Abstract: This paper analyzed the annual dynamics of the net primary productivity (NPP) of three-Stipa-communities along Northeast China Transect,and based on an integral regression model,discussed the responses of the NPP to the seasonal distribution of precipitation,aimed to reveal the effects of precipitation availability on plant NPP.The results indicated that the main factor restricting the annual dynamics of three-Stipa-communities NPP was the annual fluctuation of the monthly precipitation from November to next August.The precipitation from November to next April had a positive effect on the NPP,while the effect of that from May to July was decreased in different degrees.The seasonal distribution pattern of precipitation was quite similar for test-Stipa-communities,but S.grandis community had a higher utilization efficiency of precipitation than S.krylovii community,andS.baicalensis community had a much higher utilization efficiency of precipitation. Therefore,the seasonal distribution pattern of precipitation and its different effects on Stipa-communities could be the main reasons inducing the zonal distribution of three test Stipa-communities.

Key words: Windbreak, Shrub, Numerical simulation, Relative velocity