| To explore the forestation effects on the growth rules of the 1-4 years juvenile forest of Robinia pseudoacacia, two different forestation methods, tree planting and seeding, were taken to investigate the growth characteristics, species diversity and water retention properties of litter in the waste dump of iron mines, and to provide the suitable afforestation method of R. pseudoacacia. It is helpful for vegetation restoration in the waste dump. The main results were as follows:(1) The average height and ground diameter of the tree planting method were 2.66 m, 2.44 cm, and 1.96 m, 1.81 cm of the seeding method respectively. The relationship between height and growth was extremely significant nonlinear. The Tree height growth model of tree planting method was H =-0.0419D2+1.1486D+0.088 and H=1.0757D1.0461 of seeding method respectively. Therefore, the growth effects of Tree planting were better than seeding and showed different growth rules.(2) There were differences in the root growth characteristics of different forestation methods between ages. The root length, surface-area, volume and tips of T showed significant difference between 1-2 ages and 4 ages in diameters of 2~3mm,3~4mm, 4~5mm and >5mm; and those diameters all had statistical significance between 1 age and 3-4 ages. The root length and numbers of root tips of two methods were the biggest in ≦1mm diameters, and the root surface-area and volume were the biggest in >5mm diameters.The results of the correlation analysis demonstrated that length of root were significantly correlated with tips for T, and the length of root was significantly correlated with tips, length, surface areas for S. Moreover, the roots increased,but only the root features were remarkable difference from one to two years, and not significant difference with the extension of time. Meanwhile, the growth rate was various different between two forestation modes. The roots of T grew fast in two to three years, while S roots was fast-growing in one to three years.(3) The total biomass of T and S accumulated with the age increasing, and increased by 34.06g、197.16 g respectively. In the different parts biomass of R. pseudoacacia, the proportions of root and stem were 33.90%,35.09% respectively. The ratio between underground biomass and aboveground biomass decreased, indicating that matter accumulation of root was decline with age increasing and transferred to ground. In addition, the total biomass of R. pseudoacacia of T was higher than S. The root biomasses in each diameter were consistent with it. The ratio of root biomasses in diameter changed inconsistently with age creasing, which the diameters higher than 5mm increased with it, but the diameters lower than 5mm decreased. This showed that the most growth of fine root transferred to thick root with ageing.(4) The dominant species were mainly annual herb-Setaira viridis and without shrub layer under the R. pseudoacacia of two forestation methods. From the changes in species diversity index with forestation age, the plant diversity of two methods were decline and different. The species richness index of T declined in turn from 1.02 to 0.61, and indexs of diversity under S were reach lowest in the fourth year.(5) The litter amount, water-holding capacity and effective retain capacity were increased with plant age. Besides, regress equation(W= k ln(t) + p,R2>0.940) about the water-holding capacity and immersion time of litter was built by Regress Analysis. The relationship between water content and immersion time of litter was power function(V=k·tn, R2: 0.982~0.985).(6) Both two methods were adapted to the waste dump, and the tree planting could reach vegetation in short time, but the plant grew faster in seeding method. By composite analysis, R. pseudoacacia could bring better vegetation recovery because of the fast-growth, and the increase of litter volume and water-holding capacity. It was good for soil and water conservation capacity in waste dump. |
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