A nearly thousand-year-old sessile oak, which has grown by weathering storms and the passing of centuries, is the witness that will help us understand how the climate in the Mediterranean basin has changed and will continue to change.
A steep slope, exposed to harsh weather, strong winds, snow and sun. Reachable only by experienced climbers. This is where Demetra, the oldest sessile oak in the world, discovered by researchers in the Aspromonte national park, has grown. "Trees age for far longer in harsh environments, where they remain smaller in size," Gianluca Piovesan tells LifeGate, a lecturer at the University of Tuscia and one of the authors of the discovery. It is in these environments that scientists have managed to date the age of five large sessile oaks (Quercus petraea) using the radiocarbon method, revealing a surprising longevity previously unknown, reaching up to (nearly) one thousand years. To be precise, 934 years, not counting measurement uncertainty.
The discovery, published in the scientific journal Ecology and entitled "Radiocarbon dating of Aspromonte sessile oaks reveals the oldest dated temperate flowering tree in the world", (DOI: 10.1002/ecy.3179), adds another hugely important piece to our knowledge of ancient trees and old-growth forests around the world. "This is the oldest temperate-climate broadleaf tree in the world," Piovesan continues. "During some sampling work we came across a nucleus of old-growth forest and a group of five sessile oaks whose advanced age was already known." At that point the researchers decided to date the trees using radiocarbon analysis, arriving at the surprising finding that the five identified sessile oaks are between 934 (±65) and 570 (±45) years old. The radiocarbon dating analyses were carried out using AMS (Accelerator mass spectrometry) at Cedad (Center for applied physics, dating and diagnostics) of the University of Salento in Lecce.
"Trees do not die as animals do — not because they age at the cellular level, but because they are attacked by external factors such as insects, lightning or fungal diseases," Piovesan explains. "By growing in these extremely harsh environments, they manage to keep their structure intact and grow for centuries and centuries." But this also creates difficulties for researchers, because very old trees are often hollow inside the trunk. This means that the oldest rings are frequently missing or severely degraded, making it very difficult to identify and collect the rings closest to the pith for radiocarbon dating — so much so that researchers were obliged to use a scalpel to extract the samples nearest to the pith, and therefore the oldest ones.
The discovery is part of a much broader study conducted by researchers from Tuscia in collaboration with Spanish colleagues, to study the response of forests in the Mediterranean environment to climate change. Aspromonte lies at the heart of the Mediterranean basin, a fundamental area for climate reconstructions. These trees "can tell us how the climate has changed at the centre of the Mediterranean, which is a biodiversity hotspot but also one of the places where climate change is happening most rapidly." By measuring not only the width of the rings but also studying the presence of certain isotopes of carbon, oxygen and hydrogen, they can tell us how the environment has changed over the centuries.
"The discovery of these long-lived sessile oaks in the high-altitude mountain environment of Aspromonte confirms the high level of naturalness of the forest ecosystems in the protected areas of southern Apennines," states Antonino Siclari of the Aspromonte national park in a press release. An enormous ecological value — yet another confirmation that southern Italy is a refuge for biodiversity, as Piovesan confirms: "From the Pollino, through the Sila, to Aspromonte, a unique biodiversity persists. And it seems that these ecosystems have a remarkable capacity to respond to climate change, because here there is no dieback or tree death, but a positive response. This is why we are trying to understand the reason behind it."
The oldest trees are all found here, in the South. Not only Demetra and the other four sessile oaks, but also the two 620-year-old beech trees discovered two years ago in the Pollino national park and nicknamed Michele and Norman, join the list of the oldest scientifically dated trees in Europe, alongside the Bosnian pine nicknamed Italus. All the more reason to focus on the conservation of these unique environments, relic witnesses of the past. Capable of withstanding what man cannot control: time.