Anthropogenic Drivers of the Long-Term Spread and Persistence of Olive Trees in the Central Mediterranean

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For thousands of years, the olive tree has stood as a symbol of resilience and tradition in the Mediterranean. But a groundbreaking study reveals that this iconic plant is not just a product of nature—it is a living archive of human ambition, cultural exchange, and adaptation.

By analyzing ancient pollen, climate records, and archaeological findings, researchers have uncovered how Sicilian communities transformed their landscape through olive cultivation over 3,700 years.

This story, hidden in the mud of a coastal lake, challenges long-held assumptions about the origins of Mediterranean agriculture and offers urgent lessons for today’s climate challenges.

How Sicily’s Olive Trees Shaped Mediterranean History

The study centered on Pantano Grande, a salt marsh near Sicily’s Strait of Messina. Salt marshes are coastal wetlands flooded by tides, known for preserving organic material like pollen in their oxygen-poor sediments. This strategic location, a crossroads for ancient traders, preserved layers of sediment dating back to 1800 BCE.

Scientists extracted cores of mud, each layer acting like a time capsule. Within these layers, pollen grains told a vivid story: olive trees dominated the landscape during three key periods—the Bronze Age, Roman times, and the modern era.

To distinguish human influence from natural growth, researchers developed the Olea Index, a tool comparing olive pollen to wild shrubs and oaks. The Olea Index uses two metrics:

• Olea Index MED: Compares olive pollen to Mediterranean shrubs like Pistacia (a genus of flowering plants) and Phillyrea (evergreen shrubs).

• Olea Index OAK: Compares olive pollen to evergreen oaks (Quercus ilex).
  When olive levels outpace these plants (values >0), it signals human intervention rather than natural growth.

Radiocarbon dating, a method that measures the decay of carbon-14 isotopes in organic material, and volcanic ash layers (tephra) provided precise timelines. For example, ash from Mount Etna’s FL eruption around 1100 BCE helped correlate Sicilian data with other Mediterranean records.

 Climate proxies, such as oxygen isotopes (δ¹⁸O) in lake carbonates, revealed wet or dry phases. Oxygen isotopes are atoms of oxygen with different molecular weights; higher δ¹⁸O values indicate drier conditions.

Meanwhile, archaeological evidence—olive pits (stone seeds inside olives), wood fragments, and oil lamps—confirmed that people were actively using olives long before previously assumed.

Bronze Age Origins of Olive Cultivation in Sicily

The oldest evidence of olive exploitation in Sicily dates to the Early-Middle Bronze Age (1800–1100 BCE). The Bronze Age marks a period when humans first widely used bronze tools, revolutionizing agriculture and trade.

During this period, olive pollen accounted for 35% of all plant remains in Pantano Grande, peaking at 50% in some layers.

This surge coincided with the rise of the Thapsos-Milazzese culture, a Sicilian society known for its fortified settlements and trade ties to Mycenaean Greece and Cyprus.

Mycenaean pottery (ceramics from ancient Greece) and Cypriot copper ingots (metal trade bars) found in Sicilian tombs suggest a bustling exchange network. Olives likely traveled these routes as luxury goods, with oil used for cooking, lighting, and rituals.

But these early olives were not the cultivated varieties we know today. Instead, Bronze Age Sicilians practiced proto-domestication, a term describing early human management of wild plants without full genetic domestication. Proto-domestication involved protecting wild groves, pruning trees, and selectively harvesting fruit.

Wood from olive trees built homes and ships, while leaves fed livestock. Fruit was pressed into oil or preserved as food. This system required no formal farming—people simply encouraged wild groves to thrive.

Climate proxies played a supporting role. Oxygen isotopes from lake sediments indicate relatively wet conditions, with steady rainfall nurturing both wild and managed trees. However, this balance would soon collapse.

The Role of Human Intervention in Olive Tree Expansion

Around 1100 BCE, olive pollen levels plummeted to less than 5%. This sharp decline aligns with the Late Bronze Age Collapse, a period of societal disintegration across the Mediterranean caused by invasions, droughts, and trade breakdowns. In Sicily, the trigger was twofold.

• First, Mount Etna’s FL eruption (named for the Fornazzo-Linguaglossa region) blanketed the region in ash, blocking sunlight and damaging crops. Volcanic ash layers, called tephra, are critical for dating because they create precise time markers in sediment cores.
• Second, the collapse of Mycenaean Greece—a dominant Bronze Age civilization—severed trade networks. Without access to eastern markets, Sicilian communities abandoned coastal settlements and retreated inland.

Archaeological evidence paints a grim picture. Coastal villages like Thapsos were deserted, while fortified hilltop settlements emerged. Pollen records show grasses and weeds replacing olives, suggesting a return to subsistence farming (farming only for survival, not trade). Yet, even in this decline, the stage was set for future revival.

Roman Engineering and Sicily’s Ancient Olive Groves

Olive pollen surged again during Roman rule (138 BCE–235 CE), though never reaching Bronze Age peaks. At its height, olive levels hit 20–25%, alongside cereals like wheat and barley.

The Romans, masters of agricultural engineering, transformed Sicily into a breadbasket (a region producing surplus grain) and oil jar for their empire.

They introduced terracing (carving steps into hillsides to prevent soil erosion) and built irrigation channels to combat drier conditions, evident in rising oxygen isotope values.

Large estates called latifundia (industrial-scale Roman farms) mass-produced olive oil. Archaeological sites reveal olive presses (machines to extract oil) and amphorae (clay jars for storage). Amphorae stamped with Sicilian origins have been found as far as Britain, proving the island’s role in long-distance trade.

However, Roman olives were genetically distinct from Bronze Age varieties, imported from the eastern Mediterranean to meet imperial demand. This shift marked the beginning of a genetic bottleneck (reduced genetic diversity due to selective breeding), which still affects Sicilian groves today.

• After the Roman Empire fell, olive cultivation withered. Pollen levels dropped to 5–10% during the Arab invasions (827–1061 CE), as political instability and arid climates made large-scale farming untenable.

Abandoned groves were replaced by scrubland (land dominated by shrubs), with hardy plants like Pistacia and Phillyrea taking over. Yet, even in decline, olives persisted in small household gardens, a testament to their cultural staying power.

Modern Threats to Sicily’s Iconic Olive Landscapes

From the 18th century onward, olives returned with a vengeance. Pollen levels soared to 40%, but this revival came at a cost. Modern Sicilian groves rely heavily on imported Middle Eastern varieties, sidelining native wild olives.

Genetic studies show that 98% of today’s trees descend from just five ancient lineages, leaving them vulnerable to diseases like Xylella fastidiosa, a bacterial pathogen that blocks water flow in plants.

Since 2013, Xylella has destroyed over 1 million trees in Sicily, highlighting the risks of monoculture farming (cultivating a single crop species).

Industrial farming methods exacerbated soil degradation and water scarcity. Wild olive populations, once thriving in Bronze Age forests, have declined by 72%.

Despite these challenges, the study highlights a silver lining: Sicilian farmers are now reviving agroforestry (mixing trees with crops) and planting drought-resistant wild varieties, blending traditional knowledge with modern science.

Lessons from Sicily’s Olive-Driven Agricultural Past

The 3,700-year pollen record from Pantano Grande offers more than historical insight—it provides a roadmap for sustainable agriculture. First, it proves that olives thrived not because of ideal climates, but through human adaptability.

Bronze Age communities weathered volcanic winters by diversifying crops, while Romans engineered solutions to droughts. Second, it warns against over-reliance on monocultures. The genetic uniformity of modern groves mirrors mistakes made by the Romans, who prioritized yield over diversity.

Perhaps most importantly, the study redefines “natural” landscapes. What we see as timeless olive groves are, in fact, human creations—shaped by millennia of trial, error, and cultural exchange.

As climate change intensifies, this long-term perspective is vital. Farmers are already drawing inspiration from the past, reviving Bronze Age agroforestry techniques to build resilient groves.

The Future of Sicily’s Olive Trees Amid Climate Change

While groundbreaking, the study leaves gaps. Without ancient DNA analysis of olive pits (stone seeds), researchers cannot pinpoint domestication dates. Comparisons with North African sites are scarce, skewing the narrative toward European perspectives.

Future projects aim to sequence Bronze Age olive DNA and expand pollen studies to Sardinia and Malta, two islands with similar Mediterranean climates.

Another priority is understanding modern threats. Xylella fastidiosa, unknown in ancient times, requires urgent attention. By combining ancient data with climate models, scientists hope to predict how the disease will spread in a warming world.

Conclusion

The story of Sicily’s olive trees is a mirror reflecting humanity’s best and worst traits—ingenuity, resilience, but also shortsightedness.

From Bronze Age traders navigating the Strait of Messina to Roman engineers terracing hillsides, each generation left its mark on the land. Today, as we face unprecedented ecological crises, this history reminds us that solutions often lie in the past.

As lead researcher Jordan Palli notes, “Every olive grove is a dialogue between humans and nature. To protect them, we must listen to both voices.” By learning from 3,700 years of adaptation, we can ensure that Sicily’s olives—and the cultures they sustain—endure for millennia to come.