Laurus - History

History

The laurus genus is characteristic of the formations of laurel forest and was more widespread in the Tertiary. It has led to endemic species on islands, but not so widespread geographically as in the past.

The ecological requirements of the species, are those of the laurel forest and like most of their counterparts laurifolia in the world, they are vigorous species with a great ability to populate the habitat that is conducive. The phylogeography of this group provides a nice example of various speciation mechanisms at work. This group became isolated during the Quaternary glaciations and expansion of the polar ice caps, resulting in widespread cooling of the climate, the flora of central and southern Europe retreated to more southerly latitudes in search of milder conditions. Also the sea level was lower, with lands today submerged forming land bridges.

The end of glaciations coincided with the spread of deserts in North Africa, notably the Sahara, so this type of forest was reduced to those areas, which act as boundaries between temperate and tropical. At that time, the climate of southern Europe was warmer and wetter than today, and the vegetation that surrounded the ancient shores of the Mediterranean Sea was likely similar to that of the current Macaronesian laurisilva. The Ice Age which took place at the end of that period and for much of the Quaternary forced the laurel forests to move to warmer southern regions, where conditions were more conducive to their survival, settling in this way on the northwest coast of Africa and in the Macaronesian archipelagos. The ocean permitted the plants' migration to more suitable areas, where they survived.

With the general warming of the atmosphere and the consequent withdrawal of the ice, flora tertiary survivors could not regain their range in southern Europe, as the new post-glacial climate was drier than that of the Tertiary, and to these new environmental requirements, the primitive tropical European flora evolved and gave rise to the present flora of the Mediterranean sclerophyll.

At the same time, isolated from the mainland, the tertiary Macaronesian laurel species evolved independently, which has led endemic species. Physical separation of the poblations begin a process of change to adapt to new conditions. This mechanism is called allopatric speciation. Over time, survivors specimens of the laurus genus, adapted to different ecological niches. This led to reproductive isolation, an example of ecological speciation.

In Europe the genus is represented by a single species, the named Laurus nobilis. In macaronesian islands this former arose from a common ancestor in the area of laurisilva in the Mediterranean area. The islander laurels of Macaronesia in the eastern Atlantic, are present in the Azores, Madeira Islands, and western Canary Islands, from 400 m to 1200 m elevation, in the laurel forest habitat in the islands.

The laurisilva forests of Macaronesia are relicts of a vegetation type which originally covered much of the Mediterranean Basin when the climate of the region was more humid. With the drying of the Mediterranean Basin during the Pliocene, the laurel forests gradually retreated, replaced by more drought-tolerant sclerophyll plant communities. Most of the last remaining laurisilva forests around the Mediterranean are believed to have disappeared approximately 10,000 years ago at the end of the Pleistocene, when the Mediterranean basin became drier and with a harsher climate, although some remnants of the laurel forest flora still persist in the mountains of southern Spain, north-center of Portugal and northern Morocco, and two constituent species (Laurus nobilis and Ilex aquifolium) remain widespread. The location of the Macaronesian Islands in the North Atlantic Ocean moderated these climatic fluctuations, and maintained the relatively humid and mild climate which has allowed these forests to persist to the present day.