But Zhang did not give up. He bought books to teach himself forestry, and went to forest farms out of town to consult experts.

He worked under harsh conditions. In the first few years, he and his wife's faces were roughened by winds and their lips blistered and bled. Once, their eldest daughter who went back home did not even recognize the couple, whose appearances changed so much after being exposed to the elements.

Lack of money was another problem. To finance the planting program, Zhang used up his savings of 300,000 yuan ($46,700), plus 200,000 yuan his eldest daughter borrowed from a bank and 100,000 yuan of savings from his son. Zhang himself also borrowed from the bank twice.

In spite of hardships, Zhang was optimistic. "I plant trees for the Party and the people. I don't feel bitter, I am happy," Zhang said.

In 2011, Zhang was diagnosed with lung cancer. After an operation, he did not wait until he was fully recovered, rushing back home afterward to continue planting trees.

As the forested area expanded in Zuoyun county, Zhang's cancer continued its spread. In 2014, it metastasized to the bone. This time, Zhang only spent one month in hospital and went back home to resume planting trees.

But those years of efforts have paid off. The survival rate of the trees reached more than 95 percent, and more than 2 million trees have been planted in Zuoyun.

The forest coverage of the county has increased from 38.6 percent in 2003 to 45.03 percent at present.

However, Zhang claimed neither the property rights of the 2 million trees, nor that of the land on which the trees were planted. He promised to return the forested land to the village after his lease of 30 years expires.

Under Zhang's influence, his son Zhang Xiaobin also returned to the village after his army retirement to plant trees.

Asked why he did not use his personal connections and resources in the army to assist his son in a brighter military career, Zhang said: "A good reputation among the people and a fine family tradition will be the biggest assets I leave to my children."

Zhang himself lives a simple and modest life. He usually eats potatos, tofu and Chinese cabbage, and wears an old-fashioned military uniform.

Villagers said Zhang "never puts on airs and does not look like a general."

Thanks to unsung heroes like Zhang, the Mu Us Desert has shrunk by 80 percent in the past six decades.