Quoting Beijing: From Imperial Capital to Olympic City by Li, Dray-Novey and Kong (p.99-100):

Eighteenth- and nineteenth-century travelers considered Beijing's natural surroundings quite pleasant; in summer and fall, the city seemed park-like.  The view from the Western Hills toward the city was a sea of green, interrupted only by a few yellow-tiled rooftops peeking out from the foliage.  Looking west from the Imperial City during his 1849-1850 stay, the Russian envoy Kovalevsky enjoyed the "remarkable view, bright, shining, enchanting...  Before us rose the massive indented walls, surrounding a series of palaces" under the "wonderful sky, clear, blue, transparent... and the clear aromatic air." 

In his book When a Billion Chinese Jump, Jonathan Watts argues that China has become a dumping ground for the west's polluting industries and the country's bountiful supplies of coal present an all too tempting energy source.  The human misery wrapped up in coal extraction and polluting factories will undoubtedly fill volumes.  Still, I can understand how China came to have those problems; I'm less understanding of their embrace of the American disease, this idea that a middle-class lifestyle depends on owning a private automobile.  Just as our young are increasingly rejecting auto dependence, Chinese cities are crowding out bicycles.  When the air quality index in Beijing goes "crazy bad", I think we know what to blame.

And yet, Beijing has done a damned good job on trees.  Here we have a rapidly-growing city where acquiring land to build residential properties can be quite difficult, yet trees are protected.  Towers rise above the trees, sure, but in between the towers are lots of trees.  I can't think of any area of Beijing as big as Chicago's Loop that's as devoid of trees. 

In the photo to the right, the strip of green just on the other side of Zhongguancun Street is where subway line #4 runs.  Above it, they could have built parking lots or widened the road, but instead we have trees.

The photo at the top of this article was taken in Jingshan Park, right in the middle of the city.  You're looking northwest toward our Center.  Were I to walk in a straight line northwest, I might have to cross four lakes: Beihai, Qianhai, Houhai and Xihai.  And soon I'd start hitting University campuses every so often, some nice and some just ok.  Beyond the Center, though, would be Peking University, which is drop-dead gorgeous.  The Summer Palace is further west and the Old Summer Palace north.  Both Peking U and the palaces have lakes, too.  After that is the Botannical Gardens and then you hit the Fragrant Hills.

On clear days, Beijing is still a sea of green, albeit a city with towers rising thru the trees.