The ecological environment along the Qinghai-Tibet Railway, the world's highest railway, is recovering after its first five years of operation, said a report issued by a Chinese national research institute on Wednesday.

"Parts of the areas are in a state which is close to or even better than the natural state of its surrounding regions," said an environment change evaluation report on the Tibetan plateau, organized by the Institute of Tibetan Plateau Research of the Chinese Academy of Sciences (CAS).

Ecological protection measures taken during and after the construction of the railway have ensured it was built as "a green railway," the report said.

Noting that environmental pollution has been brought under effective control, it said the alpine vegetation ecosystem has been effectively protected, the permafrost environment has been stable for years, the eco-function regions have been doing well and the plateau landscape remains intact.

During its first five years of operation, the railway had no obvious influence on vegetation, composition or layout in the areas along the lines, according to the report.

No invasive alien species were found during its construction, it said.

The 1,956-kilometer-long Qinghai-Tibet Railway, which began service in July 2006, is the world's highest and longest plateau railroad and also the first railway connecting the Tibet Autonomous Region with other parts of China.