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Quaternary environments and N. hemisphere temperate
forests Distribution Holocene dynamics The interglacial cycle “Long core” records Last Glacial Maximum refuges Migrations (rates and agents) Genetic divergence Quaternary extinctions
Global distribution of temperate forests
Temperate forest
30°N
45°N
60°N
45°S
60°S
30°S
15°S
15°N
Eq.
Pollen sites,
easternNorth
America
Pollen diagram, Kirchner Marsh, Minnesota.
from: Webb (1980) J. Interdisciplinary History, 10, 749-772.
Reconstructing post-glacial climate change (Kirchner Marsh, MINN)
Reconstructing post-glacial vegetation change at a site
The post-glacial (Blytt-Sernander) sequence
Interglacial cycle of
vegetation and soils
(based on Iversen, 1948)
Interglacial vegetation succession, Japan
ClimatePhase Dominants Temperature Moisture
Upper Cryptomeria, Sciadopitys Temperate Wet
Middle Cyclobalanopsis, Warm Wet Castanopsis
Lower Fagus, Lepidobalanus Cool Wet
from: Miyoshi et al., (1999) Rev. Palaeobot. Palynol, 104, 267-283.
Is there a repetitive
interglacial cycle?
e.g. vegetation succession in mid to late Quaternary
interglacials in Britain
Does an increase in Pinus signal the end of an
interglacial?
Kirchner Marsh, MINN.
> 50 ka >100 ka
Long cores from temperate forest areas
30°N
45°N
60°N
45°S
60°S
30°S
15°S
15°N
Eq.
from: PAGES website
Pollen record, Lago di
Monticchio (Italy)
Pollen record, Grande
Pile (France)
From: Guiot (1998) Nature 388, 25-27.
Pollen record, Lake Biwa
(Japan)Pinus = cool indicator;
Cryptomeria = warmIndicator;
Artemisia -grass-herb (not shown)
“steppe/tundra” in full-glacial phases
Pollen record, Carp Lake, WA.
from: Whitlock and Bartlein (1997) Nature, 388, 57-61.
from: Whitlock and Grigg, in: Webb et al., (1999) Mechanisms of Global Change at Millenial Time Scales, AGU Monograph, p 227-
241.
Heinrich events
recorded at Lake Tulane,
FLA.
Present (potential)vegetation
of North America
Biome maps from: www.esd.ornl.gov/projects/qen
LGM vegetatio
n(18 ka 14C yrs BP):North
America
Present (potential
)vegetatio
n of Europe
LGM vegetatio
n(22-14 ka
14C yrs BP):
Europe
LGM (a) and present (b) pollen and vegetation (c,d) patterns in East Asia
from
: H
arr
ison e
t al. (
20
01
) N
atu
re 4
13
, 1
29
-13
0.
NB continental shelf extent
Reconstructing LGM refuges and post-glacial migrations: isopoll data
from: Davis and Shaw (2001) Science 292, 673-679.
LGM refuges (R) and post-glacial
isochrons in eastern North
America. Where there
separate Atlantic and Gulf refuges?
R?
R?
R?
R?White pine
E. hemlock
Oaks
Elms
How quickly did trees migrate in eastern North America in the post-
glacial?
0 100 200 300 400 500
Jack/Red pineWhite pine
SpruceLarch
ElmHemlock
Balsam firMapleBeech
OakHickory
Chestnut
m / yr
Data: Davis; in West et al. (1980) “Forest Succession: Concepts and Applications”. Springer-Verlag p. 153; and Delcourt and Delcourt (1987) “Quaternary Ecology” (after Webb, 1986)
(=a x b)
(a)
(b)
(c)
(=a x c)
Was the rate of post-glacial
migration controlled by
rates of climatic
change or seed size?
m /
year
Data: see previous slide and USDA (1974) “Seeds of Woody Plants in the
United States” Agric. Handbook No. 450.
500
400
300
200
100
0
seed wt. (mg)1 10 100 1 000 10 000
oaks
whitepine
sprucelarch
elm
hemlockhickory
maplefir
beech
chestnut
jack pine
red pine
Are seed-caching birds the main agents of
dispersal in post-glacial time for ‘nut trees’?
Fagus grandiflora
Quercus macrocarpa
blue jay passenger pigeon
see: Webb (1986) Quat. Res. 26, 367-375for discussion
Postglacial fossil finds:passenger
pigeon (dots)
and blue jay
(triangles )
from: Delcourt and Delcourt (1987) “Quaternary Ecology”
Were some endochorous temperate trees marooned?
(i.e. refugial relicts?)e.g. Maclura pomifera
(osage orange) fruit weighs up to 1 kg
Source: USDA Handbook - Silvics of Forest Trees
Range
Was this a product of the extinction of
potential megafaunal
vectors?
e.g. Megalonyx
jeffersoni(Jefferson’s
ground-sloth)extinct by 10ka BP
Did post-glacial migration result in reduced genetic diversity in northern
populations?Allelic diversity
low highfrom: Cwynar and MacDonald (1988) Amer. Nat. 129, 463-469.
Colonizationdate in ka BP
from pollen data
Which refugial
populations supply the migrants?
e.g.Fagus crenata
(a montane species during interglacials) recolonized northern
Honshu and Hokkaido from
northern coastal refuges after LGM
LGMcoastalrefuges
from: Davis and Shaw (2001) Science 292, 673-679.
Hypothetical refugia and migration paths of Alnus rubra
since the LGM based on genetic variation
from: Hamann et al., (1998) Can. J. Forest Res., 28, 1557-1565.
Post-glacial colonization routes of tree species based
on DNA variation
Fagus sylvatica Quercus sp.
Taberlet et al., (1998) Molecular Ecology 7, 453-464
Post-glacial colonization routes of tree species based
on DNA variation
Taberlet et al., (1998) Mol. Ecol. 7, 453-464; Scottii et al. (2000) Mol. Ecol. 9, 699-708.
Abies alba Picea abies
Post-glacial colonization routes of animals based on DNA
variation
from: Hewitt (2000) Nature, 405, 907-913.
Post-glacial colonization routes of
animals and
subsequenthybrid contact zones
from: Hewitt (2000) Nature, 405, 907-913.
From: Jackson and Weng (1999) Proc. Nat. Acad. Sci. US, 96, 13847-13852.
Extinction: Picea critchfeldii was a dominant tree
in eastern North America in LGM; it died out about 15 000 cal. yrs
BP
Above: cross-sections of needles (E-G are P. critchfeldii).
Left: cones of P. critchfeldii
Why is the European forest depauperate?
Quercus (oak)Acer (maple)
Fagus (beech)Castanea (chestnut)
Carya (hickory)Ulmus (elm)
Tilia (basswood)Juglans (walnut)
Liquidambar (sweet gum) Nyssa (sour
gum)
E N Am Europe E AsiaX X XX X XX X XX X XX F XX X XX X XX X XX F XX F X
X = extant; F = fossil
Quaternary extinctions of trees in the Netherlands
loss ofsub-tropicalgenera
Causes of Quaternary plant extinctions
1. Abrupt climate change?
2. Barriers to migration (e.g. E-W
mountain ranges)?
3. Loss of seed dispersal agents?