This is not about conservation, it is about collateral. YOUR land is being stolen by the government and used to secure loans the government really had no business taking out in the first place. Given that the government cannot get out of debt, and is collateralizing more and more land to avoid foreclosure, the day is not long off when the people of the United States will one day wake up and discover they are no longer citizens, but tenants.
The tracts of land and resources on and below the land are, however, public land and public resources, meaning that the government owns them and manages them. They could reduce the public debt to a degree by issuing more licenses and permits for mineral development, but pressure to release such natural resources is not intense. Drill ANWR, but there is no critical shortage; oil is flowing from many sources and in greater quantity than ever, and cheaply. Harvest timber in the national forests, but there is no shortage. Open Alaskan coal fields to entry, but the demand is not there. License asteroids and the moon to metal mining, but no one will make the initial investment to create the space mining infrastructure.
Some day these resources may be needed, that day could come suddenly, perhaps even later today, or the need may grow gradually as time goes by. Develop the resources when they are needed by the market. As long as government is managing the land and the natural resources, they will manage in a spirit of conservation. Or they could give up management and let capitalism run everything.
Either way, national debt is not unmanageable at this time, it is about equal to private debt, which appears to be largely voluntary and under control. There is no problem, although constant vigilence in this and other matters such as maintenance of freedom should be exercised.