Climate change since the last glacial period in Lebanon and the persistence of Mediterranean species
Rachid Cheddadi & Carla Khater
1 University of Montpellier II, CNRS-UM2-IRD, ISEM, France,
2 Center for Remote Sensing, National Council for Scientific Research e Lebanon, BP 11-8281, Bir Hassan, Beirut, Lebanon
Background. The Near East, including Lebanon territory, is considered as a hotspot of biodiversity as well as a refugial area in the Mediterranean. Lebanon is a territory which represents the southernmost edge of the range of some valuable plant species such as firs and cedars. Genetic studies suggest that it is crucial to evaluate the climate changes and their impacts at the rear edge of relict populations of species such as those found in Lebanon.
Methods. Three fossil pollen records, encompassing the Holocene and partially the last post-glacial period, were collected in Lebanon. Temperature and precipitation variables were reconstructed using the modern ranges of the Eastern Mediterranean plant taxa identified in the fossil pollen records and their related modern climate. We quantified the mean January temperature (Tjan) and both winter (Pw) and summer (Ps) precipitation.
Results. Tjan shows a strong correlation with the global temperature changes retrieved in the NGRIP Greenland ice core. The amplitude of ca. 8°C between the Younger Dryas (YD) period and the Holocene is coherent with climate reconstructions from the Eastern Mediterranean. The overall amount of precipitation was lower during the YD than during the Holocene but the contrast between Pw and Ps was much more reduced (less than 2 times) during the YD than during the Holocene (up to 8 times). Such different seasonal contrast compare to the present day is coherent with other climate proxies from the Levant that tend to indicate the presence of moisture during the last glacial period. In effect, the low Pw during the YD reflects the replacement of the forest ecosystem by a more shrubby or herbaceous vegetation.
Conclusions. During the last glacial period, Lebanon was not under a typical Mediterranean climate such as the one we know today, i.e. with a strong precipitation and temperature contrast between summer and winter seasons, but rather under a less contrasted climate. Mediterranean species persisted in this area due to the low amplitude of temperature change between the last glacial period and the Holocene as well as to an availability of moisture throughout the year instead of an occurrence mainly during the winter season as is the case today.
Cheddadi, R., & Khater, C. (2016). Climate change since the last glacial period in Lebanon and the persistence of Mediterranean species. Quaternary Science Reviews, 150, 146–157.