<P> Tundra tends to be windy, with winds often blowing upwards of 50--100 km / h (30--60 mph). However, in terms of precipitation, it is desert - like, with only about 15--25 cm (6--10 in) falling per year (the summer is typically the season of maximum precipitation). Although precipitation is light, evaporation is also relatively minimal . During the summer, the permafrost thaws just enough to let plants grow and reproduce, but because the ground below this is frozen, the water cannot sink any lower, and so the water forms the lakes and marshes found during the summer months . There is a natural pattern of accumulation of fuel and wildfire which varies depending on the nature of vegetation and terrain . Research in Alaska has shown fire - event return intervals (FRIs) that typically vary from 150 to 200 years, with dryer lowland areas burning more frequently than wetter highland areas . </P> <P> The biodiversity of tundra is low: 1,700 species of vascular plants and only 48 species of land mammals can be found, although millions of birds migrate there each year for the marshes . There are also a few fish species . There are few species with large populations . Notable animals in the Arctic tundra include caribou (reindeer), musk ox, Arctic hare, Arctic fox, snowy owl, lemmings, and polar bears (only near ocean - fed bodies of water). Tundra is largely devoid of poikilotherms such as frogs or lizards . </P> <P> Due to the harsh climate of Arctic tundra, regions of this kind have seen little human activity, even though they are sometimes rich in natural resources such as oil and uranium . In recent times this has begun to change in Alaska, Russia, and some other parts of the world . </P> <P> A severe threat to tundra is global warming, which causes permafrost to melt . The melting of the permafrost in a given area on human time scales (decades or centuries) could radically change which species can survive there . </P>

Why do you find large mammals in the arctic tundra but not in alpine tundra