什麼是凍原；苔原

極地區泰加林帶以上（北極凍原）或高山上（高山凍原）的無樹的平地或滑地，特徵是裸露的地面和岩石，或者有苔蘚、地衣、小草以及矮灌木等植被。由於環境惡劣，所以動物品種有限。在北極凍原有旅鼠、北極狐、北極狼、北美馴鹿、馴鹿以及麝香牛等。高山凍原上的許多動物，包括山羊和野貓，冬季裡就下到較溫暖的區域。比起北極凍原來，高山凍原的氣候要溫和些，雨量也多些。北極凍原冰冷的氣候產生了一層永久性的凍土層（永凍土）。覆蓋在上面的土壤層則隨著季節溫度的變化而在凍結與融化之間交替。高山凍原有凍結－融化交替層，但沒有永凍土。由於北極凍土接受極長時間的日光與黑暗（持續在一個到四個月之間），所以生物節律更多地要按溫度的變化而不是日光的變化來調節。北極凍原覆蓋了約地球表面的十分之一。在雲杉和冷杉的樹木線以上開始出現高山凍原。由於凍原區域動植物的種類稀少，食物鏈很脆弱，所以對它們生活區的任何一點破壞都會影響整個生態系統。

tundra

Treeless, level or rolling ground above the taiga in polar regions (Arctic tundra) or on high mountains (alpine tundra), characterized by bare ground and rock or by such vegetation as mosses, lichens, small herbs, and low shrubs. Animal species are limited by harsh environmental conditions. In the Arctic tundra they include lemmings, the Arctic fox, the Arctic wolf, caribou, reindeer, and musk-oxen. In the alpine tundra many animals, including mountain sheep and wildcats, descend to warmer zones during winter. The climate of alpine tundra is more moderate and has a higher amount of rainfall than does Arctic tundra. The freezing climate of the Arctic produces a layer of permanently frozen soil (permafrost). An overlying layer of soil alternates between freezing and thawing with seasonal temperature variations. Alpine tundras have a freeze-thaw layer but no permafrost. Because Arctic tundras receive extremely long periods of daylight and darkness (lasting between one and four months), biological rhythms tend to be adjusted more to variations in temperature than to variations in sunlight. Arctic tundra covers about one-tenth of the earth's surface. Alpine tundras begin above the timberline of spruce and firs. Because of the small number of plant and animal species and the fragility of the food chains in tundra regions, natural or mechanical damage to any element of the habitat affects the whole ecosystem.