Cryptic no more: soil macrofossils uncover Pleistocene forest microrefugia within a periglacial desert

Abstract

Summary Despite their critical importance for understanding the local effects of global climate change on biodiversity, glacial microrefugia are not well studied because they are difficult to detect by using classical palaeoecological or population genetics approaches. We used soil macrofossil charcoal analysis to uncover the presence of cryptic glacial refugia for European beech (Fagus sylvatica) and other tree species in the Landes de Gascogne (southwestern France). Using botanical identification and direct radiocarbon dating (140 14C‐dates) of macrofossil charcoal extracted from mineral soils, we reconstructed the glacial and postglacial history of all extant beech stands in the region (n = 11). Soil charcoal macrofossils were found in all sites, allowing the identification of up to at least 14 distinct fire events per site. There was direct evidence of the presence of beech during the last glacial period at three sites. Beech was detected during Heinrich stadial‐1, one of the coldest and driest intervals of the last glacial period in Western Europe. Together with previous results on the genetic structure of the species in the region, these findings suggest that beech persisted in situ in several microrefugia through full glacial and interglacial periods up to the present day.

The Holocene history of low altitude Mediterranean Fagus sylvatica forests in southern France

“…Fagus charcoals are found in upper Magdalenian levels (13,500–12,000 years cal BP) from archeological sites in southeast France (Figure , no 1, 2 and 3; Bazile‐Robert, ; Vernet, ) and in Glacial to Late Glacial (44,000–12,000 years cal BP) pedosedimentary sequences of the Landes de Gascogne region in southwest France (de Lafontaine, Amasifuen Guerra, Ducousso, & Petit, ). On the other hand, the oldest significant presence (1–5%) of Fagus pollen in southern France (“Les Frignants” sequence; Figure ) dates only to the earliest phase of the Holocene (Triat‐Laval, ), with only isolated, trace amounts of Fagus pollen appearing elsewhere in the region at this time.…”

Patterns and dynamics of European vegetation change over the last 15,000 years

“…Genetic markers in extant populations confirm earlier claims that Fagus survived the LGM on the Iberian Peninsula (Magri et al ., ) and possibly also in south‐western France (de Lafontaine et al ., ), yet these areas contributed little to the post‐glacial colonization of Europe. Similarly, the populations on the Apennine and Balkan peninsulas did not contribute to the post‐glacial spread of the tree.…”

Recent similarity in distribution ranges does not mean a similar postglacial history: a phylogeographical study of the boreal tree species Alnus incana based on microsatellite and chloroplast DNA variation

“…Although a majority of temperate tree species survived the Late Pleniglacial (LPG), 24–15 kyr bp (Tzedakis et al ., ), presumably in southerly located refugia (i.e. the Iberian, Italian and Balkan peninsulas) according to the ‘southern refugia paradigm’ (Hewitt, ; but see Magri et al ., ; de Lafontaine et al ., , ,b), boreal tree species were probably distributed more widely (Tzedakis et al ., ). This is supported by the presence of genetically very rich populations found in the area north of the Alps (e.g.…”