Anoxic conditions are generally good for pollen preservation. Pollen grains may show different degrees of deterioration depending on the thickness and type of exine. Therefore a selective deterioration may occur in highly calcareous or oxidative sediments, or when hydratation-dehydratation cycles occurred.

There are no reason to have a selective deterioration of pollen (gametophyte) based on the habitus of the sporophyte.

If a deterioration occurred in these samples, I think that it has not involved only pollen grains of trees, and that it was not related to the anoxic conditions.

If the deterioration has not occurred, possible explanations of the absence of trees may be that trees were truly few (open grassland?) and with low pollen productivity; some high-productive pollen therefore masked rare pollen grains.

I suggest to count more pollen grains or to prepare again the samples.

And what about herbaceous pollen?

What is the age of sediments?

Anoxic conditions are generally good for pollen preservation. Pollen grains may show different degrees of deterioration depending on the thickness and type of exine. Therefore a selective deterioration may occur in highly calcareous or oxidative sediments, or when hydratation-dehydratation cycles occurred.

There are no reason to have a selective deterioration of pollen (gametophyte) based on the habitus of the sporophyte.

If a deterioration occurred in these samples, I think that it has not involved only pollen grains of trees, and that it was not related to the anoxic conditions.

If the deterioration has not occurred, possible explanations of the absence of trees may be that trees were truly few (open grassland?) and with low pollen productivity; some high-productive pollen therefore masked rare pollen grains.

I suggest to count more pollen grains or to prepare again the samples.

Dear Anna, thanks for such a nice explanation.

Could you please suggest me some reference about 'deterioration of pollens in calcareous layers'.

Dear Dimiter

None of the pollen preserve in the sediment (not even herbaceous pollens).

The age of sediments is early holocene.

Hi Preveen. Ana explains perfect. The lack of pollen is strange. Can you give more information - type of sediments, position of core, etc. May be something in chenical treatement is wrong? .....

Hi Praaven, I have not understood well your reply to Dimiter, but if you have not pollen grains (not trees nor herbs) you have to check the pollen treatments and the other variables that Dimiter has suggested.

About polen preservation, there is a 'classic' paper:

Hall S.A. 1981 - Deteriorated pollen grains and the interpretation of quaternary pollen diagrams. Review of palynology and palaeobotany, 32: 193-206

You can find information also in these books:

Dimbleby, G., 1985. The Palynology of Archaeological Sites. Academic Press, London.

Horowitz, A., 1992. Palynology of Arid Lands. Elsevier, Amsterdam.

Traverse A. 2005. Sedimentation of organic particles. Cambridge.

These are also recent papers that I have not read yet:

Wilmshurst and McGlone 2005, Corroded pollen and spores as indicators of changing lake sediment sourcesand catchment disturbance. Journal of palaeolimnology, 34: 503-517

Twiddle and Bunting 2010, Review of palynology and palaeobotany, 162: 621-630

What extraction process did you use to recover the pollen? Please list the chemicals, the order, and basically the steps you took. Also whether the step was at room temperature or heated. For instance, did you use bleach (Sodium hypochlorite)?

Hello praveen, how's the ur core sedimets nature , you just inform me. core sediments containing sand, silt, clay or silt clay or black color sticky clay? because i am also working on the core sediments, so i used palynological technique for pollen analysis at Birbal sahani institute of paleobotany. i got pollent into sticky clay sediments.

I am in agree with Anna María Mercuri. In fact, pollen cores from northwestern Spain show that anoxic conditions preserved well tree pollen types