On the one hand, Buddhist traditions can be seen as environmentally friendly. The precept against harming living beings, the simple life of monastics living with little consumption of resources, many of the rules for monastics such as recycling robes and not polluting rivers, the implications of rebirth (you will suffer the consequences of the many ways in which humans are destroying the planet yourself, not just your great-grandchildren), the Mahayana idea of Buddha-nature in all things are all resources for creating an ecologically-minded Buddhism. Today, there are many practical environmental projects inspired by Buddhism such as the memorable activity in Thailand of ordaining trees as monastics in order to prevent them being cut down. An internet search, including projects listed by the Alliance of Religions and Conservation http://www.arcworld.org, can reveal many examples of ‘Green Dharma’ in practice.
However, like contemporary feminism or gay rights, environmentalism as we know it today, was not an ‘issue’ at the time of the Buddha or for much of Buddhist history. Humans just did not make such a negative impact 2,500 years ago. There are aspects of Buddhist teaching that suggest that environmental action is not the most important thing on which to be working. The physical world is impermanent and will decay anyway, and in one sense, in some Buddhist thought, not even real. Samsara altogether, including rebirth as human or animal in the material world, is something to be liberated from, so for example the precept against harming is not really about saving the planet, but for your own spiritual development. Nevertheless, the fundamental Buddhist quest for the reduction of suffering for all would seem to support environmental action.