A 3,700-year-old olive tree in Portugal keeps producing olives as old trunk sections sprout again, revealing how one of nature’s longest-lived trees can repeatedly rejuvenate itself across thousands of years

Some trees are old enough to make human history look surprisingly recent. In Portugal, ancient olive trees have been estimated at more than 2,000 years old, with one in the Alentejo region assigned an age of about 3,713 years. If that estimate is correct, the tree was already growing when Bronze Age societies were reshaping the Mediterranean. But determining the age of an olive tree is far harder than simply counting its rings, and that is where researchers at the University of Trás-os-Montes and Alto Douro, or UTAD, have developed an unusual approach.

The difficulty begins inside the trunk. In many familiar trees, age can be estimated by counting annual growth rings. Each season of growth leaves another layer of wood, allowing researchers to work outward from the oldest central wood. Olive trees do not make this job easy. As they become very old, their trunks can become twisted, hollow and divided into separate living sections. The oldest wood may disappear through decay, leaving no simple path back to the tree's first year.

That is why the Portuguese method does not depend on cutting an ancient olive tree open. Instead, UTAD researchers developed a mathematical model that connects the physical dimensions of the trunk with estimated age. The method uses several measurements, including three measurements of the trunk's perimeter at different heights and a measurement of tree height. Those values are then compared with information about how olive trees grow in the region being studied.

Why counting olive tree rings can fail

Dendrochronology, the science of studying tree rings, remains one of the most useful ways to determine tree age. But it works best when annual rings are clearly formed and preserved. Olive trees growing in Mediterranean environments can produce growth patterns that are difficult to interpret, and old trunks often lose their central wood to decay. A massive circumference therefore does not automatically mean that every centimetre of wood represents another year of growth.

That distinction matters because the age of monumental olive trees has often been estimated from their enormous trunks. Scientific studies have shown why that can be misleading. A 2021 study combining tree-ring evidence with radiocarbon dating found that many monumental olive trees previously considered thousands of years old were more likely to be roughly 300 to 500 years old. A separate 2024 study concluded that most monumental olives are centuries old, although genuinely ancient individuals may exist, particularly in harsh environments where growth is exceptionally slow.

Portugal's approach represents a different kind of age estimation. Rather than trying to recover the complete history of a hollow trunk, researchers use measurable characteristics of living trees and a regional growth model. The idea is relatively straightforward: if researchers know how trunk dimensions change with age across a population, the measurements of an unknown tree can be fed into the model to produce an estimated age. The method is non-destructive and can be repeated on living trees.

How UTAD estimates the age of an ancient olive tree

The important part is not simply measuring how wide the trunk is. Growth depends on climate, soil, water availability, management and local conditions, so the same trunk diameter cannot necessarily mean the same age in every landscape. UTAD's system therefore relies on information about the growth of olive trees in the relevant region. Researchers built a database from which the relationship between tree dimensions and age can be modelled.

This is essentially a biological growth problem translated into mathematics. A tree's physical form contains information about its history, but that information has to be interpreted against known examples. The Portuguese researchers developed their method specifically because conventional ring counting becomes unreliable in very old olives. The resulting system can process the measurements and generate an age estimate without drilling into or cutting down the tree.

The work was associated with José Luís Louzada, a UTAD researcher who developed a patented method for estimating the age of old trees. UTAD's own research records list the patent “Método para estimativa da idade de árvores idosas,” while earlier university material described the approach as a non-destructive method based on stem dimensions and mathematical modelling.

The 3,350-year-old Oliveira do Mouchão

One of Portugal's best-known examples is Oliveira do Mouchão in the municipality of Abrantes. UTAD has estimated the olive tree at around 3,350 years old. That would place its earliest growth roughly in the second millennium BCE, long before the Roman occupation of the Iberian Peninsula and centuries before many of the civilizations later associated with Mediterranean olive cultivation.

The tree is remarkable not only because of the number attached to its age. Its survival illustrates one of the olive's unusual biological advantages. An old olive can lose major portions of its trunk and still remain capable of producing new growth. Instead of behaving like a rigid structure that simply becomes older and more fragile, the tree can repeatedly replace damaged or dying portions with new shoots. That regenerative ability helps explain why olives can survive severe injury and remain productive for centuries.

The same characteristic also complicates the question of what exactly “age” means in an ancient olive. The visible trunk may not represent one uninterrupted column of wood extending back to the original seedling. Sections can die while other portions continue growing. New stems can develop from older structures, producing a living organism whose physical architecture is constantly being rebuilt. For scientists, that makes an ancient olive very different from a straight, single-stemmed tree with a preserved central core.

Portugal’s older claim: Oliveira do Peso

The most striking Portuguese estimate belongs to Oliveira do Peso, on the Herdade do Peso estate near Vidigueira in the Alentejo region. Oliveiras Milenares, which has worked with UTAD on the certification of ancient olive trees, says the tree was assessed in 2021 at 3,713 years old. The company describes it as the oldest known olive tree in Portugal.

That figure would make the tree more than three centuries older than Oliveira do Mouchão. It would also place its beginnings deep in the Bronze Age, when communities around the Mediterranean were living through major changes in trade, agriculture and settlement. The estate says the surrounding group of olive trees has a combined estimated age exceeding 7,000 years, adding another layer to the landscape's historical significance.

Other Portuguese olive trees have also received extraordinary estimates. UTAD has highlighted trees in places including Monsaraz, Estremoz, Montemor-o-Novo, Lagoa, Beja, Vilamoura, Évora and Porto. One tree at Santa Iria de Azóia, near Loures, was estimated at about 2,850 years old at the time it was assessed, while an olive in Monsaraz has been estimated at roughly 2,450 years.

Why ancient olives can keep growing for centuries

Olive longevity is not simply a matter of growing slowly. The species, Olea europaea, is adapted to Mediterranean conditions, where summer drought can place intense stress on plants. Its ability to survive damage and regenerate shoots gives it an unusual advantage. Even when an old section of trunk is badly degraded, living tissue can continue producing new branches and leaves. Research on olive recovery has documented strong vegetative resprouting after severe stress, including growth from the lower trunk.

This regenerative strategy changes the meaning of old age in an olive tree. A tree does not necessarily have to preserve every part of its original body to remain alive. Its roots and surviving tissues can support new shoots, while older sections gradually disappear. In practical terms, the organism can persist even as parts of its structure are repeatedly lost and rebuilt.

That may help explain why some ancient olives remain productive despite enormous, hollow or scarred trunks. Their longevity comes partly from their ability to regenerate rather than simply endure. The same biology that keeps them alive, however, makes their exact age unusually difficult to reconstruct.

Why the 3,700-year figure needs careful interpretation

There is an important scientific caution behind these extraordinary numbers. The 3,713-year figure for Oliveira do Peso is an estimate produced through a specific modelling and certification approach. It should not automatically be treated as equivalent to a radiocarbon date taken from the tree's original pith. Independent scientific literature has repeatedly shown that estimating the age of monumental olive trees is difficult and that very large trunks can produce misleading age estimates.

Radiocarbon dating offers another route, but it has its own problem. Carbon-14 can establish the age of a piece of wood, not necessarily the age of the entire living tree. If the oldest central wood has rotted away, researchers may be dating a younger part of the organism. In ancient olives, that distinction can be crucial because the oldest material may no longer exist.

That uncertainty does not make Portugal's ancient olive trees any less remarkable. It makes them scientifically more interesting. Their enormous ages force researchers to ask what “one tree” really means when a living organism can lose its oldest wood, regenerate from surviving tissues and continue producing fruit for generation after generation.

For thousands of years, people have planted, pruned, harvested and protected olives around the Mediterranean. Trees such as Oliveira do Mouchão and Oliveira do Peso now sit at the intersection of that cultural history and a difficult scientific question. Whether every extreme age estimate ultimately survives independent testing, Portugal's ancient olives clearly demonstrate something extraordinary: under the right conditions, an olive tree can persist through centuries of environmental change, human history and biological renewal while still producing new growth today.