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 500 and 1,000 m (1,640 and 3,281 ft), depending on the location. The montane zone extends from 800 to 1,700 m (2,625 to 5,577 ft), followed by the sub-Alpine zone from 1,600 to 2,400 m (5,249 to 7,874 ft). The Alpine zone, extending from tree line to 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.
What is the lowest zone of the Alps called? (If the question is unanswerable, say "unanswerable")
colline zone