Switzerland's ecosystems can be particularly fragile, because the many delicate valleys separated by high mountains often form unique ecologies. The mountainous regions themselves are also vulnerable, with a rich range of plants not found at other altitudes, and experience some pressure from visitors and grazing. The climatic, geological and topographical conditions of the alpine region make for a very fragile ecosystem that is particularly sensitive to climate change. Nevertheless, according to the 2014 Environmental Performance Index, Switzerland ranks first among 132 nations in safeguarding the environment, due to its high scores on environmental public health, its heavy reliance on renewable sources of energy (hydropower and geothermal energy), and its control of greenhouse gas emissions.