By Peng Dailiang, Zhang Helin, Zhang Bing

China is contributing to a greener Earth

T his report references data compiled by NASA's Aqua and Terra Earth observation satellites.

From 2000 to 2017, global areas covered by greenery increased by 5 percent, of which 25 percent lie in China.In fact, China accounts for only 6.6 percent of global vegetation coverage. So, how did these changes happen?

To find out, we invited experts from the Institute of Remote Sensing and Digital Earth under the Chinese Academy of Sciences who have been engaged in monitoring vegetation change to explain the process by interpreting statistical data and satellite remote sensory images.

Earlier this year, a multinational cooperative research paper led by Boston University and mainly funded by NASA was published in Nature Sustainability. The paper was entitled “China and India Lead in Greening of the World Through Land-Use Management,” and found that during the period from 2000 to 2017, China and India dominated global land greening (increases in leaf-covered areas). More importantly, in the process of making China greener,forests contributed 42 percent,greater than the 32 percent contribution of agricultural land and much more than India's forest contribution of 4.4 percent.

What Has China Done to Protect the Earth?

China's afforestation and forest protection are crucial chunks of the results.

Since the 1970s, China has successively launched many large ecological projects including six projects directly related to land greening: the“Three-North” Shelter Forest Program, the Natural Forest Resource Protection Project, the Project of Returning Farmland to Forest (Grass), the Shelterbelt Forestry Project of the Yangtze/Pearl River Basin, the Beijing-Tianjin Sandstorm Source Control Project and the Project of Returning Grazing Lands to Grasslands. These projects cover most regions of China.

Since 1979, the “Three-North” Shelter Forest Program involving 13 provinces,autonomous regions and municipalities directly under the central government has achieved a total construction area of 4.069 million square kilometers, accounting for 42.4 percent of China's total land area, with total investment adding up to more than 50 billion yuan so far.

Launched in 1998, the Natural Forest Resource Protection Project involving 724 counties, 160 key enterprises and 14 nature reserves in 17 provinces and autonomous regions reached cumulative investment of 48.83 billion yuan by 2004.

Launched in 1999, the Project of Returning Farmland to Forest (Grass) involves 1,897 counties in 25 provinces and autonomous regions.It is one of the largest-ever ecological projects to be carried out worldwide. The central government alone has invested more than 430 billion yuan in the project.

Two workers plant pine seeds on the southern edge of Mu Us Desert in Yulin,Shaanxi Province, in June 2011.

Phase I of the Shelterbelt Forestry Project of the Yangtze/Pearl River Basin was carried out between 1989 and 2010.According to forest inventory data and the forestry statistical yearbook, a total of 63,000 square kilometers of forest were planted and 55,000 square kilometers were afforested.Phase II covers a wider range,of which the Shelterbelt Forestry Project of the Yangtze River Basin Phase II includes 1,033 counties (cities and urban districts) in 17 provinces(municipalities directly under the central government) with a planned afforestation goal of 69,000 square kilometers.

Launched in 2002, the Beijing-Tianjin Sandstorm Source Control Project involves 75 counties across five provinces (autonomous regions and municipalities directly under the central government) including Beijing, Tianjin, Hebei,Shanxi and Inner Mongolia,with a total area of 458,000 square kilometers. The initial estimated investment for Phase I was 55.8 billion yuan.

Since 2003, the Project of Returning Grazing Lands to Grasslands has covered 640,000 square kilometers in seven northern provinces and autonomous regions.The central government has invested 29.57 billion yuan in the project.

Data Illustrates Drivers of the Green Miracle

The most effective way to understand the results of these afforestation projects in China is to observe changes in collected data. In the field of ecological environment change monitoring, the most widely used technology is that of acquiring images of the Earth for continuous monitoring through remote satellite sensing.

Here are a few sets of data which illustrate the drivers of this green miracle.

Fig. 1 (Yulin)

Fig. 2 (Saihanba)

Fig. 3 (Tianshui)

Fig. 4 (Baoji)

In the field of remote sensing applications, the“vegetation index” is widely used for evaluating vegetation coverage and vegetation growth and the “normalized difference vegetation index” (NDVI) is most widely used. In general,the higher the NDVI, the higher the vegetation coverage.

The NDVI (at the national level) in China, India and most European countries showed significant increases in 2015 compared with 1982, indicating that land in these countries turned significantly greener.However, the NDVI in the countries in North America,Australia, Africa and South America showed a decreasing trend in 2015 compared with 1982.

Another measurement indicator is net primary productivity (NPP).

NPP is the amount of photosynthetic products or organic carbon formed by plants after converting carbon dioxide in the atmosphere through photosynthesis and is the material basis for the survival and reproduction of other organisms in the ecosystem.

We quantified moderateresolution imaging spectroradiometer (MODIS)NPP from 2000 to 2014 at the country level, and the results show that the combined NPP for 53 countries represents over 90 percent of global NPP. The top three and top 12 countries accounted for 30 percent and 60 percent of total global NPP,respectively. China accounts for about 5 percent of the world's total NPP, ranking 4th globally. However, it must be noted that western China is mostly covered by desert or sparse vegetation, and the average NPP per unit area in China is about 300gC/m2/y —not high in the global ranking,at a similar level to Canada,Australia, India and other countries.

According to the trend of change from 2000 to 2014, NPP in large areas of China is rising,especially in western regions.Among several countries with high NPP, China's NPP has increased by about 11Tg C per year, far exceeding that of Brazil (～5Tg C/y)—ranking 1st in terms of total NPP—and the United States (～2Tg C/y)—ranking 3rd.

Participants experience new technologies for desertification control at the 6th Kubuqi International Desert Forum held in Ordos, Inner Mongolia, on July 28, 2017.

In terms of the inter-annual variation rate of NPP in China from 2000 to 2014, most areas of the “Three-North” Shelter Forest Program show an increasing trend, especially in Shaanxi Province.

In addition to the statistical changes, the image is convincing.

The first area reviewed is the city of Yulin in Shaanxi Province.

According to classification from the American Landsat series satellite images of 1987 and 2014, as shown in Fig. 1,forested land area in Yulin in 2014 was about four times higher than in 1987, and bare land area in 2014 was only one quarter of that of 1987.In addition, grassland area increased by 3,000 square kilometers.

Another illustration shows the city of Baoji in Shaanxi Province.

Although there was some vegetation in the vicinity of Baoji in 1984, as shown in Fig. 4, the vegetation coverage rate was only about 40 percent,while 32 years later in 2016,the vegetation coverage rate exceeded 90 percent. According to the China Forestry Statistical Yearbook, from 2002 to 2016, Baoji introduced a total afforestation area of 4,064.9 square kilometers including an artificial afforestation area of 2,117.06 square kilometers, an aerial afforestation area of 779.51 square kilometers and newly closed hillsides for afforestation of 1,168.33 square kilometers.

The next example is the city of Tianshui, Gansu Province.

Satellite images show that during the 1980s, in Fig. 3, most of the land in the area was bare.According to the China Forestry Statistical Yearbook, during the period from 2002 to 2016 alone, Tianshui benefited from afforestation of 3,427.56 square kilometers, including artificial afforestation of 2,877.52 square kilometers, afforestation by aerial seeding of 29.45 square kilometers and newly closed hillsides for afforestation covering 520.59 square kilometers. Today, Tianshui is a lush city, enjoying fame as “a rich area south of the Yangtze River” in the northwest.

Perhaps most noteworthy is the green miracle of Saihanba,Hebei Province.

Two satellite images in Fig. 2, show that the forest coverage rate of Saihanba increased significantly between 1984 and 2016.

Saihanba was basically desert before the founding of the People's Republic of China.After more than 50 years of unremitting efforts across three generations, the forest coverage rate of Saihanba increased from 11.4 percent to 80 percent. Now, Saihanba is a contiguous artificial forest. In December 2017, the United Nations Environment Programme announced that the builders of the Saihanba Forest Farm in China were to be awarded the “Champions of the Earth” prize in 2017 — the United Nations' highest honor for environmental protection.

China is home to the largest artificial afforestation area in the world, and its forest coverage rate has reached 22 percent. China has been moving forward with earnest on tackling climate change and saving the earth. Green hills and clear waters are gold and silver mountains to the Chinese.In the future, an even greater number of places in China will host green miracles as the country continues transforming deserts into forests.