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Modelling Spatial Compositional Data : Reconstructions of past land cover and uncertainties

Author:
  • Behnaz Pirzamanbein
  • Johan Lindström
  • Anneli Poska
  • Marie José Gaillard
Publishing year: 2018-04-01
Language: English
Pages: 14-31
Publication/Series: Spatial Statistics
Volume: 24
Document type: Journal article
Publisher: Elsevier

Abstract english

In this paper we construct a hierarchical model for spatial compositional data which is used to reconstruct past land-cover compositions (in terms of coniferous forest, broadleaved forest, and unforested/open land) for five time periods during the past 6000 years over Europe. The model consists of a Gaussian Markov Random Field (GMRF) with Dirichlet observations. A block updated Markov chain Monte Carlo (MCMC), including an adaptive Metropolis adjusted Langevin step, is used to estimate model parameters. The sparse precision matrix in the GMRF provides computational advantages leading to a fast MCMC algorithm. Reconstructions are obtained by combining pollen-based estimates of vegetation cover at a limited number of locations with scenarios of past deforestation and output from a dynamic vegetation model. To evaluate uncertainties in the predictions a novel way of constructing joint confidence regions for the entire composition at each prediction location is proposed. The hierarchical model's ability to reconstruct past land cover is evaluated through cross validation for all time periods, and by comparing reconstructions for the recent past to a present day European forest map. The evaluation results are promising, and the model is able to capture known structures in past land-cover compositions.

Keywords

  • Physical Geography
  • Probability Theory and Statistics
  • Adaptive Metropolis adjusted Langevin
  • Confidence regions
  • Dirichlet observation
  • Gaussian Markov Random Field
  • Pollen records

Other

Published
  • ISSN: 2211-6753
E-mail: anneli [dot] poska [at] nateko [dot] lu [dot] se

Department of Physical Geography and Ecosystem Science
Lund University
Sölvegatan 12
S-223 62 Lund
Sweden

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