but can vary greatly across localities, from glacial conditions on the mountaintops to the near-Mediterranean climate at Switzerland's southern tip. Some valley areas in the southern part of Switzerland offer cold-hardy palm trees. Summers tend to be warm and humid at times with periodic rainfall, ideal for pastures/grazing. The less humid winters in the mountains may see weeks-long intervals of stable conditions. At the same time, the lower lands tend to suffer from inversion during such periods, hiding the sun. A weather phenomenon known as the föhn (with an identical effect to the chinook wind) can occur any time and is characterised by an unexpectedly warm wind, bringing low relative humidity air to the north of the Alps during rainfall periods on the south-facing slopes. This works both ways across the alps but is more efficient if blowing from the south due to the steeper step for oncoming wind. Valleys running south to north trigger the best effect. The driest conditions persist in all inner alpine valleys that receive less rain because arriving clouds lose a lot of their moisture content while crossing the mountains before reaching these areas. Large alpine areas such as Graubünden remain drier than pre-alpine areas, and as in the main valley of the Valais, wine grapes are grown there. The wettest conditions persist in the high Alps and in the Ticino canton, which has much sun yet heavy bursts of rain from time to time. Precipitation tends to be spread moderately throughout the year, with a peak in summer. Autumn is the driest season, winter receives less precipitation than summer, yet the weather patterns in Switzerland are not in a stable climate system. They can vary from year to year with no strict and predictable periods. Environment Switzerland contains two terrestrial ecoregions: Western European broadleaf forests and Alps conifer and mixed forests. Switzerland's many small valleys separated by high mountains often host unique ecologies. The mountainous regions themselves offer a rich range of plants not found at other altitudes. The climatic, geological and topographical conditions of the alpine region make for a fragile ecosystem that is particularly sensitive to climate change. 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 level of greenhouse gas