SUMMARY (Hayley): “A new method is presented on splitting the log – transformed taxa accumulation curve into sections (natural breaks where the curve deviates from a linear trend), with the hypothesis that breaks in the curve could indicate shifts in abundance between high (e.g. wind pollinated taxa) and low producers of pollen (e.g. insect pollinated taxa), this hypothesis is tested on pollen diagrams from three separate pollen diagrams from varying landscapes.”
SUMMARY (Adele): “This elegant paper highlights the changeability of pollen grains and their responses to their environment, giving those of us who identify pollen based on morphological characteristics plenty to think about.”
The PCRG contribution to the meeting was made by Hayley Keen who presented the first paper related to her doctoral research to an exteral audience entitled “Pollen counting for diverse tropical ecosystems”. The paper presented:
A statistical model (developed by co-author Felix Hanke) which simulaltes pollen counting in order to estimate the size of pollen count required to develop a robust ecological insight from the fossil pollen record, and
compared model predictions with empirical data from a diverse tropopical ecosystem (Mera, Ecuador) to assess the reliablity of the model.
It is hoped the application of the model to fossil pollen counting will allow more efficient and effective use of palynologists time. The paper was very well recieved despite the audible intake of breath when Hayley recommened that to characterize pollen richness (diversity) in some settings pollen counts in excess of 2000 grains might be required!
HOW DO WE UNDERSTANT PAST VEGETATION CHANGE? Our understating of vegetation in the past, and how it has changed through time, comes mainly from the examination of macrofossils (e.g. wood and leaves) and microfossils (e.g. pollen and spores) found in the sedimentary record. The potential for microscopic fossils to provide an insight into past vegetation change on a landscape scale was pioneered by von Post (Von Post, 1916, reprinted 1967) and has been subsequently used to understand changes in regional floras (Godwin, 1956), and address conservation issues (Willis et al., 2007). Analysis of fossil pollen and spores (palynology) is now widely used on late Quaternary timescales to answer ecological questions linking vegetation and wider environmental/climatic change; these include:
Has there been a change in major vegetation type (biome)? For example a change between woodlands and grassland vegetation.
How have the ecosystem dynamics altered? For example the presence or absence of fire.
How has the diversity within the ecosystem changed? For example increase or decrease in sample richness.
Palynological analysis relies on obtaining a sub-sample of the pollen contained within the sediment at a specific depth (time) which allows the vegetation at that time to be reconstructed. This sub-sample is known as a pollen count. To build up a picture of vegetation change through time it is necessary to generate a sequence of pollen counts. The size of the sub-sample (pollen count) required from any particular depth (time period) is dependent on the nature of the vegetation association being investigated and the ecological question being addressed . For example, the amount of pollen analysed to determine if the vegetation was predominantly wooded or grassland is different to that required to provide information on the biological diversity within the vegetation assemblage.
Discussed below are some of the conventions related to choosing an appropriate pollen count size within palynology, with particular reference to the challenges of dealing with diverse tropical floras.