The Lost Forest

Remnant laurel forest on the Canary Islands

In the latter part of the Messinian Stage (5.9-5.3 million years ago) at the end of the Miocene Epoch an ice age and some tectonic activity near the Strait of Gibraltar conspired to lower global sea level and cut off the connection between the Mediterranean. The water in the sea evaporated because the rivers couldn’t keep it filled without the ocean’s input. But at the end of the Miocene the basin filled with water again and the humid late Neogene climate returned to the region. Mediterranean rainfall has varied repeatedly through geologic time, most recently in synch with the coming and going of the glaciers of the Pleistocene. A humid interval at the end of the last glacial period might have been the last stand (as it were) for a widespread laurel forest.

Vestiges of the laurel forest remain on the Canary Islands and in humid valleys of Andalusia in Spain, but it has otherwise entirely disappeared. Some of these forests were cut down to use in making charcoal, an important ingredient in the process of alloying tin and copper to make bronze. Some were cleared for agriculture. The erosion of steep slopes removed the topsoil, making it nearly impossible for the forest to recover even after rural areas were abandoned.

The moist understory of a laurel forest.

Laurel forests require a humid climate with only moderate seasonal change. They can endure only short and infrequent freezes. In the Canary Islands, where they survive they are on west-facing slopes that collect the moisture carried by the westerly winds off the Atlantic Ocean.

The laurel (or laurisilva) forests declined in extent throughout the Pliocene and Pleistocene (5.3 m.y.a. to 10,000 years ago.) as the climate of the Mediterranean became less humid. So the forests of the Bronze Age (roughly 5,000 to 4,000 years ago in the Mediterranean) would have been making the transition from the laurisilva to the sclerophyllic (dry climate-adapted) communities that exist today where there are forests.

But laurisilva community does survive in isolated pockets and so can be described by observation rather than having to reconstruct it entirely from the geologic record. One of its distinctive charcteristics is the diversity of the canopy. Temperate forests are usually dominated by five or fewer species at a given location, but laurisilva assemblages supported more than 30 species of canopy tree and also had a diverse sub-canopy complement. Ecologists have called the laurisilva assemblage a transitional ecosystem between the temperate and tropical forest types.

The bay laurel (Laurus nobilis)

Because they were (and are) in humid climates the leaves of many species in this forest have evolved waxy coatings and “drip tips” to shed water from their surfaces efficiently. Drip tips are thought to resist the growth of epiphyllous fungi, lichens, bryophytes and algae on leaf surfaces by promoting the drainage of water following rain (although research has yet to bear this out).

The bay laurel (Laurus nobilis) is a relict species of this community. It is still widespread in the Mediterranean region and was an important part of the Bronze and Iron Age cultures of Greece and Rome. The laurel wreath awarded to victors of any sort of contest (although most familiarly with athletic and military events) was constructed from the branches of this tree. Apollo was frequently depicted wearing a laurel wreath.

Modern kitchens often have a tin of dried bay leaves somewhere on the spice rack. These are from the same tree (which also grows as a large shrub) and a familiar addition to the red sauces of many an Italian grandmother. The aromatic that gives the bay leaf its flavor is cineole (also called eucalyptol). It can persist in the leaf for a year after drying, but plenty of people end up throwing out their tin of bay leaves after keeping them for years and never using them for anything other than red sauces. They can actually be ground up and used in soups and they do a Bloody Mary some good too.