New insights on Beringian plant distribution patterns

Alaska Park Science, 2013

The history and geography of the arctic flora in Beringia has been complex—influenced by glacial retreats during the Quaternary, exchange via the Bering Land Bridge, in situ survival in refugia, and differing climatic regimes. Much of the details of these diversifications in Beringia are still lacking and to begin to address this issue we provide results from stochastic character mapping reconstruction to recover historical signals from occurrence data at the Herbarium, University of Alaska Fairbanks. A taxon matrix of 13 selected ecoregions in Beringia and 1549 extant vascular plant species was constructed and analyzed with RAxML and Mesquite software. The flora of Western Beringia appears younger than that of Eastern Beringia, with the ecoregions in Western Beringia derived from within those of Eastern Beringia. The Seward Peninsula ecoregion shares the most taxa with the ecoregions from Chukotka that form a clade. The Seward Peninsula is also the richest ecoregion, with 777 taxa recorded, a sharp contrast to the impoverished Bering Sea Islands ecoregions, where only 276 taxa are recorded. Overall, when examining stochastic mapping reconstructions, current species distributions in Beringia have been independently shaped by dispersal, extinction, and in some cases vicariance events due to ecological or physical barriers (e.g., Bering Strait). Mid-July temperature and precipitation differ across Beringia and at same latitudes, presenting a driver or “climatic barrier” for the overall ecosystem setup. Our study shows that distributional museum data can be informative in generating testable hypotheses on the history and evolution of the flora in an area such as Beringia.

Alsk Park Sci, 2009

We dedicate this science summary to the memory of Les Viereck (1930Viereck ( -2008, fellow Alaskan botanist, ecologist and contributor of many superb herbarium specimens to the ALA herbarium.

This review shows a close biogeographic connection between eastern Asia and western North America from the late Cretaceous to the late Neogene in major lineages of vascular plants (flowering plants, gymnosperms, ferns and lycophytes). Of the eastern Asian–North American disjuncts, conifers exhibit a high proportion of disjuncts between eastern Asia and western North America. Several lineages of ferns also show a recent disjunct pattern in the two areas. In flowering plants, the pattern is commonly shown in temperate elements between northeastern Asia and northwestern North America, as well as elements of the relict boreotropical and Neogene mesophytic and coniferous floras. The many cases of intercontinental biogeographic disjunctions between eastern Asia and western North America in plants supported by recent phylogenetic analyses highlight the importance of the Bering land bridge and/or the plant migrations across the Beringian region from the late Cretaceous to the late Neogene, especially during the Miocene. The Beringian region has permitted the filtering and migration of certain plant taxa since the Pliocene after the opening of the Bering Strait, as many conspecific taxa or closely related species occur on both sides of Beringia.

Aim The Bering Land Bridge (BLB) connected Asia and North America during glacial periods, supported a diverse ecosystem of now-vanished megafauna, and is a proposed glacial refugium. This study tests whether southern coastal Berin-gia was a refugium for woody taxa during the Last Glacial Maximum (LGM) and hypotheses about habitats available on the BLB before and after megafau-nal extinction. Location St. Paul Island, Alaska. Methods We analysed sediment cores from the Lake Hill, with a new age model anchored by 18 radiocarbon dates and multiple palaeoecological indicators (sedimentary ancient DNA [sedaDNA], macrobotanical fossils, and pollen) for the presence/absence of four woody genera: Picea, Betula, Alnus and Salix. We reconstructed vegetation history and compare St. Paul tundra composition to mainland counterparts. Results St. Paul has been continuously occupied by graminoid-forb tundra with prostrate shrubs (Salix, Ericaceae) since 18,000 years before present (yr bp). Fossil pollen of Picea, Pinus, Betula and Alnus is present in the Lake Hill sediments at low relative abundances and accumulation rates, consistent with long-distance transport. Macrobotanical fossils and sedaDNA analyses do not support Picea, Betula and Alnus presence. The St. Paul modern and fossil pollen assemblages are compositionally unlike mainland counterparts, but most closely resemble Arctic herbaceous tundra. Stratigraphically constrained cluster analysis indicates no major change in the vegetation after woolly mammoth extinction at 5600 yr bp, although Poaceae, Cyperaceae, Equisetum and forb abundances increase. Main conclusions This study strongly indicates that St. Paul and, by implication , southern coastal Beringia were not refugia for woody taxa during the LGM. The persistence of prostrate shrub-graminoid tundra supports interpretations that herbaceous tundra prevailed on southern Beringia during the LGM, whilst not ruling out the possibility of mesic shrub tundra in the interior. This herbaceous tundra supported an island refugium for woolly mammoth for 8000 years, showing no major vegetation composition changes after extinction.

Ecology, 2005

At northern high latitudes, biosphere responses to and interactions with climate warming are expected to be significant during the 21st century. Most predictions of climate-biosphere interactions rely on experiments and observations in contemporary landscapes, e.g., modern distributions of vegetation types and their structural features are used to delimit potential biosphere-atmosphere feedbacks. Paleorecords look beyond the present to examine vegetation configurations under climatic regimes that approximate future scenarios. To enhance the knowledge of arctic and subarctic ecosystems under varying climatic conditions, we analyzed pollen and macrofossil data from Beringia (northeast Siberia, Alaska, and northwest Canada; 130Њ E to 130Њ W) over the past 21 000 years, with a focus on structural and functional features of the vegetation. During the early Holocene (ϳ13 000-10 000 cal yr BP), shrub tundra ecosystems responded to climate warming through a shift from shrub tundra to deciduous forest or woodland. Early-Holocene vegetation was structurally, and hence functionally, novel compared with today's dominant vegetation types. ''Modern'' boreal forest developed in the mid-Holocene (ϳ10 000-6000 cal yr BP), when evergreen conifers expanded in much of the region. The shift from tundra to deciduous forest could have happened rapidly and in situ as the result of individual (phenotypic) and/ or population-scale responses to climate warming. Because the structural and functional properties of deciduous forest differ from those of evergreen coniferous forest and tundra, deciduous boreal forest should be included in the range of future scenarios used to assess the probable feedbacks of vegetation to the climatic system that result from global warming at northern high latitudes.

Ecology, 2005

At northern high latitudes, biosphere responses to and interactions with climate warming are expected to be significant during the 21st century. Most predictions of climate-biosphere interactions rely on experiments and observations in contemporary landscapes, e.g., modern distributions of vegetation types and their structural features are used to delimit potential biosphere-atmosphere feedbacks. Paleorecords look beyond the present to examine vegetation configurations under climatic regimes that approximate future scenarios. To enhance the knowledge of arctic and subarctic ecosystems under varying climatic conditions, we analyzed pollen and macrofossil data from Beringia (northeast Siberia, Alaska, and northwest Canada; 130Њ E to 130Њ W) over the past 21 000 years, with a focus on structural and functional features of the vegetation. During the early Holocene (ϳ13 000-10 000 cal yr BP), shrub tundra ecosystems responded to climate warming through a shift from shrub tundra to deciduous forest or woodland. Early-Holocene vegetation was structurally, and hence functionally, novel compared with today's dominant vegetation types. ''Modern'' boreal forest developed in the mid-Holocene (ϳ10 000-6000 cal yr BP), when evergreen conifers expanded in much of the region. The shift from tundra to deciduous forest could have happened rapidly and in situ as the result of individual (phenotypic) and/ or population-scale responses to climate warming. Because the structural and functional properties of deciduous forest differ from those of evergreen coniferous forest and tundra, deciduous boreal forest should be included in the range of future scenarios used to assess the probable feedbacks of vegetation to the climatic system that result from global warming at northern high latitudes.

Alaska Park Science, 2013

The Aleutian Islands and the Northern Bering Sea Islands have primarily upheld their status as distinct floristic subregions of the Arctic/Subarctic in published treatments, although multiple studies have also suggested a floristic similarity between the two island groups because of their oceanic influences and relative proximity. Using a combination of digitized occurrence data, review of pertinent literature, and recent floristic surveys across both island groups, we examined the influence of Asia on the island groups as well as their oceanic character. We restricted our comparison to the Western Aleutian Islands and the Northern Bering Sea Islands. Species composition was coarsely compared between the island groups by the number of overlapping species, distinctive species presence, and by the species’ growth habit. We also used Sørensen’s similarity coefficient as a statistical measure of difference between the island groups. The Western Aleutians (386 species, 0.47 species/square mile) were found to be separated from the Northern Bering Sea Islands (317 species, 0.16 species/square mile) by more than half of their floristic composition, with only 136 shared species between the two island groups, and were considerably more diverse in the number of species/area. The Western Aleutian Islands and the Northern Bering Sea Islands have similar proportions of forbs, graminoids, and shrubs/subshrubs in their flora, although the Western Aleutian Islands show ferns/fern allies in larger proportion than shrubs/subshrubs. Ferns are largely absent in the Northern Bering Sea Islands. The colder midsummer temperatures and Beringian biogeographical history of the Northern Bering Sea Islands may help explain the disparate floristic composition of these two island groups.

Journal of Vegetation Science, 1994

Journal of Systematics and Evolution, 2018

Beringia (eastern Asia, Alaska, northwest Canada) has been a land-bridge dispersal route between Asia and North America intermittently since the Mesozoic Era. The Quaternary, the most recent period of exchange, is characterized by large, geologically rapid climate fluctuations and sea-level changes that alternately expose and inundate the land-bridge region. Insights into how Quaternary land-bridge geography has controlled species exchange and assembly of the North American flora comes from focusing on a restricted community with narrow ecological tolerances: species that are today restricted to isolated steppe habitats (dry grasslands) in the Subarctic. We evaluated (i) potential controls over current spatial distributions of steppe plants and their pollinators in Alaska and Yukon and (ii) their ecological distributions in relation to potential biogeographic histories. Taxa present in North America that are disjunct from Asia tended to have larger altitudinal ranges (tolerating colder temperatures) than taxa disjunct from farther south in North America, which were largely restricted to the warmest, lowestelevation sites. Ecological findings support the following biogeographic scenarios. Migration from Asia via the land-bridge occurred during Quaternary glacial periods when conditions were colder and drier than today. While a corridor for migration of cold-tolerant species of cold steppe and tundra, the land bridge acted as a filter that excluded warmth-demanding species. Migration from North America occurred under warm, dry interglacial conditions; thermophilous North American disjuncts taking this route may have long histories in Beringia, or they may have migrated recently during the relatively warm and dry early Holocene, when forest cover was incomplete.

Journal of Biogeography, 2000

The objective biomization method developed by Prentice et al. (1996) for Europe was extended using modern pollen samples from Beringia and then applied to fossil pollen data to reconstruct palaeovegetation patterns at 6000 and 18,000 14 C yr bp. The predicted modern distribution of tundra, taiga and cool conifer forests in Alaska and northwestern Canada generally corresponds well to actual vegetation patterns, although sites in regions characterized today by a mosaic of forest and tundra vegetation tend to be preferentially assigned to tundra. Siberian larch forests are delimited less well, probably due to the extreme under-representation of Larix in pollen spectra. The biome distribution across Beringia at 6000 14 C yr bp was broadly similar to today, with little change in the northern forest limit, except for a possible northward advance in the Mackenzie delta region. The western forest limit in Alaska was probably east of its modern position. At 18,000 14 C yr bp the whole of Beringia was covered by tundra. However, the importance of the various plant functional types varied from site to site, supporting the idea that the vegetation cover was a mosaic of different tundra types.