A cushion plant is a compact, low-growing, mat-forming plant that is found in alpine , subalpine , arctic , or subarctic environments around the world. The term "cushion" is usually applied to woody plants that grow as spreading mats, are limited in height above the ground (a few inches at most), have relatively large and deep tap roots , and have life histories adapted to slow growth in a nutrient-poor environment with delayed reproductivity and reproductive cycle adaptations. The plant form is an example of parallel or convergent evolution with species from many different plant families on different continents converging on the same evolutionary adaptations to endure the harsh environmental conditions.
47-401: Donatia is a genus of two cushion plant species in the family Stylidiaceae . The name commemorates Vitaliano Donati , an Italian botanist. Donatia has been placed in the subfamily Donatioideae , described by Johannes Mildbraed in his 1908 taxonomic monograph of the family Stylidiaceae . The subfamily was created to distinguish the difference between the single genus Donatia from
94-415: A keystone species in a climax community . As such, the plants are often colonizers of bare habitat with little or no soil . Due to their role as initiators of primary succession in alpine habitats, the plants have specific adaptations to the desiccation and mechanically harsh environment of windy alpine slopes. The establishment of a new cushion plant on a windy slope, or freshly exposed Arctic tundra
141-589: A computerized climate system model suggests that if atmospheric carbon dioxide concentration were to increase to 860 ppm by the year 2100 (roughly double today's concentration), the SAMW will decrease in density and salinity. The resulting reductions in the subduction and transport capacity of SAMW and AAIW water masses could potentially decrease the absorption and storage of CO 2 in the Southern Ocean. The Antarctic realm and Antarctic Floristic Kingdom include most of
188-416: A recent time period. The glaciers of Laurens Peninsula, whose maximum elevation is only 500 m above sea level, are smaller and shorter than most of the other Heard Island glaciers, and therefore much more sensitive to temperature effects. Accordingly, their total area has decreased by over 30 percent. Jacka Glacier on the east coast of Laurens Peninsula has also demonstrated marked recession since 1955. In
235-543: A result of volcanic activity. In addition to new land being produced by volcanism, global warming of the climate is causing the retreat of glaciers on the islands ( see section below ). These combined processes produce new ice-free terrestrial and freshwater ecoregions , such as moraines and lagoons , which are now available for colonization by plants and animals. Heard Island has vast colonies of penguins and petrels , and large harems of land-based marine predators such as elephant seals and fur seals . Due to
282-409: A return visit in early 1980. Retreat of Heard Island glaciers is most dramatic on the eastern section of the island, where the termini of former tidewater glaciers are now located inland. Glaciers on the northern and western coasts have narrowed significantly, while the area of glaciers and ice caps on Laurens Peninsula have shrunk by 30% – 65%. During the time period between 1947 and 1988,
329-507: A small perennial, or sometimes hundreds of small flowers. This is necessary to attract pollinators over long distances, and in the short season of growth. Cushion plants have been described as ecosystem engineers because of their ability to locally maintain increased moisture and soil temperatures below the cushion ±15 °C (±27 °F) relative to adjacent soil temperatures. Some, specifically Mulinum leptacanthum and Oreopolus glacialis , have been positively identified as species that alter
376-403: Is a stub . You can help Misplaced Pages by expanding it . Cushion plant Cushion plants form large, low-growing mats that can grow up to 3 m (10 ft) in diameter. The typical form is a compact mass of closely spaced stems with minimal apical dominance that terminate in individual rosettes . Each stem grows at a consistent rate so that no one rosette is more exposed than the rest of
423-516: Is also well documented. Many subantarctic glaciers are also in retreat. Mass balance is significantly negative on many glaciers on Kergeulen Island, Heard Island, South Georgia and Bouvet Island. Heard Island is a heavily glacierized, subantarctic volcanic island located in the Southern Ocean , roughly 4000 kilometers southwest of Australia . 80% of the island is covered in ice, with glaciers descending from 2400 meters to sea level . Due to
470-562: Is defined as any latitude further south than 60° (the continental limit according to the Antarctic Treaty). Together, the Subantarctic Mode Water (SAMW) and Antarctic Intermediate Water (AAIW) act as a carbon sink , absorbing atmospheric carbon dioxide and storing it in solution. If the SAMW temperature increases as a result of climate change , the SAMW will have less capacity to store dissolved carbon dioxide. Research using
517-481: Is estimated to have decreased by roughly 29% between 1947 and 2004. This degree of loss of glacier mass is consistent with the measured increase in temperature of +0.9 °C over that time span. The coastal ice cliffs of Brown Glacier and Stephenson Glacier, which in 1954 were over 50 feet (15 m) high, had disappeared by 1963 when the glaciers terminated as much as 100 yards (91 m) inland. Baudissin Glacier on
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#1732930598974564-527: Is found in the alpine and subalpine regions of New Zealand and Tasmania while D. fascicularis is native to similar habitats in southern South America to latitude 40°S . In Chile Donatia fascicularis is, together with Astelia pumila , dominant in the cushion bogs that exists in areas exposed to the Pacific coast. As such it is not usually found together with Sphagnum which tend to grow slightly more inland. This Stylidiaceae article
611-586: Is increased longevity, with the largest cushions of some species attaining ages of up to 350 years. A study on Azorella compacta in southern Peru determined that, based on a growth rate of 1.4 mm per year, individual plants in the study area were upwards of 850 years old with occasional specimens approaching 3,000 years old. Cushion plants commonly grow in rapidly draining rocky or sandy soils in exposed and arid subalpine, alpine, arctic, subarctic or subantarctic feldmark habitats. In certain habitats, such as peaty fens or bogs, cushion plants can also be
658-486: Is not a common event. The established plants may be hundreds of years old, although they extend only a few inches above the surface. The plants are spreading and are wider than they are tall, but they are not extensive above the ground. The plant will grow for many years before it is ready to begin its first reproductive cycle. The plant actively grows only during the limited period when enough warmth and sunlight are available for photosynthesis, but may begin this cycle prior to
705-529: The Furious Fifties . Unlike other subantarctic islands, these islands have trees , temperate grasslands (mostly tussac grass ), and even arable land . They also lack tundra and permanent snow and ice at their lowest elevations. Despite their more southerly location, it is debatable whether these islands should be considered as such because their climate and geography differs significantly from other subantarctic islands. At between 52° – 57° south of
752-633: The Antarctic region. This translates roughly to a latitude of between 46° and 60° south of the Equator . The subantarctic region includes many islands in the southern parts of the Atlantic , Indian , and Pacific oceans, especially those situated north of the Antarctic Convergence . Subantarctic glaciers are, by definition, located on islands within the subantarctic region. All glaciers located on
799-585: The continent of Antarctica are by definition considered to be Antarctic glaciers . The subantarctic region comprises two geographic zones and three distinct fronts . The northernmost boundary of the subantarctic region is the rather ill-defined Subtropical Front (STF), also referred to as the Subtropical Convergence. To the south of the STF is a geographic zone, the Subantarctic Zone (SAZ). South of
846-447: The macronutrient concentrations in the soil. These attributes allow other species to more easily colonize the harsh environments that cushion plants inhabit. Species richness is therefore demonstrably increased where cushion plants have colonized. The cushion plant form is not endemic to any single area or plant family. About 338 species worldwide in 78 genera in areas ranging from Tasmania , New Zealand , and Tierra del Fuego to
893-669: The APF or Antarctic Convergence (in particular the Subantarctic Surface Water (Subantarctic Mode Water or SAMW), Antarctic Surface Water , and the Antarctic Intermediate Water ). This convergence creates a unique environment, noted for its very high marine productivity , especially for antarctic krill . Because of this, all lands and waters situated south of the Antarctic Convergence are considered to belong to
940-641: The Antarctic Convergence (with the Kerguelen Islands south of the Convergence) and are properly considered to be subantarctic islands. At between 51° – 56° south of the Equator, the Falkland Islands , Isla de los Estados , Ildefonso Islands , Diego Ramírez Islands , and other islands associated with Tierra del Fuego and Cape Horn , lie north of the Antarctic Convergence in the region often referred to as
987-592: The Antarctic Treaty). Therefore, although some are located south of the Antarctic Convergence, they should still be considered as subantarctic islands by virtue of their location north of 60° S. At between 60° – 69° south of the Equator, in the region often referred to as the Shrieking Sixties , the South Orkney Islands , South Shetland Islands , Balleny Islands , Scott Island , and Peter I Island are all properly considered to be Antarctic islands for
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#17329305989741034-536: The Antarctic from a climatological , biological and hydrological standpoint. However, the text of the Antarctic Treaty , article VI ("Area covered by Treaty") states: "The provisions of the present Treaty shall apply to the area south of 60° South latitude ". Therefore, Antarctica is defined from a political standpoint as all land and ice shelves south of 60°S latitude. At between about 46° – 50° south of
1081-543: The Brown Glacier, in an effort to determine whether glacial retreat is rapid or punctuated. Using a portable echo sounder , the team took measurements of the volume of the glacier. Monitoring of climatic conditions continued, with an emphasis on the impact of Foehn winds on glacier mass balance. Based on the findings of that expedition, the rate of loss of glacier ice on Heard Island appears to be accelerating. Between 2000 and 2003, repeat GPS surface surveys revealed that
1128-1002: The Equator, in the region often referred to as the Roaring Forties , are the Crozet Islands , the Prince Edward Islands , Wager Island , the Bounty Islands , the Snares Islands , the Kerguelen Islands , the Antipodes Islands , and the Auckland Islands . The geography of these islands is characterized by tundra, with some trees on the Snares Islands and the Auckland Islands. These islands are all located near
1175-693: The Equator, the Campbell Island Group , Heard Island and McDonald Islands , Bouvet Island , the South Georgia Group , Macquarie Island , and the South Sandwich Islands are also located in the Furious Fifties. The geography of these islands is characterized by tundra, permafrost , and volcanoes . These islands are situated close to or south of the Antarctic Convergence, but north of 60° S latitude (the continental limit according to
1222-783: The Indian and Pacific Ocean and between 42°S and 48°S in the Atlantic Ocean, defines the northern boundary of the Antarctic Circumpolar Current (or ACC). The ACC is the most important ocean current in the Southern Ocean , and the only current that flows completely around the Earth. Flowing eastward through the southern portions of the Atlantic, Indian, and Pacific Oceans, the ACC links these three otherwise separate oceanic basins . Extending from
1269-770: The SAZ is the Subantarctic Front (SAF). South of the SAF is another marine zone, called the Polar Frontal Zone (PFZ). The SAZ and the PFZ together form the subantarctic region. The southernmost boundary of the PFZ (and hence, the southern border of the subantarctic region) is the Antarctic Convergence, located approximately 200 kilometers south of the Antarctic Polar Front (APF). The subantarctic Front, found between 48°S and 58°S in
1316-465: The ambient air temperature and extend their short growing season. Many alpine cushion plants also have thick matted hairs that warm up and heat the air trapped in between the hairs when the sun shines. These hairs also act as a greenhouse by preventing the warmer air from rising away from the plant, and they also act as wind breaks, preventing the wind from blowing away the trapped heat. The cushion plant may have flowers that are large and showy for such
1363-530: The arctic tundra of Svalbard have convergently evolved the same plant form in response to similar environmental conditions. Thirty-four diverse plant families, such as Apiaceae , Asteraceae , Caryophyllaceae , Donatiaceae , and the Stylidiaceae , include cushion plant species. Subantarctic The subantarctic zone is a region in the Southern Hemisphere , located immediately north of
1410-419: The climate of the subantarctic region, though to a much lesser extent than the thermohaline circulation, is the formation of Antarctic Bottom Water (ABW) by halothermal dynamics . The halothermal circulation is that portion of the global ocean circulation that is driven by global density gradients created by surface heat and evaporation . Several distinct water masses converge in the immediate vicinity of
1457-522: The cushion. Observations on senescence have concluded that cushion plants typically die en masse rather than individual rosettes dying at separate times. Underneath the living rosettes, the plants typically produce nonphotosynthetic material or allow previous leaves to die, creating an insulating effect. Cushion plants grow very slowly. In the case of Silene acaulis , growth rates have been measured at 0.06 cm (0.02 in) to 1.82 cm (0.72 in) per year. Coinciding with this impeded growth
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1504-516: The early 1950s, Jacka Glacier had receded only slightly from its position in the late 1920s, but by 1997 it had receded about 700 m back from the coastline. Possible causes of glacier recession on Heard Island include: The Australian Antarctic Division conducted an expedition to Heard Island during the austral summer of 2003–04. A small team of scientists spent two months on the island, conducting studies on avian and terrestrial biology and glaciology. Glaciologists conducted further research on
1551-572: The five typical genera of the Stylidiaceae that Mildbraed placed in the Stylidioideae subfamily. The subfamily taxonomy represented the taxonomic uncertainty of Donatia , which had at one point also been placed in the Saxifragaceae . Donatia differs sufficiently from the genera in the Stylidiaceae in that it has free stamens and petals, paracytic stomata , and a pollen morphology distinct from
1598-427: The following three reasons: In light of the above considerations, the following should be considered to be subantarctic islands : This is a list of glaciers in the subantarctic . This list includes one snow field ( Murray Snowfield ). Snow fields are not glaciers in the strict sense of the word, but they are commonly found at the accumulation zone or head of a glacier. For the purposes of this list, Antarctica
1645-461: The ground, but its taproot can extend for a couple of feet below the soil surface. The long taproot is necessary because of both the limited precipitation in many alpine and arctic environments, mostly as snowfall, and because of the rapid drainage of a newly formed and shallow soil. Besides obtaining water, the plant must also retain moisture to survive in a dry and desiccating environment. The compact growth form of cushion plants reduces air flow over
1692-487: The ice formations above 5,000 feet (1,500 m) on the southwestern slopes of Big Ben , possibly as a result of volcanic activity . By 1963, major recession was obvious below 2,000 feet (610 m) on almost all glaciers, and minor recession was evident as high as 5,000 feet (1,500 m). Retreat of glacier fronts across Heard Island is evident when comparing aerial photographs taken in December 1947 with those taken on
1739-467: The north coast has lost at least 100 vertical feet (30 vertical m), and Vahsel Glacier on the west coast has lost at least 200 vertical feet (61 vertical m). Winston Glacier , which retreated approximately one mile (1.6 km) between 1947 and 1963, appears to be a very sensitive indicator of glacier change on the island. The young moraines flanking Winston Lagoon show that Winston Glacier has lost at least 300 vertical feet (91 vertical m) of ice within
1786-505: The other genera. Because of this and the recent phylogenetic analysis based on rbcL genes, more recent treatments have segregated Donatia into its own family, the Donatiaceae. The molecular phylogenetic analysis has placed Donatia as a sister-group to Stylidiaceae, thus leaving the Stylidiaceae as a monophyletic family. As early as three years after Mildbraed's publication of the subfamily Donatioideae, other authors began to question
1833-405: The placement and argued for recognition of Donatiaceae. In 1915, Carl Skottsberg formally published the Donatiaceae. The APG II system recommended the inclusion of Donatia in Stylidiaceae but allowed for the optional recognition of the family Donatiaceae. The APG III system merges Donatiaceae into Stylidiaceae. The two species in the genus represent a wide geographic range. D. novae-zelandiae
1880-488: The sea surface to depths of 2000–4000 meters, and with a width of as great as 2000 kilometers, the ACC transports more water than any other ocean current. The ACC carries up to 150 Sverdrups (150 million cubic meters per second), equivalent to 150 times the volume of water flowing in all the world's rivers. The ACC and the global thermohaline circulation strongly influence regional and global climate as well as underwater biodiversity . Another factor that contributes to
1927-457: The snow melting. The plant's form is well adapted to trapping warm summer air within its body to extend the time during which it can photosynthesize . Cushions at higher elevation are typically smaller and denser. Plants growing in the alpine or subalpine regions face the challenge of obtaining and retaining water. One solution for obtaining water is the growth of an extensive root system. A small alpine forget-me-not may stand only inches above
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1974-922: The southern hemisphere. With respect to glaciers of the Andes mountains in South America , abundant evidence has been collected from ongoing research at Nevado del Ruiz in Colombia , Quelccaya Ice Cap and Qori Kalis Glacier in Peru , Zongo , Chacaltaya and Charquini glaciers in Bolivia , the Aconcagua River Basin in the central Chilean Andes , and the Northern Patagonian and Southern Patagonian ice fields . Retreat of glaciers in New Zealand and Antarctica
2021-439: The steep topography of Heard Island, most of its glaciers are relatively thin (averaging only about 55 meters in depth). The presence of glaciers on Heard Island provides an excellent opportunity to measure the rate of glacial retreat as an indicator of climate change. Available records show no apparent change in glacier mass balance between 1874 and 1929. Between 1949 and 1954, marked changes were observed to have occurred in
2068-547: The subantarctic islands native biota , with many endemic genera and species of flora and fauna . The physical landscape and biota communities of Heard Island and McDonald Islands are constantly changing due to volcanism , strong winds and waves, and climate change . Volcanic activity has been observed in this area since the mid-1980s, with fresh lava flows on the southwest flanks of Heard Island. Satellite imagery shows that McDonald Island increased in size from about 1 to 2.5 square kilometers between 1994 and 2004, as
2115-464: The surface of the epidermis , reducing the rate of water loss. Additionally, many cushion plants have small and fleshy leaves which reduce the surface area of the plant, which reduces transpiration and conserves water. In alpine environments well above the tree line, cold is a limiting factor for growth. So, by having tightly packed stems and foliage, cushion plants are able to convert and trap heat from sunlight, causing them to warm several degrees above
2162-481: The total area of Heard Island's glaciers decreased by 11%, from 288 km (roughly 79% of the total area of Heard Island) to only 257 km . A visit to the island in the spring of 2000 found that the Stephenson , Brown and Baudissin glaciers, among others, had retreated even further. The terminus of Brown Glacier has retreated approximately 1.1 kilometres since 1950. The total ice-covered area of Brown Glacier
2209-510: The very high numbers of seabirds and marine mammals on Heard Island, the area is considered a "biological hot spot". The marine environment surrounding the islands features diverse and distinctive benthic habitats that support a range of species including corals , sponges , barnacles and echinoderms . This marine environment also serves as a nursery area for a range of fishes, including some species of commercial interest. Glaciers are currently retreating at significant rates throughout
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