Mediterranean, the forest that resisted the power of the Sun

The forests that today border the Mediterranean basin (the ones we have already talked about hither), the Mare Nostrum of the ancient Romans, originated on the shores of the Tethys Sea, approximately 100 million years ago, and ended up forming at the end of the last glaciation, now about 20,000 years ago. Its geological and biological history constituted the vital scenario in which human beings of the old world, for 8,000 years ago, cultivated the land, hunted deer, fished in its rivers and ate the fruits of its thickets. From the Greece of Pericles to the Castile of the Catholic Monarchs, from the Rome of Mark Antony to Abd Rahman III, the first Andalusian caliph, the Mediterranean forest was the great Biome from southern Europe. So we can talk about the Mediterranean, the forest that resisted the power of the Sun

The fascinating adaptation of the plant kingdom to aridity, fires and high temperatures.

Twenty thousand years, we were saying, the end of the last ice age. The great climate change that occurred then will cause a real catastrophe; a significant increase in temperatures that will exert selective pressure on the biocenosis, as if the god Apollo, with a fire axe, had been eliminating every living being that did not know how to adapt to the new environmental conditions. Since the first oceanic bacteria that appeared 3.5 billion years ago, life has always worked the same way: the environment imposes laws and living beings adapt and prosper, or end up dying. The Mediterranean forest picked up the gauntlet and created a plant community highly specialized in dealing with aridity (water scarcity), high temperatures and recurrent fires. Needless to say, plants cannot move, search for water or food, or shelter from heat or escape herbivores, so their leaves, stems and roots became survival machines to optimize environmental resources.

Nothing is born or has ever been born without first swimming

Joaquín Araujo's phrase explains the imperative need for water for living beings, their cells and their tissues. Here came the first problem for the flora of the Mediterranean basin; the Shortage of rainfall. Trees such as oak, cork and olive trees were favored because they had low elevations, evergreen leaves, sclerophyllous (hard) and small that reduced evapotranspiration and the surface area exposed to the sun. A waxy coating reflected radiation, thus reducing water loss. The leafy horizontal canopies cast shade over their own roots, reducing soil heating and allowing the stored water to remain available longer to its prolific and absorbing roots. The fruits, on the other hand, in the form of resistant and leathery capsules (acorns) would protect the embryos from dehydration.

The transition from a cold to a warm climate was the second major challenge for these plant communities; it was necessary to address the Tall temperatures. A good adaptation for the shrub stratum was the sparse, sparse, globular growth, an anatomy that protected the stems, inner leaves and roots from heating, wind drying and loss of soil moisture. Mastic, cornicabra, strawberry tree, labernago or heart of palm found in this strategy a good way to survive and thrive.

Changes in the physical environment are an excellent laboratory of open-air evolution, and in their quest to survive, living forms generate all kinds of adaptations. Special attention deserves the foliar description of the common heart of palm (Chamaerops humilis), with an innovative design. The surface of the leaves, open like a fan and in a zigzag pattern, prevents the sun from shining perpendicularly on them, thus reducing insolation. The carob tree, on the other hand, generated leaves with highly lobed edges, trimming the contact surface and mitigating the overheating caused by sunlight.

Thousands of years of evolution weaved a fascinating variety of adaptations. The gulagas have modified their leaves into thorns and the brooches have turned them into thin and elongated linear cords. The stems, pigmented with chlorophyll, are responsible for carrying out photosynthesis. Both strategies decrease the mass of hot air in contact with their leaf tissues. The jaras, on the other hand, cover their leaves with a thin film of Pelillos called tomento, a type of sunscreen that helps dissipate radiation. Other species, such as labiadas, have developed leaves that are poor in pigments, giving them a whitish and less green appearance (Phlomis purpurea) that increases albedo (reflection of light), combining this character with the existence of revolving edges that roll over the stomata and protect them from the sun.

Another set of successful adaptations had to do with the ability of species to adapt to — and even be favored — by forest fires. The cork oaks have a thick lignified layer (cork), like armor, that delays the ignition of the plant. The pringosa jar anoints its stems and leaves with a sticky and flammable substance, labdanum, which promotes the combustion of the capsules where it stores the seeds, causing them to explode and spread throughout the environment. The fruits of the pinaceae open with the high temperatures caused by flames (45º-50º), thus freeing the pine nuts and spreading them out to colonize new spaces. Heathers have generated a thickening in the upper part of the roots called lignotuber, a kind of bud store that is activated with increasing temperatures, generating an almost immediate regrowth of dozens of new specimens.

In short, as we have seen, the adaptations of the native and coastal flora of the ancient Tethys Sea were able to thrive and colonize inland regions following these adaptations: reducing size, minimizing leaf surfaces and creating structures to protect themselves from the sun, water loss and, even, making them opportunistic from forest fires. The Mediterranean forest may not be as lush and splendorous as the deciduous formations, but its contained beauty is undeniable.

The field itself became a tree in you, brown oak

Antonio Machado's verses may be the best poetic homage to the great biome in which the peoples of Iberia thrived, a totemic landscape inseparably linked to our bull's skin, to our shared history as a species, from Algeciras to Istanbul, as Serrat sang in his sublime Mediterraneo, and, ultimately, to our culture as a people and civilization. Perhaps getting to know better the beauty of their evolutionary strategies and their desire to live and survive will help us to understand even more the splendor of nature, its delightful complexity and its disturbing fragility. Without oaks, olive trees or cork oaks, there would have been no Tartessians or Turdetans, neither Roman Betica nor Muslim Al Ándalus or Christian Castile.

The question is overwhelming: Is it possible that we have come this far thanks to the Mediterranean forest?

Chema Fernández, Biodiversity