The origin and spread of olive cultivation in the Mediterranean Basin: The fossil pollen evidence

The southern Levant

The three records available for the southern Levant demonstrate a sudden and profound increase in Olea pollen percentages around the mid-7th millennium BP (Figures 3 and S2). In the Dead Sea (–415 m below sea level (b.s.l.)) and Hula (70 m above sea level – a.s.l.) records, the estimated date for this dramatic rise in pollen is ~6500 yBP (Litt et al., 2012; Van Zeist et al., 2009, respectively), while at the Sea of Galilee (–211 b.s.l.) the estimated age is ~7000 yBP (Schiebel and Litt, 2018). In two different records recovered from Birkat Ram (Golan plateau, southern Levant), the estimated date for the marked rise in olive pollen percentages was also dated to ~6500 yBP (Neumann et al., 2007; Schiebel, 2013). In all these southern Levantine pollen diagrams, the sudden and dramatic increase in olive percentages (e.g. in the Sea of Galilee, from 3.5% at ~7300 yBP to 17.1% at ~6900 yBP) was not accompanied by increased abundance of other broadleaved trees, such as oaks and pistachios, and therefore cannot be regarded as climate related. We assume, therefore, that this rise reflects the intensification of olive cultivation (see also Supplemental Material, available online), as was first proposed by Baruch and Bottema (1999). The discovery of early residual evidence for olive oil in a pottery vessel (amphoriskos) from ‘En Zippori’ (Lower Galilee, southern Levant), dated to the Late Neolithic-Chalcolithic interface (the Wadi Rabah horizon, 8th millennium BP; Namdar et al., 2015), supports the possibility that the dramatic rise in olive pollen represents an early stage of olive cultivation. The chemical residue in the amphoriskos contains high proportions of oleic acid (C18:1 >70%) in relation to stearic and palmitic acids, accompanied by linoleic acid (C18:2) and the complete absence of linolenic (C18:3) acid (Namdar et al., 2015: Figure 4c). This chemical signature is strongly associated with the presence of olive oil (Boskou, 2002; Evershed et al., 1997; Namdar et al., 2015).

In recent decades, several large, well-preserved, and well-dated archaeobotanical assemblages from Pottery Neolithic villages submerged along the Mediterranean (Carmel) coast of Israel have resulted in a new understanding regarding the earliest date of large-scale olive oil production (Galili et al., 1989, 1997). Beginning at ~7600 yBP, significant quantities of olives were recorded in the four Pottery-Neolithic sites of Kfar Samir, Kfar Galim, Tell Hreis, and Megadim (Carmi and Segal, 1995; Galili et al., 1989, 1997; Galili and Sharvit, 1995; Kislev, 1995). The finds from the submerged villages differ from many typical archaeobotanical olive finds, in that they are numerous, non-charred, and well preserved. They were also found in clear archaeological contexts and were directly ¹⁴C dated. The data provide valuable information on subsistence prior to, as well as following, the introduction of olive oil extraction (Galili et al., 2018). In Kfar Samir (~7600–7000 yBP), several stages of the olive oil production (chaîne opératoire) were identified, including crushing basins made of stone, a pit filled with the waste (pomace) produced by olive oil extraction, and strainers made of twigs. The pomace can potentially also represent a further step of emptying the strainer after pressing (strainers are still used in current traditional methods of olive oil production). This is considered the earliest known evidence for olive oil extraction (Galili et al., 1997, 2018). These finds may be contrasted with those from the adjacent but older submerged site of Atlit-Yam (Pre-Pottery Neolithic C; 9000–8500 yBP) where olive remains (both pollen and endocarps) are present in very low quantities (Kislev, 1996), most likely derived from wild olives.

The submerged findings from Kfar Samir are dated to the same period – the Late Neolithic–Chalcolithic interface (the Wadi Rabah horizon) – as the olive oil residue in the pottery vessel from ‘En Zippori’ mentioned above (Namdar et al., 2015). However, it is possible that these finds represent a very early stage of olive tree manipulation when olive fruits for olive oil production were still collected from wild trees. DNA analysis of the olive stones from Kfar Samir provided short sequences but no conclusive evidence regarding domestication (Elbaum et al., 2006). Documenting the exact moment of domestication is complicated as it is a process that does not happen instantly; rather, it involves a long period of transformation, and the situation is even more confusing in areas where wild olive populations are part of the natural environment, as is the case in the southern Levant coast. Domesticated, cultivated, feral, and wild plants may well have been mingled in evolving management strategies, giving the archaeobotanical record a mixed character (e.g. Margaritis, 2013; Zohary et al., 2012). This study shows that the sudden and profound increase in the southern Levant pollen records may indicate large-scale olive management. Early management (proto-cultivation) of wild olive trees probably included collection of branches and intentional pruning for the exploitation of various products: fruit, fodder, timber, and probably fuel.

Olive wood remains occur in four Chalcolithic sites located in the Lower and central Jordan Valley, where wild olives are not found today and to the best of our knowledge were also not present in the 7th millennium BP (Teleilat Ghassul – Meadows, 2001; Abu Hamid and Tell esh Shuna – Neef, 1990; and the somewhat earlier site of Tel Tsaf – Langgut and Benzaquen, in press). In addition, a very important and even critical finding of large amounts of waste from olive pressing demonstrates the widespread phenomenon of olive oil production in the Chalcolithic sites (Neef, 1990), for example, at Pella (central Jordan Valley; Dighton et al., 2017). The finding of olive waste clearly indicates large-scale olive oil production, while the finding of wood in those sites located outside the natural habitats of wild olives is again strong evidence for horticulture and should be attributed to local Chalcolithic olive orchards. Chalcolithic oil production is further supported by the numerous olive stones and wood remains, as well as crushing basins, found at Chalcolithic sites in the Golan Heights (Epstein, 1978, 1993) and in Samaria (Eitam, 1993). All of these findings strongly indicate a well-established olive horticulture no later than ~6000 yBP.

The data presented above can be summarized as follows: the sudden profound rise in the southern Levant of olive pollen curves (Figure 3; for example, in the Sea of Galilee, olive percentages around 6700 yBP are eight times higher than those observed during the early Holocene) suggests that in the mid-7th millennium BP, at the beginning of the Chalcolithic period, a broad enterprise of olive management and exploitation took place. This estimated date accords well with the seminal study conducted more than four decades ago by Zohary and Spiegel-Roy (1975), based mainly on the archaeobotanical evidence (charred seeds and wood) available at the time, which indicated that the olive horticulture was already present in the type-site of Tuleilat el-Ghassul no later than 6000 yBP. The botanical remains gathered throughout the region since then corroborate the idea that the initial steps toward large-scale olive management had already been taken by ~6500 yBP and argue against the attribution of olive cultivation to the Early Bronze Age, one millennium later (Liphschitz et al., 1991). This means that the early management of olive trees corresponds to the establishment of the Mediterranean village economy and the completion of the ‘secondary products revolution’, rather than to urbanization or state formation. It was primarily a rural staple economic strategy that was only secondarily (and much later) co-opted by Early Bronze Age elites as an instrument of political-economic leverage. Similar conclusions have been recently proposed for the expansion of olive in Eastern Crete (Cañellas-Boltà et al., 2018). The palynological, archaeological, and archaeobotanical data from the southern Levant indicate that during the Early Bronze Age, olive orchards were already abundant in the Levant and that olives were an important supplement to grain cropping throughout the Levantine region (Benzaquen et al., in press; Kaniewski et al., 2012; Langgut et al., 2016; Riehl, 2009; Weiss, 2015; Zohary et al., 2012), with olive oil becoming a commodity in international trade (e.g. Langgut et al., 2016; Lev-Yadun and Gophna, 1992).

The northern Levant

In the record from the Al Jourd marsh, Olea pollen does not occur during the first half of the Holocene. Its first appearance is dated to ~4600 yBP (Figure 3; Cheddadi and Khater, 2016). This late occurrence may probably be related to the high elevation of the site (2100 m a.s.l.). Early fruit tree cultivation in the Mediterranean certainly took place at lower elevations and then spread toward higher elevations. The knowledge, and possibly even the plant material itself, could have diffused from the southern regions. In a recent pollen record from the Syrian coast (not covering the entire Holocene and therefore not included in the current dataset), a prominent increase in Olea pollen abundance occurred at ~4800 yBP (Sorrel and Mathis, 2016: Figure 5a). Other palynological investigations in the northern Levant show an increase in Olea values during the Holocene – in the Tell Nebi Mend plain and in the Ghab area (Niklewski and Van Zeist, 1970; Yasuda et al., 2000) – but were unable to establish a robust age model (e.g. Cappers et al., 1998; Meadows, 2005). Based on the relatively well-dated palynological records, it therefore appears that the spread of olive culture in the northern Levant lagged behind the southern Levant (Langgut et al., 2016: Figure 4). This proposal is further supported by Riehl’s synthesis of archaeobotanical data from 138 Levantine sites (over a 5500–2600 yBP time frame), which clearly shows that Early Bronze Age olive cultivation was focused in the southern Levant (Riehl, 2009: Figure 7). However, this study does not distinguish between the sub-phases of the Early Bronze Age and may be skewed by the relative scarcity of Early Bronze Age excavation sites in the northern Levant. Well-dated archaeobotanical evidence from Tell Fadous in northern Lebanon indicates significant olive exploitation in the Early Bronze Age II-III (Genz et al., 2009: Figure 38; Höflmayer et al., 2014). Similar evidence was derived from the archaeobotanical assemblages of Tell Mastuma in northern Syria (Yasuda, 1997: 258, Figure 8). Therefore, based on the palynological and archaeobotanical evidence, it seems that the initial management of olive tree crops in the northern Levant lagged somewhat behind the southern Levant.

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Figure 7.

Palynological records from the islands of Crete and Zakynthos demonstrating a significant increase in olive pollen at ~6000 yBP. We believe that this rise is indicative of olive horticulture in southern Greece. The sudden dramatic increase was not accompanied by pollen rise of other broadleaved trees and therefore cannot be regarded as climate related. The radiocarbon dates provided with the Tersana and Delphinos records were recalibrated using OxCal v.4.3.2 (Bronk Ramsey, 2017). Olea pollen curves were drawn based on Moody et al. (1996) – the Tersana record, Bottema and Sarpaki (2003) – the Delphinos record and Avramidis et al. (2013) – the Alykes Lagoon record. The solid black line is a fivefold exaggeration curve used to show low Olea percentages.

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Figure 8.

Suggested dates in yBP for the beginning of olive horticulture in the Mediterranean regions considered in this study. Base map: Google Earth.

In contrast to the palynological, archaeological, and archaeobotanical data, the genetic evidence seems to suggest the northern Levant as the locus of olive domestication (Besnard et al., 2013). These conflicting results may derive from sampling issues within the Besnard et al. (2013) study, as the samples from the southern Levant were collected from only one location (Mount Carmel; Besnard et al., 2013: supplementary information Table S1, available online). Owing to the highly fragmented and human-disturbed Mediterranean habitat in this area, it could not be ruled out that some of the sampled trees/populations were feral. In any event, it seems that further genetic analyses of materials from the southern Levant are required in order to resolve this apparent regional discrepancy.

Anatolia

During the first half of the Holocene, the three records available from Turkey are characterized by intermittent occurrence and very low Olea frequencies (Figure 3). The records were recovered from hinterland locations, most probably portraying favorable thermo-Mediterranean micro-climates, suitable for oleaster survival as refugia.

Within the Gölhisar Gölü sequence (951 m a.s.l.), an increase in Olea is visible at ~3200 yBP, while at the two other locations, Eski Acigöl (1270 m a.s.l.) and Lake Iznik (88 m a.s.l.), the prominent increase in olive pollen was documented about a millennium later. For example, in the latter sequence, Olea pollen rises from 3% at ~2300 yBP to 15% at ~2100 yBP and up to 26% at 1900 yBP (Figure 3). This sudden expansion was understood to mark the beginning of olive horticulture in this area (Eastwood et al., 1999; Miebach et al., 2016). An increase in Olea percentages at ~4600–4500 yBP in Lake Iznik record was suggested by Miebach et al. (2016) to reflect a short-lived small-scale episode of olive cultivation. The olive stone findings from the Early Bronze Age strata of Troy (dated to ca. the middle of the 5th millennium BP) corroborate this early short-lived pollen peak, while also serving as the earliest olive stone remains in the Troad; in the subsequent period, during the Middle Bronze Age, olive was not cultivated in this region (Riehl, 1999). In south-western Turkey, Eastwood et al. (1999) correlate large-scale olive cultivation with the Beyşehir Occupation (BO) phase which began at ~3200 yBP. Recent synthesis of fossil pollen records from the entire Anatolian region corroborates this date (Woodbridge et al., 2019). This phase included the cultivation of other fruit trees such as Juglans, Castanea, and Vitis (Eastwood et al., 1999; Woodbridge et al., 2019). While the palynological evidence suggests that Juglans horticulture in the eastern Mediterranean spread on a north-south axis (most probably from Anatolia to the Levant) and reached the southeasternmost parts of the region (southern Levant) during the first half of the 4th millennium BP (Langgut, 2015), it seems that olive culture spread in the opposite direction. Most of the archaeological findings regarding olive oil production in Anatolia derive from later periods and therefore do not shed additional light on questions regarding early olive horticulture.

Greece

The two records available from Greece indicate that the beginning of the Holocene (~10,000–9000 yBP) is characterized by a scattered olive pollen presence, while during the subsequent two millennia, it is almost absent. Higher values are documented in the Lake Voulkaria (located at sea level) record between ~7000 and 6000 yBP and after ~5200 yBP. At exactly the same time, a peak in olive pollen percentages is documented at Lake Gramousti (400 m a.s.l.). During the second half of the Holocene, the spread of Olea can be observed from the Geometric to the Classical periods (beginning in the early 3rd millennium BP). These high olive pollen frequencies point to olive horticulture, mainly along the coastal lands. Higher olive percentages during these historical periods were also identified in other records from southern Greece (e.g. Vravron area – Kouli, 2012).

In pollen records from southern mainland Greece and from locations in the Aegean and Ionian Seas that were not included in this study, due to relatively low resolution and/or the limited time span they cover, the increase in Olea percentages, indicating the beginning of olive cultivation, is more profound and is dated earlier (Figure 7). The earliest clear evidence of substantial olive pollen rise occurs at ~6000 yBP in the pollen diagrams from Crete (Bottema and Sarpaki, 2003; Moody et al., 1996). A more accurate date is available from the new, high-resolution pollen study by Cañellas-Boltà et al. (2018), who suggest an age of ~5600 yBP for the beginning of olive tree management in Crete, when Olea pollen rises from ~17% at ~5700 yBP to ~30% at 5500 yBP. A virtually coeval olive pollen increase has been identified on Zakynthos Island in the Ionian Sea (Avramidis et al., 2013). In the northeast Peloponnese, a significant increase in Olea pollen was registered at a much later date: in the region of Lake Lerna at ~4200 yBP (Argive Plain; Jahns, 1993) and in the region of Kleonai and the Kotihi lagoon at ~3800 yBP (Atherden et al., 1993; Lazarova et al., 2012, respectively). In Macedonia, in the vicinity of Lake Dojran, Olea horticulture is suggested to have begun only at ~2500 yBP (Masi et al., 2018). The differences between the palynological records regarding the date of the beginning of olive horticulture may reflect the possibility that the initial management of olive tree crops varied from one area to another, with a clear diffusion from south to north.

The late pollen evidence for olive culture in the two records discussed in this study (Lake Voulkaria and Lake Gramousti) is probably the result of their relatively northern location (Figure 1). However, it can be summarized, based on the other available regional pollen sequences presented above, that the earliest profound increase in olive pollen, indicative of olive cultivation in Greece, took place during the ~6000–5600 yBP interval (Figure 7; Crete – Bottema and Sarpaki, 2003; Cañellas-Boltà et al., 2018; Moody et al., 1996; and Zakynthos Island – Avramidis et al., 2013). In these pollen diagrams, the sudden dramatic rise in olive pollen curves was not accompanied by increasing pollen percentages of other evergreen Mediterranean sclerophyllous trees. This may suggest that Olea pollen intensification was not climate related. Furthermore, not only did the ratios of other trees of the Mediterranean forest/maquis with similar environmental requirements not increase, but oak percentages (mostly those of the evergreen type) were reduced (Avramidis et al., 2013: Figure 4; Bottema and Sarpaki, 2003: Figure 4; Moody et al., 1996: Figure 8), pointing to the possible replacement of parts of the Mediterranean forest/maquis by olive orchards through human agency, as has been suggested, for example, for the Sea of Galilee region in the southern Levant (Baruch, 1986; Horowitz, 1979: 193). Indeed, the Sea of Galilee olive pollen curve used in this study (Figure 3a) and the evergreen oak pollen type curve (Schiebel and Litt, 2018: Figure 6) present opposite trends since the beginning of olive cultivation in the region. The range of ages pointing to the beginning of large-scale olive management in Crete (~6000 yBP vs ~5600 yBP) could stem from differences in dating methods, but it may also indicate an earlier starting date for olive cultivation in Western Crete. The record reported by Moody et al. (1996) is located in western Crete while the palynological sequence of Cañellas-Boltà et al. (2018) is situated at the eastern end of the island (see also Supplemental Material, Figure S4, available online). The archaeobotanical data from southern Greece matches the palynological evidence: olive remains become common in the initial stage of the Bronze Age (from ~5300 yBP) and increase during the course of the Bronze Age (Asouti, 2003; Margaritis, 2013; Valamoti et al., 2018 and references therein).

Islands have always been regarded as sensitive indicators for environmental change and human pressure, due to their isolation and relatively low resilience. In the Balearic Islands, an abrupt increase in Olea pollen was observed almost at the same time as for the Aegean and Ionian Islands (see review by Burjachs et al., 2017). However, in the case of the Western Mediterranean islands, olive pollen escalation was synchronized with a rise in Quercus (most probably evergreen pollen type) and Erica pollen, and a marked decrease in Juniperus, Buxus, and Ephedra pollen (Burjachs et al., 2017: Figures 2–5). These changes point to an expansion of wild rather than of domesticated olive trees.

In correlation with the early Holocene pollen spectra (Figure 3), olive stones and wood-charcoal remains also point toward a rare presence of olive trees during the Late and Final Neolithic (9th–7th millennia BP) in some islands in the Aegean and Ionian seas, either growing naturally in small numbers (Valamoti et al., 2018), and/or exploited at a low level (Margaritis, 2013). The archaeological sites from northern and central mainland Greece are characterized by the almost total absence of olive macro-botanical remains during the Neolithic (see review by Valamoti et al., 2018), as well as pollen (e.g. Kouli and Dermitzakis, 2008). The number of sites where olive remains have been recovered rises dramatically in both Crete and the Peloponnese from the Bronze Age onwards. Based on the robust archaeobotanical evidence (Margaritis, 2013; Valamoti et al., 2018), and as suggested by Renfrew (1972), the Aegean stands out as the core area from which olive horticulture gradually spread at the onset of the Bronze Age, diffusing from islands and coastal locations to the central mainland and to more northerly regions.

The earliest evidence from residue analysis for the use of olive oil in Greece comes from two local jar fragments found in the small fortified hilltop site of Aphrodite’s Kephali in eastern Crete, dated to ~5200–4700 yBP (Koh and Betancourt, 2010: Table 1). Martlew (1999) reports that olive oil residues are present at the Late Neolithic site of Gerani Cave in western Crete (dated to ~5800 yBP); however, the results of this study are not conclusive and could point to other vegetal sources (see also critique by Sarpaki, 2012: 41–42).

The relatively late onset of intensive olive cultivation in the Aegean (at least several centuries after the southern Levant) allows for the possibility that it was initiated as a result of knowledge transfer – or even seedling transfer – from the Levant. However, there is no firm archaeological evidence that can point to contiguous links between the two regions. While it is broadly recognized that maritime capabilities grew markedly in the 6th millennium BP, commerce appears to have been limited to the Aegean basin and the west Anatolian coast, on one hand, and to the Levantine littoral (including occasional contacts with Cyprus), on the other hand (Bar-Yosef Mayer et al., 2015; Broodbank, 2013 and references therein), with no archaeological or archaeobotanical evidence for stepping-stones that may have filled the gap. It is therefore possible that the knowledge of olive cultivation spread through maritime connections, but no less likely that olive cultivation in Greece was an independent event. The latter possibility is supported by genetic studies (Diez et al., 2015), which appear to point to two separate domestication events, one in the eastern and the second in the Central Mediterranean.

The archaeological record related to olive oil processing differs between the two regions: while in the southern Levant the entire chaîne opératoire for the initial stage of olive horticulture can be reconstructed, in southern Greece the archaeological evidence regarding this initial stage is more obscure. For example, the earliest evidence of clay-spouted tubs, presumably used for separating oil and water following pressing, was found at Early Minoan Myrtos (Crete), at ~4200 yBP (Riley, 2002). Burnt olive waste was found also in Crete (Chamalevri-Tzambakas House), dated to ~4100–3900 yBP (Sarpaki, 1999, 2012). Stone presses were found only in the later stages of the Bronze Age. The discrepancy between the two regions regarding the visibility of the archaeological record and archaeobotanical finds are most probably the result of two factors: (1) different states of preservation and (2) the use of different techniques for olive oil extraction; for example, the possibility that at the early stage of olive oil production in the Aegean, wooden rollers were used to crush olives on stone beds. In such a technique, not only does the perishable wood rarely survive in the archaeological record, but the defleshing of the olives would occur without crushing the olive stones (Hamilakis, 1996). The olive fruits could have been crushed on multipurpose stone beds (e.g. surfaces used in the processing of other plant materials). Multifunctional mortars and pestles could have also been used to crush the olive fruit. Differences in production techniques between the Aegean and other Mediterranean regions were also observed in the case of wine production (Frankel and Ayalon, 1988: 31).

Despite the limitations presented above, the presence of olive oil residues nearly contemporaneous with the palynological evidence for large-scale olive management (Figure 7) points to the local production of olive oil early in the 6th millennium BP. It seems that olive horticulture spread from islands, such as Crete and Zakynthos, as well as from coastal locations where olive grows naturally, to mainland Greece.

Sicily

The early Holocene is characterized by a limited appearance of olive pollen in the two records available for Sicily (Lago Preola and Gorgo Basso, both located at few m a.s.l.). Beginning with the 8th millennium BP, an increase in Olea percentages was registered in both records. This rise was accompanied by the intensification of other broadleaved trees such as Quercus ilex and is considered reflective of the dominance of the evergreen forest in the coastal areas of Sicily as a result of an increase in available moisture (Calò et al., 2012; Tinner et al., 2009). A contemporaneous increase in Olea pollen has been documented in other parts of Sicily (e.g. in the Biviere di Gela record, from southern Sicily; Noti et al., 2009). In central Sicily, Lago di Pergusa is outside the natural distribution area of the wild olive tree, but its pollen curve shows a continuous presence along the last 6700 years, most probably reflecting long-distance transport. The sudden Olea pollen rise from ~3200 to 3000 yBP (from ~5% to 17%, respectively), a period in which the area was settled by Sicanians and Sicels, most probably indicates human activity in the area (Sadori et al., 2013, 2016).

Based on the two records presented in this study, the evergreen forests persisted in northern Sicily until 2200 yBP, when human presence intensified (Calò et al., 2012). Since Olea is a dominant component of the local natural forest, and since its pollen values increase significantly during humid phases, it is difficult to use this marker as an indicator for the beginning of olive cultivation in this region. For the same reason, the macro-botanical evidence also does not supply a clear answer regarding the date of cultivation of domesticated olive in Sicily. More direct evidence comes from residues in three Early Bronze pottery vessels found at Castelluccio (southern Sicily): chemical signatures of olive oil were identified, dated to the 5th and the beginning of the 4th millennium BP (Tanasi et al., 2018).

Mainland Italy

In the five Olea pollen records from mainland Italy, the frequency of this taxon is low during the first half of the Holocene (Figure 4). Its occurrence interestingly indicates that small stands, or at least some specimens of olive trees, existed in different regions of the Italian peninsula (Mercuri et al., 2013). The Olea pollen first shows an uninterrupted curve within the Albano and Nemi (293 and 318 m a.s.l., respectively) records starting around 3400 yBP. At the same time, increasing olive percentages are documented in the profile extracted from the inner part of Lake Accesa, which exhibits somewhat higher Olea values than the palynological record recovered from the margins of this lake (Figure 4). The differences are likely owed to the wider geographical catchment of the former record. At Lake Padule, maximum olive percentages were also recorded at ~3400 yBP. Olea pollen recovered from archaeological sites across the Italian peninsula confirms the wide extent of olive cultivation over the last four millennia, with a greater representation observed in southern sites, due to more favorable habitats in that part of mainland Italy (Mercuri et al., 2013). In the regional pollen diagrams, the Olea pollen increase was simultaneous with the rise of walnut and chestnut pollen and follows the spread of cultural landscapes (Mercuri et al., 2013). Evidence for a short-lived episode of olive cultivation during the Early Bronze Age (early 4th millennium BP) has been inferred from charcoal accumulation in two archaeological sites of the Tyrrhenian coast of Calabria, in southern Italy (D’Auria et al., 2017). The presence of olive waste from Tufariello (Buccino) dated ~3800–3400 yBP (the Middle Bronze Age) supplies direct evidence for olive oil production (Rowan, 2015). The earliest chemical signatures of olive oil are those of Broglio di Trebisacce (Cosenza) and Roca Vecchia (Lecce), where large storage jars (dolia) dated to the Late Bronze Age (~3200–3000 yBP) tested positive for oil presence (Tanasi et al., 2018 and references therein).

Southern Iberian Peninsula

Based on the four palynological records used for the southern Iberian Peninsula, Olea curves exhibit an almost continuous presence throughout the entire Holocene (note that the Baza sequence begins only at ~8400 yBP). The San Rafael record (located at sea level), which is the only sequence in this region that has been recovered from the distribution area of the wild olive (Figure 1), shows increasing Olea percentages starting in the early 8th millennium BP and lasting until the late 5th millennium BP. The rise in olive pollen levels was accompanied by increasing percentages of other broadleaved trees common to the thermo-Mediterranean zone and is therefore indicative of more available moisture (Yll et al., 2003). The paleoenvironmental information obtainable from the Siles record supports this vegetation-climate reconstruction. According to Carrión (2002), an early/mid-Holocene wet phase (~7500–5200 yBP) emerges regionally during the period exhibiting maximum forest development and the highest lake levels. The Siles profile is characterized by maximum Holocene Olea pollen percentages between 6800 and 6400 yBP and at ~5600 yBP.

The Baza, Villaverde, and Siles records (1900, 870, and 1320 m a.s.l., respectively) show increasing Olea pollen frequencies during the last two millennia (Figure 5; Carrión, 2002; Carrión et al., 2001, 2007). In all three palynological diagrams, the increase in olive was simultaneous with a sudden change in the appearance of other pollen indicators of human influence on the natural vegetation (Carrión et al., 2001). The same vegetational pattern is demonstrated based on the synthesis of palynological records recovered from the southeastern sector of the Iberian Peninsula conducted by Fyfe et al. (2019). Their study shows an increase in OJC (sum of Olea, Juglans, and Castanea pollen) at the beginning of the 2nd millennium BP (Fyfe et al., 2019: Figure 6). In the San Rafael sequence, the situation is less clear; Olea pollen levels increased during the 3rd millennium BP; however, they declined during the last 2000 years (Yll et al., 2003).

Based on archaeobotanical evidence (higher visibility as well as changes in both olive stone morphology and wood anatomy), an early autochthonous olive cultivation over the course of the 5th millennium BP, during the Chalcolithic/Early Bronze Age, has been posited (Terral, 1996, 2000; Terral and Arnold-Simard, 1996; Terral et al., 2004a). Other studies, also relying on the archaeobotanical record, suggest a much later date for the beginning of olive horticulture (Alonso et al., 2016; Pérez-Jordà et al., 2017). The palynological data from the southern Iberian Peninsula do not support an early cultivation scenario since the rise in Olea pollen is most probably climate related, as discussed above. The increase in olive remains (seeds and charcoal) in the Chalcolithic/Early Bronze Age botanical assemblages is also most likely linked to the early/mid-Holocene humid phase. As presented above, the increase in Olea pollen and other regional pollen indicators point to a profound anthropogenic influence on the natural vegetation only during the last two millennia. Other lines of evidence agree with the palynological data: while olive stones are present in the Chalcolithic period (~mid-5th millennium to mid-4th millennium BP), there is no indication that they were being cultivated, and while their numbers increase with the approach of the Bronze Age (after ~4000 yBP), they are still not substantial. In the Bronze Age, the olive stones found have been regarded as wild and no pottery suggestive of oil production has been found (Stika, 2000). For example, at Cueva de Toro (Malaga), olive seeds were found in a continuous sequence of levels dating from the Middle Neolithic to the Bronze Age, though in relatively low quantities (Buxó and Capdevila, 1997). According to these authors, for those relying on morphometric indices to differentiate between the wild and domesticated types of seeds, the olive seeds resemble the wild types. The wood-charcoal remains also support the suggestion that the increase in olive remains can be attributed to the more favorable climatic conditions prevailing during the early/mid-Holocene. The increase in humidity permitted the species to become very abundant and even to expand into favorable enclaves outside the limits of the thermo-Mediterranean zone (Carrión et al., 2010). A significant increase in olive remains (charcoal and olive stones) in the archaeological record is documented only in the beginning of the First Iron Age (~2800–2600 yBP), mainly from sites located in the thermo-Mediterranean zone (Alonso et al., 2016; Pérez-Jordà et al., 2017). In the middle of the Second Iron Age (~2600–2200 yBP, also called the Iberian period), the olive oil presses are already present in the region (Pérez-Jordà, 2000).

Palynological records from the Balearic Islands were not included in this study since none of the available datasets meet the criteria used for pollen sites in the current research. However, they supply some interesting supplementary observations regarding Olea history in the region. Several pollen diagrams demonstrate an abrupt and profound increase in olive pollen ratios from the mid-late 7th millennium BP, accompanied by other dramatic changes in the main component of the Mediterranean forest/maquis (Cala’n Porter, Minorca – Yll et al., 1997; Algendar, Minorca – Yll et al., 1997; Es Grau, Minorca – Burjachs, 2006; Addaia, Minorca – Servera-Vives et al., 2018; Alcúdia, Majorca – Burjachs et al., 1994). These profound changes in the vegetation composition signify a phase of transformation within the natural landscape (Burjachs et al., 2017 and references therein). Another indication which clearly signifies that the Olea increase is not linked to cultivation derives from the fact that the first documented human presence on the islands is only dated to the second half of the mid-5th millennium BP (Alcover, 2008). Wood management largely reliant on Olea produced a visible impact on the local landscape during the Bronze Age, starting from about 3700 yBP (Servera-Vives et al., 2018; Mercuri et al., 2019). As for other north-western Mediterranean areas (e.g. southern France), none of the available palynological records satisfy the selected criteria for this study. In any event, according to Leveau et al. (1991), the archaeological, archaeobotanical, and palynological data show that olive cultivation is clearly evident in southern France only from the Roman period.

Northern Iberian Peninsula

Since all three palynological records are located outside the natural habitat of wild olive (Figure 1), the low Olea pollen visibility during the early Holocene suggests the proximity of glacial refugia. It is possible that in nearby favorable thermo-Mediterranean micro-climates, survivors of oleaster were part of the Mediterranean forest. In a pollen record extracted from the northeastern coast at Lake Banyoles (Pèrez-Obiol and Julià, 1994), a similar trend to that of the southern peninsula was observed: wild Olea pollen increases during the mid-Holocene together with other evergreen sclerophyllous trees (Quercus ilex-coccifera and Phillyrea; Revelles et al., 2015: Figure 4). This simultaneous rise signifies that climate, rather than human agency, is responsible for the increase in Olea pollen.

Modest increases in olive pollen percentages during the last two millennia in the Laguna Negra and Charco da Candieira records are most probably indicative of the presence of local olive orchards (Figure 5). The latter is the westernmost record examined in this study. Fyfe et al. (2019) suggest a slightly earlier date based on palynological records retrieved from the northeastern sector of the Iberian Peninsula. Their study shows an increase in OJC index by the beginning of the 3rd millennium BP (Fyfe et al., 2019: Figure 6). According to Carrión et al. (2010), the cultivation of the olive in later periods in this region caused the olive trees to become more resistant to continental conditions and even to those prevailing along the Atlantic façade of the Iberian Peninsula. Based on the comprehensive evaluation by Rodríguez-Ariza and Moya (2005), the picture that emerges from the archaeobotanical and archaeological findings confirms the palynological evidence. During the Bronze and Iron Ages (from ~3800 yBP), charcoal remains are mostly restricted to archaeological sites within the thermo-Mediterranean zones. In fact, it is not until the Roman Period (1st–3rd centuries CE) that the range of the charcoal remains extends more strongly into the Mesomediterranean and even Supramediterranean zones and that mills and implements related to olive oil production begin to be found (Rodríguez-Ariza and Moya, 2005). The Saldropo pollen sequence is characterized by the rare and sporadic presence of Olea during the entire Holocene. This record, the northernmost profile discussed in this study, is situated outside the distribution area of both wild and cultivated olives and may be regarded as a ‘control’ record in this research.