运用植被—侵蚀动力学耦合方程组，研究了流域植被与侵蚀在人类活动特别是植树造林和工程治理影响下的演变。动力学方程组中的4个参数由实测植被侵蚀资料算出，利用这些参数发展出植被—侵蚀状态图作为分析工具，分析在停止人类干预后植被和土壤侵蚀的发展趋势。流域的植被—侵蚀状态有4种，即向着侵蚀模数增大和植被覆盖度降低方向发展的A区，向着侵蚀模数降低和植被完善方向发展的C区，植被和侵蚀模数都增长的B区，植被和侵蚀模数都减少的D区。将耦合方程组和植被—侵蚀状态图应用于黄土高原王家沟、安家沟流域，云南小江流域和北京西山地区，结果表明动力学方程组准确地模拟了植被和滑动侵蚀模数的演变过程。对植被侵蚀状态图的分析表明，在干旱寒冷的黄土高原增加植被对于减少侵蚀的作用显著，治理应该首先增加植被使其进入D区，再结合控制侵蚀进入C区，治理后仍应加强管理和防止人为破坏；在雨量较丰、气温较高的小江流域，减少侵蚀对改善植被的作用大，治理措施首选控制侵蚀；北京西山地区介于两者之间。

    This paper studies the development of vegetation and erosion of typical watersheds in China employing the vegetation-erosion dynamics:
dV/dt-αV+cE=-Kiδ(t₀)+V_R
dE/dt-dE+fV=E_R
The four parameters a, c, d, f in the couple differential equations are determined by using the data of vegetation-erosion process within the watersheds. The parameters are functions of climatic, topographical and soil conditions and independent of the vegetation and erosion, ecological stresses and human activities. With these parameters we developed the vegetationerosion chart to predict the developing trend of vegetation and erosion. The vegetation of a watershed may exists in four states: vegetation developing and erosion reducing (C zone in the chart), vegetation deteriorating and erosion increasing (A zone), both vegetation and erosion increasing (B zone) and both vegetation and erosion decreasing (D zone).
    The vegetation-erosion chart for a watershed is exclusively given by the parameters a, c, d, fThe parameters are constant and universal for the areas of the same climate, topography, soil and vegetation compositions. If the values of the parameters a and f are large, the system in most cases is in the C-Zone developing toward perfect vegetation. If the values of c and d are large, the system in most cases is in the A-Zone developing toward poor vegetation and high rate of erosion.
    We worked out the vegetation-erosion charts for the Wangjiagou, Anjiagou, Xiaojiang watersheds and Xishan areas with the determined values of a, c, d, f from data. The erosion rate in Xiaojiang watershed is extremely high and the vegetation cover is relatively poor although the area is wetter and warmer than north China. It is still in Zone A and exhibits the development trend toward poor vegetation, which can offset, to a certain extent, the human's effort for improvement of the vegetation. The dashed curve in the figure shows the suggested route for moving the system into the C-zone. First, erosion control must be performed to reduce the erosion rate by 60%-80%, thus the system is moved into Zone B. Then the development trend V'>0 may support human's reforestation project moving the system into Zone C. Erosion control is very important in the area for re-vegetating the hills. Mere planting trees and shrubs do not work well for greening the high erosion land. 
    For the Wangjiagou and Anjiagou Watersheds on the loess plateau, however, there is no Zone B but Zone D, in which V'<0,E'<0. The ecological system in the D-zone is also unstable, because both vegetation and erosion are reducing. If the vegetation reduces faster than erosion the system may enter into the A-zone and if erosion reduces faster than vegetation the system may enter into the C-zone. The C-zone in the charts for the two watersheds is very small and the D-zone is large. The tangent of the line E'=0 is high, implying high effectiveness of which vegetation may control erosion. On the other hand, the line V'=0 is almost horizontal, which suggests that erosion control helps little for vegetation development. Thus, in the loess plateau the most effective way to control erosion is to increase the vegetation cover, so to move the system from the A-zone into the D-zone. Thence the system will automatically move in the direction of erosion reduction but also vegetation reduction. Human can further increase the vegetation cover by planting trees. The dashed curve shows the route of the watershed management and vegetation development. Unfortunately, the C-zone is too small for stable vegetation development. Human effort is always needed to maintain a stable or increasing vegetation cover. For the two small watersheds, although reforestation and erosion control have been continued for more than 30 years, the rate of erosion has been reduced by 90% and the vegetation cover has increased by 8-12 times, the state of the systems is still in the D-Zone. It is quite possible for the system to return to Zone A if the vegetation is not carefully protected. To move the system into the C-Zone, both reforestation and erosion control must be continued.
    In summary, the vegetation-erosion charts demonstrate that on the Yunnan Plateau, the precipitation and temperature are high; vegetation can develop well if erosion is controlled and the vegetation is stable after improvement. On the dry and cold Loess Plateau, vegetation can effectively control erosion but erosion reduction exhibits low effectiveness on vegetation development. Vegetation in the area is not stable and management is always needed to maintain the vegetation. The Xishan area in the outskirts of Beijing is not so wet and dry, not so cold and warm, the vegetation-erosion chart illustrates that the development trend of vegetation is between the two extreme cases. The C-zone is not so big as the Xiaojiang watershed but much larger than the loess plateau, which implies a relatively stable vegetation may be maintained. Reforestation is the most effective measure to control erosion and improve vegetation in the area because the slope of the line E'=0 is very steep in the chart.