Through the investigations of sample belt transects and sample quadrats, the variation characteristics of the disturbed ecosystem by highway engineering in the permafrost region along the Qinghai-Tibet highway line were studied from the ecological elements such as permafrost ecosystem, community type, biodiversity and biological productivity and biological habitat conditions including soil environmental conditions and permafrost environmental conditions. The results show that in the sense of biology the restoration of high-cold steppe ecosystem was much better than that of high-cold meadow ecosystem after nearly 25 a of natural reconversion. This is mainly manifested in several respects: The dominant plant species of the high-cold steppe have occurred or even held a predominant position; local zonal biodiversity and population abundance have reached or even exceeded the level of the undisturbed natural steppe system. Viewed from soil environment change, organic matter content in the disturbed high-cold steppe on an average decreased by 61.5% and total N content decreased by 52.51%, but the nutrient regime of surface soil layer in most of the region corresponded to that of main grassland soil types in the and region, which is favourable to the growth of cold-resistant species. The mean nutrient contents of the disturbed high-cold meadow soil (Gelic cambosols) were higher than those of natural cryic aridsols. The maintenance of the integrity of meadow soil structure is crucial to the restoration of high-cold meadow ecosystem. However, the distribution and maintenance of high-cold meadow ecosystem were closely related to the permafrost environment, the restoration degree of the disturbed high-cold steppe ecosystem did not show an obvious restrictive relation with permafrost environment. Once the permafrost environment was destroyed by the engineering activities, the high-cold meadow ecosystem was very difficult to rehabilitate. From the comparison of the variation laws of the ecosystem along the Qinghai-Tibet highway line, the authors put forward two enlightenments for the eco-environmental protection in the construction processes of the Qinghai-Tibet railway.
