by Michelle Farrell (@DrM_Farrell)
To around 20% of the
|Coring to retrieve pollen-bearing sediments from a bog|
on Orkney, Scotland
|The stripes in this core segment indicate that the sediments|
were deposited under different environmental conditions
|Betula (birch) pollen: trizonoporate, |
with three pores arranged equidistantly
around the equator of the grain
|Fraxinus excelsior (common ash) pollen: |
trizonocolpate, with three furrows arranged
equidistantly around the equator of the grain
|Rumex obtusifolius (broad-leaved dock):|
tetrazonocolporate, with four apertures
made up of both colpi and pori
|Plantago lanceolata (ribwort plantain): |
polypantoporate, with many pores scattered
all over the surface of the grain
The pattern of sculpturing found on the surface of the exine is another crucial factor in the identification of pollen grains. Around fifteen different surface patterns have been described, and two of the more distinctive patterns are shown in the images below.
|Cirsium arvense (creeping thistle) pollen, a|
good example of echinate surface sculpture
|Ulmus (elm) pollen, displaying rugulate|
Size can also be important in distinguishing between pollen taxa, particularly members of the grass family. The two images below show the difference in size between a wild grass, Phragmites australis (common reed) and a cultivated grass, Triticum aestivum (wheat).
|Phragmites australis (common reed) pollen|
|Triticum aestivum (wheat) pollen|
The identification and recording of pollen grains from different depths within a sediment core can be used to provide information on how the vegetation surrounding the core site has changed over time. Sediment cores can often be accurately dated using radiocarbon, allowing the changes in environment to be tied to a chronology. Palynology has great potential for providing baseline data for the development of conservation management strategies, and is also useful from an ecological perspective as it can give insights into how plant communities have responded to climate change in the past, thereby allowing predictions to be made about how vegetation and ecosystems may be affected by future climate change.
One of my main research interests is in the use of palynology as a tool to unpick the ways in which humans interacted with their environments during the Holocene (the period since the end of the last ice age, approximately 11,500 years ago, until the present day). I intend to write more about the archaeological applications of palynology in future posts, but as a taster, it is possible to determine when people began farming in an area, what crops they were growing, where they grazed their animals, whether they cleared woodland to create more land for agriculture, and how they contributed to the development of cultural landscapes such as heathlands. It is also possible to investigate the ways in which people may have managed their environments and responded to climate change in the past, for example managing heathland by deliberate burning in order to maintain the quality of grazing. It may even be possible to detect woodland management practices such as coppicing, and Jane Bunting will write about her work on this in the next GEES-ology post.