The dynamics of biomass and soil moisture in semiarid land is driven by both the current rainfall and the ecosystem memory.Based on a meta-analysis of existing experiments,an ecosystem model was used to calculate the effect of the rainfall interannual variability on the pattern of biomass and soil moisture in a shrub community.It was found that rainfall interannual variability enabled shrubs to be more competitive than grasses,and to maintain the dominant role over a longer time.The rainfall interannual variability resulted in complex soil moisture dynamics.The soil water recharge in wet years alternated with discharge in drought years.
LIU JunShanXU XiaZHANG Yong,TIAN YuQiang & GAO Qiong State Key Laboratory of Earth Surface Processes and Resource Ecology,College of Resources Science & Technology,Beijing Normal University,Beijing 100875,China
The impact of inputs on farm production growth was evaluated by analyzing the economic data of the upper and middle parts of the Yellow River basin, China for the period of 1980-1999. Descriptive statistics were employed to characterize the temporal trends and spatial patterns in farm production and five pertinent inputs of cultivated cropland, irrigation ratio, agricultural labor, machinery power and chemical fertilizer. Stochastic frontier production function was applied to quantify the dependence of the farm production on these inputs. The growth of farm production was decomposed to reflect the contributions by input growths and change in total factor productivity.. The change in total factor productivity was further decomposed into the changes in technology and in technical efficiency. The gross value of farm production in the region of study increased by 1.6 fold during 1980-1999. Among the five selected farm inputs, machinery power and chemical fertilizer increased by 1.8 and 2.8 fold, respectively. The increases in cultivated cropland, irrigated cropland, and agricultural labor were all less than 0.16 fold. The growth in the farm production was primarily contributed by the increase in the total factor productivity during 1980-1985, and by input growths after 1985. More than 80% of the contributions by input growths were attributed to the increased application of fertilizer and machinery. In the change of total factor productivity, the technology change dominated over the technical efficiency change in the study period except in the period of 1985-1990, implying that institution and investment played important roles in farm production growth. There was a decreasing trend in the technical efficiency in the region of study, indicating a potential to increase farm production by improving the technical efficiency in farm activities. Given the limited natural resources in the basin, the results of this study suggested that, for a sustainable growth of farm production in the area, efforts should be directed to te
LI Xiang-lianLUO Yu-zhouGAO QiongDONG Suo-chengYANG Xiu-sheng
