Abstract
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.
Highlights
High northern latitudes such as northern Asia experience above-average temperature increases in times of past and recent global warming (Serreze et al, 2000; IPCC, 2007), known as polar amplification (Miller et al, 2010)
Vegetation changes in northern Asia within the Holocene are rather minor with only slight changes in plant functional type (PFT) abundances
Cluster analyses of grouped vegetation records from the Holocene find five clusters (Fig. A3). Their spatial distribution is largely consistent with the distribution of modern vegetation types as characterized by certain PFTs. (1) Records from the forest–steppe ecotone (e.g. G12, G21; Fig. 2a) in north-central China and the Tianshan
Summary
High northern latitudes such as northern Asia experience above-average temperature increases in times of past and recent global warming (Serreze et al, 2000; IPCC, 2007), known as polar amplification (Miller et al, 2010). Temperature rise is expected to promote vegetation change as the vegetation composition in these areas is assumed to be controlled mainly by temperature X. Cao et al.: Pollen-based quantitative land-cover reconstruction mainly because vegetation is not linearly related to temperature change (e.g. due to resilience, stable states, or timelagged responses; Soja et al, 2007; Herzschuh et al, 2016) and/or vegetation is only indirectly limited by temperature while other temperature-related environmental drivers such as permafrost conditions are more influential (Tchebakova et al, 2005)
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