Vegetation-Erosion Dynamics - River Dynamics and Integrated River Management - page 102

The differential equations of vegetation-erosion dynamics are applied to the Huizhou area, and the
parameters of a, c, b, and f are determined with the data from the experiment plots as follows:
a = 0.06(1/yr), c = 0.000005(km 2 /t), b = 0.01(1/yr), f = 500 (t/(km 2 · yr 2 )) (2.30)
The vegetation and erosion chart for this area is developed as shown in Fig. 2.48. The straight line
E '= 0 is steep and Zone C is very large. The point of the vegetation-erosion status in 1978 is in Zone A.
Planting trees and control of erosion moved the point into Zone C. Thence, the vegetation develops
automatically and the vegetation community develops from simple wood to a complex community consisting
of different species, including grasses, shrubs, liana, woods and bamboo.
Fig. 2.48 Vegetation-erosion chart for Huizhou area in Guangdong Province, southern China
From Eq. (2.24) it can be calculated that the rate of vegetation development may be accelerated from
d V/ d t = 0.002 (yr -1 ) to d V/ d t = 0.014 (yr -1 ) if the reforestation area is increased from 20% to 40% for
erosion rate equal to 2,000 t/km 2 yr. In other words, the rate of vegetation development may be increased
by 7 times if the area of tree-planting is increased by 2 times. In general, the vegetation succession from
pioneer species well-adapted to bare soil and plentiful light to longer-lived species that can regenerate
under more shaded and protected conditions takes about a century. Planting dominant tree species in the
area accelerated the plant succession. It takes only 24 years to develop a vegetation consisting of a complex
plant community including long-lived wood species and grasses and shrubs accustomed to shaded and
protected conditions. The time of vegetation development is shortened by 75%.
Figure 2.49 (b) shows the development process of the vegetation cover of woods, grasses, shrubs, liana,
and bamboo in 1981-2004. Only tree planting was performed in the beginning period in 1981-1984. In
the following years, the vegetation cover and the species composition of the vegetation developed
automatically. All species of shrubs, liana, bamboo and some wood are local species and develop naturally.
Figure 2.49(a) shows the comparison of the closed plot, in which only herbaceous and some shrubs
species, which are well-adapted to bare soil and plentiful light, have been developed.
Figure 2.50 shows the pictures of the two cases, in the experimental plot the trees of Acacia Mangium
have well grown and the natural species have also developed within the forest. In the comparison plot
only some grasses and shrubs can grow under the conditions of bare soil and plentiful light after 24 years
of natural development.