The Effect Of Short Term Enclosure On The Soil And Plant Of A Sandland Ecosystem In Northern Hebei Province And The Characteristics Of Soil Seed Bank Of The Sandland

Locating in an arid and semi-arid area, Nanshanzui Sandland is in Weichang county in northern of Hebei province. It has been seriously desertificated because of the unmanaged human activities and the dry and windy climate exerting on the frail ecological environment. So Nanshanzui sandland becomes one of the typical regions in land desertification research. In this paper, three site types were selected. They are enclosure and non-enclosure area of Nanshanzui sandland and Nanshatuozi tabulaeformis control zone which is in the climax stage of the local vegetation succession. Soil physical and chemical characteristics and vegetation characteristics of the three site types were investigated and the effect of short-term enclusion in the recovery process of the soil and vegetation was analyzed. While the water control test of the soil seed bank has been taken, the natural recovery potential of vegetation the constraints characteristics of water has been studied in the sandland, with main conclusions being achieved as follows:(1)After being fenced for 5 years, infiltration coefficient of 0～10cm soil layer signifacantly decreased in fenced region of sandland than those in non-exclosure region, while organic matter content of 10～20cm soil layer in fenced region has significantly increaced. But soil porosity, soli bulk density, moisture indexes and the content of available P and available K of 0～40cm soil layers are not significantly better in fenced region of sandland than those in non-exclosure region. The indexes indicate that soil conditions of both fenced region and non-exclosure region of sandland are at the level of tight medium or coarse sand with bad ability of moisture and fertilizer retention and the low level of nutrient supply. The soil physical and chemical characteristics of sandland still have great differrence with the control region which is in the climax stage of the local vegetation succession.(2)After short-term fenced, the number of legume plants increaces and the number of compositae plants reduces, Lespedeza floribunda is predominate instead of Artemisia scoparia, Boehmeria gracilis and Setaria viridis.(3)Vegetation condition has become much better after short-term fenced. Vegetation coverage of exclosure region has a significant increase of more than 42%, while biomass of herb layer and the litter dry weight increase more than 60%. Species richness, Shannon-Wiener index and Simpson index of herb layer also increase. (4)The effects of precipitation on niche distribution of sandland plant and proportion of dominant species has decreased by short-term fenced, so that community stability increased. At the same time, by being short-term fenced niche overlap among dominant species has a marked increase, which increases competition and coexistence among dominant species and promotes full utilization of resources.(5) In different water treatments, the soil seed bank occurrence density and species diversity of sandland are much lower than that of control region. Soil seed bank occurrence densities of sandland and the control region both reach the maximum in the good water condition. Among them, the occurrence densities of sandland was 2608 grains/m2, which shows a considerable restoration potentiality.(6) The C4 species would predominate in terms of number of species and density in drought condition. So that it more adaptes to the sandland environment which is droughty and windy. While C3 plant is significantly affected by water restrictions, particularly in the soil seed bank below surface soil.(7) Species similarity of seed banks and investigated vegetation were low both in sandland and its control region, less than 0.5. The seed bank density of drought treatment of sandland was similar to the investigated vegetation density. While in the control region, seed storage was much larger than its investigated vegetation density.(8) On the whole, Nanshanzui sandland possesses a considerable restoration potentiality. And by short-term fenced, the vegetation condition had become much better, its stability had increased, the phenomenon of species succession had appeared--number of leguminous species had increased. So that we suggest to cultivate legumes in order to speed up the process of vegetation succession and the restoration of soil.