Zhang faced "numerous conflicts" with villagers and loggers. She hired up to 100 guards at a time to protect the ecology.
She raises pigs, goats and chickens on the mountains, and sets them free once they've matured.
She eventually ran out of cash and had to borrow money.
But her efforts paid off.
She turned the wasteland into one of Beijing's greenest areas. "It's difficult but not impossible to restore a mountain's ecology, but it's almost impossible to restore society's ecological viewpoint," she says.
Zhang withdrew from society to protect her land.
Her daughter, who's in primary school, lives with Zhang's mother downtown.
"The lives of animals and plants are equal," she says. "I didn't realize this at first. But I do after cultivating this ecology."
She realized her mission was beyond her capacity. So, she opened her mountains to environmental volunteers in 2008. But she withdrew again last year.
"Some university volunteers followed me from their sophomore to senior years and gave me only one piece of advice before they left: 'Don't change the world; change yourself.'
"I was speechless. If I changed, the last land might be lost."
She has been tempted by, but resisted, offers to commercially develop her natural reserve.
Zhang suffered a devastating setback when last month's blizzard destroyed many of her trees.
"Each of those trees is an extension of me," she says.
"The sound of the branches breaking was the sound of my heart breaking."
Snow trapped her and her workers on the hill, and they were running out of food.
But she refused to descend when rescuers arrived. She stayed to feed her animals. However, the storm taught her a valuable lesson.
She began reaching out to media to mobilize resources to help her mountains recover.
Her close friend Gao Jinzhi says: "She now realizes she needs to share this responsibility with society, since she's doing it for everyone."
Feng Yongfeng, founder of an environmental protection NGO in Beijing, believes Zhang should open her natural reserve to bring in more resources.
"The fact that she has been relying on her own powers to protect such a large area deserves due respect," he says.
"However, she needs to learn to cooperate and acquire more social resources. That's the only way to sustain her reserve."
Contact the writer at xuwei@chinadaily.com.cn.