Waller, Martyn and Grant, Michael (2011) The interpretation of Holocene pollen assemblages from coastal lowlands: differentiating natural and anthropogenic causal processes and the problems of equifinality. In: XVIII INQUA Congress: Quaternary sciences – the view from the mountains; 21-27 Jul 2011, Bern, Switzerland.

Abstract

Holocene pollen assemblages from coastal lowlands and lowland floodplains often suggest changes occurring simultaneously within both wetland and dryland source areas. Evidence for wetter and more open conditions are frequently accompanied by increases in taxa regarded as anthropogenic indicators. A number of different scenarios can be proposed. Coastal / floodplain processes alone could be responsible, with changes in the wetland vegetation modifying the way in which the dryland vegetation is sensed in the pollen record. Coincidence is also plausible, as wetland change in such environments can be driven by natural processes which operate over extended periods of time (e.g. relative sea-level change). Simultaneous changes might also result from anthropogenic activity impacting on both areas or from dry land woodland destruction producing a hydrological response (though in a temporally well resolved sequence a delay should be evident). The lack of taxonomic precision in the pollen identification of key taxa (e.g. Poaceae and Cyperaceae), and in particular the ability to separate Cereal pollen from certain wild grasses, is a major limitation when attempting to distinguish between these scenarios. However, coincidence can be seen as an easy explanation and its routine acceptance removes the opportunity for improving our understanding of these processes and their potential interaction. Examples of pollen assemblages which appear to show simultaneous changes in wetland and dryland vegetation will be given from a number of areas in the UK (the East Anglian Fenland, Thames estuary, Romney Marsh) along with the results of recent investigations from two sites in the Thames estuary where high temporal resolution, improved taxonomic procedures and multivariate statistics provide new insights into the interpretation of pollen data from coastal and floodplain settings.

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