STEEPLE CLAYDON, England (NYTIMES) - A chorus of bird song gives way to the roar of a chain saw and then the creaking and splintering of timber. A 50-foot tree sways, wobbles and finally crashes to the ground, while protesters shout and jeer.

The construction of the British government's largest public works project - a high-speed rail line known as HS2 - has long been promoted as helping to save the environment. But it is under growing challenge from those who accuse it of doing the exact opposite.