The Study On Several Common Disturbance Types In Alpine Meadow

Disturbances are ubiquitous, inherent and unavoidable in nature, affecting all levels of biological organization, structure and succession. In order to probe into mechanisms and effects of disturbances in grassland ecosystem, we used two common natural disturbances (feeding of grassland caterpillar and zokor mound) in alpine meadow in Qinghai-Tibetan plateau as objectives, studied their effects on vegetation and analyzed potential factors influencing caterpillar distribution and that impacting vegetation recovery of zokor mound. In addition, we used modeled zokor disturbance, namely a kind of artificial disturbance, sward cleavage to predict its feasibility to rehabilitate degraded grassland, the main results are as follows:(1)Feeding habit of the caterpillars presented strong selectivity. The sequence of their feeding preference was: Gvperaceae>Gramineae>forbs. More particularly, they showed strong preference and tendency to feed on Kobresia sp.. Caterpillar distribution was dependent on the spatial pattern of plants they preferred. Generally, caterpillars were in aggregative distribution, but in an even distribution on small scale. The density depended on the richness of plants the larvae enjoyed feeding and on the plant diversity. The population rose significantly as their preferable plants increased, and declined significantly with plant diversity decreased. The caterpillar possessed function of counterpoising relationship among species and regulating the community structure in the alpine meadow ecosystem. It is effective to eradicate the insect pest by adopting agricultural measures to change the composition of grassland plants directionally so as to limit the number of caterpillars.(2) The slope positions and exposures of plateau zokor (Myospalax baileyi) mounds are important factors affecting vegetation recovery rate of mounds and vegetation traits. The recovery rates of different slope positions are (in order of decreasing rates): mound edge, mound middle and mound center; these differences mainly result from effects of microtopography on water and fertility conditions in soil and on propagule sources; the recovery rates of different exposures (in order of decreasing rates) are: west, north, east, and south. These differences largely depend on redistribution of soil fertility and light resource by microtopography. (3) As the intensity of sward cleavage increased, Elymus nutans and other plants that had high requirements in soil aeration and resource space presented an increased competitive edge and the species that had low requirements presented an opposite picture; low-intensity sward cleavage could help increase species diversity to a certain extent, but the diversity index appeared to decline as a whole as the cleavage intensity increased; the effects of sward cleavage on functional groups of the vegetations showed in such manner as Elymus nutans-represented grasses increased in their compositions with the intensity of sward cleavage raised, and sedges and forbs decreased in their compositions with the intensity of sward cleavage raised; sward cleavage showed a significant improving effect on primary productivity of the meadows and was capable of increasing the proportion of quality-grass biomass to the total plant biomass; sward cleavage could be independently employed as an effective measure to rehabilitate and improve alpine-meadow grasslands and thus played a basic and key role in the technical combination aiming at establishing hay fields characterized by Elymus nutans.