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Pollen-based quantitative land-cover reconstruction for northern Asia covering the last 40 ka cal BP

Abstract. We collected the available relative pollen productivity estimates (PPEs) for
27 major pollen taxa from Eurasia and applied them to estimate plant
abundances during the last 40 ka cal BP (calibrated thousand years before
present) using pollen counts from 203 fossil pollen records in northern Asia
(north of 40∘ N). These pollen records were organized into 42
site groups and regional mean plant abundances calculated using the REVEALS
(Regional Estimates of Vegetation Abundance from Large Sites) model.
Time-series clustering, constrained hierarchical clustering, and detrended
canonical correspondence analysis were performed to investigate the regional
pattern, time, and strength of vegetation changes, respectively.
Reconstructed regional plant functional type (PFT) components for each
site group are generally consistent with modern vegetation in that
vegetation changes within the regions are characterized by minor changes in
the abundance of PFTs rather than by an increase in new PFTs, particularly
during the Holocene. We argue that pollen-based REVEALS estimates of plant
abundances should be a more reliable reflection of the vegetation as pollen
may overestimate the turnover, particularly when a high pollen producer
invades areas dominated by low pollen producers. Comparisons with
vegetation-independent climate records show that climate change is the
primary factor driving land-cover changes at broad spatial and temporal
scales. Vegetation changes in certain regions or periods, however, could not
be explained by direct climate change, e.g. inland Siberia, where a
sharp increase in evergreen conifer tree abundance occurred at ca. 7–8 ka cal BP despite an unchanging climate, potentially reflecting their response
to complex climate–permafrost–fire–vegetation interactions and thus a
possible long-term lagged climate response.
