| In arid and semiarid region,for less rainfall, water is the restrictive reason for vegetation recovery and reconstruction in this area. In order to settle the inconsistent problem between vegetation recovery and water resource in reducing cultivated land to plant forest and grass in this region,with the forest of reducing cultivated land to plant forest and grass demonstration in Ge zhen er valley in Zhongyang county,Shanxi province,the research was carry out in semiarid loess hilly and gully region in growth season in 2003～2004. This search include hydrological physics character of soil, siol water space-time variety, the variety of trees transpiration and water physiology of trees.With some means and advanced apparatus,the research was done, and some advice about site type distribution of trees was given.The result has scientific instructional significance to the right vegetation selection and right site type distribution for vegetation recovery in this area.This is the main result of the research: (1)The hydrological physics character of soil in different site type ⊙The soil porosity and water retention character are affected by different slope direction,slope place,site preparation mode,type of forest and the depth of siol. Comparing the soil porosity and water retention character in different slope direction, it shows soil bulk density sunny slope>semisunny slope>semishady slope>shady slope,total porosity shady slope>semishady slope>sunny slope>semisunny slope.The capillary porosity increase with the decline of slope,and in top of the slope,middle slope, lower slope,it is 46.6%,47.5%,49.7%,that is,the ability of soil water retention increase as the decline of slope. The capillary porosity in different forestland , Juglans sp land's is50%, Robinia pseudoacacia L. land's is 54%, the wasteland's is 46%, the grassland's is 48%.The Juglans sp land's non-capillary porosity is 13%,the Robinia pseudoacacia L. land's is 9%, the wasteland's is 7%, the grassland's is 6%. The Juglans sp land's soil bulk density is 1.15g/cm3,the Robinia pseudoacacia L. land's is 1.13g/cm3, which is lesser than the soil bulk density of grassland (1.27g/cm3) and wasteland (1.21g/cm3).It shows the soil porosity and the soil ability of water retention in forestland are better than that in grassland and wasteland.With the increase of soil depth,the soil bulk density becomes bigger,and the soil porosity and the soil ability of water retention descend. ⊙the soil permeability in forestland is affected by different slope direction,slope place,site preparation mode,type of forest and the depth of siol.The stable infiltration rate in sunny slope is bigger than that in shady slope. The stable infiltration rate in top of slope is 1.16mm/min,that in low slope is 0.79 mm/min,and it shows the stable infiltration rate in top of slope is bigger than that in low slope.Different forestland has different effect to soil water stable infiltration rate.The stable infiltration rate in Caragana korshinskii Kom.land is the same as that in Robinia pseudoacacia L.land nearby the Caragana korshinskii Kom.land in the same slope direction,which is about 0.56 mm/min. The stable infiltration rate in different site preparation mode is variant,and the stable infiltration rate in socket site preparation(1.37mm/min)>fish-scale pits(0.86mm/min)>horizontal ditch(0.85mm/min)>level terrace(0.84mm/min). (2)The space-time dynamic state of soil water in forestland The soil water is affected by many reasons.The soil water in shady slope is higher than that in sunny slope,and in Robinia pseudoacacia L.land which is the same old and the same density,soil water in shady slope is higher than that in sunny slope by 7.1%.In different forestland the soil water of Robiniapseudoacacia L.land in sunny slope is higher than that of Juglans sp land in sunny slope by 11.3%.In shady slope, soil water of Caragana korshinskii Kom.land is higher than that of grassland by 28%,and higher than that of Hippophae rhamnoides L.×Rosa xanthina land by 2.4%,the soil water of Hippophae rhamnoides L.×Rosa xanthina land is higher than that of grassland by 25%.That is, comparing soil water content,forestland > grassland >wasteland. The variety of soil water is different in different soil depth.The soil water of the surface is affected intensively by weather.With the increase of soil depth,the soil water change slowly.In the depth about 60 ～100cm of grassland,the soil water is always high and changing slowly from June to October.In vertical direction of soil,the soil water changed sharply than that in grassland. The annual change shows that the soil water is the highest in July and August,and then in September and October,and it is the lowest in April and May. (3)Water consumption and precipitation utilization rate of forest In July and August,the trees transpiration is the highest and then is June, September and October,it is the lowest in April,May and November.Because of less precipitation in April and May, precipitation utilization rate of some forest,such as Robinia pseudoacacia L., Caragana korshinskii Kom., Periploca sepium,is higher than 100%,and that happen serious soil water deficiency.In July and August,the precipitation is enough,but the precipitation utilization rate of some forest is decline(RWC under 40%).So,taking some means to store precipitation on the site can change the space-time distribution of precipitation,and the precipitation in rainy season can be used in dry season,this can improve precipitation utilization rate in forestland,and can solve the problem that drought bring to forestation.Because of the little body and density,some forestland,such as Platycladus orientalis(L.) Franco., Prunus armeniaca var. ansu Maxim., Acer mono Maxim., Pinus tabulaeformiscarr.,their precipitation utilization rate are no more than 10%.So, increasing the forest's crown density properly can improve the precipitation utilization rate of this forestland. (4) The water physiology and ecology character of forest With CIRAS-2 portable photosynthesis system ,diurnal variations and response to light of gas exchange parameters of some trees were studied under different Soil water condition. from water use efficiency of trees,it show that the low limit of fitting soil water extent of some trees,such as Platycladus orientalis(L.) Franco, Caragana korshinskii Kom., Robinia pseudoacacia L., Prunus armeniaca(Carr.)Franch., Hippophae rhamnoides L., Periploca sepium's is less 39.2%(RWC). the low limit of fitting soil water extent of Prunus armeniaca var. ansu Maxim.,Acer mono Maxim.,Pinus tabulaeformis carr. and Populus hopeiensis Huet Chow. is between 39.2% and 51%,but Syringe sp. and Rosa xanthina are high of 51%. Based on the ability to adapt light,the trees which have the strongest endurance to strong light,and make the best use of light are Platycladus orientalis(L.) Franco. and Caragana korshinskii Kom.,(in fitting soil water extent this light saturation point of the two trees is 1400μmol·m-2·s-1),then is Prunus armeniaca(Carr.)Franch., Robinia pseudoacacia L., Rosa xanthina, Acer mono Maxim., (in fitting soil water extent the light saturation point of this four trees is 1100～1200μmol·m-2·s-1), Syringe sp. do not endure high light. (5)The site distribution for different trees Based on the soil water condition in different site and the trees'demand to light and water,according to the principle of tree suitability to sites,the advice about the site distribution for different trees was gave:Some economic trees,such as Juglans sp, Prunus armeniaca(Carr.)Franch.,Prunus armeniaca var. ansu Maxim.,can be planted in valley or terrace builded by machine. Acer mono Maxim. Can be put in the middle or lower sites of sunny slope. Platycladus orientalis(L.) Franco. and Caragana korshinskii Kom. can be growed in middle or top of sunny slope and semisunny slope which has strong... |
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