"I penned a string of screenplays before, but all the stories were commissioned by the directors or investors. Moerdaoga is completely different. It's my own story," says Cao.

Spanning half a century from the early 1960s until the present, the movie looks into the relationship between humans and nature through the story of a lumberjack. Abandoned by his parents but adopted by a logger, Lin Zi, the protagonist, grows to join a loggers' team in Moerdaoga's forests. But he chooses to turn against his coworkers and face off smugglers to protect the last 53 primitive trees there.

The movie, written in 2015 when Cao was studying screenwriting at the University of Southern California, has inspiration from real life. Cao left Moerdaoga to work as a police officer in Beijing in the early 2000s. She shifted to the film industry since rising to fame from penning South Korean director Kwak Jae-yong's 2014 film Meet Miss Anxiety, starring Zhou Xun and Tong Dawei.

Over 50 years or so, the forests of Moerdaoga have undergone intensive deforestation. When the local authorities banned commercial logging in 2015, the majority of primitive trees had already been cut down.

And since 2013, the Ewenki people, with their reindeer, have been relocated from the forests to areas closer to the city of Genhe, northwest of the Great Khingan Mountain, as the government hopes to improve their living conditions and protect nature.

In her movie, Cao reflects the changes.

"When we were looking for proper filming sets in the forests, it was very difficult to find big trees. I walked on foot for long stretches and found an ideal filming environment, but I had to drop the plan as heavy equipment could not be transported by manpower alone," Cao says.

"I cannot tell you how long it takes a big tree to grow to its full height. But I was told that a sapling as thin as a chopstick could take three years to grow, as winter is long there and only three months every year are suitable for plants to grow," she says.