Vegetation-Erosion Dynamics - River Dynamics and Integrated River Management - page 99

The c value is relatively large, b value is very large, and f value is small, which implies that soil
erosion may seriously impair the vegetation and deforestation may substantially increase soil erosion.
Figure 2.45(b) shows the vegetation erosion chart for the hot and dry valleys, in which there is a
relatively large Zone C, a large Zone A and very small Zone B. The points representing the current status
of vegetation and erosion are mostly in the Zone A. Although the current vegetation is very poor, if soil
erosion is controlled, a new vegetation may develop. The watershed may move into Zone C. The new
vegetation will have a relatively high capacity of self-restoration, and it will have a moderate resilience
and may sustain a certain intensity of ecological stresses.
The strategies for vegetation restoration for the hot and dry valleys should be as follows. ķ Making
use of limited sources for reforestation of small watersheds, as has been done for the Heshuihe and
Shengou watersheds. If limited resources of labor, funds, and materials are used for the whole area, the
vegetation may be improved more or less and erosion can be reduced to a certain extent after a period of
continued reforestation. Despite some reforestation effort the status point in the chart may still be in Zone
A. If the efforts for reforestation and erosion control are not continued, the vegetation may deteriorate
and the erosion rate may increase again. Only if necessary the resources are used for a small watershed will
the status point in the chart be moved into Zone C in a not long period of time. Thence, the vegetation will
perfect itself. In this way all small watersheds can be greened one by one. ĸ Controlling erosion before
planting trees. Erosion control is more important than planting trees for the hot and dry valleys at the
beginning stage of because the present status point is far for Zone C. By terracing the slopes and constructing
check dams in gullies, the erosion rate can be reduced below 5,000 t/km 2 yr. Then, reforestation will be
more effective. Ĺ Allowing limited husbandry and selected logging as fuel and fodder. For a watershed
whose status point in the chart is in the Zone C, limited husbandry and logging may be allowed.
Vegetation in Zone C is stable and limited logging cannot badly impair the vegetation.
On the Yunnan-Guizhou Plateau and in the Sichuan Basin it is warm and wet and the slope is gentle.
Therefore, the rate of soil erosion is low and vegetation develops well. The four parameters are determined
with data as follows:

2

a 0.01 0.024(1 / a); c 0.000001 0.000005(km / t);

(2.28)

22

b 0.01 0.03(1 / a); f 250 400(t / km a )

Figure 2.45(c) shows the vegetation-erosion chart for the Yunnan-Guizhou Plateau and the Sichuan Basin,
which has a rather large Zone C, a large Zone A, and a moderate Zone D. The points of current status for
Yunnan (Kunming), Guizhou (Guiyang), and Sichuan Provinces are in Zone C. The point for Chongqing
is in Zone D but very close to Zone C. The vegetation in the area may sustain moderate logging. The main
management strategy is to avoid any large scale of deforestation.

2.3.4.3 Mountainous Area with Slope Debris in North China
This area includes the mountainous and hilly areas in Hebei Province, Beijing, and Tianjin. The annual
average temperature is about 10 ć and the annual precipitation is about 600 mm. The soil layer is thin.
Human activities act as a very strong stress on the vegetation, both negative (deforestation) and positive
(reforestation). The four parameters are determined as follows:

2

a 0.006 0.009(1 / a); c 0.000004 0.0000045(km / t);

(2.29)

b 0.003 0.005(1 / a); f 180 210(t / km a )

22

Figure 2.46 shows the vegetation-erosion chart for the area, which has a very large Zone D, a small Zone
A, and a small Zone C. The vegetation in the area is not stable and may be changed by human activities
to a large extent.