Many of the oldest trees alive today are olive trees. There are olive groves planted by the ancient Greeks that still flourishing now. It has proven difficult to date most olive trees accurately, because the people who live with the oldest ones come to love and honor them, and are unwilling to expose them to the dangers that come with taking a core sample. However, there are cultivated groves that have been conclusively proven to well over a thousand years old. There is one grove in Sardinia that reliably dates back almost four thousand years. Oral tradition indicates that some are even older, and that in fact olive trees might never die.
What is the secret to the olive tree’s exceptional long life? The trunk and branches do not actually live forever. They hollow out and die off many, many times over the course of the life of the tree. The root and the parts of the olive tree that are underground do not die of natural causes. They sprout and send forth new trees again and again.
The olive tree is famous for growing in poor soil and extremely rocky environments. Olives will grow where nothing else grows. But this does not mean they are indestructible. Olive trees require very specific growing conditions. They must have a hot summer and a cool winter. The winter cannot be too cool, though. Between 35 and 60 degrees Fahrenheit the trees will flourish, but if the temperature dips below 15 degrees the roots will die. This is why only the stable climates of the Mediterranean and California are known for their olive groves.
Olive trees are also self-pollinating, which is unusual in the plant kingdom. This fact might help account for their extreme longevity. Since olive trees do not use the genes of other plants to sprout and seed, there is less possibility for genetic transcriptions to enter the system and for mutations to occur. It also helps that, because of their propensity for poor soil, olive trees are usually isolated from other trees. Any disease that makes the transition to an olive grove will simply kill the parts of the tree that extend above ground. After a suitable period, when cultivators or nature safely clear the dead tree away, the olive root will simply sprout another tree. Olive flies are a perennial pest, but they never hurt the roots, and in fact the symbiosis between olive tree and olive fly goes back so far that paleobotanists have found fossilized olive flies on trees buried by volcanoes thousands of years ago.
We are unaware of the exact reason why olive trees live so long. However, we can make some excellent guesses. One reason may be that, since they are sheltered by the soil and protected from mutation, the roots of olive tree simply have no reason to not live forever. The molds and fungi that attack most trees cannot find their way to the essential part of the tree in its bed of rock, and the diseases that come with interbreeding pass them by. Perhaps someday we will uncover the secret of these beautiful trees, but until then, they will remain humanity’s ageless and mysterious friends.