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

In semi-arid regions subject to rising temperatures and drought, palaeoecological insights into past vegetation dynamics under a range of boundary conditions are needed to develop our understanding of environmental responses to climatic changes. Here, we present a new high-resolution record of vegetation history and fire activity spanning the last 12,000 years from Lake Sidi Ali in the southern Middle Atlas Mountains, Morocco. The record is underpinned by a robust AMS radiocarbon and 210Pb/137Cs chronology and multi-proxy approach allowing direct comparison of vegetation, hydroclimate, and catchment tracers. The record reveals the persistence of steppic landscapes until 10,340 cal yr BP, prevailing sclerophyll woodland with evergreen Quercus until 6,300 cal yr BP, predominance of montane conifers (Cedrus and Cupressaceae) until 1,300 cal yr BP with matorralization and increased fire activity from 4,320 cal yr BP, and major reduction of forest cover after 1,300 cal yr BP. Detailed comparisons between the pollen record of Lake Sidi Ali (2,080m a.s.l.) and previously published data from nearby Tigalmamine (1,626m a.s.l.) highlight common patterns of vegetation change in response to Holocene climatic and anthropogenic drivers, as well as local differences relating to elevation and bioclimate contrasts between the sites. Variability in evergreen Quercus and Cedrus at both sites supports a Holocene summer temperature maximum between 9,000 and 7,000 cal yr BP in contrast with previous large-scale pollen-based climate reconstructions, and furthermore indicates pervasive millennial temperature variability. Millennial-scale cooling episodes are inferred from Cedrus expansion around 10,200, 8,200, 6,100, 4,500, 3,000, and 1,700 cal yr BP, and during the Little Ice Age (400 cal yr BP). A two-part trajectory of Late Holocene forest decline is evident, with gradual decline from 4,320 cal yr BP linked to synergism between pastoralism, increased fire and low winter rainfall, and a marked reduction from 1,300 cal yr BP, attributed to intensification of human activity around the Early Muslim conquest of Morocco. This trajectory, however, does not mask vegetation responses to millennial climate variability. The findings reveal the sensitive response ofMiddle Atlas forests to rapid climate changes and underscore the exposure of the montane forest ecosystems to future warming

Multidecadal variability in Atlas cedar growth in northwest Africa during the last 850 years: implications for dieback and conservation of an endangered species

Widespread forest dieback is a phenomenon of global concern that requires an improved understanding of the relationship between tree growth and climate to support conservation efforts. One priority for conservation is the Atlas cedar (Cedrus atlantica), an endangered species exhibiting dieback throughout its North African range. In this study, we evaluate the long-term context for recent dieback and develop a projection of future C. atlantica growth by exploring the periodic variability of its growth through time. First, we present a new C. atlantica tree- ring chronology (1150–2013 CE) from the Middle Atlas mountains, Morocco. We then compare the new chronology to existing C. atlantica chronologies in Morocco and use principal components analysis (PCA) to isolate the common periodic signal from the seven longest available records (PCA7, 1271–1984 CE) in the Middle and High Atlas portions of the C. atlantica range. PCA7 captures 55.7% of the variance and contains significant multidecadal ( ̃95yr, ̃57yr, ̃21yr) periodic components, revealed through spectral and wavelet analyses. Parallel analyses of historical climate data (1901–2016 CE) suggests that the multidecadal growth signal ori- ginates primarily in growing season (spring and summer) precipitation variability, compounded by slow- changing components of summer and winter temperatures. Finally, we model the long-term growth patterns between 1271–1984 CE using a small number (three to four) of harmonic components, illustrating that sup- pressed growth since the 1970s – a factor implicated in the dieback of this species – is consistent with recurrent climatically-driven growth declines. Forward projection of this model suggests two climatically-favourable periods for growth in the 21st century that may enhance current conservation actions for the long-term survival of the C. atlantica in the Middle and High Atlas mountains

Aridification du climat régional et remontée de la limite inférieure du cèdre de l'Atlas (Cedrus atlantica Manetti) aux confins de la plaine de Midelt (Maroc)

Le cèdre de l'Atlas (Cedrus atlanticaManetti) est un phanérophyte présentant certaines exigences saisonnières en humidité, ainsi que durant certaines phases de son développement. Largement répandu à l'état spontané au Maroc, il a une grande valeur écologico-floristique, socio-économique et patrimoniale. Longtemps, cette précieuse essence a très bien été adaptée à son environnement méditerranéo-montagnard et n'a posé aucun problème sur le plan sanitaire. Or, depuis le début des années 1980, le cèdre connaît un dépérissement préoccupant, diffus ou concentré, responsable d'un recul de ses peuplements. Le dépérissement atteint des proportions anormalement élevées dans un certain nombre de massifs forestiers de la région de Midelt, dans les Moyen et Haut-Atlas. Les premiers signes se manifestent par l'atteinte d'arbres isolés ou de bouquets couvrant des superficies variées. Le phénomène peut se généraliser, comme dans la forêt d'Aït-Oufella, en bordure sud du Moyen-Atlas central, près de la plaine aride de Midelt, où la mortalité est très élevée dans certains secteurs. Mais, dans la plupart des cas, il se concentre à la limite inférieure de l'aire de répartition de l'espèce.L'examen des précipitations et des températures mesurées de 1957 à 2005 à la station météorologique de Midelt – représentative de l'ambiance semi-aride qui prévaut à la limite inférieure de l'aire de répartition du cèdre sur le versant moulouyen du Moyen-Atlas – permet de formuler l'hypothèse que les dépérissements sont imputables à un déficit des précipitations combiné à une augmentation des températures, en liaison avec plusieurs épisodes de sécheresse au cours de la période 1982-2005.Au cours de ces années, les conditions climatiques ont eu un impact négatif sur la vitalité du cèdre, ce qui a entraîné la mort de nombreux arbres. L'aridification a eu des effets particulièrement sensibles dans les secteurs où les conditions initiales étaient déjà éloignées de l'optimum écologique de l'espèce. La disparition de niches écologiques dans les secteurs les plus bas de l'aire de répartition de l'espèce provoqué une remontée de la limite altitudinale inférieure, de 1800 à 2000 m, le cèdre abandonnant progressivement la place à une chênaie (Quercus ilex L.) à genévrier oxycèdre (Juniperus oxycedrus L.).Pour différentes raisons, toutes liées à l'exposition (ensoleillement, différence d'ambiance entre le matin et le soir, déflation neigeuse par les vents d'ouest), le dépérissement du cèdre est plus accentué sur les versants orientaux des vallons qui descendent du Moyen Atlas vers la plaine de Midelt.<br>The Atlas cedar (Cedrus atlantica Manetti), a phanerophyte, needs some humidity according to seasons as well as certain phases of its development. Very spontaneously widespread in Morocco, it has a great ecological, floristic, socio-economic and heritage value. For a long time, this precious species has been very well adapted to its highland Mediterranean environment and has no sanitary problems. However, since the early 1980s, it is affected by a worrying diffuse or concentrated decay that provokes a recession of its population. The dieback reaches abnormally high proportions in some of the Midelt forested regions, in Middle and High Atlas. The first signs are shown by attacks on isolated trees or clumps of trees covering various areas. This phenomenon can be generalized in Aït-Oufella woodlands, on the southern edge of the central Middle Atlas, near the Midelt arid plain, where mortality is locally very high. But in most cases it is concentrated on the lower limit of the species repartition area.A review of rainfall and temperature measured from 1957 to 2005 at the Midelt meteorological station – that is representative of the semi-arid environment prevailing at the lower limit of the cedar repartition area on the Middle Atlas Moulouya slope – allows to formulate the following hypothesis: failings are caused by rain deficit combined with an increasing of temperatures, in association with several droughts during the 1982-2005 period.During this period, climatic conditions had a negative impact on cedar vitality resulting in the death of numerous trees. The effects of drying are particularly perceptible in the areas where the initial conditions were already far from the species ecological optimum. Disappearance of ecological niches in the lowest sectors of the species repartition area has provoked an ascent of the lower altitudinal limit from 1800 m to 2000 m. The Atlas cedar was gradually replaced by holm oak stands (Quercus ilex L.) with prickly juniper (Juniperus oxycedrus L.).For different reasons, all related to aspect (sunlight, diurnal topoclimatic differences, west wind snow deflation), cedar decline is more important on the east slopes of small valleys flowing from the Middle Atlas down to Midelt plain

L'alfa (Stipa tenacissima L.) dans la plaine de Midelt (haut bassin versant de la Moulouya, Maroc) – Éléments de climatologie

L'alfa (Stipa tenacissima L.) est représenté dans la haute plaine de Midelt par des touffes en bon état et de grande taille pouvant atteindre parfois des hauteurs allant jusqu'à 1,20 m, avec une densité moyenne à forte. Il y constitue un écosystème steppique intramontagnard spontané, caractérisé par une bonne régénération qui témoigne de conditions topo-édapho-climatiques propices à sa croissance et à sa reproduction. L'approche climatique utilisée pour caractériser cette steppe de plaine (par opposition à la steppe de versant) est fondée sur deux critères climatiques : la pluviosité (et plus généralement les précipitations) et la température. Chacun des deux paramètres a été analysé sous différents angles en ayant recours à différents indicateurs. Ces critères ne sont pas les seuls facteurs climatiques agissant sur les conditions de vie de l'alfa et de son cortège d'espèces végétales steppiques ; mais ils sont prédominants. En effet, ces facteurs présentent d'étroites corrélations avec d'autres paramètres climatiques, tels que l'humidité relative, le vent et l'insolation. Enfin, le rapport P/2T de H. GAUSSEN a été utilisé pour cerner les modalités de la sécheresse.In Midelt high plain, alfa (Stipa tenacissima L.) is formed by mean to high density good state of health and tall tufts that can sometimes reach up to 1.2 m height. It there builds up a spontaneous steppic intramountain ecosystem, characterized by a good regeneration that attests topo-edapho-climatic conditions are favorable to its growth and reproduction. Climatic approach used for characterizing this plain steppe (in contrast with slope steppe) is based on two climatic criteria: raininess (and more generally rainfalls) and temperature. Each of these two parameters has been analysed from different points of view using different indicators. These criteria are not the only climatic factors that act on the life conditions of alfa and its accompanying steppic vegetal species; but they are predominant. Indeed, these factors have close correlations with other climatic parameters such as relative humidity, wind and insolation. Finally, the P/2T ratio of H. GAUSSEN has been used to delimit the modalities of dryness

Diversité des formes de croissance de Juniperus communis L. dans les stations refuges des hautes montagnes du bassin versant de la Moulouya (Maroc)

In Morocco, Juniperus communis L. (common juniper), which tends to be too automatically qualified as a phanerophyte because its belongs to the woody arborescent species group, acquires a dwarfed shape, always thick, and often takes on a typical mound appearance even if a wide range of growth forms exist for both isolated tufts and those grouped in mass more or less compacts. In addition to nivo-aeolian processes, topography and edaphic conditions specific to each station play a key role in the expression of this polymorphism.Whatever the morphologies adopted in response to their microenvironment, juniper tufts grows most often as creeping coppice, small rugs or wide carpets. Their spreading on steep slopes with a dispersed and sporadic distribution contributes to a very characteristic tiger mosaic pattern within the general physiognomy of the oromediterranean vegetation cover. For that and for its relict species status, the common juniper deserves here to be protected

Etude phyto-ecologique des versants de la vallee des Aiet Bou Guemmez (Haut Atlas central septentrional, Maroc)

SIGLECNRS T 57394 / INIST-CNRS - Institut de l'Information Scientifique et TechniqueFRFranc

Juniperus communis in Morocco: analyses of nrDNA and cpDNA regions

Volume: 97Start Page: 123End Page: 12

Environmental drivers of Holocene forest development in the Middle Atlas, Morocco

In semi-arid regions subject to rising temperatures and drought, palaeoecological insights into past vegetation dynamics under a range of boundary conditions are needed to develop our understanding of environmental responses to climatic changes. Here, we present a new high-resolution record of vegetation history and fire activity spanning the last 12,000 years from Lake Sidi Ali in the southern Middle Atlas Mountains, Morocco. The record is underpinned by a robust AMS radiocarbon and 210Pb/137Cs chronology and multi-proxy approach allowing direct comparison of vegetation, hydroclimate, and catchment tracers. The record reveals the persistence of steppic landscapes until 10,340 cal yr BP, prevailing sclerophyll woodland with evergreen Quercus until 6,300 cal yr BP, predominance of montane conifers (Cedrus and Cupressaceae) until 1,300 cal yr BP with matorralization and increased fire activity from 4,320 cal yr BP, and major reduction of forest cover after 1,300 cal yr BP. Detailed comparisons between the pollen record of Lake Sidi Ali (2,080 m a.s.l.) and previously published data from nearby Tigalmamine (1,626 m a.s.l.) highlight common patterns of vegetation change in response to Holocene climatic and anthropogenic drivers, as well as local differences relating to elevation and bioclimate contrasts between the sites. Variability in evergreen Quercus and Cedrus at both sites supports a Holocene summer temperature maximum between 9,000 and 7,000 cal yr BP in contrast with previous large-scale pollen-based climate reconstructions, and furthermore indicates pervasive millennial temperature variability. Millennial-scale cooling episodes are inferred from Cedrus expansion around 10,200, 8,200, 6,100, 4,500, 3,000, and 1,700 cal yr BP, and during the Little Ice Age (400 cal yr BP). A two-part trajectory of Late Holocene forest decline is evident, with gradual decline from 4,320 cal yr BP linked to synergism between pastoralism, increased fire and low winter rainfall, and a marked reduction from 1,300 cal yr BP, attributed to intensification of human activity around the Early Muslim conquest of Morocco. This trajectory, however, does not mask vegetation responses to millennial climate variability. The findings reveal the sensitive response of Middle Atlas forests to rapid climate changes and underscore the exposure of the montane forest ecosystems to future warming