Study On Ecological Effect Of Artificial Seabuckthorn Forest With Different Ages In Loess Hilly Region

Seabuckthorn is one of principal shrub soil and water conservation on the area of the Loess Plateau. As one of the few species which can grow in the Loess Plateau region of forests,forest-steppe zone and typical steppe zone ,it plays a huge role in soil and water conservation and ecological environment amelioration.The effect of different stage seabuckthorn forest on soil moisture and nutrients,water conservation function of seabuckthorn and the mixed soil,the natural seed bank of forest restoration were studied in Ansai by integrating field experiment with indoor analysis.The aim of the paper was to provide the basis for the evaluation of the ecological role and stability of seabuckthorn-lam in different stages of growth in the Loess Plateau.The results were as follows:1.The soil moisture of seabuckthorn woodland changed regularly as soil depth and season changing.. soil moisture was slightly various among different ages at the 0~600cm layer.At 150~400cm there was a obvious dried soil layer, with an average soil moisture of 5.48%.At 400~600cm, the soil moisture declined as the forest ages increasing. the soil moisture of 0~150,150~400 and 400~600 layers reduced as the forest age increasing. The soil moisture of 400~600cm were 10.2%,10.1%,8.6% and 7.2%.2.Seabuckthorn stand has remarkable effect on reducing runoff compared with barren slope.Its effect increases along with seabuckthorn age.The effect on reducing runoff increases obviously in 4 ages.Runoff is 2.54t/hm2 and runoff rate is 8.6% in 11 ages seabuckthorn stand. Enhanced with the increase of ages,the rate of forest flow of seabuckthorn and the rainfall runoff of producing was gradually decreasing trend, the ratio value beteenp roduction flow and precipitation decreased with increase of ages.that ratio was 5.43%~6.63% when seabuckthorn was 1~4 years old. when the age was bigger than 5, the ratio value decreased to 1.13 percent rapidly.The effect of reduced runoff of pure seabuckthorn forest was stronger than the mixed forest and chinese pine forest.the forest structure was stable after5 years ,when the effect of soil and water conservation was intensified,sand yielded in the pure seabuckthorn forest was 11.5% of seabuckthorn-poplar mixed forest, 49.9% of seabuckthorn-chinese pine mixed forest and10.1% of waste hillside.3.The nutrients of the seabuckthorn forests was rich in 0~10cm soil layer. The contents of total N, available N, total P, available P and organic matter decreased.as the depth of soil layer increased.As the stand age of the forests increased, total N contents in 0~10cm soil increased,and under 10cm,all layers but 20~30cm had an decreasing trend, however, total N under 10cm soil layer but not that for 20~30cm soil layer had an decreasing trend,Total P contents in 0~5cm soil layer decreased gradually and increased in other soil depth.The available P in different soil layers decreased as ages increased.There's no obvious difference among the organic matter contents in the same soil layer of different stand ages.The soil in the seabuckthorn forests presented alkaline with the pH changing from 8 to 8.6.The variation range of pH among different stand ages was 1%.4.The biomass of seabuckthorn increased with increase of the stand age of the forests.The biomass of main trunk increased most significantly, changing from 1.9 kg to 6.0kg for 4~15 years.5. The species diversity and community evenness of the standing vegetation in the seabuckthorn forests of 4, 8, 12 years were higher than that in the seabuckthorn forests of 15 years.Understory seed bank distributed mainly in 0~4cm soil layer, accounting for 60%,72%,67%and 61% of the total seeds.Seeds species in soil of different stand ages had little difference, which showed that the growth of seabuckthorn didn't destroyed the seed resources in soil.The species diversity and community evenness of seed bank both increased obviously with increase of stand ages.The richness of soil seeds of 12 years'forests was the highest among 4 different stand ages, up to 3.6926, while the richness of 8 years was the lowest as that of 15 years.