Vegetation Carrying Capacity Of Soil Water In A Semi-arid Region Of Loess Hilly In The Loess Plateau

Vegetation cover is low, soil and water loss is very serious and the ecological environment becomesworse and worse. To change this situation, large-scale afforestation has been carried out and greatprogress has been made since 1950 in the Loess Plateau. Now soil deterioration has appeared in the formof excessive soil drying under perennial grasses and forests, which are widespread in the Loess Plateau.How to use water and soil resources to ensure health of the perennial grasses and forests is one of theimportant problems in vegetation rehabilitation of the Loess Plateau. The canopy interception ofprecipitation, surface runoff, soil water dynamics and forest growth of the typical community,Caragana forest) was measured with the fixed position in Guyuan Experimental Station (latitude35°59′-36°03′N, longitude 106°26′-106°30′E) in 2002 and 2003 in Guyuan county, Ningxia HuiAutonomic Region, in the semi-arid regions of the Loess Plateau of China. The interaction of forestgrowth and soil water dynamics of artificial Caragana and Vegetation Carrying Capacity of Soil Waterwere studied, The main results are as follows:(1)The canopy interception of Caragana shrub changed between 0.25mm(on 31 May in 2003) and 18.52mm(on from 25 to 26 Aug. in 2003),with an mean value of 2.25 mm (from 20 Jun. to 30 Oct. in 2002)-2.41 mm(from 13 April to 30 Oct. in 2003),with an interception rate of 2.2% - 83.82%, being a mean of 20.9%. The canopy interception become bigger and interception rate smaller with rainfall. There is a small correlation coefficient between canopy interception and precipitation or interception rate. (2),The ratio of surface runoff to precipitation changes from 1.1% to 6.8 % because of closedcanopy. The relationship between surface runoff(Run) and the rainfall outside forest(P2)is Run=0.0101 P2 +0.1765.The largest depth of wetting is 170cm in 2002 of slight dry year and 210cm in 2003 of plenty rainfall. The relationship between soil water supply(SWS)and precipitation(P2)outside forest can be written as SWS =0.7947* P2+0.1485.(3),The dynamics of Caragana's mean height(H)and diameter at the base (D)change with time(t)fits the Logistic Equation, shown as follow: 摘要 viiH = 109 . 79 D = 8 . 83 1 + e ( ? 0 .0234 t ? 1 .7466 ) 1 + e ( ? 0 . 0331 t ? 2 . 2073 )The relationship between height or diameter and biomass or leaf can be expressed well withtow-variable allometry equation .The dynamics of root biomass of 16- year-old Caragana(Wr)with depth of soil(Z)can be written as Wr = 2.3409e?1 .122Z,the dynamics of the root diameter of 2-year-old caragana(Dr)with soil depth (Z)as follows: Dr = 61.464Z ?1.1022. (4),The inter-relationship between Caragana forest growth and soil water can be classed into fourstages: first stage is within the starting to bud and fully developing of leaves, from the second ten-days of April to the last ten-days of Jun. The water forest consume is small and plants is not sensitive to soil water in this stage. The second stage, from the first ten-days of July to the end of Aug. is the sensitive stage in which soil water seriously influenced the forest growth. The third stage is from the start of dropping leaves to the fully dropping of leaves, from Sep. to Oct. The last stage is insensitive stage from dropping leaves to starting to have leaves (next year). (5) The change of soil water supply and soil water consumption mainly happened within the largest depth of wetting. The negative balance of soil water happened from April to Aug. in 2002 while the forest growth goes into the second stage of growth-soil water relationship. Caragana grows poorly and drops most of leaves. The measure to regulation the relationship between growth and soil water need to be done by controlling the density of forest. The soil water storage is increased by 121mm in 2003 of plenty rainfall. (6) Different content of drying happened in different density of the shrub land of one-year-oldCaragana in slight dry y...