An 18 000‐year pollen and sedimentary record from the cedar forests of the Middle Atlas, Morocco

Abstract

A new record from the heart of the Moroccan Middle Atlas cedar forests spans the last 18 000 years and provides valuable insight into our understanding of the natural vegetation and environmental changes. The approach is based on the study of pollen content, geochemical elements and grain size analysis. The pollen data indicate that the vegetation was dominated by herbaceous plants until 9000 BP. Such open landscape allowed greater soil erosion and an input of chemical elements from the watershed. After 9000 BP, tree cover, mainly oak, increased slightly and was accompanied by a higher taxonomic diversity. However, several steppe elements remain well represented in the area until 5000 BP, which suggests that the climate was rather dry during the first part of the Holocene. After 6000 BP, the climate became more favourable to expansion of the forest ecosystems, including Cedrus atlantica, thereby reducing erosion. A strong reduction of the tree pollen percentages is recorded after 2000 BP, which may be related to increasing human activities during the Roman period. These forest changes are concomitant with an increase of lead and copper concentrations in the record, probably related to Roman metalworking activities

Climate change and ecosystems dynamics over the last 6000 years in the Middle Atlas, Morocco

“…3750 cal BP around Lake Hachlaf expresses its late occurrence at higher altitude. Around Lake Tigalmamine , the Ras El Ma marsh (Nour El Bait et al, 2014), and the Ait Ichou marsh (Tabel et al, 2016), which are all located at about 100 to 200 m altitude below Lake Hachlaf (ca. 1700 m a.s.l.…”

“…Changes in the pollen assemblages of a marine record from the Alboran Sea also show very synchronous fluctuations between the surrounding land ecosystem changes and the sea surface temperature fluctuations (Fletcher and Sánchez Goñi, 2008;CombourieuNebout et al, 2009). Pollen records from the Middle Atlas (Reille, 1976;Rhoujjati et al, 2010;Nour el Bait et al, 2014;Tabel et al, 2016) and the Rif Mountains show that the Holocene climate change had a major impact on the ecosystems composition with a clear succession of different species sensitive to winter frost, strong rainfall seasonality, and/or the total amount of annual rainfall throughout the year.…”

Environmental Drivers of Holocene Forest Development in the Middle Atlas, Morocco

“…Recent studies have contributed further knowledge regarding patterns and processes of Holocene vegetation change in the northwestern Middle Atlas at Ras el Ma and Dayat Hachlaf (Nourelbait et al, 2014(Nourelbait et al, , 2016Tabel et al, 2016), and forthcoming data for the Holocene are indicated for Lake Tifounassine (Cheddadi et al, 2015). At Dayat Hachlaf, forested conditions with Quercus (undifferentiated) and Pinus are recorded throughout the record from 6,000 cal yr BP, and include a shift in forest composition around 3,500 cal yr BP, with the expansion of Cedrus (Nourelbait et al, 2016).…”

“…At Dayat Hachlaf, forested conditions with Quercus (undifferentiated) and Pinus are recorded throughout the record from 6,000 cal yr BP, and include a shift in forest composition around 3,500 cal yr BP, with the expansion of Cedrus (Nourelbait et al, 2016). In contrast, the nearby record of Ras el Ma documents a late development of forest with Quercus and Cedrus only after 5,000 cal yr BP (Nourelbait et al, 2014). In the southwestern Middle Atlas, the pollen record of Ait Ichou documents the transition from steppic to forested vegetation at 6,800 cal yr BP (Tabel et al, 2016).…”

“…The biological and bioclimatic diversity of the region, particularly as contained within the Atlas mountain ranges (Ozenda, 1975;Medail and Quezel, 1997), furthermore provides a valuable "test-bed" for understanding the wider response of FIGURE 1 | The study region and location of pollen records, showing: (a) the location of the Middle Atlas (MA), High Atlas (HA) and Rif mountain ranges in Morocco; (b) the western Middle Atlas and the location of the study site and other Holocene pollen studies cited in the text; and (c) length and chronological control of dated pollen records for the Middle Atlas. Key to sites: AFO-Dayat Afourgagh (Lamb et al, 1991); ALI-Lake Sidi Ali (1-Sidi Ali sub-basin, Lamb et al, 1999; 2-Sidi Ali deep lake, this study); CDZ-Col du Zad (Reille, 1976); HAC-Dayet Hachlaff (Nourelbait et al, 2016); HAR-Taguelmam N'Harcha (Lamb et al, 1991); ICH-Ait Ichou (Tabel et al, 2016); IFF-Dayat Iffir (Lamb et al, 1991); IFR-Dayat Ifrah (Rhoujjati et al, 2010;Reddad et al, 2013); RAS-Ras el Ma (Nourelbait et al, 2014); TIF-Tifounassine (Cheddadi et al, 2015); TIG-Tigalmamine (Lamb et al, 1989Lamb and van der Kaars, 1995;Cheddadi et al, 1998).…”