When Yohannes Gizaw was a student in Ethiopia, he wasn't sure what to do with his life. But a look at the country's flag started him on a mission to plant trees all over the African nation. 

"I bought the flag of my country and there are three colors," said Gizaw, an environmentalist and university lecturer. "In these three colors, I saw meaning." The Ethiopian flag is red, yellow – and green. And a green path is the one he decided to pursue by reforesting his country. 

When he took up his job as a lecturer at Sodo University in south-central Ethiopia, Gizaw began mobilizing students to plant trees in the once-lush but now degraded mountains surrounding the town of Wolaita Sodo. That was in 2008. Since then, Sodo University has set up a nursery for trees and 31 others around the country have followed suit. Gizaw and those inspired by his actions have planted around 5 million trees to date, including in important watersheds, he says. 

Between 30 and 40 percent of Ethiopia was covered in forest up to the late 19th century. Tree cover has dwindled to around 4.5 percent due to clearing of land for agricultural use and for fuel. That's led to desertification and has exacerbated problems for farmers already struggling with drought because trees can store water for dry spells. 

"You can see lakes are dry, rivers are disappearing," said Gizaw. "That's because of poor environmental protection. So my aim is just to regain our lost green."

Until then he achieves that aim, he says he will continue to plant trees in "mind of the people" and on the ground. 

"Normally planting trees doesn't need philosophy, science, economy. It needs only a good spirit. With this spirit, it is possible to regain our lost legacy," said Gizaw.