The Holocene vegetation cover of Britain and Ireland: overcoming problems of scale and discerning patterns of openness

Abstract

The vegetation of Europe has undergone substantial changes during the course of the Holocene epoch, resulting from range expansion of plants following climate amelioration, competition between taxa and disturbance through anthropogenic activities. Much of the detail of this pattern is understood from decades of pollen analytical work across Europe, and this understanding has been used to address questions relating to vegetation-climate feedback, biogeography and human impact. Recent advances in modelling the relationship between pollen and vegetation now make it possible to transform pollen proportions into estimates of vegetation cover at both regional and local spatial scales, using the Landscape Reconstruction Algorithm (LRA), i.e. the REVEALS (Regional Estimates of VEgetation Abundance from Large Sites) and the LOVE (LOcal VEgetation) models. This paper presents the compilation and analysis of 73 pollen stratigraphies from the British Isles, to assess the application of the LRA and describe the pattern of landscape/woodland openness (i.e. the cover of low herb and bushy vegetation) through the Holocene. The results show that multiple small sites can be used as an effective replacement for a single large site for the reconstruction of regional vegetation cover. The REVEALS vegetation estimates imply that the British Isles had a greater degree of landscape/woodland openness at the regional scale than areas on the European mainland. There is considerable spatial bias in the British Isles dataset towards wetland areas and uplands, which may explain higher estimates of landscape openness compared with Europe. Where multiple estimates of regional vegetation are available from within the same region interregional differences are greater than intra-regional differences, supporting the use of the REVEALS model to the estimation of regional vegetation from pollen data.

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

“…These results support the findings of Mazier et al (2012) and Fyfe et al (2013), and confirm that the theoretical framework of the REVEALS model (Sugita 2007a) can be applied in empirical situations. Monte Carlo permutation tests suggest that the number of small sites is the most significant variable explaining the REVEALS estimates, followed by the location within a regional vegetation unit, the type of site (bog or lake, i.e.…”

“…The variability of pollen assemblages from small sites is often high, which explains the large error estimates on REVEALS results based on pollen data from small sites. Empirical tests (Mazier et al 2012;Fyfe et al 2013) using pollen data from multiple small sites (lakes and/or bogs) support the theory, i.e. the results from Sugita simulations (2007a).…”

“…Further, for all runs (RUNS 1 and 2-5), the tri-plots of the RDA analyses show that the variable ''number of sites'' is positively correlated to the variable ''bog'' and negatively correlated to the variable ''lake'', which implies that the number of site is an important variable for small bogs, but not necessarily for small lakes. Fyfe et al (2013) also showed that a low number of small lakes often provide REVEALS estimates comparable to those from large lakes, while a higher number of bogs is needed to obtain good REVEALS estimates.…”

“…Nielsen and Odgaard 2010;Cui et al 2013Cui et al , 2014Mazier et al 2015;Hultberg et al 2015), (ii) the study of regional spatio-temporal land-cover/landscape dynamics over the past millennia (e.g. Marquer et al 2014;Fyfe et al 2013;Nielsen et al 2012;Trondman 2014), (iii) the evaluation of anthropogenic land-cover change scenarios (ALCCs) (Gaillard et al 2010) and (iv) the study of land cover-climate interactions in the past (Strandberg et al 2014). Recently, Pirzamanbein et al (2014) developed a set of statistical models to create spatially continuous maps of past land cover by combining (i) pollen-based REVEALS ''point estimates'' of past land cover and (ii) spatially continuous estimates of past land cover, obtained by merging simulated potential vegetation (using the LPJ-GUESS model; Smith et al 2001) with an anthropogenic land-cover change scenario (KK10; Kaplan et al 2009).…”

From deciduous forest to open landscape: application of new approaches to help understand cultural landscape development in western Norway

“…So far, estimates achieved from this approach are found to be representative of the vegetation in Denmark, Switzerland, Sweden, Estonia and Norway (Hellman et al 2008;Nielsen and Odgaard 2010;Soepboer et al 2010;Fredh 2012;Cui et al 2013;Overballe-Petersen et al 2013;Poska et al 2014;Hjelle et al 2015), and it has been applied to reconstruct vegetation cover on different spatial scales (e.g. Nielsen et al 2012;Fyfe et al 2013;Cui et al 2014;Marquer et al 2014;Hultberg et al 2015;Trondman et al 2015).…”