什么是冻原；苔原

极地区泰加林带以上（北极冻原）或高山上（高山冻原）的无树的平地或滑地，特徵是裸露的地面和岩石，或者有苔藓、地衣、小草以及矮灌木等植被。由於环境恶劣，所以动物品种有限。在北极冻原有旅鼠、北极狐、北极狼、北美驯鹿、驯鹿以及麝香牛等。高山冻原上的许多动物，包括山羊和野猫，冬季里就下到较温暖的区域。比起北极冻原来，高山冻原的气候要温和些，雨量也多些。北极冻原冰冷的气候产生了一层永久性的冻土层（永冻土）。覆盖在上面的土壤层则随着季节温度的变化而在冻结与融化之间交替。高山冻原有冻结－融化交替层，但没有永冻土。由於北极冻土接受极长时间的日光与黑暗（持续在一个到四个月之间），所以生物节律更多地要按温度的变化而不是日光的变化来调节。北极冻原覆盖了约地球表面的十分之一。在云杉和冷杉的树木线以上开始出现高山冻原。由於冻原区域动植物的种类稀少，食物链很脆弱，所以对它们生活区的任何一点破坏都会影响整个生态系统。

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.