What is the chief reason that forestland has declined in eastern china

The answer is: They cut down trees for heating & building

Until today, the chinese government hasn't developed a sustainable plan to address the issue that arise from over exploitation of the environment.

Because of this, people and corporations in china often conduct unsafe measures when they cut down trees. They do not have to pay attention to the regeneration of the forest. Because of this, forestland has declined in eastern China.