Olea europaea L. in the North Mediterranean Basin during the Pleniglacial and the Early–Middle Holocene

Abstract

The paper aims to define the natural distribution of Olea europaea L. var. sylvestris (Miller) Lehr. in the North Mediterranean basin during the Pleniglacial and the Early-Middle Holocene by means of the identification of its wood-charcoal and/or wood at prehistoric sites.For this purpose we have reviewed the previously available information and we have combined it with new wood-charcoal analyses data. We have taken under consideration the presence and frequency of Olea europaea L. in the available wood-charcoal sequences, the characteristics of the accompanying flora, the associated chrono-cultural contexts, the broader biogeographical context and the AMS dates provided by Olea wood-charcoal or endocarps.According to the available evidence, during the Middle and Late Pleniglacial (c. 59-11,5 ka cal. BP), Olea would have persisted in thermophilous refugia located in the southern areas of the North Mediterranean basin, the southern Levant and the north of Africa. The Last Glacial Maximum (c. 22-18 ka cal. BP) probably reduced the distribution area of Olea. During the Preboreal and the Boreal (c. 11 500-8800 cal. BP) the species started to expand in the thermomediterranean bioclimatic level. In the western Mediterranean, during the Atlantic period (c. 8800-5600 cal. BP), the species became very abundant or dominant in the thermophilous plant formations and expanded to favorable enclaves outside the limits of the thermomediterranean level.

The complex history of the olive tree: from Late Quaternary diversification of Mediterranean lineages to primary domestication in the northern Levant

“…These SDM analyses indicate that suitable habitats for oleasters have persisted for a long period of time, and particularly during the LGM and the LIG (figure 2; electronic supplementary material, figure S6). Available macrofossils fit with the predictions for the LGM (figure 2b), in agreement with the persistence of oleasters in southern Europe and the Near East [3]. Putative Quaternary long-term refugia, defined rspb.royalsocietypublishing.org Proc R Soc B 280: 20122833 as areas with a continuous suitability for oleasters, were predicted in southern Europe ( particularly in southern Iberia), as well as on a coastal band in the northern Maghreb, Cyrenaica and the Levant (figure 2d).…”

“…The low ptDNA diversification in the central Mediterranean may be due to either rapid population turnover (maintaining low ptDNA diversity owing to stochasticity leading to genetic drift) or post-LGM colonization from major refugia located in the western and eastern areas. To date, there is no macrofossil for olive LGM persistence in the central Mediterranean basin, but just one piece of anthracological evidence for a presence during the Preboreal at Grotta dell'Uzzo (Sicily), suggesting an early colonization from putative proximal LGM refugia [3]. A similar distribution pattern of genetic diversity and LGM fossils was also reported for Laurus nobilis and Myrtus communis, two other circumMediterranean pre-Pliocene taxa [33,40,41].…”

“…We used the maximum entropy algorithm, as implemented in MAXENT v. 3.3 [23], because it is appropriate for presence-only data and its performance has been shown to be consistently competitive in comparison with other methods [24]. Only temperature variables were used because olive survival is limited by frost [3,25]. In particular, the present wild olive distribution was reported to be mainly explained by the mean temperature of the coldest month [25].…”

“…Among the old crops of the Mediterranean basin, the olive tree (Olea europaea ssp. europaea) is the most iconic species owing to its ecological, economical and cultural importance [2][3][4]. This plant is considered one of the best biological indicators of the Mediterranean climate [3,5], and its cultivation has accompanied the emergence of Early Mediterranean civilizations [4].…”

“…europaea) is the most iconic species owing to its ecological, economical and cultural importance [2][3][4]. This plant is considered one of the best biological indicators of the Mediterranean climate [3,5], and its cultivation has accompanied the emergence of Early Mediterranean civilizations [4]. The importance of the cultivated olive tree in people's lives has turned this species into a symbol in ancient sacred literature, and the origins of this crop are often subject to controversies [4].…”