Five years ago, a paper published in one of the world's most prestigious peer-reviewed journals made headlines across the world. The authors used NASA satellite data to claim that at least one-quarter of the world's green leaf area increase since the 2000s was due to Chinese tree planting efforts. Some celebrated, some couldn't believe it. What went on here and are China's newly planted forests as successful as they claim?

Part 1 - Understory 

Let's get the bad news over first: in the last century, humans have removed forests from the earth amounting to an area the size of the United States. And we continue to remove about a Bosnia-size worth of forested land every year. This could be disastrous for biodiversity and the climate. In many places, it already has.

Now the good: forest loss and recovery usually follows a U-shaped curve. Poorer nations with growing populations develop their economy via deforestation and the creation of more agricultural land. But, as they get richer, population growth slows, crop yield improves, and local populations burn less wood for energy. Forests recover - so long as demand isn't driven by foreign exports. So, to take Scotland for example, a millennium ago 20 percent of its land was covered in forest. By the late 1800s post-industrial revolution, that number went down to 5 percent. Today, it's back up to around 18 percent. France and England have similar curves.

China's forestry story is similar. 

"Thousands of years ago in ancient China, the forest coverage was around 60 percent, but forests were severely damaged due to population increase, wars, natural disasters and construction," Professor Zhen Yu from Nanjing University of Information Science & Technology said.

After "New China" was founded in 1949, China aimed to economically recover from decades of war and exploitation by Western empires. Vast swaths of its forests were felled again. But after that, things slowly began to change.

Part 2 - Growth

In 1956, the year that China established its first nature reserve, Mao Zedong announced a "12 Year Greening Campaign" in an attempt to reverse the ecological damage. Twenty years later, net forest loss had been stopped, but the net gain was less than one percentage point.

The following period witnessed radical economic and social change across China, which was accompanied by land reforms and a series of programs designed to incentivize tree planting.

Then the large scale forestation activity were implemented in late 1970s.

From 1978 to today, China's forest area increased by 72 percent , essentially adding 970,000km² of forested land: an area over twice the size of Sweden.

So, especially since the devastating Yangtze River floods of 1998, China has continuously given forests better legal protection and particularly targeted areas affected by desertification, erosion, and, of course, flooding. Massive and unprecedented projects like 'The Great Green Wall', are attempting to shield almost half the nation from desertification via tree planting.

And the project continues. By 2035 China plans to add additional forest area equal to the size of Italy. And did you know? In principle, most Chinese citizens are required to plant 3-5 trees a year, there's even an entire government website set up to help them to do it. And it's under these types of citizen involvement programs that regular Chinese people have planted 78 billion trees in the last 40 years, including the 400 million planted via the Ant Forest in-app game - I mean, it's so easy I've even planted thirteen.

Part 3 - Sustainable Growth?

However, China's programs have faced challenges too, which have taught the government and the rest of the world important lessons about how to plant a forest.

Many efforts in tree planting created homogenous tracts of single-species young woods - monocultures - that grew fast but lacked biodiversity. Policies that financially rewarded the planting of specific species backfired when cutting lifespans were not as long as expected or people began removing natural forests to plant new ones for profit.

But I asked Dr. Yu what lessons China has learned:

"The first one is the importance of tree species selection. The second one is that enhancing the forest quality is as important as increasing forest coverage. The third one is we need to keep in mind that trees are not always the best choice for every location. The most important thing I want to stress is that the forestation should be adapted to the local conditions, including the climate, soil biodiversity and social factors," Yu said.

The real litmus test for success will be the future, and China is well on track to meet its 26 percent forest coverage goal by 2026. It also leads the world in annual forest coverage increase. This is good news for the climate.

"We know that we have to focus on two things. One is to reduce the carbon emission. And the other thing is to enhance the carbon uptake by land ecosystems. The net carbon absorbed by China's land ecosystem is around like 200 to 300 million tonnes per year, with forests contributing to 65 to 82 percent of this absorption,"Yu said.

Of course, it is important to reiterate here that human-created forests are less effective at doing so than natural ones. So the best way to green the planet is to not cut down what we already have. But China's proven it is possible to reforest a nation and they are now spreading their experience along Belt and Road nations.

And, hopefully, one day in the future we won't have to reforest at all.

Next episode: Solar: China's global energy revolution