hover around the freezing point even during July and August. High-water levels in streams and rivers peak in June and July when the snow is still melting at the higher altitudes. The Alps are split into five climatic zones, each with different vegetation. The climate, plant life, and animal life vary among the different sections or zones of the mountains. The lowest zone is the colline zone, which exists between , depending on the location. The montane zone extends from , followed by the sub-Alpine zone from . The Alpine zone, extending from tree line to the snow line, is followed by the glacial zone, which covers the glaciated areas of the mountain. Climatic conditions show variances within the same zones; for example, weather conditions at the head of a mountain valley, extending directly from the peaks, are colder and more severe than those at the mouth of a valley which tend to be less severe and receive less snowfall. Various models of climate change have been projected into the 22nd century for the Alps, with an expectation that a trend toward increased temperatures will have an effect on snowfall, snowpack, glaciation, and river runoff. Significant changes, of both natural and anthropogenic origins, have already been diagnosed from observations. Ecology Flora Thirteen thousand species of plants have been identified in the Alpine regions. Alpine plants are grouped by habitat and soil type which can be limestone or non-calcareous. The habitats range from meadows, bogs, and woodland (deciduous and coniferous) areas to soil-less scree and moraines, and rock faces and ridges. A natural vegetation limit with altitude is given by the presence of the chief deciduous trees—oak, beech, ash and sycamore maple. These do not reach the same elevation, nor are they often found growing together, but their upper limit corresponds accurately enough to the change from a temperate to a colder climate that is further proved by a change in the presence of wild herbaceous vegetation. This limit usually lies about above the sea on the north side of the Alps, but on the southern slopes it often rises to , sometimes even to . Above the forestry, there is often a band of short pine trees (Pinus mugo), which is in turn superseded by Alpenrosen, dwarf shrubs, typically Rhododendron ferrugineum (on acid soils) or Rhododendron hirsutum (on alkaline soils). Although Alpenrose prefers acidic soil, the plants are found throughout