What Mediterranean tree is uniquely equipped to withstand wildfires with armor-like bark and high, out of reach, branches?
The stone pine!
In his 1913-1927 novel, In Search of Lost Time, French writer Marcel Proust described the power of a soft, buttery madeleine cookie dipped in tea to transport the story’s narrator back to his childhood, unlocking a flood of vivid memories, emotions, and senses. Since then, the term “Proustian memory” has come to describe the sights, smells, sounds, or tastes that bring us back to a particular place in time, one that reminds each of us that we are home.
This is how my partner talks about the stone pine (Pinus pinea) in Spain. Raised in Madrid, she moved to the U.S. when she was twenty-three. For the next decade she’d go long stretches without returning home (blame grad school, work, a global pandemic, and high airfare).
But on those occasions where she was able to return home for a visit, before that first sip of cafe con leche, it was the stone pines flickering past the taxi cab window that brought her back to the youth she’d spent running beneath them, and told her soul that she was home.
There are few markers more reliable than the stone pine to remind you that you are in the Mediterranean. Its branchless trunk rises 25-30 meters from the dry ground. Deep grooves run up the thick, rugged bark in shades of rust and ash-gray. It is bare all the way up to a rounded crown that seems to hover above the landscape. Branches bearing clusters of slender needles splay out horizontally and cast large soft shadows on the ground, giving the tree its nickname, the parasol (umbrella) pine. Its high canopy offers nesting sites and vantage points for many birds of the Med, like Eurasian Jays and Red Kites.
The stone pine’s unique silhouette foreshadows its individuality among its relatives in the genus Pinus.
The Parasol Pine
It is a resilient tree with few natural predators. High branches keep its cones away from most ground-dwelling herbivores, and that hardy bark helps shield against both prying insects and wildfire, perhaps its most common threat in the Mediterranean. The clustering of branches high above the brush also helps it withstand fire events more successfully than other species in the area. That said—it’s important to understand that pests (like the pine tortoise scale) and runaway fires do remain serious threats, even if the stone pine is better prepared to meet them.
The tree also stands apart from other species of pine in its lack of hybridization—that is, its failure to crossbreed with other pine species, despite existing in close proximity. It does not demonstrate a tendency to interbreed with its neighbors like Pinus halepensis (Aleppo pine) or Pinus pinaster (maritime pine), and that is unusual among pines. It’s really just out here doing its own thing.
This pattern of genetic isolation is a product of circumstances. The stone pine’s pollination window doesn’t often line up with other species and, even when they do, the tree’s genetic makeup has remained distinct enough (while others have hybridized) that fertilization is increasingly improbable.
And unlike other pine species, stone pine seeds are not effectively dispersed by the wind, perhaps contributing to this isolation. Instead, they rely on the few animals that can reach them, particularly birds, to shake them free and drop them elsewhere.
Digging Deeper
I hope we’ve established that the stone pine is one tough, rugged cookie, designed from the root up to thrive in a variety of ecosystems around the Mediterranean. But what’s going on below the surface?
To really understand any tree, you’ve got to look down. When we talk about “siliceous” soils, we’re talking about soils that are made up mostly of silica—essentially a mineral of silicon and oxygen that comes from rocks like quartz and sandstone. These soils are characteristically sandy and drain water quickly, but offer fewer nutrients—making them less fertile and more inhospitable for many trees. They also tend to be more acidic.
On the other half of the pH scale (which measures the acidity of acids on one end, and alkalinity of bases on the other) are what are known as “calcareous” soils—that is, soils rich in calcium carbonate from sources like limestone or chalk, but light on most other important nutrients.
Both of these types of soil are found along the rocky Mediterranean. And while its preference is for the former, more siliceous soils, the stone pine does well in both. In fact, it’s this ability to thrive in these rocky soils that earned the tree its name, the stone pine. Of course, the tree’s deep roots alone are not always enough to survive in these nutrient-deficient soils. Like other pines around the world, Pinus pinea benefits from ectomycorrhizas, the symbiotic relationship between the tree and fungi in the ground that help facilitate nutrient exchange in soils where they are harder to come by. It’s a fascinating relationship that certainly deserves its own essay, but it is important to understand the critical role Ectomycorrhizal fungi (EMF) play in maintaining thriving forest ecosystems. They form mutually beneficial relationships with trees, where the fungi exchange those coveted soil nutrients for carbon compounds produced by the trees during photosynthesis. This natural partnership supports nutrient cycling and enhances tree health and growth, allowing pines just like the stone to survive under more challenging soil conditions.
In the course of human events
We know quite a bit more about where the stone pine is, rather than where it’s from. Pinpointing its native range has proven difficult because the tree has been harvested, traded, and replanted by human since prehistory—first for their edible pine nut seeds, then by later civilizations like the Romans for their ornamental status. Even today, it is common throughout the region to find a street or garden lined with the distinctive tree.
Today, pine nuts from the stone pine remain big business, and their cultivation has been seen as an alternative crop in regions where the arid soil would make other agricultural endeavors too difficult.
I’ve realized there is more to learn about the stone pine than I could ever hope to fit on a page. In my naivety or ignorance, I did not expect that. Its deceptively simple silhouette belies a complex story of resilience, symbiosis, and ancient history and, for at least one Spaniard, a reminder that she’s home.
Brendan began his career teaching conservation education programs at the Columbus Zoo and Aquarium. He is interested in how the intersection of informal education, mass communications and marketing can be retooled to drive relatable, accessible climate action. While he loves all ecosystems equally, he is admittedly partial to those in the alpine.
Sources and Further Reading:
- Pinus pinea in Europe: distribution, habitat, usage and threats
- Molecular approach to characterize ectomycorrhizae fungi from Mediterranean pine stands in Portugal
- Ectomycorrhizal Fungi Enhance Pine Growth by Promoting Iron Uptake
- Chapter 19 – Advances in methods and practices of ectomycorrhizal research
- Soil pH and Organic Matter