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
[Objective] The aim was to study seasonal dynamics of biomass under different land use patterns. [Methed] Aboveground biomass and underground biomass of plants under 3 different surface cover conditions of Stipa krylovii, Leymus chinensis and farmland were determined in growing season （ from May to October） of 2008. [ Result ] The aboveground biomass of Stipa krylovii, Leymus chinensis and farmland in August all reached the highest value, which of Stipa krylovii, Leymus chinensis and farmland was 287.91,117.05 and 193.59 g/m2, respectively. The total biomass of plant roots of the 3 plots in July all reached the highest value, which of Stipa krylovii, Leymus chinensis and farmland was 1 683.9, 1 601.9 and 513.9 g/m2, respectively. Leymus chinensis had the biggest biomass ratio of upper plant roots （0 - 15 cm） to lower plant roots （15 -30 cm）, Stipa krylovii took second place, and farmland had the smallest one. ~ Conclusion The research provides theoretical basis for the ecological environment protection of ecological fragile area.
Basing on the limiting factor method and Composite Index method,for the northern China crop-pasture band,the authors established the system of evaluation index,and abstracted the dominant factor,then through applying expert grade and weighing way the suitability of grids are evaluated,the results showed that：without the input of a large number of cash,most of the area was not suitable for farming,and more appropriate area for farming was only 8.45% of total area,mainly located in the southeast and southwest of the study area,followed by the study area in the northeast,areas that was not suitable for farming mainly in the middle of the east,large areas of central and western regions.
