Circumpolar Arctic Floristic Provinces - Beringian Group
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All of Arctic Alaska is within the Beringian group of floristic sectors. The term "Beringia" was coined by Eric Hultén to describe the vast region centered on the Bering Strait and extending from the Kolyma River in the west to the Mackenzie River in the Northwest Territories. During the Pleistocene glacial intervals, sea level was as much as 100 m lower than present because of large amounts of water locked up in continental glaciers. This resulted in the large land mass connecting North America with Asia shown in Fig. 1.
Hultén recognized that Beringia was the center of distribution of many plant species that evolved here while most of northern North America was covered with ice. Yurtsev (1994) described the Chukotka and Alaska provinces within in the Beringia region (which he calls the Beringian sector). The PAF project combines Yurtsev's Chukotka and Alaska provinces into a single Beringia floristic group as originally suggested by Hultén (1937).
Elvebakk et al. (1999) characterize the Beringia group: "This is a highly diverse and floristically rich group of four to six regions [sectors]…, the number depending on some decisions still to be made. The importance of the group is that it contains all the important areas assumed to have been unglaciated through all or large parts of Quaternary times, including the islands in the shelf areas now submerged. On the Asiatic side are two undisputed regions, West Chukotka along the East Siberian Sea, including Wrangel Island, and East Chukotka facing the Bering Strait and Sea, the latter region with the strongest Beringian elements on the Asiatic side. Yurtsev also proposes a South Chukotka region on both sides of the Anadyr Basin, based on a floristic element connecting it to the more southern mountains and the Koryak Coast. An alternative proposal is to unite this with West Chukotka as it is a small area with insufficient characterization. Another option is to split it into the oceanic and continental parts to be assigned to the West and East Chukotka correspondingly. On the North American side are recognized the Beringian Alaska region facing the Bering Strait and Sea, with the strongest Beringian elements on the American side, and the North Alaska region of the Brooks Range and the northern coast, also extending into Canada. The eastern delimitation of North Alaska is disputed. Yurtsev proposes to draw the line west of Mackenzie River whereas others argue for including parts of the coast east of Mackenzie and western parts of Banks Isl. and Victoria Isl. in the region. The reason is mainly that parts of these islands and the mainland have been unglaciated and have subendemic plants in common with Beringian regions. The decision will depend on how the remaining of the Canadian Arctic will be subdivided [see Canada group]. Yurtsev proposes a separate North Beringian Islands region, which includes Big Diomede Island (Russian), Little Diomede Island, St. Lawrence Island, and St. Matthew Island (all North American). This region is mainly negatively characterized, except for a very few Pacific oceanic species more frequent here than on the mainlands. The islands would have been a natural part of a larger region including Pribyloff Islands, the Aleutian Islands and the Commodore Islands, but we have decided to exclude these from the Arctic. The alternative proposal is to join the islands with the neighboring regions: Big Diomede with East Chukotka, the others with Beringian Alaska." (From Elvebakk et al. 1999).
- West Chukotka sector
This sector is equivalent to the Continental Chukotka subprovince of Yurtsev (1994). "Because of the many continental western species or even genera, e.g. Chosenia, Dracocephalum, Leontopodium, Thymus, this [sector] seems to form a continuation of East Siberia. However, it differs from the latter by the presence of many amphi-Beringian and Chukotka species such as Hedinia czukotica. The frequency of occurrence of steppe species and communities reaches here its maximum for the entire Arctic." (From Yurtsev 1994.)
- East Chukotka sector
This sector is equivalent to Yurtsev's (1994) Beringian Chukotka subprovince. "At the western boundary of this sector continental western species disappear abruptly. Further eastward this trend continues, while there is a gradual increase in the number of oceanic eastern species, both Beringian and American, culminating in the easternmost part of the Chukotka Peninsula, where local endemics in the genera Arabidopsis, Oxytropis, Potentilla, Pucciphippsia and Taraxacum occur as well." (From Yurtsev 1994.)
- South Chukotka sector
This sector is equivalent to Yurtsev's (1994) South Chukotka subprovince. "The areas of the common overlapping of ranges of oceanic and continental species extends from the Amguema transitional area [a small province recognized by Yurtsev in the area of the middle and lower reaches of the Amguema River and the Iskamen' Range in the westernmost Chukotkan Peninsula] southward to the eastern part of the Anadyr lowlands (Anadyrskaya Nizmennost')-with some adjacent mountains and the easternmost Koryak Mts. included, i.e. beyond the range of Pinus pumila (Yurtsev 1978b). Here an assemblage of 'southern' species appears: alpine, hypoarctic or boreal, alien to the rest of Chukotka, such as Aruncus kamschaticus, Cassiope anadyrensis, C. ericoides, Mertensia pubescens, Rhododendron aureum, Saxifraga merckii and many others. Endemics are practically lacking, but a few interesting subendemics, in common with the neighbouring Anadyr-Koryak province of the Boreal region do occur, e.g. Oxytropis sublongipes and Potentilla anadyrensis." (From Yurtsev 1994.)
- Beringian Alaska sector
"This sector has a vast latitudinal extension and is divided by two large bays, the Kotzebue and Norton Bays, cutting deep inland. It borders a Picea forest area along almost its whole length. In contrast to the Beringian Chukotka [sector] the Beringian Alaska [sector] is situated almost entirely in southern hypoarctic tundra subzone [= Subzone E] and characterized by a still greater importance of boreal (including woodland) species. A few endemics in the general Beckwithia, Douglasia s.s., Papaver and Smelowskia are found here."
"Among the western co-differential taxa of the Beringian Alaska [sector], in common with the Chukotka Peninsula, there also prevail plants characteristic of more southern coasts of the Bering Sea and North Pacific, but there is a sufficient number of co-endemics (i.e. endemics shared by neighboring phytochoria) and subendemics of the maritime parts of Chukotka and Alaska (e.g. Artemisia globularia, Papaver walpolei, Rumex krausii, and Stellaria dicranoides = Arenaria chamissonis,) as well as predominantly Asian taxa (e.g. Oxygraphis glacialis, Rhododendron camtschaticum ssp. glandulosum and Saxifraga nudicaulis ssp. nudicaulis). The distribution pattern of many species is asymmetrical on the Asian and American side. Thus in Alaska, unlike Chukotka, Carex krausei, C. marina, Luzula rufescens avoid the coasts of the strait, while Rosa acicularis, and, to some extent, Dianthus repens and Silene repens, do not." (From Yurtsev 1994.)
- North Beringian Islands sector
"This area includes the Diomede Islands in the central part of Bering Strait along with St. Lawrence Island and St. Matthew Island in the northern, shallow part of the Bering Sea. Unlike the offshore islands, these four islands lack the majority of species characteristic of either coast of the strait, with the exception of a few Asian and American taxa. True oceanic species are more important here mostly also found on the Aleutian and Commander islands, for instance Nesodraba grandis on Big Diomede (Ramonov) Island and Conioselinium chinense on the St. Lawrence Islands (Young 1971)." (From Yurtsev 1994.)
- Northern Alaska sector
"This sector comprises the more continental (central and eastern) parts of the Brooks Range along with its northern foothills, and the Richardson Mts., as well as the Arctic slope of Alaska with its cold, true Arctic climate. The flora of the whole western part of the Brooks Range with its spurs and foothills is a transitional entity analogous, to some extent, to that of the Amguema area in Chukotka, with characteristic overlapping distribution areas of oceanic and continental (and other true Arctic) species. But the southwest-northeast gradient in both climate and floristic composition is well expressed even within the Seward Peninsula, [i.e. within the Beringian Alaska sector]."
"Among the differential and eastern co-differential taxa of the North Alaska [sector] those with a disjunction over the central parts of the Beringian [group] (including steppe plants) predominate over the purely American taxa. The secondary gaps in the distribution areas of continental species can be attributed to the influence of the Holocenic sea transgression on the climate." (From Yurtsev 1994.) The eastern boundary of this sector is disputed as mentioned above.