Poorly managed croplands induce soil erosion, diminish biodiversity and jeopardize the availability of natural resources. The resulting drought during dry seasons and floods during raining seasons are costly downsides of excessive farming, which itself becomes furthermore unprofitable by its own consequences.
Since 1999, the central Chinese government has imposed a program to reverse deforestation for farming purposes. This program, the Grain for Green Program (GGP) primarily focuses at steep-sloped, degraded and barren land. It has been implemented in 25 provinces located in central and west China ([1] and see grey areas in figure below, stars indicate communities involved in this study). As a result, by 2012, 9.06 million ha of cropland has now been turned into forest and 0.64 million ha into grassland. With a total surface of 960 million ha [2] this equals to ca. 1% of the complete land area in China.
Ironically, afforestation indeed is an effective way to reverse the detrimental effects of erosion by (deforested) cropland. This is mainly due to the accumulation of biomass in the soil, which leads to, amongst others, increased stability, a higher water-holding capacity and increased fertility. The climate may benefit from afforestation, too. In terms of carbon fixation, farmland is a poor replacement for forests and grassland. Non-fixed carbon may accumulate in the atmosphere as carbon dioxide (CO2), a potent greenhouse gas.
Now researchers for the first time analyzed the Soil Organic Carbon (SOC) within the GGP program, of areas that have been afforested or turned into grassland [1]. They found that the amount of soil organic carbon indeed has increased in afforested land. In case more time had passed since the start of afforestation, the amount of organic carbon in the soil increased, especially in the most superficial 20 cm layer: from 10 to 30 years, the SOC increased by 50% and 150%, respectively. Most effective was the introduction of woodland or bamboo; the introduction of grassland moderately increased the carbon organic soil content.
