The Restoration Of Degraded Ecosytem In Hunshandak Sandland Through Natural Process

Locating in an arid and semi-arid area, Hunshandak Sandland is a transition area from typical grassland to desert grassland. It had ever been the flourish grassland, however, has been greatly degraded because of the unmanaged human activities exerting on a frail ecological environment. For example, the percent of shifting sand dunes had increased from 2% in 1950s to almost 50% in 1990s. Now Hunshandak has been blamed as an important sand storm source to Beijing and Tianjin regions, so it becomes one of the vital regions in land degradation research and also sandstorm controls. From a point of both natural and social science views, we here report the restoration potentials through natural process. The restoration stage, the species option for re-vegetation, the production and live of local people have been also studied, with main conclusions being achieved as follows:(1) The soil seed banks included numerous seeds which play potential roles in the restoration of degraded ecosystem in Hunshandak Sandland. Those seeds would germinate into seedlings and settle to form certain coverage if the disturbance of human and livestock were avoided. The degraded grassland can be correspondingly restored then the harms of sandstorms be reduced. There are significantly similar compositions both in soil seed banks and aboveground vegetations, which forms the base of plant community stability. Therefore, the soil seed banks may affect the restoration succession, in reverse, the restoration succession could also restrict the development of soil seed banks.(2) The natural restoration successions could be marked as three stages based on plant community analysis in different fenced locations. First, the early stage exists in 2 years after fenced, characterized by changes from shifting sand dunes to semi-fixeddunes. Second, the intermediate stage is within 3-5 years of closure, the semi-fixed sand dunes being gradually stabilized. Third, the later stage of restoration can be found after 6 years of community stabilization, during which the fixed sand dunes have been gradually developed. Considering the way of changes in growth forms and species components with restoration succession, the series of vegetation succession can be summed up as: Agriophyllum squarrosum + Bassia dasyphylla Salix gordejevii + Agropyron cristatum - Artemisia intramongolica+ Agropyron cristatum - Ulmus pumila var. sabulosa+ Agropyron cristatum. Thus, the degraded grassland may be mostly restored within a short period time under fenced conditions. To achieve this, the disturbances of human activities and grazing are the keys in restricting the succession of restoration, which should be seriously considered.(3) The leaf water traits varied among both in species and habtitats. Those species with deeper rooting depths and lower leaf water contents showed the lower leaf osmotic potentials. Among the different growth forms, the shrubs had the lowest leaf osmotic potential, with a series of shrubs > trees > grass; deep rooting depth > shallow rooting depth (P< 0.05). In addition, species distributing in the wetland and lowland appeared the higher leaf osmotic potentials and leaf water contents, while those growing on the sand dunes performed the lower values. Such indicates that plants with different growth forms possessed differential water use patterns enabling them coexist in the same ecosystem.(4) Compared with the native species, the introduced species presented a lower value of net photosynthetic rate, stomatal conductance and water use efficiency, a higher value of leaf water potential under the similar photosynthetic photon flux density and leaf temperature. So the introduced species might be eliminated afterwards by the natives through water competition when the soils became acutely drought. In addition,the introduced species also showed lower PSII, indicating the poor ability in resisting drought and high air temperature. Therefore, we should be especially careful in introducing the indigenous species in ecological restorations. Once species have been introdu...