Successful Biological Methods for Combating Desertification at Degraded Areas of China - Combating Desertification in Asia, Africa and the Middle East - page 58

deep. Such plantation mixture with root systems at different depths allows moisture
and organic matter in the rooted layers to be fully used. Maximum above -ground
biomass can be achieved.
Optimum plantation density is also an important factor guaranteeing the survival
of plants used for revegetation of shifting sands. Research at Shapotou (see Chap. 2 )
compared survival of plants at various plant spacings. The space between rows
and that of individual plants was 0.3 m 0.5 m, 0.5 m 0.5 m, 0.5 m 1.0 m,

1.0 m 1.0 m; the space between rows and that between individual plants of semi-

shrubs were 0.3 m

1.0 m; these densities were so
high that the plants withered or grew unhealthily for lack of moisture. From 1964
onwards, a strip form of revegetation was adopted and certain spaces between strips
have been arranged to widen the row spacing to allow access to more moisture and
organic matter. The strip arrangement was both practical and beneficial.
Because of differences in formation and natural conditions in various sandy areas
in China, the characteristics of measures for controlling shifting sand are different.
The comprehensive models for the prevention and control of sand encroachment in
oases, the desertified land of dry steppe and desertified steppe and along railways
and highways have been successfully developed in China. The main models Ming
(2006) are as follows.

0.5 m, 0.5 m 0.5 m, 0.5 m

5 Biological Models for Protecting Different Land Use

The integrated shelter system that consist of three parts, which is fixing sand belt for
preventing wind erosion on the periphery of oasis, stocking sand belt for breaking
wind and stopping the shifting sand along the edge of oasis, and forest network
within oases for protecting the farmland. This model is the cardinal pattern of shelter
system for sand harm in China. Usually, the shrub and grass belt is 300-500 m
wide. The purpose of closing the area is to protect the land surface from wind
erosion, and to stop shifting sand. The shrub and grass belt is a first defense for
protecting the oasis. Establishing the shrub and grass belt is a pioneering measure
for the establishment of the whole system, because shrub and grass belt can be
established easily and it can take into effect rapidly. In the early stage after the
completion of an integrated system, the shrub-grass belt can stop drifting sand and
resist wind erosion, protecting the young trees within the system and the farm land
protection tree belt. Generally, the sand-stocking and sand-fixing forest belts are the
second defense, which it is from 200-300 to 1,000 m wide in the forward region of
dunes where a great number of shifting sands can encroach on oases; it is 50-100 m
in the sections where shifting sands are close to oases and the trees can be planted
at the base of sand dunes; it is 30-50 m wide in the sections where farmland adjoin
semi-fixed dunes; and it is 10-20 m wide in the sections where oases border on Gobi
where sand source is not rich.