Vegetation shifts, human impact and peat bog development in Bassa Nera pond (Central Pyrenees) during the last millennium

Abstract

High-mountain lakes are suitable ecosystems for studying local environmental shifts driven by large-scale climate changes, with potential applications to predict future scenarios. The precise features in the response of species assemblages are not fully understood, and human pressure may often hide climatic signals. To investigate the origin and impact of past environmental changes in high-mountain ecosystems and apply this palaeoecological knowledge to anticipate future changes, we performed a multi-proxy study of a sediment core from Bassa Nera, a pond located close to montane–subalpine ecotone in the southern central Pyrenees. Combining pollen and diatom analysis at multidecadal resolution, we inferred vegetation shifts and peat bog development during the past millennium. We introduced a montane pollen ratio as a new palaeoecological indicator of altitudinal shifts in vegetation. Our results emphasize the sensitivity of the montane ratio to detect upward migrations of deciduous forest and the presence of the montane belt close to Bassa Nera pond during the Medieval Climate Anomaly. Changes in aquatic taxa allowed to date the onset of the surrounding peat bog which appeared and infilled the coring site around AD 1565. Overall, our results suggest a low-intensity human pressure and changes in management of natural resources during the last millennium, where farming was the main activity from the Medieval Climate Anomaly until AD 1500. Afterwards, people turned to highland livestock raising coinciding with the ‘Little Ice Age’.

The Late-Glacial and Holocene Marboré Lake sequence (2612 m a.s.l., Central Pyrenees, Spain): Testing high altitude sites sensitivity to millennial scale vegetation and climate variability

“…Thus, as pollen produced in lowlands is easily lifted by vertical air-mass movements and deposited at subalpine and alpine zones, it may obscure the local vegetation signal, especially in treeless sites where local pollen production is low, complicating the vegetation history reconstruction (Barthelemy and Jolly, 1989;David, 1993;Tinner and Theurillat, 2003;Ortu et al, 2006;Seppä and Hicks, 2006). To tackle this problem, modern pollen rain is usually characterized along an elevation gradient and it is used as a tool to refine past vertical shifts and changes in vegetation composition (Ortu et al, 2006;Canellas-Bolta et al, 2009;Birks and Bjune, 2010;de Nascimento et al, 2015;Garcés-Pastor et al, 2016.…”

“…Holocene (e.g. Pla and Catalan, 2005;Miras et al, 2007;Pèlachs et al, 2011;Pérez-Obiol et al, 2012;Pérez-Sanz et al, 2013;Pérez-Díaz et al, 2015;Garcés-Pastor et al, 2016 and few of them include the Late Glacial-Holocene transition (LGH) (Montserrat-Martí, 1992;González-Sampériz et al, 2006Gil-Romera et al, 2014;Rius et al, 2014) a key interval to provide contrasting boundary conditions for terrestrial ecosystems, particularly at high altitudes (Brisset et al, 2015). After alpine glacier retreat, new environmental conditions developed on freshly ice-free valleys, profoundly modifying mountain landscapes (e.g.…”

“…Tinner and Theurillat, 2003;Birks and Bjune, 2010). In the Pyrenees, a montane ratio based on pollen-vegetation relationships has recently been applied by Garcés-Pastor et al,(2016 to detect vegetation altitudinal shifts during the Holocene. In Marboré, we establish a consistent pollen-vegetation relationship finding that changes in the deciduous montane belt position may be easier to infer as there is a good correspondence between deciduous taxa in current vegetation and pollen rain from moss pollsters (Figs.…”

High-resolution (sub-decadal) pollen analysis of varved sediments from Lake Montcortès (southern Pyrenean flank): A fine-tuned record of landscape dynamics and human impact during the last 500 years

“…Estanya lake; 670 m a.s.l(Riera et al, 2004)) and in high-mountain records(Garcés- Pastor et al, 2016;Ejarque et al, 2009Ejarque et al, 2010Pérez-Sanz et al, 2011) owing to its high pollen dispersion capacity(Cañellas-Boltà et al, 2009;Bell and Fletcher 2016).…”

Subalpine forest dynamics reconstructed throughout the last 700 years in the Central Pyrenees by means of tree rings and pollen

“…We used the available pollen frequencies and the derived montane pollen ratio obtained from a previous palaeoecological study focused on the vegetation dynamics of the last millennium (Garcés-Pastor et al, 2016). This sequence was obtained from the sediments of the BSN pond, a small lacustrine system located in the Aiguamòg valley, in the boundary area of the PNAESM (42° 38′ 18.5′ N, 0° 55′ 27.6′ E, 1891 m a.s.l.)…”