Palynological perspectives on vegetation survey: a critical step for\ud model-based reconstruction of Quaternary land cover

摘要

1. Quantitative reconstruction of past vegetation distribution and abundance from sedimentary pollen\udrecords provides an important baseline for understanding long term ecosystem dynamics and for the\udcalibration of earth system process models such as regional-scale climate models, widely used to predict\udfuture environmental change. Most current approaches assume that the amount of pollen produced by\udeach vegetation type, usually expressed as a relative pollen productivity term, is constant in space and\udtime.\ud2. Estimates of relative pollen productivity can be extracted from extended R-value analysis (Parsons\udand Prentice, 1981) using comparisons between pollen assemblages deposited into sedimentary contexts,\udsuch as moss polsters, and measurements of the present day vegetation cover around the sampled\udlocation. Vegetation survey method has been shown to have a profound effect on estimates of model\udparameters (Bunting and Hjelle, 2010), therefore a standard method is an essential pre-requisite for\udtesting some of the key assumptions of pollen-based reconstruction of past vegetation; such as the\udassumption that relative pollen productivity is effectively constant in space and time within a region or\udbiome.\ud3. This paper systematically reviews the assumptions and methodology underlying current models of\udpollen dispersal and deposition, and thereby identifies the key characteristics of an effective vegetation\udsurvey method for estimating relative pollen productivity in a range of landscape contexts.\ud4. It then presents the methodology used in a current research project, developed during a practitioner\udworkshop. The method selected is pragmatic, designed to be replicable by different research groups,\udusable in a wide range of habitats, and requiring minimum effort to collect adequate data for model\udcalibration rather than representing some ideal or required approach. Using this common methodology\udwill allow project members to collect multiple measurements of relative pollen productivity for major\udplant taxa from several northern European locations in order to test the assumption of uniformity of\udthese values within the climatic range of the main taxa recorded in pollen records from the region.