Changes in foliar nutrient content and resorption in Fraxinus excelsior L., Ulmus minor Mill. and Clematis vitalba L. after prevention of floods

This paper focuses on the impact of flood on tree mineral nutrition through measurement of resorption (i.e. transfer of nutrients from leaves to perennial organs). Nutrient (N, P, K, Mg, Ca) concentrations in leaves of three representative species, Fraxinus excelsior L., Ulmus minor Mill. and Clematis vitalba L. were measured before and after abscission on flooded and unflooded hardwood forests of the upper Rhine plain. The nutrient concentrations in the soils, which were measured in the top layer of the study sites, were higher in the flooded sites for P but slightly lower for N and K, and identical at both types of site for Ca and Mg. The summer foliage concentrations were higher for N and P in the flooded areas, and probably related to the flooding process, which contributes to regular nutrient inputs in the flooded forest, causes high fluctuations of water level and increases bioavailability of certain nutrients. Resorption occurred for all nutrients in the three species, and was higher for N, P and K (40-70 %) than for Ca and Mg (0-45 %), but not significantly different at the two sites. This paper stresses the variability of the test species response (nutrient content and resorption) to the soil and flood water nutrient sources, and tries to specify parameters which control resorption, i.e. soil fertility, tree species or flood stress. © 1999 Inra/Éditions scientifiques et médicales Elsevier SAS

Impact of river management history on the community structure, species composition and nutrient status in the Rhine alluvial hardwood forest

The present-day Rhine alluvial hardwood forest (Querco-Ulmetum minoris, Issler 24) in the upper Rhine valley (France/Germany) is comprised of three vegetation units, one still flooded by calm waters (F) and the two others unflooded, one for 30 years (UF30) (after the river canalisation) and the other for about 130 years (UF130) (after river straightening and embankment work in the middle nineteenth century). In the three stands, species composition, structure and diversity of vegetation and nutrient content of mature leaf, leaf litter and soil have been studied. Fungi (Macromycetae) were only studied in two stands (F and UF130). The intensity of nutrient recycling was exemplified by comparing the chemical composition of rainwater, flood, throughfall, mature leaf, leaf litter, soil and groundwater in two of these stands (F and UF30). The elimination of floods has caused a change in floristic composition, tree density and plant diversity. Tree density was higher in the two unflooded stands and was related to a large increase in sapling (< 6 cm dbh) density more than to a change of stem (> 6 cm dbh) density. Sapling density increased 2 times and three times in the UF30 and the UF130 respectively, whereas the stem density increased only 12% in the first stand and decreased 29% in the second one. The saprophytic macromycete communities have been supplemented with mycorrhizal species

Genetic polymorphism and phenotypic plasticity : two advantages for the dispersal of Japanese knotweeds

The Japanese Knotweed s.l. population of a riverine region of north-eastern France was examined for a variety of ecological and genetic parameters. The population was dominated by the hybrid Fallopia x bohemica, but the population was morphologically variable and unusual in its being comprised entirely of hermaphrodite 6x and 8x F. x bohemica plants, plus a single aneuploid adult. Chromosome counts are given, and these indicate that both aneuploid and euploid individuals are being produced and becoming established in the study area. It was also found that all plants examined had the F. japonica var japonica chloroplast haplotype. Based on differences in morphology and phenology, the clones were divided into four main categories (1 to 4). Category 1 was widely distributed (nearly 80 % of the area) with the other three having a much more restricted occurrence. Category 1 produced little seed and was not the tallest plant or the clone with the fastest growth. The other categories all produced seed and grew faster. From these results, we can conclude that from an ecological point of view, some clones are more aggressive than others with a similar chromosome composition. Aggressiveness can be linked to the absence of seed production and possession of large leaves, which might allow higher storage of nutrients and better volume of rhizome in the soilPlusieurs populations de renouées en Alsace ont été analysées du point de vue génétique et écologique. Elles sont dominées par l'hybride Fallopia x bohemica, mais celui-ci présente une grande variabilité génétique, et différents types de ploïdie : hexaploïde, octoploïde et aneuploïde. Toutes les plantes ont pour mère Fallopia japonica. Sur la base des différences morphologiques et phénologiques, les clones ont été divisés en 4 catégories. La catégorie 1 est largement distribuée (près de 80 % de l'aire d'étude). Elle produit peu de graines, mais c'est le clone le plus envahissant. D'un point de vue écologique, certains clones sont plus « agressifs » que d'autres de même composition chromosomique. L'agressivité serait liée à l'absence de production de graines et à la présence de grandes feuilles, ce qui permettrait un plus grand stockage des nutriments et un meilleur volume du rhizome dans le sol

Quel système de référence pour la restauration des systèmes alluviaux rhénans ?

Floodplain ecosystems consist of a mosaic of shifting interactive habitats (forests, river channels and alluvial aquifers). Flood pulse, hydrological connectivity and geomorphological dynamics are key factors for high species diversity and productivity, complexity in successional trajectories and importance of ecotones between terrestrial and aquatic ecosystems. Most rivers in Europe have been drastically altered by dams and reservoirs, canalisation, reduction of the welland area, eutrophication and various other land-use developments. After a very long period of destruction of ftoodplain integrity, the need for protecting and restoring alluvial ecosystems slowly emerged over the last three decades. Restoration needs to define reference conditions, present conditions and restoration objective states, according to the principle of naturalness. This principle includes hydrological functionality (taking into account the flood pulse), the spatio-temporal diversity of habitat types and species, such as alluvial forest succession and connection of lateral arms to the active channel. We take examples in the upper Rhine valley to support the naturalness concept and to propose sorne principles on this basis for a restoration programme. The preservation of the hydrological functioning (i.e. flooding) ensures an efficient purifying capacity of the soil root system, with regard to phosphate and nitrate. As a consequence, groundwater nitrate and phosphate concentrations are very low under alluvial forests. Moreover the ftooding regime maintains a certain heterogeneity of aquatic and terrestrial habitats. The hydrological network, i.e. the former lateral arms, is supplied by different types of water (ground and/or surface water) and water quality differs according to their degree of conneclion to the active channel. The connected arms, is eutrophie whereas the disconnected arms evolve towards an oligotrophic state. The aquatic macrophytes communities reftect the change in water quality. The spatio- temporal variability of habitats is higher in the ftooded sectors than in the unftooded ones. As a consequence the ftooded sectors include more aquatic macrophytes communities (3 to 5 according to the hydrological year vs 2) and each community has greater species richness. A similar relationship exists for terrestrial habitats and forest communities. Hard wood forests tend to dominate the unftooded sectors whereas the flooded areas present a very rich spatio-tempoal mosaïc of forests units including all steps of the alluvial succession. The comparison of forest architecture between ftooded and unftooded sites shows that disconnection results in an increase of the ligneous density, a decrease of the tree height, the absence of treefall and a decrease of lianas (for example ivy).The Rhinau island, a still flooded sector in the Rhine floodplain can be used as a basis for the naturalness concept, due to the preservation of a certain functionnality, even if flooding duration is lower than before the Rhine canalisation (2 days versus 15 days). The two other sites, with differing durations of isolation (30 and 130 years), show different levels of change in floristic composition and structure of forests, and aquatic macrophyte communities . Accordingly, the restoration programme needs to engage more direct interventions. A key factor to emphasize should be the restoration of natural hydrological functioning. On the basis of the concept of naturalness, we therefore propose a four- step restoration programme : 1) restoration of free flow of water in the former lateral arms by connecting them to the river, 2) restoration of natural floods based on Rhine discharges, 3) development of a specific programme for the by-passed sections, 4) finally, development of the inter-connection of the restored areas along the riverLes zones alluviales, traversées par des flux d'eau et d'énergie fournis par un cours d'eau, sont organisées en ensembles fonctionnels interactifs associant des systèmes terrestres forestiers et/ou prairiaux et des systèmes aquatiques. Le fonctionnement par pulsations (« flood pulse »), la connectivité hydrologique et la dynamique géomorphologique sont les facteurs-clés de la diversité et de la productivité biologiques. Les aménagements hydrauliques des grands fleuves ont fortement réduit la surface du lit majeur et perturbé, voire supprimé, les fonctions d'écrêtement des crues, de recharge de la nappe, d'épuration des eaux et de diversité du complexe alluvial. Il est proposé de restaurer des zones inondables et de recréer ainsi des conditions favorables à la restitution de leurs fonctions. La restauration et la gestion de ces zones passent par la détermination de différents états, état de référence (celui du fleuve « sauvage » ), état actuel et état objectif sur la base du principe de naturalité. Ce principe inclut la fonctionnalité hydrologique (maintien d'un fonctionnement par pulsations), la diversité spatio-temporelle des habitats (conservation de la succession alluviale forestière, connexion des bras latéraux au fleuve) et des espèces. Au travers des exemples pris parmi les sites rhénans, présentant des degrés variables de naturalité, nous définissons les grands principes de mise en place d'un programme de restauration du Rhin supérieu

Cent ans de dynamique forestière spontanée en plein petit âge glaciaire dans le Pays de Bitche, Lorraine

National audienceThis study is an analysis of a historical document dating back to 1758, entitled Atlas topographique du comté de Bitche (north-eastern France). This document was signed by a French engineer. It was drafted during the small ice age, following a period when forestry practices were stopped for 100 years or so because of severe political unrest. The document describes beech-oak forests (age, dimensions, sanitary state, regeneration) of the Pays de Bitche, in order to evaluate their richness. By converting the qualitative data of the atlas into semi-quantitative data, we managed to recreate landscapes at that time. The age-diameter matching proposed by the atlas was re-evaluated by coring present-day trees. The results showed the presence of a mature beech forest dominated by beech, very rich in large and very large trees, including a substantial number of oaks that died following competition with beech and repeated climate stress. The better resistance of beech to climate stress is discussed.Cette étude analyse un document historique datant de 1758, dénommé l’Atlas topographique du comté de Bitche, situé au nord-est de la France. Ce document signé d’un ingénieur français a été élaboré au cours du petit âge glaciaire, après une période d’abandon des usages d’environ 100 ans en raison de graves troubles politiques. Il y décrit les hêtraies-chênaies (âge, dimensions, état sanitaire, régénération) du Pays de Bitche, afin d’en évaluer les richesses forestières. Par conversion des données qualitatives de l’atlas en données semi-quantitatives, il a été possible de reconstituer les paysages de l’époque. Les correspondances âges et diamètres proposés par l’atlas ont été réévaluées par carottages d’arbres actuels. Les résultats indiquent une hêtraie mature dominée par le Hêtre, très riche en gros bois et très gros bois incluant aussi une grande quantité de chênes morts par compétition avec le hêtre et stress climatiques répétés. La meilleure résistance du hêtre aux stress climatiques est discutée

Distribution, données floristiques et architecture des boisements du delta du Rhône (sud-est de la France)

The Rhone delta includes many small woodlands scattered within open landscapes, in the “ Grande Camargue”, the “ Little Camargue” and the “ Plan du Bourg”. These woodlands are here described with the help of two methods : phytosociology and canopy architecture with the help of hemispherical photographies. These woodlands correspond to five different phytosociological associations. Three of them are typical floodplain forests, the two others correspond to mixed Mediterranean oak forests. The global floristic richness is 109. Among the 22 selected woodlands, only five cover more than 25 ha. The others cover only 1 to 5 ha. In spite of their floristic differences, all woodlands have relatively open canopy, and low foliar indices. The conservation state of these woodlands depends on past uses, and current protection. The most valuable woodlands are : the ash-elmwhite poplar forest in the Plan du Bourg (mas Saint-Georges), which includes a population of grapevines ; the aged forest of the Saxy island, the most aged woodland of the delta ; and the relatively large pine-oak forest of Quincandon. Globally many of these woodlands include very big trees (white or black poplars, oaks, ashes) and a considerable amount of dead wood. They benefit from various protection states, from simple protection against cutting to strict reserve. It could be important for conservative purposes to strictly protect all woodlands situated within the current or future dykes.Le delta du Rhône comporte de nombreux boisements éparpillés au sein d’espaces ouverts, en Grande et en Petite Camargue, ainsi qu’au Plan du Bourg. Ces boisements ont été étudiés du point de vue phytosociologique et architectural. Ils appartiennent à 5 associations forestières différentes. Trois sont des forêts alluviales typiques des bordures de grands fleuves (peupleraie blanche, saulaie blanche, frênaie-ormaie à peuplier blanc) et deux sont des forêts dunaires (chênaie mixte, chênaie-pineraie). La richesse floristique globale est de 109 espèces. Sur les 22 sites retenus, les forêts de Quincandon (114 ha), Tourtoulen (44 ha), mas Saint-Georges (45 ha), Arles (40 ha), Beaujeu (25 ha) sont les plus étendues. Les autres sites occupent de petites surfaces (entre 1 et 5 ha). Leur état de conservation dépend des usages du passé et de leur statut de protection actuel. Les plus intéressantes sont celles qui sont les plus anciennes, les plus étendues et les moins exploitées par l’homme. En dépit de leurs différences floristiques, les forêts étudiées ont toutes des canopées lacuneuses, caractérisées par de larges ouvertures, expliquant les valeurs élevées d’ouverture de canopée et d’indices foliaires. La frênaie-ormaie du mas Saint-Georges, la peupleraie blanche très âgée (plus de 150 ans) de l’île de Saxy et la pineraie-chênaie de Quincandon occupent des superficies conséquentes et bénéficient de gestion extensive ou de non-gestion, ce qui explique leur richesse en gros arbres et en bois mort. Mais globalement, bien des boisements de la Camargue incluent encore de très gros arbres (chênes, peupliers noirs et blancs). Ces boisements bénéficient de statuts de protection divers, qui vont de la protection contre les défrichements à la réserve intégrale, mais mériteraient d’être mieux protégés pour certains d’entre eux.Schnitzler-Lenoble Annik. Distribution, données floristiques et architecture des boisements du delta du Rhône (sud-est de la France). In: Ecologia mediterranea, tome 40 n°2, 2014. pp. 77-92

Wolf denning behaviour in response to external disturbances and implications for pup survival

International audienc

Patterns of climber distribution in temperate forests of the Americas

International audienceAims and MethodsWe propose a standard protocol at the landscape to continental scale for examining to what extent the range of ecological conditions found in temperate latitudes explains the variations in climber species richness and traits. The protocol was tested in forests of the two Americas. The data set included 151 climber species. We selected four categorical traits and grouped these species into six clusters with regard to these traits. Floristic records of American forests were first gathered into alliances, second combined with bioclimatic indices (rainfall, temperature, continentality). We obtained a total of 59 vegetational units in which we calculated values of climber species richness and proportion of clusters. Vegetational units were ultimately gathered into five forest formations (characterized by leaf longevity). Wetlands and uplands were considered separately.Important FindingsOur results emphasize clear trends in large-scale patterns of climber distribution, independently of taxonomy. Climber species richness (in particular woody climbers) peaks in moist and warm upland forests with oceanic climates, and where conifers are rare. In flooded areas, climber richness is also very high and peaks in seasonally flooded large floodplains. In ecological conditions of frost, dryness or lack of nutrients, climber species richness, abundance and trait diversity decline, resulting in the dominance of small, twining and deciduous life traits