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| Titel |
Predicting Pleistocene climate from vegetation in North America |
| VerfasserIn |
C. Loehle |
| Medientyp |
Artikel
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| Sprache |
Englisch
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| ISSN |
1814-9324
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| Digitales Dokument |
URL |
| Erschienen |
In: Climate of the Past ; 3, no. 1 ; Nr. 3, no. 1 (2007-02-12), S.109-118 |
| Datensatznummer |
250000745
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| Publikation (Nr.) |
 copernicus.org/cp-3-109-2007.pdf |
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| Zusammenfassung |
| Climates at the Last Glacial Maximum have been inferred from fossil pollen
assemblages, but these inferred climates are colder for eastern North
America than those produced by climate simulations. It has been suggested
that low CO2 levels could account for this discrepancy. In this study
biogeographic evidence is used to test the CO2 effect model. The
recolonization of glaciated zones in eastern North America following the
last ice age produced distinct biogeographic patterns. It has been assumed
that a wide zone south of the ice was tundra or boreal parkland
(Boreal-Parkland Zone or BPZ), which would have been recolonized from
southern refugia as the ice melted, but the patterns in this zone differ
from those in the glaciated zone, which creates a major biogeographic
anomaly. In the glacial zone, there are few endemics but in the BPZ there
are many across multiple taxa. In the glacial zone, there are the expected
gradients of genetic diversity with distance from the ice-free zone, but no
evidence of this is found in the BPZ. Many races and related species exist
in the BPZ which would have merged or hybridized if confined to the same
refugia. Evidence for distinct southern refugia for most temperate species
is lacking. Extinctions of temperate flora were rare. The interpretation of
spruce as a boreal climate indicator may be mistaken over much of the region
if the spruce was actually an extinct temperate species. All of these
anomalies call into question the concept that climates in the zone south of
the ice were extremely cold or that temperate species had to migrate far to
the south. An alternate hypothesis is that low CO2 levels gave an
advantage to pine and spruce, which are the dominant trees in the BPZ, and
to herbaceous species over trees, which also fits the observed pattern. Thus
climate reconstruction from pollen data is probably biased and needs to
incorporate CO2 effects. Most temperate species could have survived
across their current ranges at lower abundance by retreating to moist
microsites. These would be microrefugia not easily detected by pollen
records, especially if most species became rare. These results mean that
climate reconstructions based on terrestrial plant indicators will not be
valid for periods with markedly different CO2 levels. |
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