Floristic diversity in the transition from traditional to modern land-use in southern Sweden a.d. 1800–2008

Daniel Fredh 0 1 2 Anna Brostrom 0 1 2 Lovisa Zillen 0 1 2 Florence Mazier 0 1 2 Mats Rundgren 0 1 2 Per Lageras 0 1 2 0 P. Lageras Swedish National Heritage Board, Archaeological Excavations Department UV Syd , Odlarevagen 5, 226 60 Lund, Sweden 1 F. Mazier GEODE, UMR 5602, University of Toulouse-Le Mirail , 5 allees A. Machado, 31058 Toulouse Cedex, France 2 D. Fredh (&) A. Brostrom L. Zillen M. Rundgren Department of Geology, Quaternary Sciences, Lund University , Solveg. 12, 22362 Lund, Sweden We aim to provide a long-term ecological analysis of land-use and floristic diversity in the transition from traditional to modern land-use management in the time A.D. 1800-2008 in southern Sweden. We use the Regional Estimates of Vegetation Abundance from Large Sites (REVEALS) model to quantify land-cover changes on a regional scale at 20-year intervals, based on the fossil pollen record. Floristic richness and evenness are estimated using palynological richness and the Shannon index applied to the REVEALS output, respectively. We identified a transition period of 60 years between 1880 and 1940 when the total tree cover increased and the tree composition changed from deciduous to coniferous dominance. Within the shrinking area of open land, arable land taxa expanded, while the number and coverage of herbs in the remaining grasslands decreased. The succession from open grasslands to more tree-covered habitats initially favoured palynological richness, which reached its highest values during the first 40 years of the transition period. The highest REVEALS-based evenness was recorded in the time of traditional land-use and at the beginning of the transition period, reflecting higher habitat diversity at these time intervals. Our results support a more dynamic ecosystem management that changes between traditional land-use and phases of succession (40 years) to promote floristic diversity. We have developed and applied a palaeoecological methodology that contributes realistic estimates to be used in ecosystem management. - The Convention of Biological Diversity has agreed upon a new strategy for 2020 including 20 biodiversity targets to be implemented internationally, which will eventually modify the European environmental objectives. For this purpose we need to develop integrated science-based ecosystem management tools for biodiversity assessment which use multiple sources of information and approaches including direct observations, palaeoecological records, experiments, climate models, mechanistic ecophysiological models and population models (Dawson et al. 2011). Although possible future climates and land-use will most likely be very different from those of the past, palaeoecological records offer essential information about rates and degrees of vegetation change (Jackson and Hobbs 2009; Haslett et al. 2010; Willis et al. 2010; Willis and Bhagwat 2010). Traditional land-use during the last millennia in Europe has led to a landscape with high biodiversity (Berglund 1991; Emanuelsson 2009). However, the transition to modern land-use management in the last century has allowed only small parcels of habitats related to traditional cultural landscapes to remain. These remaining habitats, in particular those with high biodiversity, have, over the last few decades, been the focus for nature conservancy efforts (Eriksson et al. 2002; Poschlod et al. 2005; Plieninger 2006; Emanuelsson 2009). Several of these habitats, for example semi-natural grasslands and woodlands, have recently been recognized, according to the concept of ecosystem services, as providing various services to humanity, such as services which provide resources such as of food and timber and cultural resources such as aesthetic values and recreation (MA 2005; Harrison et al. 2010). The nature conservancy management of these areas has predominantly been through continuous land-use, such as over-grazing of meadows and pastures, or by leaving seminatural woods unmanaged, and has led to a decrease in diversity in both flora and fauna (Plieninger 2006; Dahlstrom and Hallgren 2008). To maintain high biodiversity we need a dynamic management approach that takes into account ecosystem change in space and time (Anton et al. 2010; Haslett et al. 2010). The traditional cultural landscape was highly dynamic with changes in land-use management at various temporal and spatial scales, for example abandonment of non-permanent fields/grasslands or of whole farms during times of crisis, but our understanding of the influence of this management practice on floristic diversity in the long term is far from complete (Johansson et al. 2008; Emanuelsson 2009; Haslett et al. 2010). However, palaeoecological records may provide the relevant timescales in decades or millennia for understanding long-term ecological processes which are important to biodiversity (Willis et al. 2010). So far, landscape development in northern Europe over the last few hundred years has been studied mainly using historical documents and maps (Eriksson et al. 2002; Bender et al. 2005; Lunt and Spooner 2005; Zimmermann et al. 2010). These historical data sources can be used to estimate the spatial extent of cultivated fields, meadows and common lands, but seldom provide compositions of taxa in different land-use types. Moreover, the historical data are highly heterogeneous in temporal and spatial coverage and cannot provide a continuous record of quantified past land-use and floristic diversity on a regional and local scale. On the other hand, pollen-based reconstructions, using fossil pollen extracted from lake or bog sediments, may provide continuous information on past changes of taxa composition. However, the non-linear nature of the relationship between vegetation abundance and pollen proportion in sediments has made it difficult to quantify vegetation cover based on pollen data (Brostrom et al. 1998; Sugita et al. 1999; Hellman et al. 2009). Many tree taxa are in general overrepresented and many herb taxa are often underrepresented in pollen assemblages compared to their abundance in the surrounding vegetation (Bradshaw and Webb 1985; Brostrom et al. 1998; Sugita et al. 1999; Davis 2000). As a consequence, the quantitative reconstruction of landscape openness, as in woodland clearings, grasslands and cultivated fields is not straightforward. However, palaeoecological methodologies have advanced in recent years especially in regard to the quantification of past vegetation change (Gaillard et al. 2010), the Landscape Reconstruction Algorithm (LRA) (Sugita 2007a, b). LRA is designed to correct for pollen representation biases and to quantify vegetation composition based on fossil pollen assemblages (Sugita 2007a, b). LRA with submodel Regional Estimates of Vegetation Abundance from Large Sites (REVEALS) uses pollen assemblages from large (C100500 ha) lakes to quantify vegetation composition at a regional scale (104105 km ) 2 (Sugita 2007a). These new tools (...truncated)