The Maghreb's Mediterranean coastal edge is home to many peatlands with boreal floristic affinities and high conservation value. This work aims at investigating the Holocene developmental history of these wetlands in Northern Morocco, based on pollen record, loss-on-ignition and radiocarbon dating. First, the comparison between modern pollen spectra and present-day hydrophytic vegetation makes it possible to identify the local pollen signal. Second, while peatlands have existed in the Rif for at least 13,000 years, their initiation mostly by paludification extends throughout the Holocene. Their plant composition remains relatively unchanged for millennia, but swamp undergrowth could locally experience changes in taxa dominance. Mid-to late-Holocene sedimentation changes appear to result from the human-induced regional decline of cedar. The major changes experienced by wetlands occurred recently, due to clearing, burning and overgrazing. Effective conservation policies should be urgently implemented in order to save the last relict peatlands of Northern Morocco. (c) 2022 Elsevier Masson SAS. All rights reserved.

The recent increase in the known richness of Limonium in Tunisia, mainly due to the description of 25 new endemic species in the last decades, has made the only existing identification key for the country obsolete.Based on an exhaustive review of the literature dealing with Limonium from Tunisia, consultation of herbarium specimens preserved in Tunisia and Sicily, and a number of new collections, we propose here a new complete key, accompanied by an updated mapping for all taxa.The obtained results reveal that most Tunisian Limonium are perennial herbs (81 %), halophytes (79 %), endemic to the country (61 %), and mainly distributed along coasts and around chotts.A significant number of taxa (51 %) present important conservation issues, mainly related to microendemism (especially on islands and peninsulas) and to the alarming acceleration of habitat degradation.Djerba Island is currently the subject of a project involving local authorities, residents and environmental protection associations aimed at conserving the microendemic Limonium formosum, whose only location is threatened in the short term by a project to turn it into a tourist attraction.

The Garaa Sejenane is an ancient lake in northern Tunisia that currently houses a mosaic of temporary wetlands. Comparison of modern pollen data and field vegetation surveys shows both a weak regional pollen signal and the homogenization of pollen assemblages at the scale of the garaa. Despite a hiatus between 19,000 and 2230 cal. BP, fossil pollen analyses provide the first Tunisian LGM record and attest to the ancient origin of the lake, which housed some taxa still present locally in the 1950s. The originality of the Pleniglacial surrounding landscape dominated by a juniper steppe contrasted with the mountain conifer forests in Kroumiria. Lastly, analyses of aerial photographs (1948, 1962, 1984), recent satellite photographs and previous botanical descriptions reveal that the lake has been drying since 1960 because of important anthropogenic activities (drainage, groundwater pumping, cultivation, grazing... ). These disturbances have generated profound changes in hydrophytic plant communities (fragmentation, diversity loss, introduction of invasive species... ) that are likely to threaten their long-term survival. (C) 2018 Elsevier B.V. All rights reserved.

Characeae are macroscopic green algae present in the Maghreb (Morocco, Algeria, Tunisia) that are known since the 19th century works of Desfontaines (1800) and Braun (1868). Feldmann (1946) published the first regional synthesis, and this study provides a new Maghreb-wide synthesis of all collections made since 1784 (570 observations distributed over 464 sites). Each of the 31 reported species is described in detail with its diagnostic features, ecology and distribution in the three Maghrebian countries. Distribution maps distinguish between the three collection periods: 1780-1939, 1940-1979, and 1980-2016. An illustrated key is provided to help botanists working in the Maghreb to identify the taxa. From a biogeographical perspective, the Characean flora of the Maghreb is dominated by elements originating from northern (European) countries (61.3%) that include regionally very rare species such as Chara strigosa and C. tomentosa. The Mediterranean-Atlantic element is also well represented (32.3%), with some Mediterranean endemics (Chara imperfecta, C. oedophylla, C. vulgaris var. gymnophylla). Finally, two taxa that have an affinity for tropical conditions (Chara zeylanica and Lamprothamnium succinctum) extend to the southern Sahara. In North Africa, 14 species (7 Chara, 2 Lamprothamnium, 4 Nitella and 1 Sphaerochara) are threatened and raise issues about their conservation; three of these are particularly endangered: Chara imperfecta, C. oedophylla and Lamprothamnium papulosum.

Enjeux de conservation d’une zone humide d’eau douce méditerranéenne exceptionnelle : la Garâa Sejenane (Tunisie septentrionale). Cet article a pour but d’évaluer les enjeux de conservation concernant la végétation hydrophytique de la plus grande zone humide naturelle d’eau douce de Tunisie, la Garâa Sejenane. Les 55 relevés phytosociologiques réalisés révèlent une richesse floristique exceptionnelle, avec 74 hydrophytes dont 26 sont à forte valeur patrimoniale. Des analyses multivariées (AFC, CHA) effectuées sur ces données distinguent trois types d’habitats : des cultures inondables, des marais temporaires, et des pelouses humides/ mares temporaires. Leur cartographie montre une structure en 3 zones concentriques : une ceinture externe constituée de pelouses humides, de mares temporaires et de prairies fourragères sèches, une zone intermédiaire occupée par des marais temporaires et des prairies fourragères humides, et une zone centrale formée de cultures inondables. Un Indice de Rareté des Espèces très élevé, et des espèces à fort enjeu conservatoire (1 endémique stricte à la Garâa Sejenane, 5 espèces dont elle constitue l’unique localité tunisienne, et 2 espèces dont elle abrite les plus grandes populations nord-africaines) révèlent l’intérêt écologique et conservatoire majeur du site, et ceci malgré de fortes pressions anthropiques subies depuis les années 60. Dans le contexte actuel d’augmentation de la pression de perturbation, la conservation à long terme de cette biodiversité exceptionnelle nécessite la mise en place de mesures de gestion appropriées intégrant les populations locales.

The study aimed to assess the effects of the potential replacement of dominant native plants by co-occurring exotic invasives on organic matter degradation in a riparian area. The questions were: i) Is there a relationship between the litter breakdown rate and species origin? ii) Is the chemical composition more relevant than species origin? iii) Does species origin influence the associated saprophagous invertebrate community?

The postglacial history of vegetation at a regional scale is mainly governed by climate. However, the action of other environmental factors can lead to differentiation of the long-term vegetation dynamics in locations that are in proximity. In this context, the vegetation history of Covey Hill, at the northern tip of the Adirondack Mountains, was reconstructed using pollen analysis of a sediment core collected in a bog near the hilltop. This history was then compared with that of other sites in the Adirondacks, in the St. Lawrence Lowlands and in the Appalachian foothills to determine whether differentiations had occurred between sites across the landscape. Regionally, climate seems to have been the main driver of vegetation development. Differences between sites are most pronounced in regard to relative abundance of aspen and alder, and mostly occurred during the Late Glacial and early Holocene. Unlike other sites, fires occurred frequently on Covey Hill for several millennia, and most probably allowed the long-term maintenance of a rare pine barren. Finally, drier conditions are probably partly responsible for the hemlock decline evident around 5100 cal BP.

Unlike southern Spain, northern Morocco has been little investigated for palaeoecological purposes. Consequently, the origin and history of the Rifan vegetation is largely unknown, as well as the past role of human activities. A review of the Plio-Pleistocene fossil data available from North Africa clearly reveals the ancient origin of much of the present-day flora and vegetation structures of the region. A well-dated pollen record covering the last 5,000 years, obtained from a fen, is compared to previous regional pollen data in order to understand the late-Holocene vegetation dynamics and the influence of anthropogenic disturbances. Modern pollen spectra have allowed the calibration of pollen diversity and evenness as indicators of tree-cover density. The results obtained show the long-term persistence of regional forests until the onset of Arab Sharifian dynasties in the 16th century, with a surprising lack of human impact during the late Neolithic, and little impact during Roman colonisation. The increasing density of deciduous forests recorded from 3,800 to 1,900 cal bp , concomitant with the expansion of cedar in the Middle Atlas, could reveal the onset of widespread cooler and moister climatic conditions. The weak and late human impact in the Rifan mountains explains, at least in part, their high diversity and the conservation of their forest ecosystems. Anthropogenic activities however have led to severe modification of the understorey structure of these forests during the four last centuries, and to the worrying on-going deforestation that presently threatens the survival of this invaluable biological heritage.

Hydrological requirements for germination and development of P. minuta were assessed through a 5-year field survey in Garaa Sejenane, Tunisia, and an experiment under controlled conditions. The spatial distribution of P. minuta was recorded in the field annually, while the experiment tested the effects of water levels and flooding dates on germination (the emergence of new individuals) and development. Water level was found to be the major factor affecting the germination and the development of P. minuta with flooding date as a secondary limiting factor. For germination to occur, the sediment must be completely waterlogged. Water depths of 5-10 cm are optimal for plant development. In addition, the plant needs a minimal flooding period of seven weeks to develop. Late-spring precipitation appears to be more critical than earlier rains. (C) 2013 Elsevier B.V. All rights reserved.

QuestionsThe high competitiveness of exotic invasive species has often been demonstrated, but usually with respect to native species known to have low competitive ability. Considering five exotic and five native riparian species with close characteristics regarding competitive ability, habitat and growth form, we addressed the following questions: (i) do the selected invasive plants produce more biomass than the selected native dominants under competitive pressure; and (ii) are the selected invasive species better competitors than the selected native dominants?LocationCommon garden experiment at the Henri Gaussen Botanical Garden, Toulouse, France.MethodsWe selected five native dominant species and five exotic invasive species co-occurring along a riparian successional gradient of the middle Garonne River (SW France). Young plants of each species were planted in pots in ten intra- and 17 inter-specific combinations in conditions of high water and nutrient availability. To simulate the effects of hydrological disturbance during earlier growth stages, a partial cutting of plants was applied 6weeks after planting. We measured above-ground and below-ground biomass of individuals of each species after 6mo of growth.ResultsThere were large disparities among species performances, regardless of whether the species were exotic or native. The exotic species produced more above-ground and below-ground biomass than the natives species for 73% of the selected species pairs. The exotic species had higher competitive ability than the native species, mainly related to the high competitive effect of I.glandulifera. The two species with the highest biomass production and competitive ability were invasive exotics, whereas the two species with the lowest were dominant natives.ConclusionsOur results predict that competition among young individuals could play a major role for the invasion success of the studied exotic species in European riparian areas.

1. A litter-bag experiment was undertaken in a pond on the margins of a large temperate floodplain in south-western France to assess the potential influence of the replacement of native by exotic riparian species on organic matter degradation. We determined initial litter chemical composition, breakdown rates and the invertebrate assemblages associated with the litter for five pairs of native dominant and exotic invasive species co-occurring at different stages along a successional gradient.2. Litter chemical composition, breakdown rates and abundance and diversity of detritivorous invertebrates were similar for the exotic and native species overall. No overall changes in organic matter degradation can thus be predicted from the replacement of dominant natives by exotic invasives. Breakdown rates were primarily driven by the C/N ratio.3. One invasive species (Buddleja davidii) showed significantly higher breakdown rates than its native counterpart (Populus nigra), resulting in the disappearance of leaf litter 6 months prior to the next litterfall. In some cases, therefore, invasion by exotic species may result in discontinuity of resource supply for decomposers.

Since several decades, American boxelder (Acer negundo) is replacing white willow (Salix alba) riparian forests along southern European rivers. This study aims to evaluate the consequences of boxelder invasion on understory community in riparian areas. We determined the understory species richness, composition and biomass in boxelder and white willow stands located in three riparian forests, representative of three rivers with distinct hydrological regimes. We investigated correlation of these variables to soil moisture and particle size, main soil nutrient stocks, potential nitrification and denitrification, tree canopy cover and photosynthetic active radiation (PAR) at the ground level. A greenhouse experiment was then conducted to identify the causal factors responsible for changes in the understory. The effect of soil type, PAR level and water level on the growth and the biomass production of Urtica dioica were examined. A lower plant species richness and biomass, and a modification of community composition were observed for boxelder understory in all sites, regardless of their environmental characteristics. The strongest modification that follows boxelder invasion was the decline in U. dioica, the dominant species of the white willow forest understory. These differences were mainly correlated with a lower incident PAR under boxelder canopy. The greenhouse experiment identified PAR level as the main factor responsible for the changes in U. dioica stem number and biomass. Our results indicate that adult boxelder acts as an ecosystem engineer that decreases light availability. The opportunistic invasion by boxelder leads to important understory changes, which could alter riparian ecosystem functioning.

In North Africa, peat mosses (genus Sphagnum) are rare and restricted to a few wet habitats distributed in two main regions: northern Morocco and the northern Algerian-Tunisian boundary. Based on herbarium specimens from 1861 to 1965, on recent collects and on floristic surveys, the present paper addresses the taxonomy, distribution, history and biogeographical significance of peat mosses of the Tingitanean-Rifan range. On the first hand, our results lead to the discovery of a new species for Morocco (Sphagnum subnitens), previously only known in North Africa from three ancient herbarium specimens from Kroumiria (northwestern Tunisia). Because S. subnitens was not recovered in Tunisia for more than 50 years, its North African distribution is thought to be now restricted to the fen complex of Krimda (Larache region), where it forms 20-30 hummocks in at least three places. On the second hand, our results confirm the presence of Sphagnum auriculatum (sometimes noted S. rufescens or confused with S. flexuosum) in two zones: Krimda and Jbel Bou Hachem. This species probably still occurs in some other mountains of Jebala Range (Jbels Alam, Sougna and Khezana), but it disappeared from its northernmost locality (Jbel Dhar Zhirou), because of human-induced disturbances. Palaeoecological data indicate than most of the sedge fens harbouring Sphagnum populations originate from past alder-can-communities, which decline was triggered by human activities during the last millennia. The occurrence of such wetlands with northern affinities within the Mediterranean vegetation of North Africa constitutes a biogeographical enigma. The understanding of the influences of Quaternary climate variations and long-distance transport would be of major concern for the sustainable conservation of these exceptional and highly threatened habitats.

Dans le contexte des invasions, l'objectif de ce travail est d'evaluer dans quelle mesure l'origine des especes vegetales conditionne le fonctionnement d'un ecosysteme en situation de dominance. Cinq paires d'especes autochtones dominantes (Agrostis stolonifera, Rubus caesius, Populus nigra, Urtica dioica et Salix alba) et introduites envahissantes (Paspalum distichum, Fallopia japonica, Buddleja davidii, Impatiens glandulifera et Acer negundo) ont ete comparees en milieu riverain pour les processus de production primaire et de degradation des litieres. Ces etudes ont ete completees par une analyse detaillee des consequences de l'invasion des ripisylves par A. negundo. Nos resultats montrent que si les especes introduites envahissantes peuvent etre plus efficaces dans la realisation de certains processus ecologiques, l'absence de coevolution entre les especes introduites et les organismes des milieux recepteurs n'a pas d'implication systematique pour le fonctionnement des ecosystemes.

Past context and dynamics of the development of a Mediterranean peatland (Mont Aigoual, France). A minerotrophic peatland (fen) located on Mont Aigoual (southern France) is investigated for both modern vegetation and fossil pollen. The site is shown to originate around 2300 cal. BP and to have been strongly influenced by agro-pastoral activities. The spread of nitrophilous and not-grazed plant communities, at the expense of hydrophilous ones, characterized the evolution of the site, even during the recent decline of agricultural activities. This study highlights the role of disturbance on the development of the Aigoual peatlands, and their present-day degradation status, and underlines the need of a well-adapted conservatory management. To cite this article: M. Bottollier-Curtet, S.D. Muller, C. R. Biologies 332 (2009). (c) 2008 Academie des sciences. Publie par Elsevier Masson SAS.