| A variety of plantations(Robinia pseudoacacia, Ulmus pumila, Pinus tabulaeformis, Platycladus orientalis, Pinus tabulaeformis and Robinia pseudoacacia mixed forests) were investigated in Tuqiaogou basin, Fangshan County, Shanxi province. Through field survey, qualitative and quantitative analysis, the structure and growth character of forest stands with different species in different density were determined, and plant community feature, hydrological effects of litter, and soil physicochemical properties in the plantations were systematically studied, and plantation density effect was assessed through principal component analysis (PCA). These data were theoretically valuable for selection of artificial vegetation restoration modes and deteriorated forest innovation. The main results are shown as follow:(1) Plantation structure character. The average diameter at breast height (DBH) of broad-leaved forest is bigger than that of evergreen needle-leaf forest at the same stand density. Stand diameter was simulated using Weibull distribution function, and it is shown that Robinia pseudoacacia plantation with density of 925 plants/hm2, Ulmus pumila plantation with density of 925 plants/hm2, Pinus tabulaeformis and Robinia pseudoacacia mixed forests with density of 550 plants/hm2 and 1850 plants/hm2 do not match Weibull distribution. In those plots, the distributions of DBH is in confusion and deviated from normal distribution, while the height distribution shows a single or double peak pattern, or shows normal distribution, and the stand volume increased firstly and then decrease with increasing stand density.(2) Biodiversity. The plant species diversity and richness of herb layer is obviously higher than those of shrub layer. In herb layer, all indexes of richness, diversity and evenness of evergreen conifer and broad-leaved mixed forest are higher than those of pure forests, and Robinia pseudoacacia or Pinus tabuleaformis pure forest is better than Ulmus pumila and Platycladus orientalis pure forest. The species in herb layer are divided into 4 groups according their relations:Artemisia scoparia group, Stipa bungeana group, Leymus scalinu group, and Leymus scalinu group. Evergreen conifer and broad-leaved mixed forest have the most plants, while the habitat condition of Robinia pseudoacacia or Pinus tabuleaformis pure forest is worst. Under the same conditions, the biomass of shrub layer in Pinus tabuleaformis and Robinia pseudoacacia mixed forest is obviously more than other plantation with the same density.(3) The hydro-ecological effects of litter. The litter mass (LM) in different plantation type vary in 2.36～8.08 t/hm2. LM of evergreen conifer and broad-leaved mixed forest is higher than that of broad-leaved forest, and LM of evergreen conifer is the lowest. The maximum water holding capacity (MWHC) of litter layer in evergreen conifer and broad-leaved mixed forest is higher than that of pure forest, in which MWHC of Pinus tabuleaformis pure forest is higher that of Ulmus pumila pure forest and Platycladus orientalis forest is with the lowest one. The relation between water holding capacity of litter and immersion time can be simulated by the following equation:W=klnt+b, in which t was time. And the equation of V=ktn can show the relation between litter absorption rate and immersion time, in which t was immersion time. The modified interception of litter under different stands varys in 2.94～12.22 t/hm2, and the difference of effective interception depth is 0.29～1.22mm. The hydro-ecological effect of litter in evergreen conifer and broad-leaved mixed forest is better than that of evergreen conifer or broad leaved pure forest.(4) Soil physical properties. All the fractal dimensions of soil particle in Robinia pseudoacacia, Pinus tabuleaformis, and Platycladus orientalis pure forest and mixed forest of Robinia pseudoacacia and Pinus tabuleaformis are smaller than that in farmland, while high density Ulmus pumila pure forest is with bigger one. On the contrary, the soil bulk density (SBD) in all kinds of forest is lower than that in farmland, and the SBD increases with increasing the soil depth under all forests. Soil porosities and aeration degrees in Robinia pseudoacacia or Pinus tabuleaformis pure forest are higher that in farmland, while porosities are lower in high density Ulmus pumila or Platycladus orientalis pure forest and low density mixed forest of Robinia pseudoacacia with Pinus tabuleaformis. In Robinia pseudoacacia pure forest, MWHC and capillary water capacity are higher than that in farmland, and water holding capacity in low density forest is higher than that in high density one. Pinus tabuleaformis and Platycladus orientalis plantation have higher water holding capacity than farmland. Under those same conditions, evergreen conifer and broad-leaved mixed forest hold higher capacity to improve soil conditions than pure forest.The Robinia pseudoacacia plantation with density of 1600 plants/hm2 is with the biggest saturated soil water content, and the Ulmus pumila pure forest with density of 925 plants/hm2 holds the biggest non-capillary water-holding capacity. Soil precipitation storage is varied in different plantations, the Ulmus pumila pure forest with density of 925 plants/hm2 is with the biggest one, while the Pinus tabuleaformis pure forest with density of 1600 plants/hm2 holds the biggest available soil water storage of 383.83mm.(5) Soil chemical properties. The content of soil organic matter, total nitrogen, available nitrogen, available kalium decrease with increasing soil depth, and show obvious surface assembly phenomenon. Soil chemical properties are obvious different in different plantations. In the same density stands with different species, the average content of soil organic matter, available phosphor, available kalium show the following order:mixed forest of Pinus tabuleaformis with Robinia pseudoacacia>Robinia pseudoacacia plantation>Pinus tabuleaformis plantation>Platycladus orientalis plantation>Ulmus pumila plantation, in general, evergreen conifer and broad-leaved mixed forest is better than pure forest. However, the average content of total nitrogen and available nitrogen show a different order:Robinia pseudoacacia plantation>mixed forest of Pinus tabuleaformis with Robinia pseudoacacia>Pinus tabuleaformis plantation>Platycladus orientalis plantation>Ulmus pumila plantation.After the conversion of cropland to forest, the soil is better than that in the farmland. The best one is Robinia pseudoacacia plantation with 1600 plants/hm2, and mixed forests of Pinus tabuleaformis and Robinia pseudoacacia with 875 plants/hm2 are better than Ulmus pumila plantation with 1850 plants/hm2.(6) Density effect assessment. Robinia pseudoacacia plantation with 1600 plants/hm2 holds the best comprehensive assessment values, and the evergreen conifer and broad-leaved mixed forests with 875 plants/hm2 is with better ones, and the density effect is worst in height density Ulmus pumila plantation and Platycladus orientalis plantations. In general, the evergreen conifer and broad-leaved mixed forests are better than pure forest under the same conditions.
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