Study On Dynamic Of Edge Effect And Vegetation Restoration On Mounds Created By Zokors (Myospalax Fontanierii) In A Alpine Meadow

There are currently 42.51 million hectares of degraded grassland, i.e. 33％of the total available grassland, in the Qinghai-Tibet Plateau. The characteristics of degraded grassland are low forage production, low vegetation cover and loss of the upper soil horizons. Historically, a variety of factors have been responsible for the deterioration of plateau grassland, including overgrazing, the escalation of rodent populations, and changes in the cryoturbation and climate. Plateau zokors have traditionally been viewed as pests, competitors with cattle, and agents of soil erosion. But as one of members in ecosystem, their positive effects were neglected usually. Meanwhile, the intermediate disturbance hypothesis suggests the appropriate disturbance can benefit for development and maintenance of ecosystems, enhance plant species diversity and efficiency of resources. In recent years, there are many disputations about zokors' function in ecosystem. It is necessary to understand the characteristics of dynamic of vegetation in soil and plants after zokoers distuebance.Base on summing-up functions of disturbances by subterranean animals, we studied four-year dynamic of vegetation on mounds created by zokors (Myospalax baileyi) in a alpine meadow of the Qinghai-Tibet Plateau.Vegetation restoration and edge effects following soil disturbance by the plateau zokor (Myospalax baileyi) were investigated from 2001 to 2004 in a alpine meadow of the Qinghai-Tibet Plateau. The ingestigation include two parts: (1)Two adjacent plots with similar ecological conditions were compared: one control community abbreviated CK (intermediate undisturbed by zokors for over 5 years) and one disturbed community (with new mounds); (2)Accroding to the different degree of disturbance, another two plots were selected:one slight disturbed community and one heavy disturbed community to biuld a series of communitis: CK, slighted, intermediate and heavy disturbed community. In the part (1), vegetation retoration on mound and edge effects of mound created by zokors were studied. And in the part (2), the influence under different degree of diturbance on plant communitis were investgated to evaluate the ecological results such as plant species diversity, plant composition, plant density and above ground biomass in different degree disturbance. The major results and conclusions are as bolw.1.The results indicated that vegetation restoration on mounds tended to increase over time. Plant diversity, cover, biomass and density reached 88.5%, 87.9%, 73.1%, and 52.7% of the values for the control community, respectively, over the four year restoration period.2.The edge effect around mounds led to a gradual increase in aboveground biomass and vegetation density from 2001 to 2004, which exerted a compensative effect on aboveground biomass restoration on the mounds.3.The loss of above ground biomass on mounds was compensated by edge effect of above ground biomass in rate of 55.7% annuly.4.The total number of species in the disturbed community increased from 15 in 2001 to 27 in 2004, and contained 3 alien species, which were not found in the control plot, which contained 30 species. The average species diversity in mound sites (＞1.8) was generally higher than that of the control plot (1.7). It isprobable that plateau zokors are important for maintaining or restoring the disturbance-dependent elements of native plant communities.5.In addition, zokor disturbance resulted in a significant change in soil particle size, increased soil water content from about 20% to 25% and soil organic carbon content from 108 g/kg to 114 g/kg (0-20 cm soil layer) after four years of restoration. The improvement in soil quality might be associated with the rate of vegetation restoration following zokor disturbance.6. Through contrasts and analysis, the comprehensive indexes such as plant species diversity, above ground biomass, plant density and vegetation coverage was best in intermediate disturbed plot, better in slight disturbed plot and CK plot than heavy disturbed plot. This results showed approprate disturbance can enhance palnt species diversity, above ground biomass and have positive influence on ecological system.Therefore, through modulation of vegetation restoration on mound and the edge effect around the mounds enhanced the stability of the communities. From this viewpoint, plateau zokors play a regulatory role and accordingly, their effect is positive. It might be said to act as ecosystem engineers in alpine meadows.