wrong with the word “eliminate” here because the policy involves burning out the fuel for larger fires. The goal is to eliminate that fuel. Whether in practice the policy only ends up reducing rather than completely eliminating doesn’t matter; the goal is still to eliminate fuel. We allow the fires for the purpose of eliminating fuel.