All in all just another tree in the wall?

Establishing tree cover in drought stricken areas is a challenge facing many countries facing problems with desertification. A new planting technique to improve drought resistance in which planting holes are lined with biodegradable plastic to reduce drainage and evaporation was tested in an arid, erosion-prone, hilly area of the Chinese Loess Plateau between 1997 and 2006, during a period of lower-than-normal precipitation. 15 types of tree were grown with and without the bag. The new tree-planting technique promoted root growth in the topsoil by keeping the soil moisture than the surrounding soil evident during the first 4 months after planting.

Tree survival rates, branch growth increment per year, tenth-year canopy area, and tenth-year canopy density in trees planted using the new method increased by an average of 41.4%, 29.0%, 16.9%, and 65.3%, respectively, compared with the values for the conventional planting technique. This suggests that the new planting technique is more suitable than the conventional method for arid areas such as the Loess plateau and may prove useful elsewhere in the globe. The results of this study offer much hope for the survival of China’s ‘Green Wall’ and long term prospects concerning the countries prevention of desertification.

Cao, S., Chen, L., Liu, Z. and Wang, G. (2007). A new tree-planting technique to improve tree survival and growth on steep and arid land in the Loess Plateau of China. Journal of Arid Environments, In Press.

Characteristics of Chinese Desertification

Source: Fullen & Mitchell 1994


The figure above shows the distribution of sandy deserts (1-8) and lands (9-12) with respect to climatic zones in China. Sandy deserts and lands are differentiated as the latter is formed out of human activity. Historically many parts of China have been susceptible to desertification, all of them located in the north-west, north and north-east dryland area. The Mu Us sandy land (see figure) has existed throughout the Quaternary but its extent has fluctuated through time with moisture availability. More recently it has been subject to encroachment by a sandy desert since the Tang Dynasty (AD 618-906). There is evidence for widespread desertification in the semi-arid steppe dating back to the Han Dynasty (202 BC-AD 220). Historically the control of the aridity has been linked to the effect of the ITCZ on the East-Asia monsoon, and its failure has been linked to the collapse of the Tang dynasty.

Source: Yong Zha and Jay Gao (2000)

China's Desertification Policy

In 2001 China adopted new legislation intended to control and ultimately reverse the worsening trend of desertification in the country, which has an estimated annual direct economic cost of $6.5 billion.

The new law:

-States that land occupants have a duty not only to prevent desertification but also to restore areas that have already become desert;

-Promises unspecified preferential policies, tax breaks, subsidies and technical support to offset the cost of this unfunded mandate;

-Creates a new class of protected areas off-limits to development and calls for farmers and herders to be removed from those areas; and

-Authorizes local governments to grant land-use rights of up to 70 years to desertified areas if the landholder promises to undertake restoration efforts.

Source:
http://www.usembassy-china.org.cn