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From Wikipedia, the free encyclopedia

Tundra
Greenland scoresby-sydkapp2 hg.jpg
Tundra in Greenland
800px-Map-Tundra.png
Map showing Arctic tundra
Geography
Area 11,563,300 km2 (4,464,600 sq mi)
Climate type ET

In physical geography, tundra is a type of biome where the tree growth is hindered by low temperatures and short growing seasons. The term tundra comes through Russian тундра (tûndra) from the Kildin Sami word tūndâr "uplands", "treeless mountain tract".[1] There are three types of tundra: Arctic tundra,[2] alpine tundra,[2] and Antarctic tundra.[3] In tundra, the vegetation is composed of dwarf shrubs, sedges and grasses, mosses, and lichens. Scattered trees grow in some tundra regions. The ecotone (or ecological boundary region) between the tundra and the forest is known as the tree line or timberline.

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  • Ecology - Rules for Living on Earth: Crash Course Biology #40
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  • Biomes of the World for Children: Oceans, Mountains, Grassland, Rainforest, Desert - FreeSchool

Transcription

For the last 38 episodes of Crash Course Biology, we've talked about how to make an organism. And you know what I've learned in those 38 weeks? Putting a living thing together is hard! There are molecules that make up organelles that run cells, which come together to form tissues, which make up organs that make up systems. And knowing this stuff is incredibly important, because it shows us the ground rules for being a living thing, on this particular planet anyway. But still, there's so much more to biology than that! I mean, understanding how an organism goes about its internal business is great, but it doesn't tell us much about its place in our world. For that, we need ecology, the study of the rules of engagement for all of us Earthlings. Ecology seeks to explain why the world looks and acts the way it does. Why the South Pole looks different from the Congo, and why there are mosquitos all over the place while black rhinos are practically extinct. The short answer to this question is: because the world is crammed with things, both animate and not, that have been interacting with each other all the time, every day, since life on this planet began. The even shorter answer is that all life and all of these things interacting with each other depend on just two things. Try to guess what they are. In the meantime, get ready, because Crash Course Biology is taking its final voyage outside the body and into the entire world! In a way, you can think of all living things, great white sharks, pond scum, potato plants, as molecules that react with each other. Each one of us organisms is pretty piddling in the scheme of things, just like a single oxygen molecule, which we need to make ATP to fuel our bodies. But it can't get much done by itself. But if you get a million oxygen molecules together with some other types of molecules, suddenly they're unleashing a googlejillion megawatts of ATP power to animate the bag of meat that is you. This same principle applies to organisms: As you put individual organisms together, they can interact with each other and their environments, to create something larger than the sum of its parts. And just as every organism has a hierarchy of biological systems, from molecules to organelles, cells, tissues and organs, so too does Earth have tiers of ecological order. Like, when a bunch of members of a species are together in a certain area, and they interact pretty often, you've got a population. Population ecologists study why populations grow or shrink over time, depending on where they are. When two or more populations of different species live together, we call that a community. Think of an ecological community as Mr. Roger's Neighborhood, but with the people in the neighborhood eating each other sometimes. Because that's what species do when they live together, they interact. Sometimes that means predation, sometimes cooperation, and sometimes competition for resources like food, water and living space. So, a community ecologist studies how the interactions between community members and their environment affect how many of each species there are within a community. One level up from communities are ecosytems, which are made up of groups of organisms in a specific area and the nonliving parts of their environment, like soil, water, and air. If you take a bunch of living things and plop them down in one place that has a specific mix of climate, soil chemistry, and topography, that's going to make up one kind of ecosystem. But if you put them down in a completely different place, they're going to work in completely different ways to form a completely different ecosystem. Ecosystem ecology specifically explores how energy and materials flow through an ecosystem, and how the physical environment impacts the stuff living there. Now, a lot of people get ecosystems confused with the next step up: which is biomes. A biome, however, is where organisms have evolved similar techniques to adapt to a general set of conditions. For example, a grassland is a kind of biome, there are scores of different grassland ecosystems all over the globe, but the organisms in each one have made similar evolutionary concessions to all the conditions that grasslands share, like hot summers, cold winters, and not too much rain but more rain than you'd find in a desert biome. Other biomes include tropical rainforest, tundra, deserts, and oceans. The only level above the biome is the biosphere, which includes the atmosphere, the whole earth and everything that gets used by anything that's alive. So, why do all of these many levels of ecological activity look the way that they do? Like, why do some organisms like to live in one place but not another? And what makes Earth's various populations, communities, ecosystems and biomes different from each other? Well, factors that determine what a place is gonna look like fall into two different categories: biotic, or living, and abiotic, not living. Biotic factors include stuff like predators, as well as animals or plants that provide either competition or some benefit, like food or shelter. Abiotic factors, on the other hand, include temperature, moisture, sunlight, elevation, elements that have nothing to do with organisms in the ecosystem, but which influence them just as much as other living things do. Now, from these two categories, the most influential factors are the ones that living things are most particular about. That is, the things they need most, but only at certain levels. And these preferences all come down to chemistry. For example, almost all chemical reactions that happen inside living things are governed by enzymes. They're the catalysts for pretty much all the action going on inside you. And these enzymes are most effective within a set of temperatures: Chemical reactions within the body slow way down when it's really cold, and very high temperatures change the shape of enzymes, making them less effective. So temperature is one of the major factors that determines why animals live in certain places. And if you look at the places on the earth with the most biodiversity, or different kinds of living things, you'll find that it's in the places where the temperature's within the ideal range for enzyme function. What else? Well, everybody's got to eat, at least if you're an animal or a fungus or some other kind of heterotroph, so you'd think that food would also be way up on the list. But actually, it's plants and other autotrophs like cyanobacteria and protists that are the base of nearly every food chain, and they have to be fed, too. So again, it comes down to chemistry. The key ingredient plants need for photosynthesis is water, which is also what we need to burn ATP, maintain homeostasis in our bodies, and all that jazz. So the quest for food ultimately comes down for a need for water. So, yeah: surprise! Water and temperature are the two things that organisms care about the most. Ergo, they're what ecologists focus on when determining why certain organisms hang out in one place over another. Together, these two factors define every biome on the planet. For instance, a Saguaro cactus has evolved to live in the Sonoran Desert of North America, which is super hot and gets very little precipitation. So, the Sonoran Desert is full of animals and plants that can, just like the Saguaro, take the heat and also the extreme, face-crumbling dryness. But if you put these animals in the Amazon rainforest, even though it's hot enough for them, it's just too wet. So, yeah, the things that live in a biome are ultimately determined by how much water is there and the temperature. And in turn, these inhabitants determine how the biome looks, called its physiognomy. So now, we are going to take a look at all the different types of biomes out there. There are places on the planet that get lots and lots of rain, around 300 centimeters a year, and are pretty warm, around 25-30 degrees C on average, which is Speedo-wearin' weather, as far as I'm concerned. These biomes are the tropical rainforests, which generally hug the equator and have unbelievably high biodiversity because everybody's wanting to get a piece of that sweet tropical action. And then on the complete opposite side of that scale, we have the tundra, most of which is above the Arctic Circle, in Antarctica, or way up at the top of some mountains. Tundra gets little precipitation and some well-below-zero temperatures. And what lives there? Not much. A couple of mosses and liverworts, maybe a few species of grasses, some birds and a handful of mammals. The same goes for the desert biome, where there's very little rainfall and very high temperatures. Like the tundra, without much water, there can't be very many large plants. And where there aren't a lot of plants, there aren't a lot of other organisms, even when temperatures are close to what makes living things happiest. Between these three extremes, we've got biomes that require more or less water, combined with high-ish or lowish temperatures. These are your moderate or temperate biomes, and they include temperate grasslands, like what you find in the North American prairie, or temperate deciduous forests, found over much of Europe and North America, and taigas or coniferous forests, found across Canada, much of northern Russia, and Scandinavia. So, if all these biomes in the middle experience pretty moderate temperatures most of the time, the availability of water must be what makes them different from each other. Some of these biomes have a lot of trees, and as we know, trees need a lot of water. So if you find yourself in a temperate forest, it's a pretty safe bet that that particular ecosystem gets a fair amount of precipitation. And if the Carboniferous forests taught us anything, it's that having a bunch of trees around changes the landscape, the climate, and even the geology of a biome. If you don't have a lot of trees in a biome, it means you probably don't get enough rainfall for their liking. And without trees, more sunlight reaches the ground and gets to grasses and other small plants, leading to more of a temperate grassland ecosystem. And where you get grass, you get animals like bison and pronghorn and other ungulates whose digestive systems are big fermentation vats that process cellulose all day long. And then when you've got ungulates, you also get predators. All these animals are way different than what you'd find in a temperate forest. So, biomes are different, because the plants are different, because the rainfall and temperatures are different. But, of course, there are also biomes entirely underwater. We can't forget that the surface of the planet is three-fourths water. And since water availability isn't an issue in the ocean, marine biomes differ in things like temperature, pressure, oxygen content, how much light is available, and stuff like that. So, thanks to the science of ecology, we know that the way the world works can be explained mostly by temperature and water. But this is just the beginning my friends. Oh yes! The end of Biology 101, maybe. And we'll always have that time we spent learning and loving, won't we? But there's so much more to find out together! How do living things affect the climate, the chemical makeup of the atmosphere, even the geology of our planet? How do they affect each other? And maybe more importantly, how are we humans affecting all of these things, and what can we do differently to ensure that we all get to keep existing? Join me as we get to know our planet on a whole new level, starting next week! Thanks for watching this final episode of Crash Course Biology and if you've been with us the whole time thank you for participating and learning with us here at Crash Course. And of course, thank you to all the people who helped write these episodes, who helped do these awesome animations, the people who filmed and edited them. It really is a team effort here at Crash Course. If you want to review anything that we talked about in this episode there's a table of contents over there. And if you have any questions, we're on Facebook, Twitter, and of course, in the comments below.

Contents

Arctic

Arctic tundra occurs in the far Northern Hemisphere, north of the taiga belt. The word "tundra" usually refers only to the areas where the subsoil is permafrost, or permanently frozen soil. (It may also refer to the treeless plain in general, so that northern Sápmi would be included.) Permafrost tundra includes vast areas of northern Russia and Canada.[2] The polar tundra is home to several peoples who are mostly nomadic reindeer herders, such as the Nganasan and Nenets in the permafrost area (and the Sami in Sápmi).

 Tundra in Siberia
Tundra in Siberia

Arctic tundra contains areas of stark landscape and is frozen for much of the year. The soil there is frozen from 25–90 cm (10–35 in) down, and it is impossible for trees to grow. Instead, bare and sometimes rocky land can only support low growing plants such as moss, heath (Ericaceae varieties such as crowberry and black bearberry), and lichen. There are two main seasons, winter and summer, in the polar tundra areas. During the winter it is very cold and dark, with the average temperature around −28 °C (−18 °F), sometimes dipping as low as −50 °C (−58 °F). However, extreme cold temperatures on the tundra do not drop as low as those experienced in taiga areas further south (for example, Russia's and Canada's lowest temperatures were recorded in locations south of the tree line). During the summer, temperatures rise somewhat, and the top layer of seasonally-frozen soil melts, leaving the ground very soggy. The tundra is covered in marshes, lakes, bogs and streams during the warm months. Generally daytime temperatures during the summer rise to about 12 °C (54 °F) but can often drop to 3 °C (37 °F) or even below freezing. Arctic tundras are sometimes the subject of habitat conservation programs. In Canada and Russia, many of these areas are protected through a national Biodiversity Action Plan.

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.[4]

 A group of muskoxen in Alaska
A group of muskoxen in Alaska

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.[5] 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).[6] Tundra is largely devoid of poikilotherms such as frogs or lizards.

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.

Relationship with global warming

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.[7]

Another concern is that about one third of the world's soil-bound carbon is in taiga and tundra areas. When the permafrost melts, it releases carbon in the form of carbon dioxide and methane,[8] both of which are greenhouse gases. The effect has been observed in Alaska. In the 1970s the tundra was a carbon sink, but today, it is a carbon source.[9] Methane is produced when vegetation decays in lakes and wetlands.[10]

The amount of greenhouse gases which will be released under projected scenarios for global warming have not been reliably quantified by scientific studies, although a few studies were reported to be underway in 2011. It is uncertain whether the impact of increased greenhouse gases from this source will be minimal or massive.[10]

In locations where dead vegetation and peat has accumulated there is a risk of wildfire such as the 1,039 square kilometres (401 sq mi) of tundra which burned in 2007 on the north slope of the Brooks Range in Alaska.[10] Such events may both result from and contribute to global warming.[11]

Antarctic

 Tundra on the Péninsule Rallier du Baty, Kerguelen Islands.
Tundra on the Péninsule Rallier du Baty, Kerguelen Islands.

Antarctic tundra occurs on Antarctica and on several Antarctic and subantarctic islands, including South Georgia and the South Sandwich Islands and the Kerguelen Islands. Most of Antarctica is too cold and dry to support vegetation, and most of the continent is covered by ice fields. However, some portions of the continent, particularly the Antarctic Peninsula, have areas of rocky soil that support plant life. The flora presently consists of around 300–400 lichens, 100 mosses, 25 liverworts, and around 700 terrestrial and aquatic algae species, which live on the areas of exposed rock and soil around the shore of the continent. Antarctica's two flowering plant species, the Antarctic hair grass (Deschampsia antarctica) and Antarctic pearlwort (Colobanthus quitensis), are found on the northern and western parts of the Antarctic Peninsula.[12] In contrast with the Arctic tundra, the Antarctic tundra lacks a large mammal fauna, mostly due to its physical isolation from the other continents. Sea mammals and sea birds, including seals and penguins, inhabit areas near the shore, and some small mammals, like rabbits and cats, have been introduced by humans to some of the subantarctic islands. The Antipodes Subantarctic Islands tundra ecoregion includes the Bounty Islands, Auckland Islands, Antipodes Islands, the Campbell Island group, and Macquarie Island.[13] Species endemic to this ecoregion include Nematoceras dienemum and Nematoceras sulcatum, the only subantarctic orchids; the royal penguin; and the Antipodean albatross.[13]

The flora and fauna of Antarctica and the Antarctic Islands (south of 60° south latitude) are protected by the Antarctic Treaty.[14]

Alpine

 Alpine tundra at Venezuelan Andes
Alpine tundra at Venezuelan Andes

Alpine tundra does not contain trees because the climate and soils at high altitude block tree growth. Alpine tundra is distinguished from arctic tundra in that alpine tundra typically does not have permafrost, and alpine soils are generally better drained than arctic soils. Alpine tundra transitions to subalpine forests below the tree line; stunted forests occurring at the forest-tundra ecotone (the treeline) are known as Krummholz.

Alpine tundra occurs in mountains worldwide. The flora of the alpine tundra is characterized by dwarf shrubs close to the ground. The cold climate of the alpine tundra is caused by the low air temperatures, and is similar to polar climate.

Climatic classification

 Tundra region with fjords, glaciers and mountains. Kongsfjorden, Spitsbergen.
Tundra region with fjords, glaciers and mountains. Kongsfjorden, Spitsbergen.

Tundra climates ordinarily fit the Köppen climate classification ET, signifying a local climate in which at least one month has an average temperature high enough to melt snow (0 °C (32 °F)), but no month with an average temperature in excess of 10 °C (50 °F). The cold limit generally meets the EF climates of permanent ice and snows; the warm-summer limit generally corresponds with the poleward or altitudinal limit of trees, where they grade into the subarctic climates designated Dfd, Dwd and Dsd (extreme winters as in parts of Siberia), Dfc typical in Alaska, Canada, parts of Scandinavia, European Russia, and Western Siberia (cold winters with months of freezing), or even Cfc (no month colder than −3 °C (27 °F) as in parts of Iceland and southernmost South America). Tundra climates as a rule are hostile to woody vegetation even where the winters are comparatively mild by polar standards, as in Iceland.

Despite the potential diversity of climates in the ET category involving precipitation, extreme temperatures, and relative wet and dry seasons, this category is rarely subdivided. Rainfall and snowfall are generally slight due to the low vapor pressure of water in the chilly atmosphere, but as a rule potential evapotranspiration is extremely low, allowing soggy terrain of swamps and bogs even in places that get precipitation typical of deserts of lower and middle latitudes. The amount of native tundra biomass depends more on the local temperature than the amount of precipitation.

See also

References

  1. ^ Aapala, Kirsti. "Tunturista jängälle". Kieli-ikkunat. Archived from the original on 2006-10-01. Retrieved 2009-01-19. 
  2. ^ a b c "The Tundra Biome". The World's Biomes. Retrieved 2006-03-05. 
  3. ^ "Terrestrial Ecoregions: Antarctica". Wild World. National Geographic. Archived from the original on 2011-10-21. Retrieved 2009-11-02. 
  4. ^ Higuera, Philip E.; Melissa L. Chipman; Jennifer L. Barnes; Michael A. Urban; et al. (December 2011). "Variability of tundra fire regimes in Arctic Alaska: millennial-scale patterns and ecological implications". Ecological Applications. 21 (8): 3211–3226. doi:10.1890/11-0387.1. ISSN 1051-0761. 
  5. ^ "Great Plain of the Koukdjuak". Ibacanada.com. Retrieved 2011-02-16. 
  6. ^ "Tundra". Blue Planet Biomes. Retrieved 2006-03-05. 
  7. ^ "Tundra Threats". National Geographic. Retrieved 2008-04-03. 
  8. ^ Walter, KM; Zimov, SA; Chanton, JP; Verbyla, D; et al. (7 September 2006). "Methane bubbling from Siberian thaw lakes as a positive feedback to climate warming". Nature. 443 (7107): 71–75. Bibcode:2006Natur.443...71W. doi:10.1038/nature05040. PMID 16957728. 
  9. ^ Oechel, Walter C.; Hastings, Steven J.; Vourlrtis, George; Jenkins, Mitchell; et al. (1993). "Recent change of Arctic tundra ecosystems from a net carbon dioxide sink to a source". Nature. 361 (6412): 520–523. Bibcode:1993Natur.361..520O. doi:10.1038/361520a0. 
  10. ^ a b c Gillis, Justin (December 16, 2011). "As Permafrost Thaws, Scientists Study the Risks". The New York Times. Retrieved December 17, 2011. 
  11. ^ Mack, Michelle C.; Bret-Harte, M. Syndonia; Hollingsworth, Teresa N.; Jandt, Randi R.; et al. (July 28, 2011). "Carbon loss from an unprecedented Arctic tundra wildfire" (PDF). Nature. 475 (7357): 489–492. Bibcode:2011Natur.475..489M. doi:10.1038/nature10283. PMID 21796209. Retrieved 2012-07-20. 
  12. ^ "Terrestrial Plants". British Antarctic Survey: About Antarctica. Retrieved 2006-03-05. 
  13. ^ a b "Antipodes Subantarctic Islands tundra". Terrestrial Ecoregions. World Wildlife Fund. Retrieved 2009-11-02. 
  14. ^ "Protocol on Environmental Protection to the Antarctic Treaty". British Antarctic Survey: About Antarctica. Retrieved 2006-03-05. 

Further reading

External links

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