Pollen‐based quantitative reconstructions of Holocene regional vegetation cover (plant‐functional types and land‐cover types) in Europe suitable for climate modelling

Abstract

We present quantitative reconstructions of regional vegetation cover in northwestern Europe, western Europe north of the Alps, and eastern Europe for five time windows in the Holocene [around 6k, 3k, 0.5k, 0.2k, and 0.05k calendar years before present (BP)] at a 1° 9 1° spatial scale with the objective of producing vegetation descriptions suitable for climate modelling. The REVEALS model was applied on 636 pollen records from lakes and bogs to reconstruct the past cover of 25 plant taxa grouped into 10 plant-functional types and three land-cover types [evergreen trees, Correspondence: A.-K. Trondman, tel. + 46 (0)480 44 61 98, fax + 46 (0)480 44 73 40, Global Change Biology summer-green (deciduous) trees, and open land]. The model corrects for some of the biases in pollen percentages by using pollen productivity estimates and fall speeds of pollen, and by applying simple but robust models of pollen dispersal and deposition. The emerging patterns of tree migration and deforestation between 6k BP and modern time in the REVEALS estimates agree with our general understanding of the vegetation history of Europe based on pollen percentages. However, the degree of anthropogenic deforestation (i.e. cover of cultivated and grazing land) at 3k, 0.5k, and 0.2k BP is significantly higher than deduced from pollen percentages. This is also the case at 6k in some parts of Europe, in particular Britain and Ireland. Furthermore, the relationship between summer-green and evergreen trees, and between individual tree taxa, differs significantly when expressed as pollen percentages or as REVEALS estimates of tree cover. For instance, when Pinus is dominant over Picea as pollen percentages, Picea is dominant over Pinus as REVEALS estimates. These differences play a major role in the reconstruction of European landscapes and for the study of land cover-climate interactions, biodiversity and human resources.

Are pollen records from small sites appropriate for REVEALS model-based quantitative reconstructions of past regional vegetation? An empirical test in southern Sweden

“…The possible overestimation of open land cover in REVEALS reconstructions using Poaceae as an indicator of open land is discussed further in Trondman et al (2015). For the three land-cover types (LCTs) summer-green trees (ST), evergreen trees (ET), and open land (OL), REVEALS generally performs much better, which confirms the results of Hellman et al (2008a).…”

“…All pollen records are from the LANDCLIM pollen data archive (Trondman 2014); the sites are listed in Table 1 with their characteristics. The methods applied to build up the chronologies, and the criteria used to define a chronology as ''reliable'' are described in Trondman et al (2015). There are 21 sites in the temperate zone, 13 sites in the hemiboreal zone, and six sites in the southern boreal zone (Fig.…”

“…We chose to work with the same five Holocene time windows as those used in the LANDCLIM project (Gaillard et al 2010;Mazier et al 2012;Trondman et al 2015), i.e. x-100 cal BP (ca.…”

“…the study of the effect of anthropogenic land-cover change on climate. We also used the same chronologies for the pollen records as those applied in the LANDCLIM project (Mazier et al 2012;Trondman et al 2015) except for the sites Ekenäs and Skärsgölarna. For those two sites, new age-depth models were established using the computer program clam version 2.1 (Blaauw 2010) that implements the IntCal09 calibration curve of Reimer et al (2009).…”

“…The mean REVEALS estimates were than calculated for small lakes and bogs together using the ''Bog-Lake fusion program'' (Sugita, unpublished computer program bog.lake.data.fusion.24Nov10.v5.exe). We used the same 25 plant taxa, PPEs, FSPs, and grouping of the 25 taxa into three land-cover types (LCTs) as the LANDCLIM project (Table 2; Mazier et al 2012;Trondman et al 2015); however, Abies (first taxon in Table 2) was not present in southern Sweden at any time in the Holocene and therefore only 24 taxa were reconstructed in this study. We kept the same taxon numbers for convenience; this implies that the 24 reconstructed taxa are numbers 2-25 in Table 2 and in Figs.…”