Biology Reference
In-Depth Information
depending on the presence or absence of barriers and the dispersal poten-
tial of the propagules. Ecosystems are not composed of the same species in
the same proportions over interminable spans of time, and within limits,
they have had different composition, and may still be expanding their range
since the last of the eighteen to twenty cycles.
Although direct paleobotanical evidence is rare for Quaternary intervals
beyond the last glaciation, the North Greenland Ice Core Project Members
(NGRIP 2004) has recovered a record back 123,000 years into the last inter-
glacial. Climates were more stable in the interglacials than in the glacial and
glacial/interglacial transitions, and it was about 5°C warmer than today. All
this information, collectively, establishes a valuable context for interpreting
the Quaternary history of plant communities and ecosystems.
METHODOLOGIES
There are several ways of collecting material for Quaternary spore and pol-
len analysis, but the most common is to drill cores through peat bogs, lake
sediments, or near-shore coastal deposits. Samples are typically collected
every 10 cm along the core and processed by the techniques described in
chapter 4. Counts of at least 300 microfossils are usually made at each
level, and the percentage of each taxon is tabulated. Identifi cations are
made mostly to genus, occasionally to family (e.g., for the grasses, sedges,
and Chenopodiaceae-Amaranthaceae, recorded as chenoams); or to groups
of families (e.g., for some ferns and for the Taxodiaceae-Cupressaceae-
Taxaceae, recorded as t-c-t). The conventional method for presenting the
results is the spore and pollen diagram (fi g. 8.5). There are many of these
high-resolution records available, and they are now being databased to cover
extensive areas of, for example, North America and Greenland (Whitmore
et al. 2005).
Most diagrams include certain standard information. The depth in cen-
timeters, radiocarbon ages, and sediment type (peat, sand, charcoal, oxi-
dized, or artifact layers) are plotted along the vertical axis, and the percent-
age of each spore or pollen type is given on the horizontal axis. The change
through time for an individual taxon is called a profi le; all the types for any
one level constitute a spectrum; and the two together constitute the spore
and pollen diagram. The ratio of arboreal (tree) pollen (AP) to nonarbo-
real (herbaceous) pollen (NAP) gives an indication of closed, dense forest
(warm, moist conditions) versus open herbaceous vegetation, which often
refl ects either colder, drier conditions, perhaps with tundra or grassland,
or disturbances caused by fi re, epidemic disease, or human presence. Pol-
