The impact of land-use change on floristic diversity at regional scale in southern Sweden 600 BC–AD 2008

cess Biogeosciences Open Access Climate of the Past Open Access Biogeosciences, 10, 3159–3173, 2013 www.biogeosciences.net/10/3159/2013/ doi:10.5194/bg-10-3159-2013 © Author(s) 2013. CC Attribution 3.0 License. Techniques Dynamics D. Fredh1 , A. Broström1,2 , M. Rundgren1 , P. Lagerås2 , F. Mazier3 , and L. Zillén1 Open Access The impact of land-use change on floristic diversity at regional scale in southern Sweden 600 BC–AD 2008 Earth System 1 Department of Geology, Quaternary Sciences, Lund University, Sölvegatan 12, 223 62 Lund, Sweden 2 Swedish National Heritage Board, Contract Archaeology Service, Odlarevägen 5, 226 60 Lund, Sweden Open Access Geoscientific Instrumentation Correspondence to: D. Fredh () Methods and Data Systems Received: 7 October 2012 – Published in Biogeosciences Discuss.: 21 December 2012 3 GEODE, UMR 5602, University of Toulouse-Le Mirail, 5 allées A. Machado, 31058 Toulouse Cedex, France Revised: 16 April 2013 – Accepted: 21 April 2013 – Published: 8 May 2013 Geoscientific Open Access a vegetation response time of less than 20 to 50 yr. We show Development the importanceModel of traditional land use to attain high biodiversity and suggest that ecosystem management should include a regional landscape perspective. 1 Introduction Hydrology and Earth System Sciences Open Access One of the main ecological challenges during this century is to mitigate the expected loss of species due to rapid landuse and climate changes (MacDonald et al., 2008; Anton et al., 2010; Barnosky etOcean al., 2011).Science To make adequate priorities and implement realistic nature conservancy efforts, we need a range of methods to understand how these processes may impact on biodiversity (Dawson et al., 2011). Because ecosystem responses may occur over decades or centuries, making them difficult to observe, palaeobotanical records Solid Earth provide important information about past responses relevant to on-going and future changes in vegetation and biodiversity (Jackson and Hobbs, 2009; Haslett et al., 2010; Willis and Bhagwat, 2010; Willis et al., 2010). In many areas, such as northwest Europe, agricultural land use has influenced vegetation and biodiversity for thousands Cryosphere of years (Berglund etThe al., 2008; Emanuelsson, 2009; Willis et al., 2010). The traditional agriculture, including crop cultivation, mowing and animal husbandry, made it possible for plants that do not naturally grow in northwest Europe to immigrate (Emanuelsson, 2009). The rapid land-use changes during the last ca. 100 yr, from a small-scaled traditional agriculture towards a modern agriculture based on largescaled crop cultivation and forestry, have led to a decrease in Open Access Open Access Published by Copernicus Publications on behalf of the European Geosciences Union. Open Access Abstract. This study explores the relationship between landuse and floristic diversity between 600 BC and AD 2008 in the uplands of southern Sweden. We use fossil pollen assemblages and the Regional Estimates of Vegetation Abundance from Large Sites (REVEALS) model to quantitatively reconstruct land cover at a regional scale. Floristic richness and evenness are estimated using palynological richness and REVEALS-based evenness, respectively. We focus on the period AD 350 to 750 to investigate the impact of an inferred, short-lived (< 200 yr) period of land-use expansion and subsequent land abandonment on vegetation composition and floristic diversity. The observed vegetation response is compared to that recorded during the transition from traditional to modern land-use management at the end of the 19th century. Our results suggest that agricultural land use was most widespread between AD 350 and 1850, which correlates broadly with high values of palynological richness. REVEALS-based evenness was highest between AD 500 and 1600 which indicates a more equal cover among taxa during this time interval. Palynological richness increased during the inferred land-use expansion after AD 350 and decreased during the subsequent regression AD 550–750, while REVEALS-based evenness increased throughout this period. The values of palynological richness during the last few decades are within the range observed during the last 1650 yr. However, REVEALS-based evenness shows much lower values during the last century compared to the previous ca. 2600 yr, which indicates that the composition of presentday vegetation is unusual in a millennial perspective. Our results show that regional scale changes in land use have had clear impacts on floristic diversity in southern Sweden, with M 3160 D. Fredh et al.: The impact of land-use change on floristic diversity available habitats, such as semi-open grasslands, that many species are restricted to (Antonsson and Jansson, 2011). Land-use transitions have occurred throughout agricultural history (Berglund, 1969; Lagerås, 2007; Froyd and Willis, 2008). By studying these transitions, using highresolution palaeobotanical records, we may reconstruct the rate and degree of change in land use and vegetation. This allows us to better understand how current ecosystems will respond to present and future land-use changes and provide information useful for ecosystem management. The Landscape Reconstruction Algorithm (LRA) enables new ways to study past land-use and biodiversity changes (Sugita, 2007a, b). Based on pollen counts extracted from lake and mire sediments, LRA, with its submodel Regional Estimates of Vegetation Abundance from Large Sites (REVEALS), compensates for differences in pollen productivity and dispersal characteristics among taxa and makes it possible to quantify past vegetation composition at a regional scale (Sugita, 2007a; Hellman et al., 2009). Moreover, it now makes it possible to reconstruct past floristic diversity using the two parameters: richness and evenness. Richness is the number of species within a specific area, which may be estimated using palynological richness, i.e the number of different pollen taxa found in a sediment sample (Birks and Line, 1992; Odgaard, 1999; Van Dyke, 2008; Meltsov et al., 2011). Evenness is a measure of the relative abundance of the different species that are present within an area (Magurran, 2004), which may be estimated for common taxa by applying evenness indices to the REVEALS output (Fredh et al., 2012). High evenness describes situations when all species within an area are represented by similar spatial cover, whereas low evenness characterizes landscapes where a few species cover large areas and other species cover small areas. For example, an ecosystem with two species that cover 50 % each is ecologically very different from an ecosystem with two species that cover 10 % and 90 %, respectively, although the number of species is the same. Fredh et al. (2012) analyzed the relationship between landuse and floristic diversity during the transition from traditional to modern land-use management AD 1 (...truncated)