| In the forest ecosystem fixed study station of Sejila Mountains in Southeast Tibet,with the method of fixed position and typical sample land study,two-year observation and comparison analyses were made towards soil physicals and water balance of the inner and the outer (fell trace) of the Abies georgei var.smithii wildwood which is the dominant distribution type of the vegetation in this region. At the same time,the quality of different-state water was studied. The results show:the soil bulk density of the fir wildwood heightens with the increase of soil depth,specifically 0.74> 0.94 andl.34g/cm3,the saturated,canaliculus and field moisture contents decrease gradually in Layer A,B and C,accordingly the soil total foveola decreases gradually,and the moisture-hold capacity of the soil lessens gradually with the increase of the soil depth;there is small difference of the soil bulk density between Layer A and B in the outer space,which are respectively 0.92 and 0.99g/cm3,and the other laws are the same as the inner in the main;reverse success often occurs in the low position of the thoroughly-fell trace and plateau marsh is formed. Through this study and according to the law by which the soil moisture content changes with the time,the soil moisture is determined as consumptive,accumulative,fade-away and stabilization periods. For the soil infiltration,generally,the order of the original and stable infiltration speed from big to small is the inner,the outer space and the paludal trace,as well as Layer A B. In the view of the rainfall balance of the wildwood,the canopy interception is averagely 61.10% of the rainfall,the trunk runoff 0.80%,the inner 38.10%,the surface and the litter evapotranspiration 18.00%,the surface runoff doesn't appear in the forest,and the interflow is also very small,which is 0.30% of the total rainfall;the conflux is 21.10%. For the rainfall balance of the non-forest land,the surface runoff of the outer space is 3.10% of the rainfall,the evapotranspiration is relatively big,which is averagely 65.70% of it,and during this course,it adds up to 94.90% in May,August the least,48.90% of the rainfall,the conflux 25.00%,and the interflow only 6.20%;the runoff in the paludal trace is 1.50% of the rainfall,the interflow relatively small,which is only 0.50% of it,the conflux 27.40%,the evapotranspirated moisture 70.60%,and in this case,the evapotranspiration up to 96.20% in May.Through water quality comparison analysis of the outer rainfall,inner rainfall,trunk runoff,runthrough,river,stream and so on of the fir wildwood in Southeast Tibet,it shows:the muddy sand content is the least of the outer rainfall,which is 5.67mg/l;that of the outflow down the hill slope is the highest,which is 393.33mg/l;that of the trunk runoff and the inner rainfall is respectively 94% and 52% higher than that of the outer rainfall;that of the outer runoff is 31% higher than that of the inner;the soil under the fir wildwood is micro-acid and the water in the river course is micro-alkaline;after the rainfall passes through the marsh soil,the content of the other elements and muddy sand increases enormously except that the PH value doesn't change,and the content of SO42-,C and P decreases,in the course of this,HCO3-increases 20 times,Fe,which has increased in the smallest range,has increased 1.5 time;concerning the whole forest ecosystem,the input of HCOj",Cl,N(NO3',NH/),Na,Ca,Mg,Fe is less than the output,so a part of the nutrients flows out;SO42",C,P,K,Cu,Zn and so on are reserved by the soil and litter,that is,the output is less than the input,so the nutrients are accumulated;the outer content of the elements in the snowfall appears higher than that of the inner.
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