This study reconstructs and interprets the changing range of Atlas cedar in northern Morocco over the last 9,000 years. A synthesis of fossil pollen records indicated that Atlas cedars occupied a wider range at lower elevations during the mid-Holocene than today. The mid-Holocene geographical expansion reflected low winter temperatures and higher water availability over the whole range of the Rif Mountains relative to modern conditions. A trend of increasing aridity observed after 6,000 years BP progressively reduced the range of Atlas cedar and prompted its migration toward elevations above 1,400 masl. To assess the impact of climate change on cedar populations over the last decades, we performed a transient model simulation for the period between 1960 and 2010. Our simulation showed that the range of Atlas cedar decreased by about 75% over the last 50 years and that the eastern populations of the range in the Rif Mountains were even more threatened by the overall lack of water availability than the western ones. Today, Atlas cedar populations in the Rif Mountains are persisting in restricted and isolated areas (Jbel Kelti, Talassemtane, Jbel Tiziren, Oursane, Tidighine) that we consider to be modern microrefugia. Conservation of these isolated populations is essential for the future survival of the species, preserving polymorphisms and the potential for population recovery under different climatic conditions.

The present study aims to review palaeoecological evidence for environmental changes induced by human activities over the last few millennia in the montane landscapes of Morocco. The study is based on well-dated pollen and geochemical records from the Rif and the Middle Atlas mountains, to show spatial and temporal variation in the onset and intensity of exploitation of forest, soil and mineral resources. Before ca. 2000 BP, anthropogenic impact was minimal. At about that time, abrupt changes of the arboreal pollen proportions, with a decline in all tree taxa, indicate a reduction of the forest cover interpreted as being anthropogenic. In the Rif Mountains, increased influx of carbonates (Ca) in the sedimentary records indicates enhanced soil erosion coincident with the reduction in tree cover. In the Middle Atlas, reduced forest cover is linked to geochemical evidence for mining and metallurgy of lead (Pb), copper (Cu) and zinc (Zn). These industrial activities correspond to the expansion of the Roman Empire into Morocco at around AD 40 and show a decline when the Romans were displaced by the Vandals about five centuries later

A new fossil record from the southern Middle Atlas spans continuously the last 25 000 years and provides evidence of an increased amount of snow precipitation during the last glacial period and a warm early Holocene with rather dry climate conditions. This environmental reconstruction is based on a multi‐proxy approach that integrates pollen, micro‐charcoals, grain size and geochemical analysis. During the last glacial period we observe a strong presence of aquatic plants species that today flower during late spring and summer. These occurrences are related to an increased amount of snow precipitation on the surrounding mountains which fed the marsh during the summer season. Although the early Holocene reveals a slight and steady expansion of Mediterranean oaks, the semi‐arid Artemisia steppe remained dominant in the landscape until 6.8 ka cal BP. Thus, the early Holocene seems to have been less humid than elsewhere in North Africa. The Atlas cedars began to establish around 6 ka cal BP. This indicates that the amount of annual rainfall increased after the mid‐Holocene. The late Holocene is marked by an increase of fire events, which may be related to a strengthening of the dry season and/or a higher seasonality.

The greening of the Sahara, associated with the African Humid Period (AHP) between ca. 14,500 and 5,000 y ago, is arguably the largest climate-induced environmental change in the Holocene; it is usually explained by the strengthening and northward expansion of the African monsoon in response to orbital forcing. However, the strengthened monsoon in Early to Middle Holocene climate model simulations cannot sustain vegetation in the Sahara or account for the increased humidity in the Mediterranean region. Here, we present an 18,500-y pollen and leaf-wax δD record from Lake Tislit (32° N) in Morocco, which provides quantitative reconstruction of winter and summer precipitation in northern Africa. The record from Lake Tislit shows that the northern Sahara and the Mediterranean region were wetter in the AHP because of increased winter precipitation and were not influenced by the monsoon. The increased seasonal contrast of insolation led to an intensification and southward shift of the Mediterranean winter precipitation system in addition to the intensified summer monsoon. Therefore, a winter rainfall zone must have met and possibly overlapped the monsoonal zone in the Sahara. Using a mechanistic vegetation model in Early Holocene conditions, we show that this seasonal distribution of rainfall is more efficient than the increased monsoon alone in generating a green Sahara vegetation cover, in agreement with observed vegetation. This conceptual framework should be taken into consideration in Earth system paleoclimate simulations used to explore the mechanisms of African climatic and environmental sensitivity.

The origin of modern disjunct plant distributions in the Brazilian Highlands with strong floristic affinities to distant montane rainforests of isolated mountaintops in the northeast and northern Amazonia and the Guyana Shield remains unknown. We tested the hypothesis that these unexplained biogeographical patterns reflect former ecosystem rearrangements sustained by widespread plant migrations possibly due to climatic patterns that are very dissimilar from present-day conditions. To address this issue, we mapped the presence of the montane arboreal taxa Araucaria, Podocarpus, Drimys, Hedyosmum, Ilex, Myrsine, Symplocos, and Weinmannia, and cool-adapted plants in the families Myrtaceae, Ericaceae, and Arecaceae (palms) in 29 palynological records during Heinrich Stadial 1 Event, encompassing a latitudinal range of 30°S to 0°S. In addition, Principal Component Analysis and Species Distribution Modelling were used to represent past and modern habitat suitability for Podocarpus and Araucaria. The data reveals two long-distance patterns of plant migration connecting south/southeast to northeastern Brazil and Amazonia with a third short route extending from one of them. Their paleofloristic compositions suggest a climatic scenario of abundant rainfall and relative lower continental surface temperatures, possibly intensified by the effects of polar air incursions forming cold fronts into the Brazilian Highlands. Although these taxa are sensitive to changes in temperature, the combined pollen and speleothems proxy data indicate that this montane rainforest expansion during Heinrich Stadial 1 Event was triggered mainly by a less seasonal rainfall regime from the subtropics to the equatorial region.

Abstract. The present study aims at reconstructing past climate changes and their environmental impacts on plant ecosystems during the last 6000 years in the Middle Atlas, Morocco. Mean January temperature (T jan ), annual precipitation (P ann ), winter (P w ) and summer (P s ) precipitation, and a seasonal index (SI) have all been quantified from a fossil pollen record. Several bio-and geo-chemical elements have also been analysed to evaluate the links between past climate, landscape, and ecosystem changes.Over the last 6000 years, climate has changed within a low temperature and precipitation range with a trend of aridity and warming towards the present. T jan has varied within a ca. 2 • C range, and P ann within less than 100 mm yr −1 . The longterm changes reconstructed in our record between 6 ka cal BP and today are consistent with the aridity trend observed in the Mediterranean basin. Despite the overall limited range of climate fluctuation, we observe major changes in the ecosystem composition, the carbon isotopic contents of organic matter (δ 13 C), the total organic carbon and nitrogen amount, and the carbon to nitrogen ratio (C / N) after ca. 3750 cal BP. The main ecosystem changes correspond to a noticeable transition in the conifer forest between the Atlas cedar, which expanded after 3750 cal BP, and the pine forest. These vegetation changes impacted the sedimentation type and its composition in the lake.Between 5500 and 5000 cal BP, we observe an abrupt change in all proxies which is coherent with a decrease in T jan without a significant change in the overall amount of precipitation.

Le Moyen Atlas marocain est une région climatiquement sensible aux variations des masses d'air de la mer Méditerranée, du désert du Sahara et de l'océan Atlantique. Cette région recèle plusieurs retenues d'eaux naturelles généralement à l'abri des perturbations anthropiques. Une carotte sédimentaire d'environ 10 mètres de longueur extraite du centre du lac Iffer a fourni un enregistrement des conditions paléoclimatiques et paléohydrologiques du Moyen Atlas durant les derniers 6 500 ans. L'étude de la granulométrie, la géochimie élémentaire ainsi que la mesure des teneurs en carbone organique, des carbonates et de la susceptibilité magnétique des sédiments montrent que la séquence est formée d'une alternance de sédiments détritiques et de sédiments relativement riches en matière organique d'origine terrestre et aquatique liée aux conditions climatiques et environnementales régionales. Les résultats montrent que :-la base de la séquence, dont l'âge remonterait à ~6 500 ans BP, est formée de sables carbonatés qui témoignent des conditions climatiques arides associées aux faibles apports hydriques,-la période 4 600-2 000 ans BP est caractérisée par l'installation de conditions climatiques plus humides traduites par des hauts niveaux lacustres entrecoupés par des événements relativement arides de courtes durées,-à partir de 2 000 ans BP, on assiste à une anthropisation qui se traduit par le recul des forêts et l'intensification des activités agricoles. Cette déforestation est indiquée par un déséquilibre total des profils pédologiques (érosion des sols) et par des flux détritiques très importants arrivant dans le lac.

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