The plan aims to increase forest coverage on the Hebei-Beijing border, in part by tapping into rivers, reservoirs, wetlands and farmland, an official statement said. Though the plan calls for greater wetlands preservation, it does not mention that Beijing suffers from a chronic drought, so there is very little water on which to draw.

The plan also emphasizes the need for “ventilation corridors” that would channel wind and air movement to help disperse smog. In February 2016, Chinese news organizations reported that Beijing officials were considering creating five giant “ventilation corridors,” each at least 1,500 feet wide, to run through the city and improve air circulation. The reports said officials were also considering constructing an unspecified number of narrower corridors.

Earlier that month, the website of the government-controlled China Science Daily, officially called Science Times in English, published an opinion article that said the root cause of the smog in Beijing was declining wind strength. And one of the factors behind that was the planting of trees where none had existed before, the article said.

That would seem to contradict the official claims that creating a “green necklace” around Beijing would reduce pollution levels.

China has tried ambitious tree-planting projects before to address environmental problems. The most famous have been in the Inner Mongolia region and other parts of northern China, where people have been ordered or encouraged to plant trees to hold back the spread of the Gobi Desert. Scientists have debated the extent to which those measures help, and deserts have continued expanding in critical regions.