Effects of Enclosure on Quantitative Characteristics and Species Diversity of the Understory Vegetation Community in the Pinus sylvestris var. Mongolica Sandy-fixation Plantation

In order to reveal influences of enclosure on the understory vegetation community and the ecosystem of artificial Pinus sylvestris var. mongolica sand-fixing forest,the forests of 37-year-old and 46-year-old Pinus sylvestris var. mongolica at Zhanggutai were enclosed and selected as the research objects,and the adjacent unclosed forest was selected as the control. The community characteristics and species diversity of understory vegetation communities under different conditions were studied by field investigations. The results showed that 58 species of undergrowth vegetations of 18 families and 42 genera were found in the study area. Under enclosure conditions,the numbers of Gramineae and perennial plants increased,and the important values of perennial and shrub plants increased. The enclosure decreased the important value of pioneer species and increased the important value of Leymus chinensis significantly. The enclosure increased the average coverage,height and biomass of the understory vegetation community of the Pinus sylvestris var. mongolica forests,and different growth trends were showed with increasing of enclosure years. Species diversity index,dominance index and evenness index of the understory vegetation community in the half-enclosed of 5 years were slightly higher than those in the unclosed condition,but those in the full-enclosed of 10 years were lower than those in the unclosed state. Therefore,the enclosure is conducive to the restoration and growth of the understory vegetation community of the Pinus sylvestris var. mongolica,and the moderate enclosure is conducive to increase diversity of the understory community and thus ensures the succession of community and maintains the ecosystem stability.